Piezoelectric over Silicon-on-Nothing (pSON) process

This paper presents a novel fabrication process for piezoelectric micro-electromechanical systems (MEMS) using a membrane over a sealed cavity formed first in bulk silicon using silicon migration. A thin-film piezoelectric layer is then added on the membrane, conferring the structure with an electromechanical transduction mechanism. Suspended MEMS devices on tethers can be defined by etching the silicon membrane to release the structure. A 40 MHz piezoelectric resonator has been demonstrated in this process, but the same process flow can also be applicable to many other piezoelectric MEMS devices. Excellent control over the cavity and membrane dimensions as well as layer alignment is achievable in this process.