An Intrinsically Switchable FBAR Filter Based on Barium Titanate Thin Films

A switchable thin film bulk acoustic wave resonator (FBAR) filter based on barium titanate (BTO) thin films is reported for the first time. BTO is a ferroelectric material which possesses electrostriction, giving the filter the ability to be placed in either an on state or an off state by changing the applied dc bias voltage. A 1.5 stage ladder type bandpass filter using BTO FBARs has been designed, fabricated, and measured. The application of a 15 V dc bias results in the filter being place in an on state with a center frequency of 2.14 GHz, a 40 MHz bandwidth and 6.2 dB of insertion loss. Conversely, the application of a - 3 V dc bias results in the filter being placed in an off state with 15 dB of rejection. This filter is very compact with dimensions of 40 mum by 80 mum.