JP2024155732A - Optical detection device and signal processing method - Google Patents

Abstract

There are provided a light detection device and a signal processing method in which the fall time of the output after irradiation with pulsed light is short.
[Solution] This photodetection device includes a first photoelectric conversion element that outputs a first output when irradiated with a light pulse, and a second photoelectric conversion element that outputs a second output when irradiated with the light pulse. The photodetection device is configured to combine a first signal resulting from the first output and a second signal resulting from the second output when the first photoelectric conversion element and the second photoelectric conversion element are irradiated with the same light pulse, in a state that satisfies a first condition and a second condition. The first condition is that the time position of the peak of the first signal is different from the time position of the peak of the second signal. The second condition is that the positive and negative of the amount of change until the first signal reaches its peak is different from the positive and negative of the amount of change until the second signal reaches its peak.
[Selected Figure] Figure 1

Description

The present invention relates to a light detection device and a signal processing method.

Photoelectric conversion elements are used for a variety of purposes.

For example, Patent Document 1 describes a receiving device that receives an optical signal using a photodiode. The photodiode is, for example, a pn junction diode that uses a semiconductor pn junction, and converts light into an electrical signal.

For example, Patent Document 2 discloses a novel receiving device, receiving system, transmitting/receiving device, communication system, and photodetector element that uses a magnetic element. This receiving device, receiving system, transmitting/receiving device, communication system, and photodetector element enable high-speed communication.

JP 2001-292107 A JP 2022-069387 A

To achieve high-speed communication, there is a demand for further improvements in the high-speed response of photoelectric conversion devices. To improve the high-speed response of photoelectric conversion devices, when a pulsed light is irradiated onto a photoelectric conversion element, the output from the photoelectric conversion element needs to rise and fall at high speed. The fall time of the output from a photoelectric conversion element is often longer than the rise time, and there is a demand for improvements in the fall characteristics of the output from the photoelectric conversion element.

The present invention has been made in consideration of the above problems, and aims to provide a light detection device and a signal processing method that have a short fall time of the output after irradiation with pulsed light.

To solve the above problems, the following measures are provided:

(1) A photodetection device according to a first aspect includes a first photoelectric conversion element that outputs a first output when irradiated with a light pulse, and a second photoelectric conversion element that outputs a second output when irradiated with the light pulse. The photodetection device is configured to combine a first signal resulting from the first output and a second signal resulting from the second output when the first photoelectric conversion element and the second photoelectric conversion element are irradiated with the same light pulse, in a state that satisfies a first condition and a second condition. The first condition is that the time position of the peak of the first signal is different from the time position of the peak of the second signal. The second condition is that the positive and negative of the amount of change until the first signal reaches the peak is different from the positive and negative of the amount of change until the second signal reaches the peak.

(2) In the light detection device according to the above aspect, the first photoelectric conversion element may be a first magnetic element, and the second photoelectric conversion element may be a second magnetic element. The first magnetic element and the second magnetic element each include a first ferromagnetic layer to which the light pulse is irradiated, a second ferromagnetic layer, and a spacer layer sandwiched between the first ferromagnetic layer and the second ferromagnetic layer.

(3) The light detection device according to the above aspect may further include a delay circuit. The delay circuit delays the signal resulting from the second output.

(4) In the optical detection device according to the above aspect, when the first magnetic element and the second magnetic element are not irradiated with the light pulse, the relationship between the magnetization directions of the first ferromagnetic layer and the second ferromagnetic layer of the first magnetic element may be different from the relationship between the magnetization directions of the first ferromagnetic layer and the second ferromagnetic layer of the second magnetic element.

(5) In the light detection device according to the above aspect, the polarity of the DC power source connected to the output terminal side surface of the first magnetic element may be configured to be different from the polarity of the DC power source connected to the output terminal side surface of the second magnetic element.

(6) In the light detection device according to the above aspect, the polarity of the DC power source connected to the output terminal side surface of the first magnetic element may be configured to be the same as the polarity of the DC power source connected to the output terminal side surface of the second magnetic element.

(7) The light detection device according to the above aspect may further include an inversion circuit. The inversion circuit inverts the polarity of the signal resulting from the second output.

(8) In the optical detection device according to the above aspect, the first optical distance until the optical pulse is irradiated to the first photoelectric conversion element may be different from the second optical distance until the optical pulse is irradiated to the second photoelectric conversion element.

(9) The light detection device according to the above aspect may have a light irradiation surface onto which the light pulse is irradiated, a first intermediate layer between the light irradiation surface and the first photoelectric conversion element, and a second intermediate layer between the light irradiation surface and the second photoelectric conversion element. The first intermediate layer and the second intermediate layer have different refractive indices.

(10) The light detection device according to the above aspect may further include a first optical waveguide and a second optical waveguide. The first optical waveguide is configured to propagate the light pulse to the first photoelectric conversion element. The second optical waveguide is configured to propagate the light pulse to the second photoelectric conversion element. The first optical waveguide has a different length from the second optical waveguide.

(11) The light detection device according to the above aspect may further include a first optical waveguide and a second optical waveguide. The first optical waveguide is configured to propagate the light pulse to the first photoelectric conversion element. The second optical waveguide is configured to propagate the light pulse to the second photoelectric conversion element. The refractive index of the first optical waveguide is different from the refractive index of the second optical waveguide.

(12) A photodetection device according to a second aspect includes a first photoelectric conversion element that outputs a first output when irradiated with a light pulse. The photoelectric conversion device is configured to combine a first signal and a second signal resulting from the first output when the first photoelectric conversion element is irradiated with the light pulse in a state that satisfies a first condition and a second condition. The first condition is that the time position of the peak of the first signal is different from the time position of the peak of the second signal. The second condition is that the positive and negative of the amount of change until the first signal reaches its peak is different from the positive and negative of the amount of change until the second signal reaches its peak.

(13) In the light detection device according to the above aspect, the first photoelectric conversion element is a first magnetic element. The first magnetic element includes a first ferromagnetic layer to which the light pulse is irradiated, a second ferromagnetic layer, and a spacer layer sandwiched between the first ferromagnetic layer and the second ferromagnetic layer.

(14) The light detection device according to the above aspect may further include a delay circuit. The delay circuit delays one of the signals resulting from the first output.

(15) The light detection device according to the above aspect may further include an inversion circuit. The inversion circuit inverts the polarity of at least one of the signals resulting from the first output.

(16) A signal processing method according to a third aspect combines a first signal resulting from a first output output from a first photoelectric conversion element and a second signal resulting from a second output output from a second photoelectric conversion element when the same optical pulse is irradiated, in a state where a first condition and a second condition are satisfied. The first condition is that the time position of the peak of the first signal is different from the time position of the peak of the second signal. The second condition is that the positive and negative of the amount of change until the first signal reaches its peak is different from the positive and negative of the amount of change until the second signal reaches its peak.

(17) A signal processing method according to a fourth aspect combines a first signal and a second signal resulting from a first output output from a first photoelectric conversion element when the first photoelectric conversion element is irradiated with an optical pulse, in a state where a first condition and a second condition are satisfied. The first condition is that the time position of the peak of the first signal is different from the time position of the peak of the second signal. The second condition is that the positive and negative of the amount of change until the first signal reaches its peak is different from the positive and negative of the amount of change until the second signal reaches its peak.

The optical detection device and signal processing method according to the above aspect have a short fall time in the output after irradiation with pulsed light.

FIG. 2 is a circuit diagram of the light detection device according to the first embodiment. 2 is a perspective view of the vicinity of a first magnetic element and a second magnetic element of the photodetector according to the first embodiment. FIG. 3 is a cross-sectional view of the vicinity of a first magnetic element and a second magnetic element according to the first embodiment. FIG. 5A to 5C are diagrams illustrating an example of the operation of the first magnetic element according to the first embodiment. 5A to 5C are diagrams for explaining an example of operation of the first magnetic element according to the first embodiment. 3 is a schematic diagram showing output characteristics of the light detection device according to the first embodiment with respect to a light pulse. FIG. 11 is a graph showing measured values of a first signal resulting from a first output from a first magnetic element, a second signal resulting from a second output from a second magnetic element, and a total output from the optical detection device of the first embodiment. 13 is a graph showing a first signal resulting from a first output from a first magnetic element, a second signal resulting from a second output from a second magnetic element, and a total output from the photodetector according to the first embodiment, each normalized by its respective peak value. FIG. 11 is a circuit diagram of a light detection device according to a second embodiment. FIG. 11 is a cross-sectional view of the vicinity of a first magnetic element and a second magnetic element according to a second embodiment. 13 is a graph showing measured values of a first signal resulting from a first output from a first magnetic element, a second signal resulting from a second output from a second magnetic element, and a total output from the optical detection device of the second embodiment. 13 is a graph showing a first signal resulting from a first output from a first magnetic element, a second signal resulting from a second output from a second magnetic element, and a total output from the photodetector according to a second embodiment, each normalized by its respective peak value. 13 is a cross-sectional view of the vicinity of a first magnetic element and a second magnetic element according to a first modified example of the second embodiment. FIG. 13 is a cross-sectional view of the vicinity of a first magnetic element and a second magnetic element according to a second modified example of the second embodiment. FIG. FIG. 11 is a circuit diagram of a light detection device according to a third embodiment. 13 is a graph showing measured values of a first signal resulting from a first output from a first magnetic element, a second signal resulting from a second output from a second magnetic element, and a total output from the optical detection device of the third embodiment. 13 is a graph showing a first signal resulting from a first output from a first magnetic element, a second signal resulting from a second output from a second magnetic element, and a total output from the photodetector according to a third embodiment, each normalized by its respective peak value. FIG. 13 is a circuit diagram of a light detection device according to a fourth embodiment. FIG. 13 is a cross-sectional view of the vicinity of a first magnetic element and a second magnetic element of a light detection device according to a fourth embodiment. FIG. 13 is a plan view of a light detection device according to a fifth embodiment. FIG. 13 is a cross-sectional view of a light detection device according to a fifth embodiment. FIG. 13 is another cross-sectional view of the light detection device according to the fifth embodiment. FIG. 23 is a plan view of a light detection device according to a first modified example of the fifth embodiment. FIG. 13 is a circuit diagram of a light detection device according to a sixth embodiment. FIG. 11 is a block diagram of a transceiver device according to a first application example. FIG. 1 is a conceptual diagram of an example of a communication system.

The following describes the embodiments in detail with reference to the drawings as appropriate. The drawings used in the following description may show characteristic parts in an enlarged scale for the sake of clarity, and the dimensional ratios of each component may differ from the actual ones. The materials, dimensions, etc. exemplified in the following description are merely examples, and the present invention is not limited to them. They may be modified as appropriate within the scope of the effects of the present invention.

The directions are defined as follows. One direction in the plane of the surface on which the substrate Sub extends is the x-direction, and the direction perpendicular to the x-direction in the plane is the y-direction. The direction perpendicular to the substrate Sub is the z-direction. The z-direction is an example of the stacking direction of the first magnetic element 10 and the second magnetic element 20. Hereinafter, the +z direction may be expressed as "up" and the -z direction as "down". The +z direction is the direction from the second ferromagnetic layer to the first ferromagnetic layer. Up and down do not necessarily coincide with the direction in which gravity is applied.

"First embodiment"
Fig. 1 is a circuit diagram of a photodetection device 100 according to the first embodiment. In Fig. 1, the direction of magnetization of a ferromagnetic material when the photodetection device 100 is not irradiated with light is indicated by an arrow.

The light detection device 100 includes, for example, a first magnetic element 10, a second magnetic element 20, a delay circuit 40, a capacitor 91, an inductor 92, an output terminal _t1, and a reference potential terminal _t2 . The light detection device 100 may include a power supply 31 and a power supply 32, and the power supplies 31 and 32 may be external to the light detection device 100. The first magnetic element 10 is an example of a first photoelectric conversion element, and the second magnetic element 20 is an example of a second photoelectric conversion element. The first photoelectric conversion element (first magnetic element 10) outputs a first output when irradiated with a light pulse, and the second photoelectric conversion element (second magnetic element 20) outputs a second output when irradiated with a light pulse. The first magnetic element 10 and the second magnetic element 20 may be replaced with known photoelectric conversion elements such as pn junction type photodiodes. In this case, the cathode of the semiconductor photodiode serving as the first photoelectric conversion element is connected to the positive terminal of the power supply 31, and the anode is connected to the negative terminal of the power supply 31, and the cathode of the semiconductor photodiode serving as the second photoelectric conversion element is connected to the positive terminal of the power supply 32, and the anode is connected to the negative terminal of the power supply 32. The first magnetic element 10, the second magnetic element 20, the power supplies 31 and 32, the delay circuit 40, the capacitor 91, the inductor 92, the output terminal _t1 , and the reference potential terminal _t2 are each connected by a line.

The output terminal _t1 is a terminal that outputs a signal from the photodetector 100. The photodetector 100 outputs, for example, a combined resistance, a combined potential, etc. of the first magnetic element 10 and the second magnetic element 20 from the output terminal _t1 .

The reference potential terminal _t2 is connected to a reference potential and determines the reference potential of the photodetector 100. The reference potential terminal _t2 is connected to, for example, each of the first magnetic element 10 and the second magnetic element 20. The reference potential shown in Fig. 1 is ground. The ground may be provided outside the photodetector 100. The reference potential may be something other than ground.

The power supply 31 is a DC power supply and is connected to the first magnetic element 10. The power supply 31 may be a known one. The power supply 31 may be, for example, a DC current source capable of generating a constant DC current. The power supply 31 may be a DC current source capable of changing the magnitude of the generated DC current value. When the first photoelectric conversion element and the second photoelectric conversion element are pn junction type photodiodes, the power supply 31 and a power supply 32 described later may be DC voltage sources capable of applying a constant DC voltage. The power supply 31 applies a DC current or a DC voltage to the first magnetic element 10. The light detection device 100 is configured such that, for example, the first surface 10A of the first magnetic element 10 on the output terminal _t1 side is connected to the negative terminal of the power supply 31, and the second surface 10B of the first magnetic element 10 facing the first surface 10A is connected to the positive terminal of the power supply 31.

The power supply 32 is a DC power supply and is connected to the second magnetic element 20. The power supply 32 may be the same as the power supply 31. The power supply 32 applies a DC current or a DC voltage to the second magnetic element 20. The light detection device 100 is configured such that, for example, the first surface 20A of the second magnetic element 20 on the output terminal _t1 side is connected to the positive terminal of the power supply 32, and the second surface 20B of the second magnetic element 20 facing the first surface 20A is connected to the negative terminal of the power supply 32.

The light detection device 100 is configured such that the polarity (positive/negative) of the power source 31 connected to the first _surface 10A on the output terminal t1 side of the first magnetic element 10 is different from the polarity (positive/negative) of the power source 32 connected to the first surface 20A on the output terminal _t1 side of the second magnetic element 20. Here, an example is shown in which the first surface 10A is connected to the negative terminal of the power source 31, the second surface 10B is connected to the positive terminal of the power source 31, the first surface 20A is connected to the positive terminal of the power source 32, and the second surface 20B is connected to the negative terminal of the power source 32, but the first surface 10A may be connected to the positive terminal of the power source 31, the second surface 10B may be connected to the negative terminal of the power source 31, the first surface 20A may be connected to the negative terminal of the power source 32, and the second surface 20B may be connected to the positive terminal of the power source 32.

The inductor 92 is, for example, between the power supply 31 and the first magnetic element 10, and between the power supply 32 and the second magnetic element 20. For example, a chip inductor, an inductor formed by a pattern line, or a resistive element having an inductor component can be used as the inductor 92.

The capacitor 91 is, for example, between the first magnetic element 10 and the output terminal _t1 , and between the second magnetic element 20 and the output terminal _t1 . A known capacitor can be used for the capacitor 91. The capacitor 91 passes only high-frequency components of the change in the output voltage of the first magnetic element 10 and the second magnetic element 20 toward the output terminal _t1 .

Figure 2 is a perspective view of the first magnetic element 10 and the second magnetic element 20 of the light detection device 100 according to the first embodiment.

The optical detection device 100 converts the irradiated light L into an electrical signal. The first magnetic element 10 and the second magnetic element 20 are irradiated with the light L.

The light L is not limited to visible light, but also includes infrared light, which has a longer wavelength than visible light, and ultraviolet light, which has a shorter wavelength than visible light. The wavelength of visible light is, for example, 380 nm or more and less than 800 nm. The wavelength of infrared light is, for example, 800 nm or more and 1 mm or less. The wavelength of ultraviolet light is, for example, 200 nm or more and less than 380 nm. The light L is, for example, irradiated to the first magnetic element 10 and the second magnetic element as light pulses. The light L includes, for example, a high-frequency optical signal composed of multiple light pulses repeated at a high frequency. The high-frequency optical signal is, for example, a signal having a frequency of 100 MHz or more. The light L may be laser light.

The first magnetic element 10 and the second magnetic element 20 are each a columnar body. The first magnetic element 10 and the second magnetic element 20 may be a cylinder, a rectangular prism, or a triangular prism. The area of the first ferromagnetic layer 11 of the first magnetic element 10 when viewed from the z direction may be the same as or different from the area of the first ferromagnetic layer 21 of the second magnetic element 20 when viewed from the z direction.

The first magnetic element 10 is connected to a first electrode 14 and a second electrode 15. The first electrode 14 contacts the surface of the first magnetic element 10 that is irradiated with light L. The second electrode 15 contacts the surface of the first magnetic element 10 that faces the light irradiated surface. The first electrode 14 and the second electrode 15 sandwich the first magnetic element 10 in the z direction.

The first electrode 14 is made of a material having electrical conductivity. The first electrode 14 is, for example, a transparent electrode that is transparent to light in the wavelength band used. The first electrode 14 preferably transmits, for example, 80% or more of the light in the wavelength band used. The first electrode 14 is, for example, an oxide such as indium tin oxide (ITO), indium zinc oxide (IZO), zinc oxide (ZnO), or indium gallium zinc oxide (IGZO). The first electrode 14 may be configured to have a plurality of columnar metals in the transparent electrode material of these oxides. It is not essential to use the above-mentioned transparent electrode material for the first electrode 14, and a metal material such as Au, Cu, or Al may be used with a thin film thickness to allow the irradiated light L to reach the first ferromagnetic layer 11 of the first magnetic element 10. When a metal is used as the material for the first electrode 14, the film thickness of the first electrode 14 is, for example, 3 to 10 nm. The first electrode 14 may also have an anti-reflection film on the irradiation surface to which light is irradiated.

The second electrode 15 is located on the opposite side of the first electrode 14 across the first magnetic element 10. The second electrode 15 is made of a conductive material. The second electrode 15 is made of a metal such as Cu, Al, or Au. Ta or Ti may be laminated above and below these metals. A laminated film of Cu and Ta, a laminated film of Ta, Cu, and Ti, or a laminated film of Ta, Cu, and TaN may also be used. TiN or TaN may also be used as the second electrode 15. The film thickness of the second electrode 15 is, for example, 200 nm to 800 nm.

The second electrode 15 may be transparent to the light L irradiated to the first magnetic element 10. As the material of the second electrode 15, similar to the first electrode 14, for example, a transparent electrode material of an oxide such as indium tin oxide (ITO), indium zinc oxide (IZO), zinc oxide (ZnO), or indium gallium zinc oxide (IGZO) may be used. Even when light is irradiated from the first electrode 14, the light may reach the second electrode 15 depending on the intensity of the light. In this case, since the second electrode 15 is composed of a transparent electrode material of an oxide, the reflection of light at the interface between the second electrode 15 and the layer in contact with it can be suppressed compared to when the second electrode 15 is composed of a metal.

The second magnetic element 20 is connected to a first electrode 24 and a second electrode 25. The first electrode 24 contacts the surface of the second magnetic element 20 that is irradiated with light L. The second electrode 25 contacts the surface of the second magnetic element 20 that faces the light irradiated surface. The second electrode 25 may be integrated with the second electrode 15. The first electrode 24 and the second electrode 25 sandwich the second magnetic element 20 in the z direction. The first electrode 24 can be made of the same material as the first electrode 14, and the second electrode 25 can be made of the same material as the second electrode 15.

Figure 3 is a cross-sectional view of the vicinity of the first magnetic element 10 and the second magnetic element 20 according to the first embodiment. In Figure 3, the arrows indicate the direction of magnetization of the ferromagnetic material when no light is irradiated onto the light detection device 100.

The periphery of the first magnetic element 10 and the second magnetic element 20 is covered with, for example, an insulating layer 93. The insulating layer 93 is, for example, an oxide, nitride, or oxynitride of Si, Al, or Mg. The insulating layer 93 is, for example, silicon oxide (SiO _x ), silicon nitride (SiN _x ), silicon carbide (SiC), chromium nitride (CrN), silicon carbonitride (SiCN), silicon oxynitride (SiON), aluminum oxide (Al ₂ O ₃ ), zirconium oxide (ZrO _x ), or the like.

The first magnetic element 10 has, for example, a first ferromagnetic layer 11, a second ferromagnetic layer 12, and a spacer layer 13. The spacer layer 13 is located between the first ferromagnetic layer 11 and the second ferromagnetic layer 12. The first magnetic element 10 may have other layers in addition to these. Light L is irradiated onto the first magnetic element 10 from the first ferromagnetic layer 11 side. The first ferromagnetic layer 11 is closer to the first electrode 14 than the second ferromagnetic layer 12. The second ferromagnetic layer 12 is closer to the second electrode 15 than the first ferromagnetic layer 11.

The second magnetic element 20 has, for example, a first ferromagnetic layer 21, a second ferromagnetic layer 22, and a spacer layer 23. The spacer layer 23 is located between the first ferromagnetic layer 21 and the second ferromagnetic layer 22. The second magnetic element 20 may have other layers in addition to these. Light L is irradiated onto the second magnetic element 20 from the first ferromagnetic layer 21 side. The first ferromagnetic layer 21 is closer to the first electrode 24 than the second ferromagnetic layer 22. The second ferromagnetic layer 22 is closer to the second electrode 25 than the first ferromagnetic layer 21.

In the first magnetic element 10 shown in Fig. 3, the magnetization _M11 of the first ferromagnetic layer 11 and the magnetization _M12 of the second ferromagnetic layer 12 are antiparallel to each other when the first magnetic element 10 is not irradiated with light. In the second magnetic element 20 shown in Fig. 3, the magnetization _M21 of the first ferromagnetic layer 21 and the magnetization M22 of the second ferromagnetic layer 22 are antiparallel to each other when the second magnetic element 20 is not irradiated with light. In the first embodiment, when the first magnetic element 10 and the second magnetic element 20 are not irradiated with light, the relationship between the magnetization directions of the first ferromagnetic layer ₁₁ and the second ferromagnetic layer 12 of the first magnetic element 10 is the same as the relationship between the magnetization directions of the first ferromagnetic layer 21 and the second ferromagnetic layer 22 of the second magnetic element 20. Here, an example has been shown in which, when the first magnetic element 10 and the second magnetic element 20 are not irradiated with light, the relationship between the magnetization directions of the first ferromagnetic layer 11 and the second ferromagnetic layer 12 of the first magnetic element 10 and the relationship between the magnetization directions of the first ferromagnetic layer 21 and the second ferromagnetic layer 22 of the second magnetic element ₂₀ are all anti-parallel. However, the relationship between these magnetization directions may be parallel, or the relationship between these magnetization directions may be different from parallel and anti-parallel, such as a state in which the direction of the magnetization M11 of the first ferromagnetic layer 11 or the magnetization _M21 of the first ferromagnetic layer 21 is inclined with respect to the stacking direction and the in-plane direction.

The first magnetic element 10 and the second magnetic element 20 are, for example, MTJ (Magnetic Tunnel Junction) elements in which the spacer layers 13, 23 are made of insulating materials. The first magnetic element 10 is, for example, an element in which the resistance value in the z direction (resistance value when a current is passed in the z direction) changes depending on the relative change between the magnetization state of the first ferromagnetic layer 11 and the magnetization state of the second ferromagnetic layer 12. Such an element is also called a magnetoresistance effect element. Similarly, the second magnetic element 20 is, for example, an element in which the resistance value in the z direction (resistance value when a current is passed in the z direction) changes depending on the relative change between the magnetization state of the first ferromagnetic layer 21 and the magnetization state of the second ferromagnetic layer 22.

When the intensity of the light L irradiated to the first magnetic element 10 changes, the voltage (potential difference between the first electrode 14 and the second electrode 15) output from the first magnetic element 10 changes in response to the change in the intensity of the light L. When an optical pulse is irradiated, the first magnetic element 10 outputs a first output. The amount of change in the voltage of the first output (the amount of change based on the output voltage from the first magnetic element 10 in a state where no optical pulse is irradiated) is output from the output terminal _t1 . For example, the change in the voltage of the first output is output from the output terminal _t1 as a first signal caused by the first output.

When the intensity of the light L irradiated to the second magnetic element 20 changes, the voltage (potential difference between the first electrode 24 and the second electrode 25) output from the second magnetic element 20 changes in response to the change in the intensity of the light L. When an optical pulse is irradiated, the second magnetic element 20 outputs a second output. The amount of change in the voltage of the second output (the amount of change based on the output voltage from the second magnetic element 20 in a state where no optical pulse is irradiated) is delayed from the first signal caused by the first output and is output from the output terminal _t1 . For example, a signal obtained by extracting and delaying the change in the voltage of the second output is output from the output terminal _t1 as the second signal caused by the second output.

The first ferromagnetic layer 11 is a light detection layer whose magnetization state changes when irradiated with light from the outside. The first ferromagnetic layer 11 is also called a magnetization free layer. The magnetization free layer is a layer containing a magnetic material whose magnetization state changes when a specific external energy is applied. The specific external energy is, for example, light L irradiated from the outside, a current flowing in the z direction of the first ferromagnetic layer 11, or an external magnetic field. The magnetization state of the first ferromagnetic layer 11 changes depending on the intensity of the light L irradiated to the first ferromagnetic layer 11.

The first ferromagnetic layer 11 includes a ferromagnetic material. The first ferromagnetic layer 11 includes at least one of magnetic elements such as Co, Fe, or Ni. The first ferromagnetic layer 11 may include a nonmagnetic element such as B, Mg, Hf, or Gd in addition to the magnetic elements described above. The first ferromagnetic layer 11 may be, for example, an alloy including a magnetic element and a nonmagnetic element. The first ferromagnetic layer 11 may be composed of multiple layers. The first ferromagnetic layer 11 may be, for example, a CoFeB alloy, a laminate in which a CoFeB alloy layer is sandwiched between Fe layers, or a laminate in which a CoFeB alloy layer is sandwiched between CoFe layers. In general, "ferromagnetic" includes "ferrimagnetic". The first ferromagnetic layer 11 may exhibit ferrimagnetic properties. On the other hand, the first ferromagnetic layer 11 may exhibit ferromagnetic properties that are not ferrimagnetic. For example, a CoFeB alloy exhibits ferromagnetic properties that are not ferrimagnetic.

The first ferromagnetic layer 11 may be an in-plane magnetized film having an axis of easy magnetization in the in-plane direction (any direction in the x-y plane) or a perpendicular magnetized film having an axis of easy magnetization perpendicular to the film plane (z-direction).

The thickness of the first ferromagnetic layer 11 is, for example, 1 nm or more and 5 nm or less. The thickness of the first ferromagnetic layer 11 is preferably, for example, 1 nm or more and 2 nm or less. When the first ferromagnetic layer 11 is a perpendicular magnetization film, if the thickness of the first ferromagnetic layer 11 is thin, the perpendicular magnetic anisotropy application effect from the layers above and below the first ferromagnetic layer 11 is strengthened, and the perpendicular magnetic anisotropy of the first ferromagnetic layer 11 is enhanced. In other words, if the perpendicular magnetic anisotropy of the first ferromagnetic layer 11 is high, the force that causes the magnetization to return to the z direction is strengthened. On the other hand, if the thickness of the first ferromagnetic layer 11 is thick, the perpendicular magnetic anisotropy application effect from the layers above and below the first ferromagnetic layer 11 is relatively weak, and the perpendicular magnetic anisotropy of the first ferromagnetic layer 11 is weakened.

When the thickness of the first ferromagnetic layer 11 is reduced, its volume as a ferromagnetic body is reduced, and when the thickness is increased, its volume as a ferromagnetic body is increased. The responsiveness of the magnetization of the first ferromagnetic layer 11 when external energy is applied is inversely proportional to the product (KuV) of the magnetic anisotropy (Ku) and the volume (V) of the first ferromagnetic layer 11. In other words, when the product of the magnetic anisotropy and the volume of the first ferromagnetic layer 11 is reduced, the responsiveness to light is increased. From this perspective, in order to increase the responsiveness to light, it is preferable to reduce the volume of the first ferromagnetic layer 11 after appropriately designing the magnetic anisotropy of the first ferromagnetic layer 11.

If the thickness of the first ferromagnetic layer 11 is greater than 2 nm, an insertion layer made of, for example, Mo or W may be provided within the first ferromagnetic layer 11. That is, the first ferromagnetic layer 11 may be a laminate in which a ferromagnetic layer, an insertion layer, and a ferromagnetic layer are stacked in this order in the z direction. The interfacial magnetic anisotropy at the interface between the insertion layer and the ferromagnetic layer enhances the perpendicular magnetic anisotropy of the entire first ferromagnetic layer 11. The thickness of the insertion layer is, for example, 0.1 nm to 0.6 nm.

The second ferromagnetic layer 12 is a magnetization fixed layer. The magnetization fixed layer is a layer made of a magnetic material in which the state of magnetization is less likely to change than the magnetization free layer when a predetermined external energy is applied. For example, the magnetization direction of the magnetization fixed layer is less likely to change than the magnetization free layer when a predetermined external energy is applied. Also, for example, the magnitude of magnetization of the magnetization fixed layer is less likely to change than the magnetization free layer when a predetermined external energy is applied. The coercive force of the second ferromagnetic layer 12 is, for example, greater than the coercive force of the first ferromagnetic layer 11. The second ferromagnetic layer 12 has an easy magnetization axis in the same direction as the first ferromagnetic layer 11, for example. The second ferromagnetic layer 12 may be an in-plane magnetization film or a perpendicular magnetization film.

The material constituting the second ferromagnetic layer 12 is, for example, the same as that of the first ferromagnetic layer 11. The second ferromagnetic layer 12 may be, for example, a laminate in which Co is 0.4 nm to 1.0 nm thick, Mo is 0.1 nm to 0.5 nm thick, a CoFeB alloy is 0.3 nm to 1.0 nm thick, and Fe is 0.3 nm to 1.0 nm thick, stacked in this order.

The magnetization of the second ferromagnetic layer 12 may be fixed, for example, by magnetic coupling with the third ferromagnetic layer via a magnetic coupling layer. In this case, the combination of the second ferromagnetic layer 12, the magnetic coupling layer, and the third ferromagnetic layer may be referred to as a magnetization fixed layer.

The third ferromagnetic layer is, for example, magnetically coupled to the second ferromagnetic layer 12. The magnetic coupling is, for example, an antiferromagnetic coupling, which occurs due to RKKY interaction. The material constituting the third ferromagnetic layer is, for example, the same as that of the first ferromagnetic layer 11. The magnetic coupling layer is, for example, Ru, Ir, etc.

The spacer layer 13 is a non-magnetic layer disposed between the first ferromagnetic layer 11 and the second ferromagnetic layer 12. The spacer layer 13 is composed of a layer made of a conductor, an insulator, or a semiconductor, or a layer containing a current-carrying point made of a conductor in an insulator. The thickness of the spacer layer 13 can be adjusted according to the orientation direction of the magnetization of the first ferromagnetic layer 11 and the magnetization of the second ferromagnetic layer 12 in the initial state described later.

For example, when the spacer layer 13 is made of an insulator, the first magnetic element 10 has a magnetic tunnel junction (MTJ) consisting of the first ferromagnetic layer 11, the spacer layer 13, and the second ferromagnetic layer 12. Such an element is called an MTJ element. In this case, the first magnetic element 10 can exhibit a tunnel magnetoresistance (TMR) effect. For example, when the spacer layer 13 is made of a metal, the first magnetic element 10 can exhibit a giant magnetoresistance (GMR) effect. Such an element is called a GMR element.

When the spacer layer 13 is made of an insulating material, a material containing aluminum oxide, magnesium oxide, titanium oxide, silicon oxide, or the like can be used. These insulating materials may also contain elements such as Al, B, Si, Mg, or magnetic elements such as Co, Fe, Ni. A high magnetoresistance change rate can be obtained by adjusting the film thickness of the spacer layer 13 so that a high TMR effect is generated between the first ferromagnetic layer 11 and the second ferromagnetic layer 12. To efficiently utilize the TMR effect, the film thickness of the spacer layer 13 may be about 0.5 to 5.0 nm, or about 1.0 to 2.5 nm.

When the spacer layer 13 is made of a non-magnetic conductive material, conductive materials such as Cu, Ag, Au, or Ru can be used. To efficiently utilize the GMR effect, the thickness of the spacer layer 13 may be about 0.5 to 5.0 nm, or about 2.0 to 3.0 nm.

When the spacer layer 13 is made of a non-magnetic semiconductor material, materials such as zinc oxide, indium oxide, tin oxide, germanium oxide, gallium oxide, or ITO can be used. In this case, the thickness of the spacer layer 13 may be about 1.0 to 4.0 nm.

When a layer including a current-carrying point formed by a conductor in a nonmagnetic insulator is used as the spacer layer 13, a structure including a current-carrying point formed by a nonmagnetic conductor such as Cu, Au, or Al in a nonmagnetic insulator made of aluminum oxide or magnesium oxide may be used. The conductor may also be made of magnetic elements such as Co, Fe, or Ni. In this case, the thickness of the spacer layer 13 may be about 1.0 to 2.5 nm. The current-carrying point is, for example, a columnar body with a diameter of 1 nm to 5 nm when viewed from a direction perpendicular to the film surface. As described above, the first magnetic element 10 may be called an MTJ element, a GMR element, or the like, depending on the material of the spacer layer 13, but is also collectively called a magnetoresistance effect element.

The first magnetic element 10 may also have an underlayer, a cap layer, a perpendicular magnetization induction layer, and the like. The underlayer is located below the second ferromagnetic layer 12. The underlayer is a seed layer or a buffer layer. The seed layer enhances the crystallinity of the layer stacked on the seed layer. The seed layer is, for example, Pt, Ru, Hf, Zr, or NiFeCr. The thickness of the seed layer is, for example, 1 nm or more and 5 nm or less. The buffer layer is a layer that relieves lattice mismatch between different crystals. The buffer layer is, for example, Ta, Ti, W, Zr, Hf, or a nitride of these elements. The thickness of the buffer layer is, for example, 1 nm or more and 5 nm or less.

The cap layer is located above the first ferromagnetic layer 11. The cap layer prevents damage to the lower layer during the process and improves the crystallinity of the lower layer during annealing. The thickness of the cap layer is, for example, 3 nm or less so that sufficient light is irradiated to the first ferromagnetic layer 11. The cap layer is, for example, MgO, W, Mo, Ru, Ta, Cu, Cr, or a laminated film of these.

The perpendicular magnetization induced layer is formed when the first ferromagnetic layer 11 is a perpendicular magnetization film. The perpendicular magnetization induced layer is laminated on the first ferromagnetic layer 11. The perpendicular magnetization induced layer induces perpendicular magnetic anisotropy in the first ferromagnetic layer 11. The perpendicular magnetization induced layer is, for example, magnesium oxide, W, Ta, Mo, etc. When the perpendicular magnetization induced layer is magnesium oxide, it is preferable that the magnesium oxide has oxygen deficiency in order to increase the conductivity. The film thickness of the perpendicular magnetization induced layer is, for example, 0.5 nm or more and 2.0 nm or less.

The first ferromagnetic layer 21 in the second magnetic element 20 corresponds to the first ferromagnetic layer 11 in the first magnetic element 10. The constituent material, film thickness, layer structure, etc. of the first ferromagnetic layer 21 can be the same as those of the first ferromagnetic layer 11. The second ferromagnetic layer 22 in the second magnetic element 20 corresponds to the second ferromagnetic layer 12 in the first magnetic element 10. The constituent material, film thickness, layer structure, etc. of the second ferromagnetic layer 22 can be the same as those of the second ferromagnetic layer 12. The spacer layer 23 in the second magnetic element 20 corresponds to the spacer layer 13 in the first magnetic element 10. The constituent material, film thickness, layer structure, etc. of the spacer layer 23 can be the same as those of the spacer layer 13. The second magnetic element 20 may also have an underlayer, a cap layer, a perpendicular magnetization induction layer, etc., like the first magnetic element 10.

The first magnetic element 10 and the second magnetic element 20 are fabricated, for example, by a lamination process, an annealing process, and a processing process for each layer. Each layer is formed, for example, by sputtering. Annealing is performed, for example, at 250°C or higher and 450°C or lower. The laminated film is processed, for example, by photolithography and etching. The shortest width of the first magnetic element 10 and the second magnetic element 20 when viewed from the z direction may be, for example, 10 nm or higher and 2000 nm or lower, or 30 nm or higher and 500 nm or lower.

Although FIG. 3 shows an example of the first magnetic element 10 and the second magnetic element 20, the magnetic element may have a ferromagnetic material whose magnetization state changes when irradiated with light, and the resistance value may change with the change in the magnetization state. In addition to the above-mentioned MTJ element and GMR element, the magnetic element may be, for example, an anisotropic magnetoresistance (AMR) effect element, a colossal magnetoresistance (CMR) effect element, or the like.

The delay circuit 40 is, for example, between the second magnetic element 20 and the output terminal _t1 . The delay circuit 40 delays a signal resulting from the second output from the second magnetic element 20 (in this example, a signal in which a change in the voltage of the second output is extracted). The delay circuit 40 may be a known one.

Next, the operation of the light detection device 100 will be described. When the first magnetic element 10 is irradiated with a light pulse, the first magnetic element 10 outputs a first output. A change in the voltage of the first output (a voltage change based on the output voltage from the first magnetic element 10 in a state where no light pulse is irradiated) is output from the output terminal _t1 . As described above, the change in the voltage of the first output is an example of a first signal. Similarly, when the second magnetic element 20 is irradiated with a light pulse, the second magnetic element 20 outputs a second output. A change in the voltage of the second output (a voltage change based on the output voltage from the second magnetic element 20 in a state where no light pulse is irradiated) is delayed from the first signal caused by the first output and is output from the output terminal _t1 . As described above, a signal obtained by extracting and delaying the change in the voltage of the second output is an example of a second signal. In other words, when the first magnetic element 10 and the second magnetic element 20 are irradiated with the same light pulse, a voltage that is a combination of the change in voltage of the first output (first signal) and a signal (second signal) that is obtained by extracting and delaying the change in voltage of the second output is output from output terminal _t1 .

The optical detection device 100 combines the first output and the second output according to a predetermined signal processing method and outputs the result from the output terminal _t1 . The optical detection device 100 combines the first signal resulting from the first output and the second signal resulting from the second output when the same optical pulse is irradiated to the first magnetic element 10 and the second magnetic element ₂₀ , in a state where the first condition and the second condition are satisfied. In the example shown in FIG. 1, the line between the first magnetic element 10 and the output terminal t1 and the line between the second magnetic element 20 and the output terminal _t1 are simply connected, but if the length of these lines is long, the occurrence of problems such as signal reflection may be suppressed by connecting these lines using an appropriate power combiner. The first signal is caused by the first output, and may be, for example, an extracted voltage change of the first output, the first output itself, an extracted voltage change of the first output with the polarity inverted, or the intensity of the first output changed. The second signal is caused by the second output, and may be, for example, an extracted change in voltage of the second output, or the second output itself, or an extracted change in voltage of the second output with the polarity inverted, or a modified intensity of the second output, or any of these delayed.

In the example shown in Fig. 1, the photodetector 100 outputs from the output terminal t1 a voltage obtained by combining a voltage change in the first output (first signal) and a signal (second signal) obtained by extracting and delaying a voltage change in the second output when the same optical pulse is irradiated to the first magnetic element ₁₀ and the second magnetic element 20. The first condition is that the time position of the peak of the first signal is different from the time position of the peak of the second signal. The second condition is that the positive and negative of the amount of change until the first signal reaches its peak is different from the positive and negative of the amount of change until the second signal reaches its peak.

First, the principle of outputting a first output from the first magnetic element 10 when an optical pulse is irradiated to the first magnetic element 10 and the principle of outputting a second output from the second magnetic element 20 when an optical pulse is irradiated to the second magnetic element 20 will be described. The principles of operation of the first magnetic element 10 and the second magnetic element 20 are the same, so the operation of the first magnetic element 10 will be described below as an example.

A light pulse is irradiated to the first ferromagnetic layer 11. The resistance value in the z direction of the first magnetic element 10 changes when the first ferromagnetic layer 11 is irradiated with light. The output voltage from the first magnetic element 10 changes when the first ferromagnetic layer 11 is irradiated with light.

Figures 4 and 5 are diagrams for explaining an example of operation of the first magnetic element 10 according to the first embodiment. Figure 4 is a diagram for explaining a first mechanism of the example of operation, and Figure 5 is a diagram for explaining a second mechanism of the example of operation. In the upper graphs of Figures 4 and 5, the vertical axis represents the intensity of light irradiated to the first ferromagnetic layer 11, and the horizontal axis represents time. In the lower graphs of Figures 4 and 5, the vertical axis represents the resistance value of the first magnetic element 10 in the z direction, and the horizontal axis represents time.

First, in a state where the first ferromagnetic layer 11 is irradiated with light of a first intensity _W1 (hereinafter referred to as an initial state), the magnetization _M11 of the first ferromagnetic layer 11 and the magnetization _M12 of the second ferromagnetic layer 12 are in an antiparallel relationship, and the resistance value in the z direction of the first magnetic element 10 indicates a second resistance value _R2 . Here, a case where the intensity of the light irradiated to the first ferromagnetic layer 11 is zero may be regarded as a state where light of a first intensity _W1 is irradiated.

By passing a sense current Is through the first magnetic element 10 in the z direction, a voltage is generated across both ends of the first magnetic element 10 in the z direction. The output voltage from the first magnetic element 10 is generated between the first electrode 14 and the second electrode 15.

4, it is preferable to flow the sense current Is from the second ferromagnetic layer 12 toward the first ferromagnetic layer 11. By flowing the sense current Is in this direction, a spin transfer torque in the opposite direction to the magnetization _M12 of the second ferromagnetic layer 12 acts on the magnetization _M11 of the first ferromagnetic layer 11, and the magnetization _M11 and the magnetization _M12 tend to be antiparallel to each other in the initial state.

Then, the intensity of the light irradiated to the first ferromagnetic layer 11 changes from the first intensity _W1 to the second intensity _W2 . For example, when a light pulse is irradiated to the first magnetic element 10, the intensity of the light irradiated to the first ferromagnetic layer 11 changes from the first intensity _W1 to the second intensity _W2 . The light of the second intensity _W2 is greater than the light of the first intensity _W1 .

The second intensity _W2 is greater than the first intensity _W1 , and the magnetization _{M11 of the first ferromagnetic layer 11 changes from its initial state. The state of the magnetization M11} of the first ferromagnetic layer 11 when the first ferromagnetic layer 11 is not irradiated with light is different from the state of the magnetization _M11 of the first ferromagnetic layer ₁₁ when irradiated with light of the second intensity _W2 . The state of the magnetization _M11 refers to, for example, the inclination angle or magnitude with respect to the z direction.

For example, as shown in Fig. 4, when the intensity of light irradiated to the first ferromagnetic layer 11 changes from the first intensity _W1 to the second intensity _W2 , the magnetization _M11 tilts with respect to the z direction. Also, for example, as shown in Fig. 5, when the intensity of light irradiated to the first ferromagnetic layer 11 changes from the first intensity _W1 to the second intensity _W2 , the magnitude of the magnetization _M11 decreases. For example, when the magnetization _M11 of the first ferromagnetic layer 11 tilts with respect to the z direction due to the irradiation intensity of light, the tilt angle is, for example, greater than 0° and smaller than 90°.

When the magnetization _M11 of the first ferromagnetic layer 11 changes from its initial state by irradiating the first magnetic element 10 with a light pulse, the resistance value in the z direction of the first magnetic element 10 indicates a first resistance value _R1 , and the magnitude of the output voltage from the first magnetic element 10 changes from a first value to a second value (the first magnetic element 10 outputs a first output). The first resistance value _R1 is smaller than the second resistance value _R2 . The second value is smaller than the first value. The first resistance value _R1 is between the resistance value (second resistance value _R2 ) when the magnetization _M11 and the magnetization _M12 are antiparallel and the resistance value when the magnetization _M11 and the magnetization _M12 are parallel.

In the case shown in Fig. 4, a spin transfer torque in the opposite direction to the magnetization _M12 of the second ferromagnetic layer 12 acts on the magnetization _M11 of the first ferromagnetic layer 11. Therefore, the magnetization _M11 tries to return to an antiparallel state to the magnetization _M12 , and when the intensity of the light irradiated to the first ferromagnetic layer 11 changes from the second intensity to the first intensity, the magnetization _M11 returns to an antiparallel state to the magnetization _M12 . In the case shown in Fig. 5, when the intensity of the light irradiated to the first ferromagnetic layer 11 returns to the first intensity _W1 , the magnitude of the magnetization _M11 of the first ferromagnetic layer 11 returns to the original, and the first magnetic element 10 returns to the initial state. In either case, the resistance value in the z direction of the first magnetic element 10 returns to the second resistance value _R2 . In other words, when the intensity of the light irradiated to the first ferromagnetic layer 11 changes from the second intensity _W2 to the first intensity _W1 , the resistance value in the z-direction of the first magnetic element 10 changes from the first resistance value _R1 to the second resistance value _R2 .

4 and 5, when the intensity of the light irradiated to the first ferromagnetic layer 11 changes from the second intensity _W2 to the first intensity _W1 , the resistance value in the z direction of the first magnetic element 10 changes from the first resistance value _R1 to the second resistance value _R2 . The time (fall time) required for the resistance value in the z direction of the first magnetic element 10 to change from the first resistance value _R1 to the second resistance value _R2 and for the magnitude of the output voltage from the first magnetic element 10 to change from the second value to the first value is longer than the time required for the intensity of the light irradiated to the first ferromagnetic layer 11 to change from the second intensity _W2 to the first intensity _W1 , and is longer than the time (rise time) required for the magnitude of the output voltage from the first magnetic element 10 to change from the first value to the second value.

Here, the case where the magnetization _M11 and the magnetization _M12 are antiparallel in the initial state has been described as an example, but the magnetization _M11 and the magnetization _M12 may be parallel in the initial state. In this case, the resistance value in the z direction of the first magnetic element 10 increases as the state of the magnetization _M11 changes (for example, as the angle change from the initial state of the magnetization _M11 increases). When the magnetization _M11 and the magnetization _M12 are parallel in the initial state, it is preferable to flow the sense current Is from the first ferromagnetic layer 11 toward the second ferromagnetic layer 12. By flowing the sense current Is in this direction, a spin transfer torque in the same direction as the magnetization _M12 of the second ferromagnetic layer 12 acts on the magnetization _M11 of the first ferromagnetic layer 11, and the magnetization _M11 and the magnetization _M12 become parallel in the initial state. In addition, when the magnetization _M11 and the magnetization _M12 are in an anti-parallel relationship in the initial state, the fall time until the output voltage from the magnetic element returns to its original state after irradiation with a light pulse is shorter than when the magnetization _M11 and the magnetization _M12 are in a parallel relationship in the initial state.

The output voltage from the first magnetic element 10 changes in response to the intensity of light irradiated to the first ferromagnetic layer 11. The first magnetic element 10 can convert the intensity of the irradiated light into the output voltage from the first magnetic element 10, and can also convert a change in the intensity of the irradiated light into a change in the output voltage from the first magnetic element 10. The capacitor 91 passes only high-frequency components of the output voltage, so that the amount of change in the voltage of the first output based on the output voltage from the first magnetic element 10 in the initial state is output as a first signal from the output terminal _t1 .

Similarly, the output voltage from the second magnetic element 20 changes in response to the intensity of light irradiated to the first ferromagnetic layer 21. The second magnetic element 20 can convert the intensity of the irradiated light into a change in the output voltage from the second magnetic element 20, and can also convert a change in the intensity of the irradiated light into a change in the output voltage from the second magnetic element 20. The capacitor 91 passes only high-frequency components of the output voltage, and therefore the amount of change in the voltage of the second output based on the output voltage from the second magnetic element 20 in the initial state is output from the output terminal _t1 .

The optical detection device 100 combines the first and second signals generated when the first and second magnetic elements 10 and 20 are irradiated with the same optical pulse in a state that satisfies the first and second conditions.

The first condition is satisfied by, for example, a delay circuit 40. The delay circuit 40 delays a signal resulting from the second output (in this example, a signal in which a change in the voltage of the second output is extracted). The signal resulting from the second output is delayed by the delay circuit 40 to become the second signal. At the output terminal _t1 , the time position of the peak of the first signal is different from the time position of the peak of the second signal. Here, the time position of the peak is the time when the value of the signal becomes a peak. For example, the delay circuit 40 makes the time position of the peak of the first signal precede the time position of the peak of the second signal at the output terminal _t1 . It is preferable that the difference between the time position of the peak of the first signal and the time position of the peak of the second signal is shorter than the time from the peak of the first signal to the value of the first signal becoming 30% of the peak value of the first signal in the falling part of the first signal. This is because the time position of the peak of the second signal is preferably at a time position where the absolute value of the falling slope of the first signal is large.

In addition, in the photodetection device 100 according to the first embodiment, the second condition is satisfied by the fact that the polarity (positive/negative) of the power source 31 connected to the first surface 10A on the output terminal _t1 side of the first magnetic element 10 is different from the polarity (positive/negative) of the power source 32 connected to the first surface 20A on the output terminal _t1 side of the second magnetic element 20.

The first magnetic element 10 and the second magnetic element 20 have different directions in which the sense current Is flows. The change amount ΔV ₁₀ of the first output from the first magnetic element 10 due to irradiation of the first magnetic element 10 with a light pulse is calculated by ΔV ₁₀ = ΔR ₁₀ × I. In the formula, I is the absolute value of the current amount of the sense current Is. The change amount ΔV ₂₀ of the second output from the second magnetic element 20 due to irradiation of the second magnetic element 20 with a light pulse is calculated by ΔV ₂₀ = ΔR ₂₀ × -I. ΔR ₁₀ is the change amount of the resistance value in the z direction of the first magnetic element 10 due to irradiation of the first magnetic element 10 with a light pulse. ΔR ₂₀ is the change amount of the resistance value in the z direction of the second magnetic element 20 due to irradiation of the second magnetic element 20 with a light pulse.

The resistance value in the z direction of the first magnetic element 10 decreases from the second resistance value _R2 to the first resistance value R1 when the intensity of the light irradiated to the first ferromagnetic layer 11 changes from the first intensity to the second intensity, and increases from the first resistance value _R1 to the second resistance value _R2 when the intensity of the light irradiated to the first ferromagnetic layer 11 changes from the second intensity to the first intensity. Similarly, the resistance value in the z direction of the second magnetic element 20 decreases when the intensity of the light irradiated to the first ferromagnetic layer ₂₁ changes from the first intensity to the second intensity, and increases when the intensity of the light irradiated to the first ferromagnetic layer 21 changes from the second intensity to the first intensity. That is, the first magnetic element 10 and the second magnetic element 20 have the same positive and negative change in resistance value due to irradiation with a light pulse.

The first magnetic element 10 and the second magnetic element 20 have different directions of flow of the sense current Is, and the change in resistance value due to irradiation with a light pulse is the same in sign, so the change in the first output from the first magnetic element 10 due to irradiation with a light pulse is opposite to the change in the second output from the second magnetic element 20 due to irradiation with a light pulse.

The intensity of the first output from the first magnetic element 10 and the intensity of the second output from the second magnetic element 20 may be the same or different. The intensity of the first output is changed by changing the value of the current supplied by the power supply 31. The larger the value of the current supplied by the power supply 31 to the first magnetic element 10, the larger the first output and the larger the intensity of the first signal. Similarly, the intensity of the second output and the second signal is changed by changing the value of the current supplied by the power supply 32. Therefore, by adjusting the values of the current supplied by the power supplies 31 and 32, the absolute value of the amount of change until the first signal reaches its peak and the absolute value of the amount of change until the second signal reaches its peak can be adjusted.

FIG. 6 shows the output characteristic of the photodetector 100 according to the first embodiment with respect to the optical pulse. The first signal S1 is a signal caused by the first output from the first magnetic element 10, and is obtained by extracting and delaying the voltage change of the first output. The second signal S2 is a signal caused by the second output from the second magnetic element 20, and is a signal obtained by extracting and delaying the voltage change of the second output. As shown in FIG. 6, when the first magnetic element 10 and the second magnetic element 20 are irradiated with light L in a pulsed manner, the first signal S1 and the second signal S2 are output. The change amount ΔV _10m until the first signal S1 reaches a peak due to irradiation of the optical pulse is positive, and the change amount ΔV _20m until the second signal S1 reaches a peak due to irradiation of the optical pulse is negative. In this way, the photodetector 100 satisfies the second condition. The delay circuit 40 delays the time position tb of the peak of the second signal S2 from the time position ta of the peak of the first signal S1. The time position ta of the peak of the first signal S1 is different from the time position tb of the peak of the second signal S2. In this manner, the photodetection device 100 satisfies the first condition.

The optical detection device 100 combines the first signal S1 and the second signal S2. Since the first signal S1 and the second signal S2 have opposite polarities, this process corresponds to a process of finding the difference between the magnitude (absolute value) of the first signal S1 and the magnitude (absolute value) of the second signal S2. The first signal S1 and the second signal S2 each have a long fall time from reaching a peak to returning to their original value, but the total output signal S from the optical detection device 100, which is a combination of the first signal S1 and the second signal S2, has a short fall time. By combining the first signal S1 and the second signal S2 generated when the first magnetic element 10 and the second magnetic element 20 are irradiated with the same light pulse in a state that satisfies the first and second conditions, the absolute value of the falling portion of the total output signal S becomes small because the falling portion of the first signal S1 and the portion including the peak portion of the second signal S2 cancel each other out, while the absolute value of the peak portion of the total output signal S does not become very small because the rising portion of the second signal is simply subtracted from the peak portion of the first signal S1. In other words, the photodetection device 100 according to the first embodiment has a short fall time of the output after being irradiated with pulsed light.

If the fall time of the output after irradiation with pulsed light is long, when successive pulsed light is irradiated, the next pulsed light may be irradiated before the output from the previous pulsed light has completely fallen. In this case, the output change of the optical detection device 100 cannot keep up with the successive pulses, and the output change of the optical detection device 100 becomes smaller over time. In contrast, an optical detection device 100 with a short fall time of the output after irradiation with pulsed light can suppress the output change from becoming smaller over time, even when successive pulsed light is incident.

Figures 7 and 8 show the output characteristics of the optical detection device of the first embodiment with respect to optical pulses. Figures 7 and 8 show the results of determining the output characteristics of the optical detection device 100 with the circuit diagram configuration shown in Figure 1.

Fig. 7 is a graph showing measured values of the output (total output signal S) from output terminal _t1 of the photodetector ₁₀₀ , the output (first signal S1) resulting from the first output from the first magnetic element 10, and the output (second signal S2) resulting from the second output from the second magnetic element 20, among the outputs from output terminal t1. Fig. 8 is a graph showing the first signal S1, the second signal S2, and the total output signal S from the photodetector 100 normalized by their respective peak values.

7 and 8, the first magnetic element 10 is a cylinder having a diameter of 200 nm, the magnitude of the direct current applied from the power source 31 to the first magnetic element 10 is 0.76 mA, the second magnetic element 20 is a cylinder having a diameter of 200 nm, and the magnitude of the direct current applied from the power source 32 to the second magnetic element 20 is 0.76 mA. In a state in which the first magnetic element 10 and the second magnetic element 20 are not irradiated with light, the first magnetic element 10 has a magnetization _M11 of the first ferromagnetic layer 11 and a magnetization _M12 of the second ferromagnetic layer 12 in an antiparallel relationship, and the second magnetic element 20 has a magnetization _M21 of the first ferromagnetic layer 21 and a magnetization _M22 of the second ferromagnetic layer 22 in an antiparallel relationship. The delay time of the second signal S2 with respect to the first signal S1 was 4.4 nsec. The absolute value of the amount of change until the first signal S1 reaches a peak is set to be the same as the absolute value of the amount of change until the second signal S2 reaches a peak.

As shown in Figures 7 and 8, the photodetection device 100 according to the first embodiment has a shorter fall time of the output after irradiation with pulsed light compared to when the first magnetic element 10 or the second magnetic element 20 is used alone.

Second Embodiment
Fig. 9 is a circuit diagram of a photodetection device 101 according to the second embodiment. In the second embodiment, the same components as those in the first embodiment are denoted by the same reference numerals, and the description thereof will be omitted. In Fig. 9, the magnetization direction of the ferromagnetic body when the photodetection device 101 is not irradiated with light is indicated by an arrow.

The photodetector 101 includes, for example, a first magnetic element 10, a second magnetic element 20, a capacitor 91, an inductor 92, an output terminal _t1 , a reference potential terminal _t2 , a magnetic field application unit 51, and a magnetic field application unit 52. The photodetector 101 may include a power supply 31 and a power supply 33, or the power supply 31 and the power supply 33 may be external to the photodetector 101.

Figure 10 is a cross-sectional view of the vicinity of the first magnetic element 10 and the second magnetic element 20 according to the second embodiment. In Figure 10, the arrows indicate the direction of magnetization of the ferromagnetic material when no light is irradiated onto the light detection device 101.

The second magnetic element 20 according to the second embodiment differs from the second magnetic element 20 according to the first embodiment in that, when the second magnetic element 20 is not irradiated with light, the magnetization _M21 of the first ferromagnetic layer 21 and the magnetization _M22 of the second ferromagnetic layer 22 are parallel to each other.

In the second embodiment, in a state where the first magnetic element 10 and the second magnetic element 20 are not irradiated with light, the relationship between the magnetization directions of the first ferromagnetic layer 11 and the second ferromagnetic layer 12 of the first magnetic element 10 is different from the relationship between the magnetization directions of the first ferromagnetic layer 21 and the second ferromagnetic layer 22 of the second magnetic element 20. For example, the relationship between the magnetization directions of the first ferromagnetic layer 11 and the second ferromagnetic layer 12 of the first magnetic element 10 is antiparallel, and the relationship between the magnetization directions of the first ferromagnetic layer 21 and the second ferromagnetic layer 22 of the second magnetic element 20 is parallel. The second embodiment is not limited to this example, and in a state where the first magnetic element 10 and the second magnetic element 20 are not irradiated with light, the relationship between the magnetization directions of the first ferromagnetic layer 11 and the second ferromagnetic layer 12 of the first magnetic element 10 may be parallel, and the relationship between the magnetization directions of the first ferromagnetic layer 21 and the second ferromagnetic layer 22 of the second magnetic element 20 may be antiparallel.

The power supply 33 is a DC power supply and is connected to the second magnetic element 20. The power supply 33 may be the same as the power supply 31. The power supply 33 applies a DC current or a DC voltage to the second magnetic element 20. The light detection device 101 is configured such that, for example, the first surface 20A of the second magnetic element 20 on the output terminal _t1 side is connected to the negative terminal of the power supply 33, and the second surface 20B of the second magnetic element 20 facing the first surface 20A is connected to the positive terminal of the power supply 33.

The light detection device 101 is configured so that the polarity (positive/negative) of the power source 31 connected to the first surface 10A on the output terminal _t1 side of the first magnetic element 10 is the same as the polarity (positive/negative) of the power source 33 connected to the first surface 20A on the output terminal _t1 side of the second magnetic element 20. Here, an example is shown in which the first surface 10A is connected to the negative terminal of the power source 31, the second surface 10B is connected to the positive terminal of the power source 31, the first surface 20A is connected to the negative terminal of the power source 33, and the second surface 20B is connected to the positive terminal of the power source 33, but the first surface 10A may be connected to the positive terminal of the power source 31, the second surface 10B may be connected to the negative terminal of the power source 31, the first surface 20A may be connected to the positive terminal of the power source 33, and the second surface 20B may be connected to the negative terminal of the power source 33.

The magnetic field application units 51 are positioned to sandwich the first magnetic element 10, for example, in an in-plane direction (x-direction in the example of FIG. 10). When a leakage magnetic field from the magnetic field application units 51 is applied as a bias magnetic field, the magnetization _M11 of the first ferromagnetic layer 11 is oriented anti-parallel to the magnetization _M12 of the second ferromagnetic layer 12 in a state in which the first magnetic element 10 is not irradiated with light. The magnetic field application units 51 are positioned so as not to block the light irradiated to the first magnetic element 10. The magnetic field application units 51 include, for example, a hard magnetic material.

The magnetic field application units 52 are positioned to sandwich the second magnetic element 20, for example, in an in-plane direction (x-direction in the example of FIG. 10 ). When a leakage magnetic field from the magnetic field application units 52 is applied as a bias magnetic field, the magnetization _M21 of the first ferromagnetic layer 21 is oriented in a direction parallel to the magnetization _M22 of the second ferromagnetic layer 22 in a state in which the second magnetic element 20 is not irradiated with light. The magnetic field application units 52 are positioned so as not to block the light irradiated to the second magnetic element 20. The magnetic field application units 52 include, for example, a hard magnetic material.

Next, the operation of the light detection device 101 will be described. When an optical pulse is irradiated to the first magnetic element 10, the first magnetic element 10 outputs a first output, and a change in the voltage of the first output based on the output voltage from the first magnetic element 10 in the initial state is output from the output terminal _t1 as a first signal. The first signal is a signal caused by the first output. Similarly, when an optical pulse is irradiated to the second magnetic element 20, the second magnetic element 20 outputs a second output, and a change in the voltage of the second output based on the output voltage from the second magnetic element 20 in the initial state is output from the output terminal _t1 . The change in the voltage of the second output is delayed until it reaches the output terminal _t1 , and becomes a second signal. The second signal is a signal caused by the second output.

The photodetector 101 combines the first signal and the second signal according to a predetermined signal processing method and outputs the combined signal from the output terminal t _1. The photodetector 101 combines the first signal and the second signal obtained when the first magnetic element 10 and the second magnetic element 20 are irradiated with the same light pulse in a state that satisfies the first condition and the second condition.

The first condition is satisfied, for example, by the delay circuit 40. By delaying the signal resulting from the second output (in this example, a signal in which a change in the voltage of the second output is extracted) by the delay circuit 40, it is possible to make the time position of the peak of the first signal and the time position of the peak value of the second signal at the output terminal _t1 different.

The second condition can be satisfied when, in a state in which the first magnetic element 10 and the second magnetic element 20 are not irradiated with light, the relationship between the magnetization directions of the first ferromagnetic layer 11 and the second ferromagnetic layer 12 of the first magnetic element 10 is different from the relationship between the magnetization directions of the first ferromagnetic layer 21 and the second ferromagnetic layer 22 of the second magnetic element 20.

The resistance value in the z direction of the first magnetic element 10 decreases from the second resistance value _R2 to the first resistance value R1 when the intensity of the light irradiated to the first ferromagnetic layer 11 changes from the first intensity to the second intensity, and increases from the first resistance value _R1 to the second resistance value _R2 when the intensity of the light irradiated to the first ferromagnetic layer 11 changes from the second intensity to the first intensity. In contrast, the resistance value in the z direction of the second magnetic element 20 increases when the intensity of the light irradiated to the first ferromagnetic layer ₂₁ changes from the first intensity to the second intensity, and decreases when the intensity of the light irradiated to the first ferromagnetic layer 21 changes from the second intensity to the first intensity. That is, the first magnetic element 10 and the second magnetic element 20 have different positive and negative changes in resistance value due to irradiation with a light pulse.

The first magnetic element 10 and the second magnetic element 20 have the same direction of the sense current Is flowing, and the change in resistance value due to irradiation with a light pulse is different in sign, so the change in the first signal due to the first output from the first magnetic element 10 due to irradiation with a light pulse and the change in the second signal due to the second output from the second magnetic element 20 due to irradiation with a light pulse are opposite in sign. Therefore, in the photodetector 101 according to the second embodiment, for the first signal and the second signal generated when the first magnetic element 10 and the second magnetic element 20 are irradiated with the same light pulse, the time position of the peak of the first signal and the time position of the peak of the second signal are different, and the change in the first signal to reach the peak and the change in the second signal to reach the peak are opposite in sign, and by combining these, the fall time of the output of the photodetector 101 after irradiation with a pulsed light is short.

Figures 11 and 12 show the output characteristics of the photodetector according to the second embodiment with respect to optical pulses. Figures 11 and 12 show the results of determining the output characteristics of the photodetector 101 in the circuit configuration shown in Figure 9.

Fig. 11 shows measured values of the output (total output signal S') from output terminal _t1 of the photodetector ₁₀₁ , the output (first signal S1') resulting from the first output from the first magnetic element 10, and the output (second signal S2') resulting from the second output from the second magnetic element 20, among the outputs from output terminal t1. Fig. 12 is a graph showing the first signal S1', the second signal S2', and the total output signal S' from the photodetector 101 normalized by their respective peak values.

In the example shown in the graphs of Figures 11 and 12, the first magnetic element 10 is a cylinder with a diameter of 200 nm, the magnitude of the DC current applied from the power source 31 to the first magnetic element 10 is 0.76 mA, the second magnetic element 20 is a cylinder with a diameter of 200 nm, and the magnitude of the DC current applied from the power source 33 to the second magnetic element 20 is 0.34 mA. Since the magnitude of the DC current applied to the first magnetic element 10 is different from the magnitude of the DC current applied to the second magnetic element 20, the absolute value of the amount of change until the first signal reaches its peak is different from the absolute value of the amount of change until the second signal reaches its peak. The delay time of the second signal relative to the first signal was 12 nsec.

As shown in Figures 11 and 12, the photodetector 101 according to the second embodiment has a shorter fall time of the output after irradiation with pulsed light compared to when the first magnetic element 10 or the second magnetic element 20 is used alone.

So far, an example of the second embodiment has been illustrated, but the light detection device 101 according to the second embodiment is not limited to this example.

For example, FIG. 13 is a cross-sectional view of the vicinity of the first magnetic element 10 and the second magnetic element 20 of the first modified example of the photodetector according to the second embodiment. In FIG. 13, the arrows indicate the direction of magnetization of the ferromagnetic material when the first magnetic element 10 and the second magnetic element 20 are not irradiated with light.

The optical detection device 101A is provided with a magnetic field application unit 53 instead of the magnetic field application unit 51 of the optical detection device 101.

The magnetic field application unit 53 is located at a position overlapping with the first magnetic element 10 in the z direction. The magnetic field application unit 53 is disposed, for example, in an intermediate layer 95 between the substrate Sub and the insulating layer 93. When a leakage magnetic field from the magnetic field application unit 53 is applied as a bias magnetic field, the magnetization _M11 of the first ferromagnetic layer 11 is oriented in a direction antiparallel to the magnetization _M12 of the second ferromagnetic layer 12 in a state in which the first magnetic element 10 is not irradiated with light. The magnetic field application unit 53 is located at a position that does not block the light irradiated to the first magnetic element 10. The magnetic field application unit 53 includes, for example, a hard magnetic material.

The photodetection device 101A satisfies the first and second conditions to combine the first and second signals, and therefore has the same effect as the photodetection device 101 according to the second embodiment. In FIG. 13, an example is shown in which a magnetic field application unit 53 is provided instead of the magnetic field application unit 51 of the photodetection device 101, but a magnetic field application unit may be provided in a position overlapping the second magnetic element 20 in the z direction instead of the magnetic field application unit 52.

For example, FIG. 14 is a cross-sectional view of the vicinity of the first magnetic element 10 and the second magnetic element 20 of a second modified example of the light detection device according to the second embodiment. In FIG. 14, the arrows indicate the direction of magnetization of the ferromagnetic material when the first magnetic element 10 and the second magnetic element 20 are not irradiated with light.

The photodetector 101B is different from the photodetector 100 in that it does not have the magnetic field application unit 51 and the magnetic field application unit 52. In addition, in the photodetector 101B, when the first magnetic element 10 and the second magnetic element 20 are not irradiated with light, the direction of the magnetization _M12 of the second ferromagnetic layer 12 of the first magnetic element 10 is opposite to the direction of the magnetization _M22 of the second ferromagnetic layer 22 of the second magnetic element 20. The orientation direction of the magnetization of the second ferromagnetic layer 12 and the second ferromagnetic layer 22 can be designed at the time of manufacture. In addition, when the first magnetic element 10 and the second magnetic element 20 are not irradiated with light, the magnetization _M11 of the first ferromagnetic layer 11 and the magnetization _M12 of the second ferromagnetic layer 12 are in an antiparallel relationship, and the magnetization _M21 of the first ferromagnetic layer 21 and the magnetization _M22 of the second ferromagnetic layer 22 are in a parallel relationship.

The optical detection device 101B combines the first signal and the second signal while satisfying the first and second conditions, and therefore has the same effect as the optical detection device 101 according to the second embodiment.

"Third embodiment"
Fig. 15 is a circuit diagram of a light detection device 102 according to the third embodiment. In the third embodiment, the same components as those in the second embodiment are denoted by the same reference numerals, and the description thereof will be omitted. In Fig. 15, the magnetization direction of the ferromagnetic body in the initial state in which the light detection device 102 is not irradiated with light is indicated by an arrow.

The photodetector 102 includes, for example, a first magnetic element 10, a second magnetic element 20, a delay circuit 40, an inverting circuit 41, a capacitor 91, an inductor 92, an output terminal _t1, and a reference potential terminal _t2 . The photodetector 102 may include a power supply 31 and a power supply 33, or the power supply 31 and the power supply 33 may be external to the photodetector 102.

The second magnetic element 20 according to the third embodiment differs from the second magnetic element 20 according to the second embodiment in that the magnetization _M21 of the first ferromagnetic layer 21 and the magnetization _M22 of the second ferromagnetic layer 22 are antiparallel to each other when the second magnetic element 20 is not irradiated with light. In the third embodiment, when the first magnetic element 10 and the second magnetic element 20 are not irradiated with light, the relationship between the magnetization directions of the first ferromagnetic layer 11 and the second ferromagnetic layer 12 of the first magnetic element 10 is the same as the relationship between the magnetization directions of the first ferromagnetic layer 21 and the second ferromagnetic layer 22 of the second magnetic element 20.

The inversion circuit 41 is, for example, between the second magnetic element 20 and the output terminal _t1 . The inversion circuit 41 may be between the first magnetic element 10 and the output terminal _t1 . The inversion circuit 41 inverts the polarity of an input signal input to the inversion circuit 41 and outputs the inverted signal. The inversion circuit 41 is, for example, an inverting amplifier circuit (e.g., an operational amplifier).

When the first magnetic element 10 is irradiated with an optical pulse, the first magnetic element 10 outputs a first output, and a change in the voltage of the first output based on the output voltage from the first magnetic element 10 in the initial state is output as a first signal from the output terminal _t1 . The first signal is a signal caused by the first output. When the second magnetic element 20 is irradiated with an optical pulse, the second magnetic element 20 outputs a second output, and a change in the voltage of the second output based on the output voltage from the second magnetic element 20 in the initial state is extracted by the capacitor 91, and a signal obtained by inverting the polarity of the signal obtained by extracting the change in the voltage of the second output by the inversion circuit 41 and delaying the signal by the delay circuit 40 is output as a second signal from the output terminal _t1 . The second signal is a signal caused by the second output. The optical detection device 102 combines the first signal and the second signal according to a predetermined signal processing method and outputs the result from the output terminal _t1 . The optical detection device 102 combines a first signal and a second signal generated when the first magnetic element 10 and the second magnetic element 20 are irradiated with the same optical pulse in a state that satisfies a first condition and a second condition.

The first condition is satisfied, for example, by the delay circuit 40. The delay circuit 40 delays a signal resulting from the second output (in this example, a signal obtained by extracting a change in the voltage of the second output and inverting the polarity of the signal by the inversion circuit 60), so that the time position of the peak of the first signal and the time position of the peak of the second signal at the output terminal _t1 can be made to differ from each other.

The second condition can also be satisfied by inverting the polarity of the signal resulting from the second output from the second magnetic element 20 using the inversion circuit 41. In this case, the second signal is a signal that extracts the change in the voltage of the second output, with the polarity inverted and further delayed.

The first signal resulting from the first output from the first magnetic element 10 and the second signal resulting from the second output from the second magnetic element 20 satisfy the first condition and the second condition at the output terminal _t1 . Therefore, the photodetector 102 combines the first signal and the second signal while satisfying the first condition and the second condition, and thus exerts the same effect as the photodetector 100 according to the first embodiment.

Figures 16 and 17 show the output characteristics of the light detection device of the third embodiment with respect to the light pulse. Figures 16 and 17 show the results of determining the output characteristics of the light detection device 102 in the circuit diagram configuration shown in Figure 15.

Fig. 16 shows measured values of the output from output terminal _t1 of the photodetector 102 (total output signal S"), and the output from output terminal _t1 resulting from the first output from the first magnetic element 10 (first signal S1"), and the output resulting from the second output from the second magnetic element 20 (second signal S2"). Fig. 17 is a graph showing the first signal S1", the second signal S2", and the total output signal S" from the photodetector 102 normalized by their respective peak values.

In the example shown in the graphs of Figures 16 and 17, the first magnetic element 10 is a cylinder with a diameter of 200 nm, the magnitude of the direct current applied to the first magnetic element 10 from the power source 31 is 0.76 mA, the second magnetic element 20 is a cylinder with a diameter of 200 nm, and the magnitude of the direct current applied to the second magnetic element 20 from the power source 33 is 0.76 mA. In a state in which the first magnetic element 10 and the second magnetic element 20 are not irradiated with light, the first magnetic element 10 has a magnetization _M11 of the first ferromagnetic layer 11 and a magnetization _M12 of the second ferromagnetic layer 12 in an anti-parallel relationship, and the second magnetic element 20 has a magnetization _M21 of the first ferromagnetic layer 21 and a magnetization _M22 of the second ferromagnetic layer 22 in an anti-parallel relationship. The delay time of the second signal with respect to the first signal was 11.4 nsec. The gain of the inversion circuit 41 was 0.4 times.

As shown in Figures 16 and 17, the photodetector 102 according to the third embodiment has a shorter fall time of the output after irradiation with pulsed light compared to when the first magnetic element 10 or the second magnetic element 20 is used alone.

"Fourth embodiment"
Fig. 18 is a circuit diagram of a photodetection device 103 according to the fourth embodiment. In the fourth embodiment, the same components as those in the first embodiment are denoted by the same reference numerals, and the description thereof will be omitted. In Fig. 18, the direction of magnetization of the ferromagnetic material when the photodetection device 103 is not irradiated with light is indicated by an arrow.

The photodetector 103 includes, for example, a first magnetic element 10, a second magnetic element 20, a capacitor 91, an inductor 92, an output terminal _t1, and a reference potential terminal _t2 . The photodetector 103 may include a power supply 31 and a power supply 32, or the power supplies 31 and 32 may be external to the photodetector 103. The photodetector 103 does not include the delay circuit 40 in the photodetector 100.

Figure 19 is a cross-sectional view of the vicinity of the first magnetic element 10 and the second magnetic element 20 according to the fourth embodiment. In Figure 19, the arrows indicate the direction of magnetization of the ferromagnetic material when no light is irradiated onto the light detection device 103.

The light detection device 103 is irradiated with a light pulse. The surface of the light detection device 103 that is irradiated with light is called the light irradiation surface LS. The light detection device 103 has a first intermediate layer 61 between the light irradiation surface LS and the first magnetic element 10. The light detection device 103 also has a second intermediate layer 62 between the light irradiation surface S1 and the second magnetic element 20.

The first intermediate layer 61 is, for example, on the first magnetic element 10. The second intermediate layer 62 is, for example, on the second magnetic element 20. The first intermediate layer 61 and the second intermediate layer 62 have different refractive indices. When the first intermediate layer 61 and the second intermediate layer 62 have different refractive indices, the first optical distance until the light pulse is irradiated to the first magnetic element 10 and the second optical distance until the light pulse is irradiated to the second magnetic element 20 are different. For example, the refractive index of the second intermediate layer 62 is larger than the refractive index of the first intermediate layer 61. In this case, the second optical distance until the light pulse is irradiated to the second magnetic element 20 is longer than the first optical distance until the light pulse is irradiated to the first magnetic element 10.

When the first magnetic element 10 is irradiated with an optical pulse, the first magnetic element 10 outputs a first output, and a change in the voltage of the first output based on the output voltage from the first magnetic element 10 in the initial state is output as a first signal from the output terminal _t1 . The first signal is a signal caused by the first output. When the second magnetic element 20 is irradiated with an optical pulse, the second magnetic element 20 outputs a second output, and a change in the voltage of the second output based on the output voltage from the second magnetic element 20 in the initial state is output as a second signal from the output terminal _t1 . The second signal is a signal caused by the second output. The optical detection device 103 combines the first signal and the second signal according to a predetermined signal processing method and outputs the result from the output terminal _t1 . The optical detection device 103 combines the first signal caused by the first output and the second signal caused by the second output when the same optical pulse is irradiated to the first magnetic element 10 and the second magnetic element 20, in a state that satisfies the first condition and the second condition.

The first condition is satisfied, for example, when the first optical distance is different from the second optical distance, such that the time positions of the peaks of the first signal and the second signal at the output terminal _t1 are different from each other.

In addition, in the photodetector 103 according to the fourth embodiment, the second condition is satisfied by the fact that the polarity (positive/negative) of the power source 31 connected to the first surface 10A on the output terminal _t1 side of the first magnetic element 10 is different from the polarity (positive/negative) of the power source 32 connected to the first surface 20A on the output terminal _t1 side of the second magnetic element 20.

The first signal resulting from the first output from the first magnetic element 10 and the second signal resulting from the second output from the second magnetic element 20 satisfy the first condition and the second condition at the output terminal _t1 . Therefore, the photodetector 103 combines the first signal and the second signal while satisfying the first condition and the second condition, and thus exerts the same effect as the photodetector 100 according to the first embodiment.

Fifth Embodiment
FIG. 20 is a plan view of a characteristic portion of the light detection device 104 according to the fifth embodiment. FIGS. 21 and 22 are cross-sectional views of the characteristic portion of the light detection device 104 according to the fifth embodiment. FIG. 21 is a cross-section taken along line A-A in FIG. 20, and FIG. 22 is a cross-section taken along line B-B in FIG. 20. The circuit diagram of the light detection device 104 according to the fifth embodiment is equivalent to the circuit diagram of the light detection device 103. In the fifth embodiment, the same components as those in the first embodiment are denoted by the same reference numerals, and the description thereof will be omitted. In FIGS. 21 and 22, the magnetization direction of the ferromagnetic material in a state where the light detection device 104 is not irradiated with light is indicated by an arrow.

The optical detection device 104 has, for example, a first optical waveguide 65, a second optical waveguide 66, and a cladding 67. A light pulse is irradiated onto a light irradiation surface LS of the optical detection device 104. The first optical waveguide 65 is configured to propagate the light pulse to the first magnetic element 10. The second optical waveguide 66 is configured to propagate the light pulse to the second magnetic element 20. The first optical waveguide 65 and the second optical waveguide 66 have different lengths.

At least a part of the first optical waveguide 65 is on, for example, the first magnetic element 10. At least a part of the second optical waveguide 66 is on, for example, the second magnetic element 20. The first optical waveguide 65 and the second optical waveguide 66 are covered with a clad 67. The first optical waveguide 65 and the second optical waveguide 66 contain, for example, lithium niobate as a main component. Some elements of the lithium niobate may be substituted with other elements. The clad 67 is, for example, SiO ₂ , Al ₂ O ₃ , MgF ₂ , La ₂ O ₃ , ZnO, HfO ₂ , MgO, Y ₂ O ₃ , CaF ₂ , In ₂ O ₃ , or a mixture thereof. The materials of the first optical waveguide 65 and the second optical waveguide 66 and the materials of the clad 67 are not limited to this example. For example, the cores constituting the first optical waveguide 65 and the second optical waveguide 66 may be made of silicon or silicon oxide to which germanium oxide has been added, and the clad 67 may be made of silicon oxide.

Since the first optical waveguide 65 and the second optical waveguide 66 have different lengths, the second optical distance until the optical pulse is irradiated to the second magnetic element 20 is different from the first optical distance until the optical pulse is irradiated to the first magnetic element 10. For example, the second optical distance until the optical pulse is irradiated to the second magnetic element 20 is longer than the first optical distance until the optical pulse is irradiated to the first magnetic element 10.

When the first magnetic element 10 is irradiated with an optical pulse, the first magnetic element 10 outputs a first output, and a change in the voltage of the first output based on the output voltage from the first magnetic element 10 in the initial state is output as a first signal from the output terminal _t1 . The first signal is a signal caused by the first output. When the second magnetic element 20 is irradiated with an optical pulse, the second magnetic element 20 outputs a second output, and a change in the voltage of the second output based on the output voltage from the second magnetic element 20 in the initial state is output as a second signal from the output terminal _t1 . The second signal is a signal caused by the second output. The optical detection device 104 combines the first signal and the second signal according to a predetermined signal processing method and outputs the result from the output terminal _t1 . The optical detection device 104 combines the first signal caused by the first output and the second signal caused by the second output when the same optical pulse is irradiated to the first magnetic element 10 and the second magnetic element 20, in a state that satisfies the first condition and the second condition.

The first condition is satisfied, for example, by the first optical waveguide 65 and the second optical waveguide 66 having different lengths. When the first optical waveguide 65 and the second optical waveguide 66 have different lengths, the first optical distance and the second optical distance are different, and the time positions of the peaks of the first signal and the second signal at the output terminal _t1 are different.

In addition, in the photodetector 104 according to the fifth embodiment, the second condition is satisfied by the fact that the polarity (positive/negative) of the power source 31 connected to the first surface 10A on the output terminal _t1 side of the first magnetic element 10 is different from the polarity (positive/negative) of the power source 32 connected to the first surface 20A on the output terminal _t1 side of the second magnetic element 20.

The first signal resulting from the first output from the first magnetic element 10 and the second signal resulting from the second output from the second magnetic element 20 satisfy the first condition and the second condition at the output terminal _t1 . Therefore, the photodetector 104 combines the first signal and the second signal while satisfying the first condition and the second condition, and thus exerts the same effect as the photodetector 100 according to the first embodiment.

Here, an example has been shown in which the first condition is satisfied by changing the lengths of the first optical waveguide 65 and the second optical waveguide 66, but the configuration for satisfying the first condition is not limited to this example. For example, as in a photodetection device 104A according to a first modified example shown in Fig. 23, the lengths of the first optical waveguide 65 and the second optical waveguide 66 may be the same, and the refractive indexes of the first optical waveguide 65 and the second optical waveguide 66 may be changed. If the refractive indexes of the first optical waveguide 65 and the second optical waveguide 66 are different, the first optical distance and the second optical distance are different, and the time positions of the peaks of the first signal and the second signal at the output terminal _t1 are different.

Sixth Embodiment
Fig. 24 is a circuit diagram of a photodetector 105 according to the sixth embodiment. In the sixth embodiment, the same components as those in the first embodiment are denoted by the same reference numerals, and the description thereof will be omitted. In Fig. 24, the magnetization direction of the ferromagnetic body when the photodetector 105 is not irradiated with light is indicated by an arrow.

The photodetector 105 includes, for example, a first magnetic element 10, a delay circuit 40, an inverting circuit 41, a capacitor 91, an inductor 92, an output terminal _t1, and a reference potential terminal _t2 . The inverting circuit 41 is the same as that in the second embodiment. The photodetector 105 may include a power supply 31, which may be external to the photodetector 105.

24, a line connecting the first magnetic element 10 and the output terminal _t1 branches into a first line 71 and a second line 72. A first output from the first magnetic element 10 propagates to each of the first line 71 and the second line 72.

The delay circuit 40 is connected to only one of the first line 71 and the second line 72. The inversion circuit 41 is connected to only one of the first line 71 and the second line 72. The delay circuit 40 and the inversion circuit 41 may be connected to the same line or may be connected to different lines. For example, in the example shown in FIG. 24, the delay circuit 40 and the inversion circuit 41 are connected to the second line 72.

The photodetector 105 combines the first signal and the second signal according to a predetermined signal processing method and outputs the combined signal from the output terminal _t1 . In the photodetector 105, when an optical pulse is irradiated to the first magnetic element 10, a first signal is generated that reaches the output terminal _t1 via the first line 71 and a second signal is generated that reaches the output terminal _t1 via the second line 72. The photodetector 105 combines the first signal and the second signal in a state where a first condition and a second condition are satisfied. The first condition is that the time position of the peak of the first signal is different from the time position of the peak of the second signal. The second condition is that the positive and negative of the amount of change until the first signal reaches the peak is different from the positive and negative of the amount of change until the second signal reaches the peak.

First, when an optical pulse is irradiated onto the first magnetic element 10, the first magnetic element 10 outputs a first output. A signal that represents the change in voltage of the first output is extracted by the capacitor 91 and distributed to the first line 71 and the second line 72. The distribution ratio at which the first output is distributed to the first line 71 and the second line 72 may be equal or different. The signal distributed to the first line 71 becomes the first signal. The signal distributed to the second line 72 becomes the second signal by being inverted in polarity by the inversion circuit 41 and delayed by the delay circuit 40.

The first condition is satisfied, for example, by the delay circuit 40. When the delay circuit 40 delays the signal caused by the first output from the first magnetic element 10 and propagating through the second line 72, the time position of the peak of the first signal and the time position of the peak of the second signal at the output terminal _t1 become different.

The second condition can be satisfied by inverting the signal resulting from the first output from the first magnetic element 10 and propagating through the second line 72 with the inversion circuit 41. When the inversion circuit 41 inverts the polarity of the signal resulting from the first output from the first magnetic element 10 and propagating through the second line 72, the positive and negative amounts of change until the first signal reaches a peak at the output terminal _t1 become different from the positive and negative amounts of change until the second signal reaches a peak.

The first signal and the second signal satisfy the first condition and the second condition at the output terminal _t1 . The photodetection device 105 satisfies the first condition and the second condition and combines the first signal and the second signal, and therefore has the same effect as the photodetection device 100 according to the first embodiment.

The present invention is not limited to the above-mentioned embodiment and modified examples, and various modifications and variations are possible within the scope of the gist of the present invention as described in the claims. For example, the characteristic configurations of the above-mentioned embodiment and modified examples may be combined.

For example, in the first embodiment and the third to fifth embodiments, a magnetic field application unit may be provided. Also, for example, in the fourth to fifth embodiments, a delay circuit may be combined. Also, for example, in the fourth to fifth embodiments, a power supply 33 and an inversion circuit 41 may be used.

For example, in the first to fifth embodiments described above, the capacitor 91 is used to extract the voltage change in the first output and the second output, but the first output itself and the second output itself may be used without providing the capacitor 91. Similarly, in the sixth embodiment, the capacitor 91 is used to extract the voltage change in the first output, but the first output itself may be used without providing the capacitor 91.

The light detection devices according to the above embodiments and modifications can be applied to transmitters and receivers in communication systems.

Figure 25 is a block diagram of a transceiver 1000 according to a first application example. The transceiver 1000 includes a receiver 200 and a transmitter 300. The receiver 200 receives an optical signal L1, and the transmitter 300 transmits an optical signal L2.

The receiving device 200 includes, for example, a photodetection device 100 and a signal processing unit 110. The photodetection device 100 may be replaced with another embodiment or modification described above. In the receiving device 200, the first magnetic element 10 and the second magnetic element 20 are irradiated with a plurality of light pulses that are repeated at a high frequency. The light signal L1 is composed of these plurality of light pulses. The photodetection device 100 converts the light signal L1 into an electrical signal. The signal processing unit 110 processes the electrical signal converted by the photodetection device 100. The signal processing unit 110 receives a signal included in the light signal L1 by processing the electrical signal generated by the photodetection device 100. The receiving device 200 receives the signal included in the light signal L1 based on the output signal from the photodetection device 100.

The transmitting device 300 includes, for example, a light source 301, an electrical signal generating element 302, and an optical modulation element 303. The light source 301 is, for example, a laser element. The light source 301 may be external to the transmitting device 300. The electrical signal generating element 302 generates an electrical signal based on the transmission information. The electrical signal generating element 302 may be integrated with the signal conversion element of the signal processing unit 110. The optical modulation element 303 modulates the light output from the light source 301 based on the electrical signal generated by the electrical signal generating element 302, and outputs an optical signal L2.

Figure 26 is a conceptual diagram of an example of a communication system. The communication system shown in Figure 26 has two terminal devices 500. The terminal devices 500 are, for example, a smartphone, a tablet, a personal computer, etc.

Each of the terminal devices 500 includes a receiving device 200 and a transmitting device 300. An optical signal transmitted from the transmitting device 300 of one of the terminal devices 500 is received by the receiving device 200 of the other terminal device 500. The light used for transmission and reception between the terminal devices 500 is, for example, visible light. The receiving device 200 includes a photodetecting device 100. The photodetecting device 100 described above has a short signal fall time, so that output saturation can be suppressed even during high-speed communication.

10...first magnetic element, 10A, 20A...first surface, 10B, 20B...second surface, 11, 21...first ferromagnetic layer, 12, 22...second ferromagnetic layer, 13, 23...spacer layer, 14, 24...first electrode, 15, 25...second electrode, 20...second magnetic element, 31, 32, 33...power supply, 40...delay circuit, 41...inversion circuit, 51, 52, 53...magnetic field application unit, 61...first intermediate layer, 62...second intermediate layer, 65...first optical waveguide, 66...second optical waveguide, 67...clad, 71...first line, 72...second line, 91...capacitor, 92...inductor, 93...insulating layer, 100, 101, 102, 102A, 102B, 103, 104, 105...light detection device, 110...signal processing unit, 200...receiving device, 300...transmitting device, 301...light source, 302...electrical signal generating element, 303...optical modulation element, 500...terminal device, 1000...transmitting/receiving device

Claims (17)

a first photoelectric conversion element that outputs a first output when irradiated with a light pulse;
a second photoelectric conversion element that outputs a second output when the light pulse is irradiated thereto;
a first signal resulting from the first output and a second signal resulting from the second output when the first photoelectric conversion element and the second photoelectric conversion element are irradiated with the same optical pulse are combined in a state that satisfies a first condition and a second condition,
the first condition is a condition that a time position of a peak of the first signal is different from a time position of a peak of the second signal;
The optical detection device, wherein the second condition is that the positive and negative signs of an amount of change until the first signal reaches a peak are different from the positive and negative signs of an amount of change until the second signal reaches a peak. the first photoelectric conversion element is a first magnetic element,
the second photoelectric conversion element is a second magnetic element,
2. The optical detection device of claim 1, wherein the first magnetic element and the second magnetic element each include a first ferromagnetic layer to which the light pulse is irradiated, a second ferromagnetic layer, and a spacer layer sandwiched between the first ferromagnetic layer and the second ferromagnetic layer. A delay circuit is further provided,
2. The optical sensing device of claim 1, wherein the delay circuit delays the signal resulting from the second output. The optical detection device according to claim 2, wherein when the first magnetic element and the second magnetic element are not irradiated with the optical pulse, the relationship between the magnetization directions of the first ferromagnetic layer and the second ferromagnetic layer of the first magnetic element is different from the relationship between the magnetization directions of the first ferromagnetic layer and the second ferromagnetic layer of the second magnetic element. The optical detection device according to claim 2, wherein the polarity of the DC power source connected to the output terminal side surface of the first magnetic element is different from the polarity of the DC power source connected to the output terminal side surface of the second magnetic element. The optical detection device according to claim 4, wherein the polarity of the DC power source connected to the output terminal side surface of the first magnetic element is the same as the polarity of the DC power source connected to the output terminal side surface of the second magnetic element. An inverting circuit is further provided,
2. The optical sensing device of claim 1, wherein the inverting circuit inverts the polarity of the signal resulting from the second output. The optical detection device according to claim 1, wherein a first optical distance until the optical pulse is irradiated to the first photoelectric conversion element is different from a second optical distance until the optical pulse is irradiated to the second photoelectric conversion element. a light irradiation surface onto which the light pulse is irradiated,
a first intermediate layer between the light irradiation surface and the first photoelectric conversion element;
a second intermediate layer is provided between the light irradiation surface and the second photoelectric conversion element;
The optical sensing device of claim 8 , wherein the first and second intermediate layers have different refractive indices. Further comprising a first optical waveguide and a second optical waveguide,
the first optical waveguide is configured to propagate the optical pulse to the first photoelectric conversion element;
the second optical waveguide is configured to propagate the optical pulse to the second photoelectric conversion element;
9. The optical sensing device of claim 8, wherein the first optical waveguide has a different length than the second optical waveguide. Further comprising a first optical waveguide and a second optical waveguide,
the first optical waveguide is configured to propagate the optical pulse to the first photoelectric conversion element;
the second optical waveguide is configured to propagate the optical pulse to the second photoelectric conversion element;
9. The optical sensing device of claim 8, wherein the refractive index of the first optical waveguide is different from the refractive index of the second optical waveguide. a first photoelectric conversion element that outputs a first output when irradiated with a light pulse;
a first signal and a second signal resulting from the first output when the first photoelectric conversion element is irradiated with the light pulse are combined in a state where a first condition and a second condition are satisfied;
the first condition is a condition that a time position of a peak of the first signal is different from a time position of a peak of the second signal;
The optical detection device, wherein the second condition is that the positive and negative signs of an amount of change until the first signal reaches a peak are different from the positive and negative signs of an amount of change until the second signal reaches a peak. the first photoelectric conversion element is a first magnetic element,
The optical detection device of claim 11 , wherein the first magnetic element comprises a first ferromagnetic layer irradiated with the optical pulse, a second ferromagnetic layer, and a spacer layer sandwiched between the first ferromagnetic layer and the second ferromagnetic layer. A delay circuit is further provided,
12. The optical sensing device of claim 11, wherein the delay circuit delays one of the signals resulting from the first output. An inverting circuit is further provided,
12. The optical sensing device of claim 11, wherein the inverting circuit inverts the polarity of one of the signals resulting from the first output. a first signal resulting from a first output output from the first photoelectric conversion element and a second signal resulting from a second output output from the second photoelectric conversion element when the same optical pulse is irradiated to the first photoelectric conversion element and the second photoelectric conversion element are combined in a state where a first condition and a second condition are satisfied;
the first condition is a condition that a time position of a peak of the first signal is different from a time position of a peak of the second signal;
The signal processing method, wherein the second condition is that the amount of change in the first signal until it reaches a peak is different in sign from the amount of change in the second signal until it reaches a peak. a first signal and a second signal resulting from a first output output from a first photoelectric conversion element when the first photoelectric conversion element is irradiated with an optical pulse are combined in a state where a first condition and a second condition are satisfied;
the first condition is a condition that a time position of a peak of the first signal is different from a time position of a peak of the second signal;
The signal processing method, wherein the second condition is that the amount of change in the first signal until it reaches a peak is different in sign from the amount of change in the second signal until it reaches a peak.

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