BAW filter design method based on intrinsically switchable ferroelectric BST FBARs

Abstract

A design method for BAW filters based on intrinsically switchable ferroelectric BST FBARs is presented. A complete set of design equations for ladder-type FBAR filters is derived based on the popular filter synthesis method using image parameters. For the first time, a complete analysis is performed that accurately calculates both the image impedance and propagation constant for BAW filters. Closed-form design equations as a function of FBAR and filter specifications are provided. As an experimental verification, a 1.5-stage switchable ferroelectric BST FBAR filter is designed, fabricated, and measured. When a dc bias is applied, a switchable filter is in its on-state and provides an insertion loss of 5.77 dB with a fractional bandwidth of 1.22% at 1.97 GHz. When in its off-state, the filter exhibits more than 22 dB isolation. Circuit-level simulation results are in very good agreement with the measurement results, validating the proposed BAW filter design method.