Sense Mode Resonant Frequencies Research Articles

Design and Analysis of a High-Gain and Robust Multi-DOF Electro-thermally Actuated MEMS Gyroscope.

This paper presents the design and analysis of a multi degree of freedom (DOF) electro-thermally actuated non-resonant MEMS gyroscope with a 3-DOF drive mode and 1-DOF sense mode system. The 3-DOF drive mode system consists of three masses coupled together using suspension beams. The 1-DOF system consists of a single mass whose motion is decoupled from the drive mode using a decoupling frame. The gyroscope is designed to be operated in the flat region between the first two resonant peaks in drive mode, thus minimizing the effect of environmental and fabrication process variations on device performance. The high gain in the flat operational region is achieved by tuning the suspension beams stiffness. A detailed analytical model, considering the dynamics of both the electro-thermal actuator and multi-mass system, is developed. A parametric optimization is carried out, considering the microfabrication process constraints of the Metal Multi-User MEMS Processes (MetalMUMPs), to achieve high gain. The stiffness of suspension beams is optimized such that the sense mode resonant frequency lies in the flat region between the first two resonant peaks in the drive mode. The results acquired through the developed analytical model are verified with the help of 3D finite element method (FEM)-based simulations. The first three resonant frequencies in the drive mode are designed to be 2.51 kHz, 3.68 kHz, and 5.77 kHz, respectively. The sense mode resonant frequency is designed to be 3.13 kHz. At an actuation voltage of 0.2 V, the dynamically amplified drive mode gain in the sense mass is obtained to be 18.6 µm. With this gain, a capacitive change of and is achieved corresponding to the sense mode amplitude of and at atmospheric air pressure and in a vacuum, respectively.

Control System of an Electromagnetic Vibrating Ring Gyroscope

Presented is a control system that is designed for an electromagnetic vibrating ring gyroscope. Three functions are realized in this control system. First, fixed amplitude of the drive-mode is guaranteed by using a variable gain control (VGC). Test result shows that the stability of the drive-mode amplitude is about 0.4% in the range of-40°C~80°C. Second, suitable drive-frequency is set up. And experimental result indicates that the suitable drive-frequency should be set between the drive-and sense-mode resonance frequencies, which results in a superior sensitivity. Third, regulation module is employed to further improve the performance.

2-DOF vibratory gyroscope fabricated by SU-8 based UV-LIGA process

This paper reports fabrication of 2-DOF vibratory gyroscope using SU-8 based UV-LIGA process. The device structure is designed to be symmetrical in order to match the resonance frequencies of drive and sense mode oscillators and also to minimize their relative temperature dependent drift. The overall arrangement is such that the two vibration modes do not affect each other and therefore, mechanical decoupling is achieved which helps in minimizing bias drift. The design is optimized to be compatible with the UV-LIGA process having 10 μm thick electroformed nickel as structural layer. Photolithography to create 11 μm thick SU-8 molds for electroforming sacrificial copper and structural nickel layer is optimized using multiple exposure technique that ensures near vertical side walls. Since the highly cross-linked SU-8 remaining after development is difficult to remove reliably from high aspect ratio structures without damage or alteration to the electroformed metals, a 2.45 GHz MW plasma etching process is developed with CF4/O2 mixes. The fabricated device is checked for off-plane misalignment between the stationary and movable comb fingers using white light interferometry and it is found to be almost negligible. Also, the prototype device is characterized for amplitude and phase spectral responses using Polytec MSA-500 Micro System Analyzer. The drive and sense mode resonance frequencies are observed at 7.3 and 7.1 kHz respectively against the mode matched designed frequency of 7.5 kHz.

Design, Modelling and Fabrication of a 40-330 Hz Dual-Mass MEMS Gyroscope on Thick-SOI Technology

This work reports the design, modelling, fabrication and preliminary functionality testing of a dual-mass MEMS vibratory gyroscope for application in medical instrumentation, among others. The two-framed gyro has drive and sense mode resonance frequencies of 2500Hz and 2830Hz, with its bandwidth tunable between 40-330Hz. Adopted design and technological features such as the use of double-folded springs, quadrature-error-compensation electrodes and 50μm thick-SOI mechanical layer enable high resolution sensing. The designed sensor characteristics have been validated using FEM simulation and equivalent circuit modelling.

Electrothermally actuated resonant rate gyroscope fabricated using the MetalMUMPs

This paper presents an electrothermally actuated resonant microgyroscope fabricated using commercially available standard MEMS process, MetalMUMPs. A Chevron-shaped thermal actuator has been used to drive the proof mass, whereas parallel plate electrodes have been used for sensing the rotation induced Coriolis force. The proposed model consists of three coupled proof masses that are driven together using a frame. To achieve larger bandwidth and increased sensitivity, the microgyroscope is operated with a slight mismatch in the resonant frequencies of the drive and sense-mode. Modal analysis in IntelliSuite predicted the drive and sense-mode resonant frequency at 5.37 and 5.2kHz, respectively. A brief theoretical description of the resonant microgyroscope and mechanical design considerations of the proposed model are also discussed. Prototype fabrication using MetalMUMPs has also been investigated in this study. Microsystem Analyzer MSA-400 has been used to test the prototype at atmospheric pressure. The resonant frequency of the fabricated device is measured to be 5.98kHz for the sense-mode. A drive displacement of 4.2μm peak-to-peak is achieved by the proof mass when the device is operated at 1.3Vac applied at 2.99kHz consuming a power of 0.36W. The proposed device has a size of 1.8×2.0mm2. The large voltage–stroke ratio and low damping of chevron-shaped thermal actuator compared to traditional comb drive may result in a high quality factor microgyroscope operating at atmospheric pressure.

Micromachined gyroscope concept allowing interchangeable operation in both robust and precision modes

This paper presents a new gyroscope design concept with a multi-degree of freedom (DOF) sense mode enabling interchangeable operation in robust or precision modes. This is accomplished using a complete 2-DOF coupled system which, unlike previous multi-DOF designs based on dynamic vibration absorbers, allows for the specification of the sense mode resonances and coupling between the masses independent of operational frequency. The robust mode corresponds to operation between the 2-DOF sense mode resonant peaks providing a response gain and bandwidth controlled at the design level by frequency spacing; the precision mode, however, relies on mode-matching the drive to one of the sense mode resonant frequencies where larger response gains are achieved through vacuum operation. The complete 2-DOF sense mode provides the gyroscope with distinct advantages over similar devices based on 1-DOF systems: the robust mode introduces a gain advantage versus conventional mismatched operation, while the precision mode gain-bandwidth is larger for the same pressures. Experimental rate characterization of a silicon-on-insulator prototype in air for both robust and precision modes demonstrated scale factors of 0.282 and 0.690 mV/°/s, respectively, while the scale factor improvement due to precision mode operation is projected to increase by 40 dB for operation in 1 mTorr vacuum.

Thermal Actuation Based 3-DoF Non-Resonant Microgyroscope Using MetalMUMPs

High force, large displacement and low voltage consumption are a primary concern for microgyroscopes. The chevron-shaped thermal actuators are unique in terms of high force generation combined with the large displacements at a low operating voltage in comparison with traditional electrostatic actuators. A Nickel based 3-DoF micromachined gyroscope comprising 2-DoF drive mode and 1-DoF sense mode oscillator utilizing the chevron-shaped thermal actuators is presented here. Analytical derivations and finite element simulations are carried out to predict the performance of the proposed device using the thermo-physical properties of electroplated nickel. The device sensitivity is improved by utilizing the dynamical amplification of the oscillation in 2-DoF drive mode using an active-passive mass configuration. A comprehensive theoretical description, dynamics and mechanical design considerations of the proposed gyroscopes model are discussed in detail. Parametric optimization of gyroscope, its prototype modeling and fabrication using MetalMUMPs has also been investigated. Dynamic transient simulation results predicted that the sense mass of the proposed device achieved a drive displacement of 4.1μm when a sinusoidal voltage of 0.5V is applied at 1.77 kHz exhibiting a mechanical sensitivity of 1.7μm /°/s in vacuum. The wide bandwidth frequency response of the 2-DoF drive mode oscillator consists of two resonant peaks and a flat region of 2.11 kHz between the peaks defining the operational frequency region. The sense mode resonant frequency can lie anywhere within this region and therefore the amplitude of the response is insensitive to structural parameter variations, enhancing device robustness against such variations. The proposed device has a size of 2.2 × 2.6 mm2, almost one third in comparison with existing M-DoF vibratory gyroscope with an estimated power consumption of 0.26 Watts. These predicted results illustrate that the chevron-shaped thermal actuator has a large voltage-stroke ratio shifting the paradigm in MEMS gyroscope design from the traditional interdigitated comb drive electrostatic actuator. These actuators have low damping compared to electrostatic comb drive actuators which may result in high quality factor microgyroscopes operating at atmospheric pressure.

Effects of Operational Frequency Scaling in Multi-Degree of Freedom MEMS Gyroscopes

This paper analyzes the design tradeoffs associated with increasing the operational frequency of single-axis microelectromechanical systems (MEMS) gyroscopes with multi-degree of freedom (DOF) sense modes. Previously, a <i xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">z</i> -axis multi-DOF gyroscope (1-DOF drive, 2-DOF sense) was shown to be robust to thermal variations using a prototype with a subkilohertz operational frequency; automotive applications, however, require higher frequencies of operation to suppress the effect of ambient vibrations. To study scaling effects on the multi-DOF concept, design equations were obtained in terms of operational frequency. These revealed a constraint on system parameters that introduces two scaling methods that dictate a tradeoff between gain, die size, and sense capacitance. Second generation multi-DOF gyroscopes were designed and fabricated resulting in 0.7-, 3.1-, and 5.1-kHz devices with smaller sense mode resonant frequency spacings than previously achievable. Experimental rate characterization resulted in scale factors of 14.2, 5.08, and 2.34 mu V/deg /s, respectively, confirming the predicted scaling effects while also demonstrating the feasibility of increased frequency multi-DOF gyroscopes.

A single-crystal silicon symmetrical and decoupled MEMS gyroscope on an insulating substrate

This paper presents a single-crystal silicon symmetrical and decoupled (SYMDEC) gyroscope implemented using the dissolved wafer microelectromechanical systems (MEMS) process on an insulating substrate. The symmetric structure allows matched resonant frequencies for the drive and sense vibration modes for high-rate sensitivity and low temperature-dependent drift, while the decoupled drive and sense modes prevents unstable operation due to mechanical coupling, achieving low bias-drift. The 12-15-/spl mu/m-thick single-crystal silicon structural layer with an aspect ratio of about 10 using DRIE patterning provides a high sense capacitance of 130 fF, while the insulating substrate provides a low parasitic capacitance of only 20 fF. A capacitive interface circuit fabricated in a 0.8-/spl mu/m CMOS process and having a sensitivity of 33 mV/fF is hybrid connected to the gyroscope. Drive and sense mode resonance frequencies of the gyroscope are measured to be 40.65 and 41.25 kHz, respectively, and their measured variations with temperature are +18.28 Hz//spl deg/C and +18.32 Hz//spl deg/C, respectively, in -40/spl deg/C to +85/spl deg/C temperature range. Initial tests show a rate resolution around 0.56 deg/s with slightly mismatched modes, which reveal that the gyroscope can provide a rate resolution of 0.030 deg/s in 50-Hz bandwidth at atmospheric pressure and 0.017 deg/s in 50-Hz bandwidth at vacuum operation with matched modes.

A novel bulk micromachined gyroscope with slots structure working at atmosphere

Abstract Design, fabrication and testing of a novel silicon micromachined gyroscope prototype with slots structure are presented. The device structure which we called “slots gyroscope” consists of a proof mass with slots linked up to substrate by suspend springs and is fabricated by silicon–glass bonding and deep reactive ion etching (DRIE). The gyroscope makes use of electrostatic driving and capacitive sensing. As the proof mass used as the movable electrodes is parallel to the plane of fixed driving and sensing electrodes, there is only slide film damping in the driving and sensing mode. The gyroscope can operate at atmospheric pressure due to almost same high quality factor in the sensing direction and driving direction. The experiment result shows that the drive and sense mode resonant frequencies are 460.4 and 549.6 Hz, respectively, and the quality factor of the drive and sense are 102.5 and 106.5, respectively at atmospheric pressure. The scale factor and non-linearity of the micromachined gyroscope are 20 mV/(° s) and 0.56%, respectively at atmospheric pressure.

A symmetric surface micromachined gyroscope with decoupled oscillation modes

This paper reports a new symmetric gyroscope structure that allows not only matched resonant frequencies for the drive and sense vibration modes for better resolution, but also decoupled drive and sense oscillation modes for preventing unstable operation due to mechanical coupling. The symmetry and decoupling features are achieved at the same time with a new suspension beam design. The gyroscope structure is designed using a standard three-layer polysilicon surface micromachining process (MUMPs) and simulated using the MEMCAD software. Measured results show that the drive and sense mode resonant frequencies are 28,535Hz and 30,306Hz, respectively, which are in agreement with the finite element simulations. The small mismatch can be reduced further by applying different DC bias voltages to the drive and sense electrodes, improving the performance. The performance of the fabricated sensor is limited due to large parasitic capacitance between the proof mass and the substrate, nevertheless, measurements and calculations show that the sensor can sense angular rates as small as 0.37 deg/sec even in atmospheric pressure. A capacitive readout circuit for the sensor was also developed in a 0.8µm CMOS process, and the fabricated circuit detects capacitance changes smaller than 0.1fF with a sensitivity of 45mV/fF.