Characterization method for extremely weak dark current of infrared chip

Abstract

The invention discloses a characterization method for extremely weak dark current of an infrared chip, which comprises the following steps of: calculating the lower limit and the upper limit of the number of array pixels according to the limit of a test system, the expected blind pixel rate of the infrared chip and the dark current; leading a pixel array of the infrared chip to a test pin; measuring the total dark current of the pixel array by using a digital source meter; the dark current is normalized according to the array specification; eliminating an abnormal result that the dark current introduced by the short-circuit pixel is obviously large; and dark current of a single pixel of the device is obtained. According to the method, the total dark current of the array can be accurately measured by an existing test system by adopting a multi-pixel parallel connection method, a calculation method of the number of the array pixels is given, and a simple, rapid and high-universality characterization method is provided for the infrared chip with the extremely weak dark current.

Description

Technical Field

[0001] The invention relates to the field of infrared and measurement, and in particular to a method for characterizing extremely weak dark current of an infrared chip. Background Art

[0002] Dark current is an important performance indicator of infrared photodetection devices. The dark current level is directly related to noise and can measure the effect and stability of the material chip process. The measurement of dark current of infrared photodetectors mainly includes two methods: IV test and device long-term integration. IV test connects the pixel and common electrode of the detector chip to the digital source meter respectively, uses the digital source meter to apply bias to specific pixels and directly measure the corresponding current. The measurement accuracy is limited by the digital source meter test system and can generally only reach 10 -14 With the reduction of pixel size and the advancement of key process technology, the dark current of infrared chips has reached 10 -16 A. 10 -17 A level, its reverse bias dark current will be submerged in the test system noise, and no effective test results can be obtained. The long-term device integration method requires a specially designed high-sensitivity readout circuit and a long integration time. The test cost is high and the universality is poor.

[0003] Therefore, there is currently a lack of a simple and fast method to measure the extremely weak dark current of infrared chips. Summary of the invention

[0004] The purpose of the present invention is to provide a method for characterizing the extremely weak dark current of an infrared chip, which mainly solves the technical problems existing in the above-mentioned prior art. By connecting multiple pixels of a device to be tested in parallel to the same test pin to accumulate to reach the digital source meter test threshold, the total dark current after parallel connection is accurately measured, and then the dark current level of a single pixel is obtained by normalization according to the number of pixels. At the same time, it is necessary to increase the test samples and control the number of parallel pixels to avoid the influence of blind pixels with large dark current on the test results.

[0005] The technical solution of the present invention is as follows:

[0006] A method for characterizing extremely weak dark current of an infrared chip, characterized in that it comprises the following steps:

[0007] S1: Select the number of array pixels; assume the expected value of the dark current to be measured is I estimated , the measurement system test threshold is I threshold , R bad is the expected blind pixel rate of the pixel array, and the number of pixels in the pixel array, i.e. the array specification, is a i (i=1,2,...,n),sam i Representative specification is a iThe number of pixel array samples is a, that is, the number of samples prepared on the infrared photoelectric detection material with a specification of i The pixel array has a total of sam i Select a according to the expected parameters of the infrared chip i The value of

[0008] S2: Select the pixel array to be tested on the infrared chip and bond the pixel array to the external test pin; i All pixels are connected in parallel to the same test pin, and connected to a test device such as a digital source meter through the test pin;

[0009] S3: Measure the total dark current of the pixel array, recorded as I test ;

[0010] S4: Dark current normalized to array specifications:

[0011]

[0012] Get the average dark current of the pixels in the array.

[0013] S5: Abnormal results caused by short-circuited pixels are eliminated; the normalized dark current of some arrays may exceed other results by several orders of magnitude, mainly due to the short-circuit current formed by the short-circuited pixels after the reverse bias voltage is applied.

[0014] Easy to distinguish and eliminate from normal test results;

[0015] S6: Analyze the normalized dark current of different arrays to obtain the dark current of a single pixel of the device.

[0016] The method for characterizing the extremely weak dark current of an infrared chip is characterized by:

[0017] The specific implementation method of step S1 includes the following sub-steps:

[0018] S11: Calculate the lower limit a1 of the number of pixels. The lower limit a1 of the number of pixels must satisfy:

[0019] a1·I estimated ≥I threshold (1)

[0020] To ensure that the expected total dark current of at least two pixel arrays can exceed the measurement system test threshold, so that the results can be mutually verified;

[0021] S12: Calculate the upper limit of the number of pixels a n , the upper limit of the number of pixels is a n Need to meet:

[0022] a n ·R bad≤sam i (2)

[0023] where R bad includes two parts: unconnected pixels and short-circuit pixels. By increasing the number of samples sam i , at least one pixel array in a group of samples has no blind pixels in terms of mathematical expectation, so as to suppress the influence of blind pixels on the measurement result;

[0024] S13: Calculate the median value a of the number of pixels i (1 < i < n). The median value of the number of pixels can be determined by a geometric sequence:

[0025]

[0026] Form a gradient of orders of magnitude in the selection of the number of pixels, so that the dark current test results also have a span of orders of magnitude, enhancing the robustness of the test method to abnormal situations such as dark current and blind pixel rate deviating from the expected values. Description of the Drawings

[0027] Figure 1 is a flowchart of a method for characterizing extremely weak dark current of an infrared chip according to the present invention.

[0028] Figure 2 is a detailed flowchart of step S1 in the method of the present invention.

[0029] Figure 3 is a schematic diagram of the device structure involved in step S2 of the method of the present invention; wherein: 1 - P-type doping region of the mercury cadmium telluride infrared chip, 2 - N-type doping region of the mercury cadmium telluride infrared chip, 3 - indium column interconnection structure, 4 - insulating protective layer, 5 - metal lead (connected to the external test pin), 6 - gemstone chip. Detailed Embodiment

[0030] The present invention discloses a method for characterizing extremely weak dark current of an infrared chip.

[0031] The method includes: preparing a photodetector device containing pixel arrays with different numbers of parallel pixels, and its structure is as Figure 3 shown. Measure the total dark current of the pixel array, and calculate the normalized dark current according to the array specifications, and the dark current normalization results of different specifications of arrays are mutually verified.

[0032] Please refer to Figure 1 、 2 , the method of the present invention includes the following steps:

[0033] S1: Select the number of array pixels. Let the expected value of the dark current to be measured be I estimated , the test threshold of the measurement system is I threshold , R badis the expected blind pixel rate of the pixel array, and the number of pixels in the pixel array (array specification) is a i (i=1,2,...,n),sam o Representative specification is a o The number of pixel array samples (i.e., the number of pixel array samples prepared on the infrared photoelectric detection material with a specification of a i The pixel array has a total of sam i Select a according to the expected parameters of the infrared chip i The value of .

[0034] The step S1 comprises the following sub-steps:

[0035] S11: Calculate the lower limit of the number of pixels a1. The lower limit of the number of pixels a1 must satisfy:

[0036] a1·I estimated ≥I threshold (1)

[0037] This ensures that the expected total dark current of at least two pixel arrays can exceed the measurement system test threshold so that the results can be mutually verified.

[0038] S12: Calculate the upper limit of the number of pixels a n The upper limit of the number of pixels is a n Need to meet:

[0039] a n ·R bad ≤sam i (2)

[0040] Where R bad It includes two parts: disconnected pixels and short-circuit pixels. By increasing the number of samples, sam i , a group of samples has at least one pixel array that does not contain blind pixels in mathematical expectation, so as to suppress the influence of blind pixels on the measurement results.

[0041] S13: Calculate the median value a of the number of pixels i (1<i<n). The median value of the number of pixels can be determined by a geometric progression:

[0042]

[0043] A gradient of orders of magnitude is formed in the selection of the number of pixels, so that the dark current test results also have a span of orders of magnitude, enhancing the robustness of the test method to abnormal situations such as dark current and blind pixel rate deviating from expected values.

[0044] S2: Select the pixel array to be tested on the infrared chip and bond the pixel array to the external test pin. iAll pixels are connected in parallel to the same test pin, and connected to test equipment such as a digital source meter through the test pin.

[0045] S3: Measure the total dark current of the pixel array, recorded as I test .

[0046] S4: Dark current normalized to array specifications:

[0047]

[0048] Get the average dark current of the pixels in the array.

[0049] S5: Eliminate abnormal results caused by short-circuited pixels. The normalized dark current of some arrays may exceed other results by several orders of magnitude. This is mainly due to the short-circuit current formed by short-circuited pixels after applying reverse bias voltage. It is easy to distinguish and eliminate from normal test results.

[0050] S6: Analyze the normalized dark currents of different arrays to obtain the dark current of a single pixel of the device.

[0051] Embodiment 1:

[0052] According to the method of the present invention, an infrared chip for extremely weak dark current testing is prepared. The relevant parameters include: the blind pixel rate is about 0.1%, the expected dark current is about 10 -16 A, the test system limit is about 10 -14 A.

[0053] The number of samples of the pixel array determined by the external test pin is 5, so the minimum number of pixels in the array is selected as 100, the maximum number of pixels is 3200, and intermediate values ​​such as 200, 400, 800, and 1600 are set.

[0054] If the test process finds that the actual blind pixel rate of the infrared chip is greater than the expected blind pixel rate, which is about 0.3%, the probability of blind pixels appearing in pixel arrays with specifications of 1600 and 3200 will increase greatly, and a large number of abnormal test results will be easily affected by short-circuited pixels. However, the probability of blind pixels appearing in pixel arrays with specifications of 100, 200, 400 and 800 is still within an acceptable range, and a gradient total dark current test result can still be formed.

[0055] Embodiment 2:

[0056] According to the method of the present invention, an infrared chip for extremely weak dark current testing is prepared. The relevant parameters include: the blind pixel rate is about 1.5%, the expected dark current is about 10 -15 A, the test system limit is about 10 -14 A.

[0057] The number of samples of the pixel array determined by the external test pin is 10, so the minimum number of pixels in the array is selected as 10, the maximum number of pixels is 640, and the intermediate values ​​such as 20, 40, 80, 160, and 320 are set. If the test process finds that the actual dark current of the infrared chip is less than the expected dark current, about 4×10 -16 A, the total dark current of the pixel arrays with specifications of 10 and 20 still exceeds the measurable range of the test system, and the test results are manifested as the noise of the test system. However, the total dark current of the pixel arrays with specifications of 40, 80, 160, 320 and 640 is within the limit of the test system, and a gradient total dark current test result can be formed.

Claims

1. A method for characterizing extremely weak dark current of an infrared chip, characterized in that: It includes the following steps: S1: Select the number of array pixels; set the expected value of the dark current to be measured to be I estimated , the measurement system test threshold is I threshold , R bad is the expected blind pixel rate of the pixel array, and the number of pixels in the pixel array, i.e. the array specification, is a i (i=1,2,…,n),sam i Representative specification is a i The number of pixel array samples is a, that is, the number of samples prepared on the infrared photoelectric detection material with a specification of i The pixel array has sam i Select a according to the expected parameters of the infrared chip i The value of S2: Select the pixel array to be tested on the infrared chip and bond the pixel array to the external test pin; i All pixels are connected in parallel to the same test pin, and connected to a test device such as a digital source meter through the test pin; S3: Measure the total dark current of the pixel array, recorded as I test ; S4: Dark current normalized according to array specifications: Get the average dark current of the pixels in the array. S5: Eliminate abnormal results caused by short-circuited pixels; the normalized dark current of some arrays may exceed other results by several orders of magnitude, mainly due to the short-circuit current formed by the short-circuited pixels after the reverse bias voltage is applied, which can be easily distinguished from the normal test results and eliminated; S6: Analyze the normalized dark currents of different arrays to obtain the dark current of a single pixel of the device.

2. The method for characterizing the extremely weak dark current of an infrared chip according to claim 1, characterized in that: The specific implementation method of step S1 includes the following sub-steps: S11: Calculate the lower limit a1 of the number of pixels, which must satisfy: a1·I estimated ≥I threshold (1) To ensure that the expected total dark current of at least two pixel arrays can exceed the measurement system test threshold, so that the results can be mutually verified; S12: Calculate the upper limit of the number of pixels a n , the upper limit of the number of pixels is a n Need to meet: a n ·R bad ≤sam i (2) Where R bad It includes two parts: disconnected pixels and short-circuit pixels. By increasing the number of samples, sam i , a group of samples has at least one pixel array that does not contain blind pixels in mathematical expectation, so as to suppress the influence of blind pixels on the measurement results; S13: Calculate the median value a of the number of pixels i (1 < i < n). The median value of the number of pixels can be determined by a geometric sequence: A gradient of orders of magnitude is formed in the selection of the number of pixels, so that the dark current test results also have a span of orders of magnitude, enhancing the robustness of the test method to abnormal situations such as dark current and blind pixel rate deviating from expected values.

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