Long-wave type-Ⅱ superlattice SF6 gas detector

Abstract

The application discloses a long-wave type-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 is connected with a readout circuit to form an infrared focal plane detector assembly, the photosensitive pixel comprises a GaSb substrate, a GaSb buffer layer, an n 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 are 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; an Au nano array is prepared on the n-type upper ohmic contact layer as a plasmonic structure; a bottom ring 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 precisely and efficiently monitored in a non-contact, real-time and long-distance mode, and the leakage point of the SF6 gas can be quickly and accurately found.

Description

TECHNICAL FIELD

[0001] The application relates to the technical field of gas detection, and particularly relates to a long-wave type-Ⅱ superlattice SF6 gas detector. BACKGROUND

[0002] Sulfur hexafluoride (SF6) gas has been widely applied to various electrical equipment in many industrial fields such as coal, petroleum, electric power, metal smelting and aerospace due to its excellent insulation and arc extinguishing performance. However, SF6 gas has a strong greenhouse effect, and the greenhouse effect potential is 23900 times that of CO2. Large-scale industrial use leads to the gradual increase of the concentration of SF6 gas in the earth's atmosphere. Moreover, SF6 is a harmful gas with serious corrosiveness and toxicity. SF6 gas leakage not only has an adverse effect on the electrical performance, but also directly threatens the personal safety of operation and maintenance personnel. If the leakage of the gas cannot be found and disposed in time, fire, explosion or poisoning and suffocation may occur, which may cause serious loss of life and property safety of the public. Therefore, real-time monitoring and leakage warning of SF6 gas are very important, which is not only the key to prevent accidents and ensure the safety of production, but also the safety guarantee for production personnel and the surrounding people, and has great significance for the safe and stable operation of the industrial system.

[0003] In the commonly used gas monitoring method, mainstream conventional gas monitors mainly use catalytic combustion type, semiconductor type and electrochemical type sensors. Although the above several commonly used sensors have certain price advantages, they have the disadvantages of chemical reaction with gas, frequent calibration, high working temperature, small detection range, and the like. Usually, multiple detection instruments need to be used to cooperatively judge the leakage situation. The detection precision is directly related to the number and position of the instruments, and the gas leakage point cannot be quickly and accurately positioned due to the complex arrangement. SUMMARY

[0004] The application aims to provide a long-wave type-Ⅱ superlattice SF6 gas detector. Since SF6 has extremely strong absorption capacity for infrared waves (10.55 um), the usually invisible gas leakage can be made visible with the help of an infrared detector. Meanwhile, the SF6 gas can be accurately and efficiently monitored in a non-contact and real-time long-distance mode, and the leakage point of the SF6 gas can be quickly and accurately found.

[0005] To solve the above technical problems, the application adopts the following technical solutions: a long-wave type-Ⅱ superlattice SF6 gas detector, the detector comprising a focal plane array, the focal plane array comprising a plurality of independent photosensitive pixels, the focal plane array and a readout circuit being connected to form an infrared focal plane detector assembly, the photosensitive pixels corresponding one-to-one to amplifiers on the readout circuit, the amplifiers integrating and amplifying the photoelectric current of the photosensitive pixels, and then sequentially reading out through row and column shift registers, the photosensitive pixel comprising a GaSb substrate, a GaSb buffer layer, an n 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 being sequentially arranged on the GaSb substrate; the epitaxial material of each layer is transferred by a photolithography process and an ICP dry etching process to transfer a focal plane mesa mask pattern; a portion of the epitaxial material is etched to the bottom n-type contact layer to form a bottom electrode window, and a portion of the epitaxial material is etched to the top n-type contact layer to form a top electrode window; and

[0006] The n-type upper ohmic contact layer is prepared by an electron beam evaporation process and a wet etching process to prepare an Au nano array as a plasmonic structure;

[0007] The bottom electrode window is deposited to prepare a bottom ring electrode, and the top electrode window is deposited to prepare a top electrode;

[0008] The bottom ring electrodes of the photosensitive pixels are connected to a bottom common electrode through a metal thin film wire.

[0009] Preferably, after the film 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; a flip-chip welding process is used to connect the focal plane array and the readout circuit to form the infrared focal plane detector assembly.

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

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

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

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

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

[0015] Preferably, the passivation layer and plasmonic structure are etched through a wet process to form a via for the upper electrode, and a dry etching process is used to transfer a ring electrode pattern to the bottom n-type contact layer, and an electron beam evaporation deposition is used to prepare the bottom ring electrode and the top electrode.

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

[0017] Preferably, the detector further comprises an infrared imaging lens and a visible light camera, which combines the infrared image with the real environment image, facilitating more realistic and clear monitoring and searching for the leakage source.

[0018] Beneficial effects: 1. The infrared detection assembly prepared from type II superlattice material is used for SF6 gas detection, which greatly reduces the tunneling current, making the device have smaller dark current, and achieving higher detection rate in the long-wave band than other infrared detection materials such as mercury cadmium telluride, especially in the detection of SF6 gas (10.55um, long wave), and has more excellent performance, and has higher efficiency and accuracy than ordinary SF6 gas detectors. In addition, unlike the difficulty in preparing mercury cadmium telluride material and the low yield, which causes the material to be expensive, the uniformity and stability of type II superlattice material are easier to guarantee, and the type II superlattice infrared focal plane detector based thereon has more advantages than mercury cadmium telluride detector in low-cost mass production.

[0019] 2. By making a bottom ring electrode around each pixel of the focal plane array and connecting each ring electrode to a common lower electrode through a metal thin film wire, the transport distance of photo-generated carriers in the epitaxial semiconductor material is greatly reduced, the recombination loss of carriers in the long-distance transport process is avoided, the lifetime of photo-generated carriers is increased, the photocurrent signal strength of the focal plane array is improved, and the photoresponse performance of the focal plane array is greatly improved.

[0020] 3. By adopting a back Au nanoarray plasmonic structure, the light transmission effect is enhanced and the photon absorption rate is increased, thereby significantly enhancing the optical detection performance of the device. When light irradiates the detector surface, some photons pass through the superlattice absorption region and reach this plasmonic structure, generating plasmonic resonance at the interface between the semiconductor epitaxial layer and the Au nanorods, exciting the plasmonic enhancement mechanism (SPP), thereby significantly improving the light absorption rate and thus enhancing the detector responsivity.

[0021] 4. The Au nanoarray plasmonic enhancement structure is fabricated on the back side, which will not cause damage to the structure and epitaxial material when the substrate is removed. It can also be well integrated with the readout circuit, solving the problem that common front plasmonic structures such as grating coupling and bullseye are difficult to apply in long-wave infrared focal plane arrays.

[0022] 5. By combining infrared spectral imaging and visible light imaging, the generated image can not only display the gas imaging portion marked by the infrared image, but also have visible imaging of the background environment. The combination of the two makes it easier to intuitively discover gas leak points. Attached Figure Description

[0023] The accompanying drawings are provided to further illustrate the invention and form part of the specification. They are used together with the embodiments of the invention to explain the invention and do not constitute a limitation thereof.

[0024] In the attached diagram:

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

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

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

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

[0029] The diagram labels are as follows: 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 and storage module; 11. Visible light camera. Detailed Implementation

[0030] Embodiments of the present application will be described herein below with reference to the drawings. The terms used in the embodiments section of the present application are used only to explain specific embodiments of the present application and are not intended to limit the present application. Embodiments of the present application will be described below with reference to the accompanying drawings.

[0031] Embodiments: Reference Figures 2-4 As shown in the figure, 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 a readout circuit are connected to form an infrared focal plane detector assembly 5, 640*512 photosensitive pixels and 640*512 amplifier units on the corresponding readout circuit are one-to-one corresponding, the amplifier units integrate and amplify the photoelectric current of the photosensitive pixels, and then the photoelectric current is sequentially read out through row and column shift registers. The photosensitive pixels include a GaSb substrate at the bottom layer, the GaSb substrate provides a basic structure for the infrared detector to grow the superlattice material required for the detector on it;

[0032] The GaSb substrate is sequentially provided with:

[0033] A GaSb buffer layer and an n InAsSb buffer layer, the thickness of the buffer layer is 300-500 nm, 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 a high-performance infrared gas detector;

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

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

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

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

[0038] The ohmic contact layer is prepared by TiPtAu alloy, so that the detector forms ohmic contact with the metal wire to better collect electrons;

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

[0040] On the top ohmic contact layer, an Au nano array is prepared as a plasmonic structure 3 by an electron beam evaporation process and a wet etching process, the nano array has a period L of 2 µm, a height of 40 nm, and a diameter of 1.5 µm;

[0041] The Au nano array is arranged on the back of the detector; when light irradiates the surface of the detector, part of the photons pass through the superlattice absorption region and reach the plasmonic structure 3, and plasmonic resonance is generated at the interface between the semiconductor epitaxial layer and the Au nanorod, thereby exciting a plasmonic enhancement mechanism (SPP), so as to greatly improve the light absorption rate and further enhance the response rate of the detector.

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

[0043] The passivation layer and the plasmonic structure 3 are etched by a wet process to form an upper electrode via hole, and the pattern of the ring electrode 1 is transferred to the bottom n-type contact layer by a dry etching process; then, the bottom ring electrode 1 and the top electrode 2 are prepared by an electron beam evaporation deposition process; the process can not only realize the isolation of the plasmonic structure, but also create a window for the indium column flip-chip bonding process to connect the readout circuit; the bottom ring electrode 1 of each photosensitive pixel is connected to the bottom common electrode 4 through a metal thin film wire;

[0044] The photo-generated carriers generated in the focal plane array absorption region need to be transmitted to the lower electrode through the lower contact layer for collection, especially the photo-generated carriers generated in the central mesa absorption region of the focal plane array need to be transmitted to the lower electrode through a long transmission distance, and the carriers will be recombined and annihilated at the defects of the lower contact layer epitaxial material during the transmission process, which will affect the carrier lifetime and reduce the signal strength of the focal plane chip; at the same time, since the photo-generated carriers generated in the mesa absorption region of different positions of the focal plane chip have different transmission distances to the lower electrode, the signal strength received by the lower electrode from different regions of the focal plane chip will be different, which will affect the response uniformity of the focal plane chip and ultimately affect the comprehensive performance of the focal plane chip;

[0045] By making a bottom ring electrode 1 around each pixel of the focal plane array and connecting each ring electrode 1 to a common lower electrode through a metal thin film wire, the transport distance of photo-generated carriers in the epitaxial semiconductor material is greatly reduced, the carrier loss in the long-distance transport process is avoided, the photo-generated carrier lifetime is increased, the photocurrent signal strength of the focal plane array is improved, and the light response performance of the focal plane array is greatly improved.

[0046] After the coating is completed, a acetone solution is used as a stripping agent to strip the metal outside the electrode area to form the required electrode metal; finally, a flip-chip process is used to connect the focal plane array and 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 main body to detect SF6 gas, or can be used in combination with a corresponding module as a whole system solution to realize real-time monitoring imaging and leakage warning;

[0048] Reference Figure 1 As shown: equipped with a Stirling cooler 6, a Dewar, an infrared imaging lens 7, a visible light camera 11 and a lens, a signal processing and transmission module 8, a leakage warning module 9, a remote display and storage module 10, the whole assembly, the infrared focal plane detector assembly 5 detects SF6 gas, the Stirling cooler 6 provides refrigeration conditions, the infrared focal plane detector assembly 5 and the Stirling cooler 6 are connected after being packaged by the Dewar and are connected with 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 and storage module 10 receives and stores the transmitted data, the leakage warning module 9 performs leakage warning based on the data processing result, and the SF6 gas detector adopts the combination of infrared spectral imaging and visible light imaging, and is equipped with a visible light camera 11 and an infrared imaging lens 7, the generated image is not only an infrared picture, but also a combination of an infrared image and a real environment image, which is convenient for more real and clear monitoring and finding of the leakage source.

[0049] The wavelength range of the type II superlattice detector is 8-12.5 μm, the peak detection wavelength is 10.5 μm, the noise equivalent temperature difference (NETD) is 30 mK under a 150 μs integration time, and real-time monitoring and leakage warning of SF6 gas (1.5 μm) in an industrial large scene can be realized.

[0050] The embodiments of the application are described in detail above with reference to the drawings, but the application is not limited to the above-described embodiments, and those of ordinary skill in the art can make some equivalent changes and substitutions based on the content disclosed in the application without departing from the principles of the application, and these equivalent changes and substitutions should also be considered to belong to the protection scope of the application.

Claims

1. A long-wave class II superlattice SF6 gas detector, the detector comprising a focal plane array, the focal plane array comprising a plurality of independent photosensitive picture elements, the focal plane array and readout circuitry being connected to form an infrared focal plane detector assembly, the photosensitive picture elements corresponding one-to-one to amplifier units on the readout circuitry, the amplifier units integrating-amplifying the photocurrent of the photosensitive picture elements, and the integrated-amplified photocurrents being sequentially read out through row and column shift registers, characterized in that: The photosensitive pixel comprises a GaSb substrate, a GaSb buffer layer, an n InAsSb buffer layer, an n-type lower ohmic contact layer, an n-type InAs / GaSb intrinsic two-type superlattice light absorption layer, an AlGaAsSb barrier layer and an n-type upper ohmic contact layer which are 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 is etched to the top n-type contact layer to form a top electrode window; and ​ An Au nano array is prepared on the n-type upper ohmic contact layer as a plasmonic structure; A bottom ring electrode is prepared by deposition on the bottom electrode window, and a top electrode is prepared by deposition at the top electrode window; The bottom ring electrode of each photosensitive pixel is connected to a bottom common electrode through a metal thin film wire; The nano array period L of the Au nano array is 2 µm, the height is 40 nm, and the diameter is 1.5 µm; The Au nano array is arranged on the back of the detector.

2. A long-wave class 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 process.

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

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

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

6. A long-wave class II superlattice SF6 gas detector according to claim 5, characterized in that: The passivation layer and the plasmonic structure are etched for an upper electrode via hole using a wet process, the ring electrode pattern is transferred to the bottom n-type contact layer using a dry etching process, and the bottom ring electrode and the top electrode are prepared by electron beam evaporation deposition.

7. A long-wave class II superlattice SF6 gas detector according to claim 1, characterized in that: The detector further comprises a signal processing and transmission module, a leakage warning module and a remote display and storage module, the infrared focal plane detector assembly detects SF6 gas, the signal processing and transmission module receives and processes the detected data and transmits the data, the remote display and storage module receives and stores the transmitted data, and the leakage warning module performs leakage warning based on the data processing result.

8. A long-wave class II superlattice SF6 gas detector according to claim 1 or 7, characterized in that: The detector further comprises an infrared imaging lens and a visible light camera.

Images