High-Temperature Piezoelectric Bulk Acoustic Wave Sensors Based on Ca3TaGa3Si2O14 and YCa4O(BO3)3 Single Crystals

In this dissertation, the basic properties and advanced sensor applications of two novel high-temperature piezoelectric single crystals-CTGS and YCOB are investigated. The real and complex dielectric, elastic, and piezoelectric constants, as well as their temperature dependence are fully characterized over the temperature range of 21 to 800°C, which not only provides the significant basic information of the crystals, but also demonstrates that they are capable of sensing at 800°C or even higher temperatures because of their stable performance and low dissipations under elevated temperatures. Through the comprehensive study of the stability, linearity, and sensitivity of the samples, CTGS Y-cut TSM resonators are considered to be the optimal choice for the high-temperature sensing applications because of their overall best performance. Furthermore, the high-temperature temperature senor, mass sensor, and pressure sensor based on CTGS Y-cut TSM resonators are studied sequentially: the temperature sensor shows a perfect linear (R2>0.999) relationship between the resonant frequency and the temperature up to 1000°C; the mass sensor is proved to be able to accurately monitor the mass change of micro- and nano-scale polymer layers up to 800°C with the sensitivity of 24 HZ/μg; the test system for high-temperature pressure sensor is designed and processed, and theoretical model is derived. The pressure sensor shows a purely linear relationship between the frequency variation and the pressure difference in the test temperature (21 to 300°C) and pressure (0 to 45 PSI) ranges. Additionally, the non-linear effects under DC bias fields and stress fields are studied and the following higher order dielectric and elastic coefficients are determined:s_166^*, s_366^*, ε_2222, c_6666^D, and h_22,66^*