An Intrinsically Switchable, Monolithic BAW Filter Using Ferroelectric BST

This letter presents an intrinsically switchable monolithic filter based on laterally acoustically coupled bulk acoustic wave resonators. The filter is based on a barium strontium titanate-on-silicon (BST-on-Si) composite structure which can be turned on and off by the application of a dc bias. In its off state, the filter provides an isolation of 40 dB. In its on state, the filter exhibits an insertion loss of 7.1 dB and greater than 30 dB of out-of-band rejection. The center frequency and bandwidth of the filter are 748 MHz and 13.8 MHz, respectively. The mechanical quality factor of the coupled resonators is calculated to be 99.