High-Velocity Whip-Mode Microresonator in LTOI Unimorph: Measurement Methodology and Large-Signal Characterization

Abstract

This paper presents the design, characterization, and large-signal measurement methodology of a high-order whip-mode flexural microresonator on a lithium tantalate-on-insulator (LTOI) unimorph platform. A tapered cantilever concentrates kinetic energy at the free tip through a structural velocity amplification effect, with a targeted whip mode at 9.175 MHz exhibiting a measured Q of 691 in air. The results indicate a substantially reduced susceptibility to viscous damping at high modal frequencies. In-air large-signal testing on a separate device confirms tip velocities up to 20 m/s before the reliable measurement range of the laser Doppler vibrometer (LDV) at the tapered tip is exceeded, while the device itself sustains drive levels up to 240 Vpp before failure. Transitioning to vacuum reveals photothermal-induced static bending of the LTOI cantilever under LDV laser illumination, an effect that prohibits direct velocity measurement for these resonators. Hence, it motivates an indirect extraction methodology to be implemented. In this work, a 3.85 times base-to-tip geometric amplification factor, independently calibrated at low drive, is applied to base velocity measurements to infer tip velocity under large-signal conditions. Using this approach with narrowband chirp excitation, a maximum extracted tip velocity of 58.9 m/s is obtained at 192 Vpp, with spectral analysis of the base velocity placing a conservative lower bound of 36.2 m/s on this estimate. Large-signal failure-mode analysis identifies Pt/Au electrode melting at 210 Vpp as the current velocity ceiling. These results suggest that geometric amplification in high-order flexural modes offers a viable pathway toward the high proof-mass velocities targeted for next-generation MEMS inertial sensors.