A surface acoustic wave sensor and a method of manufacturing the same

Abstract

The application discloses a surface acoustic wave sensor and a preparation method thereof, and relates to the technical field of sensors.The surface acoustic wave sensor and the preparation method thereof comprise a bonding layer, a metal layer and a monocrystal piezoelectric film layer which are sequentially laid on a silicon substrate, and the monocrystal piezoelectric film layer is provided with an interdigital electrode.The surface acoustic wave sensor and the preparation method thereof can improve the sensitivity of the surface acoustic wave sensor and enhance the electromechanical coupling effect.

Description

Technical Field

[0001] This application relates to the field of sensor technology, and more specifically, to a surface acoustic wave sensor and its fabrication method. Background Technology

[0002] Surface acoustic wave (SAW) devices consist of a piezoelectric substrate and interdigital transducers with different functions deposited on the substrate. Interdigital transducers are metal electrodes shaped like crossed fingers, hence the name. The piezoelectric conversion element of a SAW sensor possesses two important properties: spontaneous and reversible, known as the piezoelectric effect. The principle of the piezoelectric effect is that if pressure is applied to a piezoelectric material, it generates a potential difference (called the direct piezoelectric effect); conversely, if a voltage is applied, it generates mechanical stress (called the inverse piezoelectric effect). If the pressure is a high-frequency vibration, it generates a high-frequency current. When a high-frequency electrical signal is applied to the piezoelectric ceramic, a high-frequency acoustic signal (mechanical vibration) is generated, which is what we commonly call an ultrasonic signal. SAW sensors have broad application prospects due to their advantages such as small size, light weight, simple structure, reliable operation, high natural frequency, high sensitivity and signal-to-noise ratio, and long-distance detection capability, and are developing towards portability, multi-parameter measurement, and high sensitivity.

[0003] Existing surface acoustic wave (SAW) sensors generally lack a bottom electrode, which prevents them from achieving optimal performance. Even if a SAW resonator with a bottom electrode is to be fabricated, directly depositing the bottom electrode and piezoelectric thin film sequentially on a silicon substrate will result in a non-monocrystalline piezoelectric thin film, leading to poor SAW sensor performance. Therefore, the performance of the SAW resonator is not optimal. Summary of the Invention

[0004] The purpose of this application is to provide a surface acoustic wave sensor and its fabrication method, which can improve the sensitivity of the surface acoustic wave sensor and enhance the electromechanical coupling effect.

[0005] One embodiment of this application provides a surface acoustic wave sensor, including a bonding layer, a metal layer and a single crystal piezoelectric thin film layer sequentially deposited on a silicon substrate, wherein interdigitated electrodes are disposed on the single crystal piezoelectric thin film layer.

[0006] As one feasible approach, reflective gratings are provided on both sides of the interdigitated electrode along the direction of the interdigitated arrangement, and the reflective gratings are provided in the same layer as the interdigitated electrode.

[0007] As one feasible approach, a first strip-shaped through-slot is formed on the single-crystal piezoelectric thin film layer, which encloses a working area with a free end and a fixed end. A second strip-shaped through-slot is formed on the metal layer corresponding to the position of the first strip-shaped through-slot, and a third strip-shaped through-slot is formed on the bonding layer corresponding to the second strip-shaped through-slot. The first strip-shaped through-slot is located outside the reflective gate and the interdigitated electrode. A groove is formed on the silicon substrate, and the third strip-shaped through-slot communicates with the groove. The cross-sectional area of ​​the groove is larger than that of the working area.

[0008] As one feasible approach, the first strip through-slot includes three, which are perpendicular to each other and connected end to end. The line connecting the endpoints of the three first strip through-slots forms a rectangle, and the projections of the three first strip through-slots fall within the projection range of the groove, so that the working area and the silicon substrate form a cantilever beam structure.

[0009] As one feasible approach, the first strip channel comprises three, which are connected end to end and the line connecting the endpoints of the three first strip channels forms a trapezoid, with the base of the trapezoid being the free end of the working area.

[0010] As one feasible approach, the groove is set to correspond to the working area, and the projections of the three first strip-shaped through slots coincide with the three edges of the projection of the groove.

[0011] As one feasible approach, the single-crystal piezoelectric thin film layer is an AlN layer or a ScAlN layer.

[0012] A method for fabricating a surface acoustic wave (SAW) sensor includes: providing a device wafer, the device wafer including a single-crystal substrate and a single-crystal piezoelectric thin film layer, a metal layer and a first bonding layer sequentially stacked on the single-crystal substrate; providing a cap wafer, the cap wafer including a silicon substrate and a second bonding layer disposed on the silicon substrate; bonding the device wafer and the cap wafer through the first bonding layer and the second bonding layer; removing the single-crystal substrate of the device wafer; and fabricating interdigitated electrodes and a reflective gate on the single-crystal piezoelectric thin film layer.

[0013] As an feasible approach, after fabricating interdigitated electrodes and a reflective grating on a single-crystal piezoelectric thin film layer, the fabrication method of the surface acoustic wave sensor further includes: etching a silicon substrate to form a square groove at the center of the side of the silicon substrate away from the second bonding layer; etching a device wafer and the second bonding layer to form a fourth through-slot on the device wafer; and forming a fifth through-slot on the second bonding layer corresponding to the fourth through-slot. The fourth through-slot includes three slots, which are perpendicular to each other and connected end to end. The projections of the three fourth through-slots coincide with the edges of the projections of the square groove.

[0014] As one feasible method, fabricating interdigitated electrodes and reflective gates on a single-crystal piezoelectric thin film layer includes setting the interdigitated electrodes and reflective gates in the same layer and with the same material.

[0015] The beneficial effects of the embodiments of this application include:

[0016] The surface acoustic wave (SAW) sensor provided by this invention includes a bonding layer, a metal layer, and a single-crystal piezoelectric thin film layer sequentially deposited on a silicon substrate. Interdigitated electrodes are disposed on the single-crystal piezoelectric thin film layer. The bonding of the bonding layer allows the metal layer and the single-crystal piezoelectric thin film layer to coexist within the same SAW sensor. The metal layer serves as the lower electrode of the SAW sensor, and its high acoustic impedance enhances the electromechanical coupling coefficient of the sensor. The single-crystal piezoelectric thin film layer has a more regular crystal structure than polycrystalline piezoelectric thin films, resulting in lower energy loss and a higher coupling coefficient for the SAW sensor. Therefore, this invention improves the sensitivity of the SAW sensor and enhances the electromechanical coupling effect. Attached Figure Description

[0017] To more clearly illustrate the technical solutions of the embodiments of this application, the accompanying drawings used in the embodiments will be briefly introduced below. It should be understood that the following drawings only show some embodiments of this application and should not be regarded as a limitation of the scope. For those skilled in the art, other related drawings can be obtained based on these drawings without creative effort.

[0018] Figure 1 This is a schematic diagram of the structure of a surface acoustic wave sensor provided in an embodiment of this application;

[0019] Figure 2 A schematic diagram of a surface acoustic wave sensor from another perspective provided in the embodiments of this application;

[0020] Figure 3 This is a schematic diagram of another surface acoustic wave sensor provided in an embodiment of this application;

[0021] Figure 4 A flowchart illustrating the fabrication process of a surface acoustic wave sensor provided in this application embodiment;

[0022] Figure 5 This is one of the fabrication state diagrams of a surface acoustic wave sensor provided in an embodiment of this application;

[0023] Figure 6 This is the second fabrication state diagram of a surface acoustic wave sensor provided in an embodiment of this application.

[0024] Figure 7 The third diagram showing the fabrication state of a surface acoustic wave sensor provided in this application embodiment;

[0025] Figure 8 The fourth diagram showing the fabrication state of a surface acoustic wave sensor provided in this application embodiment;

[0026] Figure 9 This is the fifth diagram illustrating the fabrication process of a surface acoustic wave sensor provided in this application embodiment.

[0027] Icons: 100 - Surface acoustic wave sensor; 110 - Silicon substrate; 111 - Groove; 120 - Bonding layer; 121 - Third strip groove; 130 - Metal layer; 131 - Second strip groove; 140 - Single crystal piezoelectric thin film layer; 141 - First strip groove; 150 - Interdigitated electrode; 160 - Reflective grating; 170 - Working area; 181 - First bonding layer; 182 - Second bonding layer; 190 - Single crystal substrate. Detailed Implementation

[0028] To make the objectives, technical solutions, and advantages of the embodiments of this application clearer, the technical solutions of the embodiments of this application will be clearly and completely described below with reference to the accompanying drawings. Obviously, the described embodiments are only some embodiments of this application, and not all embodiments. The components of the embodiments of this application described and shown in the accompanying drawings can generally be arranged and designed in various different configurations.

[0029] Therefore, the following detailed description of the embodiments of this application provided in the accompanying drawings is not intended to limit the scope of the claimed application, but merely to illustrate selected embodiments of the application. All other embodiments obtained by those skilled in the art based on the embodiments of this application without inventive effort are within the scope of protection of this application.

[0030] It should be noted that similar labels and letters in the following figures indicate similar items. Therefore, once an item is defined in one figure, it does not need to be further defined and explained in subsequent figures.

[0031] In the description of this application, it should be noted that the terms "center," "vertical," "horizontal," "inner," and "outer," etc., indicate the orientation or positional relationship based on the orientation or positional relationship shown in the accompanying drawings, or the orientation or positional relationship commonly used when the product is in use. They are used only for the convenience of describing this application and for 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 application. Furthermore, the terms "first," "second," and "third," etc., are used only to distinguish descriptions and should not be construed as indicating or implying relative importance.

[0032] In the description of this application, it should also be noted that, unless otherwise expressly specified and limited, the terms "setup" and "connection" should be interpreted broadly, and those skilled in the art can understand the specific meaning of the above terms in this application according to the specific circumstances.

[0033] For surface acoustic wave (SAW) sensors, the crystal morphology of the piezoelectric material affects its performance, which in turn affects the performance of the SAW sensor. When the piezoelectric material is a single crystal, the SAW sensor performs well. Placing electrodes on the side of the piezoelectric material can also improve the performance of the SAW sensor. However, if the electrodes and piezoelectric films are deposited sequentially on a silicon substrate, the resulting piezoelectric film is not a single crystal, which leads to poor performance of the SAW sensor. Therefore, the performance of the SAW resonator is not optimal.

[0034] This invention provides a surface acoustic wave sensor 100, such as... Figure 1 , Figure 2 As shown, the substrate includes a bonding layer 120, a metal layer 130 and a single crystal piezoelectric thin film layer 140 sequentially deposited on a silicon substrate 110, and an interdigitated electrode 150 is disposed on the single crystal piezoelectric thin film layer 140.

[0035] like Figure 2 As shown, the interdigitated electrode 150 includes a plurality of strip-shaped input electrodes and a plurality of strip-shaped output electrodes arranged sequentially along a first direction. A strip-shaped output electrode is disposed between two adjacent strip-shaped input electrodes. One end of all the strip-shaped input electrodes is connected to form an input electrode, and the other end of all the strip-shaped output electrodes is connected to form an output electrode. The input electrodes convert the input electrical signal into an ultrasonic signal through the inverse piezoelectric effect, and the output electrodes convert the ultrasonic signal back into an electrical signal and output it.

[0036] Specifically, when the target under test approaches the input electrode, the input electrode converts the input electrical signal into an ultrasonic signal through the inverse piezoelectric effect. The ultrasonic signal propagates along the single-crystal piezoelectric thin film layer 140 to the output electrode, which converts the ultrasonic signal into an electrical signal and outputs it. The target under test can be calculated based on the electrical signal on the output electrode.

[0037] The surface acoustic wave sensor 100 of the present invention includes a metal layer 130, which serves as the lower electrode of the surface acoustic wave sensor 100. The metal layer 130 has a large acoustic impedance, thereby improving the electromechanical coupling coefficient of the surface acoustic wave sensor 100.

[0038] It should be noted that the specific form of the surface acoustic wave sensor is not limited in this invention. It can be a gas sensor, an acceleration sensor, a flow measurement sensor, etc. Any device that works based on the propagation of surface acoustic waves and piezoelectric properties is within the protection scope of this invention.

[0039] It should also be noted that the specific material of the metal layer 130 is not limited in this invention, as long as it is a metal. For example, Mo can be used because Mo has a large acoustic impedance.

[0040] The surface acoustic wave (SAW) sensor 100 provided by this invention includes a bonding layer 120, a metal layer 130, and a single-crystal piezoelectric thin film layer 140 sequentially deposited on a silicon substrate 110. Interdigitated electrodes 150 are disposed on the single-crystal piezoelectric thin film layer 140. The bonding of the bonding layer 120 allows the metal layer 130 and the single-crystal piezoelectric thin film layer 140 to coexist in the same SAW sensor 100. The metal layer 130 serves as the lower electrode of the SAW sensor 100, improving the roughness of the piezoelectric thin film, thereby reducing the loss of the SAW sensor 100 and increasing its sensitivity. Furthermore, its high acoustic impedance enhances the electromechanical coupling coefficient of the SAW sensor. The single-crystal piezoelectric thin film layer 140 has a more regular crystal structure than polycrystalline piezoelectric thin films, resulting in lower energy loss and a higher coupling coefficient for the SAW sensor 100. Therefore, this invention improves the sensitivity of the SAW sensor 100 and enhances the electromechanical coupling effect.

[0041] Optional, such as Figure 2 As shown, reflective grids 160 are respectively provided on both sides of the interdigital electrode 150 along the interdigital arrangement direction, and the reflective grids 160 are provided in the same layer as the interdigital electrode 150.

[0042] When ultrasound propagates in the single-crystal piezoelectric thin film layer 140, some of the ultrasound signal will propagate along the single-crystal piezoelectric thin film layer 140 to the edge of the surface acoustic wave sensor 100 until it disappears, thereby causing loss of ultrasound signal, reducing the ultrasound signal received by the output electrode, and thus reducing the sensitivity of the surface acoustic wave sensor 100.

[0043] To avoid loss of ultrasonic signals at the edges, the present invention provides reflective grids 160 on both sides of the interdigital electrode 150. When the ultrasonic signal is transmitted to the reflective grid 160, the reflective grid 160 can reflect the ultrasonic signal, so that the ultrasonic signal can be received by the output electrode, thereby increasing the ultrasonic signal received by the output electrode and improving the sensitivity of the acoustic surface wave sensor.

[0044] It should be noted that the propagation direction of the ultrasonic wave is along the direction of the interdigital arrangement of the interdigital electrodes 150. Therefore, the reflective grid 160 is disposed on both sides of the interdigital arrangement direction of the interdigital electrodes 150. The specific structure of the reflective grid 160 is not limited in this invention, as long as it can reflect the ultrasonic signal. For example, the reflective grid 160 of this invention is a metal strip. Since the interdigital electrodes 150 are metal electrodes, and the reflective grid 160 and the interdigital electrodes 150 are in the same layer, the reflective grid 160 and the interdigital electrodes 150 can be formed simultaneously in a single deposition, which can save on the fabrication process.

[0045] In one possible implementation of this invention, such as Figure 1 , Figure 2As shown, a first strip-shaped through-slot 141 is formed on the single-crystal piezoelectric thin film layer 140, which encloses a working area 170 with a free end and a fixed end. A second strip-shaped through-slot 131 is formed on the metal layer 130 corresponding to the position of the first strip-shaped through-slot 141. A third strip-shaped through-slot 121 is formed on the bonding layer 120 corresponding to the second strip-shaped through-slot 131. The first strip-shaped through-slot 141 is located outside the reflective gate 160 and the interdigitated electrode 150. A groove 111 is provided on the silicon substrate 110. The third strip-shaped through-slot 121 is connected to the groove 111. The cross-sectional area of ​​the groove 111 is larger than that of the working area 170.

[0046] The third strip groove 121 is connected to the groove 111, and the second strip groove 131 is correspondingly arranged with the first strip groove 141 and the third strip groove 121, so that the first strip groove 141, the second strip groove 131, the third strip groove 121 and the groove 111 are all connected, thereby making one side of the single crystal piezoelectric thin film layer 140 a free end, which can increase the deformation degree of the surface acoustic wave sensor 100, making the electrical signal more obvious and improving the sensitivity of the surface acoustic wave sensor 100.

[0047] It should be noted that the present invention does not limit the specific structure of the first strip-shaped through groove 141. It can be a curved through groove or at least two straight through grooves connected end to end, as long as they can form a semi-closed shape with an opening. The opening of the through groove is the fixed end of the working area 170.

[0048] It should also be noted that the second strip groove 131 and the third strip groove 121 must have the same structure as the first strip groove 141 in order to ensure that the working area 170 forms a free end.

[0049] Optional, such as Figure 2 As shown, the first strip channel 141 includes three, which are perpendicular to each other and connected end to end. The three first strip channels 141 form a working area 170. The line connecting the endpoints of the three first strip channels 141 forms a rectangle. The projection of the three first strip channels 141 falls within the projection range of the groove 111, so that the working area 170 and the silicon substrate 110 form a cantilever beam structure.

[0050] When the working area 170 and the silicon substrate 110 form a cantilever beam structure, the input electrode, output electrode, and part of the single-crystal piezoelectric thin film layer 140 are suspended, forming free ends. When the surface acoustic wave sensor is an accelerometer, the deformation of the single-crystal piezoelectric thin film layer 140 increases during accelerometer testing, making the electrical signal more pronounced. Under external influences, the piezoelectric layer material properties change, and the interdigital spacing also changes. These two changes together determine the resonant frequency of the surface acoustic wave sensor 100. In the cantilever beam structure, the greater the cantilever beam deformation, the more significant the change in resonant frequency, thereby improving the sensitivity of the surface acoustic wave sensor 100.

[0051] The first strip-shaped through groove 141 includes three sections. The second strip-shaped through groove 131 is correspondingly arranged with the first strip-shaped through groove 141 and the third strip-shaped through groove 121. Thus, it can be seen that both the second strip-shaped through groove 131 and the third strip-shaped through groove 121 include three sections. The three second strip-shaped through grooves 131 are perpendicular to each other and connected end to end. The three third strip-shaped through grooves 121 are perpendicular to each other and connected end to end.

[0052] Optional, such as Figure 3 As shown, the first strip-shaped through groove 141 includes three, the three first strip-shaped through grooves 141 are connected end to end and the line connecting the endpoints of the three first strip-shaped through grooves 141 forms a trapezoid, and the base of the trapezoid is the free end of the working area 170.

[0053] When the endpoints of the first strip-shaped channel 141 are connected to form a trapezoid, the stress on the fixed end of the working area 170 increases under external forces, and the properties of the piezoelectric layer material change more significantly, resulting in a more pronounced change in the resonant frequency. This improves the sensitivity of the surface acoustic wave sensor 100.

[0054] In one possible implementation of this invention, such as Figure 1 As shown, the groove 111 is correspondingly set to the working area 170, and the projections of the three first strip-shaped through grooves 141 coincide with the three edges of the projection of the groove 111.

[0055] The groove 111 is correspondingly set to the working area 170, meaning that the cross-section of the groove 111 has the same shape as the working area 170. For example, when the lines connecting the endpoints of the three first strip-shaped through-slots 141 form a rectangle, the groove 111 is a square groove. Furthermore, when the projections of the three first strip-shaped through-slots 141 coincide with the three edges of the square groove, the working area 170 is the same size as the square groove, avoiding the need for a large groove 111 on the silicon substrate 110, which would affect the strength of the surface acoustic wave sensor 100. Similarly, when the lines connecting the endpoints of the three first strip-shaped through-slots 141 form a trapezoid, the cross-sectional area of ​​the groove 111 is a trapezoidal groove. Furthermore, when the projections of the three first strip-shaped through-slots 141 coincide with the three edges of the trapezoidal groove, the working area 170 has a consistent trapezoidal groove size, avoiding the need for a large groove 111 on the silicon substrate 110, which would affect the strength of the surface acoustic wave sensor 100.

[0056] Optionally, the single-crystal piezoelectric thin film layer 140 is an AlN layer or a ScAlN layer.

[0057] The present invention does not limit the material of the single-crystal piezoelectric thin film layer 140, as long as it is a material that generates an electrical signal after pressure is applied. For example, it can be AlN or ScAlN (Sc-doped AlN), because AlN has a high electromechanical coupling coefficient. Of course, this is not a limitation of the present invention, and those skilled in the art can use other materials with piezoelectric effect.

[0058] This application also provides a method for fabricating the surface acoustic wave sensor 100, such as... Figure 4 As shown, it includes:

[0059] S110: Provides device wafers, such as Figure 5 As shown, the device wafer includes a single crystal substrate 190 and a single crystal piezoelectric thin film layer 140, a metal layer 130 and a first bonding layer 181 sequentially stacked on the single crystal substrate 190.

[0060] S120: Provides capped wafers, such as Figure 6 As shown, the cap wafer includes a silicon substrate 110 and a second bonding layer 182 disposed on the silicon substrate 110;

[0061] S130: As Figure 7 As shown, the device wafer and the cap wafer are bonded together through a first bonding layer 181 and a second bonding layer 182;

[0062] S140: As Figure 8 As shown, the single-crystal substrate 190 of the device wafer is removed;

[0063] S150: As Figure 9As shown, interdigitated electrodes 150 and reflective gratings 160 are fabricated on a single-crystal piezoelectric thin film layer 140.

[0064] The fabrication method of the surface acoustic wave sensor 100 of the present invention firstly fabricates a single-crystal piezoelectric thin film layer 140 on a single-crystal substrate 190. Because it is a single-crystal substrate 190, and the deposition is performed directly on the single-crystal substrate 190, a single-crystal piezoelectric thin film with good film quality can be fabricated. Next, a metal layer 130 is fabricated on the single-crystal piezoelectric thin film layer 140. Subsequently, the single-crystal piezoelectric thin film and the metal layer 130 are transferred to a silicon substrate 110 through a bonding process. This allows the metal layer 130 and the single-crystal piezoelectric thin film layer 140 to coexist on the same surface acoustic wave sensor 100, avoiding the sensor performance degradation caused by the absence of a lower electrode in existing technologies where only a single-crystal piezoelectric thin film exists. It also avoids the sensor performance degradation caused by the presence of a lower electrode but the piezoelectric thin film being polycrystalline in existing technologies.

[0065] It should be noted that the specific material of the single crystal substrate 190 is not limited in this invention, as long as the single crystal morphology is guaranteed. For example, it can be sapphire or silicon carbide, because sapphire and silicon carbide are relatively easy to obtain and have similar crystal structures to the single crystal piezoelectric thin film AlN, which makes it easier to grow the single crystal piezoelectric thin film layer 140 on the single crystal substrate 190.

[0066] Optionally, after fabricating the interdigitated electrodes 150 and the reflective grating 160 on the single-crystal piezoelectric thin film layer 140, as follows: Figure 4 , Figure 1 As shown, the fabrication method of the surface acoustic wave sensor 100 further includes:

[0067] S160: Etch silicon substrate 110 to form a groove 111 at the center of the side of silicon substrate 110 away from the second bonding layer 182;

[0068] S170: Etch the device wafer and the second bonding layer 182 to form a fourth stripe through-hole on the device wafer, and form a fifth stripe through-hole on the second bonding layer 182 corresponding to the fourth stripe through-hole. The fourth stripe through-hole includes three, which are perpendicular to each other and connected end to end. The projection of the three fourth stripe through-holes coincides with the edge of the projection of the square groove.

[0069] A fourth through-slot is etched on the device wafer, and a square groove is etched on the silicon substrate 110. The fourth through-slot includes three slots, which are perpendicular to each other and connected end to end. The projections of the three slots coincide with the edges of the projections of the square grooves, so that the silicon substrate 110 and the device wafer form a cantilever beam structure. This allows the input electrode, output electrode, and part of the single-crystal piezoelectric thin film layer 140 to be suspended, forming free ends. During electroacoustic conversion at the input electrode, the electroacoustic conversion efficiency at the input electrode can be improved. When the ultrasonic wave propagates in the single-crystal piezoelectric thin film layer 140, the ultrasonic signal transmission efficiency is improved and the loss is reduced, which is beneficial to the efficiency of the surface acoustic wave sensor 100 during testing, and thus improves the sensitivity of the surface acoustic wave sensor.

[0070] It should be noted that the fourth through-slot is formed on the device wafer, meaning that the fourth through-slot passes through the device wafer. The single crystal piezoelectric thin film layer 140, the metal layer 130 and the first bonding layer 181 on the device wafer are all provided with through-slots.

[0071] There are no restrictions on the order of steps S160 and S170. Those skilled in the art can implement them according to the actual situation.

[0072] In one possible implementation of this invention, removing the single-crystal substrate 190 of the device wafer includes: removing the single-crystal substrate 190 by dry etching or wet etching.

[0073] The single-crystal substrate 190 serves as the base for fabricating the single-crystal piezoelectric thin film. After the single-crystal piezoelectric thin film layer 140 is fabricated and transferred onto the silicon substrate 110, it needs to be etched to continue fabricating the interdigitated electrode 150 and the reflective gate 160 on the side of the single-crystal piezoelectric thin film layer 140 near the single-crystal substrate 190. For example, dry etching and wet etching can be used.

[0074] In one possible embodiment of the present invention, the fabrication of interdigitated electrodes 150 and reflective gratings 160 on a single-crystal piezoelectric thin film layer 140 includes the interdigitated electrodes 150 and reflective gratings 160 being disposed in the same layer and with the same material. Since the reflective grating 160 is used to reflect ultrasonic signals on the single-crystal piezoelectric thin film layer 140, and the interdigitated electrodes 150 are used to generate and absorb ultrasonic signals, they should be disposed in the same layer. Because the interdigitated electrodes 150 and reflective gratings 160 are made of the same material, they can be obtained in a single deposition using the same substrate, simplifying the fabrication process of the surface acoustic wave sensor.

[0075] The above description is merely a preferred embodiment of this application and is not intended to limit this application. Various modifications and variations can be made to this application by those skilled in the art. Any modifications, equivalent substitutions, improvements, etc., made within the spirit and principles of this application should be included within the protection scope of this application.

Claims

1. A surface acoustic wave sensor, characterized in that, It includes a bonding layer, a metal layer and a single crystal piezoelectric thin film layer sequentially deposited on a silicon substrate, wherein interdigitated electrodes are disposed on the single crystal piezoelectric thin film layer; The surface acoustic wave sensor is formed by bonding the device wafer and the cap wafer and then removing the single-crystal substrate of the device wafer; The device wafer includes the single crystal substrate and the single crystal piezoelectric thin film layer, the metal layer and the first bonding layer sequentially stacked on the single crystal substrate; The capped wafer includes the silicon substrate and a second bonding layer disposed on the silicon substrate; The device wafer and the cap wafer are bonded together by the first bonding layer and the second bonding layer to form the bonding layer; A reflective grating is provided on both sides of the interdigitated electrode along the direction of the interdigitated arrangement, and the reflective grating is provided in the same layer as the interdigitated electrode; A first strip-shaped through-slot is formed on the single-crystal piezoelectric thin film layer, which encloses a working area with a free end and a fixed end. A second strip-shaped through-slot is formed on the metal layer corresponding to the position of the first strip-shaped through-slot. A third strip-shaped through-slot is formed on the bonding layer corresponding to the second strip-shaped through-slot. The first strip-shaped through-slot is located outside the reflective gate and the interdigitated electrode. A groove is formed on the silicon substrate. The third strip-shaped through-slot communicates with the groove. The cross-sectional area of ​​the groove is larger than that of the working area.

2. The surface acoustic wave sensor according to claim 1, characterized in that, The first strip-shaped channel includes three, which are perpendicular to each other and connected end to end. The line connecting the endpoints of the three first strip-shaped channels forms a rectangle, and the projection of the three first strip-shaped channels falls within the projection range of the groove, so that the working area and the silicon substrate form a cantilever beam structure.

3. The surface acoustic wave sensor according to claim 1, characterized in that, The first strip-shaped channel includes three, which are connected end to end and the line connecting the endpoints of the three first strip-shaped channels forms a trapezoid, and the base of the trapezoid is the free end of the working area.

4. The surface acoustic wave sensor according to claim 2 or 3, characterized in that, The groove is provided corresponding to the working area, and the projections of the three first strip-shaped through slots coincide with the three edges of the projection of the groove.

5. The surface acoustic wave sensor according to claim 2, characterized in that, The single-crystal piezoelectric thin film layer is an AlN layer or a ScAlN layer.

6. A method for fabricating a surface acoustic wave sensor, characterized in that, include: A device wafer is provided, the device wafer comprising a single crystal substrate and a single crystal piezoelectric thin film layer, a metal layer and a first bonding layer sequentially stacked on the single crystal substrate; A capped wafer is provided, the capped wafer comprising a silicon substrate and a second bonding layer disposed on the silicon substrate; The device wafer and the cap wafer are bonded together by the first bonding layer and the second bonding layer; Remove the single-crystal substrate from the device wafer; Interdigitated electrodes and a reflective grid are fabricated on the single-crystal piezoelectric thin film layer; A first strip-shaped through-slot is formed on the single-crystal piezoelectric thin film layer, which encloses a working area with a free end and a fixed end. A second strip-shaped through-slot is formed on the metal layer corresponding to the position of the first strip-shaped through-slot. A third strip-shaped through-slot is formed on the bonding layer corresponding to the second strip-shaped through-slot. The first strip-shaped through-slot is located outside the reflective gate and the interdigitated electrode. A groove is formed on the silicon substrate. The third strip-shaped through-slot communicates with the groove. The cross-sectional area of ​​the groove is larger than that of the working area.

7. The method for fabricating a surface acoustic wave sensor according to claim 6, characterized in that, After fabricating the interdigitated electrodes and reflective gate on the single-crystal piezoelectric thin film layer, the method further includes: Etch a silicon substrate to form a square trench at the center of the side of the silicon substrate away from the second bonding layer; The device wafer and the second bonding layer are etched to form a fourth through-slot on the device wafer. A fifth through-slot is formed on the second bonding layer corresponding to the fourth through-slot. The fourth through-slot includes three slots, which are perpendicular to each other and connected end to end. The projections of the three slots coincide with the edges of the projections of the square slot.

8. The method for fabricating a surface acoustic wave sensor according to claim 6, characterized in that, The process of fabricating interdigitated electrodes and a reflective grating on the single-crystal piezoelectric thin film layer includes the interdigitated electrodes and the reflective grating being disposed in the same layer and made of the same material.

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