Design and characterization of stop-band filters using PZT layer on silicon substrate phononic crystals

Phononic crystals are periodic structures exhibiting absolute band gaps i.e. frequency bands in which the propagation of elastic waves is forbidden in all directions. Filtering is then a possible application of phononic crystals. Recently, the existence of absolute band gaps has also been theoretically demonstrated for guided elastic waves in a piezoelectric plate on a substrate [J. Vasseur et al, J. Appl. Phys, 101, 114904 (2007)], which is a geometry of interest for possible co-integration on silicon chip. The 2D phononic crystal was constituted by a square arrangement of cylindrical holes in a PZT layer deposited on a silicon substrate. In this communication, the realization of a stop-band filter constituted by a periodically patterned PZT layer, polarized along thickness, on silicon substrate and interdigitated electrodes (IDE) for emission/reception of guided elastic waves, is investigated. The filter characteristics are theoretically evaluated by using finite element simulations: dispersion curves of patterned PZT layer are computed for various pattern geometries to obtain the absolute band gap. Complete structure is then modeled, with appropriate IDE to propagate a guided mode in the piezoelectric layer. Finally, filtering capability of the structure is evaluated. Work supported by STMicroelectronics (Nano2008 program of French ministry of industry).