Abstract
Langasite (LGS) surface acoustic wave (SAW) temperature sensors have a large second order temperature coefficient of frequency, which leads to their non-linear and non-monotonic responses in a wide temperature range and possibly makes the measured temperatures non-unique for a specific sensor response. Here, we propose a high-temperature Pt/LGS SAW sensor with linear frequency-temperature behavior in a wide temperature range, which was fabricated on a LGS (0 degrees, 138.5 degrees, 72 degrees) substrate. The sensor has a single acoustic mode, but dual resonances with similar second- and third-order temperature sensitivities that were utilized for achieving a linear frequency-temperature response by a method of difference. A linear relationship between the measured sensor output (Delta f(m21)) and temperature was obtained in the range of -60 degrees C to 700 degrees C, consistent with the theoretical analysis. The sensor has a high sensitivity of -167 ppm/K for the whole temperature range. All the results demonstrated exciting prospects of the sensor for wide temperature monitoring in harsh environments.