Surface acoustic wave sensor and packaging structure thereof

Abstract

The invention provides a surface acoustic wave sensor and a packaging structure thereof, based on a POI piezoelectric substrate and a multifunctional reflecting grating layout, temperature, pressure and acceleration sensing units are highly integrated on a single chip, and in order to realize decoupling of multiple sensing quantities, two reference gates located on two sides of a uniform interdigital transducer are respectively designed, so that the sensor can be used for realizing multi-sensing-quantity decoupling. The two reference gates are used for differential time delay measurement of sensitive quantities, the temperature measurement reflecting gate is arranged close to the reference gates, it is effectively guaranteed that temperature measurement is not affected by other sensing quantities, and environmental noise interference is effectively restrained; efficient separation and synchronous detection of temperature, pressure and acceleration multi-parameter signals are achieved, and the electromagnetic coupling problem of a traditional multi-interdigital transducer structure is avoided; the packaging structure of the surface acoustic wave sensor adopts an SMD packaging structure, the overall structure of the device is compact, and the installation difficulty and the system maintenance cost in a complex environment are greatly reduced.

Description

TECHNICAL FIELD

[0001] The present application belongs to the technical field of sensors, and particularly relates to a surface acoustic wave sensor and a packaging structure thereof. BACKGROUND

[0002] A surface acoustic wave (SAW) sensor is a passive wireless sensor based on piezoelectric effect and acoustic wave propagation characteristics. Its working principle is to excite and receive surface acoustic waves through interdigital transducers (IDT) on the surface of a piezoelectric substrate, and to realize sensing by using the modulation effect of external physical quantities (such as temperature, pressure, acceleration, etc.) on the acoustic wave propagation characteristics. Compared with traditional wired sensors, SAW sensors have the advantages of small size, high sensitivity, anti-electromagnetic interference, and no need for external power supply, and have been widely used in aerospace, industrial monitoring, medical devices, etc.

[0003] However, existing SAW sensors are mostly limited to single-parameter detection and lack integrated design. For example, when monitoring temperature parameters, it is not possible to simultaneously monitor pressure, strain and other parameters. This single-parameter detection mode results in the need to deploy multiple independent sensors to cover the requirements of temperature, pressure, acceleration and other parameters in complex application scenarios (such as aircraft state monitoring and engine health diagnosis). This not only greatly increases the system complexity and wiring cost, but also reduces the overall reliability due to space competition and signal interference between sensors.

[0004] In recent years, although some research has attempted to integrate multi-parameter detection functions into a single SAW sensor, there are still significant defects. A few sensors that can achieve multi-parameter detection use a multi-group interdigital transducer (IDT) and reflector stack design, and use discrete reflectors to achieve differential measurement, but they have limitations in terms of integration, signal separation efficiency, etc. Such structures not only increase signal transmission loss, but also cause cross interference due to multi-physical field coupling, and too many reflectors make it difficult to miniaturize the device, making it difficult to meet the application requirements in narrow spaces. In addition, the increase in the number of reflectors also increases the process complexity, affecting the yield and consistency of the device.

[0005] In summary, existing SAW sensors have significant shortcomings in multi-parameter integration, miniaturization and anti-interference capability. Developing a new integrated SAW sensor with compact structure that can simultaneously detect temperature, pressure and acceleration with high precision is a key requirement to break through the bottleneck of real-time monitoring of multiple physical quantities in complex conditions. SUMMARY

[0006] In view of the shortcomings of the prior art described above, the purpose of the present application is to provide a surface acoustic wave sensor and a packaging structure thereof, which solves the problems of single function, large size and low anti-interference capability of the prior art surface acoustic wave sensor.

[0007] To achieve the above and other related objectives, the present invention provides a surface acoustic wave (SAW) sensor, comprising: a piezoelectric substrate, a uniform interdigital SAW transducer, a temperature measurement reflective grating, a pressure measurement reflective grating, an acceleration measurement reflective grating, and two reference gratings disposed on the piezoelectric substrate, and bonded to a substrate under the piezoelectric substrate; wherein,

[0008] The uniform interdigital transducer is used to excite and receive surface acoustic waves.

[0009] The piezoelectric substrate is a POI piezoelectric substrate composed of a high-resistivity substrate layer, an insulating layer and a piezoelectric single crystal layer;

[0010] The two reference grids are respectively disposed on both sides near the uniform interdigital transducer;

[0011] The pressure measurement reflective grating and the acceleration measurement reflective grating are respectively disposed on two sides away from the uniform interdigital transducer;

[0012] The temperature measurement reflective grid is disposed between the reference grid and the pressure measurement reflective grid, which are located on the same side of the uniform interdigital transducer as the pressure measurement reflective grid.

[0013] The substrate exposes at least the piezoelectric substrate beneath the acceleration measurement reflective grating to form a cantilever beam;

[0014] A pressure measuring cavity is formed in the piezoelectric substrate between the temperature measuring reflective grating and the pressure measuring reflective grating, penetrating the high-resistivity substrate layer and the insulating layer.

[0015] Optionally, the material of the piezoelectric single crystal layer in the piezoelectric substrate is lithium niobate, lithium tantalate, quartz, lead zirconate titanate, or aluminum nitride; the insulating layer is a silicon dioxide layer, a silicon nitride layer, or an aluminum oxide layer; and the high-resistivity substrate layer is a high-resistivity silicon layer, a high-resistivity silicon carbide layer, or a high-resistivity gallium arsenide layer.

[0016] Optionally, the high-resistivity substrate layer is a high-resistivity silicon layer, the substrate is a glass substrate, and the high-resistivity substrate layer and the substrate are pre-formed with an alumina transition layer at the bonding interface and bonded based on a low-temperature anodic bonding process.

[0017] Optionally, a mass block is fixed under the piezoelectric substrate below the acceleration measurement reflective grating.

[0018] Furthermore, the cantilever beam extends at least to the reference gate near its side, and the cantilever beam is provided with a micropore slit sensitization structure in the acceleration sensitive region. The micropore slit sensitization structure is a plurality of micropores and / or microslits extending inward from the lower surface of the high-resistivity substrate towards the piezoelectric single crystal layer and extending to a depth not exceeding the thickness of the high-resistivity substrate.

[0019] Optionally, the metal electrode of the uniform interdigital transducer is an aluminum film electrode, the line width is 0.5-1.0 μm, the interval is 0.5-1.0 μm, the number of interdigital pairs is 20-50, the length is 50-200 μm, and the length is consistent along the propagation direction of the surface acoustic wave, the surface acoustic wave is excited towards both sides, and the working frequency is in a frequency range of 10 MHz-10 GHz.

[0020] The application further provides a surface acoustic wave sensor packaging structure, which comprises the surface acoustic wave sensor, a cover plate and a containing base according to any one of the above.

[0021] The surface acoustic wave sensor is contained in the containing base.

[0022] The cover plate is buckled on the containing base to form an SMD packaging structure.

[0023] An antenna is fixed below the containing base.

[0024] Optionally, the cover plate is a glass cover plate, and the containing base is a ceramic base.

[0025] Optionally, the packaging structure further comprises a soldering binding lead wire, which is electrically connected with the uniform interdigital transducer.

[0026] Further, the soldering binding lead wire is a gold wire, a silicon-aluminum wire or a platinum wire.

[0027] Optionally, the packaging structure further comprises a gas permeation hole, which is arranged on the cover plate or the bottom wall of the containing base; when the gas permeation hole is arranged on the cover plate, the gas permeation hole penetrates the cover plate and is located above the pressure measuring cavity; when the gas permeation hole is arranged on the bottom wall of the containing base, the gas permeation hole penetrates the bottom wall of the containing base and the substrate of the surface acoustic wave sensor to communicate with the pressure measuring cavity.

[0028] Further, when the gas permeation hole is arranged on the cover plate, the pressure measuring cavity forms a sealed space and is filled with inert gas; when the gas permeation hole is arranged on the bottom wall of the containing base, a sealed space is formed between the cover plate and the piezoelectric substrate and is filled with inert gas.

[0029] Optionally, the packaging structure further comprises an overload damping block, which is arranged on the inner wall of the cover plate and / or the inner side of the bottom wall of the containing base and corresponds to the acceleration measurement reflection grating area of the surface acoustic wave sensor.

[0030] Further, the material of the overload damping block is a silicon rubber material.

[0031] As described above, the surface acoustic wave sensor and the packaging structure thereof according to the present application, based on the POI piezoelectric substrate and the multi-functional reflective grating layout, highly integrate the temperature, pressure and acceleration sensitive units in a single chip, and in the design, not only the structural optimization of a single sensor in the prior art is considered, but also the cross-coupling effect between multiple sensors in the prior art is considered. In order to realize the decoupling of multiple sensing quantities, two groups of reference reflective gratings are respectively designed, that is, two reference gratings located on both sides of the uniform interdigital transducer, and a group of acceleration measurement reflective gratings, temperature measurement reflective gratings and pressure measurement reflective gratings. The two reference gratings are used for differential time delay measurement of the sensitive quantity, the temperature measurement reflective grating is arranged close to the reference grating, which effectively ensures that the temperature measurement is not affected by other sensing quantities and effectively suppresses the environmental noise interference; the acceleration measurement reflective grating and the pressure measurement reflective grating are arranged on both sides of the uniform interdigital transducer, which can not only realize the measurement of pressure and acceleration, but also effectively avoid the cross-sensitivity effect of pressure and acceleration physical quantities; the response signal of the temperature measurement reflective grating not only provides an independent temperature measurement value, but also serves as a reference parameter for dynamic compensation of pressure and acceleration signals. For example, the delay time variation of the pressure measurement reflective grating contains the thermal expansion effect of the piezoelectric single crystal layer caused by temperature, and by deducting the linear contribution of the temperature component, the net deformation quantity caused by pressure can be accurately extracted. The sensitivity of the acceleration measurement reflective grating is affected by temperature drift, and the temperature signal is used to correct the elastic modulus variation of the cantilever beam in real time, thereby ensuring the temperature stability of the acceleration measurement. In this way, efficient separation and synchronous detection of temperature, pressure and acceleration multi-quantity signals are realized, and the electromagnetic coupling problem of the traditional multi-interdigital transducer structure is avoided. The surface acoustic wave sensor packaging structure adopts the SMD packaging structure, the overall structure of the device is compact, and the installation difficulty and system maintenance cost in a complex environment are greatly reduced. BRIEF DESCRIPTION OF DRAWINGS

[0032] Figures 1 to 3 Structure schematic diagrams of four examples of the surface acoustic wave sensor according to the present application are shown.

[0033] Figure 4 A working principle schematic diagram of the surface acoustic wave sensor according to the present application is shown.

[0034] Figures 5 to 7 Structure schematic diagrams of three examples of the surface acoustic wave sensor packaging structure according to the present application are shown.

[0035] Element number explanation

[0036] 10 surface acoustic wave sensor

[0037] 11 piezoelectric substrate

[0038] 110 high-resistance substrate layer

[0039] 111 insulating layer

[0040] 112 piezoelectric single crystal layer

[0041] 113 cantilever beam

[0042] 12 uniform interdigital transducer

[0043] 13 reference grating

[0044] 130 first reference grating

[0045] 131 second reference grating

[0046] 14 temperature measurement reflection grating

[0047] 15 pressure measurement reflection grating

[0048] 150 pressure measurement cavity

[0049] 16 acceleration measurement reflection grating

[0050] 160 mass

[0051] 161 micro-hole gap sensitization structure

[0052] 17 substrate

[0053] 18 surface acoustic wave sensor package structure

[0054] 19 cover plate

[0055] 20 accommodating base

[0056] 21 soldered binding lead

[0057] 22 air vent

[0058] 23 overload damping block

[0059] 24 antenna DETAILED DESCRIPTION

[0060] The present application is herein described, by way of example only, with reference to certain embodiments thereof. It is to be understood that the terminology used herein is for the purpose of describing specific embodiments only and is not intended to be limiting, since the scope of the present application will be limited only by the appended claims. Numerous specific aspects of the application are set forth in the following description.

[0061] Reference will now be made to the drawings, wherein: Figures 1 to 7 It is to be understood that the above-referenced elements of the present application are merely suggested examples of components of different embodiments of the present application and that actual implementation of the present application in specific applications can utilize different components or different component arrangements or structures.

[0062] Example 1

[0063] like Figures 1 to 3 As shown, this embodiment provides a surface acoustic wave (SAW) sensor 10, which includes: a piezoelectric substrate 11, a uniform interdigital transducer 12, a temperature measurement reflection grating 14, a pressure measurement reflection grating 15, an acceleration measurement reflection grating 16, and two reference gratings 13 disposed on the piezoelectric substrate 11, and a substrate 17 bonded to the piezoelectric substrate 11; wherein, the uniform interdigital transducer 12 is used to excite and receive surface acoustic waves; the piezoelectric substrate 11 is a POI piezoelectric substrate composed of a high-resistivity substrate layer 110, an insulating layer 111, and a piezoelectric single crystal layer 112; the two reference gratings 13 are respectively disposed near the uniform interdigital transducer 12. Both sides; the pressure measurement reflective grating 15 and the acceleration measurement reflective grating 16 are respectively disposed on both sides away from the uniform interdigital transducer 12; the temperature measurement reflective grating 14 is disposed between the reference grating 13 and the pressure measurement reflective grating 15, which are located on the same side of the uniform interdigital transducer 12 as the pressure measurement reflective grating 15; the substrate 17 exposes at least the piezoelectric substrate 11 below the acceleration measurement reflective grating 16 to form a cantilever beam 113; a pressure measuring cavity 150 is formed in the piezoelectric substrate 11 between the temperature measurement reflective grating 14 and the pressure measurement reflective grating 15, penetrating the high-resistivity substrate layer 110 and the insulating layer 111.

[0064] A uniform interdigital transducer is a surface acoustic wave (SAW) device based on the piezoelectric effect. Its main function is to convert electrical signals into acoustic signals through electroacoustic conversion. In its working principle, the uniform interdigital transducer consists of two sets of cross-arranged metal combs. Each set of combs consists of multiple electrode strips of equal width and spacing, which are alternately arranged and connected to the input and output ports. When a high-frequency electrical signal is applied to the input port, the electric field generates a piezoelectric effect between the electrodes, thereby exciting SAW waves on the surface of the piezoelectric substrate. These sound waves propagate along the surface at a specific frequency. Simultaneously, when the sound waves reach the output port, the SAW waves convert acoustic energy into electrical signals through the inverse piezoelectric effect, thus realizing signal transmission and processing. In this embodiment, the uniform interdigital transducer 12 is used to excite and receive SAW waves, i.e., it is a transceiver integrated device.

[0065] like Figure 4In practical applications, the reader generally emits a point frequency pulse signal, which is received by the signal transmission device, such as an antenna, and is converted into a surface acoustic wave by the uniform interdigital transducer 12. The surface acoustic wave propagates outward along the piezoelectric single crystal layer 112 in the piezoelectric substrate 11 to both sides of the uniform interdigital transducer 12, is partially reflected by the first reference grating 130 on the left side of the uniform interdigital transducer 12, the temperature measurement reflective grating 14, and the pressure measurement reflective grating 15, and is partially reflected by the second reference grating 131 on the right side of the uniform interdigital transducer 12 and the acceleration measurement reflective grating 16. The reflected surface acoustic wave is reconverted into an electrical signal by the uniform interdigital transducer 12 and is transmitted back to the reader through the antenna. By analyzing the time delay difference and frequency characteristics of each reflective grating, the signal components corresponding to temperature, pressure, and acceleration are separated, that is, the surface acoustic wave sensor structure of the embodiment realizes independent detection of temperature, pressure, and acceleration through a delay line structure. Specifically:

[0066] 1. The independent detection principle for temperature is that when the detected temperature changes, the temperature change will cause the change of the surface acoustic wave propagation speed v(T), thereby changing the surface acoustic wave propagation time delay τ. The temperature measurement principle formula is:

[0067]

[0068] Δτ T =Δτ 温度栅 -Δτ 参考栅2

[0069]

[0070] wherein TCD is the temperature coefficient of the piezoelectric single crystal layer 112, with a unit of ppm / ℃; ΔT is the temperature change amount; τ0 is the reference propagation time delay of the surface acoustic wave between the uniform interdigital transducer 12 and the temperature measurement reflective grating 14, which is calculated by the phase of the return wave obtained by the reader; Δτ is the delay time change amount, for example, Δτ 温度栅 is the delay time change amount of the surface acoustic wave between the uniform interdigital transducer 12 and the temperature measurement reflective grating 14, Δτ 参考栅 2 is the delay time change amount of the surface acoustic wave between the uniform interdigital transducer 12 and the first reference grating 130, Δτ T is the delay time change amount of the surface acoustic wave between the temperature measurement reflective grating 14 and the first reference grating 130; l is the distance between the uniform interdigital transducer 12 and the temperature measurement reflective grating 14, v s is the propagation speed of the surface acoustic wave.

[0071] 2、For the independent detection principle of pressure is: when the pressure has changed, the pressure acting on the sensor sensitive area, resulting in piezoelectric single crystal layer 112 stress change, and then affect the surface acoustic wave propagation delay τ. Pressure measurement principle formula is:

[0072]

[0073] Δτ P = Δτ 压力栅 - Δτ 温度栅

[0074] Wherein, PCD for piezoelectric single crystal layer 112 pressure sensitivity coefficient, unit is ppm / Pa; ΔP for pressure change; τ0 for surface acoustic wave in uniform interdigital transducer 12 and pressure measurement reflector 15 between the propagation delay; Δτ 压力栅 For surface acoustic wave in uniform interdigital transducer 12 and pressure measurement reflector 15 between the delay time change, Δτ 温度栅 For surface acoustic wave in uniform interdigital transducer 12 and temperature measurement reflector 14 between the delay time change, Δτ P For surface acoustic wave in pressure measurement reflector 15 and temperature measurement reflector 14 between the delay time change.

[0075] 3、For the independent detection principle of acceleration is: when the acceleration has changed, the acceleration causes the deformation of cantilever beam 113 (such as Figure 1 Indicated) lead to piezoelectric single crystal layer 112 stress distribution change, so as to change the surface acoustic wave propagation delay τ. Acceleration measurement principle formula is:

[0076]

[0077] Δτ a = Δτ 加速度栅 - Δτ 参考栅1

[0078] Wherein, ACD for piezoelectric single crystal layer 112 acceleration sensitivity coefficient, unit is ppm / (m / s 2 ); ΔA for acceleration change; τ0 for surface acoustic wave in uniform interdigital transducer 12 and acceleration measurement reflector 16 between the propagation delay; Δτ 加速度栅 For surface acoustic wave in uniform interdigital transducer 12 and acceleration measurement reflector 16 between the delay time change, Δτ 参考栅 1For surface acoustic wave in uniform interdigital transducer 12 and the second reference grid 131 between the delay time change, Δτ a For surface acoustic wave in acceleration measurement reflector 16 and the second reference grid 131 between the delay time change.

[0079] The surface acoustic wave sensor of the embodiment is based on the POI piezoelectric substrate and the multi-functional reflective grating layout, and integrates temperature, pressure and acceleration sensitive units in a single chip. In the design, not only the structure optimization of a single sensor in the prior art is considered, but also the cross coupling between multiple sensors in the prior art is considered. In order to realize the decoupling of multiple sensing quantities, two groups of reference reflective gratings are designed, that is, two reference gratings located on both sides of the uniform interdigital transducer, and a group of acceleration measurement reflective gratings, temperature measurement reflective gratings and pressure measurement reflective gratings. The two reference gratings are used for differential time delay measurement of the sensitive quantity, the temperature measurement reflective grating is arranged close to the reference grating, which effectively ensures that the temperature measurement is not affected by other sensing quantities and effectively suppresses the environmental noise interference; the acceleration measurement reflective grating and the pressure measurement reflective grating are arranged on both sides of the uniform interdigital transducer, which can not only realize the measurement of pressure and acceleration, but also effectively avoid the cross-sensitivity effect of pressure and acceleration physical quantities; the response signal of the temperature measurement reflective grating not only provides an independent temperature measurement value, but also serves as a reference parameter for dynamic compensation of pressure and acceleration signals. For example, the delay time variation of the pressure measurement reflective grating contains the thermal expansion effect of the piezoelectric single crystal layer caused by temperature, and by deducting the linear contribution of the temperature component, the net deformation quantity caused by pressure can be accurately extracted. The sensitivity of the acceleration measurement reflective grating is affected by temperature drift, and the temperature signal is used to correct the elastic modulus change of the cantilever beam in real time, thereby ensuring the temperature stability of the acceleration measurement. In this way, efficient separation and synchronous detection of temperature, pressure and acceleration multi-quantity signals are realized, the electromagnetic coupling problem of the traditional multi-interdigital transducer structure is avoided, the overall structure of the sensor is compact, the installation difficulty and system maintenance cost in a complex environment are greatly reduced, and the sensor is especially suitable for high-density monitoring scenes with limited space.

[0080] As shown in Figure 1 As an example, the material of the piezoelectric single crystal layer 112 in the piezoelectric substrate 11 can be selected from lithium niobate, lithium tantalate, quartz, lead zirconate titanate or aluminum nitride, the insulating layer 111 can be selected from a silicon dioxide layer or a silicon nitride layer or an aluminum oxide layer, and the high-resistance substrate layer 110 can be selected from a high-resistance silicon layer or a high-resistance silicon carbide layer or a high-resistance gallium arsenide layer, but is not limited thereto. Other suitable materials as POI piezoelectric substrates can also be used, which can be selected according to actual needs.

[0081] As a preferred example, the high-resistance substrate layer 110 is a high-resistance silicon layer, the substrate 17 is a glass substrate, and the high-resistance substrate layer 110 and the substrate 17 are bonded together based on a low-temperature anodic bonding process with an aluminum oxide transition layer (not shown in the figure) formed on the bonding interface. This bonding method can alleviate the difference in thermal expansion coefficient between the piezoelectric single crystal layer 112 and the high-resistance silicon substrate layer 110, and avoid bonding failure at high temperature.

[0082] It should be noted that the propagation direction of the surface acoustic wave in the embodiment is along the direction of the interdigital arrangement of the uniform interdigital transducer 12, so the corresponding reflection grating and reference grating are arranged on both sides of the direction of the interdigital arrangement of the uniform interdigital transducer 12, and the specific structure of the reflection grating and the reference grating is not limited too much, as long as the surface acoustic wave signal can be reflected. For example, the reflection grating and the reference grating in the embodiment are metal strips, which can be formed at the same time as the uniform interdigital transducer 12 to save the preparation process.

[0083] As an example, for a surface acoustic wave sensor with a frequency range of 10 MHz to 10 GHz, the parameters of the uniform interdigital transducer 12 are selected as follows: the metal electrode is an aluminum film electrode, the line width is 0.5 μm to 1.0 μm, the pitch is 0.5 μm to 1.0 μm, the number of interdigital pairs is 20 to 50, the length is 50 μm to 200 μm, and the direction of propagation of the surface acoustic wave is consistent. The surface acoustic wave is excited to the two sides. For other operating frequencies, the parameters of the uniform interdigital transducer 12 are adjusted accordingly, and the specific selection is made according to actual needs.

[0084] As shown in Figure 2 As a preferred example, the mass 160 is fixed below the piezoelectric substrate 11 below the acceleration measurement reflection grating 16, that is, the mass 160 is arranged at the end of the cantilever beam 113. The mass 160 can be made of glass, for example. The mass 160 can increase the vibration inertia of the cantilever beam, increase the bending deformation of the cantilever beam 113, thereby providing an amplified inertial stress to the POI piezoelectric substrate to change the surface acoustic wave propagation time delay, improve the acceleration measurement sensitivity and measurement range, and at the same time ensure the stability of the high-frequency vibration signal response.

[0085] As shown in Figure 3 As another preferred example, the cantilever beam 113 extends at least to the reference grating 13 on the side, for example, Figure 3 As shown in Figure 3The extension depth of the micro-hole and micro-slit sensitizing structure 161 in the middle of the piezoelectric substrate 11 is just the thickness of the high-resistance substrate layer 110, and in practice, it can also not exceed the thickness of the high-resistance substrate layer 110. In addition, the shape and size of the micro-hole and / or micro-slit in the micro-hole and micro-slit sensitizing structure 161 are not excessively limited. Similarly, the micro-hole and micro-slit sensitizing structure 161 can increase the vibration inertia of the cantilever beam, increase the bending deformation of the cantilever beam 113, thereby providing an amplified inertial stress to the POI piezoelectric substrate to change the surface acoustic wave propagation time delay, improve the acceleration measurement sensitivity and measurement range, and at the same time guarantee the stability of the high-frequency vibration signal response. Therefore, in order to obtain better acceleration measurement sensitivity, larger measurement range and guarantee the stability of the high-frequency vibration signal response, the mass block 160 and the micro-hole and micro-slit sensitizing structure 161 can be arranged at the same time. Figure 3

[0086] As shown in Figure 2 and Figure 3 , the pressure measuring cavity 150 formed in the piezoelectric substrate 11 between the temperature measuring reflector 14 and the pressure measuring reflector 15 and penetrating the high-resistance substrate layer 110 and the insulating layer 111 can be formed by back cavity etching. During detection, the POI piezoelectric substrate deforms due to the change of pressure in the pressure measuring cavity 150, changes the surface acoustic wave reflection characteristics, causes the surface acoustic wave time delay to shift, and can achieve high-sensitivity capture of small deformation and improve the measurement accuracy of pressure.

[0087] Embodiment Two

[0088] The embodiment provides a surface acoustic wave sensor packaging structure, which encapsulates the surface acoustic wave sensor 10 disclosed in embodiment one. The beneficial effects of the surface acoustic wave sensor 10 in embodiment one can be referred to the description in embodiment one, and the embodiment will not be described in detail.

[0089] As shown in Figures 5 to 7 , the surface acoustic wave sensor packaging structure 18 comprises the surface acoustic wave sensor 10 as described in embodiment one, a cover plate 19 and a containing base 20; wherein,

[0090] The surface acoustic wave sensor 10 is contained in the containing base 20;

[0091] The cover plate 19 is buckled on the containing base 20 to form an SMD packaging structure;

[0092] The antenna 24 is fixed below the containing base 20.

[0093] ​The surface acoustic wave sensor packaging structure 18 of the embodiment adopts an SMD packaging structure, which can be typically used for multi-parameter monitoring of pressure, temperature and acceleration of aerospace vehicles, such as internal temperature monitoring of engines, temperature distribution monitoring of wings and tail wings, evaluation of thermal protection systems on the surface of vehicles, health monitoring of internal equipment of vehicles, real-time monitoring in flight experiments, etc. In actual application scenarios, the surface acoustic wave sensor packaging structure 18 of the embodiment can be fixed to the surface of an object to be measured, to ensure that the containing base 20 is tightly attached to the mounting surface, to avoid external stress interference, and to realize mechanical fixation by means of epoxy resin or high-temperature adhesive, while keeping the radiation direction of the antenna 24 unobstructed. During detection, the reader periodically transmits query pulses, and the echo signals of the surface acoustic wave sensor 10 are transmitted to the reader through a wireless channel. The signal processing unit extracts the time delay and frequency shift information of each reflection grating by fast Fourier transform (FFT), separates the temperature, pressure and acceleration signals in combination with the preset encoding mapping relationship, and calls the temperature compensation algorithm to correct the cross-sensitivity error. Before first use, full-range calibration is performed in a standard temperature and pressure environment, a time delay-physical quantity mapping database of each parameter is established, and online calibration is periodically performed by a reference source (such as a constant temperature tank or a standard pressure gauge) to correct the sensitivity drift caused by environmental aging.

[0094] As a specific use example, taking aircraft engine monitoring as an example, the surface acoustic wave sensor packaging structure 18 is installed outside the engine combustion chamber, and temperature, pressure and acceleration vibration data are collected in real time by a wireless reader. The temperature measurement reflection grating monitors the thermal distribution of the combustion chamber surface, the pressure measurement reflection grating detects the pressure fluctuation of the fuel pipeline, and the acceleration measurement reflection grating captures high-frequency mechanical vibration signals. The reader fuses multi-parameter data, eliminates the influence of the thermal environment on pressure and acceleration measurement by a temperature compensation algorithm, and finally outputs a high-precision working condition health status evaluation result.

[0095] The surface acoustic wave sensor packaging structure 18 of the embodiment adopts an SMD packaging structure, which has a compact overall structure and greatly reduces the installation difficulty and system maintenance cost in complex environments, and is especially suitable for high-density monitoring scenarios with limited space, such as aerospace, energy equipment and other technical fields with strict requirements for extreme working condition monitoring.

[0096] As an example, the cover plate 19 is selected as a glass cover plate, and the containing base 20 is selected as a ceramic base, which can improve the high-temperature resistance of the packaging structure, so that the packaging structure can withstand high alternating temperature differences.

[0097] As an example, the acoustic surface wave sensor packaging structure 18 realizes the electrical signal transmission of the acoustic surface wave sensor 10 in the packaging structure through the soldering binding lead 21; wherein the soldering binding lead 21 is electrically connected with the uniform interdigital transducer 12 in the acoustic surface wave sensor 10. The soldering binding lead 21 can be selected as a gold wire or a silicon-aluminum wire or a platinum wire, but is not limited thereto, and other suitable bonding lead materials can also be used, which are specifically selected according to actual needs. In the embodiment, the soldering binding lead 21 is preferably a gold wire, and the uniform interdigital transducer 12 is bonded and connected with the soldering binding lead 21 through a gold bump, so as to ensure the high-frequency signal integrity.

[0098] As shown in Figure 5 and Figure 6 As an example, the acoustic surface wave sensor packaging structure 18 further includes an air hole 22, which is arranged on the cover plate 19 or the bottom wall of the accommodating base 20; when the air hole 22 is arranged on the cover plate 19, the air hole 22 penetrates through the cover plate 19 and is located above the pressure measuring cavity 150; when the air hole 22 is arranged on the bottom wall of the accommodating base 20, the air hole 22 penetrates through the bottom wall of the accommodating base 20 and the substrate 17 of the acoustic surface wave sensor 10 to communicate with the pressure measuring cavity 150. When the air hole 22 is arranged on the cover plate 19, the air hole 22 does not communicate with the pressure measuring cavity 150, but a sealed space is formed between the pressure measuring cavity 150 and the substrate 17, and the measured air pressure from the outside enters the packaging structure through the air hole 22, so as to form a pressure difference with the reference air pressure in the pressure measuring cavity 150 to measure the pressure, at this time, inert gas can be filled in the pressure measuring cavity 150 to reduce the acoustic wave sensing loss; when the air hole 22 is arranged on the bottom wall of the accommodating base 20, the air hole 22 communicates with the pressure measuring cavity 150, but other spaces in the packaging structure are sealed spaces under the fixation of the substrate 17 and the piezoelectric base 11, at this time, the space between the cover plate 19 and the piezoelectric base 11 can be further arranged as a sealed space, the measured air pressure from the outside enters the packaging structure through the air hole 22, so as to form a pressure difference with the reference air pressure in the packaging structure to measure the pressure, at this time, inert gas can be filled in the sealed space to reduce the acoustic wave sensing loss.

[0099] The air hole 22 directly communicates with the inside of the packaging structure, can balance the internal and external air pressures, ensures that the external pressure is transmitted without lag, and avoids overloading to cause the pressure measuring cavity to fail.

[0100] As shown in Figures 5 to 7 As an example, the acoustic surface wave sensor packaging structure 18 further includes an overload damping block 23, which is arranged on the inner wall of the cover plate 19 (as shown in Figure 6 and Figure 7 shown) and / or the inner side of the bottom wall of the accommodating base 20 (asFigures 5 to 7 The over-damping block 23 is arranged on the cantilever beam 113, and corresponds to the acceleration measurement reflection grating region of the surface acoustic wave sensor 10. When the cantilever beam 113 vibrates up and down under the impact of acceleration, the packaging space of the cantilever beam 113 region leaves a buffer gap. When the amplitude is large and collides with the over-damping block 23, the over-damping block 23 absorbs the mechanical impact and prevents the cantilever beam 113 from breaking, thereby weakening the influence of the mechanical impact on the measurement accuracy. Preferably, the material of the over-damping block 23 is selected to be a viscoelastic material, such as a silicone rubber material. The energy dissipation mechanism of the viscoelastic material absorbs the impact vibration and prevents the cantilever beam from breaking.

[0101] In summary, the present application provides a surface acoustic wave sensor and a packaging structure thereof. Based on the POI piezoelectric substrate and the multi-functional reflection grating layout, temperature, pressure and acceleration sensitive units are highly integrated on a single chip. In the design, not only the structure optimization of a single sensor in the prior art is considered, but also the cross-coupling effect between multiple sensors in the prior art is considered. In order to realize the decoupling of multiple sensing quantities, two groups of reference reflection gratings are designed, i.e. two reference gratings located on both sides of the uniform interdigital transducer, and an acceleration measurement reflection grating, a temperature measurement reflection grating and a pressure measurement reflection grating. The two reference gratings are used for differential time delay measurement of the sensitive quantity. The temperature measurement reflection grating is arranged close to the reference grating, which effectively ensures that the temperature measurement is not affected by other sensing quantities and effectively suppresses environmental noise interference. The acceleration measurement reflection grating and the pressure measurement reflection grating are arranged on both sides of the uniform interdigital transducer, which can not only realize the measurement of pressure and acceleration, but also effectively avoid the cross-sensitivity effect of pressure and acceleration physical quantities. The response signal of the temperature measurement reflection grating not only provides an independent temperature measurement value, but also serves as a reference parameter for dynamic compensation of pressure and acceleration signals. For example, the change in delay time of the pressure measurement reflection grating includes the thermal expansion effect of the piezoelectric single crystal layer caused by temperature. By deducting the linear contribution of the temperature component, the net deformation quantity caused by pressure can be accurately extracted. The sensitivity of the acceleration measurement reflection grating is affected by temperature drift. The elastic modulus change of the cantilever beam is corrected in real time using the temperature signal to ensure the temperature stability of the acceleration measurement. In this way, efficient separation and synchronous detection of temperature, pressure and acceleration multi-quantity signals are realized, and the electromagnetic coupling problem of the traditional multi-interdigital transducer structure is avoided. The surface acoustic wave sensor packaging structure adopts an SMD packaging structure, and the overall structure of the device is compact, which greatly reduces the installation difficulty and system maintenance cost in a complex environment. Therefore, the present application effectively overcomes the shortcomings of the prior art and has high industrial utilization value.

[0102] The above examples only illustrate the principles of the present application and its effects and are not intended to limit the present application. In the above examples, the description of each example focuses on different aspects, and the parts not described in detail in one example can be understood with reference to the relevant description of other examples. 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, modifications, equivalent replacements or improvements of the technical solutions recorded in the foregoing examples can still be made by those skilled in the art, and any modifications, equivalent replacements, improvements, etc. made within the spirit and principles of the present application shall be included in the protection scope of the present application.

Claims

1. A surface acoustic wave sensor, characterized in that, The surface acoustic wave (SAW) sensor includes: a piezoelectric substrate, a uniform interdigital SAW transducer, a temperature measurement reflective grating, a pressure measurement reflective grating, an acceleration measurement reflective grating, and two reference gratings disposed on the piezoelectric substrate, and bonded to a substrate under the piezoelectric substrate; wherein... The uniform interdigital transducer is used to excite and receive surface acoustic waves. The piezoelectric substrate is a POI piezoelectric substrate composed of a high-resistivity substrate layer, an insulating layer and a piezoelectric single crystal layer; The two reference grids are respectively disposed on both sides near the uniform interdigital transducer; The pressure measurement reflective grating and the acceleration measurement reflective grating are respectively disposed on two sides away from the uniform interdigital transducer; The temperature measurement reflective grid is disposed between the reference grid and the pressure measurement reflective grid, which are located on the same side of the uniform interdigital transducer as the pressure measurement reflective grid. The substrate exposes at least the piezoelectric substrate beneath the acceleration measurement reflective grating to form a cantilever beam; A pressure measuring cavity is formed in the piezoelectric substrate between the temperature measuring reflective grating and the pressure measuring reflective grating, penetrating the high-resistivity substrate layer and the insulating layer.

2. The surface acoustic wave sensor according to claim 1, characterized in that: The material of the piezoelectric single crystal layer in the piezoelectric substrate is lithium niobate, lithium tantalate, quartz, lead zirconate titanate, or aluminum nitride; the insulating layer is a silicon dioxide layer, a silicon nitride layer, or an aluminum oxide layer; and the high-resistivity substrate layer is a high-resistivity silicon layer, a high-resistivity silicon carbide layer, or a high-resistivity gallium arsenide layer.

3. The surface acoustic wave sensor according to claim 1, characterized in that: The high-resistivity substrate layer is a high-resistivity silicon layer, the substrate is a glass substrate, and the high-resistivity substrate layer and the substrate are pre-formed with an alumina transition layer at the bonding interface and bonded based on a low-temperature anodic bonding process.

4. The surface acoustic wave sensor according to claim 1, characterized in that: A mass block is fixed under the piezoelectric substrate below the acceleration measurement reflective grating.

5. The surface acoustic wave sensor according to claim 1 or 5, characterized in that: The cantilever beam extends at least to the reference gate near its side, and the cantilever beam is provided with a micro-pore slit sensitization structure in the acceleration sensitive region. The micro-pore slit sensitization structure is a plurality of micro-pores and / or micro-slits extending inward from the lower surface of the high-resistivity substrate towards the piezoelectric single crystal layer and extending to a depth not exceeding the thickness of the high-resistivity substrate.

6. The surface acoustic wave sensor according to claim 1, characterized in that: The metal electrodes of the uniform interdigital transducer are aluminum thin film electrodes with a linewidth of 0.5μm to 1.0μm, a spacing of 0.5μm to 1.0μm, 20 to 50 pairs of interdigitates, and a length of 50μm to 200μm. They are kept consistent along the direction of surface acoustic wave propagation and excite surface acoustic waves to both sides. The operating frequency is in the frequency range of 10MHz to 10GHz.

7. A surface acoustic wave sensor packaging structure, characterized in that, The packaging structure includes: a surface acoustic wave sensor, a cover plate, and a housing base as described in any one of claims 1 to 6; wherein... The surface acoustic wave sensor is housed in the housing base; The cover plate is fastened onto the receiving base to form an SMD packaging structure; An antenna is fixed below the accommodating base.

8. The surface acoustic wave sensor packaging structure according to claim 7, characterized in that: The cover plate is a glass cover plate, and the accommodating base is a ceramic base.

9. The surface acoustic wave sensor packaging structure according to claim 7, characterized in that: The packaging structure also includes solder bonding leads, which are electrically connected to the uniform interdigital transducer.

10. The surface acoustic wave sensor packaging structure according to claim 9, characterized in that: The welding bonding leads are gold wire, silicon-aluminum wire, or platinum wire.

11. The surface acoustic wave sensor packaging structure according to claim 7, characterized in that: The encapsulation structure further includes a vent hole, which is disposed on the cover plate or the bottom wall of the accommodating base. When the vent hole is disposed on the cover plate, it penetrates the cover plate and is located above the pressure measuring chamber. When the vent hole is disposed on the bottom wall of the accommodating base, it penetrates the bottom wall of the accommodating base and the substrate of the surface acoustic wave sensor to communicate with the pressure measuring chamber.

12. The surface acoustic wave sensor packaging structure according to claim 11, characterized in that: When the vent is located on the cover plate, the pressure measuring chamber forms a sealed space and is vented with inert gas; when the vent is located on the bottom wall of the accommodating base, a sealed space is formed between the cover plate and the piezoelectric substrate and is vented with inert gas.

13. The surface acoustic wave sensor packaging structure according to claim 7, characterized in that: The encapsulation structure also includes an overload damping block, which is disposed on the inner wall of the cover plate and / or the inner side of the bottom wall of the accommodating base and corresponds to the acceleration measurement reflection grating area of ​​the surface acoustic wave sensor.

14. The surface acoustic wave sensor packaging structure according to claim 13, characterized in that: The overload damping block is made of silicone rubber.

Images