W. K. Sung

A mode-matched 0.9 MHZ single proof-mass dual-axis gyroscope

This paper reports on the design, fabrication, and characterization of a high-frequency single proof-mass dual-axis gyroscope. The hollow-disk pitch-and-roll resonant gyroscope has electrostatically tunable in-plane and out-of-plane resonance modes to enable mode-matched operation at ∼ 0.9MHz in the presence of process non-idealities such as thickness variations of the SOI wafer. A prototype device demonstrates x- and yaxis rate sensitivity of 127µV/deg/sec and 214µV/deg/sec, respectively. High quality factors (Q) of ∼ 10,000 are observed in vacuum for the in-plane drive and out-of-plane sense resonance modes. The device is implemented using a revised version of the HARPSS™ process, thereby enabling a single-chip tri-axial implementation when integrated with a yaw disk gyroscope.

A 3MHz spoke gyroscope with wide bandwidth and large dynamic range

This paper reports on the design and characterization of a high-frequency silicon bulk acoustic wave (BAW) spoke gyroscope operating in air. The gyroscope described here operates at 3.12MHz in a near mode-matched condition (without tuning) and has a −1dB bandwidth of ∼1.5kHz. The device has a linear full-scale range in excess of 30,000°/sec with a sensitivity of 15.0µV/°/sec using a 10V DC polarization voltage. The wide bandwidth and large dynamic range of this device are beneficial for applications requiring rapid motion sensing.

Electrostatic self-calibration of vibratory gyroscopes

This paper introduces a new approach to self-calibration of Coriolis-based vibratory gyroscopes that does not require the use of any additional moving parts or a calibration stage. Instead, the effect of the Coriolis force on the device is mimicked by the application of a rotating excitation to the device drive and sense modes. This calibration method is based on the theoretical analysis of an equivalent 2-DOF mass-spring model, which can be used to describe the behavior of a variety of MEMS gyroscopes. The method is validated both by the results of finite-element simulations and by experimental measurement.

Wafer-level vacuum-packaged triaxial accelerometer with nano airgaps

This paper reports on the design, implementation and characterization of triaxial capacitive accelerometers operating in a low-pressure environment (~1 Torr). Small form-factor devices, with proof-mass area of less than 1mm2, were fabricated on a 40 μm-thick SOI substrate using the HARPSS™ process to attain in-plane and out-of-plane nanoscale capacitive airgaps (~300 nm). Increased sensitivity and stable open-loop operation were simultaneously achieved by using additional damping electrodes. Large electromechanical coupling provided by the deep sub-micron airgaps allow for the design of high-frequency accelerometers (~15 kHz) that yield better shock and vibration immunity. Scale factors of 7.5 mV/g and 8.7 mV/g were measured for the in-plane (X/Y-axis) and out-of-plane (Z-axis) accelerometers, respectively, with measured cross-axis sensitivity of less than 0.5 % for accelerations of up to ±6g.

Single proof-mass tri-axial pendulum accelerometers operating in vacuum

This paper reports on the design, fabrication and characterization of single proof-mass tri-axial capacitive accelerometers coexisting in a low-pressure environment with high-frequency gyroscopes, for the implementation of monolithic 6-degree-of-freedom inertial measurement units. The accelerometers are designed to operate as quasi-static devices (i.e. non-resonant sensors) in mid vacuum levels (1-10 Torr) by increasing squeeze-film air damping through the use of capacitive nano-gaps (<; 300 nm). Reduced die area is achieved utilizing a pendulum-like structure composed of a 450×450×40 μm3 proof-mass anchored to the substrate by a cross-shaped polysilicon spring. The small capacitive gaps, allow for the design of devices with high resonance frequency (~ 15 kHz) that provide large shock and vibration immunity.