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1. Three-Dimensional Microfabrication Techniques for High-Q Materials

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Micro blowtorching process

Cross-sectional SEM image

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Fused silica micro birdbath shell

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World's smallest wineglass with a drop of wine!

Micro birdbath resonator (metallized with Cr/Au) next to an apple seed

The performance of micro-sensors degrades with an increase in the Brownian noise. Fused silica is a preferred material for macro-scale sensors due to its extremely high mechanical and optical quality factors (Q); however, it is challenging to create fused-silica microstructures due to the difficulty in etching and depositing thick films. We developed a new technique to create very tall fused silica shells. The technique uses a blowtorch, which can reflow fused silica and other high-Q material substrates into a variety of three-dimensional geometries. We made three-dimensional micro-shells with very good mechanical symmetry, which can be used as a micro vibratory gyroscope.

2. Novel Design, Fabrication, and Control of Micro Vibratory Rate- and Rate-Integrating Gyroscopes

1) High-Q Fused-Silica Micro Birdbath Resonator Gyroscope (BRG)

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Micro Birdbath Resonator Gyroscope (BRG)

Allan Deviation Plot

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Angular measurement under 100, 200, 300, and 400 deg/s rotation rates.

Angular gain under -700 to 700 deg/s rotation rates.

Micro-vibratory gyroscopes are used in a large number of applications. The performance of a gyroscope suffers from the thermal noise, frequency change caused by temperature change, and external vibrations and shocks. Many applications also require larger full-scale range and bandwidth. We created a fused-silica micro-gyroscope, named the birdbath resonator gyroscope (BRG). The key feature of the BRG is the fused silica micro birdbath resonator with a large frequency difference between the wineglass modes and the parasitic modes, a high mechanical Q, a small frequency split, and a large angular gain. The BRG is tested in both rate and rate integrating modes.

2) Single-Crystal-Silicon Cylindrical Rate-Integrating Gyroscope (CING)

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Wave orientation (degrees) following 60-degrees-per-second rotation rate

Single-Crystal-Silicon Cylindrical Rate-Integrating Gyroscope (CING)

We developed the single-crystal-silicon Cylindrical Rate-Integrating Gyroscope (CING) with good mechanical symmetry. The multiple-ring-cylinder resonator is made with (111) Si using only a single masking step and has good mechanical symmetry. The gyroscope is controlled in the rate-integrating mode using digital interface circuitry. We are also investigating the control algorithms for reducing measurement errors due to frequency and Q asymmetry

3) Single-Crystal-Silicon Balance Oscillating Gyroscope (BOG)

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Single-Crystal-Silicon Balanced Oscillating Gyroscope (BOG)

We developed a balanced-mode tuning-fork gyroscope for measuring planar rotation rates. The BOG can differentially cancel vibrations along both drive and sense axes. The BOG also has a single anchor, which makes this sensor less sensitive to stress. The BOG is fabricated using the silicon-on-glass (SOG) process on a 100-micrometer-thick silicon substrate.

3. Wafer-Level Environment-Resistant Micro Package

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We developed a wafer-level vacuum package that can isolate a packaged sensor (e.g. vibratory gyroscope and resonator) from temperature change as well as external vibrations and shocks. The key feature of this package is the microfabricated isolating suspension, which is made of a thin Pyrex substrate. We demonstrated a near-navigation-grade gyro performance with a packaged vibratory tuning-fork gyroscope (developed by researchers at the Georgia Institute of Technology) over a wide range of temperature. This technology is currently being commercialized by Epack, Inc.

4. Silicon-on-Glass (SOG) Process

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Vertical comb-drive electrodes formed using selective anodic bonding technique

Cross-sectional SEM image of CING

The Si-on-Glass (SOG) process is attractive due to large device thickness, high mechanical Q, and small parasitic capacitance to the bottom substrate. The SOG process is used in many of the devices that I have developed.

© 2017 by Jae Yoong Cho