Buried electrode electroacoustic technology for the fabrication of thin film based resonant components

A fabrication process for thin film electroacoustic devices utilizing buried electrodes is presented. A one-step lithography process has been developed to bury electrodes resulting in a planarized surface. The proposed technology is expected to bring about a number of benefits concerning the performance of a variety of thin film electroacoustic devices. With respect to thin film plate acoustic resonators (FPAR), burying the reflector electrodes results in improved reflectivity and potentially lower susceptibility to acousto-migration effects. It is also shown that employing the proposed technology for the fabrication of both thin film bulk acoustic resonators (FBAR) and thin film solidity mounted bulk acoustic resonators (SBAR) eliminates certain macro-structural defects in the piezoelectric film which is a prerequisite for substantially improved device performance and higher power handling capability. The buried electrode electroacoustic ( EA) technology is demonstrated for a thin aluminium nitride (AlN) piezoelectric film with electrodes of both molybdenum (Mo) and tungsten (W). The latter have been primarily chosen because of their high electroacoustic material quality. Thin film resonant structures produced by this technology are characterized and their features are discussed.