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Title: Performance Parameters of Micromechanical Resonators
Keywords: Micromechanical, resonators, bulk-acoustic-mode, oscillators, temperature compensation
Issue Date: 16-Jul-2010
Source: KHINE LYNN (2010-07-16). Performance Parameters of Micromechanical Resonators. ScholarBank@NUS Repository.
Abstract: In this work, performance parameters of various flexural-mode and bulk-acoustic-mode micromechanical resonators are presented. Investigated parameters are quality factor (Q), pressure stability, power handling, nonlinearity, and temperature stability. Resonators studied in this work are electrostatically driven-and-sensed, and they are fabricated in SOIMUMPs process provided by MEMSCAP. The bulk of this work has focused on the study of quality factor. Tested flexural-mode beam resonators can provide Q values in tens of thousands range, but much higher quality factors above one million have been measured for bulk-acoustic-mode resonators. One of the main vibration energy losses for bulk-mode resonators is the losses through the anchor support. The dependence of Q on structural geometry, as well as on the shape of anchor design, is explored in detail for Lame-mode square resonators. Measured results suggest that T-shaped anchor design can improve the Q performance with lower motional resistance compared to straight-beam anchor for supporting bulk-mode resonators. At pressure levels below 100Pa, the quality factor of bulk-mode resonators is measured to be relatively independent of pressure, which can be considered as the threshold pressure. On the other hand for the beam resonators, this threshold pressure is roughly 10Pa. Given the same amount of air damping, bulk-mode resonators with orders of magnitude higher mechanical stiffness can uphold their maximum Q better at higher pressures compared to the beam resonators. Bulk-mode resonators studied in this work are able to handle higher power levels before their vibrations become nonlinear compared to beam resonators, mainly due to orders of magnitude higher energy storage capability. High power handling of bulk-mode resonators is beneficial for oscillator implementation because the combined effect of ultra-high Q and high energy storage capacity can improve both close-to-carrier phase noise and the noise floor of the oscillator. The resonant frequency notably drifts with temperature for silicon resonators. Large amount of resonant frequency shifts with temperature is useful for temperature sensing, but undesirable for frequency references. Hence, a temperature compensation method is required for resonator oscillators. A new idea of temperature compensation is demonstrated with experimental verifications in this work, which is based on frequency mixing of two oscillation signals, and this method has the potential to compensate the frequency shifts in bulk-mode resonators as well.
Appears in Collections:Ph.D Theses (Open)

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