Effects of release holes on microscale solid–solid phononic crystals

Abstract

Solid–solid phononic crystals exhibit wider band gaps than those observed with air–solid phononic crystals. For micromachined phononic crystal devices it is advantageous to release the phononic crystal to avoid propagation losses. In a solid–solid phononic crystal operating in the low megahertz range, due to the large lattice constant, it is necessary to place release holes in the center of the inclusions to release devices from the substrate while minimizing the effect the release hole has on the band gap. In this report, we investigate the effect of release holes on phononic band gaps and highlight the need for careful design. It was determined that release holes of radius rair holes/rinclusion=0.26 can reliably release a phononic crystal membrane composed of W inclusions in SiO2 without significantly compromising the phononic band gap.