Temperature and Bias-Dependent Switchability and Tuneability of Very High-Quality Factor GHz Resonators

In this work, we report the excitation of extremely high-quality factor (Q) bulk acoustic wave modes with a degree of switchability and tuneability achievable by utilizing the electric field-induced piezoelectric effect in the transducing barium strontium titanate (BST) thin film of a high overtone bulk acoustic resonator (HBAR). The HBAR exhibits Qs in the order of 10
⁵
over multiple resonant modes around 5 GHz measured at 50 K temperature and with a DC electric field applied across the transducer stack. The diversion from the conventional piezoelectric material route as a transducer material in such HBAR can facilitate additional functionality such as reconfigurability with competitive values of quality factors compared to traditional piezoelectric-based HBARs. The work demonstrates the highest recorded Q for a polycrystalline ferroelectric thin film based Bulk Acoustic Wave (BAW) resonator.