High-temperature extreme environment-oriented high-thermal-stability thin film strain gauge and preparation method thereof

Abstract

This invention relates to a high thermal stability thin-film strain gauge for high-temperature extreme environments and its fabrication method. On the surface of the component under test, from bottom to top, are the component under test, a dielectric insulating layer, a strain-sensitive thin film, and a high-temperature electrode. The strain-sensitive thin film is a composite film of indium tin oxide (ITO: In₂O₃-10% SnO₂) and aluminum oxide (Al₂O₃) fabricated using MEMS technology. Al₂O₃ is introduced as a second phase and uniformly distributed within the ITO film through a heat treatment process. The introduction of Al₂O₃ not only forms an insulating grain boundary phase within the ITO, improving its oxidation resistance, but also... 3+ Replace In 3+ This invention reduces carrier mobility, thereby improving the thermal stability of the thin-film strain gauge. It is applicable to high-precision in-situ measurement of high-temperature strain in high-temperature components in aerospace, nuclear industry, and other applications, without affecting normal operation.

Description

Technical Field

[0001] This invention belongs to the field of thin-film sensor design and manufacturing technology, and relates to a thin-film strain gauge with high thermal stability for high-temperature extreme environments and its preparation method. Background Technology

[0002] As highly complex aerodynamic and thermodynamic rotating machines, aero engines are frequently subjected to high loads and thermal shocks, which can easily cause ablation, creep, or even fracture of core components, ultimately leading to severe flight disasters. Monitoring the strain of core components can effectively monitor their fatigue damage, thereby providing early warning of engine failures and ensuring flight safety. Thin-film strain gauges, with their advantages of small size, light weight, non-interference with the measured flow field, and non-invasive operation, have become an effective technical means to solve these problems.

[0003] Due to its high melting point and the absence of a phase transition from room temperature to sublimation temperature, ITO is widely used as a strain-sensitive film in thin-film strain gauges. However, at high temperatures, the crystallization, volatilization, and changes in charge carriers in ITO films can cause severe thermal drift in the strain gauge, significantly reducing the accuracy of the test results.

[0004] To improve the thermal stability of ITO thin films, the literature "Microstructure and thermoelectric properties of In2O3 / ITO thin film thermocouples with Al2O3 protecting layer" describes the preparation of an Al2O3 protective layer on the surface of the ITO thin film. This dense Al2O3 protective layer suppresses the volatilization of the ITO film, thereby enhancing the sensor's thermal stability. However, the Al2O3 protective layer preparation process is complex and time-consuming, and the thermal stress mismatch at high temperatures in multilayer heterostructures can easily lead to cracking or delamination, which can easily cause sensor failure. The patent "Application of Indium Tin Oxide with (400) Preferred Crystal Plane in Thin Film Strain Gauges" (CN109596041A) describes the preparation of an ITO sensitive thin film with a (400) preferred orientation to optimize the thermal stability of the ITO thin film. The patent shows that this device exhibits superior thermal stability from room temperature to 200°C compared to ITO films without a (400) preferred orientation. However, ITO recrystallizes at 300-350°C, making this type of device unsuitable for higher service temperatures. Summary of the Invention

[0005] Technical problems to be solved

[0006] To overcome the shortcomings of existing technologies, this invention proposes a high thermal stability thin-film strain gauge for high-temperature extreme environments and its fabrication method. Addressing the deficiencies in the technical background, and to improve the thermal stability of ITO thin-film strain gauges under high-temperature extreme conditions, this invention proposes a high thermal stability thin-film strain gauge for high-temperature extreme environments and its fabrication method, effectively improving the accuracy of ITO thin-film strain gauge detection under high-temperature extreme conditions.

[0007] Technical solution

[0008] A high thermal stability thin-film strain gauge for high-temperature extreme environments is characterized by a two-layer structure comprising a dielectric insulating layer 2, a strain-sensitive thin film 3, and a high-temperature electrode 4. The dielectric insulating layer 2 is deposited on the surface of the component under test 1, and the strain-sensitive thin film 3 and the high-temperature electrode 4 are deposited on the dielectric insulating layer 2 in the same layer. The strain-sensitive thin film 3 has an image-based structural design, and the two ends of the structure are connected to the high-temperature electrode 4. Both the strain-sensitive thin film and the high-temperature electrode are deposited on the dielectric insulating layer and connected by sidewalls to form an ohmic contact.

[0009] The strain-sensitive film is a composite film of ITO and Al2O3. Al2O3 is introduced as a second phase and uniformly distributed inside the ITO film to improve its thermal stability in high-temperature extreme environments and reduce the drift rate.

[0010] The mass ratio of Al to In in the strain-sensitive film is Al / In = 1-10 wt%.

[0011] The dielectric insulating layer is a composite dielectric insulating layer composed of Al2O3, SiO2, YSZ, or a combination thereof.

[0012] The high-temperature electrode is Ni, Ag, Au, or Pt.

[0013] The image structure of the strain-sensitive thin film 3 is a series connection of multiple positive and negative concave structures.

[0014] A method for preparing a high thermal stability thin-film strain gauge for high-temperature extreme environments, characterized by the following steps:

[0015] A dielectric insulating layer was prepared on the substrate of the component under test by magnetron sputtering, and then photoresist was spin-coated.

[0016] A patterned strain-sensitive gate mask is placed on a photoresist, subjected to UV exposure and development, and then an ITO-Al2O3 strain-sensitive thin film is prepared by magnetron sputtering.

[0017] The photoresist was removed by acetone, rinsed with deionized water, and dried to obtain a patterned strain-sensitive thin film. Photoresist was then spin-coated onto the surface, and a high-temperature electrode mask was placed on the photoresist for UV exposure and development.

[0018] High-temperature electrodes were prepared by magnetron sputtering.

[0019] The photoresist was removed by acetone, followed by rinsing with deionized water and drying to obtain a patterned high-temperature electrode.

[0020] Finally, heat treatment is performed to ensure that the Al2O3 insulating phase is uniformly distributed inside the ITO film based on the diffusion effect, resulting in a thin film strain gauge with high thermal stability.

[0021] When preparing ITO-Al2O3 strain-sensitive thin films using the magnetron sputtering method, sputtering is performed using a doped target with an Al / In ratio of 1-10 wt%; or co-sputtering is performed using both ITO and Al2O3 targets. The proportions of Al and In in the composite thin film are controlled by adjusting the sputtering power of the ITO and Al2O3 targets.

[0022] The final heat treatment temperature is 700-1400℃, the heat treatment atmosphere is air / vacuum / nitrogen / oxygen, and the heat treatment time is 1-10 hours.

[0023] The final heat treatment temperature is 750°C, the heat treatment atmosphere is nitrogen, and the heat treatment time is 3 hours.

[0024] Beneficial effects

[0025] This invention proposes a high thermal stability thin-film strain gauge for high-temperature extreme environments and its fabrication method. On the surface of the component under test, from bottom to top, are the component under test, a dielectric insulating layer, a strain-sensitive thin film, and a high-temperature electrode. The strain-sensitive thin film is a composite film of indium tin oxide (ITO: In2O3-10% SnO2) and aluminum oxide (Al2O3) fabricated using MEMS technology. Al2O3 is introduced as a second phase and uniformly distributed within the ITO film through a heat treatment process. The introduction of Al2O3 not only forms an insulating grain boundary phase within the ITO, improving its oxidation resistance, but also... 3+ Replace In 3+ This invention reduces carrier mobility, thereby improving the thermal stability of the thin-film strain gauge. It is applicable to high-precision in-situ measurement of high-temperature strain in high-temperature components in aerospace, nuclear industry, and other applications, without affecting normal operation.

[0026] Compared with the prior art, the present invention has the following beneficial effects:

[0027] This invention discloses a high thermal stability thin-film strain gauge designed for high-temperature extreme environments. Addressing the problem of poor thermal stability and accuracy of ITO thin-film strain gauges under high-temperature conditions, this invention significantly improves the thermal stability of the strain gauge under high-temperature conditions by fabricating an ITO-Al₂O₃ composite strain-sensitive thin film. The Al₂O₃ second phase is uniformly distributed within the ITO film, forming an insulating grain boundary phase that inhibits recrystallization of the film at high temperatures. Simultaneously, Al… 3+ Replace In 3+ This reduces carrier mobility, suppresses mobility variation with temperature, and thus stabilizes the film resistance variation with temperature. Compared with traditional unmodified ITO thin-film strain gauges, the high thermal stability thin-film strain gauge proposed in this invention reduces thermal drift by two orders of magnitude at 1000℃ (see examples), and can be used for high-accuracy measurement of high-temperature strain parameters.

[0028] Furthermore, the high thermal stability thin-film strain gauge proposed in this invention for high-temperature extreme environments does not require the additional fabrication of thermal protection layers such as Al2O3 / ZrO2. This not only avoids cracking or delamination caused by thermal stress mismatch in multilayer heterogeneous structures during large temperature gradient heating and cooling cycles, but also minimizes the impact of the thinner device thickness on the tested component and the flow field environment. This is of great significance for the online testing of aerodynamic rotating precision structures such as aero engines. Attached Figure Description

[0029] Figure 1 A schematic diagram of a thin-film strain gauge structure designed for high-temperature extreme environments (a: top view; b: cross-sectional view).

[0030] Figure 2 SEM and EDS images of the high thermal stability thin film strain gauge prepared in the example, Al / In = 2.8 wt%;

[0031] Figure 3 Resistance curves of ITO thin film strain gauges as a function of strain and time during piezoresistive testing at 1000℃;

[0032] Figure 4 The resistance of the high thermal stability thin-film strain gauge (Al / In = 2.8 wt%) prepared in the example is shown as a function of strain and time in a piezoresistive test at 1000 °C. Detailed Implementation

[0033] The present invention will now be further described in conjunction with the embodiments and accompanying drawings:

[0034] The following embodiments will help those skilled in the art to further understand the present invention, but do not limit the invention in any way. It should be noted that those skilled in the art can make various modifications and improvements without departing from the concept of the present invention. These all fall within the scope of protection of the present invention.

[0035] A high thermal stability thin-film strain gauge for high-temperature extreme environments comprises a three-layer structure, from bottom to top: the measured component 1, a dielectric insulating layer 2, a strain-sensitive thin film 3, and a high-temperature electrode 4, wherein:

[0036] The dielectric insulating layer is deposited on the surface of the component under test to achieve electrical isolation between the component under test and the strain-sensitive thin film; both the strain-sensitive thin film and the high-temperature electrode are deposited on the dielectric insulating layer and connected by sidewalls to form an ohmic contact.

[0037] Preferably, the component under test is a high-temperature alloy, and the application temperature is between 600-1400℃.

[0038] Preferably, the dielectric insulating layer is a composite dielectric insulating layer composed of Al2O3, SiO2, YSZ, or a combination thereof.

[0039] Preferably, the strain-sensitive film is a composite film of ITO and Al2O3, with Al2O3 introduced as a second phase and uniformly distributed inside the ITO film to improve its thermal stability in high-temperature extreme environments.

[0040] Furthermore, the weight ratio of aluminum to indium in the strain-sensitive film is Al / In = 1-10 wt%.

[0041] Preferably, the high-temperature electrode is Ni, Ag, Au, or Pt.

[0042] A method for fabricating a high thermal stability thin-film strain gauge for high-temperature extreme environments includes the following steps:

[0043] Step 1. Electrolytically degrease and clean the component under test.

[0044] Step 2. Prepare a dielectric insulating layer on the component under test using magnetron sputtering.

[0045] Step 3. Spin-coat photoresist onto the high-temperature alloy component after completing Step 2, perform UV exposure using a strain-sensitive gate mask, and then develop.

[0046] Step 4. Prepare an ITO-Al2O3 strain-sensitive thin film on the component under test obtained in Step 3 using magnetron sputtering. In Step 4, the ITO-Al2O3 strain-sensitive thin film is prepared using magnetron sputtering technology. It can be prepared by sputtering with a doped target (ITO and Al2O3 doped in different ratios, where Al / In = 1-10 wt%); or by co-sputtering with both an ITO target and an Al2O3 target. The proportions of Al and In in the composite film are controlled by adjusting the sputtering power of the ITO and Al2O3 targets.

[0047] Step 5. Use acetone to wash away the photoresist, rinse with deionized water, and dry to obtain a patterned strain-sensitive film.

[0048] Step 6. Spin-coat photoresist onto the surface of the component under test after completing step 5, and perform UV exposure and development using a high-temperature electrode mask.

[0049] Step 7. Prepare a high-temperature electrode on the component under test after completing Step 6 by magnetron sputtering.

[0050] Step 8. Use acetone to wash away the photoresist, rinse with deionized water, and dry to obtain a patterned high-temperature electrode.

[0051] Step 9. Perform heat treatment on the test component after completing step 8. Based on the diffusion effect, the Al2O3 insulating phase is uniformly distributed inside the ITO thin film, resulting in a thin film strain gauge with high thermal stability.

[0052] Preferably, the strain-sensitive thin film is a composite film of ITO and Al2O3, prepared by magnetron sputtering. It can be prepared by sputtering with doped targets (ITO and Al2O3 doped in different ratios, where Al / In = 1-10 wt%); or by co-sputtering with both ITO and Al2O3 targets. The proportions of Al and In in the composite film can be controlled by adjusting the sputtering power of the ITO and Al2O3 targets.

[0053] Preferably, the heat treatment temperature is 700-1400℃, with examples of 700, 750, 900, and 1400℃; preferably 750℃.

[0054] Preferably, the heat treatment atmosphere is air / vacuum / nitrogen / oxygen, with nitrogen being the most preferred.

[0055] Preferably, the heat treatment time is 1-10 hours, with examples of 1, 3, 6, and 10 hours; preferably 3 hours.

[0056] like Figure 1 The diagram shows a structural schematic of a thin-film strain gauge for high-temperature extreme environments proposed in this invention.

[0057] See Figure 1 A thin-film strain gauge for high-temperature extreme environments includes: a measured component 1, an alumina insulating layer 2, a strain-sensitive thin film 3, and a platinum electrode 4, wherein:

[0058] The component under test is a K465 nickel-based high-temperature alloy.

[0059] The alumina insulating layer is deposited on the surface of the component under test, with a thickness between 3 and 4 μm, as shown in examples 3, 3.5, 3.6, and 4.

[0060] The strain-sensitive thin film is deposited on the surface of the alumina insulating layer with a thickness of 4-5 μm, as shown in examples 4, 4.5, 4.6, and 5.

[0061] The strain-sensitive film is a composite film of ITO and Al2O3. The SEM and EDS images of the film are shown below. Figure 2 As shown, EDS test results indicate that the Al / In ratio in the composite film is 2.8 wt%.

[0062] The platinum electrode is deposited on the surface of the alumina insulating layer, forming an ohmic contact with the strain-sensitive thin film via its sidewalls, with a thickness of 4-5 μm; in the examples, 4, 4.5, 4.6, and 5. Further, the electrical signal is extracted via platinum wire and platinum paste.

[0063] A method for fabricating a thin-film strain gauge designed for high-temperature extreme environments includes the following steps:

[0064] Step 1. Clean the component under test 1 with anhydrous ethanol, acetone, and deionized water by ultrasonic and electrolytic degreasing.

[0065] Step 2. Place the component to be tested, 1, into the magnetron sputtering machine, using a 99.99% high-purity alumina target. The base vacuum is 5E-04 Pa, with argon and oxygen gas introduced (Ar: 100 sccm, O2: 12.5 sccm), operating pressure 1.0 Pa, and power density 5 W / cm³. 2 Sputtered alumina was deposited to a thickness of 3-4 μm.

[0066] Examples 3, 3.5, 3.6, and 4 are given in the embodiments.

[0067] Step 3: Spin-coat photoresist onto the surface of the component under test after completing Step 2, and perform UV exposure and development using a strain-sensitive grid mask.

[0068] Step 4: Place the component under test (as per Step 3) into the magnetron sputtering machine, using a doped target (In₂O₃:SnO₂:Al₂O₃ = 87.6:9.7:2.7wt%). Base vacuum: 5E-04 Pa; Ar gas flow: 100 sccm; operating pressure: 0.9 Pa; power density: 3.5 W / cm³. 2Sputtering deposition of strain-sensitive thin films of 4-5 μm.

[0069] Examples 4, 4.5, 4.6, and 5 are given in the embodiments.

[0070] Table 1. Drift rate of thin film strain gauges in piezoresistive tests at 1000℃ under different Al2O3 doping concentrations.

[0071]

[0072] Step 5: Use acetone to wash away the photoresist, rinse with deionized water, and dry.

[0073] Step 6: Spin-coat photoresist onto the surface of the component under test after completing Step 5, and perform UV exposure and development using a platinum electrode mask.

[0074] Step 7: Place the component under test (as per Step 6) into the magnetron sputtering machine, using a high-purity platinum target. Base vacuum: 5E-04 Pa. Ar gas is introduced (100 sccm), working pressure: 0.8 Pa, power density: 3 W / cm³. 2 , sputter-deposited platinum electrodes 4-5 μm; in the examples 4, 4.5, 4.6, 5.

[0075] Step 8: Remove the photoresist with acetone, rinse with deionized water, and dry.

[0076] Step 9: The component under test after step 8 is subjected to high-temperature heat treatment at 750°C in a nitrogen atmosphere for 3 hours to ensure that the Al2O3 insulating phase is uniformly distributed within the ITO thin film and to eliminate the internal stress generated during the preparation process. This yields the high thermal stability thin-film strain gauge designed for extreme high-temperature environments.

[0077] In this embodiment, those skilled in the art can adjust the thickness of the alumina insulating layer, the strain-sensitive film, and the platinum electrode according to the actual application conditions.

[0078] To verify the high-temperature thermal stability of the strain gauge of the present invention, the high-temperature piezoresistive response of the high thermal stability thin-film strain gauge prepared in the embodiments was tested, and an ITO thin-film strain gauge prepared with the same process parameters was set up for comparison. Figure 3 The figure shows the resistance of an unmodified ITO thin-film strain gauge as a function of strain and time at 1000℃. The resistance change of the strain gauge is negatively correlated with the applied strain, and the strain sensitivity factor is -4.29. With increasing test time, a significant baseline resistance drift is observed, with a drift rate of 0.21% / h. This large resistance drift will severely affect the accuracy of the test results. Figure 4The figure shows the resistance variation curve of the high thermal stability thin-film strain gauge prepared in this embodiment as a function of strain and time at 1000℃. The resistance change of the strain gauge is also negatively correlated with the applied strain, and the strain sensitivity factor is -3.43. No significant baseline resistance drift was observed with increasing test time; the drift rate was only 0.008% / h, which is lower than the drift rate reported in current literature. This indicates that the thin-film strain gauge proposed in this paper for high-temperature extreme environments has superior thermal stability.

[0079] Specific embodiments of the present invention have been described above. It should be understood that the present invention is not limited to the specific embodiments described above, and those skilled in the art can make various modifications or variations within the scope of the claims, which do not affect the essence of the present invention.

Claims

1. A high thermal stability thin-film strain gauge for high-temperature extreme environments, characterized in that... The structure comprises a two-layer structure consisting of a dielectric insulating layer (2), a strain-sensitive thin film (3), and a high-temperature electrode (4). The dielectric insulating layer (2) is deposited on the surface of the component under test (1). The strain-sensitive thin film (3) and the high-temperature electrode (4) are deposited on the dielectric insulating layer (2) in the same layer. The strain-sensitive thin film (3) is designed with an image structure, and the two ends of the structure are connected to the high-temperature electrode (4). The strain-sensitive thin film and the high-temperature electrode are both deposited on the dielectric insulating layer and connected by sidewalls to form an ohmic contact. The strain-sensitive thin film is a composite film of ITO and Al2O3. Al2O3 is introduced as a second phase and uniformly distributed inside the ITO film to improve its thermal stability in high-temperature extreme environments and reduce the drift rate.

2. The high thermal stability thin-film strain gauge for high-temperature extreme environments according to claim 1, characterized in that: The mass ratio of Al to In in the strain-sensitive thin film is Al / In = 1-10 wt%.

3. The high thermal stability thin-film strain gauge for high-temperature extreme environments according to claim 1, characterized in that: The dielectric insulating layer is a composite dielectric insulating layer composed of Al2O3, SiO2, YSZ, or a combination thereof.

4. The high thermal stability thin-film strain gauge for high-temperature extreme environments according to claim 1, characterized in that: The high-temperature electrode is Ni, Ag, Au, or Pt.

5. The high thermal stability thin-film strain gauge for high-temperature extreme environments according to claim 1, characterized in that: The image structure of the strain-sensitive thin film (3) is a series of multiple positive and negative concave structures.

6. A method for preparing a high thermal stability thin-film strain gauge for high-temperature extreme environments as described in any one of claims 1 to 5, characterized in that... The steps are as follows: A dielectric insulating layer was prepared on the substrate of the component under test by magnetron sputtering, and then photoresist was spin-coated. A patterned strain-sensitive gate mask is placed on a photoresist, subjected to UV exposure and development, and then an ITO-Al2O3 strain-sensitive thin film is prepared by magnetron sputtering. The photoresist was removed by acetone, rinsed with deionized water, and dried to obtain a patterned strain-sensitive thin film. Photoresist was then spin-coated onto the surface, and a high-temperature electrode mask was placed on the photoresist for UV exposure and development. High-temperature electrodes were prepared by magnetron sputtering. The photoresist was removed by acetone, followed by rinsing with deionized water and drying to obtain a patterned high-temperature electrode. Finally, heat treatment is performed to ensure that the Al2O3 insulating phase is uniformly distributed inside the ITO film based on the diffusion effect, resulting in a thin film strain gauge with high thermal stability.

7. The method according to claim 6, characterized in that: When preparing ITO-Al2O3 strain-sensitive thin films using the magnetron sputtering method, sputtering is performed using a doped target with an Al / In ratio of 1-10 wt%; or co-sputtering is performed using both ITO and Al2O3 targets. The proportions of Al and In in the composite thin film are controlled by adjusting the sputtering power of the ITO and Al2O3 targets.

8. The method according to claim 6, characterized in that: The final heat treatment temperature is 700-1400℃, the heat treatment atmosphere is air / vacuum / nitrogen / oxygen, and the heat treatment time is 1-10 hours.

9. The method according to claim 6 or 8, characterized in that: The final heat treatment temperature is 750°C, the heat treatment atmosphere is nitrogen, and the heat treatment time is 3 hours.

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