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Recent years have witnessed breakthrough researches in micro- and nano-mechanical resonators with small dissipation. Nano-precision micromachining has enabled the realization of integrated micromechanical resonators with record high Q and high frequency, creating new research horizons. Not too long ago, there was a perception in the MEMS community that the maximum f.Q product of a microresonator is limited to a frequency-independent constant determined by the material properties of the resonator. In this paper, the contribution of phonon interactions in determining the upper limit of f.Q product in micromechanical resonators will be discussed and shown that after certain frequency, the f.Q product is no longer constant but a linear function of frequency. This makes it possible to reach very high Qs in GHz micro- and nano-mechanical resonators and filters. Contributions of other dissipation mechanisms such as thermoelastic damping and support loss in the quality factor of a microresonator will be discussed as well.

This paper presents recent advances in the HARPSS micromachining technology, which enables implementation of movable Single Crystal Silicon (SCS) structures with high aspect ratio vertical air gaps on low-resistivity silicon substrate. This is suitable for applications of micro-gravity accelerometers, low voltage tunable capacitors, and high-resolution gyroscopes that require aspect ratios as large as 100:1 to achieve high sensitivity and wide tuning range. The single-sided HARPSS process eliminates the need for double-sided processing, and wafer bonding to subsequently package the device. The device thickness and gap spacing can be varied in a wide range, 30-150mm and 0.2-2mm respectively, to select the performance range. The movable MEMS elements are made of bulk silicon substrate, resulting in higher mass, higher quality factor (Q), and better shock resistance, compared to using polysilicon (poly) as the movable structure. This process provides a mechanism for creating corrugation in SCS electrodes to reduce the Brownian noise of sensors. This technique realxes the need to reduce the noise by using the maximum available mass and through-wafer etch. The corrugations are created by a DRIE technique for etching poly surrounded by oxide inside the isolation trenches. Also, uniform capacitive gap spacings are created by growing sacrificial oxide inside the trenches.

This paper reports on a low-cost low-temperature (