Jianbing Xie

A Three Degree-of-Freedom Weakly Coupled Resonator Sensor With Enhanced Stiffness Sensitivity

This paper reports a three degree-of-freedom (3DoF) microelectromechanical systems (MEMS) resonant sensing device consisting of three weakly coupled resonators with enhanced sensitivity to stiffness change. If one resonator of the system is perturbed by an external stimulus, mode localization occurs, which can be detected by a change of modal amplitude ratio. The perturbation can be, for example, a change in stiffness of one resonator. A detailed theoretical investigation revealed that a mode aliasing effect, along with the thermal noise floor of the sensor and the associated electrical system ultimately limit the dynamic range of the sensor. The nonlinearity of the 3DoF sensor was also analyzed theoretically. The 3DoF resonator device was fabricated using a silicon on insulator process. Measurement results from a prototype device agreed well with the predictions of the analytical model. A significant, namely 49 times, improvement in sensitivity to stiffness change was evident from the fabricated 3DoF resonator sensor compared with the existing state-of-the-art 2DoF resonator sensors, while the typical nonlinearity was smaller than ±2% for a wide span of stiffness change. In addition, measurements indicate that a dynamic range of at least 39.1 dB is achievable, which could be further extended by decreasing the noise of the device and the interface electronics.

Integrated Behavior Simulation and Verification for a MEMS Vibratory Gyroscope Using Parametric Model Order Reduction

In this paper, a parameterized reduced model of a vibratory microelectromechanical systems (MEMS) gyroscope is established using a parametric model order reduction algorithm. In the reduction process, not only the input angular velocity, material density, Youngs modulus, and Rayleigh damping coefficient but also the coefficient of thermal expansion and the change in temperature were all preserved. Based on this model, the integrated behavior simulation of the MEMS gyroscope, including many environmental factors in engineering situations, was performed in an accurate and fast way. Compared with the finite-element method, the relative error of the reduced-order model was less than 4.2%, while the computational efficiency was improved about five times. The cosimulation with a complete interface circuit was successfully performed in a very fast way, which provides a convenient platform for designers to evaluate the performance of sensors. The experimental verification proves that the reduced model can provide a reliable simulation result, although some errors exist.

A sensor for stiffness change sensing based on three weakly coupled resonators with enhanced sensitivity

This paper reports on a novel MEMS resonant sensing device consisting of three weakly coupled resonators that can achieve an order of magnitude improvement in sensitivity to stiffness change, compared to current state-of-the-art resonator sensors with similar size and resonant frequency. In a 3 degree-of-freedom (DoF) system, if an external stimulus causes change in the spring stiffness of one resonator, mode localization occurs, leading to a drastic change of mode shape, which can be detected by measuring the modal amplitude ratio change. A 49 times improvement in sensitivity compared to a previously reported 2DoF resonator sensor, and 4 orders of magnitude enhancement compared to a 1DoF resonator sensor has been achieved.

Design and Implementation of an Optimized Double Closed-Loop Control System for MEMS Vibratory Gyroscope

This paper describes the development and experimental evaluation of a microelectromechanical system vibratory gyroscope using an optimized double closed-loop control strategy. An automatic gain control self-oscillation interface is used to resonate the gyroscope in the drive mode; the sense mode is controlled by a sixth-order continuous-time and force-feedback band-pass sigma-delta modulator. The parameters of both control loops are optimized by a genetic algorithm (GA). System level simulations show that the settling time of the drive mode self-oscillation is 125 ms, the root mean square displacement of the proof mass is in the sense mode, and the signal-to-noise ratio is 90 dB in a bandwidth of 64 Hz with a 200 °/s angular rate input signal. The system is implemented using symmetrical and fully decoupled silicon on insulator gyroscope operating at atmospheric with the circuit implemented on printed circuit board. The measured power spectral density of the output bitstream shows an obvious band-pass noise shaping and a deep notch at the gyroscope resonant frequency. The measured noise floor is approximately -120 dBV/Hz1/2. In the drive mode, the relative drift of the resonant frequency and amplitude is 3.2 and 10.7 ppm for 1 h measurements, respectively. The settling time, scale factor, zero bias stability, and bandwidth of the gyroscope controlled by the optimized control system are 200 ms, 22.5 mV/°/s, 34 °/h, and 110 Hz, respectively. This is compared with a non-optimized system for which the corresponding values are 300 ms, 17.3 mV/°/s, 58 °/h, and 98 Hz; hence, by GA optimization a considerable performance improvement is achieved.

A dicing-free SOI process for MEMS devices based on the lag effect

This paper presents a dicing-free process for silicon-on-insulator (SOI) microelectromechanical systems (MEMS). In the process, the lag effect in deep reactive ion etching (DRIE) is used to form the breaking trenches. In the backside DRIE, the wide backside cavities are etched down to the buried oxide layer. The narrow breaking trenches, in contrast, are not etched to the buried oxide layer. Therefore, the narrow trench can be used to break the wafer after the entire process; in addition, the handle layer can still act as a bracing structure before ?breaking?. Finally, the device layer is patterned, and a DRIE step is used to form the MEMS devices. In this way, the dicing step can be omitted to prevent further damages from high pressure water jets and silicon dust. Meanwhile, the process can also prevent notching simply because the insulating layer is removed before device etching. To demonstrate the feasibility of the proposed fabrication process, a micromachined gyroscope is designed and fabricated.

Design, Fabrication, and Testing of a Bulk Micromachined Inertial Measurement Unit

A bulk micromachined inertial measurement unit (MIMU) is presented in this paper. Three single-axis accelerometers and three single-axis gyroscopes were simultaneously fabricated on a silicon wafer using a bulk micromachining process; the wafer is smaller than one square centimeter. In particular, a global area optimization method based on the relationship between the sensitivity and layout area was proposed to determine the layout configuration of the six sensors. The scale factors of the X/Y-axis accelerometer and Z-axis accelerometer are about 213.3 mV/g and 226.9 mV/g, respectively. The scale factors of the X/Y-axis gyroscope and Z-axis gyroscope are about 2.2 mV/°/s and 10.8 mV/°/s, respectively. The bias stability of the X/Y-axis gyroscope and the Z-axis gyroscope are about 2135 deg/h and 80 deg/h, respectively. Finally, the resolutions of X/Y-axis accelerometers, Z-axis accelerometers, X/Y-axis gyroscopes, and Z-axis gyroscopes are 0.0012 g/Hz, 0.0011 g/Hz, 0.314 ° /s/Hz, and 0.008 ° /s/Hz, respectively.

Design and Verification of a Structure for Isolating Packaging Stress in SOI MEMS Devices

This paper proposes and verifies a structure for the isolation of packaging stress in silicon-on-insulator-based microelectromechanical systems devices. The packaging-stress isolation structure resides on the handle layer and consists of a circular disk, eight elastic beams, and a support frame. The disk is located in the center of the die and occupies less than 5% of the handle-layer area; this can reduce packaging stress and avoid uneven stress distribution. The elastic beams are L-shaped and symmetrically distributed to decouple the deformation from the disk to the frame and suppress the stress evenly. The in-plane and out-of-plane deformation induced by packaging stress was modeled and experimentally measured. The comparison results demonstrate that the packaging stress was successfully isolated.

Design and fabrication of a rotary comb-actuated microgripper with high driving efficiency

This paper reports a novel microgripper with high driving efficiency. The proposed microgripper utilizes the rotational motion of rotary comb actuators to grip the target object directly. Therefore, the inefficient conversion system which is commonly used in recent works is avoided. The gripper is fabricated using a SOI process with a 60μm structural layer. Test results show that this gripper achieves a displacement of 94μm with a driving voltage of 100V and its driving efficiency is increased at least 12 times compared to the existing microgrippers.

Design and Simulation of a MEMS Control Moment Gyroscope for the Sub-Kilogram Spacecraft

A novel design of a microelectromechanical systems (MEMS) control moment gyroscope (MCMG) was proposed in this paper in order to generate a torque output with a magnitude of 10−6 N·m. The MCMG consists of two orthogonal angular vibration systems, i.e., the rotor and gimbal; the coupling between which is based on the Coriolis effect and will cause a torque output in the direction perpendicular to the two vibrations. The angular rotor vibration was excited by the in-plane electrostatic rotary comb actuators, while the angular gimbal vibration was driven by an out-of-plane electrostatic parallel plate actuator. A possible process flow to fabricate the structure was proposed and discussed step by step. Furthermore, an array configuration using four MCMGs as an effective element, in which the torque was generated with a phase difference of 90 degrees between every two MCMGs, was proposed to smooth the inherent fluctuation of the torque output for a vibrational MCMG. The parasitic torque was cancelled by two opposite MCMGs with a phase difference of 180 degrees. The designed MCMG was about 1.1 cm × 1.1 cm × 0.04 cm in size and 0.1 g in weight. The simulation results showed that the maximum torque output of a MCMG, the resonant frequency of which was approximately 1,000 Hz, was about 2.5 × 10−8 N·m. The element with four MCMGs could generate a torque of 5 × 10−8 N·m. The torque output could reach a magnitude of 10−6 N·m when the frequency was improved from 1,000 Hz to 10,000 Hz. Using arrays of 4 × 4 effective elements on a 1 kg spacecraft with a standard form factor of 10 cm × 10 cm × 10 cm, a 10 degrees attitude change could be achieved in 26.96 s.

Comparative study of different output metrics for a three weakly coupled resonator sensor

This paper, for the first time, investigates the characteristics of different output metrics for a three degree-of-freedom (DoF) coupled resonator sensor. The main aspects examined are sensitivity and linear range. It is shown from theoretical estimations, equivalent RLC circuit model simulations and electrical measurements that using the vibration amplitude ratio as an output signal provides improved sensitivity and linearity range, compared to other methods such as shift in eigenstate, mode frequency or amplitude difference.