Thin-film piezoelectric transformers operating in harmonics of out-of-plane flexure modes

This paper documents disc-shaped flexure-mode piezoelectric transformers constructed with 0.5 μm lead-zirconate-titanate (PZT) on 4-μm silicon resonators. The transformers are electrode shaped to excite out-of-plane flexure modes at ~12, ~34, and ~63 MHz. The incorporation of silicon enables the excitation of out-of-plane flexural modes which exploit large quasi-static material coupling factors (using both e₃₁ and e₃₂). Transformer efficiencies >50% with ~5X open-circuit voltage gains are predicted. Experimental transformer figures of merit equivalent to previously-reported extensional modes [1] are demonstrated with 3X-13X size reductions. Electromechanical coupling factors, k_eff², of 3.4% exceed those measured for extensional modes (with 4 μm silicon) by ~3.5X.