Investigation of Ca3TaGa3Si2O14 piezoelectric crystals for high temperature sensors

Abstract

The dielectric and electromechanical properties of fully ordered Ca3TaGa3Si2O14 (CTGS) crystals were investigated over the temperature range of −60∼700 °C. The highest electromechanical coupling factor, k26 (18.9%) and piezoelectric coefficient, d26 (−11.5 pC/N) were obtained for (YXl)-25° cuts. The temperature dependent behavior of resonance frequency (fr) was investigated in single-rotated thickness shear mode (TSM) (YXl)θ cuts (θ = −35°∼10°). The turnover temperatures of resonance frequency were found to increase from 20 °C to 330 °C, as the rotation angle θ varied from −22.5° to −35°. Bulk acoustic wave (BAW) resonators based on Y(−30°) monolithic disks with a fundamental frequency ∼2.87 MHz were fabricated, where the in air mechanical quality factor Q was found to be on the order of 24000 and 10000 at 20 °C and 700 °C, respectively. The high coupling k26, high mechanical Q, and high electrical resistivity (16 MΩ·cm) at 700 °C, together with the near zero TCF characteristics at elevated temperatures, demonstrate the potential of CTGS crystals for high temperature sensor applications.