Surface acoustic wave pressure sensor based on constant-strength thin film design

Abstract

The invention discloses a surface acoustic wave pressure sensor based on constant-strength thin film design. The surface acoustic wave pressure sensor comprises a silicon substrate, a piezoelectric sensitive thin film, a resonator and a silicon-based cover plate, the silicon substrate is provided with an induction hole, and the outer end of the induction hole is exposed to an external environment to be detected; the piezoelectric sensitive film is formed by laminating and compounding a temperature compensation layer and a lithium niobate layer; the lower end edge of the temperature compensation layer is fixedly connected with the upper end of the silicon substrate; the upper end edge of the lithium niobate layer is hermetically fixed with the lower end of the silicon-based cover plate; a stress balance groove is formed in the lower end of the temperature compensation layer above the sensing hole and is used for achieving equal stress in each area on the surface of the pressure sensing area of the piezoelectric sensitive film under the action of maximum allowable stress; the resonator is composed of an interdigital transducer electrode and a reflecting grating; the interdigital transducer electrode is fixed in the middle of the upper end of the lithium niobate layer; the reflecting gratings are respectively fixed on the lithium niobate layer on two sides of the interdigital transducer electrode; and a pressure sensing cavity is arranged at the lower end of the silicon-based cover plate above the sensing hole.

Description

Technical Field

[0001] The invention belongs to the technical field of pressure sensors, and in particular relates to a surface acoustic wave pressure sensor based on an equal-strength film design. Background Art

[0002] Pressure sensors are widely used in many industrial fields, especially in high-precision environments such as aerospace, deep-sea exploration, and intelligent manufacturing, where environmental pressure monitoring is usually required. Traditional pressure sensors are generally difficult to miniaturize and measure pressure signals with high precision, and are difficult to adapt to wireless passive technology. In recent years, sensors based on surface acoustic wave (SAW) technology have shown good performance in environmental pressure monitoring, especially in terms of sensor sensitivity and accuracy.

[0003] However, existing SAW pressure sensors still have certain problems in terms of stress distribution. When a pressure-sensitive film of equal thickness is under pressure, the stress and strain distribution is often uneven. The stress at the fixed edge is large, which leads to unstable performance of the sensor under high-pressure environment, affecting its measurement accuracy and range. In addition, the uneven strain will cause sensor signal crosstalk and excessive bandwidth, resulting in a sharp drop in the device Q value. Therefore, how to optimize the design of the pressure-sensitive film so that its surface stress distribution is uniform under maximum stress and the sharp drop in the device Q value caused by uneven strain has become a key issue in improving sensor performance. Summary of the invention

[0004] In order to solve the above problems, the present invention proposes a surface acoustic wave pressure sensor based on an equal-strength film design.

[0005] To achieve the above object, the present invention adopts the following technical solutions:

[0006] A surface acoustic wave pressure sensor based on equal-strength film design comprises a silicon substrate, a piezoelectric sensitive film, a resonator and a silicon-based cover plate; the silicon substrate is provided with a sensing hole, the outer end of the sensing hole 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 to form a composite film; the lower edge of the temperature compensation layer is fixedly connected to the upper end of the silicon substrate, and the upper edge of the lithium niobate layer is sealed and fixed to the lower end 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, which is used to achieve equal stress in various areas of the surface of the pressure-sensitive area of ​​the piezoelectric sensitive film under the maximum allowable stress; the resonator is composed of an interdigital transducer electrode and a reflection grid; the interdigital transducer electrode is fixed to the middle of the upper end of the lithium niobate layer, and the reflection grid is respectively fixed on the lithium niobate layer on both sides of the interdigital transducer electrode, and the pressure-sensitive area generates a variety of surface acoustic waves including Rayleigh waves and SH-SAW waves through resonator excitation; a pressure-sensing cavity is provided at the lower end of the silicon-based cover plate above the sensing hole.

[0007] Preferably, the sensing hole and the pressure sensing cavity are both circular; the piezoelectric sensitive film is designed with equal strength in the pressure sensing area, and the thickness of the piezoelectric sensitive film in the pressure sensing area changes with the distance from the center of the piezoelectric sensitive film (2). The thickness calculation formula of the piezoelectric sensitive film is:

[0008]

[0009] Wherein, t(r) is the thickness of the piezoelectric sensitive film at the radius r; R is the radius of the piezoelectric sensitive film, that is, 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 is the maximum allowable stress of the piezoelectric sensitive film; P is the pressure difference on both sides of the piezoelectric sensitive film.

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

[0011] Preferably, the metal ratio of the resonator is 0.5, and the center spacing between adjacent fingers of the interdigital transducer electrode is 0.5λ, where λ is the wavelength of the sensitive signal.

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

[0013] Preferably, the frequency response of the surface acoustic wave pressure sensor senses the pressure by measuring the surface acoustic wave frequency shift caused by the surface strain of the piezoelectric sensitive film, and the subsequent signal processing circuit converts the frequency shift caused by the surface strain of the piezoelectric sensitive film into a corresponding pressure signal.

[0014] Preferably, the surface acoustic wave sensor adopts a single-port resonator structure, and the resonant frequency is fed back according to an input return loss parameter.

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

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

[0017] After adopting the above technical scheme, the present invention has the following beneficial effects: the surface acoustic wave pressure sensor based on equal-intensity film design of the present invention includes a silicon substrate, a piezoelectric sensitive film, a resonator and a silicon-based cover plate. The temperature compensation layer of the stress balance groove is constructed by etching technology in the pressure-sensing area and the lithium niobate layer is composited to form a piezoelectric sensitive film, the environmental pressure difference is sensed by the piezoelectric sensitive film, and a resonator is designed to realize the excitation and reception of Rayleigh waves and SH-SAW waves, and the pressure signal is fed back by the shift of the resonant frequency; at the same time, the equal-intensity design method is used to optimize the thickness distribution of the piezoelectric sensitive film in the pressure-sensing area, so that the stress can be evenly distributed under the maximum allowable stress of the piezoelectric sensitive film, especially the edge part of the piezoelectric sensitive film is designed with a gradually increasing thickness to compensate for the stress concentration at the edge, thereby improving the stability and sensitivity of the surface acoustic wave pressure sensor in a high-pressure environment. The surface acoustic wave pressure sensor realizes real-time detection of external pressure by measuring the surface acoustic wave frequency shift caused by the strain of piezoelectric sensitive film. The surface acoustic wave pressure sensor can work reliably in high temperature and high pressure environment, while extending the service life of the surface acoustic wave pressure sensor and improving the measurement accuracy. It is widely used in aerospace, deep sea exploration, intelligent manufacturing and other fields. BRIEF DESCRIPTION OF THE DRAWINGS

[0018] Figure 1 It is a schematic diagram of the cutaway structure of the present invention;

[0019] Figure 2 It is a schematic diagram of the explosion structure of the present invention;

[0020] Figure 3 It is a schematic diagram of the three-dimensional structure when the silicon-based cover plate of the present invention is not installed on the glass paste layer;

[0021] Figure 4 It is a schematic diagram of the cutaway structure of the present invention;

[0022] Figure 5 The stress distribution diagram of the pressure-sensitive area of ​​the present invention along the diameter direction before and after optimization under the maximum allowable stress;

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

[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 balance groove; 21. Lithium niobate layer; 3. Resonator; 30. Interdigital transducer electrode; 31. Reflection grid; 4. Silicon-based cover plate; 40. Pressure-sensitive cavity; 5. Glass slurry layer. DETAILED DESCRIPTION

[0026] In order to make the purpose, technical solution and advantages of the present invention more clearly understood, the present invention is further described in detail below in conjunction with the embodiments. It should be understood that the specific embodiments described herein are only used to explain the present invention and are not used to limit the present invention.

[0027] like Figures 1 to 6 As shown, a surface acoustic wave pressure sensor based on equal strength 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 is provided with a sensing hole 10, and the outer end of the sensing hole 10 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 to form a composite film, wherein the material of the temperature compensation layer 20 can be 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 1 ... A stress balancing groove 200 is provided to achieve equal stress in each area of ​​the surface of the pressure-sensitive area of ​​the piezoelectric sensitive film 2 under the maximum allowable stress; the resonator 3 is composed of an interdigital transducer electrode 30 and a reflection grid 31; the interdigital transducer electrode 30 is fixed to the middle of the upper end of the lithium niobate layer 21, and the reflection grid 31 is respectively fixed on the lithium niobate layer 21 on both sides of the interdigital transducer electrode 30, and the pressure-sensitive 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, the sensing hole 10 and the pressure sensing cavity 40 are both 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 changes with the distance from the center of the piezoelectric sensitive film 2. The thickness calculation formula of the piezoelectric sensitive film 2 is:

[0029]

[0030] Wherein, t(r) is the thickness of the piezoelectric sensitive film 2 at the radius r; R is the radius of the piezoelectric sensitive film 2, that is, the radius of the sensing hole 10; μ is the Poisson's ratio of the material of the temperature compensation layer 20; 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 on both sides of the piezoelectric sensitive film 2.

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

[0032] like Figures 1 to 6As shown, the metal ratio of the resonator 3 is 0.5, and the center spacing between adjacent fingers of the interdigital transducer electrode 30 is 0.5λ, where λ is the wavelength of the sensitive signal.

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

[0034] like Figures 1 to 6 As shown, the frequency response of the surface acoustic wave pressure sensor senses the pressure by measuring the surface acoustic wave frequency shift caused by the surface strain of the piezoelectric sensitive film 2. The subsequent signal processing circuit converts the frequency shift caused by the surface strain of the piezoelectric sensitive film 2 into a 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 according to the input return loss parameter.

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

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

[0038] Simulation and optimization testing:

[0039] Finite element simulation software (such as COMSOL Multiphysics) is used to model and optimize the sensor. Before optimization, the stress balance groove 200 is not set at the lower end of the temperature compensation layer 20 of the sensor. The stress and strain distribution diagram of the pressure sensing area in the optimization front diameter direction under the maximum allowable stress is as follows: Figure 5 , 6 As shown in the left figure in the figure; after optimization, a stress balance 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 film design of the present invention. The stress and strain distribution diagram of the pressure sensing area along the diameter direction after optimization under the maximum allowable stress is as shown in Figure 5 , 6 As shown in the right figure.

[0040] The above is only a preferred specific embodiment of the present invention, but the protection scope of the present invention is not limited thereto. Any changes or substitutions that can be easily thought of by a person skilled in the art within the technical scope disclosed by the present invention should be included in the protection scope of the present invention. Therefore, the protection scope of the present invention should be based on the protection scope of the claims.

Claims

1. A surface acoustic wave pressure sensor based on an equal strength film design, characterized in that: The invention comprises 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 the sensing hole (10) being exposed to an 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) to form a film; 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) is provided with a stress balancing groove (200) for balancing the stress at the piezoelectric sensitive film. Each area on the surface of the pressure-sensitive area of ​​the sensing film (2) reaches equal stress under the action of the maximum allowable stress; the resonator (3) is composed of an interdigital transducer electrode (30) and a reflective grid (31); the interdigital transducer electrode (30) is fixed to the middle of the upper end of the lithium niobate layer (21), and the reflective grid (31) is respectively fixed to the lithium niobate layer (21) on both sides of the interdigital transducer electrode (30); the pressure-sensitive area is excited by the resonator (3) to generate a variety of surface acoustic waves including Rayleigh waves and SH-SAW waves; and a pressure-sensitive cavity (40) is provided at the lower end of the silicon-based cover plate (4) above the sensing hole (10).

2. A surface acoustic wave pressure sensor based on equal strength film design as claimed in claim 1, characterized in that: The sensing hole (10) and the pressure sensing cavity (40) are both circular; the piezoelectric sensitive film (2) is designed with equal strength in the pressure sensing area; the thickness of the piezoelectric sensitive film (2) in the pressure sensing area changes with the distance from the center of the piezoelectric sensitive film (2); the thickness calculation formula of the piezoelectric sensitive film (2) is: Wherein, 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), that is, the radius of the sensing hole (10); μ is the Poisson's ratio of the material of the temperature compensation layer (20); 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); and P is the pressure difference between the two sides of the piezoelectric sensitive film (2).

3. A surface acoustic wave pressure sensor based on equal strength film design as claimed in claim 1, characterized in that: The material of the interdigital transducer electrode (30) is aluminum; the thickness of the interdigital transducer electrode (30) is 0-100 nm, and the width of the interdigital fingers is 0-1.5 μm.

4. A surface acoustic wave pressure sensor based on equal strength film design as claimed in claim 1, characterized in that: The metal ratio of the resonator (3) is 0.5, and the center spacing between adjacent interdigital transducer electrodes (30) is 0.5λ, where λ is the wavelength of the sensitive signal.

5. A surface acoustic wave pressure sensor based on equal strength film design as claimed in claim 1, characterized in that: The pressure sensing cavity (40) maintains atmospheric pressure, and the surface acoustic wave pressure sensor senses pressure through the film strain caused by the difference in external environmental pressure at the sensing hole (10) on both sides of the piezoelectric sensitive film (2).

6. A surface acoustic wave pressure sensor based on equal strength film design as claimed in claim 5, characterized in that: The frequency response of the surface acoustic wave pressure sensor realizes pressure sensing by measuring the surface acoustic wave frequency deviation caused by the surface strain of the piezoelectric sensitive film (2), and the subsequent signal processing circuit converts the frequency deviation caused by the surface strain of the piezoelectric sensitive film (2) into a corresponding pressure signal.

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

8. A surface acoustic wave pressure sensor based on an equal-strength film design as claimed in any one of claims 1 to 6, characterized in that: The signal transmission at the input end and the output end of the surface acoustic wave sensor is of wireless passive type, wireless active type or wired active type.

9. A surface acoustic wave pressure sensor based on equal strength film design as claimed 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 via a glass slurry layer (5).

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