Mohammad Faisal Zaman

A Mode-Matched Silicon-Yaw Tuning-Fork Gyroscope With Subdegree-Per-Hour Allan Deviation Bias Instability

In this paper, we report on the design, fabrication, and characterization of an in-plane mode-matched tuning-fork gyroscope (M2-TFG). The M2-TFG uses two high-quality-factor (Q) resonant flexural modes of a single crystalline silicon mi- crostructure to detect angular rate about the normal axis. Operating the device under mode-matched condition, i.e., zero-hertz frequency split between drive and sense modes, enables a Q -factor mechanical amplification in the rate sensitivity and also improves the overall noise floor and bias stability of the device. The M2 -TFG is fabricated on a silicon-on-insulator substrate using a combination of device and handle-layer silicon etching that precludes the need for any release openings on the proof-mass, thereby maximizing the mass per unit area. Experimental data indicate subdegree-per-hour Brownian noise floor with a measured Allan deviation bias instability of 0.15deg /hr for a 60-mum-thick 1.5 mm X 1.7 mm footprint M2-TFG prototype. The gyroscope exhibits an open-loop rate sensitivity of approximately 83 mV/deg/s in vacuum. [2007-0100].

A 104-dB Dynamic Range Transimpedance-Based CMOS ASIC for Tuning Fork Microgyroscopes

In this paper, the design, implementation and characterization of a continuous time transimpedance-based ASIC for the actuation and sensing of a high-Q MEMS tuning fork gyroscope (TFG) is presented. A T-network transimpedance amplifier (TIA) is used as the front-end for low-noise, sub-atto-Farad capacitive detection. The T-network TIA provides on-chip transimpedance gains of up to 25 MOmega, has a measured capacitive resolution of 0.02 aF/radicHz at 15 kHz, a wide dynamic range of 104 dB in a bandwidth of 10 Hz and consumes 400 muW of power. The CMOS interface ASIC uses this TIA as the front-end to sustain electromechanical oscillations in a MEMS TFG with motional impedance greater than 10 MOmega. The TFG interfaced with the ASIC yields a two-chip angular rate sensor with measured rate noise floor of 2.7deg/hr/radicHz, bias instability of 1deg/hr and rate sensitivity of 2 mV/deg/s. The IC is fabricated in a 0.6-mum standard CMOS process with an area of 2.25 mm2 and consumes 15 mW.

High Performance Matched-Mode Tuning Fork Gyroscope

This paper presents the perfect matched-mode operation of a type I non-degenerate z-axis tuning-fork gyroscope (i.e., 0 Hz frequency split between high-Q drive and sense modes). The matched-mode tuning fork gyroscope (M2-TFG) is fabricated on 50-µ m thick SOI substrate and displays an overall rate sensitivity of 24.2 mV/º/s. Allan Variance analysis of the mode-matched device demonstrates an angle random walk (ARW) of 0.045 º/√ hr and a measured bias instability of 0.96 º/hr. Temperature characterization of the M2-TFG verifies that mode matching is maintained over a temperature range of 20-100 ° C.

A Sub-0.2

This paper describes a system architecture and CMOS implementation that leverages the inherently high mechanical quality factor (Q) of a MEMS gyroscope to improve performance. The proposed time domain scheme utilizes the often-ignored residual quadrature error in a gyroscope to achieve, and maintain, perfect mode-matching (i.e., ~ 0 Hz split between the high-Q drive and sense mode frequencies), as well as electronically control the sensor bandwidth. A CMOS IC and control algorithm have been interfaced with a 60 mum thick silicon mode-matched tuning fork gyroscope (M2-mathchar TFG) to implement an angular rate sensing microsystem with a bias drift of 0.16deg/hr. The proposed technique allows microsystem reconfigurability-the sensor can be operated in a conventional low-pass mode for larger bandwidth, or in matched mode for low-noise. The maximum achieved sensor Q is 36,000 and the bandwidth of the microsensor can be varied between 1 to 10 Hz by electronic control of the mechanical frequencies. The maximum scale factor of the gyroscope is 88 mV/deg/s . The 3 V IC is fabricated in a standard 0.6 mum CMOS process and consumes 6 mW of power with a die area of 2.25 mm2.

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This paper presents an architecture that utilizes the often ignored residual quadrature error in a gyroscope to achieve and maintain perfect mode-matching, i.e., ~ 0 Hz split between the drive and sense mode frequencies, as well as electronically control the sensor bandwidth. A 6 mW, 3 V CMOS ASIC and control algorithm have been interfaced with a 60 mum thick mode-matched tuning fork gyroscope (M2-TFG) to implement an angular rate sensor with bias drift as low as 0.15deg/radichr and angle random walk (ARW) of 0.003deg/radichr - the lowest recorded to date for a silicon MEMS gyro. The maximum scale factor of the gyroscope is 88 m V/deg/s and the microsystem bandwidth can be configured between 1 to 10 Hz.

hr Bias Drift Micromechanical Silicon Gyroscope With Automatic CMOS Mode-Matching

This paper presents a generic vacuum packaging technology for environment-resistant MEMS devices. This packaging approach simultaneously provides low-power oven-controlled thermal environment and vibration isolation using an isolation platform. The oven-controlled structure is thermally isolated from the environment by crab-leg suspensions made out of a 100 ¿m-thick glass wafer, an anti-radiation shield, and vacuum encapsulation. Performance is evaluated by packaging Pirani gauges and mode-matched tuning fork gyroscopes (M2-TFGs). The package has maintained vacuum pressure of ~6 mTorr for ~1 year. A packaged M2-TFG shows a high-Q mode-matched operation (Q~65,000) at a constant temperature of -5 °C. Allan variance analysis displays an estimated angle random walk (ARW) of 0.012 °/¿hr and a bias instability value of 0.55 °/hr at a constant -5 °C. Drive frequency stability of 0.22 ppm/°C is obtained using a compensated oven-control approach. Low power consumption of 33 mW for oven-control at 80 °C is demonstrated when the environment temperature is -30 °C.

A 0.1°/HR bias drift electronically matched tuning fork microgyroscope

This paper introduces the resonating star gyroscope (RSG), a new vibratory shell-type structure for rate sensing. The structure formed as a merged superposition of two square shells, yields in-plane degenerate flexural modes that are used to sense z-axis rotation. A high aspect ratio polysilicon implementation utilizing the primary degenerate flexural modes of the gyroscope exhibits an open-loop rate sensitivity of 1.6mV//spl deg//s. The Brownian noise floor of the sensor with a quality factor (Q) of 1500 and drive amplitude of 100nm is 0.03/spl deg//s//spl radic/Hz. The RSG may also function at higher-order flexural modes. A single crystal silicon design explores such an operation. Preliminary characterization results yield matched-mode operation and very high-Q higher-order degenerate flexural modes (Q/spl sim/100k).

A Low-Power Oven-Controlled Vacuum Package Technology for High-Performance MEMS

We report on the design, fabrication and characterization of a novel multiple-shell silicon vibratory microgyroscope. The resonating star gyroscope (RSG) is formed as a merged superposition of two square shells, yielding in-plane flexural modes that are utilized to sense rotation along the normal axis. The first prototypes of the single-shell RSG were implemented with 65 mum thick trench-refilled polysilicon structural material using the HARPSS process. These devices exhibited open-loop rate sensitivity of approximately 800 muV/deg/s. Despite high-aspect ratio sensing gaps, the device yielded poor sensitivity caused by low resonant-mode quality factors. To alleviate the Q TED losses caused by the inevitable formation of voids in trench-refilled structural material, the RSG was implemented in (111) single crystalline silicon. A 2.5-mm multiple-shell RSG was fabricated in 40 mum-thick SOI device layer using a simple two-mask process. Multiple-shells enable a higher operating frequency and larger resonant mass, essential components for reducing the mechanical noise floor of the sensor. Experimental data of a high-Q (111) multiple-shell prototype indicates sub-5 deg/hr Brownian noise floor, with a measured Allan deviation bias drift of 3.5 deg/hr. The gyroscope exhibits an open-loop rate sensitivity of approximately 16.7 mV/deg/s in vacuum.

The resonating star gyroscope

The design and implementation of a new input switching capacitive microaccelerometer interface circuit with /spl mu/g resolution is presented. The accelerometers were fabricated on 50 /spl mu/m thick silicon-on-insulator (SOI) substrates using a two-mask, dry-release and low temperature process. Fabricated devices were interfaced with a high resolution, low noise and low power switched-capacitor integrated circuit (IC) implemented in a 2.5V 0.25 /spl mu/m N-well CMOS process with the chip size of 0.5/spl times/1.3mm/sup 2/. The measured sensitivity is 0.45V/g and the output noise floor is 4.4/spl mu/g//spl radic/Hz at 150Hz. The total power consumption is 5mW.

The Resonating Star Gyroscope: A Novel Multiple-Shell Silicon Gyroscope With Sub-5 deg/hr Allan Deviation Bias Instability

This paper presents an analytical and experimental study of energy loss mechanisms in a bulk-micromachined tuning fork gyroscope. An exact solution to TED in such devices is obtained and its Debye peak is identified. Compared with its counterpart in a beam resonator of same dimensions, the Debye peak is shifted by a proof mass. For the current design and fabrication process, the measured data from four batches prove that TED is a dominant loss source. Batch-to-batch variation in the combination of support loss and surface loss indicates that surface loss is comparable to support loss.