Surface acoustic wave bound state in the continuum for 1200 °C high temperature sensing

Abstract

The langasite (LGS) SAW are often used in high temperature wireless passive sensing above 1000 °C. And the about 400 nm thick metal electrodes film such as platinum-rhodium (Pt-Rh) are usually used to avoid high-temperature melting, however it could seriously pull down the quality factor and sensitivity of SAW sensors because the heavy metal electrodes result in high reflection coefficient and mass loading effect. In order to satisfy the thick electrode and the high-quality factor of SAW sensors simultaneously, this paper developed a new mode SAW which is based on the bound states in the continuum (BIC) on (0, 138.5°, θ) LGS wafers. The BIC-mode SAW sensor with a 410 nm thick Pt-Rh show an extremely high Q factor, which is four times to traditional SAW. The high temperature testing verified this BIC-state SAW sensor can maintain high quality (Q) factor after 1200 °C for 3 h.