A method for preparing a high-temperature-resistant, low-power-consumption flexible thin-film resistance strain gauge

Abstract

The present invention relates to the technical field of flexible thin film resistance strain gauge preparation, and discloses a method for preparing a high-temperature resistant, low-power consumption flexible thin film resistance strain gauge, comprising: (1) using a glass fiber mesh reinforced polyimide film as a substrate, coating a photoresist on the substrate surface for photolithography, and patterning a strain gauge pattern; (2) depositing a NiCr alloy film as a sensitive grid layer on the strain gauge pattern of the substrate; (3) providing an anti-oxidation film layer on the sensitive grid; and (4) removing excess photoresist from the surface, annealing, and obtaining a flexible thin film resistance strain gauge. The obtained thin film strain gauge can operate normally in a high temperature environment of 200 to 400°C, has good reliability, and has an internal resistance value of up to 3000Ω, which greatly reduces power consumption. The resistance temperature coefficient of the resistance strain gauge is low. At the same time, the use of photolithography and magnetron sputtering processes improves the processing accuracy and processing quality of the strain gauge, making it suitable for mass production.

Description

Technical Field

[0001] The present invention relates to the technical field of preparing flexible thin film resistance strain gauges, and in particular to a method for preparing a high-temperature-resistant, low-power-consumption flexible thin film resistance strain gauge. Background Art

[0002] A flexible thin-film resistance strain gauge is a thin-film strain gauge made by depositing strain-sensitive materials onto the surface of a flexible substrate. Compared to rigid substrates such as quartz and sapphire used in traditional thin-film strain gauges, flexible substrates offer improved flexibility, lightness, stretchability, compressibility, and bendability. They also provide a degree of comfort that allows them to conform to the human body or clothing, offering unlimited potential for the development of wearable devices and electronic skin. They are an indispensable component of flexible integrated electronic systems. Currently developed flexible substrates include polydimethylsiloxane, thermoplastic polyurethane elastomers, hydrogels, polyesters, carbonized biomaterials, fabrics, and 3D sponge materials. With the use of new strain-sensitive materials such as metal nanomaterials, conductive polymers, graphene, and carbon nanotubes, the flexibility, mechanical strength, and sensing performance of flexible thin-film resistance strain gauges have been further improved.

[0003] However, most of the current flexible thin film resistance strain gauges cannot be used at high temperatures. This is because the flexible material substrate is mostly organic, which is easy to melt and decompose at 200-300°C. At the same time, the strain-sensitive film layer of the metal material is also easily oxidized, leading to failure. Therefore, high-temperature resistant flexible thin film resistance strain gauges are still a challenge, which limits the application of flexible thin film resistance strain gauges in some fields, such as high-temperature weighing in the metallurgical industry. At present, there are no domestic manufacturers that can produce high-precision, long-life, and high-temperature resistant (such as 200°C) flexible thin resistance strain gauges. In addition, the high power consumption caused by the high resistance of flexible thin film resistance strain gauges also limits the use of flexible strain sensors.

[0004] Flexible electronics technology is rapidly developing, hailed as one of the top ten emerging technologies of the 21st century and poised to revolutionize electronics. Against this backdrop, new flexible substrate materials and sensing materials are emerging. By optimizing high-temperature-resistant flexible substrate materials and employing high-temperature-resistant strain-sensitive materials, new high-precision, low-power, and high-temperature-resistant flexible thin-film resistance strain gauges have been developed. These are of great significance not only for the intelligent weighing industry but also for wearable devices for human motion detection and human-computer interaction. Summary of the Invention

[0005] In view of the problems that existing flexible thin film resistance strain gauges have poor high temperature resistance and unstable performance at high temperatures, the purpose of the present invention is to provide a method for preparing a flexible thin film resistance strain gauge. The prepared flexible thin film resistance strain gauge has the characteristics of high temperature resistance and low power consumption.

[0006] A method for preparing a flexible thin film resistance strain gauge comprises the following steps:

[0007] (1) Using a glass fiber mesh reinforced polyimide film as a substrate, photoresist is coated on the substrate surface for photolithography to pattern the strain gauge pattern;

[0008] (2) depositing a NiCr alloy film as a sensitive gate layer on the strain gauge pattern of the substrate;

[0009] (3) providing an anti-oxidation film layer on the sensitive gate;

[0010] (4) Remove excess photoresist from the surface and perform annealing to obtain a flexible thin film resistance strain gauge.

[0011] The preparation method of the present invention uses a polyimide film reinforced with glass fiber mesh as the substrate and a NiCr alloy as the sensitive material. Polyimide material itself can withstand high temperatures above 400°C and can operate at 200-300°C, making it an ideal substrate material for flexible sensors. However, although the operating temperature of 200-400°C does not cause macroscopic damage to the polyimide material, it will affect the microstructure and adhesion strength of the polyimide film, thereby affecting the transmission of strain. Therefore, using a polyimide film reinforced with glass fiber mesh and using the glass fiber mesh as the skeleton can enhance the heat resistance of the polyimide, suppress thermal deformation, and have higher high-temperature resistance, giving the strain gauge better operating performance at 200-400°C. NiCr alloy has the advantages of high resistivity, low power consumption, and high sensitivity coefficient. Combining the polyimide film reinforced with glass fiber mesh with the NiCr alloy sensitive material makes the prepared flexible thin film resistor have the characteristics of high temperature resistance and low power consumption.

[0012] As a preferred method of the present invention, the NiCr alloy film is prepared by the following magnetron sputtering method: NiCr alloy is used as the target material, the background vacuum is 3×10 -3 Pa~5.0×10 -3 Pa, the working gas is argon, the sputtering power is 50-100 W, the sputtering pressure is 0.4-0.8 Pa, the bias voltage is 100-300 V, the argon flow rate is 15-20 sccm, and the sputtering time is 30-40 min.

[0013] The sputtering power and sputtering pressure will affect the structure of the alloy film, thereby changing the resistivity of the alloy film. Under the above preferred parameters, the resistance of the strain gauge can reach more than 3000Ω, reducing the power consumption of the strain gauge.

[0014] As a preferred method of the present invention, the Ni content in the NiCr alloy is ≥85%, and preferably Ni90Cr10 alloy is selected.

[0015] As a preferred embodiment of the method of the present invention, the method further comprises pre-depositing a NiCrTi alloy film before preparing the sensitive grid, wherein the thickness of the NiCrTi alloy film is 0.1 to 0.2 times that of the NiCr alloy film.

[0016] Ti cannot form a solid solution with either Ni or Cr. The introduction of Ti can inhibit the formation of NiCr solid solution and promote the growth of small grains. At the same time, the Ti alloy has good plasticity, which helps to transmit strain. Moreover, the NiCrTi alloy film has a similar composition to the NiCr alloy film, has low internal stress and high adhesion. Therefore, the provision of the NiCrTi alloy film helps to improve the resistance temperature coefficient, resistivity, and strain sensitivity coefficient of the alloy strain gauge. However, the thickness of the NiCrTi alloy film should not be too large, otherwise it will amplify the difference between it and the NiCr alloy film, bringing adverse effects.

[0017] As a preferred embodiment of the method of the present invention, the NiCrTi alloy film is obtained by magnetron sputtering of a NiCrTi alloy, wherein the NiCrTi alloy has a Ti content of 5-10%, a Ni content of ≥75%, and the balance being Cr. Preferably, Ni82Cr10Ti8 alloy is selected.

[0018] As a preferred embodiment of the method of the present invention, the working atmosphere used in magnetron sputtering of the NiCrTi alloy thin film is a mixture of nitrogen and argon, with a partial pressure ratio of nitrogen to argon of 1:8-10. Nitrogen plays two roles: first, it inhibits grain growth in the alloy thin film, promotes the formation of nanocrystals, and improves the temperature coefficient of resistance and resistivity of the alloy strain gauge; second, it forms a TiN component with Ti, enhancing the thermal shock resistance and strength of the alloy thin film, and improving high-temperature performance. However, the nitrogen content should not be too high.

[0019] As a preferred embodiment of the method of the present invention, a pre-annealing is also performed after depositing the NiCrTi alloy film. The annealing conditions are: 200-300°C in a vacuum annealing furnace for 60-90 minutes, with argon and hydrogen introduced as a protective atmosphere, and the partial pressure ratio of hydrogen to argon is 1:15-20. Pre-annealing allows Ti to absorb hydrogen, reducing the thermal deformation resistance of Ti and refining the composition of the titanium alloy. However, the partial pressure of hydrogen cannot be too high, otherwise it will cause Cr to absorb a large amount of hydrogen at the same time. At the same time, pre-annealing cannot be performed after depositing the NiCr film, as the NiCr film hinders Ti from absorbing hydrogen, and the NiCr film itself absorbs hydrogen.

[0020] As a preferred embodiment of the method of the present invention, the anti-oxidation film layer is a Pt metal layer or an Al2O3 film layer.

[0021] As a preferred embodiment of the method of the present invention, the annealing in step (4) is carried out in a vacuum furnace at a temperature of 200-400° C. for 2-3 hours. Vacuum annealing can eliminate internal defects in the alloy and reduce the temperature coefficient of resistance.

[0022] As a preferred embodiment of the method of the present invention, the photolithography process in step (1) is as follows: positive photoresist is spin-coated on the front side of the substrate, the substrate is placed on a coating machine with a rotation speed of 1500-2000 r / min and coated for 15-20 seconds, then heated and dried, and then the light intensity is 100-120 mW / cm 2 Expose for 15 to 20 seconds, dry after exposure, and develop.

[0023] The beneficial effects of the present invention are as follows:

[0024] The preparation method of the present invention has the following advantages:

[0025] (1) The glass fiber mesh reinforced polyimide film is used as a flexible substrate, which is flexible and can be used in wearable devices for human motion detection, human-computer interaction, etc.

[0026] (2) Thin film strain gauges can work normally in high temperature environments of 200 to 400°C and have good reliability;

[0027] (3) Using NiCr alloy as the sensitive material and controlling the preparation process of NiCr alloy thin film, the internal resistance value of the obtained thin film strain gauge can be as high as 3000Ω, which greatly reduces the power consumption;

[0028] (4) The use of photolithography and magnetron sputtering technology improves the processing accuracy and quality of strain gauges, making them suitable for mass production;

[0029] (5) The resistance temperature coefficient of the resistance strain gauge is low. BRIEF DESCRIPTION OF THE DRAWINGS

[0030] Figure 1 It is a preparation flow chart of the method of the present invention.

[0031] Figure 2 is a graph of strain gauges for a full-bridge Wheatstone design.

[0032] Figure 3 GF calculation curve of the flexible thin film strain resistor gauge of Example 1 at 200°C.

[0033] In the figure, 1, substrate, 2, photoresist layer, 3, NiCr alloy film, 4, Pt metal layer. DETAILED DESCRIPTION

[0034] The specific embodiments of the present invention are further described below.

[0035] Unless otherwise specified, the raw materials used in the present invention can be purchased from the market or are commonly used in the art. Unless otherwise specified, the methods in the following embodiments are all conventional methods in the art.

[0036] The method for preparing a flexible thin film resistance strain gauge provided by the present invention comprises the following steps:

[0037] (1) A polyimide film reinforced with glass fiber mesh is used as a substrate, and a photoresist is coated on the surface of the substrate for photolithography to pattern the strain gauge pattern.

[0038] Glass fiber mesh reinforced polyimide film is prepared by the following process: impregnating the glass fiber mesh in a polyimide adhesive to obtain an impregnated film, which is then heat-pressed and cured. This is a conventional process. The following examples and comparative examples refer to the preparation method of Chen Yihua et al. (Performance of High-Strength Glass Cloth Reinforced Polyimide Composite Materials [J], Solid Rocket Technology, 2010, 34(5): 648-651).

[0039] In some embodiments provided by the present invention, the substrate should be cleaned before use, including cleaning the substrate surface with acetone and anhydrous ethanol in sequence to remove organic matter and other contaminants thereon, and then drying in an oven.

[0040] In some embodiments provided by the present invention, a photoresist is applied for photolithography, and the patterning process of the strain gauge pattern is as follows: a positive photoresist, preferably KMPC5315 positive photoresist, is spin-coated on the front of a glass fiber mesh reinforced polyimide film substrate, and the substrate is placed on a desktop spin coater with a rotation speed of 1500 to 2000 r / min, and the spin coat is performed for 15 to 20 seconds, followed by heating and drying. The drying process is performed in a drying oven, such as an electric constant temperature blast drying oven, at a drying temperature of 80 to 100° C. for 0.5 to 1 hour, and then cooled after drying;

[0041] Exposure was performed in a UV curing box of an ATE-1028 parallel light lithography machine with a light intensity of 100 to 120 mW / cm 2 The exposure time is 15 to 20 seconds, followed by post-baking. The drying process is carried out in a drying oven, such as an electric constant temperature blast drying oven, with a drying temperature of 80 to 100°C and a time of 0.5 to 1 hour. After cooling, it is developed with KMP PD2384-Ⅱ developer for 45 to 60 seconds to obtain a glass fiber mesh reinforced polyimide film substrate of the corresponding photolithography process.

[0042] In some embodiments provided by the present invention, the strain gauge pattern is a full-bridge Wheatstone bridge design that is temperature self-compensating.

[0043] (2) A NiCr alloy film is deposited on the strain gauge pattern of the substrate as a sensitive gate layer with a thickness of 300 to 600 nm.

[0044] In some embodiments provided by the present invention, the NiCr alloy film is prepared by the following magnetron sputtering method: NiCr alloy is used as the target material, the background vacuum is 3×10 -3 Pa~5.0×10 -3 Pa, the working gas is argon, the sputtering power is 50-100 W, the sputtering pressure is 0.4-0.8 Pa, the bias voltage is 100-300 V, the argon flow rate is 15-20 sccm, and the sputtering time is 30-40 min.

[0045] In some embodiments provided by the present invention, the Ni content in the NiCr alloy is ≥85%, preferably Ni90Cr10.

[0046] In some embodiments provided by the present invention, a NiCrTi alloy film is pre-deposited before preparing the sensitive gate, and the thickness of the NiCrTi alloy film is 0.1 to 0.2 times that of the NiCr alloy film.

[0047] In some embodiments provided by the present invention, the NiCrTi alloy film is obtained by magnetron sputtering of a NiCrTi alloy, wherein the Ti content of the NiCrTi alloy is 5-10%, the Ni content is ≥75%, and the balance is Cr; preferably, Ni82Cr10Ti8.

[0048] In some embodiments provided by the present invention, the working atmosphere used for magnetron sputtering of the NiCrTi alloy thin film is a mixture of nitrogen and argon, and the partial pressure ratio of nitrogen to argon is 1:8-10.

[0049] In some embodiments provided by the present invention, pre-annealing can also be performed after depositing the NiCrTi alloy film. The annealing conditions are: 200-300°C in a vacuum annealing furnace for 60-90 minutes, with argon and hydrogen introduced as a protective atmosphere, and the partial pressure ratio of hydrogen to argon is 1:15-20.

[0050] (3) An anti-oxidation film layer is provided on the sensitive gate with a deposition thickness of 100 to 200 nm.

[0051] In some embodiments provided by the present invention, the anti-oxidation film layer is a Pt metal layer or an Al2O3 film layer, which can be prepared by a magnetron sputtering method.

[0052] (4) Remove excess photoresist from the surface and perform annealing to obtain a flexible thin film resistance strain gauge.

[0053] In some embodiments provided by the present invention, annealing is performed in a vacuum furnace, the annealing temperature is 200-400° C., and the heat treatment time is 2-3 hours.

[0054] In some embodiments provided by the present invention, argon is used as a protective atmosphere during annealing.

[0055] Example 1

[0056] A method for preparing a flexible thin film resistance strain gauge, such as Figure 1 As shown, the following steps are included:

[0057] (1) Based on the size of the strain gauge sensitive grid, a 20 mm × 20 mm × 0.03 mm glass fiber mesh reinforced polyimide film was selected as substrate 1. The substrate surface was cleaned with acetone and anhydrous ethanol in sequence, and then dried in an oven at 100°C.

[0058] (2) Perform photolithography on the pre-treated substrate:

[0059] First, a KMPC5315 positive photoresist was spin-coated on the front surface of a glass fiber mesh reinforced polyimide film substrate to form a photoresist layer 2. The substrate was then placed on a tabletop spin coater at a rotation speed of 1500 rpm for 20 seconds, and then dried in an electric constant temperature blast drying oven at 100°C for 1 hour and then cooled.

[0060] Secondly, according to Figure 2 The full-bridge Wheatstone bridge pattern shown in the figure is exposed. Specifically, the substrate is placed in the UV curing box of the ATE-1028 parallel light lithography machine with a light intensity of 100w / cm 2 , the exposure time is 20s, followed by post-baking at 100℃ in an electric constant temperature blast drying oven for 0.5h, and after cooling, developing with KMP PD2384-Ⅱ developer to remove the photoresist and pattern the strain gauge pattern. The development time is 45s to obtain a photolithographic glass fiber mesh reinforced polyimide film substrate;

[0061] (3) On a JGP-560 dual-chamber sputtering machine, a NiCr alloy film 3 was deposited as a sensitive gate layer on a glass fiber mesh reinforced polyimide film substrate that had been photolithographically processed. Specifically, the substrate was placed in a vacuum chamber of 5.0×10 -3 In a Pa magnetron sputtering machine, Ni90Cr10 alloy was used as the target material, and argon gas with a purity of 99.999% (volume percentage) was introduced as the working medium to deposit NiCr alloy thin films. The deposition power was 100 W, the sputtering pressure was 0.6 Pa, the bias voltage was 200 V, the Ar flow rate was 15 sccm, and the deposition time was 30 min to obtain NiCr alloy thin films.

[0062] (4) Turn off the Ni90Cr10 alloy target and sputter deposit Pt as the target for 5 min to obtain a Pt metal layer 4;

[0063] (5) All photoresists on the surface of the glass fiber mesh reinforced polyimide film substrate were removed using KMP PD2384-Ⅱ developer, and then cleaned with anhydrous ethanol and acetone in sequence, and then dried in an oven to obtain a preliminary strain gauge;

[0064] (6) The preliminary strain gauge is placed in a vacuum heat treatment furnace for heat treatment, with argon as the protective atmosphere, the heat treatment temperature is 300°C, the heat treatment time is 2.5h, and after cooling in the furnace, a high temperature resistant, low power consumption flexible thin film resistance strain gauge is obtained.

[0065] Example 2

[0066] A method for preparing a flexible thin film resistance strain gauge, such as Figure 1 As shown, the following steps are included:

[0067] (1) According to the size of the strain gauge sensitive grid, a 20 mm × 20 mm × 0.03 mm glass fiber mesh reinforced polyimide film was selected as the substrate. The substrate surface was cleaned with acetone and anhydrous ethanol in sequence, and then dried in an oven at 100°C.

[0068] (2) Perform photolithography on the pre-treated substrate:

[0069] First, KMPC5315 positive photoresist was spin-coated on the front side of a glass fiber mesh reinforced polyimide film substrate. The substrate was then placed on a tabletop spin coater at a speed of 2000 rpm for 15 seconds, then dried in an electric constant temperature blast drying oven at 100°C for 0.5 hours and then cooled.

[0070] Secondly, according to Figure 2 The full-bridge Wheatstone bridge pattern shown in the figure is exposed. Specifically, the substrate is placed in the UV curing box of the ATE-1028 parallel light lithography machine with a light intensity of 120mw / cm 2 The exposure time is 15 seconds, followed by post-baking at 100°C in an electric constant temperature blast drying oven for 1 hour. After cooling, it is developed with KMP PD2384-Ⅱ developer to remove the photoresist and pattern the strain gauge pattern. The development time is 50 seconds to obtain a photolithographic glass fiber mesh reinforced polyimide film substrate.

[0071] (3) In a JGP-560 dual-chamber sputtering machine, a NiCr alloy film was deposited as a sensitive gate layer on a glass fiber mesh reinforced polyimide film substrate that had been photolithographically processed. Specifically, the substrate was placed in a vacuum chamber of 3.0×10 -3In a Pa magnetron sputtering machine, Ni90Cr10 alloy was used as the target material, and argon gas with a purity of 99.999% (volume percentage) was introduced as the working medium to deposit NiCr alloy thin films. The deposition power was 50 W, the sputtering pressure was 0.8 Pa, the bias voltage was 100 V, the Ar flow rate was 20 sccm, and the deposition time was 40 min to obtain NiCr alloy thin films.

[0072] (4) Turning off the Ni90Cr10 alloy target, sputtering and depositing Pt as the target for 10 min to obtain a Pt metal layer;

[0073] (5) All photoresists on the surface of the glass fiber mesh reinforced polyimide film substrate were removed using KMP PD2384-Ⅱ developer, and then cleaned with anhydrous ethanol and acetone in sequence, and then dried in an oven to obtain a preliminary strain gauge;

[0074] (6) The obtained preliminary strain gauge is placed in a vacuum heat post-treatment furnace for heat treatment, with argon as the protective atmosphere, the heat post-treatment temperature is 200°C, the heat treatment time is 3 hours, and after cooling in the furnace, a high-temperature resistant, low-power consumption flexible thin film resistance strain gauge is obtained.

[0075] Example 3

[0076] A method for preparing a flexible thin film resistance strain gauge, such as Figure 1 As shown, the following steps are included:

[0077] (1) According to the size of the strain gauge sensitive grid, a 20 mm × 20 mm × 0.03 mm glass fiber mesh reinforced polyimide film was selected as the substrate. The substrate surface was cleaned with acetone and anhydrous ethanol in sequence, and then dried in an oven at 100°C.

[0078] (2) Perform photolithography on the pre-treated substrate:

[0079] First, KMPC5315 positive photoresist was spin-coated on the front side of a glass fiber mesh-reinforced polyimide film substrate. The substrate was then placed on a tabletop spin coater at a speed of 1800 rpm for 18 seconds, then dried in an electric constant temperature blast drying oven at 100°C for 0.6 hours and then cooled.

[0080] Secondly, according to Figure 2 The full-bridge Wheatstone bridge pattern shown in the figure is exposed. Specifically, the substrate is placed in the UV curing box of the ATE-1028 parallel light lithography machine with a light intensity of 110mw / cm 2, exposure time 17s, followed by post-baking in an electric constant temperature forced air drying oven at 100℃ for 1h, and after cooling, developing with KMP PD2384-Ⅱ developer to remove the photoresist and pattern the strain gauge pattern. The development time is 60s to obtain a photolithographic glass fiber mesh reinforced polyimide film substrate;

[0081] (3) In a JGP-560 dual-chamber sputtering machine, a NiCr alloy film was deposited as a sensitive gate layer on a glass fiber mesh reinforced polyimide film substrate that had been photolithographically processed. Specifically, the substrate was placed in a vacuum chamber of 5.0×10 -3 In a Pa magnetron sputtering machine, Ni90Cr10 alloy was used as the target material, and argon gas with a purity of 99.999% (volume percentage) was introduced as the working medium to deposit NiCr alloy thin films. The deposition power was 80 W, the sputtering pressure was 0.4 Pa, the bias voltage was 300 V, the Ar flow rate was 18 sccm, and the deposition time was 35 min to obtain NiCr alloy thin films.

[0082] (4) Turn off the Ni90Cr10 alloy target and sputter deposit Pt as the target for 8 min to obtain a Pt metal layer;

[0083] (5) All photoresists on the surface of the glass fiber mesh reinforced polyimide film substrate were removed using KMP PD2384-Ⅱ developer, and then cleaned with anhydrous ethanol and acetone in sequence, and then dried in an oven to obtain a preliminary strain gauge;

[0084] (6) The obtained preliminary strain gauge is placed in a vacuum heat post-treatment furnace for heat treatment, with argon as the protective atmosphere, the heat post-treatment temperature is 400°C, the heat treatment time is 2h, and after cooling in the furnace, a high-temperature resistant, low-power consumption flexible thin film resistance strain gauge is obtained.

[0085] Example 4

[0086] A method for preparing a flexible thin film resistance strain gauge, which is different from Example 1 in that:

[0087] Before depositing the NiCr alloy film as the sensitive gate layer, a NiCrTi alloy film was first deposited by magnetron sputtering using Ni82Cr10Ti8 as the target. The magnetron sputtering conditions were the same as those for depositing the NiCr alloy film, but the sputtering time was shortened so that the thickness of the NiCrTi alloy film was 0.2 times that of the NiCr alloy film.

[0088] Example 5

[0089] A method for preparing a flexible thin film resistance strain gauge, which is different from Example 1 in that:

[0090] Before depositing the NiCr alloy film as the sensitive gate layer, a NiCrTi alloy film was first deposited by magnetron sputtering using Ni82Cr10Ti8 as the target. The magnetron sputtering conditions were the same as those for depositing the NiCr alloy film, but the sputtering time was shortened, making the thickness of the NiCrTi alloy film 0.4 times that of the NiCr alloy film.

[0091] Example 6

[0092] A method for preparing a flexible thin film resistance strain gauge, which differs from Example 4 in that the working atmosphere for magnetron sputtering of the NiCrTi alloy film is a mixture of nitrogen and argon, wherein the partial pressure ratio of nitrogen to argon is 1:8.

[0093] Example 7

[0094] A method for preparing a flexible thin film resistance strain gauge, which differs from Example 4 in that pre-annealing is performed after depositing the NiCrTi alloy film. The annealing conditions are: 200°C in a vacuum annealing furnace for 90 minutes, with argon and hydrogen introduced as a protective atmosphere, and the partial pressure ratio of hydrogen to argon is 1:15.

[0095] Comparative Example 1

[0096] The difference from Example 1 is that a polyimide film is used as the substrate, and the thickness of the polyimide film is the same as that of the glass fiber mesh reinforced polyimide film in Example 1.

[0097] Comparative Example 2

[0098] The difference from Example 4 is that the thickness of the NiCrTi alloy film is the same as that of the NiCr alloy film.

[0099] Comparative Example 3

[0100] The difference from Example 4 is that the NiCr film is magnetron sputtered in advance and the alloy target material used is Ni89Cr11.

[0101] The performance tests of the flexible thin film strain gauges prepared in the above embodiments and comparative examples were conducted, mainly focusing on the strain sensitivity coefficient GF, resistance temperature coefficient, and resistance value, as shown below:

[0102] (1) Strain sensitivity coefficient: GF = (R-R0) / εR0;

[0103] Taking 25℃ as the reference temperature, R0 is the resistance at 25℃, and R is the resistance after microstrain ε is applied to the thin film resistance strain gauge at a certain temperature. The curve of resistance change and applied microstrain is plotted, as shown in Figure 3 The curve shown is at 200°C. To calculate the strain sensitivity coefficient, 5 samples were tested for each embodiment or comparative example, and the average value was taken.

[0104] (2) For each embodiment or comparative example, three new samples were taken, and the strain sensitivity coefficient at 25°C was the same as the average value. They were heated to 400°C and maintained for 12 hours. After cooling, the strain sensitivity coefficient was repeatedly measured at 25°C.

[0105] (3) Temperature coefficient of resistance: With 25°C as the reference temperature, use a digital multimeter to measure the resistance. Then place the thin film resistance strain gauge in a temperature-controlled heating furnace, raise the temperature to 200°C, measure the resistance, and calculate the temperature coefficient of resistance at 200°C: TCR = (R-R0) / 175R0, where R0 is the resistance at 25°C and R is the resistance at 200°C. For each embodiment or comparative example, take 5 samples for testing and take the average value.

[0106] Table 1 Performance parameters of thin film strain gauges in various embodiments and comparative examples

[0107]

[0108]

[0109] As can be seen from the above table, the flexible thin film strain gauge prepared by the method of the present invention has a resistance of not less than 3000Ω, low power consumption, and a low resistance temperature coefficient at 200°C. The strain sensitivity coefficient GF of the NiCr alloy film decreases with increasing temperature. Specifically, in the embodiment of the present application, it can be seen that the use of a polyimide film reinforced with glass fiber mesh as a substrate reduces the decrease in the strain sensitivity coefficient GF compared to the direct use of a polyimide film in Comparative Example 1, and the reliability of the measurement results at high temperatures is improved. Furthermore, as shown in Examples 4 to 5, after pre-deposition of the NiCrTi alloy film, the decrease in the strain sensitivity coefficient at high temperature compared to room temperature is greatly reduced and remains basically unchanged. At the same time, after the high temperature is maintained for 12 hours, the decrease in the GF of the repeated test at room temperature is also significantly reduced compared to the original GF at room temperature, and the reliability of the resistance strain gauge is improved. However, as shown in Comparative Examples 2 or 3, the thicker the NiCrTi alloy film or the pre-deposition of the NiCr alloy film cannot achieve the corresponding effect. When a nitrogen atmosphere is introduced during the deposition of the NiCrTi alloy film as shown in Example 6, or when a low hydrogen partial pressure atmosphere is used for pre-annealing as shown in Example 7, the GF at room temperature after high temperature maintenance not only decreases less, but also the GF of the samples are similar, and the dispersion is reduced, which is more obvious in the low hydrogen partial pressure atmosphere pre-annealing, thereby improving the life and reliability of the strain resistance gauge.

Claims

1. A method for preparing a flexible thin film resistance strain gauge, characterized in that: The following steps are involved: (1) Using a glass fiber mesh reinforced polyimide film as a substrate, photoresist is coated on the substrate surface for photolithography to pattern the strain gauge pattern; (2) A NiCrTi alloy film is first deposited on the strain gauge pattern of the substrate and pre-annealed in a vacuum annealing furnace at 200-300°C for 60-90 min, with argon and hydrogen introduced as a protective atmosphere, with a partial pressure ratio of hydrogen to argon of 1:15-20; then a NiCr alloy film is deposited as a sensitive gate layer, with the thickness of the NiCrTi alloy film being 0.1-0.2 times that of the NiCr alloy film; (3) Providing an anti-oxidation film layer on the sensitive gate; (4) Remove excess photoresist from the surface and perform annealing to obtain a flexible thin film resistor strain gauge.

2. The method for preparing a flexible thin film resistance strain gauge according to claim 1, characterized in that: The NiCr alloy film was prepared by the following magnetron sputtering method: NiCr alloy was used as the target material and the background vacuum was 3×10 -3 Pa~5.0×10 -3 Pa, the working gas is argon, the sputtering power is 50-100 W, the sputtering pressure is 0.4-0.8 Pa, the bias voltage is 100-300 V, the argon flow rate is 15-20 sccm, and the sputtering time is 30-40 min.

3. The method for preparing a flexible thin film resistance strain gauge according to claim 1 or 2, characterized in that: The Ni content in NiCr alloy is ≥85%.

4. The method for preparing a flexible thin film resistance strain gauge according to claim 3, wherein: The NiCr alloy is Ni90Cr10 alloy.

5. The method for preparing a flexible thin film resistance strain gauge according to claim 1, wherein: The NiCrTi alloy film is obtained by magnetron sputtering of a NiCrTi alloy. In the NiCrTi alloy, the Ti content is 5-10%, the Ni content is ≥75%, and the balance is Cr.

6. The method for preparing a flexible thin film resistance strain gauge according to claim 5, wherein: NiCrTi alloy is Ni82Cr10Ti8 alloy.

7. The method for preparing a flexible thin film resistance strain gauge according to claim 5, wherein: The working atmosphere used for magnetron sputtering NiCrTi alloy thin films is a mixture of nitrogen and argon, and the partial pressure ratio of nitrogen to argon is 1:8-10.

8. The method for preparing a flexible thin film resistance strain gauge according to claim 1, wherein: The anti-oxidation film layer is a Pt metal layer or an Al2O3 film layer.

9. The method for preparing a flexible thin film resistance strain gauge according to claim 1, wherein: The annealing in step (4) is carried out in a vacuum furnace at an annealing temperature of 200 to 400° C. and a heat treatment time of 2 to 3 hours.

10. The method for preparing a flexible thin film resistance strain gauge according to claim 1, wherein: The photolithography process in step (1) is as follows: spin-coat the positive photoresist on the front of the substrate, place the substrate on a coating machine with a rotation speed of 1500-2000 r / min and coat for 15-20 seconds, then heat and dry, and then irradiate with a light intensity of 100-120 mW / cm 2 Expose for 15 to 20 seconds, dry after exposure, and develop.

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