A surface acoustic wave pressure sensor based on an equal-strength thin film design

Abstract

This invention discloses a surface acoustic wave pressure sensor based on an equal-strength thin film design, comprising a silicon substrate, a piezoelectric sensitive film, a resonator, and a silicon-based cover plate. The silicon substrate has a sensing hole, the outer end of which is exposed to the external environment to be measured. The piezoelectric sensitive film is formed by stacking a temperature compensation layer and a lithium niobate layer. The lower edge of the temperature compensation layer is fixedly connected to the upper edge of the silicon substrate, and the upper edge of the lithium niobate layer is sealed and fixed to the lower edge of the silicon-based cover plate. A stress balancing groove is provided at the lower end of the temperature compensation layer above the sensing hole to achieve equal stress in each region of the pressure-sensing area of ​​the piezoelectric sensitive film under the maximum allowable stress. The resonator consists of interdigitated transducer electrodes and a reflective grid. The interdigitated transducer electrodes are fixed to the middle of the upper end of the lithium niobate layer, and the reflective grids are fixed to the lithium niobate layers on both sides of the interdigitated transducer electrodes. A pressure-sensing cavity is provided at the lower end of the silicon-based cover plate above the sensing hole.

Description

Technical Field

[0001] This invention belongs to the field of pressure sensor technology, specifically relating to a surface acoustic wave pressure sensor based on an equal-strength thin film design. Background Technology

[0002] Pressure sensors are widely used in various industrial sectors, especially in high-precision environments such as aerospace, deep-sea exploration, and smart manufacturing, where monitoring environmental pressure is often required. Traditional pressure sensors generally struggle to achieve miniaturized, high-precision pressure signal measurement and are difficult to adapt to wireless passive technologies. In recent years, sensors based on surface acoustic wave (SAW) technology have demonstrated excellent performance in environmental pressure monitoring, particularly in terms of sensitivity and accuracy.

[0003] However, existing SAW pressure sensors still have certain problems with stress distribution. Under pressure, the stress and strain distribution of a pressure-sensitive diaphragm of uniform thickness is often uneven, with higher stress at the fixed edges. This leads to unstable sensor performance under high pressure, affecting its measurement accuracy and range. Furthermore, uneven strain can cause crosstalk in the sensor signal, resulting in excessive bandwidth and a sharp decrease in the device's Q value. Therefore, optimizing the design of the pressure-sensitive diaphragm to achieve uniform surface stress distribution under maximum stress and reduce the sharp decrease in the device's Q value caused by uneven strain has become a key issue in improving sensor performance. 。 Summary of the Invention

[0004] To address the above problems, this invention proposes a surface acoustic wave pressure sensor based on an equal-strength thin film design.

[0005] To achieve the above objectives, the present invention adopts the following technical solution:

[0006] A surface acoustic wave (SAW) pressure sensor based on an equal-strength thin film design includes a silicon substrate, a piezoelectric sensitive film, a resonator, and a silicon-based cover plate. The silicon substrate has a sensing hole, the outer end of which is exposed to the external environment. The piezoelectric sensitive film is formed by stacking a temperature compensation layer and a lithium niobate layer. The lower edge of the temperature compensation layer is fixedly connected to the upper edge of the silicon substrate, and the upper edge of the lithium niobate layer is sealed and fixed to the lower edge of the silicon-based cover plate. A stress balancing groove is provided at the lower end of the temperature compensation layer above the sensing hole to achieve equal stress in each region of the pressure-sensing area of ​​the piezoelectric sensitive film under the maximum allowable stress. The resonator consists of interdigitated transducer electrodes and a reflective grid. The interdigitated transducer electrodes are fixed to the middle of the upper end of the lithium niobate layer, and the reflective grids are fixed to the lithium niobate layers on both sides of the interdigitated transducer electrodes. The pressure-sensing area is excited by the resonator to generate various surface acoustic waves, including Rayleigh waves and SH-SAW waves. A pressure-sensing cavity is provided at the lower end of the silicon-based cover plate above the sensing hole.

[0007] Preferably, both the sensing hole and the pressure-sensing cavity are circular; the piezoelectric sensitive film adopts an equal strength design in the pressure-sensing area, and the thickness of the piezoelectric sensitive film in the pressure-sensing area varies with the distance from the center of the piezoelectric sensitive film (2). The formula for calculating the thickness of the piezoelectric sensitive film is:

[0008]

[0009] Where t(r) is the thickness of the piezoelectric sensitive film at radius r; R is the radius of the piezoelectric sensitive film, i.e., the radius of the sensing hole; μ is the Poisson's ratio of the temperature compensation layer material; r is the distance from the center of the piezoelectric sensitive film; σ max denoted as σ0, where σ0 is the maximum allowable stress of the piezoelectric sensitive film; P is the pressure difference across the piezoelectric sensitive film.

[0010] Preferably, the interdigitated transducer electrode is made of aluminum; the thickness of the interdigitated transducer electrode is 0-100 nm, and the width of the interdigitated fingers is 0-1.5 μm.

[0011] Preferably, the resonator has a metallicity of 0.5, and the center-to-center distance between adjacent interdigital electrodes of the interdigital transducer is 0.5λ, where λ is the wavelength of the sensitive signal.

[0012] Preferably, atmospheric pressure is maintained inside the pressure-sensing cavity, and the surface acoustic wave pressure sensor senses the pressure by the strain of the film caused by the difference in external environmental pressure on both sides of the piezoelectric sensitive film at the sensing hole.

[0013] Preferably, the frequency response of the surface acoustic wave pressure sensor is achieved by measuring the frequency shift of the surface acoustic wave caused by the surface strain of the piezoelectric sensitive film to sense the pressure. The subsequent signal processing circuit then converts the frequency shift caused by the surface strain of the piezoelectric sensitive film into the corresponding pressure signal.

[0014] Preferably, the surface acoustic wave sensor adopts a single-port resonator structure and feeds back the resonant frequency based on the input return loss parameter.

[0015] Preferably, the signal transmission at the input and output ends of the surface acoustic wave sensor is wireless passive, wireless active, or wired active.

[0016] Preferably, the upper edge of the lithium niobate layer is sealed and fixed to the lower end of the silicon-based cover plate by a glass slurry layer.

[0017] After adopting the above technical solution, the present invention has the following beneficial effects: The surface acoustic wave pressure sensor based on the equal-strength thin film design of the present invention includes a silicon substrate, a piezoelectric sensitive film, a resonator, and a silicon-based cover plate. The pressure-sensing region is constructed by etching a stress-balancing groove, forming a temperature-compensating layer and a lithium niobate layer to form a piezoelectric sensitive film. This piezoelectric sensitive film senses the ambient pressure difference, and a resonator is designed to excite and receive Rayleigh waves and SH-SAW waves. The pressure signal is fed back through the shift in the resonant frequency. Simultaneously, the equal-strength design method optimizes the thickness distribution of the piezoelectric sensitive film in the pressure-sensing region, ensuring uniform stress distribution under the maximum allowable stress. In particular, the thickness of the piezoelectric sensitive film gradually increases at the edges to compensate for stress concentration, thereby improving the stability and sensitivity of the surface acoustic wave pressure sensor under high-pressure environments. This surface acoustic wave (SAW) pressure sensor achieves real-time detection of external pressure by measuring the frequency shift of SAW caused by the strain of the piezoelectric sensitive film. The SAW pressure sensor can work reliably in high temperature and high pressure environments, while extending the service life of the SAW pressure sensor and improving the measurement accuracy. It is widely used in aerospace, deep-sea exploration, intelligent manufacturing and other fields. Attached Figure Description

[0018] Figure 1 This is a schematic diagram of the cross-sectional structure of the present invention;

[0019] Figure 2 This is a schematic diagram of the exploded structure of the present invention;

[0020] Figure 3 This is a three-dimensional structural diagram of the silicon-based cover plate of the present invention when it is not installed on the glass slurry layer;

[0021] Figure 4 This is a schematic diagram of the cross-sectional structure of the present invention;

[0022] Figure 5 The stress distribution diagram along the diameter direction of the pressure-sensing zone of the present invention before and after optimization under the maximum allowable stress is shown.

[0023] Figure 6 This is a strain distribution diagram along the diameter direction of the pressure-sensing zone before and after optimization under the maximum allowable stress of the present invention.

[0024] The reference numerals in the figure are as follows:

[0025] 1. Silicon substrate; 10. Sensing hole; 2. Piezoelectric sensitive film; 20. Temperature compensation layer; 200. Stress balancing groove; 21. Lithium niobate layer; 3. Resonator; 30. Interdigitated transducer electrode; 31. Reflective grid; 4. Silicon cover plate; 40. Pressure sensing cavity; 5. Glass slurry layer. Detailed Implementation

[0026] To make the objectives, technical solutions, and advantages of this invention clearer, the invention will be further described in detail below with reference to embodiments. It should be understood that the specific embodiments described herein are merely illustrative and not intended to limit the invention.

[0027] like Figures 1 to 6 As shown, a surface acoustic wave pressure sensor based on an equal-strength thin film design includes a silicon substrate 1, a piezoelectric sensitive film 2, a resonator 3, and a silicon-based cover plate 4. The silicon substrate 1 has a sensing hole 10, the outer end of which is exposed to the external environment to be measured. The piezoelectric sensitive film 2 is formed by stacking a temperature compensation layer 20 and a lithium niobate layer 21, wherein the temperature compensation layer 20 can be made of silicon dioxide or an alloy. The lower edge of the temperature compensation layer 20 is fixedly connected to the upper end of the silicon substrate 1, and the upper edge of the lithium niobate layer 21 is sealed and fixed to the lower end of the silicon-based cover plate 4. The lower end of the temperature compensation layer 20 above the sensing hole 10... A stress balancing groove 200 is provided to achieve equal stress in each region of the pressure-sensing area surface of the piezoelectric sensitive film 2 under the action of the maximum allowable stress; the resonator 3 is composed of interdigitated transducer electrodes 30 and reflective grids 31; the interdigitated transducer electrodes 30 are fixed to the upper middle part of the lithium niobate layer 21, and the reflective grids 31 are respectively fixed on the lithium niobate layers 21 on both sides of the interdigitated transducer electrodes 30; the pressure-sensing area is excited by the resonator 3 to generate a variety of surface acoustic waves including Rayleigh waves and SH-SAW waves; a pressure-sensing cavity 40 is provided at the lower end of the silicon-based cover plate 4 above the sensing hole 10.

[0028] like Figures 1 to 6 As shown, both the sensing hole 10 and the pressure sensing cavity 40 are circular; the piezoelectric sensitive film 2 adopts a uniform strength design in the pressure sensing area, and the thickness of the piezoelectric sensitive film 2 in the pressure sensing area varies with the distance from the center of the piezoelectric sensitive film 2. The formula for calculating the thickness of the piezoelectric sensitive film 2 is as follows:

[0029]

[0030] Where t(r) is the thickness of the piezoelectric sensitive film 2 at a radius of r; R is the radius of the piezoelectric sensitive film 2, i.e., the radius of the sensing hole 10; μ is the Poisson's ratio of the temperature compensation layer 20 material; r is the distance from the center of the piezoelectric sensitive film 2; σ max is the maximum allowable stress of the piezoelectric sensitive film 2; P is the pressure difference across the piezoelectric sensitive film 2.

[0031] like Figures 1 to 6 As shown, the interdigitated transducer electrode 30 is made of aluminum; the thickness of the interdigitated transducer electrode 30 is 0-100nm, and the width of the interdigitated fingers is 0-1.5μm.

[0032] like Figures 1 to 6As shown, the metallicity of the resonator 3 is 0.5, and the center-to-center distance between adjacent interdigital electrodes 30 is 0.5λ, where λ is the wavelength of the sensitive signal.

[0033] like Figures 1 to 6 As shown, atmospheric pressure is maintained inside the pressure-sensing cavity 40, and the surface acoustic wave pressure sensor senses the pressure by sensing the strain of the thin film caused by the difference in external environmental pressure on both sides of the piezoelectric sensitive film 2 at the sensing hole 10.

[0034] like Figures 1 to 6 As shown, the frequency response of the surface acoustic wave pressure sensor is achieved by measuring the frequency shift of the surface acoustic wave caused by the surface strain of the piezoelectric sensitive film 2 to sense the pressure. The subsequent signal processing circuit then converts the frequency shift caused by the surface strain of the piezoelectric sensitive film 2 into the corresponding pressure signal.

[0035] like Figures 1 to 6 As shown, the surface acoustic wave sensor adopts a single-port resonator structure and feeds back the resonant frequency based on the input return loss parameter.

[0036] like Figures 1 to 6 As shown, the signal transmission at the input and output ends of the surface acoustic wave sensor can be wireless passive, wireless active, or wired active.

[0037] like Figures 1 to 6 As shown, the upper edge of the lithium niobate layer 21 is sealed and fixed to the lower end of the silicon-based cover plate 4 by a glass slurry layer 5.

[0038] Simulation and optimization testing:

[0039] The sensor was modeled and optimized using finite element simulation software (such as COMSOL Multiphysics). Before optimization, the lower end of the temperature compensation layer 20 of the sensor did not have a stress balancing groove 200. The stress and strain distribution diagram along the diameter direction of the optimization front of the pressure-sensing zone under the maximum allowable stress is shown in the figure below. Figure 5 , 6 As shown in the left figure; after optimization, a stress balancing groove 200 is provided at the lower end of the temperature compensation layer 20 of the sensor. At this time, the sensor is the surface acoustic wave pressure sensor based on the equal strength thin film design of the present invention. The stress and strain distribution diagram along the diameter direction of the pressure sensing area after optimization under the maximum allowable stress is shown in the figure. Figure 5 , 6 As shown in the right figure.

[0040] The above description is merely a preferred embodiment of the present invention, but the scope of protection of the present invention is not limited thereto. Any variations or substitutions that can be easily conceived by those skilled in the art within the technical scope disclosed in the present invention should be included within the scope of protection of the present invention. Therefore, the scope of protection of the present invention should be determined by the scope of the claims.

Claims

1. A surface acoustic wave pressure sensor based on an equal-strength thin film design, characterized in that, The device includes a silicon substrate (1), a piezoelectric sensitive film (2), a resonator (3), and a silicon-based cover plate (4). The silicon substrate (1) is provided with a sensing hole (10), the outer end of which is exposed to the external environment to be measured. The piezoelectric sensitive film (2) is formed by stacking a temperature compensation layer (20) and a lithium niobate layer (21). The lower edge of the temperature compensation layer (20) is fixedly connected to the upper end of the silicon substrate (1), and the upper edge of the lithium niobate layer (21) is sealed and fixed to the lower end of the silicon-based cover plate (4). A stress balancing groove (200) is provided at the lower end of the temperature compensation layer (20) above the sensing hole (10) for the piezoelectric sensitive film to be tested. The pressure-sensing area of ​​the pressure-sensing thin film (2) reaches equal stress in each region under the maximum allowable stress; the resonator (3) is composed of interdigitated transducer electrodes (30) and reflective grids (31); the interdigitated transducer electrodes (30) are fixed to the middle of the upper end of the lithium niobate layer (21), and the reflective grids (31) are fixed on the lithium niobate layers (21) on both sides of the interdigitated transducer electrodes (30); the pressure-sensing area is excited by the resonator (3) to generate various surface acoustic waves including Rayleigh waves and SH-SAW waves; a pressure-sensing cavity (40) is provided at the lower end of the silicon-based cover plate (4) above the sensing hole (10). Both the sensing hole (10) and the pressure sensing cavity (40) are circular; the piezoelectric sensitive film (2) adopts an equal strength design in the pressure sensing area, and the thickness of the piezoelectric sensitive film (2) in the pressure sensing area varies with the distance from the center of the piezoelectric sensitive film (2). The formula for calculating the thickness of the piezoelectric sensitive film (2) is as follows: in, R is the thickness of the piezoelectric sensitive film (2) at a radius of r; R is the radius of the piezoelectric sensitive film (2), that is, the radius of the sensing hole (10); is the Poisson's ratio of the temperature compensation layer (20) material; r is the distance from the center of the piezoelectric sensitive film (2); is the maximum allowable stress of the piezoelectric sensitive film (2); P is the pressure difference across the piezoelectric sensitive film (2).

2. The surface acoustic wave pressure sensor based on an equal-strength thin film design as described in claim 1, characterized in that: The interdigitated transducer electrode (30) is made of aluminum; the thickness of the interdigitated transducer electrode (30) is 0-100nm, and the width of the interdigitated fingers is 0-1.5μm.

3. The surface acoustic wave pressure sensor based on an equal-strength thin film design as described in claim 1, characterized in that: The resonator (3) has a metallization of 0.5, and the center spacing between adjacent interdigital electrodes (30) is 0.5λ, where λ is the wavelength of the sensitive signal.

4. The surface acoustic wave pressure sensor based on an equal-strength thin film design as described in claim 1, characterized in that: The pressure-sensing cavity (40) maintains atmospheric pressure. The surface acoustic wave pressure sensor senses the pressure by sensing the strain of the piezoelectric sensitive film (2) caused by the difference in external environmental pressure at the sensing hole (10).

5. A surface acoustic wave pressure sensor based on an equal-strength thin film design as described in claim 4, characterized in that: The frequency response of the surface acoustic wave pressure sensor is achieved by measuring the frequency shift of the surface acoustic wave caused by the surface strain of the piezoelectric sensitive film (2). The subsequent signal processing circuit then converts the frequency shift caused by the surface strain of the piezoelectric sensitive film (2) into the corresponding pressure signal.

6. A surface acoustic wave pressure sensor based on an equal-strength thin film design as described in any one of claims 1-5, characterized in that: The surface acoustic wave sensor adopts a single-port resonator structure and feeds back the resonant frequency based on the input return loss parameter.

7. A surface acoustic wave pressure sensor based on an equal-strength thin film design as described in any one of claims 1-5, characterized in that: The signal transmission at the input and output ends of the surface acoustic wave sensor can be wireless passive, wireless active, or wired active.

8. A surface acoustic wave pressure sensor based on an equal-strength thin film design as described in claim 1, characterized in that: The upper edge of the lithium niobate layer (21) and the lower end of the silicon-based cover plate (4) are sealed and fixed by a glass slurry layer (5).

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