Low-concentration hydrogen detection MIS type thin film sensor and preparation method thereof

Abstract

The application discloses a low-concentration hydrogen detection MIS type thin film sensor and a preparation method thereof, and belongs to the technical field of on-line fault monitoring of oil-immersed transformers. The sensor comprises, from bottom to top, a metal nickel sheet substrate, a nickel oxide semiconductor layer, an insulating layer, a primer layer and an electrode layer; the electrode layer comprises a catalytic electrode layer and a gold connecting electrode layer; the insulating layer is any one of silicon oxide, aluminum oxide, silicon nitride and aluminum nitride; the primer layer is any one of chromium, titanium, nickel-chromium and titanium-tungsten; and the catalytic electrode layer is one of platinum and palladium or a composite thereof. The application provides the low-concentration hydrogen detection MIS type thin film sensor, which has high sensitivity and a low detection lower limit, reduces the processing and packaging difficulty of the sensor, and has a good application prospect, in view of the demand for on-line monitoring of hydrogen concentration in transformer insulating oil and fully considering the problems of large environmental temperature change and low hydrogen concentration of the transformer insulating oil.

Description

Technical Field

[0001] This invention belongs to the field of online fault monitoring technology for oil-immersed transformers, and specifically relates to a hydrogen sensor for online monitoring of hydrogen concentration in oil-immersed transformers and its preparation method. Background Technology

[0002] Substations are the hubs of the power system, and their importance is self-evident. Transformers, as key equipment in substations, are directly related to the safety of the power system. Therefore, it is necessary to monitor and diagnose the operating status of transformers to prevent problems before they occur. Transformers mainly consist of coils, magnetic cores, and insulating oil. The main functions of insulating oil are cooling, insulation, and arc suppression, ensuring the safe operation of the transformer. Internal faults such as partial discharge, spark discharge, arcing, and overheating can cause the transformer insulating oil to decompose, producing gases such as H2, CH4, C2H4, and C2H2. These gases dissolve in the oil through convection and diffusion, causing sudden changes in gas concentration, typically at the ppm level. Among the gases produced by the decomposition of transformer insulating oil, the concentration of hydrogen is often used as an important indicator for monitoring the condition of the transformer insulating oil. Online monitoring of the hydrogen concentration in transformer insulating oil is crucial for early detection of latent faults within the equipment and for monitoring their development. This is of great significance for ensuring the safety of the power supply system and promoting the construction of intelligent power systems.

[0003] Remote online monitoring of transformer insulating oil is an important development direction in the field of transformer diagnostics. However, existing technologies for detecting hydrogen concentration in transformer insulating oil mainly rely on gas chromatography and calorimetry, which require sampling, pretreatment, equipment configuration, measurement, and analysis. These methods cannot achieve online monitoring. Therefore, there is an urgent need to develop intelligent remote online monitoring systems to achieve real-time monitoring of hydrogen concentration in insulating oil. Existing hydrogen detection sensors have high detection limits and weak resistance to water vapor and oxygen interference. Therefore, there is an urgent need to develop hydrogen detection sensor technology with low detection limits, high sensitivity, and strong resistance to water vapor and oxygen interference to meet the needs of remote online monitoring of transformer insulating oil. This undoubtedly has significant engineering application value.

[0004] MIS (Metal-Insulator-Semiconductor) hydrogen sensors have advantages such as miniaturization, low power consumption, low operating temperature, high sensitivity, and excellent selectivity, making it possible to remotely monitor the hydrogen concentration in transformer insulating oil online. However, the complex manufacturing and packaging processes of existing MIS hydrogen sensors limit their large-scale application.

[0005] Chinese patent application CN117607213A discloses a hydrogen sensor and its fabrication method. The hydrogen sensor comprises, from bottom to top, a semiconductor substrate, a patterned insulating layer, and a hydrogen-sensitive metal layer. A cutout portion of the patterned insulating layer exposes the semiconductor substrate. This hydrogen sensor exposes a portion of the semiconductor substrate by forming a patterned insulating layer between the semiconductor substrate and the hydrogen-sensitive metal layer, allowing them to form a Schottky contact. This adjusts the potential barrier height between the metal and the semiconductor, making it intermediate between that of a Schottky diode hydrogen sensor without an insulating layer and a semiconductor hydrogen sensor with a fully insulating layer. Therefore, it exhibits higher sensitivity compared to a Schottky diode hydrogen sensor without an insulating layer and higher current resolution compared to a semiconductor hydrogen sensor with a fully insulating layer. However, the detection sensitivity of this hydrogen sensor is still relatively low and requires further improvement. Summary of the Invention

[0006] The technical problem to be solved by this invention is how to solve the problems of complex manufacturing process and low detection sensitivity of existing MIS-type hydrogen sensors.

[0007] The present invention solves the above-mentioned technical problems through the following technical means:

[0008] This invention discloses a low-concentration hydrogen detection MIS-type thin-film sensor, which comprises, from bottom to top: a nickel substrate, a nickel oxide semiconductor layer, an insulating layer, a substrate layer, and an electrode layer; the electrode layer includes a catalytic electrode layer and a gold-connected electrode layer; the insulating layer is any one of silicon oxide, aluminum oxide, silicon nitride, and aluminum nitride; the substrate layer is any one of chromium, titanium, nickel-chromium alloy, and titanium-tungsten alloy; and the catalytic electrode layer is one of platinum and palladium, or a combination thereof.

[0009] Preferably, the nickel oxide semiconductor layer is obtained by oxidizing the surface of a nickel sheet into a nickel oxide semiconductor layer through a thermal oxidation process.

[0010] Preferably, the insulating layer, the underlayer, the catalytic electrode layer, and the gold connection electrode layer are prepared by deposition. More preferably, the insulating layer is prepared by reactive radio frequency magnetron sputtering; the underlayer, the catalytic electrode layer, and the gold connection electrode layer are prepared by DC magnetron sputtering.

[0011] Preferably, the thickness of the nickel oxide semiconductor layer is ≥2μm, the thickness of the insulating layer is 50-150nm, the thickness of the underlayer is 50-300nm, the thickness of the catalytic electrode layer is ≥1μm, and the thickness of the gold connection electrode layer is ≥2μm.

[0012] Preferably, when preparing the insulating layer, the target material used is a silicon target or an aluminum target, both with a purity of ≥99.5%, and the process gas is argon and oxygen (high-purity argon Ar ≥99.999%, high-purity oxygen O2 ≥99.999%).

[0013] Preferably, the flow rate ratio of argon to oxygen is 6:1.

[0014] Preferably, when preparing the substrate and catalytic electrode layer, the target material used has a purity of ≥99.5%, and the process gas is argon (high-purity argon Ar ≥99.999%).

[0015] Preferably, when preparing the gold-connected electrode layer, the target material used is a gold target with a purity ≥99.5%, and the process gas is argon (high-purity argon Ar ≥99.999%).

[0016] A second aspect of the present invention provides a method for preparing the above-mentioned low-concentration hydrogen detection MIS-type thin-film sensor, comprising the following steps:

[0017] S1: After cleaning and drying the nickel sheet, perform thermal oxidation treatment to generate a nickel oxide semiconductor layer on the upper and lower surfaces of the nickel sheet;

[0018] S2: After cleaning and drying the nickel sheet processed in step S1, an insulating layer is deposited on the nickel oxide semiconductor layer on the upper surface of the nickel sheet.

[0019] S3: Then spin-coat a layer of photoresist on the insulating layer, photolithographically print a rectangular groove on the photoresist, dry clean, deposit a base layer, and then deposit a catalytic electrode layer on the base layer.

[0020] S4: After ultrasonically stripping away the photoresist in step S3, spin-coat another layer of photoresist, and photolithographically create another rectangular groove next to the catalytic electrode layer. After dry cleaning, deposit a base layer, and then deposit a gold interconnect electrode layer on the base layer.

[0021] S5: After ultrasonically peeling off the photoresist from step S4, the product is obtained.

[0022] Preferably, the temperature of the thermal oxidation treatment in step S1 is 800-900℃ and the time is 2-5h; more preferably, it is 850℃ for 3h.

[0023] Preferably, in steps S3 and S4, a metal mask is used instead of photoresist.

[0024] The beneficial effects of this invention are as follows:

[0025] 1. This invention addresses the need for online monitoring of hydrogen concentration in transformer insulating oil, taking into full account the large temperature variations and low hydrogen concentration in transformer insulating oil. It provides a low-concentration hydrogen detection MIS-type thin-film sensor, which, from bottom to top, comprises: a nickel metal substrate, a nickel oxide semiconductor layer, an insulating layer, a substrate layer, and an electrode layer. It exhibits excellent performance with high sensitivity (80mV / ppm) and a low detection limit (below 1ppm), and has good application prospects.

[0026] 2. This invention also proposes a method for preparing a low-concentration hydrogen detection MIS-type thin-film sensor for transformer insulating oil, which can meet the current demand for low-concentration hydrogen detection in transformer insulating oil. It is small in size, easy to prepare and package on a large scale, and is further applicable to low-concentration hydrogen environments such as outer space and pipeline hydrogen leaks.

[0027] 3. This invention uses a metal substrate to fabricate a MIS-type thin-film sensor, which reduces the difficulty of sensor processing and packaging, and provides new ideas for sensor substrate design and selection.

[0028] 4. This type of low-concentration hydrogen detection MIS thin-film sensor for transformer insulating oil can be mass-produced using thin-film technology. Attached Figure Description

[0029] Figure 1 This is a three-dimensional schematic diagram of the low-concentration hydrogen detection MIS-type thin-film sensor of Embodiment 1 of the present invention;

[0030] Figure 2 for Figure 1 Front view;

[0031] Figure 3 This is a schematic diagram of the fabrication process of the low-concentration hydrogen detection MIS-type thin-film sensor of Embodiment 1 of the present invention;

[0032] Figure 4 This is a schematic diagram illustrating the working principle of the low-concentration hydrogen detection MIS-type thin-film sensor of Embodiment 1 of the present invention;

[0033] Figure 5 The graph shows the response of the low-concentration hydrogen detection MIS-type thin-film sensor of Embodiment 1 of the present invention to hydrogen gas with a concentration of 0-50ppm at 75°C and 1MHz.

[0034] In the figure, 1-Nitrogen substrate, 2-Nitrogen oxide semiconductor layer, 3-Insulating layer, 4-Underlay layer, 5-Catalytic electrode layer, 6-Gold connection electrode layer, 7-Photoresist. Detailed Implementation

[0035] To make the objectives, technical solutions, and advantages of the embodiments of the present invention clearer, the technical solutions of the embodiments of the present invention will be clearly and completely described below in conjunction with the embodiments of the present invention. Obviously, the described embodiments are only some embodiments of the present invention, not all embodiments. Based on the embodiments of the present invention, all other embodiments obtained by those skilled in the art without creative effort are within the scope of protection of the present invention.

[0036] The terms "up," "down," "left," "right," "front," and "back" mentioned in the embodiments are merely illustrative and should not be considered as limitations on the solution itself.

[0037] Unless otherwise specified, all test materials and reagents used in the following examples are commercially available.

[0038] Unless otherwise specified in the embodiments, the techniques or conditions described in the literature in this field or in accordance with the product manual may be followed.

[0039] The photoresist used is Suzhou Ruihong RZJ-304 25cp.

[0040] Example 1:

[0041] A low-concentration hydrogen detection MIS-type thin-film sensor, comprising, from bottom to top: a nickel substrate, a nickel oxide semiconductor layer, an insulating layer, a substrate layer, and an electrode layer; the electrode layer includes a catalytic electrode layer and a gold-connected electrode layer, which are arranged side by side. (Structural schematic diagram shown) Figure 1 (As shown); the insulating layer is a silicon dioxide insulating layer, the underlayer is a chromium underlayer, and the catalytic electrode layer is a palladium catalytic electrode layer.

[0042] The method for fabricating this sensor includes the following steps: (a schematic diagram of the fabrication process is shown below) Figure 2 (As shown)

[0043] (1) Pretreatment of nickel sheet: The nickel sheet was cleaned in sequence with acetone, alcohol and deionized water for 10 minutes in each solvent. The cleaned nickel sheet was then dried in an oven at 60°C.

[0044] (2) Preparation of nickel oxide semiconductor layer: The dried nickel sheet was placed in a clean ceramic crucible, which was then placed in a tube furnace. The thermal oxidation temperature was 850℃, the heating and cooling rates were both 5℃ / min, and the holding time was 3h. After cooling, the surface-oxidized nickel sheet was removed (i.e., the nickel oxide semiconductor layer was obtained), cleaned, and dried; the thickness of the prepared nickel oxide semiconductor layer was 2μm.

[0045] (3) Deposition of insulating layer: A silicon dioxide insulating layer film is sputtered on the upper surface of the surface-oxidized nickel sheet using silicon as the target (silicon purity 99.5%) by reactive radio frequency magnetron sputtering; wherein the back-side vacuum is 5×10 -3 Pa, working gas pressure is 0.4 Pa, sputtering power is 100 W, sputtering gas is argon and oxygen (argon purity 99.999%, oxygen purity 99.999%), their flow ratio is 6:1, substrate temperature is 80℃, substrate bias voltage is 100 V, and the thickness of the insulating thin film is 50 nm.

[0046] (4) Spin-coating photoresist: A layer of photoresist is spin-coated on the insulating film using a spin coating process. Then, a rectangular groove is photolithographically formed on the photoresist (the depth of the groove is equal to the thickness of the photoresist). The oxidized nickel sheet with the photoresist film is cleaned by dry cleaning with a cleaning power of 100W and a cleaning time of 10min.

[0047] (5) Deposition of the underlayer and catalytic electrode layer: On the photoresist surface, a chromium underlayer is first sputtered using DC magnetron sputtering with chromium as the target (chromium purity 99.5%). Then, on the chromium underlayer, a palladium catalytic electrode layer film is sputtered using DC magnetron sputtering with palladium as the target (palladium purity 99.5%). The background vacuum is 5×10⁻⁶. -3 Pa, working gas pressure is 0.4 Pa, sputtering power is 100 W, sputtering gas is argon, substrate temperature is 120 °C, substrate bias voltage is 100 V, and a 100 nm chromium base layer and a 1.5 μm thick palladium catalytic electrode layer film are prepared.

[0048] (6) Photoresist stripping, spin coating, and photolithography: Acetone is used as the stripping solution for ultrasonic stripping with an ultrasonic power of 120W. After the photoresist is stripped, another layer of photoresist is spin coated. Another rectangular groove is then photolithographically formed next to the catalytic electrode layer (the depth of the groove is equal to the thickness of the photoresist). Dry cleaning is then performed.

[0049] (7) Deposition of the underlayer and gold bonding electrode layer: Repeat step (5) to deposit a chromium underlayer, and then, on the chromium underlayer, use gold as the target material (gold purity 99.5%) to sputter a thin film of gold bonding electrode layer by DC magnetron sputtering; wherein, the back vacuum degree is 5×10 -3 Pa, working pressure is 0.4 Pa, sputtering power is 100 W, sputtering gas is argon, substrate temperature is 120 °C, substrate bias voltage is 100 V, and a 100 nm chromium base layer and a 2 μm thick gold interconnect electrode film are prepared.

[0050] (8) Using acetone as the stripping fluid, ultrasonic stripping was performed with an ultrasonic power of 120W. After stripping, the membrane was cleaned and dried to obtain a low-concentration hydrogen detection MIS-type thin film sensor.

[0051] In use, the sensor is soldered onto the circuit board, specifically as follows:

[0052] A blue film is attached to one side of the sensor electrode. The side of the nickel sheet without electrode is mechanically polished to remove the oxide from its surface. After polishing, the nickel sheet is placed in a cutting machine with a resin blade. The cutting spacing is set according to the required size, and the cutting speed is 0.09 mm / min. After cutting, the blue film is peeled off, and step one is repeated to clean the substrate.

[0053] Nickel-containing solder was used to solder the polished side of the nickel sheet to the pad at the reserved position on the printed circuit board at a soldering temperature of 260℃. The connecting electrode was connected to another reserved pad using a gold wire bonding process, with 99.99% pure 25μm gold wire as the bonding lead material. The bonding ultrasonic power was 16W, the bonding pressure was 14g, and the bonding time was 100ms.

[0054] The working principle of the sensor in this embodiment is as follows: Figure 3 As shown, the sensor operates based on the Schottky diode principle. It consists of a metal (palladium Pd) layer, an insulating layer (silicon dioxide, SiO2), and a semiconductor layer (nickel oxide). Applying a bias voltage to the MIS diode induces a current in the Schottky diode. When hydrogen gas comes into contact with the sensor, hydrogen molecules diffuse within the Pd metal layer and are catalytically decomposed into hydrogen atoms. These hydrogen atoms are adsorbed at the interface between the metal layer and the oxide insulating layer. The adsorbed hydrogen atoms become polarized at the metal-oxide insulating layer interface, forming a bipolar layer. This bipolar layer alters the work function of the metal layer and the energy level of the metal-insulator interface, thus affecting the height and width of the Schottky barrier. The sensor's IV curve is biased under hydrogen gas conditions relative to when no hydrogen gas is present, and the bias amplitude monotonically increases with increasing hydrogen concentration (the bias amplitude is represented by ΔV). By recording the bias voltage of the MIS sensor's IV curve, hydrogen concentration can be detected.

[0055] The sensor in this embodiment was subjected to performance testing, specifically a response test at 75°C and 1MHz to hydrogen gas with a concentration of 0-50ppm. The test results are as follows: Figure 5 As shown, its detection limit is below 1 ppm and its sensitivity is above 80 mV / ppm.

[0056] Example 2:

[0057] The difference between this embodiment and Embodiment 1 is that the insulating layer is an alumina insulating layer, the underlayer is a titanium underlayer, and the catalytic electrode layer is a platinum catalytic electrode layer; the rest is the same as in Embodiment 1.

[0058] Example 3:

[0059] The difference between this embodiment and Embodiment 1 is that the insulating layer is a silicon nitride insulating layer, and the underlayer is a nickel-chromium alloy underlayer; the rest is the same as in Embodiment 1.

[0060] Example 4:

[0061] The difference between this embodiment and Embodiment 1 is that: in step (2), the thermal oxidation temperature is 800℃ and the time is 5h; the thickness of the nickel oxide semiconductor layer is 5μm, the thickness of the insulating layer is 100nm, and the chromium underlayer is 50nm. The rest is the same as in Embodiment 1.

[0062] Example 5:

[0063] The difference between this embodiment and Embodiment 1 is that: in step (2), the thermal oxidation temperature is 900℃ and the time is 2h; the thickness of the insulating layer is 150nm, the chromium underlayer is 300nm, the thickness of the palladium catalytic electrode layer is 3μm, and the thickness of the gold connection electrode layer is 5μm. The rest is the same as in Embodiment 1.

[0064] The performance of the sensors obtained in Examples 2-5 is similar to that in Example 1.

[0065] The above embodiments are only used to illustrate the technical solutions of the present invention, and are not intended to limit it. Although the present invention has been described in detail with reference to the foregoing embodiments, those skilled in the art should understand that modifications can still be made to the technical solutions described in the foregoing embodiments, or equivalent substitutions can be made to some of the technical features. Such modifications or substitutions do not cause the essence of the corresponding technical solutions to deviate from the spirit and scope of the technical solutions of the embodiments of the present invention.

Claims

1. A low-concentration hydrogen detection MIS-type thin-film sensor, characterized in that, The sensor comprises, from bottom to top: a nickel substrate, a nickel oxide semiconductor layer, an insulating layer, a substrate layer, and an electrode layer; the electrode layer includes a catalytic electrode layer and a gold-connected electrode layer; the insulating layer is any one of silicon oxide, aluminum oxide, silicon nitride, and aluminum nitride; the substrate layer is any one of chromium, titanium, nickel-chromium alloy, and titanium-tungsten alloy; the catalytic electrode layer is any one of platinum and palladium or a composite thereof; the nickel oxide semiconductor layer is obtained by oxidizing the surface of the nickel substrate to nickel oxide semiconductor layer through a thermal oxidation process; the thickness of the nickel oxide semiconductor layer is ≥2 μm; the thickness of the insulating layer is 50~150 nm; the thickness of the substrate layer is 50~300 nm; and the thickness of the catalytic electrode layer is ≥1 μm.

2. The low-concentration hydrogen detection MIS-type thin-film sensor according to claim 1, characterized in that, The insulating layer, the underlayer, the catalytic electrode layer, and the gold-connected electrode layer are prepared by deposition.

3. The low-concentration hydrogen detection MIS-type thin-film sensor according to claim 2, characterized in that, The insulating layer was prepared by reactive radio frequency magnetron sputtering; the underlayer, catalytic electrode layer, and gold bonding electrode layer were prepared by DC magnetron sputtering.

4. The low-concentration hydrogen detection MIS-type thin-film sensor according to claim 1, characterized in that, The nickel oxide semiconductor layer has a thickness of 2 μm, the insulating layer has a thickness of 50 nm, the underlayer has a thickness of 100 nm, the catalytic electrode layer has a thickness of 1.5 μm, and the gold interconnect electrode layer has a thickness of 2 μm.

5. The low-concentration hydrogen detection MIS-type thin-film sensor according to claim 1, characterized in that, The insulating layer is prepared using a silicon target or an aluminum target with a purity of ≥99.5%, and the process gases are argon and oxygen.

6. The low-concentration hydrogen detection MIS-type thin-film sensor according to claim 5, characterized in that, The flow rate ratio of argon to oxygen is 6:

1.

7. The low-concentration hydrogen detection MIS-type thin-film sensor according to claim 1, characterized in that, When preparing the underlayer and catalytic electrode layers, the target material used has a purity of ≥99.5%, and the process gas is argon; when preparing the gold-connected electrode layer, the target material used is a gold target with a purity of ≥99.5%, and the process gas is argon.

8. The method for preparing a low-concentration hydrogen detection MIS-type thin-film sensor according to any one of claims 1-7, characterized in that, Includes the following steps: S1: After cleaning and drying the nickel sheet, perform a thermal oxidation treatment to generate a nickel oxide semiconductor layer on the upper and lower surfaces of the nickel sheet. S2: After cleaning and drying the nickel sheet processed in step S1, an insulating layer is deposited on the nickel oxide semiconductor layer on the upper surface of the nickel sheet. S3: Then spin-coat a layer of photoresist on the insulating layer, photolithographically print a rectangular groove on the photoresist, dry clean, deposit a base layer, and then deposit a catalytic electrode layer on the base layer. S4: After ultrasonically stripping away the photoresist in step S3, spin-coat another layer of photoresist, and photolithographically create another rectangular groove next to the catalytic electrode layer. After dry cleaning, deposit a base layer, and then deposit a gold interconnect electrode layer on the base layer. S5: After ultrasonically peeling off the photoresist from step S4, the product is obtained.

9. The preparation method according to claim 8, characterized in that, In step S1, the temperature of the thermal oxidation treatment is 800~900℃ and the time is 2~5h.

10. The preparation method according to claim 8, characterized in that, In steps S3 and S4, a metal mask is used instead of photoresist.

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