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 agglomer-ation, 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 omega 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.

Automated summary

This paper proposes a Pt-Al2O3 composite nano-thick interdigital electrode (IDEs) for high-temperature SAW sensors. The IDEs have good structural stability and low impurity concentration at high temperatures. Improved quality factors and matched electrical impedance can be achieved through electroacoustic optimization. Multiple SAW temperature sensors using the composite IDEs also perform well at higher temperatures.