Scaling Effects of Micromechanical Piezoelectric-on-Silicon Radial Contour Mode Disks Resonators in Water

We present experimental results on the effect of scaling down the size of piezoelectric-on-silicon radial contour mode disk resonators tested in water, particularly with regards to quality (Q) factor and motional resistance (R_m). These findings are highly essential for implementing suitable device topologies that can be applied as resonant mass sensors for liquid phase sensing (which includes biological and chemical sensing). We show that in reducing the disk size in pursuit of increasing mass sensitivity, the Q factor in water increases almost inversely with the disk radius, leading to a moderate increase in R_m. The radial contour mode of resonance enhances the electromechanical efficiency thus greatly lowering Rm. Based on a disk resonator with a radius of 200 μm (sufficient to provide a mass sensitivity of 2.68 Hzcm²/ng) tested in water, we experimentally demonstrate a Q factor of 250 (possibly the highest value among contour mode resonators) and Rm of 2.77 kΩ.