Lithium Tantalate Bulk Acoustic Resonator for Piezoelectric Power Conversion

We present the first lithium tantalate (LT) thickness-extensional (TE) mode bulk acoustic resonators for piezoelectric power conversion, showcasing a low temperature coefficient of frequency (TCF) of −13.56 ppm/K. These resonators also exhibit high quality factors <tex xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">$(Q)$</tex> of 1698, and electromechanical coupling coefficients <tex xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">$(k^{2})$</tex> of 8.8%, making them suitable for efficient power conversion applications. A grounded ring structure is leveraged for spurious mode-free response and figure-of-merit <tex xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">$(\text{FoM}=k^{2}\cdot Q)$</tex> enhancement near the series resonance, within the power converter's operational range. The temperature dependency of <tex xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">$Q$</tex> and <tex xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">$k^{2}$</tex> are experimentally tested over a wide temperature range, from 25°C to 130°C, demonstrating the resonator's thermal stability and consistent performance under varying conditions. This work highlights the potential of LT resonators in the future development of thermally stable power electronic systems, enabling more reliable and efficient piezoelectric power converters.