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This paper presents a novel wafer-level thin-film encapsulation process that allows both narrow and wide trenches, which are necessary for traditional structures such as comb-drives. Fully functional devices with trench widths up to 50 $\mu \text{m}$ are fabricated by employing a vapor phase XeF2 isotropic silicon etch to create large cavities and an epitaxial deposition seal to encapsulate the...
This paper presents a topology optimization approach for reducing thermo-elastic dissipation (TED) in MEMS resonators. This algorithm is applied to a clamped-clamped resonant beam to maximize the quality factor (Q). Optimal designs have a Q ten times higher than a solid beam and are 75% higher than previously optimized devices. Furthermore, new designs have intuitive topologies. Beams are fabricated...
We report a new Lorentz force magnetic sensor employing a matched pair of silicon micromechanical resonators on the same die. The two resonators are operated as closed-loop oscillators, where the change in oscillation amplitude is used as a measure of the magnetic field strength. The magnetometer, consisting of the two identical oscillators having opposing axes of field sensitivity, produces two similar...
This paper reports, for the first time, on-chip ovenization of an epitaxially encapsulated resonant accelerometer to improve the stability of scale factor and bias. A double-ended tuning fork (DETF) resonator that shares the anchor with the sensing resonators is used to measure the device temperature. The measured temperature is maintained at a fixed set point using an on-chip silicon heater defined...
We measure the influence of ambient temperature (from −40 °C to 80 °C) on the threshold current for self-oscillations inathermal-piezoresistively pumped, capacitively sensed resonator. We demonstrate that for our flexural mode self-oscillator, the threshold current decreases with decreasing ambient temperature. We observe the generation of harmonics during self-oscillation with amplitudes that decrease...
This paper presents a novel, versatile process for the fabrication of wide and deep cavities for silicon MEMS devices without the need for wafer bonding. Instead of filling large trenches with sacrificial materials before encapsulation or directly using wafer bonding, we present a method that utilizes isotropic etching with XeF2 gas through a thin silicon dioxide film prior to the deposition of encapsulation...
This paper presents a new dual-resonator MEMS magnetic sensor utilizing the Lorentz force. Sensor operation is demonstrated using quadrature frequency modulated (QFM) readout, where the magnetic field strength is measured by monitoring the change in oscillation frequency. The Lorentz force sensor, comprising of a matched pair of differentially operated closed-loop resonators on the same silicon die,...
This paper presents an electrostatic mechanism for tuning the temperature coefficient of frequency (TCf) of disk-shaped resonators fabricated in highly doped (100) single-crystalline silicon. Taking advantage of the degenerate nature of “wineglass” mode resonators such as rings and disks, we show that rotating the resonant mode shapes by electrostatically changing the boundary conditions can effectively...
In this work, we propose a novel temperature compensation method that utilizes a tri-mode operation scheme to generate a temperature-stable frequency reference over a large temperature range. Three resonant modes are excited simultaneously on a highly doped silicon MEMS resonator, and the unique TCf characteristic of each mode is fitted to a parabolic curve. A linear combination of the three frequencies...
We present an epitaxially-encapsulated 2×2mm2 quad-mass resonator (QMR) with shaped comb fingers for frequency tuning. While shaped electrodes have been used for frequency tuning of linear resonators, the device studied here has very high quality factor (g=100,000) resulting in a very narrowband resonance which, without the shaped electrodes, results in undesirable nonlinear behavior such as amplitude-frequency...
This work demonstrates, for the first time, a post-fabrication technique for creating highly compliant structures inside a hermetic, wafer-scale encapsulation process. By tethering large, free-moving structures during fabrication this method mitigates in-process stiction by selectively detaching devices post-fabrication. The tethers in this work were attached to differential resonant beam accelerometers...
We demonstrate how to identify regions of major thermo-elastic dissipation (TED) in MEMS resonators and reduce this energy loss by modifying the device geometry. To demonstrate this, various geometries of a disk resonating gyroscope (DRG) are used. Devices are fabricated and tested to show that the TED-limited quality factor (Q) can indeed be increased using geometric manipulation, as predicted by...
This work demonstrates a unique temperature-compensated differential resonant accelerometer fabricated in a wafer-scale encapsulation process. By utilizing a pair of ultra-stable, high quality factor (>50,000) resonant beams as a strain gauge, we show differential operation with a scale factor of 427Hz/g and a bias instability of 0.16μg at 21s integration time. Furthermore, matched temperature...
This work demonstrates, for the first time, ovenization of a fully-encapsulated dual-mode silicon MEMS resonator operational over a large ambient temperature range. We maintain a localized, elevated operating temperature by utilizing the temperature coefficient of frequency (TCf) difference between two excitation modes of the same resonant body as a thermometer, and by integrating a micro-oven in...
In this study we demonstrate for the first time integration of differential internal electrodes into a Disk Resonator Gyroscope (DRG) design within a wafer-scale encapsulation process. The differential internal electrodes design enables the mode-matching operation of the device with low DC power supplies (±5 V) thanks to the enhanced transduction area, while maintaining similar performance to the...
This paper reports, for the first time, over-travel stops actively driven into resonance to help overcome stiction forces between contacting silicon surfaces. By resonating over-travel stops during contact with proof masses, we show that effective adhesion forces are decreased by over 60% compared to cases with static bump stops. Furthermore, by monitoring shift in resonant frequency during contact,...
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