Capacitive micromechanical (MEMS) resonators promise to dramatically improve the design of RF front-ends for wireless communications by virtue of their high quality factor (Q). Unfortunately, the physical limitations of MEMS resonators’ Q are poorly understood, and the highest Qs have proven difficult to achieve reliably. In order to further development of reliably high-Q resonators, a levitated resonator is proposed. This device aims to eliminate anchor loss, which affects the quality factor of resonators in vacuum conditions. By removing the anchors, the intrinsic Q of the material can be measured, as determined by material, surface, and other losses.
A spherical geometry is chosen, and its resonant modes are analyzed. Three modes are considered to be of interest: the first-and second-order radial modes, and the first-order ellipsoidal mode. The mode shapes, resonance frequencies, and equivalent masses of all three modes are calculated using analytical formulas and verified using finite-element analysis.
A prototype fabrication process is developed and carried out, using off-the-shelf metal spheres for the resonator and commercial printed circuit boards (PCBs)for the electrode structures. This process can produce resonators with radii down to 150 μm or less. An alternative, wafer-based fabrication process is proposed for future work with smaller device dimensions.
An electrostatic levitation mechanism is proposed. Dynamically stabilized electrostatic levitation is found to be possible with voltages less than 100 V. The levitated resonator requires sensitive electronics to excite and detect its resonance, as well as to stabilize it under applied electrostatic fields. A preliminary design of these electronics is carried out.