Surface acoustic wave temperature sensor, manufacturing method and demodulation system

Abstract

The invention provides a surface acoustic wave temperature sensor, a manufacturing method and a demodulation system, and belongs to the technical field of sensors. The sensor comprises a piezoelectric substrate, four groups of interdigital transducers formed on the piezoelectric substrate, four groups of reflecting gratings and a group of planar antennas, wherein the surface of the piezoelectric substrate between the two groups of interdigital transducers is covered with a temperature sensitive film, and the two groups of reflecting gratings, the two groups of interdigital transducers, the temperature sensitive film and the piezoelectric substrate form a detection resonance area; the other two groups of interdigital transducers, the other two groups of reflecting gratings and the piezoelectric substrate form a reference resonance region; an isolation groove is formed in the piezoelectric substrate between the detection resonance area and the reference resonance area; and one end of the planar antenna is connected with the group of interdigital transducers in the detection resonance area, and the other end of the planar antenna is connected with the group of interdigital transducers in the reference resonance area. According to the invention, differential compensation of common-mode interference is realized, propagation of surface acoustic waves of the detection resonance area to the reference resonance area is blocked through the isolation groove, and coupling interference between the two resonators is reduced.

Description

Technical Field

[0001] This invention relates to the field of sensor technology, specifically to a surface acoustic wave (SAW) temperature sensor, a method for manufacturing the SAW temperature sensor, and a demodulation system. Background Technology

[0002] Surface Acoustic Wave (SAW) temperature sensors offer advantages such as being wireless and passive, having strong anti-interference capabilities, and long lifespan, making them suitable for applications in industrial equipment monitoring, power system maintenance, and aerospace. The principle of SAW temperature sensors is based on how temperature changes alter the elastic properties of a piezoelectric substrate, causing a shift in the resonant frequency of the surface acoustic wave. Temperature measurement is achieved by detecting this frequency change.

[0003] Existing wireless passive SAW temperature sensors typically employ a single resonator structure, where an interdigital transducer (IDT) and a reflective grating are fabricated on a piezoelectric substrate to form a resonator. An external reader transmits a radio frequency signal to excite the resonator, and the frequency of the signal reflected by the resonator changes with temperature. The reader infers the temperature value by demodulating the frequency offset.

[0004] Existing SAW temperature sensors with a single resonator structure improve accuracy by enhancing resonant frequency stability, but they cannot solve the common-mode interference problem. The single resonator signal lacks a reference, resulting in significant errors in complex environments. Existing SAW temperature sensors, which combine two independently packaged temperature-sensing resonator chips and a reference resonator chip, use differential compensation to compensate for errors. However, the two independently packaged resonator chips exhibit temperature hysteresis, meaning the temperatures of the reference resonator and the temperature-sensing resonator will differ at the same time. Therefore, the improvement in differential compensation is limited, and common-mode interference suppression is poor. Summary of the Invention

[0005] To address the shortcomings of existing technologies, this invention provides a surface acoustic wave temperature sensor, its manufacturing method, and a demodulation system.

[0006] The first aspect of the present invention provides a surface acoustic wave temperature sensor, comprising: a piezoelectric substrate, at least four sets of interdigital transducers, at least four sets of reflective gratings and a planar antenna formed on the piezoelectric substrate;

[0007] A temperature-sensitive film is covered on the surface of the piezoelectric substrate between the two sets of interdigital transducers. The two sets of reflective gratings, the two sets of interdigital transducers, and the temperature-sensitive film between the two sets of interdigital transducers together with the piezoelectric substrate form a detection resonance region. The other two sets of interdigital transducers and the other two sets of reflective gratings together with the piezoelectric substrate constitute the reference resonant region. An isolation groove is provided in the piezoelectric substrate between the detection resonant region and the reference resonant region. The isolation groove is used to block the propagation of surface acoustic waves generated by the interdigital transducer in the detection resonant region to the reference resonant region, and to block the propagation of surface acoustic waves generated by the interdigital transducer in the reference resonant region to the detection resonant region. One end of the planar antenna is connected to a set of interdigital transducers in the detection resonant region, and the other end of the planar antenna is connected to a set of interdigital transducers in the reference resonant region. The planar antenna is used to receive radio frequency signals and transmit them to the interdigital transducers, and to transmit the frequency signal of the surface acoustic wave generated by the interdigital transducers under the excitation of the radio frequency signals.

[0008] In this embodiment of the invention, the surface of the piezoelectric substrate between the other two sets of interdigital transducers is covered with an inert film, and the other two sets of reflective gratings, the other two sets of interdigital transducers, and the inert film between the two sets of interdigital transducers together with the piezoelectric substrate constitute a reference resonant region.

[0009] In this embodiment of the invention, the isolation groove is filled with an insulating medium material.

[0010] In this embodiment of the invention, the lengths of the interdigitated fingers in each group of interdigitated transducers are not equal; the length of each interdigitated finger is determined by performing apodization weighting on interdigitated transducers with interdigitated fingers of equal length using a window function.

[0011] In this embodiment of the invention, of the two sets of interdigital transducers used to detect the resonant region, one set of interdigital transducers serves as the input interdigital transducer, and the other set serves as the output interdigital transducer. In the two sets of interdigital transducers in the reference resonant region, one set of interdigital transducers serves as the input interdigital transducer, and the other set serves as the output interdigital transducer. One end of the planar antenna is connected to the input interdigital transducer of the detection resonant region, and the other end of the planar antenna is connected to the input interdigital transducer of the reference resonant region.

[0012] A second aspect of the present invention provides a method for manufacturing a surface acoustic wave temperature sensor, comprising: At least four sets of interdigital transducers and at least four sets of reflective gratings are formed on the same piezoelectric substrate; A temperature-sensitive film is formed on the surface of a piezoelectric substrate between two sets of interdigital transducers; the two sets of reflective gratings, the two sets of interdigital transducers, and the temperature-sensitive film between the two sets of interdigital transducers together with the piezoelectric substrate constitute a detection resonance region; the other two sets of interdigital transducers and the other two sets of reflective gratings together with the piezoelectric substrate constitute a reference resonance region. An isolation groove is formed in the piezoelectric substrate between the detection resonant region and the reference resonant region; the isolation groove is used to block the propagation of surface acoustic waves generated by the interdigital transducer in the detection resonant region to the region where the reference resonant region is located. A set of planar antennas is formed on the surface of a piezoelectric substrate outside the detection resonant region and the reference resonant region, such that one end of the planar antenna is connected to a set of interdigital transducers in the detection resonant region, and the other end of the planar antenna is connected to a set of interdigital transducers in the reference resonant region; the planar antenna is used to receive radio frequency signals and transmit them to the interdigital transducers, and to transmit the frequency signal of the surface acoustic wave generated by the interdigital transducers under the excitation of the radio frequency signals.

[0013] In this embodiment of the invention, the manufacturing method of the surface acoustic wave temperature sensor further includes: An inert film is formed on the surface of the piezoelectric substrate between the other two sets of interdigital transducers; the other two sets of reflective gratings, the other two sets of interdigital transducers, and the inert film between the two sets of interdigital transducers together with the piezoelectric substrate constitute a reference resonant region.

[0014] In this embodiment of the invention, the manufacturing method of the surface acoustic wave temperature sensor further includes: The isolation groove is filled with insulating medium material.

[0015] In this embodiment of the invention, at least four sets of interdigital transducers and at least four sets of reflective gratings are formed on the same piezoelectric substrate, including: Photoresist is coated onto the cleaned piezoelectric substrate surface. Through exposure and development processes, the patterns of interdigitated transducers and reflective gratings are formed on the photoresist on the piezoelectric substrate surface. Metal is sputtered onto the surface of a piezoelectric substrate to form a metal film of the pattern, which serves as an interdigital transducer and a reflective grating.

[0016] In this embodiment of the invention, forming an isolation trench in the piezoelectric substrate between the detection resonant region and the reference resonant region includes: The surface of the piezoelectric substrate between the detection resonant region and the reference resonant region is ground and polished to remove part of the piezoelectric substrate material and form an isolation groove of a preset depth. Alternatively, dry or wet etching processes can be used to etch the piezoelectric substrate between the detection resonant region and the reference resonant region to form an isolation trench of a predetermined depth. The preset depth is greater than or equal to one-quarter of the wavelength of the surface acoustic wave.

[0017] In this embodiment of the invention, a set of planar antennas is formed on the surface of the piezoelectric substrate outside the detection resonant region and the reference resonant region, including: A metal thin film is deposited on the surface of a piezoelectric substrate outside the detection resonant region and the reference resonant region; a photoresist is coated on the surface of the metal thin film, and a planar antenna pattern is formed on the photoresist through exposure and development processes; The piezoelectric substrate is etched using either dry or wet etching processes to form the planar antenna with the aforementioned pattern.

[0018] A third aspect of the present invention provides a demodulation system applied to the above-mentioned surface acoustic wave temperature sensor, the demodulation system comprising: a radio frequency transmitting module, a signal receiving module, a differential processing unit, and a temperature demodulation unit; The radio frequency transmitting module is used to generate radio frequency signals and send radio frequency signals to the surface acoustic wave temperature sensor. The signal receiving module is used to receive a first frequency signal and a second frequency signal from the surface acoustic wave temperature sensor. The first frequency signal represents the frequency of the surface acoustic wave generated by the detection resonant region of the surface acoustic wave temperature sensor under the excitation of the radio frequency signal, and the second frequency signal represents the frequency of the surface acoustic wave generated by the reference resonant region of the surface acoustic wave temperature sensor under the excitation of the radio frequency signal. The differential processing unit is used to calculate the difference between the frequency represented by the first frequency signal and the frequency represented by the second frequency signal; The temperature demodulation unit is used to determine the temperature value based on the frequency difference calculated by the differential processing unit.

[0019] In this embodiment of the invention, the temperature demodulation unit pre-stores a calibration curve based on the frequency difference and temperature value; The temperature demodulation unit determines the temperature value corresponding to the frequency difference calculated by the differential processing unit based on the calibration curve based on the frequency difference and temperature value.

[0020] In this embodiment of the invention, the expression for the calibration curve based on the frequency difference and temperature value is as follows: T =(Δf -Δf0) / (kt - kt') + T0; Where T represents the actual temperature value, T0 represents the preset temperature value, Δf is the frequency difference between the detection resonance region and the reference resonance region corresponding to the actual temperature value T, Δf0 is the frequency difference between the detection resonance region and the reference resonance region corresponding to the preset temperature value T0, kt is the temperature coefficient of the temperature-sensitive film in the detection resonance region, and kt' is the temperature coefficient of the piezoelectric substrate material in the reference resonance region or the temperature coefficient of the inert film in the reference resonance region.

[0021] In this embodiment of the invention, the demodulation system further includes a power management module, which is used to convert solar or radio frequency energy into electrical energy to power the demodulation system.

[0022] The above technical solution forms a dual resonator structure with a detection resonant region and a reference resonant region on the same piezoelectric substrate, so that the detection resonant region and the reference resonant region are subject to the same common-mode interference. A differential compensation mechanism is used to achieve differential compensation for the common-mode interference. An isolation groove is set in the piezoelectric substrate between the detection resonant region and the reference resonant region. The isolation groove blocks the propagation of surface acoustic waves from the detection resonant region to the reference resonant region, reduces the coupling interference between the two resonators, and improves the cross-interference suppression ratio between the two resonators.

[0023] Other features and advantages of the technical solution of the present invention will be described in detail in the following detailed embodiments section. Attached Figure Description

[0024] The accompanying drawings, which are included to provide a further understanding of the invention and form part of this invention, illustrate exemplary embodiments of the invention and are used to explain the invention, but do not constitute an undue limitation of the invention. In the drawings: Figure 1 This is a schematic diagram of the structure of the surface acoustic wave temperature sensor provided in an embodiment of the present invention; Figure 2 This is a flowchart of a method for manufacturing a surface acoustic wave temperature sensor provided in an embodiment of the present invention; Figure 3 This is a block diagram of the demodulation system provided in an embodiment of the present invention.

[0025] Explanation of reference numerals in the attached figures 1-Piezoelectric substrate, 2-Detection resonant region, 3-Reference resonant region, 4-Isolation groove, 5-Planar antenna 21-First interdigital transducer, 22-First reflective grating, 23-Second interdigital transducer, 24-Second reflective grating, 25-Temperature-sensitive film. 31-Third interdigital transducer, 32-Third reflector, 33-Fourth interdigital transducer, 34-Fourth reflector. Detailed Implementation

[0026] To make the technical solutions and advantages of the embodiments of the present invention clearer, the exemplary embodiments of the present invention will be further described in detail below with reference to the accompanying drawings. Obviously, the described embodiments are only a part of the embodiments of the present invention, and not an exhaustive list of all embodiments. It should be noted that, unless otherwise specified, the embodiments and features in the embodiments of the present invention can be combined with each other.

[0027] In the description of this invention, it should be understood that the terms "center," "longitudinal," "lateral," "length," "width," "thickness," "upper," "lower," "front," "rear," "left," "right," "vertical," "horizontal," "top," "bottom," "inner," and "outer," etc., indicate the orientation or positional relationship based on the orientation or positional relationship shown in the accompanying drawings. They are only for the convenience of describing this invention and simplifying the description, and do not indicate or imply that the device or element referred to must have a specific orientation, or be constructed and operated in a specific orientation. Therefore, they should not be construed as limitations on this invention.

[0028] Furthermore, the terms "first" and "second" are used for descriptive purposes only and should not be construed as indicating or implying relative importance or implicitly specifying the number of technical features indicated. Thus, a feature defined as "first" or "second" may explicitly or implicitly include one or more of that feature. In the description of this invention, "a plurality of" means at least two, such as two, three, etc., unless otherwise explicitly specified.

[0029] In this invention, unless otherwise explicitly specified and limited, the terms "connected," "linked," and "interlocked" should be interpreted broadly, referring to mechanical connections, electrical connections, or connections that allow for mutual communication; direct connections or indirect connections via an intermediate medium; and connections within two components or interactions between two components. Those skilled in the art can understand the specific meaning of these terms in this invention based on the specific circumstances.

[0030] Existing SAW temperature sensors with a single resonator structure improve accuracy by enhancing resonant frequency stability, but they cannot solve the common-mode interference problem. The single resonator signal lacks a reference, resulting in significant errors in complex environments. Existing SAW temperature sensors, which combine two independently packaged temperature-sensing resonator chips and a reference resonator chip, use differential compensation to compensate for errors. However, the two independently packaged resonator chips exhibit temperature hysteresis, meaning the temperatures of the reference resonator and the temperature-sensing resonator will differ at the same time. Therefore, the improvement in differential compensation is limited, and common-mode interference suppression is poor.

[0031] To address the problems of existing technologies, this invention provides a surface acoustic wave (SAW) temperature sensor. It constructs a dual-resonator structure with at least four sets of interdigital transducers, at least four sets of reflective gratings, and a planar antenna on the same piezoelectric substrate. This structure creates a detection resonant region and a reference resonant region, ensuring that both regions are subject to the same common-mode interference. A differential compensation mechanism is used to compensate for this interference. Furthermore, an isolation groove is placed in the piezoelectric substrate between the detection and reference resonant regions. This groove blocks the propagation of SAW waves from the detection resonant region to the reference resonant region, reducing coupling interference between the two resonators and improving the cross-interference suppression ratio. This invention enables high-precision, interference-resistant wireless passive temperature measurement, meeting the long-term stable temperature monitoring requirements in complex environments such as industrial monitoring and power systems.

[0032] Figure 1 This is a schematic diagram of the structure of the surface acoustic wave temperature sensor provided in an embodiment of the present invention. Figure 1 As shown, the surface acoustic wave temperature sensor provided in this embodiment includes: a piezoelectric substrate 1, four sets of interdigital transducers (IDTs), four sets of reflective gratings, and a planar antenna 5 formed on the piezoelectric substrate 1. In each pair of interdigital transducers, one set serves as the input interdigital transducer, and the other set serves as the output interdigital transducer. The four sets of reflective gratings are respectively positioned close to the four sets of interdigital transducers. The four sets of interdigital transducers include: a first interdigital transducer 21 as input, a second interdigital transducer 23 as output, a third interdigital transducer 31 as input, and a fourth interdigital transducer 33 as output. The four sets of reflective gratings include: a first reflective grating 22 close to the first interdigital transducer 21, a second reflective grating 24 close to the second interdigital transducer 23, a third reflective grating 32 close to the third interdigital transducer 31, and a fourth reflective grating 34 close to the fourth interdigital transducer 33. The four sets of interdigital transducers can have the same or different structures and conductive materials; the four sets of reflective gratings can also have the same or different structures and conductive materials. A temperature-sensitive film 25 covers the surface of the piezoelectric substrate 1 between the first interdigital transducer 21 and the second interdigital transducer 23. The first interdigital transducer 21, the second interdigital transducer 23, the first reflective grating 22, the second reflective grating 24, and the temperature-sensitive film 25 between the first interdigital transducer 21 and the second interdigital transducer 23, together with the piezoelectric substrate 1, constitute a detection resonance region 2; the third interdigital transducer 31, the fourth interdigital transducer 33, the third reflective grating 32, the fourth reflective grating 34, together with the piezoelectric substrate 1, constitute a reference resonance region 3.

[0033] An isolation groove 4 is provided in the piezoelectric substrate 1 between the detection resonant region 2 and the reference resonant region 3. The isolation groove 4 is used to block the propagation of surface acoustic waves generated by the interdigital transducers in the detection resonant region 2 to the reference resonant region 3, and to block the propagation of surface acoustic waves generated by the interdigital transducers in the reference resonant region 3 to the detection resonant region 2. One end of the planar antenna 5 is connected to the first interdigital transducer 21, which serves as the input, in the detection resonant region 2, and the other end of the planar antenna 5 is connected to the third interdigital transducer 31, which serves as the input, in the reference resonant region 3. The planar antenna 5 is used to receive radio frequency signals and transmit them to the first interdigital transducer 21 and the third interdigital transducer 31, and to transmit the frequency signals of the surface acoustic waves generated by the first interdigital transducer 21 and the third interdigital transducer 31 under the excitation of the radio frequency signals.

[0034] The planar antenna 5 can receive radio frequency (RF) signals from the demodulation system (i.e., the reader). The RF signals excite the first interdigital transducer 21 (input) of the detection resonant region 2 and the third interdigital transducer 31 (input) of the reference resonant region 3 to generate surface acoustic waves (SAWs). The first frequency signal of the SAW from the detection resonant region 2 and the second frequency signal of the SAW from the reference resonant region 3 are transmitted to the demodulation system. The demodulation system calculates the temperature value based on the difference between the frequencies of the SAWs in the detection resonant region and the reference resonant region. Since the detection resonant region and the reference resonant region are formed on the same piezoelectric substrate, the resonators (i.e., the resonators composed of interdigital transducers and reflectors) in both regions are subject to the same common-mode interference. Therefore, the difference between the frequencies of the SAWs in the detection resonant region and the reference resonant region cancels out the influence of common-mode interference, thus achieving differential compensation for common-mode interference.

[0035] In an optional embodiment, the surface of the piezoelectric substrate 1 between the third interdigital transducer 31 and the fourth interdigital transducer 33 in the reference resonant region 3 may be covered with an inert film (not shown in the figures) formed of an inert material. The third interdigital transducer 31, the fourth interdigital transducer 33, the third reflective grating 32, the fourth reflective grating 34, and the inert film between the third interdigital transducer 31 and the fourth interdigital transducer 33, together with the piezoelectric substrate 1, constitute the reference resonant region 3.

[0036] The depth of the isolation groove 4 is ≥λ / 4, where λ is the wavelength of the surface acoustic wave. The isolation groove 4 can be filled with an insulating dielectric material or left empty, forming a cavity. In an optional embodiment, the isolation groove is filled with silicone rubber insulating material to block the lateral propagation of acoustic waves between the detection resonant region 2 and the reference resonant region 3, thereby reducing coupling interference.

[0037] The conductive materials of the interdigital transducer and reflector in the detection resonant region 2 and the interdigital transducer and reflector in the reference resonant region 3 can be the same or different. The lengths of the interdigital fingers in the interdigital transducer (IDT) can be equal, or they can be non-equal-length interdigital fingers that have undergone apodization weighting processing of equal-length IDTs using a window function.

[0038] In an optional embodiment, the lengths of the interdigital fingers in each group of interdigital transducers are not equal. The length of each interdigital finger can be determined by applying an apodization weighting process to interdigital transducers with equal-length interdigital fingers using a window function. The window function can be at least one of the following: Blackman window, rectangular window, Bartlett window, triangular window, Hanning window, Hamming window, Taylor window, and Kaiser window.

[0039] The piezoelectric substrate 1 serves as the carrier for surface acoustic wave propagation. The piezoelectric substrate can be a piezoelectric crystal or a POI (Piezoelectric on Insulator) substrate. The piezoelectric crystal can be selected from at least one of the following: quartz crystal, lithium niobate crystal, lithium tantalate (LiTaO3) crystal, polycrystalline piezoelectric ceramics (barium titanate, lead zirconate titanate, lead magnesium niobate (PMN) and related ternary ceramics), or other piezoelectric crystals (lithium gallate, bismuth germanate). Quartz crystals have a low temperature coefficient (TCF≈-15ppm / ℃), making them suitable as a reference resonator substrate; lithium tantalate (LiTaO3) crystals (TCF≈-80ppm / ℃) have high sensitivity, making them suitable as a detection resonator substrate. The POI substrate comprises: a top piezoelectric single-crystal layer, a middle silicon dioxide insulating layer, and a bottom high-resistivity silicon substrate. The top piezoelectric single-crystal layer typically uses at least one of the following piezoelectric thin film materials: lithium tantalate, lithium niobate, ZnO, AlN, ScAlN, and PZT. The temperature coefficient (TCF) difference in the POI substrate is controlled by the film layer.

[0040] This invention also provides a method for manufacturing the above-described surface acoustic wave temperature sensor. For example... Figure 2 As shown, the manufacturing method of the surface acoustic wave temperature sensor provided in this embodiment includes the following steps: S210, at least four sets of interdigital transducers and at least four sets of reflective gratings are formed on the same piezoelectric substrate; S220, a temperature-sensitive film is formed on the surface of a piezoelectric substrate between two sets of interdigital transducers; the two sets of reflective gratings, the two sets of interdigital transducers, and the temperature-sensitive film between the two sets of interdigital transducers and the piezoelectric substrate constitute a detection resonance region; the other two sets of interdigital transducers and the other two sets of reflective gratings and the piezoelectric substrate constitute a reference resonance region. S230, an isolation groove is formed in the piezoelectric substrate between the detection resonant region and the reference resonant region; the isolation groove is used to block the propagation of surface acoustic waves generated by the interdigital transducer in the detection resonant region to the region where the reference resonant region is located. S240, a set of planar antennas is formed on the surface of the piezoelectric substrate outside the detection resonant region and the reference resonant region, such that one end of the planar antenna is connected to a set of interdigital transducers (as input interdigital transducers) in the detection resonant region, and the other end of the planar antenna is connected to a set of interdigital transducers (as input interdigital transducers) in the reference resonant region; the planar antennas are used to receive radio frequency signals and transmit them to the interdigital transducers, and to transmit the frequency signal of the surface acoustic wave generated by the interdigital transducers under the excitation of the radio frequency signal.

[0041] In step S210 above, the specific method for forming the interdigital transducer and the reflective grating is as follows: photoresist is coated on the surface of the cleaned piezoelectric substrate, and the patterns of the interdigital transducer and the reflective grating are formed on the photoresist on the surface of the piezoelectric substrate through exposure and development. Then, metal is sputtered on the surface of the piezoelectric substrate to form a metal film of the pattern, and the metal film serves as the interdigital transducer and the reflective grating.

[0042] The piezoelectric substrate can be a piezoelectric crystal or a POI (Piezoelectric on Insulator) substrate. The piezoelectric crystal can be selected from at least one of the following: quartz crystal, lithium niobate crystal, lithium tantalate (LiTaO3) crystal, polycrystalline piezoelectric ceramics (barium titanate, lead zirconate titanate, lead magnesium niobate (PMN) and related ternary ceramics), or other piezoelectric crystals (lithium gallate, bismuth germanate). Quartz crystals have a low temperature coefficient (TCF≈-15ppm / ℃), making them suitable as a reference resonator substrate; lithium tantalate (LiTaO3) crystals (TCF≈-80ppm / ℃) have high sensitivity, making them suitable as a detection resonator substrate. The POI substrate consists of: a top piezoelectric single-crystal layer, a middle silicon dioxide insulating layer, and a bottom high-resistivity silicon substrate. The top piezoelectric single-crystal layer typically uses at least one of the following piezoelectric thin film materials: lithium tantalate, lithium niobate, ZnO, AlN, ScAlN, PZT, etc.

[0043] In step S220 above, the specific method for forming a temperature-sensitive film on the surface of the piezoelectric substrate is as follows: Chemical vapor deposition (CVD) is used, where a gaseous precursor undergoes a chemical reaction on the substrate surface to generate a solid temperature-sensitive film; plasma-enhanced CVD (PECVD) technology can also be used, utilizing radio frequency or DC plasma to excite the reactive gas, which can lower the deposition temperature and improve film adhesion. Alternatively, physical vapor deposition (PVD) is used, where target atoms are deposited onto the substrate surface through physical processes (such as sputtering and evaporation) to generate a temperature-sensitive film. For example, sputtering deposition involves bombarding a target with ions to sputter and deposit atoms onto the substrate to form a thin film; evaporation deposition involves heating the material in a vacuum environment to evaporate and deposit it onto the substrate to form a thin film.

[0044] In step S230 above, there are two specific methods for forming the isolation trench: 1. Grinding and polishing the surface of the piezoelectric substrate between the detection resonant region and the reference resonant region using grinding tools and polishing materials to remove part of the piezoelectric substrate material and form an isolation trench of a preset depth; 2. Etching the piezoelectric substrate between the detection resonant region and the reference resonant region using dry etching or wet etching processes to form an isolation trench of a preset depth. The preset depth is greater than or equal to one-quarter of the wavelength of the surface acoustic wave, i.e., the depth of the isolation trench is ≥λ / 4, where λ is the wavelength of the surface acoustic wave.

[0045] In step S240 above, the specific method for forming a planar antenna on the piezoelectric substrate surface is as follows: First, a metal thin film is deposited on the piezoelectric substrate surface outside the detection resonant region and the reference resonant region. The metal thin film serves as the conductive material for the planar antenna. Then, photoresist is coated on the metal thin film surface, and the pattern of the planar antenna is formed on the photoresist through exposure and development. Finally, the piezoelectric substrate is etched using a dry etching or wet etching process (transferring the pattern on the photoresist onto the metal thin film) to form the planar antenna with this pattern. Dry etching, such as reactive ion etching (RIE), utilizes ions and active free radicals in plasma to chemically react with and physically bombard the metal thin film, removing unwanted metal parts to form the planar antenna pattern. The deposition method for the metal thin film can be physical vapor deposition (PVD), such as electron beam evaporation or magnetron sputtering; or chemical vapor deposition (CVD), such as magnetron sputtering, which can deposit a uniform gold, silver, or aluminum thin film on the substrate with a thickness between tens and hundreds of nanometers.

[0046] In an optional embodiment, after step S220, the following step is further included: coating an inert material onto the surface of the piezoelectric substrate between the other two sets of interdigital transducers to form an inert film; the other two sets of reflective gratings, the other two sets of interdigital transducers, and the inert film between the two sets of interdigital transducers, together with the piezoelectric substrate, constitute a reference resonant region. Specifically, refer to... Figure 1 An inert film (not shown in the figure) formed by coating an inert material is applied to the surface of the piezoelectric substrate 1 between the third interdigital transducer 31 and the fourth interdigital transducer 33 in the reference resonant region 3. The third interdigital transducer 31, the fourth interdigital transducer 33, the third reflective grating 32, the fourth reflective grating 34, and the inert film between the third interdigital transducer 31 and the fourth interdigital transducer 33, together with the piezoelectric substrate 1, constitute the reference resonant region 3.

[0047] In an optional embodiment, after step S230, the following step is further included: filling the isolation groove with an insulating dielectric material. For example, silicone rubber insulating material is filled into the isolation groove to block the lateral propagation of acoustic waves between the detection resonant region 2 and the reference resonant region 3, thereby reducing coupling interference. The method of filling the isolation groove with silicone rubber insulating material is as follows: according to the size and insulation performance requirements of the isolation groove, silicone rubber substrate and filler are mixed in proportion, the silicone rubber and filler are thoroughly mixed, and the mixture is processed into a specified shape by compression molding, extrusion molding or casting molding, and then filled into the isolation groove to ensure that the filler material is tightly attached to the isolation groove. The filled isolation groove is then deburred and leveled to ensure that the surface of the filling layer is smooth and to improve the insulation performance.

[0048] Embodiments of the present invention also provide a demodulation system for the aforementioned surface acoustic wave temperature sensor. For example... Figure 3 As shown, the demodulation system provided in this embodiment includes: an RF transmitting module, a signal receiving module, a differential processing unit, and a temperature demodulation unit. The RF transmitting module generates an RF signal and transmits it to the surface acoustic wave (SAW) temperature sensor. The RF signal transmitted by the RF transmitting module can be transmitted to the planar antenna of the SAW temperature sensor via an antenna containing a reader of the demodulation system, thereby exciting the SAW temperature sensor to generate surface acoustic waves. The signal receiving module receives a first frequency signal and a second frequency signal from the SAW temperature sensor. The first frequency signal represents the frequency of the SAW generated by the detection resonant region of the SAW temperature sensor under the excitation of the RF signal, and the second frequency signal represents the frequency of the SAW generated by the reference resonant region of the SAW temperature sensor under the excitation of the RF signal. The differential processing unit calculates the difference between the frequencies represented by the first frequency signal and the second frequency signal. The temperature demodulation unit calculates the temperature value based on the frequency difference.

[0049] The surface acoustic wave (SAW) temperature sensor's detection resonator (i.e., the detection resonant region) is a high-temperature-coefficient SAW resonant structure. The temperature-sensitive material coated on the piezoelectric substrate is temperature-sensitive and affected by common-mode interference. The resonant frequency f1 of the detection resonator (i.e., the frequency represented by the first frequency signal) varies with temperature T and common-mode interference C: f1 = f 10 +kt T+kc C;f 10 To detect the reference frequency of the resonator, kt is the temperature coefficient of the temperature-sensitive film in the resonant region, T is the temperature value, kc is the interference coefficient, and C is the common-mode interference.

[0050] The reference resonator (i.e., the reference resonant region) of the surface acoustic wave (SAW) temperature sensor employs a low-temperature-coefficient SAW resonant structure, exhibiting low temperature sensitivity but susceptible to the same common-mode interference C. The resonant frequency f2 of the reference resonator (i.e., the frequency characterized by the second frequency signal) is expressed as: f2 = f 20 + kt' T + kc C;f 20 Here, kt' is the reference frequency of the reference resonator, kt' is the temperature coefficient of the piezoelectric substrate material in the reference resonant region or the temperature coefficient of the inert film in the reference resonant region, T is the temperature value, kc is the interference coefficient, and C is the common-mode interference.

[0051] The differential processing unit achieves common-mode interference compensation by differentially detecting the frequency difference between two resonators (the detection resonator and the reference resonator). The frequency difference Δf is expressed as: Δf = f1 - f2, that is: Δf = (f 10 -f 20 ) + (kt - kt') T) + (kc C-kc C); Since the detection resonant region and the reference resonant region are formed on the same piezoelectric substrate, the detection resonant region (detection resonator) and the reference resonant region (reference resonator) are subject to the same common-mode interference kc. C, therefore, the difference Δf between the surface acoustic wave frequency in the detection resonant region and the surface acoustic wave frequency in the reference resonant region is the common-mode interference kc. The effect of C is offset (kc) C-kc C), which eliminates common-mode interference.

[0052] The differential processing unit can be an FPGA (Field Programmable Gate Array) or a dedicated chip, with a processing latency of ≤1ms.

[0053] The differential processing unit calculates the difference Δf between the frequency f1 represented by the first frequency signal and the frequency f2 represented by the second frequency signal. The temperature demodulation unit pre-stores a calibration curve based on the frequency difference and temperature value. Based on the calibration curve, the temperature demodulation unit determines the temperature value T corresponding to the frequency difference Δf calculated by the differential processing unit. The expression for the calibration curve based on the frequency difference and temperature value is: T =(Δf -Δf0) / (kt - kt') + T0; Where T represents the actual temperature value, T0 represents the preset temperature value, Δf is the frequency difference between the detection resonance region and the reference resonance region corresponding to the actual temperature value T, Δf0 is the frequency difference between the detection resonance region and the reference resonance region corresponding to the preset temperature value T0, kt is the temperature coefficient of the temperature-sensitive film in the detection resonance region, and kt' is the temperature coefficient of the piezoelectric substrate material in the reference resonance region or the temperature coefficient of the inert film in the reference resonance region.

[0054] In an optional embodiment, the demodulation system further includes a power management module, which can convert solar or radio frequency energy into electrical energy to power the demodulation system and enable long-term passive operation.

[0055] The surface acoustic wave temperature sensor and demodulation system provided in this invention have the following advantages: (1) Strong common-mode interference suppression capability: Through the dual-resonator differential design, the detection resonator and the reference resonator are subjected to the same common-mode interference, and the frequency difference Δf can completely cancel the interference effect. Compared with the single resonator scheme, the measurement error in temperature and humidity fluctuation scenarios is reduced from ±2℃ to ±0.5℃, and the accuracy is improved by four times; (2) Excellent anti-coupling interference performance: The isolation slot blocks the lateral propagation of sound waves, making the coupling coefficient between the two resonators ≤-40dB. Compared with the unisolated dual resonator scheme (coupling coefficient ≥-20dB), the cross-interference suppression ratio is improved by more than 20dB. (3) High wireless demodulation accuracy: The dedicated differential processing unit of the demodulation system, combined with hardware filtering, achieves a frequency detection resolution of 100Hz, which is 50 times higher than that of general RF modules (resolution ±5kHz). (4) Low power consumption and long lifespan: The demodulation system adopts a low power consumption design (power consumption ≤ 10mW), supports energy harvesting power supply, and does not require frequent battery replacement; the wireless passive characteristics of the sensor avoid wiring and are suitable for long-term operation in harsh environments (lifespan ≥ 10 years). (5) Self-calibration capability: The drift caused by substrate aging and stress relaxation is corrected in real time by the reference resonator, eliminating the need for manual periodic calibration and reducing maintenance costs by 80%.

[0056] The optional embodiments of the present invention have been described in detail above with reference to the accompanying drawings. However, the embodiments of the present invention are not limited to the specific details in the above embodiments. Within the scope of the technical concept of the embodiments of the present invention, various simple modifications can be made to the technical solutions of the embodiments of the present invention, and these simple modifications all fall within the protection scope of the embodiments of the present invention. Furthermore, it should be noted that the various specific technical features described in the above specific embodiments can be combined in any suitable manner without contradiction. As long as such combination does not violate the spirit of the embodiments of the present invention, it should also be considered as the content disclosed in the embodiments of the present invention.

Claims

1. A surface acoustic wave temperature sensor, characterized in that, include: A piezoelectric substrate, comprising at least four sets of interdigital transducers, at least four sets of reflective gratings, and a planar antenna formed on the piezoelectric substrate; A temperature-sensitive film is covered on the surface of the piezoelectric substrate between the two sets of interdigital transducers. The two sets of reflective gratings, the two sets of interdigital transducers, and the temperature-sensitive film between the two sets of interdigital transducers together with the piezoelectric substrate form a detection resonance region. The other two sets of interdigital transducers and the other two sets of reflective gratings together with the piezoelectric substrate constitute the reference resonant region. An isolation groove is provided in the piezoelectric substrate between the detection resonant region and the reference resonant region. The isolation groove is used to block the propagation of surface acoustic waves generated by the interdigital transducer in the detection resonant region to the reference resonant region. One end of the planar antenna is connected to a set of interdigital transducers in the detection resonant region, and the other end of the planar antenna is connected to a set of interdigital transducers in the reference resonant region. The planar antenna is used to receive radio frequency signals and transmit them to the interdigital transducers, and to transmit the frequency signal of the surface acoustic wave generated by the interdigital transducers under the excitation of the radio frequency signals.

2. The surface acoustic wave temperature sensor according to claim 1, characterized in that, The piezoelectric substrate surface between the other two sets of interdigital transducers is covered with an inert film. The other two sets of reflective gratings, the other two sets of interdigital transducers, and the inert film between the two sets of interdigital transducers together with the piezoelectric substrate constitute a reference resonant region.

3. The surface acoustic wave temperature sensor according to claim 1, characterized in that, The isolation groove is filled with insulating medium material.

4. The surface acoustic wave temperature sensor according to claim 1, characterized in that, The lengths of the interdigitated fingers in each group of interdigitated transducers are not equal. The length of each interdigit is determined by applying apodization weighting to interdigital transducers with equal-length interdigital fingers using a window function.

5. The surface acoustic wave temperature sensor according to claim 1, characterized in that, Of the two sets of interdigital transducers in the detection resonant region, one set of interdigital transducers serves as the input interdigital transducer, and the other set serves as the output interdigital transducer. Of the two sets of interdigital transducers in the reference resonant region, one set of interdigital transducers serves as the input interdigital transducer, and the other set serves as the output interdigital transducer. One end of the planar antenna is connected to the input interdigital transducer of the detection resonant region, and the other end of the planar antenna is connected to the input interdigital transducer of the reference resonant region.

6. A method for manufacturing a surface acoustic wave temperature sensor, characterized in that, include: At least four sets of interdigital transducers and at least four sets of reflective gratings are formed on the same piezoelectric substrate; A temperature-sensitive film is formed on the surface of a piezoelectric substrate between two sets of interdigital transducers; the two sets of reflective gratings, the two sets of interdigital transducers, and the temperature-sensitive film between the two sets of interdigital transducers together with the piezoelectric substrate constitute a detection resonance region; the other two sets of interdigital transducers and the other two sets of reflective gratings together with the piezoelectric substrate constitute a reference resonance region. An isolation groove is formed in the piezoelectric substrate between the detection resonant region and the reference resonant region; the isolation groove is used to block the propagation of surface acoustic waves generated by the interdigital transducer in the detection resonant region to the region where the reference resonant region is located. A set of planar antennas is formed on the surface of a piezoelectric substrate outside the detection resonant region and the reference resonant region, such that one end of the planar antenna is connected to a set of interdigital transducers in the detection resonant region, and the other end of the planar antenna is connected to a set of interdigital transducers in the reference resonant region; the planar antenna is used to receive radio frequency signals and transmit them to the interdigital transducers, and to transmit the frequency signal of the surface acoustic wave generated by the interdigital transducers under the excitation of the radio frequency signals.

7. The method for manufacturing a surface acoustic wave temperature sensor according to claim 6, characterized in that, The method further includes: An inert film is formed on the surface of the piezoelectric substrate between the other two sets of interdigital transducers; the other two sets of reflective gratings, the other two sets of interdigital transducers, and the inert film between the two sets of interdigital transducers together with the piezoelectric substrate constitute a reference resonant region.

8. The method for manufacturing a surface acoustic wave temperature sensor according to claim 6, characterized in that, The method further includes: The isolation groove is filled with insulating medium material.

9. The method for manufacturing a surface acoustic wave temperature sensor according to claim 6, characterized in that, At least four sets of interdigital transducers and at least four sets of reflective gratings are formed on the same piezoelectric substrate, including: Photoresist is coated onto the cleaned piezoelectric substrate surface. Through exposure and development processes, the patterns of interdigitated transducers and reflective gratings are formed on the photoresist on the piezoelectric substrate surface. Metal is sputtered onto the surface of a piezoelectric substrate to form a metal film of the pattern, which serves as an interdigital transducer and a reflective grating.

10. The method for manufacturing a surface acoustic wave temperature sensor according to claim 6, characterized in that, An isolation trench is formed in the piezoelectric substrate between the detection resonant region and the reference resonant region, including: The surface of the piezoelectric substrate between the detection resonant region and the reference resonant region is ground and polished to remove part of the piezoelectric substrate material and form an isolation groove of a preset depth. Alternatively, dry or wet etching processes can be used to etch the piezoelectric substrate between the detection resonant region and the reference resonant region to form an isolation trench of a predetermined depth. The preset depth is greater than or equal to one-quarter of the wavelength of the surface acoustic wave.

11. The method for manufacturing a surface acoustic wave temperature sensor according to claim 6, characterized in that, A set of planar antennas is formed on the surface of the piezoelectric substrate outside the detection resonant region and the reference resonant region, including: A metal thin film is deposited on the surface of a piezoelectric substrate outside the detection resonant region and the reference resonant region; a photoresist is coated on the surface of the metal thin film, and a planar antenna pattern is formed on the photoresist through exposure and development processes; The piezoelectric substrate is etched using either dry or wet etching processes to form the planar antenna with the aforementioned pattern.

12. A demodulation system, characterized in that, The demodulation system is applied to the surface acoustic wave temperature sensor according to claim 1, and the demodulation system includes: a radio frequency transmitting module, a signal receiving module, a differential processing unit, and a temperature demodulation unit; The radio frequency transmitting module is used to generate radio frequency signals and send radio frequency signals to the surface acoustic wave temperature sensor. The signal receiving module is used to receive a first frequency signal and a second frequency signal from the surface acoustic wave temperature sensor. The first frequency signal represents the frequency of the surface acoustic wave generated by the detection resonant region of the surface acoustic wave temperature sensor under the excitation of the radio frequency signal, and the second frequency signal represents the frequency of the surface acoustic wave generated by the reference resonant region of the surface acoustic wave temperature sensor under the excitation of the radio frequency signal. The differential processing unit is used to calculate the difference between the frequency represented by the first frequency signal and the frequency represented by the second frequency signal; The temperature demodulation unit is used to determine the temperature value based on the frequency difference calculated by the differential processing unit.

13. The demodulation system according to claim 12, characterized in that, The temperature demodulation unit has a pre-stored calibration curve based on the frequency difference and temperature value; The temperature demodulation unit determines the temperature value corresponding to the frequency difference calculated by the differential processing unit based on the calibration curve based on the frequency difference and temperature value.

14. The demodulation system according to claim 13, characterized in that, The expression for the calibration curve based on the frequency difference and temperature value is: T =(Δf -Δf0) / (kt - kt') + T0; Where T represents the actual temperature value, T0 represents the preset temperature value, Δf is the frequency difference between the detection resonance region and the reference resonance region corresponding to the actual temperature value T, Δf0 is the frequency difference between the detection resonance region and the reference resonance region corresponding to the preset temperature value T0, kt is the temperature coefficient of the temperature-sensitive film in the detection resonance region, and kt' is the temperature coefficient of the piezoelectric substrate material in the reference resonance region or the temperature coefficient of the inert film in the reference resonance region.

15. The demodulation system according to claim 12, characterized in that, The demodulation system further includes a power management module, which is used to convert solar or radio frequency energy into electrical energy to power the demodulation system.

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