Ba_0.5Sr_0.5T 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<inf xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">0.5</inf>Sr<inf xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">0.5</inf>TiO<inf xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">3</inf>(BST5)/Pt configuration on a silicon nitride (Si<inf xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">3</inf> N<inf xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">4</inf>) coated high-resistivity silicon substrate. Measured the reflection (S<inf xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">11</inf>) parameters using a vector network analyser (VNA) within the 1-3.5 GHz frequency range and extracted the impedance values from the measured S<inf xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">11</inf> 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.