Nonlinearities in bulk acoustic mode silicon micromechanical resonators
- Capacitive microelectromechanical (MEMS) oscillators represent a promising alternative to quartz-based systems as they provide benefits such as mass fabrication, size reduction, and compatibility with CMOS IC integration. However, one drawback that comes with size reduction is smaller induced currents, which leads to increased noise in the oscillator output. To overcome this challenge, resonators have to be driven to larger amplitudes of motion, and oftentimes operate in the nonlinear regime, where the resonator dynamics become much more complicated (e.g. Duffing-type nonlinearity, nonlinear damping, etc.). This work aims to characterize the nonlinear behavior in commonly used bulk acoustic mode resonators fabricated in a modified epi-seal process, where a variety of devices with reduced design limitations can be fabricated in this process while maintaining the core epi-seal process features (e.g. high stability, reliability, ultra-clean, etc.). Utilizing this process, high quality factor devices without release etch-hole in the device layer can be fabricated (e.g. Lamé resonator operated at 10.1 MHz with quality factor of 2.27e+13), which is beneficial towards characterization of nonlinear behavior in bulk mode devices. Frequency stability experiments have also been performed, with the measured stability of ± 18 ppb over one month of testing. Cavity pressure studies indicate a cavity pressure of less than 0.1Pa equivalent of air. These results justify that the modified process is comparable with the standard epi-seal process. The effect of doping on material nonlinearities is also analyzed, where three types of bulk acoustic mode resonators are used to characterize device nonlinearity with respect to doping type/concentration and orientation. Measurements on the effect of electrostatic nonlinearity are performed to justify that these devices are dominated by material nonlinearity. While recent studies have demonstrated the use of heavily p- or n-type doping for passive frequency-temperature compensation, this work demonstrates that device nonlinearity is also heavily influenced by the resonator mode shape, device crystal orientation, doping type and concentration. Lastly, a few modal coupling behaviors observed in commonly used bulk-mode resonators will be introduced, where we demonstrate that certain design parameters can be used to tune the modal coupling strength, thus directly affecting the resonator's frequency and quality factor.
|Type of resource
|electronic; electronic resource; remote
|1 online resource.
|Stanford University, Department of Mechanical Engineering.
|Kenny, Thomas William
|Kenny, Thomas William
|Statement of responsibility
|Submitted to the Department of Mechanical Engineering.
|Thesis (Ph.D.)--Stanford University, 2016.
- © 2016 by Yushi Yang
- This work is licensed under a Creative Commons Attribution Non Commercial 3.0 Unported license (CC BY-NC).
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