High-temperature Pt–Al₂O₃ composite nano-thick interdigital electrodes for surface acoustic wave sensors

High-temperature stability of ultra-thin film electrodes is vital for surface acoustic wave (SAW) devices in harsh environments. This paper proposed the Pt–Al₂O₃ composite Nano-thick interdigital electrodes (IDEs) for langasite-based high-temperature SAW sensors. The sandwich structure of the IDEs was composed of Pt layers and Al₂O₃ armors. The armor consisting of barrier and coating layers was introduced to reduce the agglomeration, oxidation, and interdiffusion of IDEs at high temperatures. Capacitive bonding pads were proposed to transmit radiofrequency signals through the closed armor. The composite IDEs (226 nm thickness) had good structural stability and impurities concentration less than 1% at 1000 °C (3 h, air condition). Improved quality factors of 8805, and matched electrical impedance of 51 Ω and −16° were achieved through the electroacoustic optimized IDEs. Finally, multiple SAW temperature sensors using the composite IDEs presented fitting errors less than 1% and hysteresis errors below 4% in 80–1000 °C exceeded 9 h, which was 150 °C higher than existing ones. The proposed composite IDEs enable SAW devices to be applicated in 80–1000 °C.