Dongsuk D. Shin

Ovenized dual-mode clock (ODMC) based on highly doped single crystal silicon resonators

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 the encapsulation layer. Preliminary results of real-time compensation demonstrate a stability of ±250ppb of the in-plane Lamé-mode frequency over -20°C to 80°C.

Phonon conduction in silicon nanobeams

Despite extensive studies on thermal transport in thin silicon films, there has been little work studying the thermal conductivity of single-crystal rectangular, cross-sectional nanobeams that are commonly used in many applications such as nanoelectronics (FinFETs), nano-electromechanical systems, and nanophotonics. Here, we report experimental data on the thermal conductivity of silicon nanobeams of a thickness of ∼78 nm and widths of ∼65 nm, 170 nm, 270 nm, 470 nm, and 970 nm. The experimental data agree well (within ∼9%) with the predictions of a thermal conductivity model that uses a combination of bulk mean free paths obtained from ab initio calculations and a suppression function derived from the kinetic theory. This work quantifies the impact of nanobeam aspect ratios on thermal transport and establishes a criterion to differentiate between thin films and beams in studying thermal transport. The thermal conductivity of a 78 nm × 65 nm nanobeam is ∼32 W m−1 K−1, which is roughly a factor of two smal...

Epitaxially encapsulated resonant accelerometer with an on-chip micro-oven

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 in the encapsulation layer. Preliminary results show significant improvement beyond the devices intrinsic passive temperature compensation. Over the temperature range from −20°C to 80°C, the 0g bias error is reduced by a factor of three, and the scale factor stability is improved by over an order of magnitude.

Fabrication of wide and deep cavities for silicon MEMS devices without wafer bonding

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 materials to create and encapsulate large cavities. The process is demonstrated to be robust and can be easily incorporated into the fabrication of a variety of MEMS structures, including pressure sensors, ultrasonic devices, microfluidics chips, hermetically encapsulated silicon resonators, inertial sensors, and more.

Encapsulated disk resonator gyroscope with differential internal electrodes

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 previously reported baseline DRG. The mode-matching operation yields a scale-factor of 1.37 mV/(7s) and an ARW of 0.29 °/√hr.

Robust Method of Fabricating Epitaxially Encapsulated MEMS Devices with Large Gaps

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

Dual-resonator MEMS magnetic sensor with differential amplitude modulation

\mu \text{m}

Transfer function tuning of a broadband shoaling mechanical amplifier near the electrostatic instability

are fabricated by employing a vapor phase XeF2 isotropic silicon etch to create large cavities and an epitaxial deposition seal to encapsulate the devices in an ultra-clean, high vacuum environment with no native oxide and humidity. In this paper, we demonstrate the robustness of the proposed fabrication process, as well as the inherent benefits of the high-temperature epitaxial encapsulation process: high quality factor, extreme stability, exceptional aging, and fatigue performance. [2017-0098]

Effective quality factor and temperature dependence of self-oscillations in a thermal-piezoresistively pumped resonator

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 oscillation amplitudes with nearly identical temperature sensitivities, providing continuous temperature compensation. Differential amplitude modulated (AM) output from the two oscillators reduces the sensors offset by a factor of 12 to 26 μT, and suppresses the effect of the resonators temperature coefficient of quality factor (TCQ) on the output, reducing the maximum drift error by a factor of 15 to ±0.49 μT, improving the sensors bias instability from 86 nT to 26 nT, and increasing the averaging time to reach the bias instability from 1 s to 10 s. With 44-μW power dissipation, the sensor achieves a resolution of 50 nT/√Hz, limited by Brownian noise.

Topology optimization for reduction of thermo-elastic dissipation in MEMS resonators

We present a tunable broadband shoaling mechanical amplifier and a method to extend its operation near the electrostatic pull-in instability. The model has been verified experimentally on a vacuum encapsulated silicon MEMS device. We show that by adding an appropriate mechanical compensation spring, the amplifier can be operated near the pull-in instability in a quasi-linear fashion. Furthermore, electrostatic band-pass region and amplification tuning is shown.