HARPSS-fabricated nano-gap comb-drive for efficient linear actuation of high frequency BAW resonators

This paper presents the design, fabrication and characterization of self-aligned nano-gap comb-drive actuators for high frequency bulk acoustic wave (BAW) resonators. The comb-drive is implemented to actuate a high-Q 1 MHz annulus BAW resonator with gyroscopic modes. Measurements show a linear force density of 261.5 pN/V
²
μm, which is to the authors' knowledge the largest force density reported to date for silicon comb-drives. As a result, vibration amplitudes as large as 350 nm are measured using relatively small voltages. An equivalent model estimation of the mechanical nonlinearity of the resonator indicates a spring hardening effect at large displacements, which is confirmed by experimental results.