Switchable and tuneable high-performance acoustic modes in the L-X band using ferroelectric thin film on sapphire

High overtone bulk acoustic resonators (HBAR) are advantageous for on-chip quantum acoustodynamics (QAD) system as it gives access to stream of phonon modes with high lifetime in the microwave frequency range while retaining low power consumption and microscale footprint. In this paper we present a HBAR based on barium strontium titanate (BST) thin-film mounted on sapphire with modes exhibiting frequency quality factor product (fQ) of 1.72 × 10¹⁵Hz which is the highest reported for a bulk acoustic wave resonator utilizing polycrystalline ferroelectric material as a means for acoustic wave excitation. Unlike other piezoelectric based HBARs, the DC field-induced piezoelectricity utilized in this work offers multiple on-chip tuneability of resonator's dynamic parameters such as phonon lifetime, frequency modulation and coupling. The higher overtone feature can enable qubit(s) in a hybrid quantum circuit to interact with one or more acoustic modes to form a quantum transducer. Here, the multi-mode resonator exhibits a unique DC bias dependency, and this feature of the ferroelectric thin film adds control variables that efficiently tune static and dynamic material, mechanical and electrical properties of the device. The resonator records a loaded quality factor of 180,000 in X band and 140,000 in the L band when measured at 10 K. A controllable robust resonator with simple fabrication technique offering high fQ can be a strong platform to be used in QAD circuits for applications in metrology, quantum memory and quantum information processing.