Resonant Inc.
XBAR FRONTSIDE ETCH PROCESS USING POLYSILICON SACRIFICIAL LAYER

Abstract:

An acoustic resonator is fabricated by etching a recess in a silicon thermal oxide (TOX) upper layer of a silicon substrate and filling the recess with sacrificial polysilicon. A surface of the silicon TOX layer and the sacrificial polysilicon-filled recess are planarized. A back surface of a single-crystal piezoelectric plate is bonded to the planarized surface of the silicon TOX layer. Openings are formed through the piezoelectric plate and an interdigital transducer (IDT) is formed on a front surface of the piezoelectric plate such that interleaved fingers of the IDT are disposed over the sacrificial polysilicon-filled recess. The sacrificial polysilicon is removed from the recess to form a cavity such that a portion of the piezoelectric plate forms a diaphragm spanning the cavity and the interleaved fingers of the IDT are disposed on the diaphragm.