High-resolution, high-linearity temperature sensor using surface acoustic wave device based on LiNbO3/SiO2/Si substrate

A high-resolution and high-linearity surface acoustic wave (SAW) temperature sensor, consisting of a SAW resonator device fabricated on novel X-cut LiNbO3/SiO2/Si piezoelectric substrate and a resonance frequency readout chip using standard 180 nm CMOS technology, is presented for the first time. High temperature performance substrate LiNbO3/SiO2/Si is prepared mainly by ion implantation and wafer bonding at first. RF SAW device with resonance frequency near 900 MHz is designed and fabricated on the substrate. Traditional probe method using network analyzer and the readout chip method are both implemented to characterize the fabricated SAW device. Further measurement of temperature using resonance frequency shift of SAW device demonstrates the feasibility of the combined system as a portable SAW temperature sensor. The obtained frequency-temperature relation of the fabricated device is almost linear. The frequency resolution of the readout chip is 733 Hz and the corresponding temperature accuracy is 0.016 ° C. Resolution of the sensor in this work is superior to most of the commercial temperature measurement sensors. Theory analysis and finite element simulation are also presented to prove the mechanism and validity of using SAW device for temperature detection applications. We conclude that the high-linearity frequency-temperature relation is achieved by the offset between high-order coefficients of LiNbO3 and SiO2 with opposite signs. This work offers the possibility of temperature measuring in ultra-high precision sensing and control applications.