Transversely-excited film bulk acoustic filter using pitch to establish frequency separation between resonators

Abstract

Acoustic filters are disclosed. An acoustic filter device includes a substrate having a surface and a single-crystal piezoelectric plate having front and back surfaces and a thickness ts, the back surface attached to the surface of the substrate except for portions of the piezoelectric plate forming a plurality of diaphragms that span respective cavities in the substrate. A conductor pattern is formed on the front surface of the piezoelectric plate, the conductor pattern comprising a plurality of interdigital transducers (IDTs) of a plurality of acoustic resonators, interleaved fingers of each IDT of the plurality of IDTs disposed on a respective diaphragm of the plurality of diaphragms. The interleaved fingers of all of the plurality of IDTs are substantially aluminum with a common thickness tm, where 0.12 ts≤tm≤0.32 ts.