Surface acoustic wave gas sensor and manufacturing method

Abstract

The invention provides a surface acoustic wave gas sensor and a manufacturing method, and belongs to the technical field of sensors. The sensor comprises a piezoelectric substrate, four groups of interdigital transducers and four groups of reflecting gratings, wherein the four groups of interdigital transducers and the four groups of reflecting gratings are formed on the piezoelectric substrate; wherein the surface of the piezoelectric substrate between the two groups of interdigital transducers is covered with a gas sensitive film, and the two groups of reflecting gratings, the two groups of interdigital transducers, the gas sensitive film and the piezoelectric substrate form a detection channel; the other two groups of interdigital transducers, the other two groups of reflecting gratings and the piezoelectric substrate form a reference channel; and an isolation groove is formed in the piezoelectric substrate between the detection channel and the reference channel. According to the method, the difference value of the propagation delay time of the surface acoustic waves of the detection channel and the reference channel is calculated, and the concentration of the target gas is calculated based on the difference value, so that differential compensation of common-mode interference is realized; the surface acoustic wave of the detection channel is prevented from spreading to the reference channel through the isolation groove, the coupling interference between the detection channel and the reference channel is reduced, and the cross interference rejection ratio is increased.

Description

Technical Field

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

[0002] Surface Acoustic Wave (SAW) gas sensors have gained widespread attention in the field of gas detection due to their advantages such as high sensitivity, fast response speed, and wireless transmission capability. The working principle of SAW gas sensors is based on the adsorption or reaction of a target gas by a gas-sensitive membrane, which causes a change in the propagation characteristics of surface acoustic waves. The gas concentration is measured by detecting this change.

[0003] Traditional SAW gas sensors mostly employ a single-channel delay line structure. This structure includes a piezoelectric substrate, an interdigital transducer (IDT), and a gas-sensitive membrane. When the target gas interacts with the gas-sensitive membrane, changes occur in the membrane's mass, elastic modulus, etc., causing changes in the propagation velocity or phase of the surface acoustic wave, which in turn reflects the gas concentration through changes in the delay time.

[0004] Existing single-channel SAW gas sensors are susceptible to common-mode interference factors in the environment (such as temperature, humidity, and air pressure). For example, temperature changes directly affect the propagation speed of surface acoustic waves by altering the thermal expansion coefficient and elastic modulus of the piezoelectric substrate, leading to changes in the time delay. These changes are superimposed on the changes caused by gas concentration, making them difficult to distinguish and thus reducing measurement accuracy.

[0005] While some solutions attempt to compensate for interference, such as using additional temperature sensors for calibration, this external calibration method increases system complexity and makes it difficult to achieve real-time, accurate synchronous compensation. Furthermore, some multi-channel sensor designs lack effective structural isolation, making them prone to acoustic coupling interference between channels, which also affects compensation effectiveness and measurement accuracy. Summary of the Invention

[0006] To address the problems of existing surface acoustic wave (SAW) gas sensors being greatly affected by common-mode interference and having poor compensation effects, this invention provides a SAW gas sensor and its manufacturing method.

[0007] The first aspect of the present invention provides a surface acoustic wave gas sensor, comprising: a piezoelectric substrate, at least four sets of interdigital transducers formed on the piezoelectric substrate, and at least four sets of reflective gratings;

[0008] A gas-sensitive membrane 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 gas-sensitive membrane between the two sets of interdigital transducers, together with the piezoelectric substrate, form a detection channel. The other two sets of interdigital transducers and the other two sets of reflective gratings together with the piezoelectric substrate form a reference channel. An isolation groove is provided in the piezoelectric substrate between the detection channel and the reference channel. The isolation groove is used to block the surface acoustic waves generated by the interdigital transducer of the detection channel from propagating to the reference channel, and to block the surface acoustic waves generated by the interdigital transducer of the reference channel from propagating to the detection channel. The detection channel and the reference channel are used to simultaneously introduce the target gas. The concentration of the target gas is calculated based on the difference in the surface acoustic wave propagation delay time caused by the target gas and common-mode interference between the detection channel and the reference channel.

[0009] 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, form a reference channel.

[0010] In this embodiment of the invention, the isolation groove is filled with an insulating medium material.

[0011] In this embodiment of the invention, of the two sets of interdigital transducers in the detection channel, one set of interdigital transducers serves as the input interdigital transducer, and the other set of interdigital transducers serves as the output interdigital transducer. Of the two sets of interdigital transducers in the reference channel, one set serves as the input interdigital transducer, and the other set serves as the output interdigital transducer.

[0012] 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 interdigit is determined by applying apodization weighting to interdigital transducers with equal-length interdigital fingers using a window function.

[0013] In this embodiment of the invention, the calculation expression for the concentration of the target gas based on the difference in surface acoustic wave propagation delay time is as follows: ; Where C represents the concentration of the target gas, To detect the difference in surface acoustic wave propagation delay time between the detection channel and the reference channel under target gas and common-mode interference, k and b are predetermined calibration coefficients.

[0014] A second aspect of the present invention provides a method for manufacturing a surface acoustic wave gas 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 gas-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 gas-sensitive film between the two sets of interdigital transducers and the piezoelectric substrate constitute a detection channel; the other two sets of interdigital transducers and the other two sets of reflective gratings and the piezoelectric substrate constitute a reference channel. An isolation groove is formed in the piezoelectric substrate between the detection channel and the reference channel; the isolation groove is used to block the propagation of surface acoustic waves generated by the interdigital transducer of the detection channel to the region where the reference channel is located.

[0015] In this embodiment of the invention, the manufacturing method of the surface acoustic wave gas 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 form a reference channel.

[0016] In this embodiment of the invention, the manufacturing method of the surface acoustic wave gas sensor further includes: The isolation groove is filled with insulating medium material.

[0017] 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, and through exposure and development processes, patterned areas of interdigitated transducers and reflective gratings are formed on the piezoelectric substrate surface. Metal is sputtered onto a patterned area on the surface of a piezoelectric substrate to form a metal film that serves as an interdigital transducer and a reflective grating.

[0018] In this embodiment of the invention, the method for forming a gas-sensitive membrane includes: A solid gas-sensitive film is generated by chemical vapor deposition, which involves a chemical reaction between a gaseous precursor and a piezoelectric substrate. Alternatively, a gas-sensitive film can be generated on the surface of the piezoelectric substrate using sputtering or evaporation coating processes.

[0019] In this embodiment of the invention, the piezoelectric substrate between the detection channel and the reference channel is etched to form an isolation trench, including: The surface of the piezoelectric substrate is ground and polished to remove part of the piezoelectric substrate material, forming an isolation groove of a predetermined depth; Alternatively, dry or wet etching processes can be used to etch the piezoelectric substrate 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.

[0020] The above technical solution forms at least four sets of interdigital transducers and at least four sets of reflective gratings on the same piezoelectric substrate to constitute a detection channel and a reference channel. This ensures that the detection channel and the reference channel are subjected to the same common-mode interference. By calculating the difference in the propagation delay time of surface acoustic waves caused by the target gas and common-mode interference between the detection channel and the reference channel, the concentration of the target gas is calculated based on this difference, thereby achieving differential compensation for common-mode interference. Furthermore, an isolation groove is set in the piezoelectric substrate between the detection channel and the reference channel to block the propagation of surface acoustic waves from the detection channel to the reference channel, thereby reducing coupling interference between the detection channel and the reference channel and improving the cross-interference suppression ratio.

[0021] 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

[0022] 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 gas sensor provided in an embodiment of the present invention; Figure 2 This is a flowchart of a method for manufacturing a surface acoustic wave gas sensor provided in an embodiment of the present invention.

[0023] Explanation of reference numerals in the attached figures 1-Piezoelectric substrate, 2-Detection channel, 3-Reference channel, 4-Isolation groove 11-First interdigital transducer, 12-First reflective grating, 13-Second interdigital transducer. 14-Second reflective grating, 15-Gas-sensitive membrane, 16-Third interdigital transducer. 17-Third reflector grating, 18-Fourth interdigital transducer, 19-Fourth reflector grating. Detailed Implementation

[0024] 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.

[0025] 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.

[0026] 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.

[0027] 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.

[0028] To address the problems of existing surface acoustic wave (SAW) gas sensors being significantly affected by common-mode interference and exhibiting poor compensation performance, this invention provides a SAW gas sensor and its manufacturing method. This invention forms at least four sets of interdigital transducers and at least four sets of reflective gratings on the same piezoelectric substrate, constituting a detection channel and a reference channel. This ensures that the detection channel and the reference channel are subjected to the same common-mode interference. By calculating the difference in SAW propagation delay time between the detection channel and the reference channel under the influence of the target gas and common-mode interference, the concentration of the target gas is calculated based on this difference, achieving differential compensation for common-mode interference. Furthermore, an isolation groove is formed in the piezoelectric substrate between the detection channel and the reference channel. This isolation groove blocks the propagation of SAW from the detection channel to the reference channel, reducing coupling interference between the detection channel and the reference channel and improving the cross-interference suppression ratio.

[0029] Figure 1 This is a schematic diagram of the structure of the surface acoustic wave gas sensor provided in an embodiment of the present invention. Figure 1As shown, the surface acoustic wave gas sensor provided in this embodiment includes: a piezoelectric substrate 1, four sets of interdigital transducers (IDTs) formed on the piezoelectric substrate 1, and four sets of reflective gratings. 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 11 as input, a second interdigital transducer 13 as output, a third interdigital transducer 16 as input, and a fourth interdigital transducer 18 as output. The four sets of reflective gratings include: a first reflective grating 12 near the first interdigital transducer 11, a second reflective grating 14 near the second interdigital transducer 13, a third reflective grating 17 near the third interdigital transducer 16, and a fourth reflective grating 19 near the fourth interdigital transducer 18. 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 gas-sensitive membrane 15 covers the surface of the piezoelectric substrate 1 between the first interdigital transducer 11 and the second interdigital transducer 13. The first interdigital transducer 11, the second interdigital transducer 13, the first reflective grating 12, the second reflective grating 14, and the gas-sensitive membrane 15 between the first interdigital transducer 11 and the second interdigital transducer 13, together with the piezoelectric substrate 1, constitute a detection channel 2. The third interdigital transducer 16, the fourth interdigital transducer 18, the third reflective grating 17, and the fourth reflective grating 19, together with the piezoelectric substrate 1, constitute a reference channel 3. An isolation groove 4 is provided in the piezoelectric substrate 1 between the detection channel 2 and the reference channel 3. The isolation groove 4 is used to block the propagation of surface acoustic waves generated by the interdigital transducers in the detection channel 2 to the reference channel 3, and to block the propagation of surface acoustic waves generated by the interdigital transducers in the reference channel 3 to the detection channel 2.

[0030] Since detection channel 2 and reference channel 3 are formed on the same piezoelectric substrate 1, and are subject to the same common-mode interference such as temperature and humidity, the influence of common-mode interference is canceled out by the difference between the surface acoustic wave (SAW) frequencies of the detection channel and the reference channel, thus achieving differential compensation for common-mode interference. When using a surface acoustic wave (SAW) gas sensor, the target gas is simultaneously introduced into detection channel 2 and reference channel 3. By calculating the difference in SAW propagation delay time between detection channel 2 and reference channel 3 under the target gas and common-mode interference (i.e., obtaining the signal change caused only by the target gas), the concentration of the target gas can be calculated based on the difference in SAW propagation delay time, enabling accurate measurement of the target gas concentration.

[0031] The working principle of the surface acoustic wave gas sensor provided in this embodiment is as follows: When the sensor is working, both the detection channel and the reference channel are affected by common-mode interference factors such as temperature and humidity. The detection channel is also affected by the interaction between the target gas and the gas-sensitive membrane. By comparing the output signals of the two channels, common-mode interference can be eliminated, and the signal change caused solely by the target gas can be obtained, thereby achieving accurate measurement. The theoretical derivation is as follows: Regarding the detection channel signal: At the reference temperature T0 and without target gas, the delay time of the detection channel is... The delay time of the detection channel when the ambient temperature changes by ΔT and the target gas concentration C is present. It consists of three parts: the delay time of the detection channel when there is no target gas. Delay changes caused by common-mode interference (temperature, etc.) Delayed changes caused by the target gas ,Right now: .

[0032] Regarding the reference channel signal: The delay time of the reference channel at the reference temperature T0 is... (Due to the consistent structure, The delay time of the reference channel when the ambient temperature changes by ΔT. Includes only the delay time at reference temperature T0 Delay variation caused by common-mode interference (Because there is no sensitive or inert membrane, it is not affected by gases), that is: ; Since the two channels have identical structures and are located in the same environment, common-mode interference has the same effect on both, that is: .

[0033] Regarding common-mode interference compensation: the time difference between the two channels for: ; By measuring this time delay difference, the signal change caused solely by the target gas can be obtained, thus achieving effective compensation for common-mode interference.

[0034] Then according to the pre-calibrated The correspondence between the gas concentration C and the target gas concentration can be deduced from this relationship: ; Where k and b are calibration coefficients, Equivalent to the difference in surface acoustic wave propagation delay time between the detection channel and the reference channel caused by the target gas and common-mode interference. .

[0035] In an optional embodiment, the surface of the piezoelectric substrate 1 between the third interdigital transducer 16 and the fourth interdigital transducer 18 of the reference channel 3 may be covered with an inert film (not shown in the figures) formed of an inert material. The third interdigital transducer 16, the fourth interdigital transducer 18, the third reflective grating 17, the fourth reflective grating 19, and the inert film between the third interdigital transducer 16 and the fourth interdigital transducer 18, together with the piezoelectric substrate 1, constitute the reference channel 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 medium 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 channel 2 and the reference channel 3, reducing coupling interference.

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

[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 surface acoustic wave gas sensor described above. For example... Figure 2As shown, the manufacturing method of the surface acoustic wave gas 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 gas-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 gas-sensitive film between the two sets of interdigital transducers and the piezoelectric substrate constitute a detection channel; the other two sets of interdigital transducers and the other two sets of reflective gratings and the piezoelectric substrate constitute a reference channel. S230, an isolation groove is formed in the piezoelectric substrate between the detection channel and the reference channel; the isolation groove is used to block the propagation of surface acoustic waves generated by the interdigital transducer of the detection channel to the region where the reference channel is located.

[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 gas-sensitive film on the piezoelectric substrate surface 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 gas-sensitive film. Alternatively, plasma-enhanced CVD (PECVD) technology can be used, utilizing radio frequency or DC plasma to excite the reactive gas, which can lower the deposition temperature and improve film adhesion. Or, 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 gas-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. The gas-sensitive film material is selected according to the type of target gas; for example, polyimide films can be used to detect formaldehyde, and copper phthalocyanine films can be used to detect ammonia.

[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 channel and the reference channel 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 channel and the reference channel 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 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 channel. Specifically, refer to... Figure 1 An inert film (not shown in the figures) formed by coating an inert material is deposited on the surface of the piezoelectric substrate 1 between the third interdigital transducer 16 and the fourth interdigital transducer 18 in the reference channel 3. The third interdigital transducer 16, the fourth interdigital transducer 18, the third reflective grating 17, the fourth reflective grating 19, and the inert film between the third interdigital transducer 16 and the fourth interdigital transducer 18, together with the piezoelectric substrate 1, constitute the reference channel 3.

[0046] In an optional embodiment, after step S230, the following step is further included: filling the isolation groove with an insulating medium material. For example, silicone rubber insulating material is filled into the isolation groove to block the lateral propagation of sound waves between the detection channel 2 and the reference channel 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.

[0047] The surface acoustic wave gas sensor and manufacturing method provided in this invention have the following advantages: (1) Significant common-mode interference compensation effect: The dual-channel design is adopted. The detection channel is affected by the target gas and common-mode interference, while the reference channel is only affected by common-mode interference. The common-mode interference can be directly eliminated by the signal difference between the two. Compared with the single-channel post-processing algorithm compensation, the real-time performance and accuracy are greatly improved. Since the interference is physically separated through structural design rather than post-processing, algorithm errors are avoided. (2) Low interference between channels: The isolation slots are set to block the lateral propagation of surface acoustic waves, effectively reducing the acoustic wave coupling between channels. Compared with the multi-channel design without isolation, the cross-interference suppression ratio is improved by at least one order of magnitude, ensuring the purity of the reference channel signal and providing a guarantee for accurate compensation. (3) It is manufactured using MEMS compatible technology and has a high degree of integration: the two channels are integrated on the same piezoelectric substrate, eliminating the need for external calibration components. Compared with external sensor compensation schemes, the system volume is reduced by more than 30%, power consumption is reduced, and it is easy to mass-produce, with lower cost, which can meet the gas detection needs in various complex environments. (4) Wide range of applications: By changing the sensitive membrane, it can be adapted to the detection of different target gases, and can still maintain high-precision measurement in complex environments with large temperature and humidity fluctuations. It is suitable for various scenarios such as environmental monitoring and industrial production.

[0048] 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 gas sensor, characterized in that, include: A piezoelectric substrate, with at least four sets of interdigital transducers and at least four sets of reflective gratings formed on the piezoelectric substrate; A gas-sensitive membrane 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 gas-sensitive membrane between the two sets of interdigital transducers, together with the piezoelectric substrate, form a detection channel. The other two sets of interdigital transducers and the other two sets of reflective gratings together with the piezoelectric substrate form a reference channel. An isolation groove is provided in the piezoelectric substrate between the detection channel and the reference channel. The isolation groove is used to block the propagation of surface acoustic waves generated by the interdigital transducer of the detection channel to the reference channel. The detection channel and the reference channel are used to simultaneously introduce the target gas. The concentration of the target gas is calculated based on the difference in the surface acoustic wave propagation delay time caused by the target gas and common-mode interference between the detection channel and the reference channel.

2. The surface acoustic wave gas 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 form a reference channel.

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

4. The surface acoustic wave gas sensor according to claim 1, characterized in that, Of the two sets of interdigital transducers in the detection channel, 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 channel, one set serves as the input interdigital transducer, and the other set serves as the output interdigital transducer.

5. The surface acoustic wave gas 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.

6. The surface acoustic wave gas sensor according to claim 1, characterized in that, The formula for calculating the concentration of the target gas based on the difference in the propagation delay time of the surface acoustic waves is as follows: ； Where C represents the concentration of the target gas, To detect the difference in surface acoustic wave propagation delay time between the detection channel and the reference channel under target gas and common-mode interference, k and b are predetermined calibration coefficients.

7. A method for manufacturing a surface acoustic wave gas 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 gas-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 gas-sensitive film between the two sets of interdigital transducers and the piezoelectric substrate constitute a detection channel; the other two sets of interdigital transducers and the other two sets of reflective gratings and the piezoelectric substrate constitute a reference channel. An isolation groove is formed in the piezoelectric substrate between the detection channel and the reference channel; the isolation groove is used to block the propagation of surface acoustic waves generated by the interdigital transducer of the detection channel to the region where the reference channel is located.

8. The method for manufacturing a surface acoustic wave gas sensor according to claim 7, 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 channel.

9. The method for manufacturing a surface acoustic wave gas sensor according to claim 7, characterized in that, The method further includes: The isolation groove is filled with insulating medium material.

10. The method for manufacturing a surface acoustic wave gas sensor according to claim 7, 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, and through exposure and development processes, patterned areas of interdigitated transducers and reflective gratings are formed on the piezoelectric substrate surface. Metal is sputtered onto a patterned area on the surface of a piezoelectric substrate to form a metal film that serves as an interdigital transducer and a reflective grating.

11. The method for manufacturing a surface acoustic wave gas sensor according to claim 7, characterized in that, Methods for forming a gas-sensitive membrane include: A solid gas-sensitive film is generated by chemical vapor deposition, which involves a chemical reaction between a gaseous precursor and a piezoelectric substrate. Alternatively, a gas-sensitive film can be generated on the surface of the piezoelectric substrate using sputtering or evaporation coating processes.

12. The method for manufacturing a surface acoustic wave gas sensor according to claim 7, characterized in that, The piezoelectric substrate between the detection channel and the reference channel is etched to form an isolation trench, including: The surface of the piezoelectric substrate is ground and polished to remove part of the piezoelectric substrate material, forming an isolation groove of a predetermined depth; Alternatively, dry or wet etching processes can be used to etch the piezoelectric substrate 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.

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