SPST Acoustic Switch Based on Poled Ferroelectrics

The first proof-of-principle demonstration for a single-pole single-throw (SPST) acoustic switch using phase inversion in ferroelectric bulk acoustic wave (BAW) resonators is presented. Independent control of piezoelectric coefficient in two shunt ferroelectric acoustic resonators is leveraged to implement the switch. The operating principle of the switch can be extended to any ferroelectric acoustic structure. Furthermore, the switch technology presented herein is suitable for replacing transistor-based switches for channel selection in acoustic filter banks for radio frequency front ends (RFFE). A prototype is presented utilizing stacked crystal filters (SCF) made from Barium Strontium Titanate (BST) providing isolation of 41.4 dB in the OFF state and insertion loss of less than 3.7 dB in the ON state. The switch prototype’s operating frequency is 3.6 GHz. The total active area of the resonators is 1126 µm².