Long-wave II-type superlattice SF6 gas detector

Abstract

The invention discloses a long-wave class-II superlattice SF6 gas detector which comprises a focal plane array, the focal plane array comprises a plurality of independent photosensitive pixels, the focal plane array and a reading circuit are connected to form an infrared focal plane detector assembly, and each photosensitive pixel comprises a GaSb substrate. The GaSb buffer layer, the n InAsSb buffer layer, the n-type lower ohmic contact layer, the n-type InAs / GaSb intrinsic second-class superlattice light absorption layer, the AlGaAsSb barrier layer and the n-type upper ohmic contact layer are sequentially arranged on the GaSb substrate; partial region of each layer of epitaxial material is etched to the bottom n-type contact layer to form a bottom electrode window, and partial region of each layer of epitaxial material is etched to the top n-type contact layer to form a top electrode window; an Au nano array is prepared on the n-type upper ohmic contact layer to serve as a plasmon structure; a bottom annular electrode is deposited and prepared on the bottom electrode window, and a top electrode is deposited and prepared at the top electrode window, so that the SF6 gas can be accurately and efficiently monitored in a non-contact, real-time and long-distance manner, and the leakage point of the SF6 gas can be quickly and accurately searched.

Description

Technical Field

[0001] The invention relates to the technical field of gas detection, in particular to a long-wave type II superlattice SF6 gas detector. Background Art

[0002] Sulfur hexafluoride (SF6) gas has been widely used in various electrical equipment in many industrial fields such as coal, petroleum, electricity, metal smelting and aerospace due to its excellent insulation and arc extinguishing properties. However, SF6 gas has a strong greenhouse effect, and its greenhouse effect potential is 23,900 times that of CO2. A large amount of industrial use has led to a gradual increase in its concentration in the earth's atmosphere. In addition, SF6 is a harmful gas with severe corrosiveness and toxicity. SF6 gas leakage will not only have an adverse effect on its electrical performance, but also directly threaten the personal safety of operation and maintenance personnel. If these gases cannot be discovered and handled in time after leakage, it may cause fire, explosion or personal poisoning, suffocation and other malignant accidents, causing serious losses to the safety of people's lives and property. Therefore, real-time monitoring and leakage warning of SF6 gas are very important. It is not only the key to prevent accidents and ensure the safe production of enterprises, but also the guarantee of the safety of production personnel and surrounding people. It is of great significance to the safe and stable operation of industrial systems.

[0003] Among the commonly used gas monitoring methods, mainstream traditional gas monitors mainly use catalytic combustion, semiconductor, and electrochemical sensors. Although the above commonly used sensors have certain price advantages, they have the disadvantages of chemical reaction with gas and need frequent calibration. In addition, due to their high operating temperature and small detection range, they usually need to use multiple detectors to coordinate and judge the leakage situation. The detection accuracy is directly related to the number and location of the instruments. There are disadvantages such as complex layout and inability to quickly and accurately locate the gas leakage point. Therefore, a long-wave type II superlattice SF6 gas detector is urgently needed to solve the above problems. Summary of the invention

[0004] The purpose of the present invention is to provide a long-wave type II superlattice SF6 gas detector. Since SF6 has a strong absorption capacity for light in the infrared band (10.55um), this characteristic can be used to make usually invisible gas leaks visible with the help of infrared detectors. At the same time, it can accurately and efficiently perform non-contact, real-time and long-distance monitoring of SF6 gas, and quickly and accurately find the leakage point of SF6 gas.

[0005] In order to solve the above technical problems, the present invention adopts the following technical solutions: a long-wave type II superlattice SF6 gas detector, the detector includes a focal plane array, the focal plane array includes a plurality of independent photosensitive pixels, the focal plane array and the readout circuit are connected to form an infrared focal plane detector assembly, the photosensitive pixels correspond to the amplifier units on the corresponding readout circuits one by one, the amplifier units integrate and amplify the photocurrents of the photosensitive pixels, and then read out in sequence through row and column shift registers, the photosensitive pixels include a GaSb substrate, a GaSb buffer layer, an n-type lower ohmic contact layer, an n-type InAs / GaSb intrinsic type II superlattice light absorption layer, an AlGaAsSb barrier layer and an n-type upper ohmic contact layer sequentially arranged on the GaSb substrate; each layer of epitaxial material transfers the focal plane table mask pattern through a photolithography process and an ICP dry etching process; a partial area of ​​the epitaxial material is etched to the bottom n-type contact layer to form a bottom electrode window, and a partial area is etched to the top n-type contact layer to form a top electrode window; and

[0006] The Au nanoarray is prepared as a plasmon structure on the n-type upper ohmic contact layer by using an electron beam evaporation process and a wet etching process;

[0007] A bottom annular electrode is deposited on the bottom electrode window, and a top electrode is deposited on the top electrode window;

[0008] The bottom annular electrode of each of the photosensitive pixels is connected to the bottom common electrode through a metal film connection line.

[0009] Preferably, after the coating is completed, an acetone solution is used as a stripping solution to strip the metal outside the electrode area to form the required electrode metal; and a flip-chip bonding process is used to connect the focal plane array to the readout circuit to form an infrared focal plane detector assembly.

[0010] Preferably, the buffer layer is 300-500nm thick; the n-type lower ohmic contact layer is 100-150nm thick; the n-type InAs / GaSb intrinsic type II superlattice light absorption layer is 0.7-1.2μm thick; the AlGaAsSb barrier layer is 300-400nm thick; and the n-type upper ohmic contact layer is 150-200nm thick.

[0011] Preferably, the n-type InAs / GaSb intrinsic type-II superlattice light absorption layer is composed of periodic InAs / InAsSb.

[0012] Preferably, the Au nanoarray has a nanoarray period L of 2 μm, a height of 40 nm, and a diameter of 1.5 μm.

[0013] Preferably, the Au nanoarray is arranged on the back of the detector.

[0014] Preferably, a 270nm SiO2 surface passivation layer is deposited on the photosensitive pixel by plasma enhanced chemical vapor deposition (PECVD) process to reduce stress, increase its surface resistivity and improve surface leakage current.

[0015] Preferably, the passivation layer and the plasmon structure are etched with a wet process to form an upper electrode through hole, the annular electrode pattern is transferred to the bottom n-type contact layer using a dry etching process, and then the bottom annular electrode and the top electrode are prepared by electron beam evaporation deposition.

[0016] Preferably, the detector also includes a Stirling refrigerator, a signal processing and transmission module, a leakage warning module, and a remote display storage module. The infrared focal plane detector assembly detects SF6 gas, the signal processing and transmission module receives the detected data and processes and transmits the data, the remote display storage module receives and stores the transmitted data, and the leakage warning module performs leakage warning based on the data processing results.

[0017] Preferably, the detector also includes an infrared imaging lens and a visible light camera, which combines the infrared image with the real environment image to facilitate more realistic and clear monitoring and finding of the leakage source.

[0018] Beneficial effects: 1. The infrared detection components made of Class II superlattice materials are used for SF6 gas detection. They can effectively reduce the tunneling current and make the device have a smaller dark current. In the long-wave band, they can achieve a higher detection rate than other infrared detection materials such as mercury cadmium telluride, especially for the detection of SF6 gas (10.55um, long wave). It has better performance and higher efficiency and accuracy than ordinary SF6 gas detectors. In addition, unlike the disadvantages of high price caused by the difficulty of preparing mercury cadmium telluride materials and low yield, the uniformity of Class II superlattice materials and device stability are easier to guarantee. The Class II superlattice infrared focal plane detector based on this has more advantages than mercury cadmium telluride detectors in low-cost large-scale production;

[0019] 2. By making bottom annular electrodes around each pixel of the focal plane array and connecting each annular electrode to the common lower electrode through metal film wiring, the transport distance of photogenerated carriers in the epitaxial semiconductor material is greatly reduced, avoiding the recombination loss of carriers during long-distance transport, thereby increasing the lifetime of photogenerated carriers, improving the photocurrent signal intensity of the focal plane array, and greatly improving the light response performance of the focal plane array.

[0020] 3. The back Au nanoarray plasmon structure is used to enhance the light transmission effect and improve the absorption rate of photons, thereby greatly enhancing the light detection performance of the device; when light irradiates the detector surface, some photons pass through the superlattice absorption area and reach this plasmon structure, generating plasma resonance at the interface between the semiconductor epitaxial layer and the Au nanorods, stimulating the plasmon enhancement mechanism (SPP), thereby greatly improving the light absorption rate and further enhancing the detector response rate;

[0021] 4. An Au nanoarray plasmon enhancement structure is prepared on the back, which will not cause damage to the structure and epitaxial material when the substrate is removed, and can be well integrated with the readout circuit, solving the problem that common front plasmon structures such as grating coupling and bull's eye are difficult to apply in long-wave infrared focal plane arrays.

[0022] 5. By combining infrared spectrum imaging and visible light imaging, the generated image can not only display the gas imaging part marked by the infrared screen, but also has visible imaging of the background environment. The combination of the two makes it easier to intuitively find gas leakage points. BRIEF DESCRIPTION OF THE DRAWINGS

[0023] The accompanying drawings are used to provide further understanding of the present invention and constitute a part of the specification. They are used to explain the present invention together with the embodiments of the present invention and do not constitute a limitation of the present invention.

[0024] In the attached picture:

[0025] Figure 1 It is a structural schematic diagram of the SF6 gas detector of the present invention;

[0026] Figure 2 It is a structural schematic diagram of the main component structure of the second type of superlattice SF6 detector of the present invention;

[0027] Figure 3 It is a schematic diagram of the structure of a single pixel of the present invention;

[0028] Figure 4 is a schematic diagram of the focal plane array structure of the present invention;

[0029] Numbers in the figure: 1. Ring electrode; 2. Top electrode; 3. Plasmon structure; 4. Common electrode; 5. Infrared focal plane detector assembly; 6. Stirling refrigerator; 7. Infrared imaging lens; 8. Signal processing and transmission module; 9. Leakage warning module; 10. Remote display storage module; 11. Visible light camera DETAILED DESCRIPTION

[0030] The embodiments of the present invention are described below in conjunction with the drawings in the embodiments of the present invention. The terms used in the implementation mode of the present invention are only used to explain the specific embodiments of the present invention, and are not intended to limit the present invention. The embodiments of the present application are described below in conjunction with the drawings.

[0031] Example: Reference Figure 2-Figure 4 As shown, a long-wave type II superlattice SF6 gas detector includes a focal plane array, the focal plane array includes 640×512 independent photosensitive pixels, the focal plane array and the readout circuit are connected to form an infrared focal plane detector assembly 5, so that the 640×512 photosensitive pixels correspond to the 640×512 amplifier units on the corresponding readout circuit. The amplifier unit integrates and amplifies the photocurrent of the photosensitive pixel, and then reads it out in sequence through the row and column shift register. The photosensitive pixel includes the bottom GaSb substrate, and the GaSb substrate provides a platform infrastructure for the infrared detector, so that the superlattice material required for the detector can be grown epitaxially thereon;

[0032] The following are arranged in sequence on the GaSb substrate:

[0033] GaSb buffer layer, n InAsSb buffer layer, the buffer layer thickness is 300-500nm, which is used to smooth the lattice and help reduce material defects caused by lattice mismatch, thereby helping to improve the quality of the superlattice and manufacture high-performance infrared gas detectors;

[0034] n-type lower ohmic contact layer, thickness is 100-150nm;

[0035] The n-type InAs / GaSb intrinsic type II superlattice light absorption layer prepared by MBE technology, the absorption layer is composed of periodic InAs / InAsSb, with a thickness of 0.7-1.2μm;

[0036] The AlGaAsSb barrier layer, with a thickness of 300-400nm, can separate the upper contact layer and the absorption layer, blocking most electron transport while allowing a few holes and photogenerated carriers to move freely, thereby effectively suppressing dark current and effectively improving the quantum efficiency and detection rate of the detector;

[0037] n-type upper ohmic contact layer, thickness is 150-200nm;

[0038] The ohmic contact layer is made of TiPtAu alloy, which enables the detector to form an ohmic contact with the metal wire to better collect electrons.

[0039] Each layer of epitaxial material is transferred to the focal plane mesa mask pattern through photolithography and ICP dry etching process; a part of the epitaxial material is etched to the bottom n-type contact layer to form a bottom electrode window, and a part of the epitaxial material is etched to the top n-type contact layer to form a top electrode window, and a mesa 640×512 array is formed by etching;

[0040] On top of the above-mentioned top ohmic contact layer, an Au nanoarray was prepared as a plasmon structure 3 by electron beam evaporation and wet etching, and the nanoarray period L was 2 μm, the height was 40 nm, and the diameter was 1.5 μm;

[0041] The Au nanoarray is set on the back of the detector; when light irradiates the surface of the detector, some photons pass through the superlattice absorption region and reach this plasmon structure 3, generating plasma resonance at the interface between the semiconductor epitaxial layer and the Au nanorods, exciting the plasmon enhancement mechanism (SPP), thereby greatly improving the light absorption rate and further enhancing the detector response rate.

[0042] A 270nm SiO2 surface passivation layer was deposited using plasma enhanced chemical vapor deposition (PECVD) to reduce stress, increase surface resistivity, and improve surface leakage current; it can effectively suppress non-radiative recombination of surface carriers and improve the response speed and sensitivity of the detector;

[0043] The passivation layer and the plasmon structure 3 are etched with a wet process to form an upper electrode through hole, and the pattern of the annular electrode 1 is transferred to the bottom n-type contact layer by a dry etching process, and then the bottom annular electrode 1 and the top electrode 2 are prepared by electron beam evaporation deposition; this is an important process that can not only realize the isolation of the plasma structure, but also prepare the upper electrode through hole and create a window for connecting with the readout circuit by the indium column flip-chip process; the bottom annular electrode 1 of each photosensitive pixel is connected to the bottom common electrode 4 through a metal film connection line;

[0044] The photogenerated carriers generated in the absorption area of ​​the focal plane array need to be transmitted to the lower electrode through the lower contact layer for collection. In particular, the photogenerated carriers generated in the absorption area of ​​the table at the center of the array need to reach the lower electrode through a longer transmission distance. During the transmission process, the carriers will be recombined and annihilated at the defects of the epitaxial material of the lower contact layer. This process will affect the carrier lifetime and reduce the signal strength of the focal plane chip. At the same time, since the photogenerated carriers generated in the table absorption area at different positions of the focal plane chip are transmitted to the lower electrode at different distances, the signal strength of different focal plane chip areas received by the lower electrode will be different, affecting the response uniformity of the focal plane chip and ultimately affecting the comprehensive performance of the focal plane chip.

[0045] By making a bottom annular electrode 1 around each pixel of the focal plane array and connecting each annular electrode 1 to a common bottom electrode through a metal film connection, the transport distance of photogenerated carriers in the epitaxial semiconductor material is greatly reduced, and the recombination loss of carriers during long-distance transport is avoided, thereby increasing the lifetime of photogenerated carriers, improving the photocurrent signal intensity of the focal plane array, and greatly improving the light response performance of the focal plane array;

[0046] After the coating is completed, an acetone solution is used as a stripping solution to strip the metal outside the electrode area to form the required electrode metal; finally, a flip-chip bonding process is used to connect the focal plane array with the readout circuit to form an infrared focal plane detector assembly 5.

[0047] The infrared focal plane detector assembly 5 can be used alone as an infrared detector to detect SF6 gas, or it can be used with corresponding modules as an overall system solution to achieve real-time monitoring imaging and leakage warning;

[0048] refer to Figure 1 As shown: equipped with Stirling refrigerator 6, dewar, infrared imaging lens 7, visible light camera 11 and lens, signal processing and transmission module 8, leakage warning module 9, remote display storage module 10 as a whole assembly, infrared focal plane detector assembly 5 detects SF6 gas, and Stirling refrigerator 6 provides cooling conditions. The infrared focal plane detector assembly 5 is connected to Stirling refrigerator 6 through dewar packaging and then connected to other components at room temperature. The signal processing and transmission module 8 receives the detected data and processes and transmits the data. The remote display storage module 10 receives and stores the transmitted data. The leakage warning module 9 performs leakage warning based on the data processing result. The SF6 gas detector adopts a combination of infrared spectrum imaging and visible light imaging. At the same time, it is equipped with a visible light camera 11 and an infrared imaging lens 7. The generated image is not just an infrared picture, but a combination of infrared images and real environment images, which is convenient for more realistic and clear monitoring and finding of leakage sources.

[0049] The operating wavelength range of this Type II superlattice detector is 8 to 12.5μm, the peak detection wavelength is 10.5um, and the noise equivalent temperature difference (NETD) is 30mK at an integration time of 150μs. It can realize real-time monitoring and leakage warning of SF6 gas (1.5um) in large industrial scenes.

[0050] The embodiments of the present invention are described in detail above in conjunction with the accompanying drawings, but the present invention is not limited to the above embodiments. For ordinary technicians in this technical field, after knowing the contents recorded in the present invention, they can make several equivalent changes and substitutions without departing from the principle of the present invention. These equivalent changes and substitutions should also be regarded as belonging to the protection scope of the present invention.

Claims

1. A long-wave type II superlattice SF6 gas detector, the detector includes a focal plane array, the focal plane array includes a plurality of independent photosensitive pixels, the focal plane array and a readout circuit are connected to form an infrared focal plane detector assembly, the photosensitive pixels correspond to the amplifier units on the corresponding readout circuits one by one, the amplifier units integrate and amplify the photocurrent of the photosensitive pixels, and then read out in sequence through row and column shift registers, characterized in that: The photosensitive pixel includes a GaSb substrate, a GaSb buffer layer, an n-type InAsSb buffer layer, an n-type lower ohmic contact layer, an n-type InAs / GaSb intrinsic type II superlattice light absorption layer, an AlGaAsSb barrier layer and an n-type upper ohmic contact layer sequentially arranged on the GaSb substrate; a part of each layer of epitaxial material is etched to the bottom n-type contact layer to form a bottom electrode window, and a part of each layer of epitaxial material is etched to the top n-type contact layer to form a top electrode window; and An Au nanoarray is prepared on the n-type upper ohmic contact layer as a plasmon structure; A bottom annular electrode is deposited on the bottom electrode window, and a top electrode is deposited on the top electrode window; The bottom annular electrode of each of the photosensitive pixels is connected to the bottom common electrode through a metal film connection line.

2. A long-wave type II superlattice SF6 gas detector according to claim 1, characterized in that: The focal plane array and the readout circuit are connected through an indium column flip-chip bonding process.

3. The long-wave type II superlattice SF6 gas detector according to claim 1, characterized in that: The buffer layer has a thickness of 300-500nm; the n-type lower ohmic contact layer has a thickness of 100-150nm; the n-type InAs / GaSb intrinsic type II superlattice light absorption layer has a thickness of 0.7-1.2μm; the AlGaAsSb barrier layer has a thickness of 300-400nm; and the n-type upper ohmic contact layer has a thickness of 150-200nm.

4. The long-wave type II superlattice SF6 gas detector according to claim 3, characterized in that: The n-type InAs / GaSb intrinsic type-II superlattice light absorption layer is composed of periodic InAs / InAsSb.

5. The long-wave type II superlattice SF6 gas detector according to claim 1, characterized in that: The Au nanoarray has a nanoarray period L of 2 μm, a height of 40 nm, and a diameter of 1.5 μm.

6. A long-wave type II superlattice SF6 gas detector according to claim 1 or 5, characterized in that: The Au nanoarray is arranged on the back of the detector.

7. The long-wave type II superlattice SF6 gas detector according to claim 1, characterized in that: A SiO2 surface passivation layer is deposited on the photosensitive pixel.

8. The long-wave type II superlattice SF6 gas detector according to claim 7, characterized in that: The passivation layer and the plasmon structure are etched with a wet process to form an upper electrode through hole, and the annular electrode pattern is transferred to the bottom n-type contact layer using a dry etching process, and then the bottom annular electrode and the top electrode are prepared by electron beam evaporation deposition.

9. The long-wave type II superlattice SF6 gas detector according to claim 1, characterized in that: The detector also includes a signal processing and transmission module, a leakage warning module and a remote display storage module. The infrared focal plane detector assembly detects SF6 gas. The signal processing and transmission module receives the detected data and processes and transmits the data. The remote display storage module receives and stores the transmitted data. The leakage warning module issues a leakage warning based on the data processing results.

10. A long-wave type II superlattice SF6 gas detector according to claim 1 or 9, characterized in that: The detector also includes an infrared imaging lens and a visible light camera.

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