RF-MEMS switchable inductors for tunable bandwidth BAW filters

This paper presents a method for reconfiguring the bandwidth of Bulk Acoustic Wave (BAW) ladder filters by adding switchable inductors to their shunt resonators. Inductance values are controlled by selecting the number of turn in spiral inductor using micro-electro-mechanical (MEMS) switches. For this purpose, a MEMS inductor has been designed, fabricated and characterized in terms of inductance value, quality factor, and resonance frequency. A measurement-based model of this inductor has been implemented in a circuit simulator to build a reconfigurable RF Ladder BAW filter intended for handset applications. The simulation results show that, using this switchable inductor, it is possible to increase the filter bandwidth by up to 25% with an improved out-of-band rejection and without degrading its selectivity.