We present a study on the quantification of energy dissipation of Micro-Electro-Mechanical System (MEMS) resonators. Toroidal Ring Gyroscope (TRG) was used as a platform to conduct the study. The ...main energy dissipation mechanisms in TRG include viscous air damping, Thermo-Elastic Damping (TED), anchor loss, and surface loss. During our experimental study, these energy dissipation mechanisms were minimized and controlled by venting the encapsulation and actively pumping down to high vacuum, cooling the temperature down to around 123 K, adjusting modal balance by electrostatic tuning, and pre-baking the device at high temperature (425 °C), respectively. At room temperature, the quality factor related to viscous air damping was measured to be 625,000, TED to be 170,000, and anchor loss to be 1,350,000. Finite Element Analysis (FEA) was conducted to support these findings. Relation between the anchor loss and electrostatic tuning was also explored. The effects of moisture-related surface loss have also been demonstrated by monitoring characteristics over a 2-year period of time. High temperature bake-out was proven to be effective in removing the moisture and reducing the surface loss. This paper combines topics that are scattered in literature on identification of energy dissipation mechanisms in kilohertz-range silicon MEMS resonators and presents the topic as a single methodology illustrating how the contribution of each energy dissipation mechanism can be quantified independently. To the best of our knowledge, this study is the first to experimentally quantify all major energy dissipation mechanisms in a kilohertz-range silicon MEMS resonator. 2020-0294
In this work we present measurements of drive-induced negative nonlinear dissipation present in doubly clamped microbeams fabricated in a hermetically sealed package. We characterize the ...amplitude-frequency nonlinearity and nonlinear dissipation present in this system under direct drive. The negative nature of the nonlinear dissipation is observed when measuring either the directly- or parametrically-actuated response. By comparing to the free ringdown response, we confirm that the nonlinear dissipation is induced by driving the resonator. Drive-induced nonlinear damping is an important consideration for resonant sensors and oscillators operated at large amplitudes. 2020-0140
This work focuses on quantifying and minimizing energy loss in encapsulated capacitive microelectromechanical (MEM) resonators. This is important to reduce phase and frequency noise in the output ...signal of these resonators. Improving upon these metrics creates accelerometers, gyroscopes, and timing references that have more resolution and higher stability. Energy loss of a MEM resonator is measured by its quality factor, which is the ratio of the energy stored in the resonator to the energy lost per cycle of motion. The common energy loss mechanisms that affect the quality factor of MEM resonators are thermoelastic dissipation (TED), gas damping, Akhiezer damping, and anchor damping. This work quantities energy loss of these loss mechanisms using the different temperature dependence of each mechanism. Insight from quantifying these energy loss mechanisms in different resonator designs is used to design a resonator with a quality factor that is limited by the material loss limit of silicon, which is the highest possible quality factor that a capacitive resonator can achieve, resulting in an fxQ product of 2.2x1013 Hz.Of all of the energy loss mechanisms, anchor damping is the least understood for resonant frequencies below 100 MHz. Anchor damping occurs because mechanical energy leaks out of the resonator at the attachment point, or anchor, to the substrate. This work experimentally explores how factors including outer packaging, substrate thickness, anchor placement, and anchor design affect anchor loss. Anchor damping in a bulk mode resonator was reduced by almost an order of magnitude by removing the silver paste adhering the die to the chip carrier. Thinning the substrate enhances the quality factor by a factor of 1.5x. The placement of anchors at two nodes on the edge of a ring resonator is has a 2x greater quality factor than that of a ring resonator with a center anchor. A more compliant anchor reduces anchor damping by an order of magnitude in bulk mode resonators. These results initiate an understanding of the mechanism by which anchor loss occurs in MEM resonators below 100 MHz.Lastly, this thesis presents a variant of the Epi-Seal encapsulation fabrication process where small and large transduction gaps can be fabricated for resonators without etch-holes. The traditional Epi-Seal process uses epitaxial silicon to seal devices at the wafer level in an oxide-free, particle-free, low pressure environment, creating resonators with long term stability. This new variant is important because it increases the design space for capacitive MEM resonators to include large etch-hole free masses and large and small transduction gaps with all the advantages of the original process.
