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

Abstract

The invention discloses a low-concentration hydrogen detection MIS type thin film sensor and a preparation method thereof, and belongs to the technical field of oil-immersed transformer online fault monitoring. The sensor sequentially comprises a metal nickel sheet substrate, a nickel oxide semiconductor layer, an insulating layer, a base layer and an electrode layer from bottom to top, the electrode layer comprises a catalytic electrode layer and a gold connection electrode layer; the insulating layer is any one of silicon oxide, aluminum oxide, silicon nitride and aluminum nitride; the bottom layer is any one of chromium, titanium, nickel-chromium and titanium-tungsten; and the catalytic electrode layer is one or a compound of platinum and palladium. The low-concentration hydrogen detection MIS type thin film sensor has the advantages that the low-concentration hydrogen detection MIS type thin film sensor is provided by fully considering the problems that the transformer insulating oil environment temperature change is large and the hydrogen concentration is low according to the requirement for on-line monitoring of the hydrogen concentration in the transformer insulating oil, the sensitivity is high, the detection lower limit is low, the sensor machining and packaging difficulty is lowered, and the cost is reduced. Good application prospects are realized.

Description

Technical Field

[0001] The invention belongs to the technical field of online fault monitoring of oil-immersed transformers, and in particular relates to a hydrogen sensor for online monitoring of hydrogen concentration of an oil-immersed transformer and a preparation method thereof. Background Art

[0002] Substations are the hub of the power system, and their importance is self-evident. As a key equipment in the substation, the stability of the transformer is closely related to the safety of the power system. Therefore, it is necessary to monitor and diagnose the working status of the transformer to prevent problems before they happen. The transformer is mainly composed of coils, magnetic cores, insulating oil, etc. The main functions of the insulating oil are cooling, insulation and arc extinguishing to ensure the safe operation of the transformer. Partial discharge, spark discharge, arc, overheating and other faults inside the transformer will cause the transformer insulating oil to decompose and produce H2, CH4, C2H4, C2H2 and other gases. After convection and diffusion, these gases continue to dissolve in the oil, causing a sudden change in gas concentration, which is usually in 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 to monitor the status of transformer insulating oil. Online monitoring of the hydrogen concentration in the transformer insulating oil can detect latent faults in the equipment as early as possible and monitor the development of the fault, which is of great significance to ensure the safety of the power supply system and promote the construction of intelligent power systems.

[0003] Remote online monitoring of the status of transformer insulating oil is an important development direction in the field of transformer diagnosis. However, the existing technologies for detecting hydrogen concentration in transformer insulating oil are mainly gas chromatography, calorimetry, etc., which require sampling, pretreatment, equipment configuration, measurement, and analysis, and cannot achieve online monitoring. Therefore, it is urgent to develop an intelligent remote online monitoring system to achieve real-time monitoring of hydrogen concentration in insulating oil. The existing hydrogen detection sensors have a high detection limit and weak resistance to water vapor and oxygen interference. Therefore, it is urgent to develop hydrogen detection sensor technology with a low detection limit, high sensitivity, and strong resistance to water vapor and oxygen interference to meet the needs of remote online monitoring of transformer insulating oil, which undoubtedly has a very important engineering application value.

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

[0005] The Chinese patent application document with publication number CN117607213A discloses a hydrogen sensor and a method for preparing the same, wherein the hydrogen sensor includes, from bottom to top, a semiconductor substrate, a patterned insulating layer, and a hydrogen-sensitive metal layer, wherein the hollowed-out portion of the patterned insulating layer exposes the semiconductor substrate. The hydrogen sensor forms a patterned insulating layer between the semiconductor substrate and the hydrogen-sensitive metal layer, thereby exposing part of the semiconductor substrate so that it forms a Schottky contact with the hydrogen-sensitive metal layer, and then adjusts the barrier height between the metal and the semiconductor so that the barrier height is between that of a Schottky diode hydrogen sensor without an insulating layer and a semiconductor hydrogen sensor fully covered by an insulating layer. Therefore, the hydrogen sensor has a higher sensitivity than a Schottky diode hydrogen sensor without an insulating layer, and has a higher current resolution than a semiconductor hydrogen sensor fully covered by an insulating layer. However, the detection sensitivity of the hydrogen sensor is still relatively low, so it needs to be further improved. Summary of the invention

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

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

[0008] The present invention discloses a MIS thin film sensor for detecting low-concentration hydrogen. 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 alloy, and titanium-tungsten alloy; the catalytic electrode layer is one of platinum and palladium, or a composite thereof.

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

[0010] Preferably, the insulating layer, base layer, catalytic electrode layer and gold connecting electrode layer are prepared by deposition method. More preferably, the insulating layer is prepared by reactive radio frequency magnetron sputtering method; the base layer, catalytic electrode layer and gold connecting electrode layer are prepared by direct current magnetron sputtering method.

[0011] Preferably, 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 primer layer is 50-300 nm; the thickness of the catalytic electrode layer is ≥1 μm, and the thickness of the gold connecting electrode layer is ≥2 μm.

[0012] Preferably, when preparing the insulating layer, the target material used is a silicon target or an aluminum target, the purity of the target material is ≥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 ratio of argon to oxygen is 6:1.

[0014] Preferably, when preparing the base layer and the 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 the gold connecting electrode layer is prepared, the target material used is a gold target with a purity of ≥99.5%, and the process gas is argon (high-purity argon Ar ≥99.999%).

[0016] The 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: cleaning the metal nickel sheet, drying it, and then performing a thermal oxidation treatment to form a nickel oxide semiconductor layer on the upper and lower surfaces of the metal nickel sheet;

[0018] S2: cleaning the metal nickel sheet treated in step S1, drying it, and then depositing an insulating layer on the nickel oxide semiconductor layer on the upper surface of the metal nickel sheet;

[0019] S3: Then a layer of photoresist is spin-coated on the insulating layer, a rectangular groove is photoetched on the photoresist, after dry cleaning, a primer layer is deposited, and then a catalytic electrode layer is deposited on the primer layer;

[0020] S4: After ultrasonically stripping off the photoresist in step S3, spin-coating a layer of photoresist, photoetching another rectangular groove next to the catalytic electrode layer, dry cleaning, depositing a primer layer, and then depositing a gold connection electrode layer on the primer layer;

[0021] S5: ultrasonically stripping off the photoresist in step S4 to obtain the product.

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

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

[0024] The beneficial effects of the present invention are:

[0025] 1. Aiming at the demand of online monitoring of hydrogen concentration in transformer insulating oil, the present invention fully considers the problem of large temperature variation and low hydrogen concentration of transformer insulating oil environment, and provides a low-concentration hydrogen detection MIS type thin film sensor, which comprises, from bottom to top, a metal nickel sheet substrate, a nickel oxide semiconductor layer, an insulating layer, a base layer, and an electrode layer. It has the excellent performance of high sensitivity (80mV / ppm) and low detection limit (less than 1ppm), and has good application prospects.

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

[0027] 3. The present invention prepares MIS type thin film sensors based on metal substrates, which reduces the difficulty of sensor processing and packaging, and provides new ideas for sensor substrate design and sensor substrate selection.

[0028] 4. The MIS thin film sensor for detecting low-concentration hydrogen in transformer insulating oil can be prepared in large quantities by using thin film technology. BRIEF DESCRIPTION OF THE DRAWINGS

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

[0030] Figure 2 for Figure 1 Front view of

[0031] Figure 3 This is a schematic diagram of the preparation process of a low-concentration hydrogen detection MIS thin film sensor according to Example 1 of the present invention;

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

[0033] Figure 5 This is a graph showing the response results of the low-concentration hydrogen detection MIS thin film sensor of Example 1 of the present invention to 0-50ppm concentration hydrogen at 75°C and 1MHz;

[0034] In the figure, 1-metal nickel sheet substrate, 2-nickel oxide semiconductor layer, 3-insulating layer, 4-base layer, 5-catalytic electrode layer, 6-gold connecting electrode layer, 7-photoresist. DETAILED DESCRIPTION

[0035] In order to make the purpose, technical solution and advantages of the embodiments of the present invention clearer, the technical solution in the embodiments of the present invention will be clearly and completely described in combination with the embodiments of the present invention. Obviously, the described embodiments are part of the embodiments of the present invention, not all of the embodiments. Based on the embodiments of the present invention, all other embodiments obtained by ordinary technicians in this field without creative work are within the scope of protection of the present invention.

[0036] The terms “upper”, “lower”, “left”, “right”, “front” and “back” mentioned in the embodiments are only for illustration and should not be regarded as limitations of the solution itself.

[0037] Unless otherwise specified, the test materials and reagents used in the following examples can be obtained from commercial sources.

[0038] If no specific techniques or conditions are specified in the examples, they can be carried out according to the techniques or conditions described in the literature in the art or according to the product instructions.

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

[0040] Embodiment 1:

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

[0042] The preparation method of the sensor comprises the following steps: (the preparation process diagram is shown in Figure 2 (shown)

[0043] (1) Pretreatment of the nickel sheet: wash the nickel sheet with acetone, alcohol, and deionized water in turn, wash for 10 min in each solvent, and dry the washed nickel sheet in an oven at 60°C;

[0044] (2) Preparation of nickel oxide semiconductor layer: Place the dried nickel sheet into a clean ceramic crucible, and place the ceramic crucible into a tube furnace. The thermal oxidation temperature is 850°C, the heating and cooling rate is 5°C / min, and the holding time is 3 hours. After cooling, take out the surface oxidized nickel sheet (i.e., obtain the nickel oxide semiconductor layer), wash and dry it; the thickness of the prepared nickel oxide semiconductor layer is 2 μm;

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

[0046] (4) Spin-coating photoresist: Spin-coat a layer of photoresist on the insulating layer film by using a uniform coating process, then photoetch a rectangular groove on the photoresist (the depth of the groove is equal to the thickness of the photoresist), and use dry cleaning to clean the surface oxidized metal nickel sheet prepared with the photoresist film, with a cleaning power of 100 W and a cleaning time of 10 min;

[0047] (5) Deposition of base layer and catalytic electrode layer: On the surface of the photoresist, a chromium base layer is firstly sputtered by DC magnetron sputtering using chromium as a target (chromium purity 99.5%), and then a palladium catalytic electrode layer is sputtered on the chromium base layer using palladium as a target (palladium purity 99.5%) by DC magnetron sputtering; wherein the back vacuum degree is 5×10 -3 Pa, working pressure is 0.4Pa, sputtering power is 100W, sputtering gas is argon, substrate temperature is 120℃, substrate bias is 100V, and the thickness of the prepared chromium base layer is 100nm and the palladium catalytic electrode layer film is 1.5μm;

[0048] (6) Stripping of photoresist, spin coating of photoresist, photolithography: Use acetone as stripping solution, perform ultrasonic stripping, and the ultrasonic power is 120W. After stripping of the photoresist, spin coat a layer of photoresist, and then photolithograph another rectangular groove next to the catalytic electrode layer (the depth of the groove is equal to the thickness of the photoresist), and dry clean;

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

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

[0051] When in use, the sensor is soldered to the circuit board, specifically:

[0052] A blue film is attached to one side of the sensor electrode, and the side of the metal nickel sheet without the electrode is mechanically polished to clean the surface oxide. After polishing, the metal nickel sheet is placed in a cutting machine, and a resin blade is used. 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 1 is repeated to clean the substrate;

[0053] Nickel-containing solder is used to weld the polished side of the metal nickel sheet to the pad at the reserved position of the printed circuit board, and the welding temperature is 260°C. A gold wire bonding process is used to connect the connecting electrode to another reserved pad, and 99.99% 25μm gold wire is used as the bonding lead material for gold wire bonding. The bonding ultrasonic power is selected as 16W, the bonding pressure is selected as 14g, and the bonding time is selected as 100ms.

[0054] The working principle of the sensor in this embodiment is as follows Figure 3 As shown in the figure, the sensor is based on the working principle of Schottky diode. It consists of a metal (palladium Pd) layer, an insulating layer (silicon dioxide SiO2), and a semiconductor layer (nickel oxide). If a bias voltage is applied to the MIS diode, a current will be generated in the Schottky diode. When hydrogen comes into contact with the sensor, the hydrogen molecules diffuse in the Pd metal layer and are catalytically decomposed into hydrogen atoms, which are adsorbed at the interface between the metal layer and the oxide insulating layer. The adsorbed hydrogen atoms are polarized at the interface between the metal and the oxide insulating layer to form a bipolar layer. This bipolar layer changes the work function of the metal layer and the energy level of the metal-insulating layer interface, thereby affecting the height and width of the Schottky barrier. Under the action of hydrogen, the IV curve of the sensor will be biased relative to when no hydrogen is passed, and as the hydrogen concentration increases, the amplitude of the IV curve bias increases monotonically (the bias amplitude is expressed as ΔV). The hydrogen concentration is detected by recording the bias voltage of the IV curve of the MIS sensor.

[0055] The performance test of the sensor of this embodiment was carried out, specifically, the response test of 0-50ppm hydrogen concentration was carried out at 75℃ and 1MHz. The test results are as follows: Figure 5 As shown, it can be seen that its detection limit is lower than 1ppm and its sensitivity is higher than 80mV / ppm.

[0056] Embodiment 2:

[0057] The difference between this embodiment and embodiment 1 is that the insulating layer is an aluminum oxide insulating layer, the base layer is a titanium base layer, the catalytic electrode layer is a platinum catalytic electrode layer, and the rest is the same as embodiment 1.

[0058] Embodiment 3:

[0059] The difference between this embodiment and the first embodiment is that the insulating layer is a silicon nitride insulating layer, the base layer is a nickel-chromium alloy base layer, and the rest is the same as the first embodiment.

[0060] Embodiment 4:

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

[0062] Embodiment 5:

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

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

[0065] The above embodiments are only used to illustrate the technical solutions of the present invention, rather than to limit the same. Although the present invention has been described in detail with reference to the aforementioned embodiments, those skilled in the art should understand that the technical solutions described in the aforementioned embodiments may still be modified, or some of the technical features may be replaced by equivalents. However, these modifications or replacements do not deviate the essence of the corresponding technical solutions 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 metal nickel sheet substrate, a nickel oxide semiconductor layer, an insulating layer, a base 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 base layer is any one of chromium, titanium, nickel-chromium alloy, and titanium-tungsten alloy; the catalytic electrode layer is one of platinum, palladium, or a composite thereof.

2. The low concentration hydrogen detection MIS type thin film sensor according to claim 1, characterized in that: The nickel oxide semiconductor layer is obtained by oxidizing the surface of a metal nickel sheet into a nickel oxide semiconductor layer through a thermal oxidation process.

3. The low concentration hydrogen detection MIS type thin film sensor according to claim 1, characterized in that: The insulating layer, base layer, catalytic electrode layer and gold connecting electrode layer are prepared by deposition method. More preferably, the insulating layer is prepared by reactive radio frequency magnetron sputtering method; the base layer, catalytic electrode layer and gold connecting electrode layer are prepared by direct current magnetron sputtering method.

4. The low concentration hydrogen detection MIS type thin film sensor according to claim 1, characterized in that: 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 primer layer is 50-300 nm; the thickness of the catalytic electrode layer is ≥1 μm, and the thickness of the gold connecting electrode layer is ≥2 μm.

5. The low concentration hydrogen detection MIS type thin film sensor according to claim 1, characterized in that: When preparing the insulating layer, the target material used is a silicon target or an aluminum target, the purity of the target material is ≥99.5%, and the process gas is argon and oxygen.

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

1.

7. The low concentration hydrogen detection MIS type thin film sensor according to claim 1, characterized in that: When preparing the base layer and the catalytic electrode layer, the target material used has a purity of ≥99.5%, and the process gas is argon; when preparing the gold connecting 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 to 7, characterized in that: The following steps are involved: S1: cleaning the metal nickel sheet, drying it, and then performing a thermal oxidation treatment to form a nickel oxide semiconductor layer on the upper and lower surfaces of the metal nickel sheet; S2: cleaning the metal nickel sheet treated in step S1, drying it, and then depositing an insulating layer on the nickel oxide semiconductor layer on the upper surface of the metal nickel sheet; S3: then spin-coating a layer of photoresist on the insulating layer, photoetching a rectangular groove on the photoresist, dry-cleaning, depositing a primer layer, and then depositing a catalytic electrode layer on the primer layer; S4: After ultrasonically stripping off the photoresist in step S3, spin-coating a layer of photoresist, photoetching another rectangular groove next to the catalytic electrode layer, dry cleaning, depositing a primer layer, and then depositing a gold connection electrode layer on the primer layer; S5: After ultrasonically stripping off the photoresist in step S4, the result is obtained.

9. The preparation method according to claim 8, characterized in that: The temperature of the thermal oxidation treatment in step S1 is 800-900° C. and the time is 2-5 hours.

10. The preparation method according to claim 8, characterized in that: In step S3 and step S4, the photoresist is replaced by a metal mask.

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