Micromachined Resonators

In this work, we present approaches of making a micromachined resonators and oscillators. In the first study, we investigated the effects of anchoring on the resonator's performance. Using the Analog Devices BiMEMS integrated technology, double-ended tuning fork resonators have been fabricated with on-chip circuitry. The results show an improvement in the resonator's quality factor when using anchors with multiple contacts to the substrate. Resonators with frequencies up to 3MHz were tested at µTorr pressures to give quality factors as high as 58,000.

In order to reduce thermoelastic damping, and therefore, minimize the volumetric change during cyclical operation, a torsional resonator has been designed and fabricated. In this attempt, we used Sandia National Laboratories IMEMS integrated technology. A vertical torsional resonator of frequency of ~1MHz was designed that also had relatively low motional resistance (~50kΩ). This resonator produced the highest quality factor in my studies (~70,000).

The effects of coatings on a resonator made from polycrystalline silicon have been studied. Such coatings frequently remain on the resonator's surface after the release process and during use. In this study, we explored the effects of self-assembled monolayer coatings. The results showed that there is a small decrease in quality factor (from ~21,000 to ~19,000) and we conclude that this monolayer coating technique is suitable for micromachined resonators.

Two processing techniques have been researched on how to minimize the electrostatic drive gap between two structures. In one, propagation of nickel through amorphous silicon, known as a nickel-silicidation process was studied. This is a low temperature process that is in accordance with thermal-budget requirements when microelectromechanical structures and circuitry are integrated on the same chip. The results showed rather non-uniform nickel propagation in amorphous silicon, making this process unsuitable. The second technique uses the oxidation of polysilicon surface, deposition of another polysilicon layer, and then using chemical-mechanical-polishing before structure release.