Monolithic Thin-Film Piezoelectric-on-Substrate Filters

This paper presents monolithic piezoelectric-on-substrate acoustic filters operating in a wide frequency range. Second order narrowband filters are realized by utilizing coupled resonance modes of a single microstructure. The substrate is selected from materials with high acoustic velocity and low acoustic loss (e.g. silicon) resulting in high Q resonant structures. The unique mechanical coupling technique employed in this work enables fabrication of narrow-band filters with a high out-of-band rejection in a small footprint. We demonstrate narrow-band filters suitable for channel-select applications in IF and RF bands. Filter Q values of 800 at 250 MHz, 470 at 360 MHz, and 400 at 3.5 GHz for small footprint second-order filters are reported. The measured power handling of these devices is high due to the use of high energy density structural material, showing a 0.2 dB compression point of >15 dBm at 360 MHz (limited by the measurement equipment).