阅读说明：本技术 声表面波应变传感器及其制备方法 (Surface acoustic wave strain sensor and preparation method thereof ) 是由 谭秋林 杨子锋 闫夏雯 张磊 熊继军 于 2021-03-21 设计创作，主要内容包括：本发明公开一种声表面波应变传感器及其制备方法,其中声表面波应变传感器包括基底,基底包括第一表面和与所述第一表面相对的第二表面,所述第一表面上的有源区内形成有叉指换能器以及分别位于所述叉指换能器两侧的第一反射栅和第二反射栅,第二表面对应所述有源区的位置形成有至少一个凹槽。本发明的传感器结构能提高声表面波应变的检测灵敏度。(The invention discloses a surface acoustic wave strain sensor and a preparation method thereof, wherein the surface acoustic wave strain sensor comprises a substrate, the substrate comprises a first surface and a second surface opposite to the first surface, an interdigital transducer, a first reflection grating and a second reflection grating are respectively positioned on two sides of the interdigital transducer and formed in an active area on the first surface, and at least one groove is formed in the second surface corresponding to the active area. The sensor structure can improve the sensitivity of detecting the strain of the surface acoustic wave.)

1. The utility model provides a surface acoustic wave strain sensor which characterized in that, includes the basement, the basement include the first surface and with the second surface that the first surface is relative, form interdigital transducer in the active area on the first surface and be located respectively the first reflection bars and the second reflection bars of interdigital transducer both sides, the second surface corresponds the position in active area is formed with at least one recess.

2. A saw strain sensor as defined in claim 1, wherein the at least one groove is a rectangular through window.

3. A saw strain sensor as claimed in claim 2, wherein the rectangular through window has a length of 10mm, a width of 6mm and a height of 0.25 mm.

4. A saw strain sensor as defined in claim 1, wherein the at least one groove is a plurality of rectangular through windows.

5. A SAW strain sensor according to any of claims 1-4, wherein the interdigital transducer, the first reflection grating and the second reflection grating have an electrode length of 2000 μm, an electrode width of 4 μm and an electrode height of 170 nm.

6. A method for preparing a surface acoustic wave strain sensor is characterized by comprising the following steps:

step one, forming a first mask at the position of the unpolished side of the substrate corresponding to the active area;

etching the substrate through the first mask to form at least one groove;

and step three, forming an interdigital transducer and a first reflection grating and a second reflection grating which are respectively positioned at two sides of the interdigital transducer in the active area at the polished side of the substrate.

7. The method of claim 6, wherein the first mask is used to form a rectangular through-window on the substrate.

8. The production method according to claim 6, wherein the first mask is used to form a plurality of rectangular through-windows on the substrate.

9. The preparation method according to any one of claims 6 to 8, wherein the second step specifically comprises: and corroding the substrate by adopting a mixed solution of nitric acid and phosphoric acid with a volume ratio of 1:1 in an environment of heating in a water bath at 80 ℃ through the first mask to form the at least one groove.

10. The method according to any one of claims 6 to 8, wherein the third step comprises: forming an active area mask on the polished side of the substrate by adopting a photoetching process; plating a Ti adhesion layer and a Pt electrode layer on the active area mask in sequence by adopting a magnetron sputtering process; and forming the interdigital transducer, the first reflection grating and the second reflection grating in the active area by adopting a semiconductor stripping process.

Technical Field

The invention relates to the technical field of surface acoustic wave devices, in particular to a surface acoustic wave strain sensor and a preparation method thereof.

Background

The engine of the aerospace craft usually works in severe environments such as high temperature, high spin, high impact and the like, and the strain sensor resistant to high temperature, high pressure and high impact has very important significance for monitoring the health state and analyzing the service life of each component in the engine.

The surface acoustic wave strain sensor performs electro-acoustic energy conversion and signal transmission through the piezoelectric effect of the substrate. By adopting the langasite crystal with higher melting point (1470 ℃) as a substrate and utilizing the characteristic that the langasite crystal has no phase change from room temperature to the melting point, the manufactured surface acoustic wave strain sensor is more suitable for sensing monitoring at high temperature and is widely applied to engines of aerospace aircrafts. In addition, the electromechanical coupling coefficient of the langasite crystal is 2-3 times larger than that of quartz, the surface acoustic wave speed is lower, and the langasite crystal is suitable for miniaturization of devices.

The traditional surface acoustic wave strain sensor generally adopts a method of directly bonding with a member to be detected through an adhesive to obtain strain information of the member to be detected, and because the adhesive is positioned between the surface acoustic wave strain sensor and the member to be detected, a hysteresis effect is inevitably generated in the process of strain transmission, so that the sensitivity of the surface acoustic wave strain sensor is reduced.

Disclosure of Invention

The invention provides a surface acoustic wave strain sensor and a preparation method thereof, which are used for overcoming the technical problems in the prior art and reducing the hysteresis effect so as to improve the sensitivity of the surface acoustic wave strain sensor.

The invention provides a surface acoustic wave strain sensor which is characterized by comprising a substrate, wherein the substrate comprises a first surface and a second surface opposite to the first surface, an interdigital transducer, a first reflection grating and a second reflection grating are formed in an active region on the first surface and are respectively positioned on two sides of the interdigital transducer, and at least one groove is formed in the second surface corresponding to the position of the active region.

The invention also provides a preparation method of the surface acoustic wave strain sensor, which is characterized by comprising the following steps:

step one, forming a first mask at the position of the unpolished side of the substrate corresponding to the active area;

etching the substrate through the first mask to form at least one groove;

and step three, forming an interdigital transducer and a first reflection grating and a second reflection grating which are respectively positioned at two sides of the interdigital transducer in the active area at the polished side of the substrate.

In the surface acoustic wave strain sensor and the preparation method thereof provided by the invention, as the structure of at least one groove is formed at the position of the corresponding active area of the second surface of the substrate, not only is larger deformation generated between electrodes on the active area of the sensor, but also the adhesive area between the surface acoustic wave strain sensor formed by the interdigital transducer and the reflecting grating on the active area and a member to be measured is reduced, so that the hysteresis effect is reduced, the sensitivity of the surface acoustic wave strain sensor is further improved, and the sensitivity of the sensor is improved compared with that of sensors in a resonance area with the same thickness; moreover, the plurality of rectangular through windows are arranged for dispersing the stress of the substrate, so that the damage of devices is reduced; lanthanum gallium silicate is used as a substrate material, so that the high-temperature-resistant material has excellent high-temperature resistance; the invention has simple and reasonable structure, small volume and easy processing, and is beneficial to improving the measurement sensitivity of the strain of the component to be measured under the high-temperature severe environment.

Drawings

In order to more clearly illustrate the embodiments of the present invention or the technical solutions in the prior art, the drawings needed to be used in the description of the embodiments or the prior art will be briefly introduced below, and it is obvious that the drawings in the following description are some embodiments of the present invention, and for those skilled in the art, other drawings can be obtained according to these drawings without creative efforts.

Fig. 1 is a schematic structural diagram of a saw strain sensor according to an embodiment of the present invention;

FIG. 2 is a schematic diagram of a SAW strain sensor with multiple grooves deformed together with a member under test in an embodiment of the present invention;

FIG. 3 is a top view of a SAW strain sensor in an embodiment of the present invention;

fig. 4 is a flowchart of a method for manufacturing a surface acoustic wave strain sensor according to an embodiment of the present invention;

FIG. 5 is a schematic flow chart of the process for preparing a single groove in the unpolished side of a substrate;

FIG. 6 is a schematic flow chart of the process for forming a plurality of grooves in an unpolished surface of a substrate;

FIG. 7 is a schematic flow chart of the fabrication of an interdigital transducer and a reflective grating on a polished surface of a substrate having a single groove;

FIG. 8 is a schematic flow chart of the fabrication of an interdigital transducer and a reflective grating on a polished surface of a substrate having a plurality of grooves.

Detailed Description

In order to make the objects, technical solutions and advantages of the present invention clearer, the technical solutions in the embodiments of the present invention will be clearly and completely described below with reference to the accompanying drawings in the embodiments of the present invention, and it is obvious that the described embodiments are some, but not all embodiments of the present invention. All other embodiments, which can be derived by a person skilled in the art from the embodiments given herein without making any creative effort, shall fall within the protection scope of the present invention.

According to the embodiment of the invention, the sensor substrate adopts a langasite wafer, the sensor is prepared by adopting wet etching and photoetching processes, firstly, a mask is formed on the unpolished side of the wafer by adopting a photoetching method, then, a through rectangular groove is etched in the front and back by adopting the wet etching process, and finally, an interdigital transducer and a reflecting gate are formed on the polished side of the wafer by adopting a magnetron sputtering method. In order to make the technical solution of the present invention clearer, embodiments of the present invention are described in detail below with reference to the accompanying drawings.

Fig. 1 is a schematic structural diagram of a saw strain sensor according to an embodiment of the present invention, fig. 2 is a schematic structural diagram of a saw strain sensor having a plurality of grooves and a member to be measured deforming together, fig. 3 is a top view of the saw strain sensor according to an embodiment of the present invention, and as shown in fig. 1 to 3, the saw strain sensor 100 includes a substrate 10 including a first surface 102 and a second surface 101 opposite to the first surface 102, an interdigital transducer 20 and a first reflection grating 30 and a second reflection grating 30 respectively located on two sides of the interdigital transducer 20 are formed in an active region (not shown) on the first surface 102, and at least one groove 40 is formed in the second surface 101 corresponding to the active region.

The interdigital transducer 20, the first reflection grating 30 and the second reflection grating 30 in fig. 1 and 3 of the present invention are only schematically represented by the number and the spacing of electrodes for detecting strain, which are not completely in one-to-one correspondence in different figures, and the present invention is not limited thereto, L is the length of the metal electrode, and H is the height of the metal electrode. According to the invention, the sensor selects the lanthanum gallium silicate as a substrate material, and the sensor has excellent high-temperature resistance. Specifically, the piezoelectric substrate is a Langasite (LGS) substrate with 1cm by 0.05cm, and the tangential direction of the langasite used is (0 °, 138.5 °, 27 °), which is sensitive to strain compared with other tangential directions. Based on the design specification of the surface acoustic wave device and the precision requirement of the processing technology, in the embodiment of the invention, the lengths of the electrodes of the interdigital transducer 20, the first reflection grating 30 and the second reflection grating 30 are 2000 μm, the width of the electrodes is 4 μm, and the height of the electrodes is 170 nm.

As shown in fig. 2, the electrodes on the sensor 100 are not shown, and when a downward load is applied to the member to be measured 200, the material inside the intermediate layer 210 is compressed by a shear stress and becomes shorter, and the material outside the intermediate layer is stretched by the shear stress and becomes longer, where the intermediate layer 210 refers to a layer that is not deformed by an external force. Assuming that the length of the material at a distance y from the intermediate layer after bending deformation is C₁C₂Is changed into C₁₁C₂₂According to the principle of elastoplastic deformation, it is strained toy is arc C₁₁C₂₂Any one of the above points specifies a distance from the intermediate layer, and K1/R is the curvature of the intermediate layer. From the above strain formula, it can be seen that, in the case of a fixed curvature, the farther any given point y' on the strain sensor is from the intermediate layer, the larger the strain generated, and the larger the corresponding strain value. Compared with the traditional method of directly bonding the thinned wafer and the component to be measured, the method increases the distance between the surface of the sensor and the middle layer of the component to be measured, generates larger deformation and the shape of the surface of the substrate by thinning the central resonance region of the sensorThe variation causes the electrode pitch, the acoustic wave propagation speed variation, and the like to become large, that is, the resonance frequency of the Surface Acoustic Wave (SAW) is more shifted due to the increased deformation, thereby improving the sensitivity of the sensor. Compared with the sensor with the resonance area with the same thickness, the sensor of the invention is provided with the groove 40 on the surface 101 of the substrate attached to the component to be measured 200, so that the surface of the substrate provided with the electrode is farther away from the component to be measured, the deformation is larger, the generated offset is larger, and the sensitivity is higher. And through the arrangement of the groove, the use of glue for adhering the component to be tested and the sensor substrate is reduced, the loss caused by hysteresis effect when the strain is transmitted from the component to be tested to the sensor is reduced, and the sensitivity of the surface acoustic wave strain sensor is favorably improved.

In a specific application, the groove 40 on the substrate may be a rectangular through window, or may be a plurality of rectangular through windows. When the sensor is a rectangular through window, the size of the whole resonance area is matched with the thinned area according to the design parameters of the sensor so as to meet the requirement of miniaturization of the sensor, and the size of the rectangular through window can be set to be 10mm in length, 6mm in width and 0.25mm in height. The stress of a single through cavity is concentrated in the center of the cavity, when a force is given, the cavity deforms, the larger the force is, the larger the deformation is, and the higher the sensitivity is. However, as the LGS is a hard and brittle material, when the force is increased, the LGS material is easy to break, and if the LGS is designed into a plurality of through cavities, the force can be dispersed by the through cavities when the LGS is stressed, the substrate is easier to deform, and the LGS is not easy to break, so that the rectangular through windows are formed by arranging the grooves, the stress can be dispersed, and the damage of the device can be reduced.

In the embodiment of the invention, as the structure of at least one groove is formed at the position of the corresponding active area of the second surface of the substrate, not only is larger deformation generated between electrodes on the active area of the sensor, but also the adhesive area between the surface acoustic wave strain sensor formed by the interdigital transducer and the reflecting grating on the active area and a member to be measured is reduced, thereby reducing the hysteresis effect, further improving the sensitivity of the surface acoustic wave strain sensor, and improving the sensitivity of the sensor compared with resonant area sensors with the same thickness; moreover, the plurality of rectangular through windows are arranged for dispersing the stress of the substrate, so that the damage of devices is reduced; lanthanum gallium silicate is used as a substrate material, so that the high-temperature-resistant material has excellent high-temperature resistance; the invention has simple and reasonable structure, small volume and easy processing, and is beneficial to improving the measurement sensitivity of the strain of the component to be measured under the high-temperature severe environment.

Fig. 4 is a flowchart of a method for manufacturing a surface acoustic wave strain sensor according to an embodiment of the present invention; FIG. 5 is a schematic flow chart of the process for preparing a single groove in the unpolished side of a substrate; fig. 6 is a schematic flow chart of preparing a plurality of grooves on an unpolished surface of a substrate, fig. 7 is a schematic flow chart of preparing an interdigital transducer and a reflective grating on a polished surface of a substrate having a single groove, and fig. 8 is a schematic flow chart of preparing an interdigital transducer and a reflective grating on a polished surface of a substrate having a plurality of grooves. As shown in fig. 4 to 8, the preparation method of the embodiment includes:

step 401, a first mask is formed at the position of the unpolished side of the substrate corresponding to the active region.

Wherein the first mask is used to form a rectangular through-window or a plurality of rectangular through-windows on the substrate.

Step 402, etching the substrate through the first mask to form at least one groove.

As shown in fig. 5 and 6, a photoresist is uniformly coated on the unpolished side of the substrate 10, and is subjected to photolithography and development, and then the substrate 10 having at least one groove is formed by wet etching, i.e., the substrate 10 is etched to form at least one groove 40 by a first mask and a mixed solution of nitric acid and phosphoric acid in a volume ratio of 1:1 in an environment of heating in a water bath at 80 ℃.

And 403, forming an interdigital transducer and a first reflection grating and a second reflection grating which are respectively positioned at two sides of the interdigital transducer in the active area at the polished side of the substrate.

In the step, an interdigital transducer and a reflection grating of the sensor are mainly prepared, and as shown in fig. 7 and 8, an active area mask is formed on the polished side of a substrate 10 by adopting a photoetching process; sequentially plating a Ti adhesion layer 202 and a Pt electrode layer 201 (shown in figure 1) on the active area mask by adopting a magnetron sputtering process; the interdigital transducer 20, the first reflection grating 30, and the second reflection grating 30 are formed in the active region using a semiconductor lift-off process.

The surface acoustic wave strain sensor prepared by the method can realize sensitive and high detection on the strain of the component to be detected by attaching one surface with the groove to the component to be detected and outputting an electrode detection signal through the lead.

In practical application, the surface acoustic wave high-temperature strain sensor based on the langasite can be realized by the following process steps:

(1) firstly, respectively ultrasonically cleaning a langasite wafer in acetone, absolute ethyl alcohol and deionized water for 5 minutes until the surface of the wafer is clean and free of impurities, and then drying the wafer by using nitrogen.

(2) And (3) uniformly coating a layer of SU-8 negative photoresist on the back surface of the wafer by using a spin coater, wherein the rotation speed of the spin coater is 500 revolutions per minute (10 seconds), 10 revolutions per minute (10 seconds), 2500 revolutions per minute (2500 revolutions per minute) and 40 seconds.

(3) Pre-baking: placing the wafer with the glue on a baking table, and heating at 65 ℃ for 7min (7 min); 95 ℃ for 37 min.

(4) And forming a rectangular through mask on one side of the wafer after the pre-baking by adopting a photoetching process.

(5) Post-baking: placing the photoetched wafer on a baking table at 65 ℃ for 5 min; 95 ℃ for 15min

(6) A mixed solution of hydrochloric acid (50ml) and phosphoric acid (50ml) in a volume ratio of 1:1 is adopted to corrode the rectangular through window for 4 hours in an environment of heating in a water bath at 80 ℃.

(7) Taking out the corroded wafer, cleaning, and uniformly coating a layer of positive photoresist AZ6130 on the other side of the wafer, wherein the rotating speed of a spin coater is 500 r/min for 5 s; baking at 3000 r/min for 30s at 100 deg.C for 60 s.

(8) And forming an interdigital transducer and a reflection grating mask by adopting a photoetching process.

(9) A magnetron sputtering process is adopted to plate a 20nmTi adhesion layer and a 150nmPt electrode layer.

(10) And putting the sputtered wafer into an acetone solution, and ultrasonically stripping to obtain the patterned electrode layer.

According to the strain sensor, at least one groove structure is prepared on one side of the langasite substrate by adopting a photoetching process and wet etching, so that the sensitivity of the surface acoustic wave strain sensor is improved; and an interdigital transducer and a reflecting grating of the sensor are formed on the other side by a photoetching process and a magnetron sputtering method so as to detect the deformation of the component to be detected. Compared with the prior art, the invention selects the lanthanum gallium silicate as the substrate material, and has excellent high temperature resistance; the sensor adopts the structure of at least one groove on the back, uses less glue, and has higher sensitivity. The invention has simple and reasonable structure, small volume and easy processing, and is beneficial to improving the measurement sensitivity of the strain of the component to be measured under the high-temperature severe environment.

Finally, it should be noted that: the above examples are only intended to illustrate the technical solution of the present invention, but not to limit it; although the present invention has been described in detail with reference to the foregoing embodiments, it will be understood by those of ordinary skill in the art that: the technical solutions described in the foregoing embodiments may still be modified, or some technical features may be equivalently replaced; and the modifications or the substitutions do not make the essence of the corresponding technical solutions depart from the scope of the technical solutions of the embodiments of the present invention.