Intrinsically Switchable and Bandwidth Reconfigurable Ferroelectric Bulk Acoustic Wave Filters.

Reconfigurable bulk acoustic wave filters provide a number of advantages for wireless communication systems, including compact size, cost effectiveness, and less complexity. This article presents the design methodology of an intrinsically switchable and bandwidth reconfigurable film bulk acoustic resonator (FBAR) filter, employing the electrostriction in ferroelectric barium strontium titanate (BST). Two examples of ferroelectric BST-based filters are designed and fabricated as a proof of concept. Under the application of a dc bias voltage, the fabricated switchable filters exhibit a bandpass response with a fractional BW of 3%. By changing the state of the ferroelectric BST FBARs through applied dc bias voltages, the bandwidth of the filters is adjusted. Without any bias, the filters switch OFF to provide isolation between the input and output ports. BST-based bandwidth reconfigurable filters can potentially reduce the number of required filters and switches in future multiband RF front ends.