Piezoelectric-on-Silicon Array Resonators With Asymmetric Phononic Crystal Tethering

The design, fabrication, and characterization of Piezoelectric-on-Silicon array resonators with asymmetric Phononic crystal (PnC) tethering for applications in high frequency reference oscillators is presented. A hybrid approach of mechanical arraying along with higher mode of operation is used for minimizing the motional resistance. For improving the Q-factor, novel asymmetric PnC tethers are developed that not only exhibit a larger bandgap than their symmetric PnC counterparts, but also have significantly better design optimization capabilities for fine tuning the tether properties. Third order longitudinal mode resonators operating at frequencies of 300 MHz with and without PnC tethering and with different number of resonators in the array were fabricated using 2 μm SOI wafers. The measured characteristics of the resonators showed a peak unloaded Q-factor of 4454 and a motional resistance of 200 Ω at 312 MHz for a seven resonator array. These results are comparable with the best reported in literature, in spite of a lesser silicon thickness.