Thin-Film Piezoelectric-on-Silicon Resonant Transformers

This paper reports the performance of lead-zirconate-titanate (PZT)-on-silicon electromechanical resonators as thin-film piezoelectric transformers. The PZT-on-silicon resonators rely on the odd harmonics of the contour length-extensional modes to provide a convenient means for voltage and current transformations with a single layer of piezoelectric PZT. The resistive-load-dependent voltage gains and efficiencies are derived along with the peak efficiencies and open circuit voltage gains. The models of efficiency and voltage gain are compared to the experimental measurements of fabricated PZT-on-silicon piezoelectric transformers with 2, 4, and 10 mu m of device silicon. The resonant frequencies of the devices range between 14 and 19 MHz. Peak efficiencies as high as 62% are measured and open circuit voltage gains as high as 5.7 are extracted from the measurements. The measured efficiencies with 50-Omega loads compare within 14% of the models on average (25% peak error). The extracted open-circuit voltage gains and their models compare within 22% on average (67% peak error). The trade between the load-dependent efficiencies and voltage gains are also presented for the n = 3, 5, 9, and 13 harmonics.