Fully-differential mechanically-coupled PZT-on-silicon filters

This paper reports on the design of a 2-pole differential MEMS filter using mechanically-coupled overtone width-extensional resonators. The resonators and filters are fabricated in the 10 mum thick device layer of a SOI wafer and transduced by a 0.5 mum PZT (lead zirconate titanate) thin film deposited on the top surface of the wafer. A 206.3 MHz overtone width-extensional filter is demonstrated with 653 kHz bandwidth, -25 dB insertion loss (IL) and -62 dB stop-band rejection in air. Uncompensated temperature coefficient of frequency (TCF) of -16 ppm/degC and third-order input intercept point (IIP3) of +52.5 dBm are demonstrated by the filter. The piezoelectric response of the filter is controlled by varying the electric field across the PZT transducer. A 20 dB improvement in IL and 0.22% center frequency tuning resulted by applying 20 V DC tuning voltage.