High-temperature-resistant piezoelectric film sensor structure, preparation method and application thereof

Abstract

The application discloses a high-temperature-resistant piezoelectric thin film sensor structure and a preparation method and application thereof. The sensor structure comprises, from bottom to top, a substrate, a piezoelectric layer, a protective layer and an electrode layer. The material of the protective layer is high-entropy alloy oxide. A first diffusion-preventing barrier layer is arranged between the substrate and the piezoelectric layer, and / or a second diffusion-preventing barrier layer is arranged between the piezoelectric layer and the protective layer. The materials of the first diffusion-preventing barrier layer and the second diffusion-preventing barrier layer are high-entropy alloys. The high-temperature-resistant piezoelectric thin film sensor structure adopts the diffusion-preventing barrier layers composed of high-entropy alloys, does not contain oxygen atoms, and can well prevent the diffusion and oxidation speed of light elements in the piezoelectric layer. The protective layer composed of high-entropy alloy oxide significantly improves the resistance of the sensor structure. Not only can the piezoelectric layer be prevented from being broken down in the high-voltage test process, but also the working stability of the sensor structure is improved.

Description

TECHNICAL FIELD

[0001] The present application relates to the technical field of intelligent temperature sensors, in particular to a high-temperature-resistant piezoelectric thin film sensor structure and a preparation method and application thereof. BACKGROUND

[0002] The ultrasonic measurement technology based on piezoelectric sensors is considered to be a reliable and non-invasive method for testing the health status of key machine components, which is usually composed of a sensor network installed on or embedded in the structure to be measured, portable diagnostic hardware and data analysis software. The core component of the ultrasonic temperature / stress sensor is based on the acoustic-elastic effect. The propagation speed of ultrasonic waves in the bolt is related to the environmental temperature / stress, so that the time of flight and the piezoelectric signal change accordingly. The function relationship between the ultrasonic propagation time and the amplitude of the sound wave and the temperature / stress is established, and the related coefficients in the function relationship are obtained through calibration test. Then, the environmental temperature / stress can be quantitatively calculated by measuring the time of flight of ultrasonic waves under different temperature / stress loads, so as to judge the temperature / stress condition of the machine component. That is, the temperature / stress monitoring can be realized by converting the temperature / stress state into the corresponding ultrasonic signal, which is high in precision, convenient and efficient, and non-destructive, and is not disturbed by environmental factors such as human, air and surrounding objects, so that real-time monitoring and remote control can be realized.

[0003] The traditional piezoelectric sensor includes a piezoelectric layer, a protective layer, a bonding layer and an electrode layer. The protective layer is usually made of SiO2, which mainly prevents the piezoelectric layer from being broken down during high-voltage testing. In a high-temperature environment, the traditional piezoelectric sensor is prone to peeling due to the difference in thermal expansion coefficient between the substrate and the piezoelectric coating, and the piezoelectric layer is easily damaged by high temperature, such as element diffusion and oxidation, which reduces the reliability and service life of the entire sensor.

[0004] Therefore, it is necessary to improve the structure of the piezoelectric sensor to improve the high-temperature resistance of the sensor. SUMMARY

[0005] In order to solve the problems existing in the prior art, the present application provides a high-temperature-resistant piezoelectric thin film sensor structure, which comprises, from bottom to top, a substrate, a piezoelectric layer, a protective layer and an electrode layer, and the material of the protective layer is high-entropy alloy oxide.

[0006] A first diffusion-preventing barrier layer is arranged between the substrate and the piezoelectric layer, and / or a second diffusion-preventing barrier layer is arranged between the piezoelectric layer and the protective layer.

[0007] The material of the first diffusion-preventing barrier layer and the second diffusion-preventing barrier layer is high-entropy alloy.

[0008] Further, the thickness of the protective layer is 4-10 μm.

[0009] The thickness of the first diffusion-preventing barrier layer and the second diffusion-preventing barrier layer is 1-10 μm.

[0010] Further, the alloy elements of the high-entropy alloy oxide and the high-entropy alloy include at least eight of Al, Ti, V, Cr, Zr, Nb, Mo, Hf, Ta, W, Y, and Si. Corresponding to these alloy elements, the material of the first diffusion-preventing barrier layer and the second diffusion-preventing barrier layer can be or be independently selected from at least one of TiVCrZrNbMoHfTaWAlSiY, TiVCrZrNbMoHfTaWAlSi, AlCrNbSiTaTiVZr, and AlMoNbSiTaTiVZr. It should be noted that the high-entropy alloy oxide is represented by the general formula X-O, wherein X represents the high-entropy alloy, and the material of the protective layer can be at least one of TiVCrZrNbMoHfTaWAlSiY-O, TiVCrZrNbMoHfTaWAlSi-O, AlMoNbSiTaTiVZr-O, and AlMoNbSiTaTiVZr-O.

[0011] Further, the thickness of the piezoelectric layer is 5-25 μm.

[0012] Further, the material of the electrode layer is a solid metal element or a solid metal alloy with a thickness of 2-20 μm.

[0013] Further, the electrode layer is divided into an inner electrode region and an outer electrode region.

[0014] It should be noted that in the present application, the substrate is not strictly limited, and can be, for example, a stainless steel plate, a silicon wafer, a bolt, or the like. The material of the piezoelectric layer is not strictly limited, and can be, for example, LiNbO3, AlN, ZnO, and metal-doped LiNbO3, AlN, ZnO, or the like. The material of the electrode layer is also not strictly limited, and can be, for example, at least one of a metal element such as Ag, Cr, Ti, or an alloy such as AgCr and a high-entropy alloy.

[0015] The present application also provides a preparation method of a high-temperature-resistant piezoelectric film sensor structure, comprising,

[0016] The piezoelectric layer, the protective layer, and the electrode layer are prepared on the surface of the substrate in sequence, wherein the piezoelectric layer is prepared after the first diffusion-preventing barrier layer is prepared on the surface of the substrate, and / or,

[0017] The second diffusion-preventing barrier layer is prepared on the surface of the piezoelectric layer to further prepare the protective layer.

[0018] The material of the protective layer is a high-entropy alloy oxide, and the materials of the first diffusion-preventing barrier layer and the second diffusion-preventing barrier layer are high-entropy alloys.

[0019] Further, the first diffusion barrier layer, piezoelectric layer, second diffusion barrier layer, protective layer, and electrode layer are prepared by a radio frequency magnetron sputtering method. The parameters of the radio frequency magnetron sputtering method include,

[0020] The first diffusion barrier layer and the second diffusion barrier layer: input pure Ar, total gas flow 1.1-2.5 Pa, radio frequency power 750-900 W, temperature 40-150℃, target-to-substrate distance 8.5-15 cm, and time 10 min-60 min;

[0021] For different types of piezoelectric coatings, the parameters of the radio frequency magnetron sputtering are different. For example, for an oxide piezoelectric layer, the target-to-substrate distance is 4-10 cm, pure Ar and O2 are input, the total gas flow is 0.8-2.1 Pa, the flow ratio of Ar / O2 is 1 / 1-6 / 1, the radio frequency power is 800-900 W, the bias voltage is 0-30 V, and the coating time is 4-10 h; for a nitride piezoelectric layer, the target-to-substrate distance is 6-12 cm, pure Ar and N2 are input, the total gas flow is 0.8-2.1 Pa, the flow ratio of Ar / O2 is 1 / 1-3 / 1, the radio frequency power is 800-900 W, and the coating time is 4-10 h;

[0022] The protective layer: input pure Ar and O2, total gas flow 1.1-2.5 Pa, flow ratio of Ar / O2 1.1 / 1-3 / 1, radio frequency power 750-900 W, temperature 40-150℃, target-to-substrate distance 8.5-15 cm, and time 5.5 h-7 h;

[0023] The electrode layer: input pure Ar, total gas flow 1.1-2.5 Pa, radio frequency power 750-900 W, temperature 40-150℃, target-to-substrate distance 5-10 cm, and time 30 min-2 h.

[0024] Further, before the preparation of the first diffusion barrier layer, piezoelectric layer, second diffusion barrier layer, protective layer, and electrode layer, surface treatment is performed by arc etching. The arc etching surface treatment can remove contaminants such as oil and dust on the substrate surface and enhance the interlayer bonding performance. The arc etching technology uses a Cr target, and 0.5 Pa-2.0 Pa of pure Ar gas is input, the etching voltage is 100 V-200 V, the duty cycle is 20%-70%, the current is 2.0 A-4.0 A, the etching time before the preparation of the first diffusion barrier layer is 5 min-10 min, and the etching time of the others is 1 min-5 min.

[0025] Preferably, after the preparation of the protective layer is completed, an insulating ring is pasted on the surface of the protective layer. Because of the existence of the internal insulating ring, the electrode layer can form an inner electrode area and an outer electrode area, which facilitates the testing of ultrasonic signals.

[0026] The application also provides a temperature detection system comprising the sensor structure.

[0027] Compared with the prior art, the application has the following beneficial effects:

[0028] The sensor structure prepared by the application adopts a diffusion-preventing barrier layer composed of a high-entropy alloy, which can be located above and below the piezoelectric layer and around the piezoelectric layer to maximize the air isolation. The diffusion-preventing barrier layer is composed of a pure metal layer and does not contain oxygen atoms, which can effectively prevent the escape and diffusion of light elements and greatly reduce the diffusion and oxidation speed of light elements in a high-temperature environment.

[0029] The sensor structure prepared by the application adopts a protective layer composed of a high-entropy alloy oxide, which is located above and around the piezoelectric layer to significantly improve the resistance of the sensor structure. The protective layer not only prevents the piezoelectric layer from being broken down during high-voltage testing and improves the working stability of the sensor structure in a high-voltage environment, but also serves as a high-temperature protective layer to improve the high-temperature stability of the sensor structure. BRIEF DESCRIPTION OF DRAWINGS

[0030] In order to more clearly illustrate the technical solutions in the embodiments of the application or the prior art, the following will briefly introduce the drawings needed to be used in the embodiments or the prior art description. Obviously, the drawings in the following description are some embodiments of the application, and other drawings can also be obtained by those skilled in the art without creative labor.

[0031] Figure 1 A schematic diagram of a high-temperature-resistant piezoelectric thin film sensor structure prepared by the application is shown in the figure, wherein 1 is a substrate, 2 is a first diffusion-preventing barrier layer, 3 is a piezoelectric layer, 4 is a second diffusion-preventing barrier layer, 5 is a protective layer, and 6 is an electrode layer.

[0032] Figure 2 A cross-sectional morphology of the sensor structure prepared in Example 1 is shown.

[0033] Figure 3 A cross-sectional element distribution of the sensor structure prepared in Example 1 is shown.

[0034] Figure 4 The surface morphology and element distribution of each layer of the sensor structure prepared in Example 1 are shown.

[0035] Figure 5 A ultrasonic signal test diagram of the sensor prepared in Example 1 after annealing at 760℃ for different times is shown.

[0036] Figure 6 A ultrasonic signal and piezoelectric constant d of the sensor structure prepared in Example 1 after annealing at 760℃ for different times are shown.33 Test results;

[0037] Figure 7 The relative changes in ultrasonic signals of the sensors prepared in Example 1 and Comparative Example 1 after annealing at 760°C for different times are shown.

[0038] Figure 8 The piezoelectric constant d of the sensors prepared in Example 1 and Comparative Example 1 after annealing at 760°C for different times is shown. 33 The relative change;

[0039] Figure 9 The ultrasonic signal and piezoelectric constant d of the sensor prepared in Example 4 are shown after annealing at 400°C, 500°C, 600°C, and 700°C for 1 hour. 33 Resulting image;

[0040] Figure 10 The relative changes in ultrasonic signals of the sensors prepared in Examples 4, 5, 6, Comparative Example 5, and Comparative Example 6 after annealing at 400°C, 500°C, 600°C, and 700°C for 1 hour are shown.

[0041] Figure 11 The piezoelectric constant d of the sensors prepared in Examples 4, 5, 6, Comparative Example 5, and Comparative Example 6 is shown after annealing at 400°C, 500°C, 600°C, and 700°C for 1 hour. 33 The relative change;

[0042] Figure 12 Raman spectra of the LiNbO3 piezoelectric layers of the sensors prepared in Example 1 and Comparative Example 3 before and after annealing at 760°C for 10 h are shown. Detailed Implementation

[0043] The endpoints and any values ​​of the ranges disclosed in this invention are not limited to the precise ranges or values, and these ranges or values ​​should be understood to include values ​​close to these ranges or values. For numerical ranges, the endpoint values ​​of the various ranges, the endpoint values ​​of the various ranges and individual point values, and individual point values ​​can be combined with each other to obtain one or more new numerical ranges, which should be considered as specifically disclosed in this invention.

[0044] The technical solutions of the present invention will be clearly and completely described below with reference to specific embodiments and accompanying drawings. Obviously, the described embodiments are only some embodiments of the present invention, and 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.

[0045] Example 1

[0046] A preparation method of a high-temperature-resistant piezoelectric thin film sensor structure, comprising the following steps:

[0047] Step one, preparing a first diffusion-preventing barrier layer 2:

[0048] (1) Prepare a TiVCrZrNbMoHfTaWAlSiY high-entropy alloy target and a clean stainless steel substrate 1, and place them in a radio frequency magnetron sputtering film coating machine, with a target-to-substrate distance of 10 cm and a vacuum degree of 4×10 -3 Pa;

[0049] (2) Adopt arc etching technology to carry out etching, remove contaminants such as oil stains and dust on the surface of the substrate 1, and enhance the bonding performance between the first diffusion-preventing barrier layer 2 and the substrate 1. The arc etching technology adopts a Cr target, and the etching is carried out under the conditions of a 1.1 Pa pure Ar atmosphere, an etching voltage of 150 V, a duty cycle of 60%, a current of 3.0 A, and an etching time of 9 min;

[0050] (3) After the vacuum degree reaches 4×10 -3 Pa, input pure Ar, and deposit for 60 min under the conditions of a total gas flow of 1.1 Pa, a radio frequency power of 750 W, a temperature of 80°C, a target-to-substrate distance of 10 cm, to obtain the first diffusion-preventing barrier layer 2 with a thickness of about 5.5 μm.

[0051] Step two, preparing a piezoelectric layer 3:

[0052] (1) Prepare a lithium niobate target, and place it in a radio frequency magnetron sputtering film coating machine, with a target-to-substrate distance of 4.5 cm and a vacuum degree of 5×10 -3 Pa;

[0053] (2) Adopt arc etching technology to carry out etching, and enhance the bonding performance between the piezoelectric layer and the first diffusion-preventing barrier layer. The arc etching technology adopts a Cr target, and the etching is carried out under the conditions of a 1.1 Pa pure Ar atmosphere, an etching voltage of 150 V, a duty cycle of 60%, a current of 3.0 A, and an etching time of 1 min;

[0054] (3) After the vacuum degree reaches 4×10 -3 Pa, input Ar and O2, and deposit for 8.5 h under the conditions of a total gas flow of 0.8 Pa, an Ar / O2 flow ratio of 6 / 1, a radio frequency power of 900 W, a temperature of 80°C, a bias voltage of 7 V, to obtain the piezoelectric layer 3 with a thickness of about 36 μm.

[0055] Step three, preparing a second diffusion-preventing barrier layer 4:

[0056] (1) Prepare TiVCrZrNbMoHfTaWAlSiY high-entropy alloy target material, and place it in a radio frequency magnetron sputtering film coating machine, with a target-to-substrate distance of 10 cm and a vacuum degree of 4x10 -3 Pa;

[0057] (2) Adopt arc etching technology to carry out etching and enhance the bonding performance between the second diffusion-preventing barrier layer 4 and the piezoelectric layer 3. The arc etching technology adopts a Cr target, and etches for 2 min under the conditions of a 1.1 Pa pure Ar atmosphere, an etching voltage of 150 V, a duty cycle of 60%, and a current of 3.0 A;

[0058] (3) After the vacuum degree reaches 4x10 -3 Pa, input pure Ar, and deposit for 60 min under the conditions of a total gas flow of 1.1 Pa, a radio frequency power of 750 W, a temperature of 80°C, and a target-to-substrate distance of 10 cm to obtain a second diffusion-preventing barrier layer 4 with a thickness of about 5.5 μm.

[0059] Step four, immediately after step three, prepare a protective layer 5:

[0060] (1) Prepare TiVCrZrNbMoHfTaWAlSiY high-entropy alloy target material and clean stainless steel substrates, and place them in a radio frequency magnetron sputtering film coating machine, with a target-to-substrate distance of 10 cm and a vacuum degree of 4x10 -3 Pa;

[0061] (2) Adopt arc etching technology to carry out etching and enhance the bonding performance between the protective layer 5 and the second diffusion-preventing barrier layer 4. The arc etching technology adopts a Cr target, and etches for 1 min under the conditions of a 1.1 Pa pure Ar atmosphere, an etching voltage of 150 V, a duty cycle of 60%, and a current of 3.0 A;

[0062] (3) After the vacuum degree reaches 4x10 -3 Pa, input Ar and O2, and deposit for 5.5 h under the conditions of a total gas flow of 1.1 Pa, an Ar / O2 flow ratio of 1.1 / 1, a radio frequency power of 750 W, a temperature of 80°C, and a target-to-substrate distance of 10 cm to obtain a protective layer 5 with a thickness of about 4.5 μm;

[0063] Step five, stick an insulating ring to the surface of the protective layer 5. The purpose of the insulating ring is to form an inner and outer electrode area, which facilitates ultrasonic signal testing. The insulating ring is made of polyester amide material, has a thickness of 0.15 mm, an inner ring diameter of 3 mm, and an outer ring diameter of 5 mm.

[0064] Step six, prepare an electrode layer 6:

[0065] (1) Prepare an AgCr target (Ag / Cr atomic ratio of 2 / 1), and place it in a radio frequency magnetron sputtering film coating machine, with a target-to-substrate distance of 8 cm and a vacuum degree of 4x10 -3 Pa;

[0066] (2) The etching is carried out by using arc etching technology to enhance the bonding performance between the electrode layer 6 and the protective layer 5. The arc etching technology uses a Cr target, and the etching is carried out under the conditions of 1.1 Pa pure Ar atmosphere, etching voltage 150 V, duty cycle 60%, current 3.0 A, and etching time 2 min;

[0067] (2) After the vacuum degree reaches 4x10 -3 Pa, Ar is input, and the electrode layer 6 with a thickness of about 6.0 μm is obtained by depositing for 1 h under the conditions of total gas flow 1.1 Pa, radio frequency power 750 W, temperature 80℃, and target-to-substrate distance 8 cm;

[0068] (3) After the temperature in the chamber is lower than 50℃, the high-temperature-resistant piezoelectric thin film sensor structure as shown in Figure 1 is obtained.

[0069] The cross-sectional morphology of the high-temperature-resistant piezoelectric thin film sensor structure prepared in Example 1 is observed by using a scanning electron microscope, as shown in Figure 2 , wherein HEA and HEAO represent high-entropy alloy and high-entropy alloy oxide, respectively. The cross-sectional morphology is the same as Figure 1 , indicating that the prepared high-temperature-resistant piezoelectric thin film sensor structure has uniformity and stability. Figure 3 The cross-sectional element distribution of the high-temperature-resistant piezoelectric thin film sensor structure is shown, and it can be seen that the element distribution in each layer is uniform. Figure 4 The surface morphology and element distribution of each layer of the high-temperature-resistant piezoelectric thin film sensor structure are shown, and it can be seen that the surface morphology of each layer is uniform, and the element distribution is uniform.

[0070] Comparative Example 1

[0071] Compared with Example 1, the difference lies in that steps one, three and four are absent, that is, the electrode layer is directly prepared after the piezoelectric layer is deposited on the surface of the stainless steel substrate, to obtain the sensor structure.

[0072] Comparative Example 2

[0073] Compared with Example 1, the difference lies in that step four is absent, that is, the electrode layer is prepared after the first diffusion barrier layer, the piezoelectric layer and the second diffusion barrier layer are sequentially prepared on the substrate, to obtain the sensor structure.

[0074] Comparative Example 3

[0075] Compared with Example 1, the difference lies in that steps one and three are absent, that is, the piezoelectric layer, the protective layer and the electrode layer are sequentially prepared on the substrate to obtain the sensor structure.

[0076] Comparative Example 4

[0077] Compared with Example 1, the difference is that steps one, three, four and five are not present, that is, the piezoelectric layer is directly deposited on the surface of the stainless steel substrate to obtain the sensor structure.

[0078] After annealing the sensor structures prepared in Example 1 and Comparative Example 1 at 760°C for 10 h, 20 h, 40 h, and 100 h, the ultrasonic signal and piezoelectric constant d were tested at an excitation voltage of 100 V and a gain of 20 dB. 33 .from Figure 5 and Figure 6 As can be seen, during the long-term annealing process at 760℃ for 100 hours, the longitudinal wave signals of the sensor structure in Example 1 were 0.50V, 0.43V, 0.36V, and 0.31V at annealing times of 10 hours, 20 hours, 40 hours, and 100 hours, respectively, and the piezoelectric constant d... 33 The values ​​are 4.5 pC / N, 4.3 pC / N, 4.0 pC / N, and 3.5 pC / N, respectively. From... Figure 7 and Figure 8 As can be seen, during the long-term annealing process at 760℃ for 100 hours, the sensor structure prepared in Example 1, compared to Comparative Example 1, exhibits improved longitudinal wave signal and piezoelectric constant d. 33 The descent rate was significantly slower, indicating the presence of the first / second anti-diffusion barrier layer and protective layer, which effectively improved the thermal stability of the sensor.

[0079] Example 2-3

[0080] Compared with Example 1, the difference is that the deposition time in step four for preparing the protective layer is 7h and 10h, respectively, resulting in protective layers with thicknesses of approximately 6.0μm and 8.5μm.

[0081] Example 4

[0082] Compared with Example 1, the difference lies in the following: In step two, a vanadium-doped lithium niobate target is used, with a vanadium doping amount of 1.8%, and the corresponding magnetron sputtering parameters are as follows, until the vacuum degree reaches 4×10⁻⁶. -3 With an input of Ar and O2, a piezoelectric layer with a thickness of approximately 16 μm was deposited for 7 hours at a total gas flow rate of 0.9 Pa, an Ar / O2 flow ratio of 6 / 1, an RF power of 900 W, a temperature of 120 °C, and a bias voltage of 7 V.

[0083] Example 5

[0084] Compared with Example 4, the difference is that step one is not present, which involves sequentially preparing a piezoelectric layer, a second anti-diffusion barrier layer, a protective layer, and an electrode layer on a stainless steel substrate to obtain the sensor structure.

[0085] Example 6

[0086] Compared with Example 4, the difference is that step three is not present, namely, the sequential fabrication of the first anti-diffusion barrier layer, piezoelectric layer, protective layer and electrode layer on the stainless steel substrate to obtain the sensor structure.

[0087] Comparative Example 5

[0088] Compared with Example 4, the difference is that step four is not present, which involves sequentially preparing the first anti-diffusion barrier layer, the piezoelectric layer, the second anti-diffusion barrier layer, and the electrode layer on the stainless steel substrate to obtain the sensor structure.

[0089] Comparative Example 6

[0090] Compared with Example 4, the difference is that steps one, three and four are not present, that is, the electrode layer is directly prepared after depositing the piezoelectric layer on the surface of the stainless steel substrate to obtain the sensor structure.

[0091] The sensor structures prepared in Examples 4, 5, and 6, and Comparative Examples 5 and 6 were annealed at 400°C, 500°C, 600°C, and 700°C for 1 hour, respectively. The ultrasonic signal and piezoelectric constant d were then tested at an excitation voltage of 100V and a gain of 20dB. 33 .from Figure 9 As can be seen, under the same time conditions, with the increase of annealing temperature, the longitudinal wave signal and piezoelectric constant d of the sensor structure in Example 4 increase. 33 It shows a downward trend; the longitudinal wave signal before annealing is 0.7V, and the piezoelectric constant d... 33 The piezoelectric constant is 11.9 pC / N. The longitudinal wave signals after annealing at 400℃, 500℃, 600℃, and 700℃ for 1 hour are 0.68V, 0.62V, 0.60V, and 0.52V, respectively. 33 The values ​​are 11.6 pC / N, 11.2 pC / N, 10.9 pC / N, and 9.2 pC / N, respectively. From... Figure 10 and Figure 11 It can be seen from the data that during the heating and annealing process at temperatures ranging from 400℃ to 700℃, the longitudinal wave signal and the piezoelectric constant d... 33 The decreasing speeds, from slowest to fastest, are as follows: Example 4, Example 5, Example 6, Comparative Example 5, and Comparative Example 6, i.e., the longitudinal wave signal and piezoelectric constant d of the sensor structure prepared in Example 4. 33 The slowest descent rate indicates the presence of the first / second anti-diffusion barrier layer and protective layer, which effectively improves the thermal stability of the sensor.

[0092] The resistance of the sensor structures prepared in some embodiments and comparative examples was tested at a measurement frequency of 100 Hz, and the results are shown in Table 1.

[0093] Table 1 Resistance test results

[0094]

[0095] The test results of Table 1 can show that the protective layer composed of high-entropy alloy oxide TiVCrZrNbMoHfTaWAlSiY-O increases the resistance of the sensor structure, and the higher resistance can prevent the piezoelectric layer from being broken down during the high-voltage test process, thereby improving the working stability of the sensor structure in a high-voltage environment.

[0096] The sensor structures prepared in Example 1, Comparative Example 1, Comparative Example 3, Comparative Example 4 were subjected to Raman and EDS element tests, and then subjected to Raman and EDS element tests again after annealing at 760°C for 10h.

[0097] For Example 1, the piezoelectric layer (hereinafter referred to as LiNbO3 coating) at a distance of 0.5μm from the second diffusion-preventing barrier layer was selected to carry out Raman and EDS element tests; for Comparative Example 3, the LiNbO3 coating at a distance of 0.5μm from the protective layer was selected to carry out Raman and EDS element tests. The Raman test results are shown in Figure 12 As shown in the Raman test results, the Raman peak values of the LiNbO3 coating of Example 1 do not change before and after annealing, i.e., the LiNbO3 content is stable; while the Raman peaks at positions 156, 237 and 625 of the LiNbO3 coating of Comparative Example 3 all show a downward trend after annealing, which means that the LiNbO3 content decreases. The O / Nb atomic ratio of the LiNbO3 coating of Example 1 is measured to be 2.83 and 2.81 before and after annealing, respectively, which almost does not change, i.e., the LiNbO3 content is stable; while the O / Nb atomic ratio of the LiNbO3 coating of Comparative Example 3 is measured to be 2.82 and 2.69 before and after annealing, respectively, which decreases obviously. The decrease of the LiNbO3 content in the Raman spectrum and the decrease of the O / Nb atomic ratio in the EDS of Comparative Example 3 mean that the Li element in the LiNbO3 coating diffuses upward to the upper coating, and part of the LiNbO3 is converted into lithium-deficient phase LiNb3O8, which also shows that the protective layer composed of high-entropy alloy oxide TiVCrZrNbMoHfTaWAlSiY-O of Comparative Example 3 cannot act as a diffusion-preventing barrier layer. The Raman and EDS element test data of Example 1 prove that the second diffusion-preventing barrier layer composed of high-entropy alloy TiVCrZrNbMoHfTaWAlSiY is indispensable and can effectively prevent the Li element in the LiNbO3 coating from diffusing upward to the upper protective layer.

[0098] Similarly, for the sample of Example 1, the LiNbO3 coating layer at a distance of 0.5 μm from the first diffusion-preventing barrier layer was selected to carry out Raman and EDS element tests; for the sample of Comparative Example 3, the LiNbO3 coating layer at a distance of 0.5 μm from the substrate was selected to carry out Raman and EDS element tests. The test results are consistent with the above, and the Raman peak values of the LiNbO3 coating layer of Example 1 do not change before and after annealing, while the Raman peaks at positions 156, 237 and 625 of the LiNbO3 coating layer of Comparative Example 3 all show a decline after annealing; the O / Nb atomic ratio of the LiNbO3 coating layer of Example 1 is almost unchanged before and after annealing, while the O / Nb atomic ratio of the LiNbO3 coating layer of Comparative Example 3 decreases significantly before and after annealing. The decrease in the LiNbO3 content in the Raman spectrum and the decrease in the O / Nb atomic ratio in the EDS of Comparative Example 3 mean that the Li element in the LiNbO3 coating layer diffuses to the substrate, and part of the LiNbO3 is converted into the lithium-deficient phase LiNb3O8. The Raman and EDS element test data of Example 1 prove that the diffusion-preventing barrier layer composed of high-entropy alloy TiVCrZrNbMoHfTaWAlSiY is indispensable and can effectively block the diffusion of the Li element in the LiNbO3 coating layer to the substrate.

[0099] Similarly, for the sample of Example 1, the LiNbO3 coating layer at a distance of 0.5 μm from the second diffusion-preventing barrier layer was selected to carry out Raman and EDS element tests, and for the sample of Comparative Example 1, the LiNbO3 coating layer at a distance of 0.5 μm from the AgCr electrode layer was selected to carry out Raman and EDS element tests. The test results are consistent with the above, and the Raman peak values of the LiNbO3 coating layer of Example 1 do not change before and after annealing, while the Raman peaks at positions 156, 237 and 625 of the LiNbO3 coating layer of Comparative Example 1 all show a decline after annealing; the O / Nb atomic ratio of the LiNbO3 coating layer of Example 3 is almost unchanged before and after annealing, while the O / Nb atomic ratio of the LiNbO3 coating layer of Comparative Example 1 decreases significantly before and after annealing. The decrease in the LiNbO3 content in the Raman spectrum and the decrease in the O / Nb atomic ratio in the EDS of Comparative Example 1 mean that the Li element in the LiNbO3 coating layer diffuses to the upper coating layer, and part of the LiNbO3 is converted into the lithium-deficient phase LiNb3O8, which also shows that the AgCr electrode layer of Comparative Example 1 cannot serve as a diffusion-preventing barrier layer. The Raman and EDS element test data of Example 1 prove that the TiVCrZrNbMoHfTaWAlSiY diffusion-preventing barrier layer is indispensable and can effectively block the diffusion of the Li element in the LiNbO3 coating layer to the upper electrode layer.

[0100] Similarly, for Example 1, the LiNbO3 coating layer at a distance of 0.5 μm from the second diffusion barrier layer was selected to carry out Raman and EDS element tests, and for the sample of Comparative Example 4, a position at a distance of 0.5 μm from the surface of the LiNbO3 coating layer was selected to carry out Raman and EDS element tests. The test results are consistent with the above, and the Raman peak values of the LiNbO3 coating layer of Example 1 do not change before and after annealing, while the Raman peaks at positions 156, 237 and 625 of the LiNbO3 coating layer of Comparative Example 4 all show a decline after annealing; the O / Nb atomic ratio of the LiNbO3 coating layer of Example 1 is almost unchanged before and after annealing, while the O / Nb atomic ratio of the LiNbO3 coating layer of Comparative Example 4 decreases significantly before and after annealing. The decrease in the LiNbO3 content in the Raman spectrum and the decrease in the O / Nb atomic ratio in the EDS of Comparative Example 4 mean that the Li element in the LiNbO3 coating layer diffuses into the air, and part of the LiNbO3 is converted into the lithium-deficient phase LiNb3O8. The Raman and EDS element test data of Example 1 prove that the TiVCrZrNbMoHfTaWAlSiY diffusion barrier layer is indispensable and can effectively block the diffusion of Li elements in the LiNbO3 coating layer into the air.

[0101] It can be seen that the first / second diffusion barrier layer composed of high-entropy alloy TiVCrZrNbMoHfTaWAlSiY in Example 1 can well prevent the escape and diffusion of Li elements into the substrate and the upper coating or the air, greatly reducing the diffusion and oxidation speed of Li elements in a high-temperature environment, and stabilizing the LiNbO3 content. At the same time, it also shows that the high-entropy alloy oxide protective layer composed of TiVCrZrNbMoHfTaWAlSiY-O cannot be used as a Li element diffusion barrier layer because it is an oxide and contains O atoms that will combine with Li atoms in the LiNbO3 coating layer, and a high-entropy alloy diffusion barrier layer must be deposited between the high-entropy alloy oxide protective layer and the LiNbO3 coating layer.

[0102] Examples 7-9

[0103] Compared with Example 1, the difference is that the TiVCrZrNbMoHfTaWAlSi, AlCrNbSiTaTiVZr and AlMoNbSiTaTiVZr targets are used in step four, respectively.

[0104] The resistance and ultrasonic signal of the sensor structure constructed in Examples 7-9 are also tested, and have similar performance to Example 1. These results show that the use of a high-entropy alloy oxide protective layer in the present application significantly improves the sensor resistance, not only preventing the piezoelectric layer from being broken down during high-voltage testing and improving the working stability of the sensor in a high-voltage environment, but also serving as a high-temperature protective layer to improve the high-temperature stability of the sensor.

[0105] Finally, it should be noted that the above only describes the preferred embodiments of the present application and is not intended to limit the present application. Although the present application has been described in detail with reference to the foregoing embodiments, those skilled in the art will appreciate that the technical solutions described in the foregoing embodiments can be modified or some technical features thereof can be replaced by equivalent features, and any modification, equivalent replacement, improvement, etc. made within the spirit and principle of the present application shall be included in the protection scope of the present application.

Claims

1. A high temperature resistant piezoelectric thin film sensor structure comprising, from bottom to top, a substrate, a piezoelectric layer, a protective layer and an electrode layer, characterized in that, The material of the piezoelectric layer is lithium niobate, and the material of the protective layer is high-entropy alloy oxide. A first diffusion-preventing barrier layer is arranged between the substrate and the piezoelectric layer, and a second diffusion-preventing barrier layer is arranged between the piezoelectric layer and the protective layer. The material of the first diffusion-preventing barrier layer and the second diffusion-preventing barrier layer is high-entropy alloy. The alloy elements of the high-entropy alloy oxide and the high-entropy alloy include at least eight of Al, Ti, V, Cr, Zr, Nb, Mo, Hf, Ta, W, Y and Si.

2. The high temperature piezoelectric thin film sensor structure according to claim 1, wherein, The thickness of the protective layer is 4-10 μm. The thickness of the first diffusion-preventing barrier layer and the second diffusion-preventing barrier layer is 1-10 μm.

3. The sensor structure of claim 1, wherein, The thickness of the piezoelectric layer is 5-50 μm.

4. The sensor structure of claim 1, wherein, The material of the electrode layer is solid metal element or solid metal alloy with a thickness of 2-20 μm.

5. The sensor structure of claim 4, wherein, The electrode layer is divided into an inner electrode region and an outer electrode region.

6. A method of fabricating a high temperature resistant piezoelectric thin film sensor structure, characterized by, The sensor structure comprises the substrate, the first diffusion-preventing barrier layer, the piezoelectric layer, the second diffusion-preventing barrier layer, the protective layer and the electrode layer. The piezoelectric layer is prepared after the first diffusion-preventing barrier layer is prepared on the surface of the substrate, and the material of the piezoelectric layer is lithium niobate. The second diffusion-preventing barrier layer is prepared on the surface of the piezoelectric layer, and the protective layer is prepared after the second diffusion-preventing barrier layer is prepared. The material of the protective layer is high-entropy alloy oxide, the material of the first diffusion-preventing barrier layer and the second diffusion-preventing barrier layer is high-entropy alloy, and the alloy elements of the high-entropy alloy oxide and the high-entropy alloy include at least eight of Al, Ti, V, Cr, Zr, Nb, Mo, Hf, Ta, W, Y and Si.

7. The method of claim 6, wherein the method further comprises: The first diffusion-preventing barrier layer, the piezoelectric layer, the second diffusion-preventing barrier layer, the protective layer and the electrode layer are prepared by radio frequency magnetron sputtering.

8. The method of claim 6, wherein the method further comprises: The surface is treated by arc etching before the first diffusion-preventing barrier layer, the piezoelectric layer, the second diffusion-preventing barrier layer, the protective layer and the electrode layer are prepared.

9. A temperature detection system, characterized by, The sensor structure comprises the substrate, the first diffusion-preventing barrier layer, the piezoelectric layer, the second diffusion-preventing barrier layer, the protective layer and the electrode layer.

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