Ba0.5Sr0.5T iO3 Thin film-Based Switchable High Overtone Bulk Acoustic Resonator on High Resistive Silicon

A high-overtone bulk acoustic resonator (HBAR) has various communication and superconducting circuit applications. This work describes the fabrication and characterisation of HBAR with an Au/ Ba
0.5
Sr
0.5
TiO
3
(BST5)/Pt configuration on a silicon nitride (Si
3
N
4
) coated high-resistivity silicon substrate. Measured the reflection (S
11
) parameters using a vector network analyser (VNA) within the 1-3.5 GHz frequency range and extracted the impedance values from the measured S
11
parameters. DC bias voltage-dependent overtones are observed due to the field-induced piezo-electric nature of BST5 film. The acoustic velocity of the substrate is calculated to be around 8000 m/s for 200-micron thick wafers using spacing of parallel resonance frequency method. The effective coupling coefficient is around 0.02, with a quality factor of 1300.