ZnO for thin film BAW devices

As a test vehicle to measure the piezoelectricity of zinc oxide films, bulk acoustic wave (BAW) re-sonators were fabricated using standard microelectronics deposition, photolithography, and etching tech-niques on 100 mm Corning glass or silicon wafers. Resonators and filters were of solidly mounted re-sonator (SMR) type. The acoustic quarter wavelength mirror consisted of high and low acoustic impe-dance materials, which were either three pairs of molybdenum and silicon dioxide or two pairs of tungs-ten and silicon dioxide, respectively. Mirrors were designed for 1 and 2 GHz frequencies. Material pro-perties of the zinc oxide films have been studied by x-ray diffraction (including rocking curve), scanning electron microscopy and atomic force microscopy. Resonators were measured from 0.5 to 6 GHz using network analyzer. The highest acoustic coupling coefficient, K2 = 10.4% at 1.6 GHz, for thin film zinc oxide was achieved. Also a passband filter, fulfilling the complete E-GSM specifications, was fabricated using zinc oxide piezoelectric in the resonators.