Research On Surface Acoustic Wave High-temperature Pressure Sensor Based On Hot-pressing Bonded Langasite Technology

One of the major bottlenecks in the development of spacecraft in high temperature and high spin environments is the measurement of the temperature,pressure,and vibration parameters of its key parts.Surface acoustic wave technology can realize long-distance wireless passive sensing.Meanwhile,the surface acoustic wave sensor has the characteristics of simple structure,small size,and strong anti-interference.Therefore,it is more suitable for working in a confined,high-temperature,and high-rotation environment.Langasite is a piezoelectric crystal with good temperature stability.It also has the characteristics of a large electromechanical coupling coefficient and low surface acoustic wave velocity.Therefore,it is an ideal material for the preparation of harsh environment sensors.The main research work of this paper is as follows:1.The structural parameters of the surface acoustic wave high-temperature pressure sensor are designed.This paper studies the propagation law of surface acoustic waves and expounds on the pressure sensitivity mechanism of the sensor.The surface acoustic wave resonance model and the diaphragm deformation model are established.Through the finite element simulation of COMSOL Multiphysics software,we have obtained the resonance frequency and bandwidth of the sensitive unit,as well as the force change of the diaphragm.2.The existing wet etching technology of langasite is optimized.This work discusses the influence of external etching conditions(etching temperature and etching solution volume ratio)on the etching rate.We test the substrate surface roughness and cavity unevenness under different etching conditions.At 80 °C,the hydrochloric acid and phosphoric acid solution with a volume ratio of 1:1 are heated in a water bath to corrode the wafer.Circular microcavities with clear boundaries and smooth surfaces are obtained.The etching rate is 0.7?m/min.Finally,we explained the reaction mechanism of wet etching langasite.3.A high-temperature direct bonding technology of langasite is proposed.Through infrared spectroscopy analysis,the best oxygen plasma activation parameters are obtained.Hydrophilicity test and atomic force microscope test showed that oxygen plasma activation can remove organic matter,improve hydrophilicity and reduce surface roughness.Under the conditions of a temperature of 1000 °C,a pressure of 6 MPa,and a duration of 2 hours,the substrate obtains a higher bonding strength(3.81 MPa).The airtightness test shows that the cavity has a good sealing performance.We observe the substrate under a transmission electron microscope and find that the interface is tightly bonded.Finally,the direct bonding mechanism of langasite is explained.4.The high-temperature pressure test platform has been built.We have fabricated and tested the surface acoustic wave high-temperature-pressure sensor.The temperature test range is 25 ?~700 ?.The pressure test range is 0 KPa~300 KPa.Within a certain range,the pressure has a linear relationship with the resonance frequency.The pressure sensitivity is1.286 KHz/KPa.