Microelectromechanical Systems Vibratory Gyroscope Research Articles

An automatic Q-factor matching method for eliminating 77% of the ZRO of a MEMS vibratory gyroscope in rate mode

Mismatching quality factors (Q-factors) is one of the main factors causing zero-rate output (ZRO) in degenerate (DE) Micro-Electro-Mechanical Systems (MEMS) vibratory gyroscopes. To eliminate the ZRO of the DE MEMS gyroscope, this study introduces a method for real-time identification and automatic matching of Q-factors in rate mode. By leveraging the vibration characteristics of the DE MEMS vibratory gyroscope in rate mode, dedicated online test methods are designed to determine the Q-factors for both the drive and sense modes, enabling online identification of the Q-factor mismatching. Furthermore, an automatic Q-factor matching system is designed utilizing the mechanical-thermal dissipation mechanism of the resistive damper. The effectiveness of this proposed method is validated through simulations and experiments conducted on a MEMS disk resonator gyroscope (DRG). The results show a measurement error within 4% for Q-factor identification, and automatic Q-factor matching effectively reduces the ZRO by 77%. Employing this automatic Q-factor matching method successfully reduces the ZRO that is caused by the mismatching of Q-factors in the MEMS DRG from 0.11°/s to 0.025°/s and improves the bias instability (BI) from 0.40°/s to 0.19°/s.

Influence of fabrication tolerances on performance characteristics of a MEMS gyroscope

Fabrication of high aspect ratio microelectromechanical systems (MEMS) like comb drive structures are mostly done by DRIE (Deep Reactive Ion Etching) process. Bosch process is a type of DRIE which involves alternate repetition of plasma etching and side wall passivation to achieve deep vertical structures. A continued plasma etching may lead to tapered wall due to some lateral etching. Although, a straight and smooth wall is expected due to combined alternate processes of etching and passivation, very often the resulting walls are having surface undulations called as scalloping. So, due to slanting, scalloping and combined slanting and scalloping defects the working and performance of a MEMS device get affected. MEMS gyrocope is one such widely comercialized device, which is required to measure angular rotation wth certain accuracy. We take a simple single-axis MEMS vibratory gyroscope to study the effect on these defects on its dynamics performance. The study presented in the paper may be useful for including undesirable effects in designing MEMS vibratory gyroscopes.

An Interface ASIC for MEMS Vibratory Gyroscopes with Nonlinear Driving Control

This paper proposes an interface application-specific-integrated-circuit (ASIC) for micro-electromechanical systems (MEMS) vibratory gyroscopes. A closed self-excited drive loop is employed for automatic amplitude stabilization based on peak detection and proportion-integration (PI) controller. A nonlinear multiplier terminating the drive loop is designed for rapid resonance oscillation and linearity improvement. Capacitance variation induced by mechanical motion is detected by a differential charge amplifier in sense mode. After phase demodulation and low-pass filtering an analog signal indicating the input angular velocity is obtained. Non-idealities are further suppressed by on-chip temperature drift calibration. In order for better compatibility with digital circuitry systems, a low passband incremental zoom sigma-delta (ΣΔ) analog-to-digital converter (ADC) is implemented for digital output. Manufactured in a standard 0.35 μm complementary metal-oxide-semiconductor (CMOS) technology, the whole interface occupies an active area of 3.2 mm2. Experimental results show a bias instability of 2.2 °/h and a nonlinearity of 0.016% over the full-scale range.

An Ultrahigh Vacuum Packaging Process Demonstrating Over 2 Million Q-Factor in MEMS Vibratory Gyroscopes

Micro resonators and vibratory gyroscopes could reach their fundamental thermo-elastic damping (TED) limit in an ultravacuum condition where the viscous damping is eliminated. This article presents a reliable and repeatable high vacuum sealing process as a standalone approach for performance evaluation of dynamic micro devices. We demonstrated a micro-Torr vacuum level in a ceramic leadless chip carrier package and achieved the Q-factor over 2million on a quad mass gyroscope, approaching the TED limit of the device by effectively eliminating the viscous damping. The long-term vacuum stability was characterized over 1 year and demonstrated that the Q-factor does not degrade over time and even continues improving. The long-term ultrahigh vacuum condition is enabled by surface desorption prior to sealing, pumping of residual gases by passive getters, and defect-free solder reflow in the sealing area. The experimental results confirmed the reliability and repeatability of the proposed sealing procedure, which can be adapted for other Micro Electro-Mechanical Systems (MEMS) with ultrahigh vacuum requirements.

System Modeling of a MEMS Vibratory Gyroscope and Integration to Circuit Simulation.

Recently, consumer applications have dramatically created the demand for low-cost and compact gyroscopes. Therefore, on the basis of microelectromechanical systems (MEMS) technology, many gyroscopes have been developed and successfully commercialized. A MEMS gyroscope consists of a MEMS device and an electrical circuit for self-oscillation and angular-rate detection. Since the MEMS device and circuit are interactively related, the entire system should be analyzed together to design or test the gyroscope. In this study, a MEMS vibratory gyroscope is analyzed based on the system dynamic modeling; thus, it can be mathematically expressed and integrated into a circuit simulator. A behavioral simulation of the entire system was conducted to prove the self-oscillation and angular-rate detection and to determine the circuit parameters to be optimized. From the simulation, the operating characteristic according to the vacuum pressure and scale factor was obtained, which indicated similar trends compared with those of the experimental results. The simulation method presented in this paper can be generalized to a wide range of MEMS devices.

Mechanical and Electrical Noise in Sense Channel of MEMS Vibratory Gyroscopes.

This paper presents a theoretical analysis of mechanical and electrical noise in the sense channel of micro-electromechanical systems (MEMS) vibratory gyroscopes. Closed-form expressions for the power spectral density (PSD) of the noise equivalent rate (NER) of gyroscopes in the open-loop and the force-rebalance operations are derived by using an averaged PSD model and an equivalent transfer function. The obtained expressions are verified through numerical simulations, demonstrating close agreements between the analytic and the numerical models. Based on the derived expressions for the PSD of the NER, the impacts of the modal frequency split, quality factor, and the gain of the feedback forcer, as well as the gain of the signal conditioning circuit, on the gyroscope noise characteristics are theoretically analyzed. In addition, the angle random walk (ARW) and the standard deviation of the NER are also discussed through the PSD models. Finally, the effects of the loop closing, the mode matching, and the gain of the feedback forcer on the PSD of the NER were verified via a MEMS vibratory gyroscope with a tunable modal frequency split.

Analysis and Design of a 3rd Order Velocity-Controlled Closed-Loop for MEMS Vibratory Gyroscopes

The time-average method currently available is limited to analyzing the specific performance of the automatic gain control-proportional and integral (AGC-PI) based velocity-controlled closed-loop in a micro-electro-mechanical systems (MEMS) vibratory gyroscope, since it is hard to solve nonlinear functions in the time domain when the control loop reaches to 3rd order. In this paper, we propose a linearization design approach to overcome this limitation by establishing a 3rd order linear model of the control loop and transferring the analysis to the frequency domain. Order reduction is applied on the built linear model's transfer function by constructing a zero-pole doublet, and therefore mathematical expression of each control loop's performance specification is obtained. Then an optimization methodology is summarized, which reveals that a robust, stable and swift control loop can be achieved by carefully selecting the system parameters following a priority order. Closed-loop drive circuits are designed and implemented using 0.35 μm complementary metal oxide semiconductor (CMOS) process, and experiments carried out on a gyroscope prototype verify the optimization methodology that an optimized stability of the control loop can be achieved by constructing the zero-pole doublet, and disturbance rejection capability (D.R.C) of the control loop can be improved by increasing the integral term.

Digital Controller Design for Sense Mode of Micro-Machined Gyroscope

This paper presents one kind of digital closed loop control system of MEMS (Micro Electro-Mechanical Systems) vibratory gyroscope, particularly concentrating on the sense mode of MEMS gyroscope. The controller consists of a sine wave source realized by CORDIC algorithm, multiplication demodulators, some low-pass filters and force feedback rebalance module. Compared with the open loop sense system of gyroscope, the closed loop sense system has larger measurement range and wider bandwidth. Besides, the sine wave source realized with CORDIC algorithm can save hardware resources. The digital system is demonstrated on a PCB with a FPGA on it. The test results show that the measurement range of the closed loop system can be increased to 3 times by the open loop, and the bandwidth can be extended to 262Hz from 27Hz of the open loop system.

Fabrication and characterization of an SOI MEMS gyroscope

This paper presents an SOI (silicon on insulator) MEMS (micro-electro-mechanical systems) vibratory gyroscope that was fabricated using bulk micromachining processes. In the gyroscope architecture, a frame structure that nests the proof mass is used to decouple the drive motion and sense motion. This approach ensures that the drive motion is well aligned with the designed drive axis, and minimizes the actual drive motion component along the sense detection axis. The thickness of the structural layer of the device is 100 μm, which induces a high elastic stiffness in the thickness direction, so it can suppress the high-order out-of-plane resonant modes to reduce deviation. In addition, the dynamics of the gyroscope indicate that higher driving mass brings about higher sensing displacements. The thick structural layer can improve the output of the device by offering a sufficient mass weight and large sensing capacitance. The preliminary test results of the vacuum packaged device under atmospheric pressure will be provided. The scale factor is 1.316 × 10−4 V/(deg/s), the scale factor nonlinearity and asymmetry are 1.87% and 0.36%, the zero-rate offset is 7.74 × 10−4 V, and the zero-rate stability is 404 deg/h, respectively.

Mechanical Vibration Characteristics for the Driving Part in Array of Microelectromechanical Systems Vibratory Gyroscopes

Mechanical Vibration Characteristics for the Driving Part in Array of Microelectromechanical Systems Vibratory Gyroscopes

Performance of MEMS Vibratory Gyroscope under Harsh Environments

Microelectromechanical systems (MEMS) gyroscope is a sensor that measures the rate of change in an angular position of an object. MEMS vibratory gyroscopes are increasingly used in applications ranging from consumer electronics to aerospace and are now one of the most common MEMS products after accelerometers.With advances in fabrication technologies, the low-cost MEMS gyroscope has opened up a wide variety of applications with environmental conditions ranging from medium to harsh. Despite their widespread use, the performance of MEMS gyroscopes in harsh environments is still under question. While some studies have been conducted to understand the effects of high mechanical shock, high frequency vibration and high frequency acoustic environment on the MEMS gyroscopes,the effects of sustained exposure to temperature combined withother harsh environment stresseshave not been well researched.Thus, it is necessary to quantify MEMS vibratory gyroscope performance under such conditions.This research reviews current harsh environment studies anddemonstrates the effects of an elevated temperature and sustained exposure to temperature combined humidity on the MEMS vibratory gyroscope. In order to quantify such effects, several tests have been performed. A short-term temperature effect on MEMS gyroscope was examined through temperature characterization test forfive thermal cycles at wider temperature ranges. A long-term temperature effect on the MEMS gyroscope was inspected through 500 thermal cycles; while, combined effects of temperature and humidity was studied through temperature humidity bias(THB) test and highly accelerated stress test (HAST).

Low-Dissipation Silicon Tuning Fork Gyroscopes for Rate and Whole Angle Measurements

We report a new family of ultra high- Q silicon microelectromechanical systems (MEMS) tuning fork gyroscopes demonstrating angular rate and, for the first time, rate integrating (whole angle) operation. The novel mechanical architecture maximizes the Q-factor and minimizes frequency and damping mismatches. We demonstrated the vacuum packaged SOI dual and quadruple mass gyroscopes with Q-factors of 0.64 and 0.86 million at 2 kHz operational frequency, respectively. Due to the stiffness and damping symmetry, the quadruple mass gyroscope was instrumented to measure the angle of rotation directly, eliminating the bandwidth and dynamic range limitations of conventional MEMS vibratory rate gyroscopes. The technology may enable silicon micromachined devices for inertial guidance applications previously limited to precision-machined quartz hemispherical resonator gyroscopes.

Robust adaptive vibration tracking control for a micro-electro-mechanical systems vibratory gyroscope with bound estimation

This study presents an adaptive sliding mode controller for a micro-electro-mechanical systems (MEMS) z-axis vibratory gyroscope. The adaptive model reference state tracking control with sliding mode controller is developed to estimate the angular velocity, the damping and stiffness coefficients of MEMS vibratory gyroscope in real time. An adaptive controller that can estimate the unknown upper bound of the parameter uncertainties and external disturbance is derived and the stability of the closed-loop system is established. The adaptive sliding mode controller is designed so that the trajectory of the driving axes can track the state of the reference vibration model. The effectiveness of the proposed scheme is demonstrated through numerical simulations on an MEMS vibratory gyroscope.

On the Mode-Matched Control of MEMS Vibratory Gyroscope via Phase-Domain Analysis and Design

This paper investigates a novel method for the mode-matched control of a microelectromechanical systems (MEMS) vibratory gyroscope through a phase-domain analysis. Compared with the previous works, the proposed method presents a simple and robust automatic mode tuning scheme for sensitivity enhancement. In designing the mode-matched control loop, the resonant characteristics of the driving axis are used as the reference mode. Then, the phase difference between sense and drive modes at the resonant frequency of drive mode is used to generate a control signal for phase error regulation. For the control loop design, a linear phase-locked loop is adapted. Through the simulation using practical MEMS gyroscope parameters, the mode-matching performance and robustness of the designed control loop is demonstrated. It is also shown that coupling effect yields no degradation of output sensitivity. Finally, the experimental results obtained by implementing the electronics of mode-matched control verify the feasibility of the proposed method.

Robust adaptive control for a MEMS vibratory gyroscope

This paper presents an adaptive sliding mode controller for a microelectromechanical systems (MEMS) vibratory z-axis gyroscope. The proposed adaptive sliding mode controller can real-time estimate the angular velocity and the damping and stiffness coefficients. The stability of the closed-loop system can be guaranteed with the proposed adaptive sliding mode control strategy. The numerical simulation for MEMS gyroscope is investigated to show the effectiveness of the proposed control scheme. It is shown that the proposed adaptive sliding mode control scheme offers several advantages such as real-time estimation of gyroscope parameters and large robustness to parameter variations and external disturbance.