Lorentz-force gyrator based on AlScN piezoelectric thin film

Abstract

This paper reports a chip-scale radio frequency Lorentz-force gyrator based on an aluminum scandium nitride (Al0.7Sc0.3N) thin film. The two-port gyrator, which is essentially a lateral overtone bulk acoustic resonator, consists of a planar coil for Lorentz-force transduction and two top-bottom electrode pairs for piezoelectric transduction. The non-reciprocity is generated by the phase transition in the Lorentz-force coupling when an external vertical magnetic field is applied. The Lorentz-force gyrators based on both AlN and Al0.7Sc0.3N thin films demonstrate good non-reciprocity, i.e., the 180° phase difference, at approximately 517 and 388 MHz, respectively. Thanks to larger piezoelectric constants, the Al0.7Sc0.3N gyrator demonstrates easier impedance matching and a wider fractional bandwidth of 6.3% at a magnetic field of 1.65 T compared to 1.3% for an AlN device. Finally, an isolator consisting of the Lorentz-force gyrator and a shunt resistor is demonstrated over 35 dB of isolation and flat unidirectional transmission.