AIN/Pt/LN structure for SAW sensors capable of operating at high temperature

摘要

There is a need for wireless sensors able to operate in the intermediate temperature range (ITR) between 300 °C and 600 °C. Surface acoustic wave (SAW) sensors are promising candidates to solve this issue. However, existing SAW sensors most often fail in the ITR, due to the quick-degradation of the sensor housing in extreme conditions. A promising way to circumvent the issue is to use "package-less" devices, where the acoustic waves are guided in a multilayered structure where they are intrinsically protected from adverse environmental effects. We present here an innovative multilayered structure that fulfills all the basic requirements, to achieve a wireless and "package-less" SAW Sensor for the ITR. The structure is made of a thin A1N layer deposited on top of a Y + 128°LN substrate and equipped with buried Pt electrodes. Numerical simulations of the acoustic waves propagating in SAW resonators built on this structure reveal the existence of a useful Rayleigh-type SAW that propagates at the A1N/LN interface with a velocity up to 4500 m/s and a high electromechanical coupling k~2=5.6%, without leakage into the substrate. The existence of this mode is due to specific properties of the Y+ 128°LN cut, which are analyzed in detail in this paper. The performances of an optimized AIN/Pt/LN structure are also compared to the ones of previously suggested "package-less" structures, including AIN/ZnO/Sapphire. It is shown that better device characteristics can be expected from the AIN/Pt/LN structure in the ITR.