ZnO for thin film BAW devices

As a test vehicle to measure the piezoelectricity of zinc oxide films, bulk acoustic wave (BAW) resonators were fabricated using standard microelectronics deposition, photolithography, and etching techniques on 100 mm Corning glass or silicon wafers. Resonators and filters were of solidly mounted resonator (SMR) type. The acoustic quarter wavelength mirror consisted of high and low acoustic impedance materials, which were either three pairs of molybdenum and silicon dioxide or two pairs of tungsten and silicon dioxide, respectively. Mirrors were designed for I and 2 GHz frequencies. Material properties of the zinc oxide films have been studied by x-ray diffraction (including rocking curve), scanning electron microscopy and atomic force microscopy. Resonators were electrically characterized by vector network analyzer. The highest acoustic coupling coefficient, K-2 = 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.