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Open Access Publications from the University of California

Scholarly Works (4 results)

  • Thesis
  • Peer Reviewed
UC Irvine Electronic Theses and Dissertations (2015)

This Ph.D. dissertation reports novel fabrication processes and architectures for implementation of Rate Integrating Gyroscopes at micro-scale. Majority of the focus is directed towards development of a surface tension and pressure driven micro-glassblowing paradigm, which is envisioned to serve as an enabling mechanism for wafer-scale fabrication of 3-D micro-wineglass gyroscopes. New 2-D silicon Micro Rate Integrating Gyroscope (MRIG) architectures are also explored to bridge the gap between conventional micro-machining techniques and micro-glassblowing processes, and to serve as a test platform for various MRIG control strategies. Closed loop Whole Angle operation of these 2-D silicon MRIG architectures is presented to identify some of the control challenges associated with MRIG control, such as energy pumping and suppression of errors caused by structural imperfections.

The main contribution of the thesis is the development of a high temperature (1700 °C) micro-glassblowing process for fabrication of highly symmetric and low internal dissipation 3-D fused silica wineglass resonators. Owing to the "self-healing'" properties of surface tension and pressure driven micro-glassblowing paradigm, and the low internal loss fused silica material, quality factors above 1 million and frequency splits less than 1 Hz have been demonstrated. In addition to a multi-purpose test-bed for micro-wineglass characterization, in-situ electrode structures with sub 10 micron capacitive gaps are reported for electrostatic transduction.

In order to streamline the realization of MRIG control strategies, two new Si-MEMS MRIG architectures were also developed as a part of this thesis: Toroidal Ring Gyroscope (TRG) and Dual Foucault Pendulum (DFP) Gyroscope. Toroidal Ring Gyroscope consists of an outer anchor, concentric ring suspension system, and inner electrode assembly. Q-factors above 100,000 were obtained with this architecture at a compact size of 1760 micron. First demonstration of a parametrically driven MRIG is also reported as a part of this work, showing better than 20 ppm scale factor stability at 360 °/s rate input. Dual Foucault Pendulum (DFP) architecture is a conventionally machined lumped mass Micro Rate Integrating Gyroscope implemented using in-house silicon-on-insulator technology. It is believed that this two mass DFP architecture is the minimal realization of a dynamically balanced, lumped mass MRIG.

Finally, a custom, multi-purpose FPGA/DSP based control system was developed to demonstrate interchangeable rate and rate integrating mechanization of micro-scale gyroscope architectures developed in this thesis. Continuous Rate Integrating Gyroscope operation is demonstrated, by electronically compensating structural imperfections via control loops, such as Phase Locked Loop (PLL), Amplitude Gain Control (AGC), quadrature null loop, and closed-loop parametric drive.

    Cover page: Micro-glassblowing Paradigm for Realization of Rate Integrating Gyroscopes
    • Article
    • Peer Reviewed
    UC Irvine Previously Published Works (2015)
    In this paper, we report magnetic neutral loop discharge (NLD) plasma etching of fused silica (FS) and borosilicate glass (BSG), demonstrating high aspect ratio deep etch ( 100~\mu \text{m} ) with vertical walls (<3° deviation from vertical). This paper for the first time presents the systematic study of FS and BSG deep etching in NLD plasma. Four different masking materials have been explored including metal, amorphous silicon, bonded silicon, and photoresist. Etch parameters were optimized to eliminate unwanted artifacts, such as micro-masking, trenching, and faceting, while retaining a high aspect ratio (up to 7:1 for FS and 8:1 for BSG). In addition, a method for sidewall roughness mitigation based on postfabrication annealing was developed, showing the sidewall roughness reduction from the average roughness ( R{a} ) 900 to 85 nm. Further advances in deep plasma etching processes may enable the use of FS and BSG in the fabrication of precision inertial MEMS, micro-fluidic, and micro-optical devices. [2015-0078]
      Cover page: Study of High Aspect Ratio NLD Plasma Etching and Postprocessing of Fused Silica and Borosilicate GlassCreative Commons 'BY' version 4.0 license
      • Article
      • Peer Reviewed
      UC Irvine Previously Published Works (2014)
      We demonstrate, for the first time, sub-1 Hz frequency symmetry in micro-glassblown wineglass resonators with integrated electrode structures. A new fabrication process based on deep glass dry etching was developed to fabricate micro-wineglasses with self-aligned stem structures and integrated electrodes. The wineglass modes were identified by electrostatic excitation and mapping the velocity of motion along the perimeter using laser Doppler interferometry. A frequency split (Δ f) of 0.15 and 0.2 Hz was demonstrated for n=2 and n=3 wineglass modes, respectively. To verify the repeatability of the results, a total of five devices were tested, three out of five devices showed Δ f<5 Hz. Frequency split stayed below 1 Hz for dc bias voltages up to 100 V, confirming that the low frequency split is attributed to high structural symmetry and not to capacitive tuning. High structural symmetry (< 1 Hz) and atomically smooth surfaces (0.23 nm Sa) of the resonators may enable new classes of high performance 3-D MEMS devices, such as rate-integrating MEMS gyroscopes. © 1992-2012 IEEE.
        Cover page: Achieving Sub-Hz Frequency Symmetry in Micro-Glassblown Wineglass Resonators
        • Article
        • Peer Reviewed
        UC Irvine Previously Published Works (2015)
        In this paper, we report Q -factor over 1 million on both n=2 wineglass modes, and high-frequency symmetry (Δ f/f ) of 132 ppm on wafer-level microglassblown 3-D fused silica wineglass resonators at a compact size of 7-mm diameter and center frequency of 105 kHz. In addition, we demonstrate for the first time, out-of-plane capacitive transduction on microelectromechanical systems wineglass resonators. High Q -factor is enabled by a high aspect ratio, self-aligned glassblown stem structure, careful surface treatment of the perimeter area, and low internal loss fused silica material. Electrostatic transduction is enabled by detecting the spatial deformation of the 3-D wineglass structure using a new out-of-plane electrode architecture. Out-of-plane electrode architecture enables the use of sacrificial layers to define the capacitive gaps and 10 μm capacitive gaps have been demonstrated on a 7-mm shell, resulting in over 9 pF of active capacitance within the device. Microglassblowing may enable batch-fabrication of high-performance fused silica wineglass gyroscopes at a significantly lower cost than their precision-machined macroscale counterparts. [2014-0251]
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