JP2000230858A - Image pick-up element - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide an image pick-up element capable of electronic scanning for easing signals of each pixel constituting the image pick-up element synchronously with the modulation of the thermal energy of each pixel. SOLUTION: Pixel sensors 15, 16, 18 are formed on a diaphragm 13 formed as a structure thermally isolated from a support board 10 through a gap 30 so that a voltage is applied/cut off between a lower electrode 15 provided on the diaphragm 13 and an electrode 25 provided on the support board 10, thereby mechanically contacting/separating the diaphragm and the board 10 to modulate the thermal energy of the sensor, and the electronic scan for reading signals of the image pick-up element is synchronized with the thermal energy modulation of each pixel. The thermal energy modulation of each pixel can be made by applying electric signals, without using a mechanical chopper mechanism, hence the thermal energy modulation of each pixel can be scanned at a desired timing by the electric signals and easily synchronized with the electronic scan for reading signals.

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

The present invention relates to an imaging device for detecting thermal energy, for example, an infrared imaging device.

[0002]

2. Description of the Related Art Electromagnetic waves such as ultraviolet light, visible light and infrared light have thermal energy corresponding to each wavelength. As a method of detecting these energies, for example, there is a thermal infrared sensor. The thermal infrared sensor absorbs the thermal energy of the incident electromagnetic wave and converts it into an electric signal.The pyroelectric type that detects the change in capacitance due to the spontaneous polarization change, the bolometer type that detects the change in resistance, and the thermoelectromotive force There is a thermopile type for detecting the pressure. Among them, the pyroelectric infrared sensor detects a differential signal generated based on a change in an electromagnetic wave. As a method of changing or modulating electromagnetic waves,
Conventionally, a method using a chopper for turning on / off electromagnetic waves such as light and infrared rays by rotating a circular plate having holes formed at regular intervals in the periphery thereof at a constant speed, or 3-194875.
There is a method of using a reflection type chopper which reduces the influence of the chopper on an image as described in Japanese Patent Application Laid-Open No. H10-260,086. In both cases, what can be said in common is to rely on a method of modulating an incident electromagnetic wave such as infrared light or light using a mechanical rotating mechanism.

FIG. 6 is a conceptual diagram showing the relationship between signal reading and a chopper for performing infrared modulation in a conventional pyroelectric infrared imaging device. This is an example where the image sensor is an array element of m rows and n columns, and this configuration will be described below. In FIG. 6, sensor pixels 2 are arranged in an image sensor chip 1 in a configuration of m rows and n columns. Here, the reading of the signal is performed by serially electronically scanning ON / OFF of a MOS switch (not shown) arranged for each pixel. Line 3 indicates the direction of electronic scanning. That is, after scanning from the first row to the n-th row in the first row, the process proceeds to the second row, and scanning is performed from the first to the n-th row. By repeating this process up to m rows, one frame can be imaged. In order to modulate the infrared light in conjunction with the electronic scanning, the end of the chopper is set to m
= 1 to m = m. conventionally,
As described above, the infrared modulation and the electronic scanning are performed asynchronously. In addition, since the infrared image takes a long time to be scanned by the chopper, the entire screen is not an instantaneous image at the same time but is formed with a time lag for each pixel.

[0004]

When the modulation of infrared rays and the electronic scanning are asynchronous as in the prior art, the detected signals are affected. This will be described with reference to FIGS. FIG. 7 is a signal waveform diagram for conceptually explaining the influence on the detection signal. Here, for the case of acquiring about 30 images or frames per second, (m, n)
= Consider the effect of the relationship between the incident infrared rays of the (1,1) th and (m, n) th pixels and the electronic scanning on the output signal. In FIG. 7, the solid line is the incident infrared intensity and output voltage at the (m, n) = (1, 1) th pixel, and the broken line is (m, n).
= Intensity of incident infrared ray and output voltage at (m, n) th pixel.

First, when the (m, n) = (1, 1) th pixel is irradiated with infrared rays through the end of the chopper, a positive output voltage waveform as shown by a solid line appears. Next 16m
When the end of the chopper comes after sec and the irradiation infrared ray is turned off, a negative output voltage waveform is obtained. Here, considering the positive output signal when the infrared ray is irradiated, the pyroelectric infrared sensor is more sensitive than the immediately after the infrared ray irradiation because of the relationship between the thermal resistance between the temperature detector and the substrate and the heat capacity of the temperature detector. output signals from being irradiated for a period of time t ₀ delay becomes maximum.
Therefore, if the signal is read out after t ₀ after the irradiation of the infrared ray, the modulation of the infrared ray and the electronic scanning are optimized, and the maximum signal can be obtained.

However, even if infrared ray modulation and electronic scanning of the (m, n) = (1, 1) th pixel are optimized,
Regarding the relationship between the modulation of the infrared ray of the (m, n) = (m, n) -th pixel and the electronic scanning, it is not optimized. Hereinafter, description will be made with reference to FIG. It is assumed that infrared ray modulation and electronic scanning of the (m, 1) th pixel are optimized. In order to electronically scan up to the (m, n) -th order, it takes time for infrared rays to scan about one line. This means that the (m, n) -th electronic scanning is performed with a delay of Δt from t _{0 at} which the maximum signal appears, as shown in FIG. As a result, a signal different from the maximum value is read. In addition, the delay is not constant but varies depending on the accuracy of the modulation of the mechanical infrared ray and the position of the pixel in the chip. Furthermore, in the description, it is assumed that the chopper scans in the direction from m = 1 to m = m orthogonally to the row direction, but the actual chopper scanning is not necessarily orthogonal to the row direction.
For this reason, the performance of each pixel is manufactured in a well-balanced manner, and even if the output signal of the pixel is actually the same, the output signal is not uniquely determined because the infrared modulation and the electronic scanning are asynchronous, and the output signal varies. become. Since this variation also affects the image of each frame, it is considered as noise in the signal processing, and deteriorates the performance of the image sensor.

Further, since a chopper is used, it takes time to scan the chopper from one end of the element to another, and m = 1
And the signal from the pixel of m = m are not obtained at the same time. That is, since each pixel does not capture an image at the same moment, the reality and the image are different for a heat source having the same motion in the same direction as the chopper.

The present invention has been made to solve the problems of the prior art as described above. The electronic scanning for reading out the signal of each pixel constituting the image sensor is synchronized with the modulation of the thermal energy of each pixel. It is an object of the present invention to provide an imaging element which can be performed by using the same. Another object of the present invention is to provide an image pickup device capable of accumulating an image at the same point in time in each pixel and sequentially reading the image.

[0009]

Means for Solving the Problems In order to achieve the above object, the present invention is configured as described in the claims. That is, according to the first aspect of the present invention, each pixel of the thermal imaging element that detects a change in thermal energy of electromagnetic waves (ultraviolet rays, visible rays, infrared rays, etc.) is formed as a thermal isolation structure via a gap from the support substrate. A sensor section of the pixel is formed on the formed diaphragm,
By applying / cutting a voltage between an electrode provided on the diaphragm and an electrode provided on the support substrate, the diaphragm and the support substrate are brought into and out of contact mechanically to modulate thermal energy of the sensor unit. And the electronic scanning of the reading of the signal of the image sensor is synchronized with the modulation of the thermal energy of each pixel.

As described above, since the thermal energy of each pixel can be modulated by applying an electric signal without using a mechanical chopper mechanism, the thermal energy of each pixel can be modulated at an arbitrary timing by the electric signal. Can be scanned. Therefore, it can be easily synchronized with the electronic scanning of signal reading.

Therefore, the electronic scanning for reading can be performed synchronously with a delay of a certain time after the modulation of the thermal energy of the pixel. Reading is performed at the most suitable time for each pixel, and a maximum signal can be detected.

As described above, by synchronizing the temperature modulation of the sensor section of the image sensor with the electronic scanning of the signal reading, the signal of each pixel can be read when the signal of each pixel is at the maximum. Can be pulled out. In addition, variations in pixel signals can be reduced, and the performance of the image sensor can be improved. Furthermore, since there is no mechanical rotation mechanism such as a chopper, the reliability of an imaging device using an imaging device can be improved. Further, temperature modulation suitable for the characteristics of the detection unit of the pixel can be performed. Further, the signal readout timing can be freely set.

Further, in the invention according to claim 3,
A means for storing a signal of each pixel constituting the image sensor for each pixel, simultaneously performing modulation of thermal energy of the pixels for all pixels, and storing a signal of each pixel in the means;
Thereafter, the reading of these signals is performed by electronic scanning.

With the above-described configuration, it is possible to capture and store an image at the same point in time in all the pixels, and then sequentially read out the images. Therefore, it is possible to capture an image without time delay for each pixel. I can do it. In the conventional mechanical chopping, when forming an image of one frame, there is a time lag between the image at the beginning and the end of scanning, but in claim 3, the thermal modulation of all pixels is performed electrically simultaneously. This delay can be eliminated. As a result, it is possible to eliminate the influence on the image.

The sensor section is a pyroelectric infrared sensor, for example.

[0016]

According to the present invention, thermal energy modulation for thermally short-circuiting / opening is performed by mechanically contacting / separating a diaphragm on which a pyroelectric material is formed from / to a supporting substrate. By performing the electronic scanning of the signal readout at regular intervals,
Reading can be performed when the pixel signal is at a maximum. Therefore, it is possible to make the performance of the pixels of the imaging element equal and reduce the variation.

Further, by simultaneously modulating the thermal energy of all the pixels, there is no delay in the temporal detection between the pixels, so that it is possible to obtain an image at the same moment for all the pixels.

Further, since a mechanical chopper is not required, the timing of modulation of thermal energy can be freely set, and a high-precision device can be obtained. Moreover, reliability is improved,
In the case of an imaging device, many effects such as reduction in weight and size and reduction in the number of components can be obtained.

[0019]

1 to 4 are views for explaining a first embodiment. FIG. 1A is a plan view of a pixel of an image sensor, and FIG. ) AA ′ sectional view, FIG.
FIG. 3 is a circuit configuration diagram around a pixel, FIG. 3 is a conceptual diagram of electronic scanning, and FIG. 4 is a conceptual diagram showing a relationship between temperature modulation and a read signal.

First, the structure and function of the pixel of the image sensor will be described with reference to FIG. In FIG. 1, a conductive layer or a metal layer 25 (hereinafter, referred to as a metal layer 25) is formed on a Si support substrate 10, and a beam portion 12 made of silicon nitride and a diaphragm portion 13 are formed with a surface microstructure through a gap 30. It is formed by a machining technique (details will be described later). A wiring 14 is formed on the beam 12 and is electrically connected to a lower electrode 15 formed on the diaphragm 13. A pyroelectric material 16 is formed on the lower electrode 15. A wiring 17 is formed on the other beam portion 19 and is connected to an upper electrode 18 formed on the pyroelectric material 16. The upper electrode 18 is formed by using a material having a high heat absorption rate or by newly forming a heat absorbing layer on the upper electrode 18 so as to improve heat absorption. For example, the lower electrode 15 and the upper electrode 1
As No. 8, a noble metal such as Pt or Ir can be formed by a sputtering method.

In the above-described surface micromachining technology, the metal layer 25 is covered with a PSG oxide film serving as a sacrificial layer formed by CVD, and a silicon nitride (beams 12, 19 and a diaphragm portion) is formed thereon. 13). Then, an etching hole is formed in the silicon nitride, and a PSG etching solution such as NH ₄ F: CH ₃ C is formed therefrom.
The PSG oxide film is etched away by introducing OOH: H ₂ 0 = 1: 1: 1 or the like. When forming the PSG film, 2
The use of the step method allows for fast PSG sacrificial layer etching. The two-step method of forming a PSG film is as follows.
For example, a 1 μm thick PSG film is formed. Next, the PSG film is subjected to lattice-like trench etching. The trench width is about 1 μm. A PSG film having a thickness of about 1 μm is further formed thereon. As a result, a tunnel (a hollow portion or a portion where the PSG is formed roughly) is formed at the location where the trench is etched. At the time of etching, the etching solution passes through this tunnel, so that the etching proceeds simultaneously in a wide range, so that the etching rate is increased. The whole PSG film becomes a sacrificial layer of the surface micromachining technology, and the void 30 is formed.

Next, the method of temperature modulation is shown in FIG.
This will be described with reference to FIG. FIG. 2 is a circuit configuration diagram around a pixel of the image sensor, and one pixel (15, 16, 18, 2,
5), transistors T1 and T2 serving as electronic scanning switches, and control lines L1 and L2 (rows)
And C1 and C2 (columns). In FIG. 2, a lower electrode 15 of the pixel is connected to the ground, and a metal layer 25 provided with a predetermined gap therebetween is connected to a line L2 via a transistor T2. The upper electrode 18 formed on the pyroelectric material 16 is connected to the line C1 via the transistor T1. The gate of the transistor T1 is connected to the line L1, and the gate of the transistor T2 is connected to the line C2.

When a predetermined voltage is applied to the gate of the transistor T2 via the line C2 to turn on the transistor T2, the metal layer 25 is connected to the line L2 and the lower electrode 1
A voltage is applied between the lower electrode 15 and the metal layer 25, and an electrostatic attractive force is generated between the lower electrode 15 and the metal layer 25. As a result, the diaphragm 13 flexes and the diaphragm 13 and the support substrate 1
0 comes into contact with the metal layer 25 on the
3 and the supporting substrate 10 are thermally short-circuited and have the same temperature. Since the diaphragm portion 13 and the electrodes and pyroelectric material formed thereon are extremely thin (on the order of μm), their heat capacities are extremely small, and the temperatures equilibrate in a very short time. This thermal short circuit corresponds to blocking infrared rays by a mechanical chopper in the conventional example.

Next, when the transistor T2 is turned off, the above-mentioned electrostatic force disappears.
Moves away from the supporting substrate 10. If the pixels are irradiated with infrared rays in this state, they react immediately and a temperature change occurs.
Thus, the lower electrode 15 and the upper electrode 18 of the pyroelectric material 16 are formed.
A capacitance change occurs between them. After waiting for a time (t ₀ ) at which the signal of the capacitance change becomes maximum, a voltage is applied to the gate of the transistor T1 via the line L1 to turn on the transistor T1. Can be read out via. After reading, the gate of the transistor T1 is turned off, the transistor T2 is turned on again, and the diaphragm 13 and the support substrate 10 (actually, the metal layer 25, the same applies hereinafter) are brought into contact with each other.
Perform a thermal short circuit. By repeating this operation, the same thermal energy modulation and signal reading as in the conventional chopping mechanism can be performed. In an actual image sensor, the number of pixels corresponding to m rows and n columns, two transistors T1 and T2, and lines L1 and L
2, C1 and C2 are provided, and each pixel is sequentially scanned to read out a signal. In the circuit of FIG. 2, since the line C2 is provided for each column of m rows and n columns, each pixel can perform scanning for bringing the diaphragm portion 13 into contact with the support substrate 10 for each column.

Next, the scanning method will be described with reference to FIG. The difference from the scanning method described with reference to FIG. 6 is that the scanning of the end of the chopper is omitted. Then, for each pixel, signal scanning electronic scanning may be performed with a delay of a predetermined time (t ₀ ) from thermal energy electronic scanning for bringing the diaphragm portion 13 into contact with the support substrate 10. By doing so, the maximum signal of the pixel can be read. Specifically, a voltage is applied to the line C2 of the pixel corresponding to the scanning order, the transistor T2 is turned on, the pixel is thermally short-circuited, the thermal short-circuit is released, and then a predetermined time (t ₀ ) Thereafter, a voltage is applied to the line L1 of the pixel to turn on the transistor T1, and a signal is read from the line C1. This scanning may be performed for each pixel in the order shown in FIG.

FIG. 4 shows the diaphragm 13 and the supporting substrate 10.
2 shows the relationship between the state of contact with the device and the read signal.
7 is different from that described in FIG. 7 in that the on / off of the contact between the diaphragm 13 and the support substrate 10 is used instead of the incident infrared modulation by the on / off of the chopper. At the (m, n) = (1, 1) -th pixel, an optimized output signal is read out at t ₀ after the contact between the diaphragm unit 13 and the support substrate 10 is turned off. Then, unlike the case of FIG. 7, the (m, n) = (m, n) -th pixel also has no delay of Δt.
The signal is read out after the same time difference t ₀ as the (m, n) = (1, 1) th. That is, (m, n) = (1,
In both the (1) pixel and the (m, n) = (m, n) pixel, the time interval from when the contact between the diaphragm unit 13 and the support substrate 10 is turned off to when the signal is read is the same optimal value t ₀ . You can do it.

FIG. 5 is a diagram showing a second embodiment.
FIG. 2 shows a circuit configuration diagram around a pixel.

In the circuit of FIG. 5, the metal layer 2 of each pixel
5 is directly connected to the line L2. The upper electrode 18 is connected to the line C1 via the transistors T1 and T2. The capacitance C is connected between the connection point of the transistors T1 and T2 and the ground. The gate of the transistor T1 is connected to the line L1 and the transistor T1 is connected to the line L1.
The two gates are respectively connected to the line L3.

In the circuit of FIG. 5, when a voltage is applied to the line L2, a voltage is simultaneously applied between the lower electrode 15 and the metal layer 25 of all the pixels in one row, and
And the supporting substrate 10 are thermally short-circuited. When a voltage is applied to the lines L2 of all the rows, all the pixels can be thermally short-circuited simultaneously.

Next, when the voltage applied to the line L2 is turned off, the diaphragm 13 moves away from the support substrate 10. If the pixels are irradiated with infrared rays in this state, they react immediately and a temperature change occurs. Thus, a capacitance change occurs between the lower electrode 15 and the upper electrode 18 of the pyroelectric material.

Next, the transistor T is connected via the line L1.
3 by applying a voltage to the gate of transistor T3.
3 is turned on, and the above-described signal of the capacitance change is transferred to the capacitance C. Above timing, since by performing thermal modulation of all pixels simultaneously, from the release of thermal short circuit after a predetermined time t ₀ performs all pixels simultaneously. Thus, the signal of each pixel is stored in each capacitance C.

Next, the transistor T is connected via the line L1.
4 by applying a voltage to the gate of the transistor T
4 is turned on, and the signal of the pixel is read out via the line C1. By scanning each pixel, an image at the same moment can be obtained.

In this embodiment, image information at a certain moment is stored in the capacitance C of each pixel, and can be sequentially read out by scanning each pixel later. Therefore, there is no delay in temporal detection between pixels, so that an instantaneous image can be obtained. By repeating the above operation, a continuous image can be obtained.

In the structure of the image pickup device of the present invention, when the support substrate 10 and the diaphragm portion 13 are brought into mechanical contact with each other and then restored, it is necessary to weaken the adhesion between the support substrate 10 and the diaphragm portion 13. is there. In particular, it is necessary to prevent a state in which contact cannot be released due to sticking. For this reason, it is preferable to form a convex portion (row-like or dot-like) made of a Si nitride film or metal having low adhesion to the diaphragm on the supporting substrate. In addition, in order for the pyroelectric material to exhibit pyroelectricity, the material needs to be axially oriented on the lower electrode. For this purpose, a base such as MgO, which is easy to be axially oriented, is provided on a Si nitride formed by LPCVD, and a lower electrode such as a Pt film is formed thereon. On this, the pyroelectric material is easily axially oriented.

[Brief description of the drawings]

FIGS. 1A and 1B are diagrams illustrating a structure of a pixel of an image sensor according to a first embodiment of the present invention, wherein FIG. 1A is a plan view and FIG.

FIG. 2 is a circuit configuration diagram around a pixel according to the first embodiment of the present invention.

FIG. 3 is a conceptual diagram of electronic scanning of a pixel according to the first embodiment of the present invention.

FIG. 4 is a conceptual diagram showing a relationship between temperature modulation of a pixel and a readout signal according to the first embodiment of the present invention.

FIG. 5 is a circuit configuration diagram around a pixel according to a second embodiment of the present invention.

FIG. 6 is a conceptual diagram showing a relationship between electronic readout of signals in a conventional pyroelectric infrared imaging device and a chopper that performs infrared modulation.

FIG. 7 is a diagram showing a relationship between infrared modulation of pixels and an output waveform in a conventional pyroelectric infrared imaging device.

[Explanation of symbols]

DESCRIPTION OF SYMBOLS 1 ... Chip 2 ... Sensor pixel 3 ... Line which shows the electronic scanning direction 4 ... Arrow which shows the scanning direction of a chopper 10 ... Si support substrate 11 ... Etching hole 12 ... One beam part 13 ... Diaphragm part 14 ... Wiring 15 ... Lower part Electrode 16 Pyroelectric material 17 Wiring 18 Upper electrode 19 Other beam 20 Silicon nitride film 22 Interlayer insulating film 25 Conductive film or metal film 30 Void T1 to T4 Transistor C Capacitance L1 L3: Line for signal transmission C1, C2: Line for signal transmission

 ────────────────────────────────────────────────── ─── Continued on the front page (72) Inventor Kryson Tronnamchai Nissan Motor Co., Ltd. F-term (reference) 2G065 AB02 BA13 BA34 BB37 BB49 BC22 BC33 DA18 4M118 AA05 AA06 AB01 BA05 BA35 CB12 CB14 DD01 FB09 FB13 FB20 GA10 5C024 AA06 CA02 CA05 FA01 GA06 GA31 JA31

Claims (4)

[Claims] 1. An imaging device having a structure in which a sensor for detecting a change in thermal energy of an electromagnetic wave is used as a unit pixel, an array is formed by a plurality of pixels, and signals are read out by electronic scanning. A sensor portion of the pixel is formed on a diaphragm formed as a thermal isolation structure, and a voltage is applied and cut off between an electrode provided on the diaphragm and an electrode provided on the support substrate, whereby the diaphragm and the support substrate are applied. And mechanically contact / separate from each other to modulate the thermal energy of the sensor unit, and that the electronic scanning for reading out the signal of the image sensor is synchronized with the modulation of the thermal energy of each pixel. An imaging device characterized by the above-mentioned. 2. The imaging device according to claim 1, wherein the electronic scanning is performed synchronously with a delay of a predetermined time after the modulation of the thermal energy of the pixel. 3. A means for storing a signal of each pixel constituting the image sensor for each pixel, modulating thermal energy of the pixels simultaneously for all pixels, storing a signal of each pixel in the means, 3. The image pickup device according to claim 1, wherein the readout of the signals is performed by electronic scanning thereafter. 4. The imaging device according to claim 1, wherein the sensor unit for detecting a change in thermal energy is a pyroelectric infrared sensor.