AlN Solidly Mounted Resonators for High Temperature Applications

Monitoring under harsh environments, particularly high temperatures (> 600 degrees C), is on high demand nowadays. Applications such as gas control in propulsion systems or fire detection in early stages are good examples. During the last decades, materials and devices have been extensively investigated for these applications. Few have proven thermal and chemical stability. Among the most used devices are surface acoustic wave (SAW) resonators using a langasite (LGS) substrate. Their main disadvantage is related to their transducer topology. Their long and narrow electrode strips are subjected to destructive agglomeration. In order to solve this problem, solidly mounted bulk resonators (SMR) are here proposed as an alternative. They provide rigidity, high performance and large electrodes. Here we investigate the performance of SMR devices after annealing under vacuum condition at 700 degrees C for a cumulative time of 24h. SMRs are composed of porous-SiO2/Mo Bragg mirrors and Ir or Mo electrodes. Their performance shows and initial overall improvement with subsequent stabilization. Q(p)xk(eff)(2) in the order of 72 are achieved. Further investigations on full dielectric Bragg mirrors will be performed. With this initial study we demonstrate that SMRs can be a good alternative to SAWs for high temperature applications.