A Fully Differential Thin Film Piezo on Silicon Flexural Mode Ring Resonator with Exceptional Quality Factor

We report an innovative four segmented electrode design of a ring based flexural mode Thin Film Piezo-on-Substrate (TPoS) resonator. It has one of the highest loaded Quality factor (Q
_l
) among its flexural mode counterparts working in the MHz range. The out-of-plane flexural mode is explored using the differential drive/sense configuration. The unique design of the driving and sensing electrodes along with the 10μm thick Single Crystal Silicon (SCS) in the device layer stack enhances the transduction efficiency and the overall quality factor respectively. The resonator is operated in both air and vacuum to study air damping effects. The device has a resonance frequency (f
_r
) of 5.25 MHz and features a Q
_l
of 628 in air for a driving power of 0 dBm. An enhancement close to 11 times was achieved when operated in vacuum. The resonator has a Q
_l
of 6,696 and Stop Band Rejection (SBR) of 50 dB in vacuum. Closed-loop measurements using a commercial Phase Locked Loop was carried out. In vacuum, the device exhibits a Phase Noise of -108 dBc/Hz at 1 kHz offset for a 10 kHz loop Bandwidth.