CN102494764B - Low-light detecting method for broad band covering visible light - Google Patents

Abstract

The invention discloses a low-light detection method covering a wide band of visible light, which is characterized in that the method connects a quantum dot-quantum well photodetector with a CMOS readout circuit and places it in a box equipped with a low-light test system, and then Direct readout of a broad wavelength band covering visible light is possible for low-light detection. Compared with the prior art, the present invention has high sensitivity, large signal-to-noise ratio, wide detection band range, and can detect low light with optical power <0.2nW. The response voltage reaches 20mV within the integration time, and the integration and exposure time is at least an order of magnitude lower than that of the existing technology, which meets the needs of different devices and scalable signal sizes, and is conducive to promoting the development of photodetectors in the field of low-light and low-irradiance detection. widely used.

Description

A low-light detection method covering a wide band of visible light

technical field

The invention relates to the technical field of circuit design, in particular to a low-light detection method for a photodetector covering a wide band of visible light.

Background technique

Low-light detectors can work under extremely weak light conditions, and are widely used in military reconnaissance, space detection, machine vision, environmental monitoring, security monitoring, medical diagnosis, and many fields of biological science. Many application fields require low-light power 10nW and below optical power for detection. The noise level in CMOS image detectors has been continuously reduced, and the sensitivity to low-light signals has also been continuously improved, but CMOS image sensors must use pixel intensifiers to multiply the number of photogenerated carriers or image intensifiers before low-light detection can be performed, and the integral The time and exposure time are relatively long, but the accuracy of low-light detection is relatively low in the case of low-light signals, which affects the further research and exploration of photodetectors, and greatly restricts the application of photodetectors in low-light and low-irradiance fields. widely used.

Contents of the invention

The purpose of the present invention is to provide a low-light detection method covering a wide band of visible light in view of the deficiencies in the prior art. In the box of the system, low-light with lower optical power than 0.2nW can be detected, and the integration and exposure time are shorter, the operation is convenient, and the low-light detection accuracy is high, which meets the needs of different devices and scalable signal size. It is conducive to promoting the wide application of photodetectors in the field of low-light and low-irradiance detection, and has great significance for further research and development of low-light detection. the

The purpose of the present invention is achieved in this way: a low-light detection method covering a wide band of visible light, which is characterized in that the method is equipped with a low-light test system after docking the quantum dot-quantum well photodetector and the CMOS readout circuit In the box, then the wide band covering visible light can be directly read out when detecting low light. The specific detection includes the following steps:

(1) The connection between the photodetector and the readout circuit

The quantum dot-quantum well photodetector and the CMOS readout circuit are docked on a substrate and welded in a Dewar bottle to reduce external electromagnetic interference;

(2) Micro-light test system

The low-light test system consists of a low-light radiation source, the first beam splitting prism, the second beam splitting prism, a microscope objective lens, a Dewar bottle, a white light lamp, an LCD display, an industrial TV monitor, a micro-motion stage, a test circuit and a digital oscilloscope. Coaxial optical test platform, in which the docked photodetector and readout circuit are welded in the Dewar bottle;

(3) Low-light readout detection

Put the above-mentioned low-light test system in a black cloth-covered box with a background signal of 0 nW, set the Dewar bottle to work at a temperature of 120K, and provide a voltage bias for the photodetector and a drive signal for the readout circuit, and the readout circuit The two output ends of the digital oscilloscope are respectively connected to the digital double-trace oscilloscope, and then the micro-movement stage is adjusted so that the laser spot is irradiated on the photosensitive element of the photodetector. The output voltage with light, the difference between the two voltages is the low-light response voltage on the photosensitive element, then adjust the micro-movement stage so that the laser spot is irradiated on the next photosensitive element of the photodetector, and repeat the above steps until all the photosensitive elements are completed. Low-light readout detection of arrayed quantum dot-quantum well detectors.

The low-light radiation source consists of a laser, a first attenuation disk, a second attenuation disk, a filter, a mirror and an optical power meter to form a continuously adjustable point light source with an irradiance of 10 ^-1 nW~1.6μW.

The test circuit provides voltage bias and driving signals for the photodetector and the readout circuit, so that the detector and the readout circuit can work within a normal range, and measure the photoelectric response voltage.

The voltage bias is the working bias voltage of the photodetector, which is determined by the responsivity, photoelectric characteristics and signal-to-noise ratio of the quantum dot-quantum well photodetector.

The driving signal is a timing signal for driving the readout circuit to scan, integrate, read out and reset the detector array. the

Compared with the prior art, the present invention has high sensitivity, large signal-to-noise ratio, wide range of detection bands, covers near ultraviolet, visible light and near infrared bands, makes up for the deficiency of CCD devices, and can detect low light with optical power <0.2nW For detection, under the illumination of 0.2nW laser light power, the response voltage of the readout circuit reaches 20mV within 80μs integration time, and the integration and exposure time is at least an order of magnitude lower than that of the existing technology, which meets the needs of different devices and scalable signal sizes. It is beneficial to promote the wide application of photodetectors in the field of low-light and low-irradiance detection.

Description of drawings

Fig. 1 is the structure schematic diagram of low-light test system of the present invention;

Fig. 2 is a schematic structural diagram of a continuously adjustable micro-light radiation source of the present invention;

Fig. 3 is a timing diagram of driving signals of the low light test system of the present invention;

Fig. 4 is quantum dot-quantum well photodetector pixel unilluminated waveform;

Fig. 5 is a low-light illumination waveform diagram of a quantum dot-quantum well photodetector pixel.

Detailed ways

Below with quantum dot-quantum well photodetector docking with CMOS readout circuit then, the specific embodiment that it carries out micro-light detection, the present invention is further elaborated:

Example 1

The present invention can directly read out the wide band covering visible light when detecting low light, and its specific detection includes the following steps:

(1) The connection between the photodetector and the readout circuit

The heterojunction quantum dot-quantum well photodetector and the CMOS readout circuit are docked on a substrate and welded in a Dewar bottle to reduce external electromagnetic interference. After the photodetector and the readout circuit are docked, the signal-to-noise ratio It is very large, and it is detected under the illumination of 0.2nW laser power, and the response voltage of the readout circuit reaches 20mV within 80μs integration time, without using an image intensifier or a photomultiplier tube. Under the condition that the process conditions of the detector remain unchanged, through the reasonable selection of the pixel structure and size of the detector and the setting of the integration time parameter of the readout circuit, it is completely possible to detect low light with an optical power lower than 0.2nW.

(2) Micro-light test system

Referring to accompanying drawing 1, low-light test system is made of low-light radiation source 2, the first dichroic prism 3, the second dichroic prism 4, microscope objective lens 5, Dewar bottle 6, white light lamp 7, LCD display 8, industrial television monitor 9. A coaxial optical test platform composed of a micro-motion table 10, a test circuit 11 and a digital dual-trace oscilloscope 12. A coaxial optical platform provided with an industrial television monitor 9 can display the position of the laser spot irradiating on the photodetector on the LCD display 8, and ensure that the image of the laser spot irradiating on the photodetector is ensured by adjusting the micro-movement stage 10. In the element, the photodetector and the readout circuit after docking are welded in the Dewar vessel 8 . The test circuit 11 provides suitable voltage bias and driving signals for the photodetector and the readout circuit, so that the detector and the readout circuit can work within the normal range, and measure the photoelectric response voltage, and the voltage bias is the work of the photodetector Bias voltage, the working bias voltage is determined by the responsivity, photoelectric characteristics and signal-to-noise ratio of the quantum dot-quantum well photodetector, and the driving signal is used to drive the readout circuit to scan, integrate, read out and reset the detector array timing signal. the

The low-light test system is placed in the black box 1 and covered with a black cloth on the outside. The purpose is to reduce the influence of the external background light. The experimental results show that the coaxial optical platform can achieve a continuous laser power of 10 ^-1 nW~1.6μW. Adjustment to meet the test conditions of low light and low radiation of photodetectors. In order to reduce test noise, all parts of the system share the ground.

Referring to accompanying drawing 2, the low-light radiation source 2 consists of a laser 21, a first attenuation disc 22, a second attenuation disc 23, an optical filter 24, a reflector 25 and an optical power meter 26 to form a continuously adjustable 10 ^-1 n~1.6μW The point light source of irradiance provides accurate light source for the low-light test through optical power calibration. Among them, the laser 21 uses a He-Ne laser with a wavelength of 633nm, and its radiated optical power is 1.6μW, which is much larger than that of the low-light radiation photoelectric test. Requirements; the first attenuation disk 22 and the second attenuation disk 23 use 360-degree continuous attenuation; the filter 24 chooses a filter degree of 10%, and the system can place three filters of 10%, 1% and 0.1% at the same time , the theoretical minimum radiant optical power can be as small as 10 ^-15 W.

(3) Low-light readout detection

Place the above-mentioned low-light test system in a black box 1 covered with a black cloth with a background signal of 0 nW, set the Dewar bottle 6 to work at a temperature of 120K, and test the circuit 11 to provide a voltage bias for the photodetector and a drive signal for the readout circuit , so that the detector and the readout circuit work within the normal range. The two output ends of the readout circuit are respectively connected to the digital double-trace oscilloscope 12, and then the micro-movement stage 10 is adjusted to irradiate the laser spot on the photosensitive element of the photodetector, and the light-shielding metal sheet 51 arranged in front of the microscope objective lens 5 is respectively Test the output voltage of the readout circuit when there is no light and light. The difference between the two voltages is the low-light response voltage on the photosensitive element. Then, adjust the micro-motion table 10 so that the laser spot is irradiated on the next photosensitive element of the photodetector. For each element, the above steps are repeated until the low-light readout detection of all quantum dot-quantum well detectors in the array is completed. Under the condition that the process conditions of the detector remain unchanged, through the reasonable selection of the pixel structure and size of the detector and the setting of parameters such as the integration time of the readout circuit, it is completely possible to detect low light with an optical power lower than 0.2nW.

The coaxial optical test platform can conveniently monitor and adjust the micro-motion stage 10 so that the laser spot is irradiated on the photosensitive element of the photodetector. The specific test and adjustment are as follows:

After the laser and low-light power are calibrated, open the reflector 25 to remove the optical path, turn on the white light lamp 7, and the laser spot and white light shine on the Dewar bottle 6 after passing through the first dichroic prism 3, the second dichroic prism 2 and the microscopic objective lens 5. On the photodetector inside, the laser spot and the photodetector can be clearly seen through the LCD display 8 connected to the industrial TV monitor 9. After adjusting the micro-movement stage 10 so that the laser spot is accurately irradiated on the photodetector pixel, close the White light lamp 7, open the first dichroic prism 3 and the second dichroic prism 4, so that the laser spot is directly irradiated on the photodetector pixel through the microscope objective lens 5, and the readout circuit provides operating voltage and operating sequence through the test circuit 11 , the output OUT1 and OUT2 of the readout circuit are respectively connected to the AgelintDSO6052A digital dual-trace oscilloscope 12, and the output voltage OUT1 and OUT2 are respectively measured by sliding the light-shielding metal plate 51 in front of the microscope objective lens 5 under the conditions of no light and light, and the actual reading The response voltage of the output circuit is the difference between the two output voltages, that is, the response voltage of the readout circuit = OUT2-OUT1. After the low-light detection of the first pixel is completed, then adjust the micro-motion table 10 to accurately irradiate the laser spot to the next pixel, and repeat the above steps until all 2×8 arrays of quantum dots-quantum wells are completed Low-light readout test of the detector.

The test circuit 11 provides suitable voltage bias and driving signals for the photodetector and the readout circuit, so that the detector and the readout circuit can work in a normal range, and the drive signal provides suitable timing for the readout circuit, so that the readout circuit can operate in a normal range. Under the action of the clock signal, row selection signal and column selection signal, the output voltages corresponding to 16 pixels are sequentially output, and the driving signals are as follows in Table 1:

Table 1 Description of driving signals of low-light test system

Referring to accompanying drawing 3, the steps of testing the timing of the driving signal are as follows:

(1) The test circuit 11 applies a START signal to the readout circuit, and after the readout circuit is initialized (about tens of μs), the shift register outputs the C8 signal;

(2) The rising edge of the C8 signal triggers a reset (RESET) signal;

(3) The rising edge of the RESET reset signal triggers the SH1 signal;

(4) The SH1 signal is delayed for a certain time to generate the SH2 signal, and the delay time is the integration time of the detector light signal by the readout circuit;

(5) After the SH2 signal ends, the shift register in the readout circuit sequentially strobes and outputs each output signal until a C8 signal is output to indicate that the last signal has been output.

Repeat the above steps (1)~(4), so that the readout circuit continuously scans, integrates, reads out and resets the detector array.

Referring to accompanying drawing 4, the quantum dot-quantum well photodetector that the present invention detects under the situation of no illumination, the experimental waveform diagram of the response voltage that photodetector and readout circuit obtain after docking, its waveform diagram represents photodetector The waveform diagram of the output voltage of the seventh pixel without light radiation under the control of the scanning signal, it can be clearly observed that the output voltage of the pixel has no change under the control of the scan signal, and the response voltage cannot be tested.

Referring to accompanying drawing 5, the quantum dot-quantum well photodetector that the present invention detects is under low-light illumination, and the experimental waveform diagram of the response voltage that photodetector and readout circuit obtains after docking, represents the photodetector in its circle The 7th pixel has the output voltage waveform diagram of light radiation under the control of the scanning signal. It can be clearly observed that the output voltage of the pixel changes in low light and the response voltage is obtained by testing. The experiment proves that the present invention can be used in low light conditions. Good for low-light testing of quantum dot-quantum well photodetectors.

The above is only a further description of the present invention, and is not intended to limit the implementation and application of this patent. All equivalent implementations of the present invention should be included in the scope of claims of this patent. the

Claims (4)

1. the broadband micro light detecting method of covering visible light, it is characterized in that the method docks quantum-dot-quantum-well photodetector to be placed in the case that is provided with low-light test macro with CMOS sensing circuit, when then low-light is surveyed, can directly read the broadband of covering visible light, its concrete detection comprises the following steps:

(1), photodetector and sensing circuit docks

Quantum-dot-quantum-well photodetector and CMOS sensing circuit are docked on a substrate and are welded in Dewar flask, to reduce external electromagnetic interference;

(2), low-light test macro

The coaxial optic test platform that low-light test macro consists of low-light radiating light source, the first Amici prism, the second Amici prism, microcobjective, Dewar flask, white light, LCD display, industrial television surveillance system device, micropositioner, test circuit and digital oscilloscope, is wherein welded with photodetector and sensing circuit after docking in Dewar flask;

(3), low-light is read detection

Above-mentioned low-light test macro is placed in the case that the black cloth of 0 nW background signal covers, Dewar flask is arranged at 120K temperature and works, test circuit provides voltage bias and drives signal for photodetector and sensing circuit, detector and sensing circuit are worked in normal range, and measure photoelectric response voltage, two output terminals of sensing circuit access respectively digital dual trace oscilloscope, then regulate micropositioner that laser facula is radiated in the photosensitive unit of photodetector, the output voltage of testing respectively the unglazed photograph of sensing circuit and having illumination by being slidably arranged in shading sheet metal before microcobjective, its two voltage difference is the low-light response voltage in this photosensitive unit, then, regulate again micropositioner that laser facula is radiated in the photosensitive unit of the next one of photodetector, repeat above-mentioned steps, until complete the low-light of the quantum-dot-quantum-well detector of all arrays, read detection.

2. the broadband micro light detecting method of covering visible light according to claim 1, is characterized in that described low-light radiating light source forms continuously adjustable 10 by laser instrument, the first decay dish, the second decay dish, optical filter, catoptron and light power meter ^-1the radiometric pointolite of n ~ 1.6 μ W.

3. the broadband micro light detecting method of covering visible light according to claim 1, is characterized in that described voltage bias is the working bias voltage of photodetector, with responsiveness, photoelectric characteristic and the signal to noise ratio (S/N ratio) of quantum-dot-quantum-well photodetector, determines.

4. the broadband micro light detecting method of covering visible light according to claim 1, is characterized in that described driving signal is for driving sensing circuit to the scanning of detector array procession, integration, the clock signal reading and reset.

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