Evidence of the existence of complete phononic band gaps in phononic crystal plates

We show, by measuring the transmission through a phononic crystal (PC) plate (slab), the evidence of the existence of large phononic band gaps (PBGs) in twodimensional PCs made by a hexagonal (honeycomb) array of holes etched through a free standing plate of silicon (Si). A CMOS compatible fabrication process is used on a Si on insulator (SOI) substrate to realize the devices. More than 30dB attenuation is observed for eight periods of the hexagonal lattice a very high frequency (VHF) region that matches very well with the theoretical predicted complete PBG using plane wave expansion (PWE) method. This result opens a new direction in the implementation of high frequency practical PC structures with a possible superior performance over the conventional micromechanical devices used in a variety of applications especially in wireless communication devices, and sensing systems. Index Terms — acoustic devices, filtering, phononic crystals, micromachining, phonons