Construction And Research Of Surface Acoustic Wave Temperature Sensor Based On Aluminum Nitride Film

As the information age develops,sensing technology is an important part of modern industrial manufacturing,mobile communications and other fields.The ability of sensors to accurately obtain real-time information can detect the working status and stability of the system.There is an urgent need for strain measurement systems for structural control and health monitoring,especially in the aerospace,energy and automotive sectors where high temperature or pressure environments are required.For high temperature applications,active sensors are not applicable due to the limitations of integrated circuits.Surface acoustic wave(SAW)sensors are very suitable for monitoring information in high-temperature environments because of their small size,fast response time,high quality factor,and wireless passive operation.As SAW sensors operate in high temperature environments,this places great demands on the stability of the sensors at high temperatures.For this reason,this paper uses aluminium nitride(AlN),a piezoelectric thin film material with excellent high temperature strain characteristics,as a piezoelectric layer to simulate the construction of a multilayer film structure for SAW temperature sensors and to test and analyze its performance.A two-dimensional finite element model of the SAW sensor based on the laminar structure of AlN film was constructed using the simulation software COMSOL.The effects of different substrate materials,AlN film thickness,fork-finger electrode thickness and fork-finger electrode period on the high-temperature sensing performance of the SAW device were investigated and analyzed,focusing on the performance of the Pt/AlN/SiC structured SAW temperature sensor.The optimal structural design parameters of the sensor were obtained by simulation: a wavelength of 8 μm,an AlN film thickness of 0.8 μm and a Pt electrode thickness of 80 nm.AlN films with high c-axis orientation were deposited on SiC substrates using a magnetron sputtering system and obtained by rapid heat treatment.The Pt/AlN/SiC multilayer film structure SAW resonators were then prepared by lithography,ion beam sputtering and RF magnetron sputtering.The prepared multilayer film SAW devices were characterized by a series of high temperature tests: firstly,the stability of the piezoelectric properties of the AlN films at high temperatures was verified.The S-parameters of the device were then tested at temperatures up to 800 °C,and the temperature-frequency characteristics of the sensor were obtained: the resonant frequency decreased linearly with increasing temperature,and the device sensitivity and frequency-temperature coefficient reached-19.4 k Hz/°C and-25.9 ppm/°C,respectively.Furthermore,the device performance is reproducible in repeated high and low temperature tests.The error between experimental and simulation results is small,which also verifies the accuracy of the simulation model.Finally,the test results were calibrated to obtain an accurate temperature frequency function for the sensor.