Zhongyang Guo

A Lateral-Axis Microelectromechanical Tuning-Fork Gyroscope With Decoupled Comb Drive Operating at Atmospheric Pressure

In this paper, a silicon bulk micromachined lateral-axis tuning-fork gyroscope (TFG) with a decoupled comb drive and torsional sensing comb capacitors is presented. The novel driving comb capacitors are used to suppress the parasitic out-of-plane electrostatic force and, hence, can decouple the mechanical crosstalk from the sensing mode to the driving mode in a simple manner. The torsional sensing combs are designed to differentially sense the out-of-plane rotational moment and are arranged centroidally to be immune to fabrication imperfections for good linearity and electrostatic force balancing. The torsional sensing combs adopted in the TFG help to lower the air damping of the sensing mode while the driving mode of the gyroscope is dominated by slide-film air damping; hence, it can work even at atmospheric pressure. The process for this lateral-axis gyroscope can also be used to fabricate z-axis gyroscopes; therefore, low-cost miniature monolithic inertial measurement units can be realized without vacuum packaging. The TFG is tested at atmospheric pressure with a sensitivity of 17.8 mV/°/s and a nonlinearity of 0.6% in a full-scale range of 1000°/s. The bias stability is measured to be 0.05°/s (1 ¿) in 30 min with an equivalent noise angular rate of 0.02°/s/Hz1/2.

Force Rebalance Controller Synthesis for a Micromachined Vibratory Gyroscope Based on Sensitivity Margin Specifications

This paper presents a design method of force rebalance control for the sense mode of a micromachined vibratory gyroscope with multiobjective. The control strategy is mainly based on constraining sensitivity margin specifications via numerical optimization approach, which embeds the sense mode in a closed-loop system to possess more robust performance. This paper also provides a quantitative methodology of configuring the system parameters to realize the functional electrostatic force feedback control for the microgyroscope in the case of nonideal coupling and external angular disturbance. Theoretical results predicted by the control loop are shown to be in close agreement with the experimental results using a practical microgyroscope, which indicated a satisfactory performance of the proposed control algorithm. The maximums of the sensitivity function and complementary sensitivity function are measured to be 4.5 and 1 dB, resulting in GM ≥ 7.84 dB and PM ≥ 35°. The gyroscope achieves a scale factor of 7.1 mV/deg/s with nonlinearity of 0.2% which is improved by one order of magnitude compared with that of the open loop. The bandwidth is extended to about 98 Hz from 30 Hz in the open loop. The quadrature error and temperature stability of the scale factor are reduced from - 10.33 to -59.22 dB and from 4858 to 646 ppm/°C with the force rebalance control, respectively.

A lateral-axis micromachined tuning fork gyroscope with torsional Z-sensing and electrostatic force-balanced driving

A single-crystal silicon-based lateral-axis tuning-fork gyroscope (TFG) with electrostatic force-balanced (EFB) driving and torsional z-sensing is presented. The EFB comb drive used in this TFG can efficiently suppress the mechanical coupling in a simple manner. The TFG structure is also optimized to further reduce the coupling. Moreover, the Coriolis acceleration-induced out-of-plane rotation of the sensing mode is detected by using bending springs and differential comb fingers. This z-sensing design has relatively high Q, so this gyroscope can work at atmospheric pressure. This TFG design has been fabricated and tested. Measured in air, the device demonstrates a sensitivity of 2.9 mV/°/s, a full range of 800° s−1 with a 0.9% nonlinearity and the noise floor of 0.035°/s/Hz1/2. This TFG design also has very low coupling, where the measured drive-to-sense coupling and sense-to-drive coupling are −45 dB and −51 dB, respectively.

Virtual Rate-Table Method for Characterization of Microgyroscopes

In this paper, we demonstrate a testing method for characterization of microgyroscopes using a virtual rate-table, which uses a series of voltage signals to emulate the Coriolis force induced by the angular rate inputs to obtain the frequency response of the gyroscope. The proposed approach holds the following advantages: 1) it provides a convenient and efficient way to evaluate the scale factor and bandwidth of the gyroscope operating in either open-loop mode or closed-loop mode, the laborious debugging by frequently utilizing the real rate-table can be avoided; 2) it can easily identify the dynamic response to external angular rate, which is the control plant during the rebalance control design for the sense mode in a large frequency range, avoiding the performance limit of the ordinary rate-table; and 3) it can be used in a self-test for the microgyroscope system for the error calibration and malfunction checking. The method was applied to a decoupled z -axis gyroscope. The test results show that the measured scale factor and bandwidth are 30.2 mV/(deg/s) and 8.0 Hz by the virtual rate-table method, which are in close agreement with the conventional rate-table method, i.e., 31.0 mV/(deg/s) and 7.4 Hz. The static calibration with the virtual rate-table was also evaluated. The scale factors measured with the conventional rate-table method and the virtual rate-table method are 31.0 mV/(deg/s) and 30.1 mV/(deg/s) with R2 nonlinearity of 0.03% and 0.02%, respectively.

An Electrically Decoupled Lateral-Axis Tuning Fork Gyroscope Operating at Atmospheric Pressure

In this paper, a bulk micromachined lateral axis TFG (tuning fork gyroscope) with torsional sensing comb capacitors is presented. Both driving and sensing modes of the gyroscope are dominated by slide film air damping, then it can work even at atmosphere. Novel driving comb capacitors are used to electrically decouple the mechanical coupling from sensing mode to driving mode. The process for this gyroscope is also compatible with z-axis gyroscope, which makes it potentially to realize low coast monolithic MIMU (miniature inertial measurement unit) without vacuum packaging. The TFG was fabricated and tested at atmosphere. The sensitivity is 17.8mV/°/s while the nonlinearity is 0.6%. The bias stability is 0.05°/s (1¿) and the noise floor is 0.02°/s/Hz1/2

Decoupled Comb Capacitors for Microelectromechanical Tuning-Fork Gyroscopes

This letter presents a novel comb capacitor which can decouple the mechanical crosstalk between the sensing and driving modes of gyroscopes. The capacitance and electrostatic force of the comb capacitor are simulated and analyzed to verify the decoupling principle. A lateral-axis tuning-fork gyroscope is used successfully to demonstrate the decoupling capability of the comb capacitor, resulting in a nonlinearity of 0.6% with full scale of 1000 °/s and a bias stability of 0.05 °/s (1¿) for 30 min.

A Latching Acceleration Switch with Multi-Contacts Independent to the Proof-Mass

An acceleration latching switch with independent multi-contacts is presented in this paper. All the contacts and their beams are independent to the proof-mass so as to prevent the contacts from the impact resulting from the rebound or vibration of the proof mass once the switch is latched. Moreover, multiple contacts are used in order to get high reliable contact, to lower the contact resistance and to increase the maximum allowable current. The switch was fabricated by low-cost process and tested. The latching shock is 4500G and the response time is less than 0.1ms. The contact resistance is no more than 5 ohms while the isolation resistance is more than 200M ohms and the maximum allowable current is up to 100mA.

Wafer-level vacuum packaging with lateral interconnections and vertical feedthroughs for microelectromechanical system gyroscopes

A wafer-level vacuum packaging based on anodic bonded glass-silicon-glass triple stack with both lateral interconnections and vertical feedthroughs is presented. A z -axis gyroscope is packaged and tested to verify the packaging process. The packaged gyroscope achieved a Q factor of 26000, increased by a factor of 30 when compared to the same gyroscope without vacuum packaging. The pressure in the packaged cavity is ∼100 Pa, and the stability of the Q factor in three months is ∼3%. Experiment results indicate that the proposed wafer-level vacuum packaging is feasible and suitable for high-performance wafer-level packaged gyroscopes.

Electrostatic isolation structure for linearity improvement of a lateral-axis tuning fork gyroscope

The electrostatic negative-stiffness behavior of vertical structures under out-of-plane motion decreases the resonant frequency and deteriorates the linearity of a lateral-axis tuning-fork gyroscope (TFG). An electrostatically isolated silicon island is proposed to suppress this behavior. The negative-stiffness behavior is observed and the effectiveness of the electrostatic isolation is experimentally verified. The nonlinearity of the TFG is reduced to 0.34% with a full range of 1,000°/s. This is a 5× improvement.

A monolithic inertial measurement unit fabricated with improved DRIE post-CMOS process

This paper reports a monolithic CMOS-MEMS inertial measurement unit (IMU), which is composed of a 3-axis accelerometer, a Z-axis and a lateral-axis gyroscope. The IMU is integrated with interface circuits on a 5×5mm2 foundry CMOS chip and fabricated with an improved DRIE post-CMOS bulk micromachining process. The new process incorporates a metal deposition to provide a thermal path for isolated structures during DRIE etching. The X/Y-axis accelerometer achieves a sensitivity of 191mV/g with a noise floor of 35µg/√Hz, and those parameters of the Z-axis are 124mV/g and 56µg/√Hz, respectively. The Z-axis gyroscope has a sensitivity of 0.3mV/°/s and a noise floor of 0.2°/s/√Hz. The characterization of X/Y-axis gyroscope is ongoing.