Thin-film bulk acoustic resonators and filters using ZnO and lead-zirconium-titanate thin films

This paper presents the findings of a design, modeling, and fabrication study of ZnO and PbZr_0.3Ti_0.7O₃ thin-film bulk acoustic resonators and filters. Measurements of the high-frequency responses of ZnO resonators having different area are used to develop an acoustic model that accurately represents resonator impedance data. The models are also used to interpret S-parameter measurements on thin-film PbZr_0.3Ti_0.7O₃-based resonators and a value for the effective coupling coefficient deduced. ZnO and PbZr_0.3Ti_0.7O₃ ladder filters were designed based on measured impedance data from single resonators. Ladder filters based on PbZr_0.3Ti_0.7O₃ have been fabricated for the first time. It is shown that the high coupling coefficient in PbZr_0.3Ti_0.7O₃ leads to bandwidths in the range 100~120 MHz at a center frequency of 1.6 GHz, larger than the bandwidths of ZnO-based filters