RU2643695C1 - Method for measuring threshold temperature difference of ir mepd - Google Patents

Abstract

FIELD: measuring equipment.

SUBSTANCE: measurements are carried out using a black body (BB) equipped with an optical modulator with an area of the radiating area not exceeding the size of the array of photosensitive elements. When implementing the method, the specified temperature of the BB (T_sign) is set, the integral noises V_{n_ij} of all PSE are measured, the transmission spectrum of the MEPD cold light filter is measured, its short-wavelength and long-wavelength cut-off λ_s and λ_l are determined, the signals of all PSE V_{sign_ij} are measured and the value of the threshold temperature difference is calculated according to the formula

, where c=2.998⋅10¹⁰ cm⋅c^-1 is the light speed; k_B=1.381⋅10^-23 W⋅c⋅K^-1 is the Boltzmann's constant; h=6.626⋅10^-34 W⋅c² is the Planck's constant; N(T_sign; λ_s; λ_l), quanta⋅c^-1⋅cm^-2 is the integral of the Planck's function, which determines the quantum irradiance in a solid angle 2⋅π in the spectral interval [λ_s; λ_l]; Z(T_sign; λ_s; λ_l) is the integral of the Planck's derived function by temperature.

EFFECT: increased accuracy and simplified measurement technique.

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Description

The invention relates to methods for measuring parameters of infrared photodetectors (IR FPU) operating in the accumulation mode. These devices are sophisticated high-tech devices. They work in the ranges of 1-2.8 microns, 3-5 microns, 8-12 microns and further up to 100-150 microns, include a matrix of photosensitive elements (MFCE) containing from 1000 (4 × 288 format) photodiodes to more than 1,000,000 (1280 × 1024 format) photodiodes and more, coupled with the same number of silicon multiplexer cells. The multiplexer performs the accumulation of photocurrents of photosensitive elements (PSE) in the cells, element-by-element reading of the accumulated charges, converting them to voltage, preliminary amplification and output of signals, as a rule, to several outputs with a given frame rate. Modern multiplexer-processors, in addition, convert the output signal from analog form to digital form and carry out preliminary digital signal processing. In this case, the operating temperature of the matrix and multiplexer can be low enough to reduce the reverse currents of the PSE. This is achieved by placing them in a vacuum case on the cold finger of the microcryogenic system (ISS), which is a complex electronic-mechanical device.

IR FPU necessarily includes the following components:

- lightproof housing with an entrance window;

- the entrance window, enlightened in a given part of the spectrum;

- a lightproof and cooled screen with a window (diaphragm), coaxial with the input window (if necessary);

- a light filter located in a cooled screen that sets the working spectrum of photosensitivity (if necessary);

- MFCHE, coaxial with the diaphragm and the input window of the FPU, surrounded by a light-tight screen with a diaphragm;

- an integrated circuit of a multiplexer, coupled element by element with the MFCE;

- a board with contact paths (sapphire, silicon, etc.), on which a multiplexer with MFCE is fixed and its contacts are welded;

- a cooling system or fixing the operating temperature (if necessary), on which the screen is fixed, a raster with contact tracks, with an MFCHE-multiplexer assembly and with a temperature sensor.

In the manufacture of FPU, the parameters of all its components are controlled, since the threshold photoelectric characteristics of the device, which determine its quality, depend on them.

One of the most important characteristics is the threshold temperature difference (NETD).

The threshold temperature difference (NETD) is the increment of the temperature of the radiation incident on the photodetector, leading to a change in the output signal by an amount equal to the integral noise of the photodetector (signal-to-noise ratio is unity). This characteristic determines the quality of the MFP.

In the domestic reference literature (GOST 17772-88 Radiation receivers. Semiconductor photoelectric and photodetector devices. Methods for measuring photoelectric parameters and determining characteristics) there is no description of the method for measuring the threshold temperature difference.

An analogue of the claimed technical solution is a method for measuring the threshold temperature difference of IR MFP (A. Rogalski, Progress in focal plane array technologies, Progress in Quantum Electronics, Elsevier Ltd, 36, 2012, P. 383). To implement this method, you must

- set the first temperature of the blackbody T ₁ ;

- measure and remember the first array of integral noise of each _PSE V _w1ij ;

- measure and remember the first array of output signals of each _PSE V _1ij ;

- set the second temperature of the blackbody T ₂ ;

- measure and remember the second array of integrated noise of each _PSE V _w2ij ;

- measure and remember the second array of output signals of each _PSE V _2ij ;

- calculate the NETD of each PSE according to the following formula:

where ΔT _c = T ₂ -T ₁ ;

ΔV _c = V ₂ -V ₁ .

This method has the following disadvantages.

1. Measurement of two arrays of output signals of the PSE IR MFPU at two different temperatures of the blackbody. In this case, the difference of the output signals of each PSE should be at least ΔV _c = V ₂ -V ₁ = 10 V (V _W1 + V _W2 ). Otherwise, the voltage noise of the PSE at the first and second temperatures of the blackbody will be too much affected by this value.

2. Measurement of two arrays of PSE noise at two different blackbody temperatures. The difference of noise for each PSE should be no more ΔV = V _w -V _{w1 w2 w1} ≤0,1⋅V. Otherwise, the choice of one of the values of V _W for subsequent calculation will give a result different from the result with the second value of the noise voltage.

3. The need to install two different temperatures in blackbody with a minimum difference in noise voltage and a maximum difference in signal voltage. In fact, this contradicts both the first and second conditions, which determine the difference between the output signals of the IR MFP at the first and second temperatures of the blackbody.

4. The unknown temperature of the blackbody (first or second) at which it is necessary to measure (select) the value of the integral noise and calculate NETD.

5. Reduced NETD measurement accuracy due to these contradictions.

The prototype of the proposed technical solution has chosen a method for measuring the threshold temperature difference of an IR MFP, resulting from the work describing the theoretical calculation of the device parameters (A.I. Patrashin et al., Analytical model for calculating the parameters of matrix photodetector devices, Applied Physics, No. 1, 2014 , p. 35-45).

In this method, infrared temperature measurement threshold difference MFP placed before blackbody emitting surface area which is much larger than the area MFCHE, establish a predetermined temperature blackbody T _Sig measured integrated signals PSE V _{int_ij} generated useful radiation extended blackbody, and the "parasitic" radiation input FPA window , a light filter, a lightproof screen with a window (aperture) and dark PSE currents, measure the sum of the PSE signals generated by "spurious" radiation, measure the integral noise V _{w_ij of} all Ф SE, calculate the differences between the integral signals and the sums of “spurious" signals, obtaining the values of the useful photo signals V _{signal_ij} generated by the radiation of extended blackbody, measure the transmission spectrum of the cold MFP filter, determine its short-wave and long-wave transmission boundaries λ _k and λ _d and calculate the value NETD _ij from the formula

where c = 2,998⋅10 ¹⁰ cm⋅s ^-1 is the speed of light;

k _B = 1.381⋅10 ^-23 W⋅s⋅K ^-1 - Boltzmann constant;

h = 6,626⋅10 ^-34 W⋅s ² - Planck's constant;

N (T _signal ; λ _k ; λ _d ), quanta⋅s ^-1 ⋅cm ^-2 is the integral of the Planck function, which determines the quantum irradiation in a solid angle of 2⋅π in the spectral range [λ _to ; λ _d ];

Z (T _signal ; λ _k ; λ _d ) is the integral of the derivative of the Planck function with respect to temperature

The dimension of the threshold temperature difference is Kelvin degrees.

The disadvantage of this technical solution is the inability to directly determine the PSE photo signals, V _{signal_ij} generated by the useful radiation of an extended blackbody, which significantly complicates the NETD measurement technique.

Indeed, in order to measure the useful photo signals of all PSEs generated by the radiation of an extended blackbody in this optical design, it is necessary to measure their integrated photosignals and the so-called “spurious” PSE signals from the radiation of the MFP input window, from the radiation of a light filter, from the radiation of a lightproof screen with a window ( diaphragm) and signals generated by dark currents of PSE. Then, from the integrated signals of the PSE, it is necessary to subtract the sum of “spurious” signals. The values obtained will be useful PSE photosignals generated by radiation of an extended blackbody.

The measurement of each of the “spurious" PSE photosignals or their total value, in contrast to the theoretical calculation, is a very difficult task, which has not yet been correctly solved. Because of this, the prototype method has not been experimentally developed, the accuracy of measuring the threshold temperature difference of the IR MFP with it will be, to put it mildly, low, the method will be quite complicated, and the measurement time will be long.

The aim of the proposed technical solution is to increase the measurement accuracy while increasing its productivity and simplifying the methodology.

This goal is achieved by the fact that in the known method for measuring the threshold temperature difference of the PSE of an IR MFP, in which an IR MFP is placed in front of the blackbody, set the target temperature of the blackbody T _signal , measure the integral noise V _{w_ij of} all the _{black particles} , measure the transmission spectrum of the cold _MFP filter, determine its short-wavelength and long-wavelength transmission limits λ _k and λ _d , calculate the value NETD _ij according to the formula

where c = 2,998⋅10 ¹⁰ cm⋅s ^-1 is the speed of light;

k _B = 1.381⋅10 ^-23 W⋅s⋅K ^-1 - Boltzmann constant;

h = 6,626⋅10 ^-34 W⋅s ² - Planck's constant;

N (T _signal ; λ _k ; λ _d ), quanta⋅s ^-1 ⋅cm ² is the integral of the Planck function, which determines the quantum irradiation in the solid angle 2⋅π in the spectral range [λ _to ; λ _d ];

Z (T _signal ; λ _k ; λ _d ) is the integral of the derivative of the Planck function with respect to temperature

use blackbody with an area of the radiating area not exceeding the size of the MFCE, between the blackbody and the MFP, near the blackbody they install an optical modulator that covers the radiation of the blackbody, turn on the modulator with a given frequency of radiation modulation, before calculating the threshold temperature difference, measure the signals of all the _{black particles} V _{signal_ij} generated by useful radiation Blackbody, stop the modulator and calculate the threshold temperature difference of all PSEs.

, являются точными расчетными величинами, зависящими лишь от температуры сигнала (АЧТ) T_сигн и ширины спектральной полосы чувствительности МФПУ [λ_к; λ_д], которые достаточно точно устанавливаются и измеряются.In the inventive method, the measured values are the useful signal of the _PSE V _{signal_ij} , depending on the boundaries of the spectral sensitivity curve, [λ _to ; λ _d ], the temperature of the blackbody, T _signal , and the number of the _PSE number ij, and the integrated noise of the _PSE V _{w_ij} , determined by the temperatures of the background, input window, housing, cold screen and cold filter, also depending on the boundaries of the spectral sensitivity curve [λ _to ; λ _d ], from the temperature of the blackbody, T _signal , and from the number ij of the PSE. Functions (3) and (4), as well as the factor

Are accurate calculated values which depend only on the temperature signal (blackbody) T _Sig and the width of the spectral sensitivity band FPA [λ _k; λ _d ], which are fairly accurately established and measured.

When using the proposed method there is no need to measure several "spurious" signals and then calculate the useful photo signal, and we measure one noise and one signal of the PSE MFPU and the subsequent calculation according to the above formula [1]. The measurement of the transmission spectrum of the cold filter to determine the wavelengths λ _to and λ _d is necessary in the present method to confirm a given spectral range of photosensitivity. This measurement is necessarily carried out in the technological route of manufacture of any MFPU.

The inventive method, in contrast to the prototype, can be implemented in a standard optical scheme of the measurement stand, corresponding to GOST 17772-88.

This optical scheme of the measurement stand (Fig. 1) includes a blackbody with a small aperture diameter, ∅ (2-10) mm, and a temperature, for example, 500 K, corresponding to the above GOST.

When it is implemented, the MFPA receives modulated signal radiation from the blackbody and stationary radiation, which create, along with the dark current of the PSE, the element-wise noise of the device. This is radiation from the surrounding background, from the housing, from the entrance windows, from cold filters and screens having fixed temperatures and emitting, as a result, in accordance with Planck’s law. The useful signal of the PSE is measured directly at a given modulation frequency. PSE noise is measured when the modulator is stopped and the blackout curtain is closed, as the standard deviation from the average output voltage. When measuring it, the intrinsic noise of the measurement stand should be taken into account and subtracted. NETD measurement is possible over the entire temperature range of the blackbody and requires only one temperature. The absence of the need for preliminary measurements of several "spurious" signals simplifies the measurement procedure, reducing labor costs, increasing the productivity of the method and the accuracy of measuring a given parameter.

Claims (10)

A method for measuring the threshold temperature difference of an IR MFP, in which an IR MFP is placed in front of the blackbody, set the target temperature of the blackbody T _signal , measure the integral noise V _{w_ij of} all PSEs, measure the transmission spectrum of the cold _MFP filter, determine its short-wave and long-wave transmission boundaries λ _to and λ _d and calculate the value of NETD _ij according to the formula

where c = 2,998⋅10 ¹⁰ cm⋅s ^-1 is the speed of light; k _B = 1.381⋅10 ^-23 W⋅s⋅K ^-1 - Boltzmann constant; h = 6,626⋅10 ^-34 W⋅s ² - Planck's constant; N (T _signal ; λ _k ; λ _d ), quanta⋅s ^-1 ⋅cm ^-2 is the integral of the Planck function, which determines the quantum irradiation in a solid angle of 2⋅π in the spectral range [λ _to ; λ _d ];

Z (T _signal ; λ _k ; λ _d ) is the integral of the derivative of the Planck function with respect to temperature

characterized in that they use blackbody with an emitting area not exceeding the size of the MFCE, between the blackbody and the MFP, an optical modulator is installed near the blackbody, blocking the blackbody radiation, a modulator with a given frequency of radiation modulation is _{turned on} , before calculating the threshold temperature difference, the signals of all PSEs V _{signal_ij} generated by the useful radiation of the blackbody, stop the modulator and calculate the threshold temperature difference of all PSEs.

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