Bulk acoustic wave transformer based on the combination of the high-ε epitaxial PbTiO3 and low-ε ScAlN thin films

Sarina Kinoshita,Takahiko Yanagitani

doi:10.1063/5.0042867

Sarina Kinoshita, Takahiko Yanagitani

Open Access

https://doi.org/10.1063/5.0042867

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Abstract

A rectifier antenna (called a rectenna) is useful for wireless power charging of electronic devices. To enhance the rectifier efficiency, we propose sub-GHz bulk acoustic wave (BAW) piezoelectric transformers based on the combination of high and low dielectric constant (ε) thin films. The input layers are sputter-epitaxial lead titanate (PbTiO3) films, which possess both high electromechanical coupling coefficient kt and high ε, and the output layers are ScAlN films with high kt but low ε. The voltage gain of 12.3 in 50 MHz ranges and 40.9 in 400 MHz ranges was experimentally observed in the thickness-extensional mode BAW transformer. The experimental results are in good agreement with the theoretical predictions of the electromechanical transmission line model. The BAW transformer is promising for a high voltage gain transformer for wireless power transfer.

Highlights

) that converts RF energies to direct currents
To enhance the rectifier efficiency, we propose sub-GHz bulk acoustic wave (BAW) piezoelectric transformers based on the combination of high and low dielectric constant (e) thin films
The voltage gain of 12.3 in 50 MHz ranges and 40.9 in 400 MHz ranges was experimentally observed in the thickness-extensional mode BAW transformer

Summary

Introduction

) that converts RF energies to direct currents. a weak RF signal cannot bias the diode sufficiently in a rectenna with low input impedance. We fabricated thickness-extensional mode BAW transformers by combining two thin films with different dielectric constants e (see Fig. 1). (2) and (3) describe the theoretical operating frequency fo and voltage gain GV of the BAW piezoelectric transformers, respectively.

Results

Conclusion