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A surface acoustic wave (SAW)-based temperature sensor has been designed and simulated using a (0°, 138.5°, 26.6°)-cut lanthanum gallium silicate (LGS; langasite; La3Ga5SiO14) substrate with reduced temperature coefficient of frequency (TCF). At elevated temperatures, a slight temperature variation produces a major change in the resonance frequency of the SAW sensors, resulting in crucial accuracy problems and erroneous outcomes. To overcome these issues, a temperature-compensated sensor is required to be designed. Deposition of SiO2 film onto the substrate is an effective approach for achieving temperature compensation in a sensor design. Accordingly, we designed a SAW resonator by depositing platinum electrodes on LGS substrate material along with a layer of SiO2 film on top. The structure has been simulated using the 3-D finite element model method. The temperature-dependent characteristics of the model have been investigated for different thicknesses of the SiO2 coating layer at elevated temperatures. It was found that the TCF is reduced to 4.3 ppm/°C at 500°C operating temperature with a 1.9-μm-thick SiO2 film. A zero TCF was also achieved for 0.9-μm-thick SiO2 film at an operating temperature of 300°C, which signifies the effective temperature compensation of the model. The simulation results also revealed that the SAW velocity increases while the coupling factor (k2) decreases with increasing SiO2 thickness. This sensor can be used for health monitoring in heavy industries as well as in combustion engines to enhance fuel efficiency.
Nagmani et al. (Mon,) studied this question.