Dual-Mass MEMS Gyroscope Structure, Design, and Electrostatic Compensation

Dual-mass MEMS gyroscope is one of the most popular inertial sensors. In this chapter, the structure design and electrostatic compensation technology for dual-mass MEMS gyroscope is introduced. Firstly, a classical dual-mass MEMS gyroscope structure is proposed, how it works as a tuning fork (drive anti-phase mode), and the structure dynamical model together with the monitoring system are presented. Secondly, the imperfect elements during the structure manufacture process are analyzed, and the quadrature error coupling stiffness model for dual-mass structure is proposed. After that, the quadrature error correction system based on coupling stiffness electrostatic compensation method is designed and evaluated. Thirdly, the dual-mass structure sensing mode modal is proposed, and the force rebalancing combs stimulation method is utilized to achieve sensing mode transform function precisely. The bandwidth of sensing open loop is calculated and experimentally proved as 0.54 times with the resonant frequency difference between sensing and drive modes. Then, proportional-integral-phase-leading controller is presented in sensing close loop to expand the bandwidth, and the experiment shows that the bandwidth is improved from 13 to 104 Hz. Finally, the results are concluded and summarized

Development of a Prototype Miniature Silicon Microgyroscope

A miniature vacuum-packaged silicon microgyroscope (SMG) with symmetrical and decoupled structure was designed to prevent unintended coupling between drive and sense modes. To ensure high resonant stability and strong disturbance resisting capacity, a self-oscillating closed-loop circuit including an automatic gain control (AGC) loop based on electrostatic force feedback is adopted in drive mode, while, dual-channel decomposition and reconstruction closed loops are applied in sense mode. Moreover, the temperature effect on its zero bias was characterized experimentally and a practical compensation method is given. The testing results demonstrate that the useful signal and quadrature signal will not interact with each other because their phases are decoupled. Under a scale factor condition of 9.6 mV/°/s, in full measurement range of ± 300 deg/s, the zero bias stability reaches 15°/h with worse-case nonlinearity of 400 ppm, and the temperature variation trend of the SMG bias is thus largely eliminated, so that the maximum bias value is reduced to one tenth of the original after compensation from -40 °C to 80 °C

MEMS Gyroscopes for Consumers and Industrial Applications

none2mixedAntonello, Riccardo; Oboe, RobertoAntonello, Riccardo; Oboe, Robert

CMOS systems and circuits for sub-degree per hour MEMS gyroscopes

The objective of our research is to develop system architectures and CMOS circuits that interface with high-Q silicon microgyroscopes to implement navigation-grade angular rate sensors. The MEMS sensor used in this work is an in-plane bulk-micromachined mode-matched tuning fork gyroscope (M² – TFG ), fabricated on silicon-on-insulator substrate. The use of CMOS transimpedance amplifiers (TIA) as front-ends in high-Q MEMS resonant sensors is explored. A T-network TIA is proposed as the front-end for resonant capacitive detection. The T-TIA provides on-chip transimpedance gains of 25MΩ, has a measured capacitive resolution of 0.02aF /√Hz at 15kHz, a dynamic range of 104dB in a bandwidth of 10Hz and consumes 400μW of power. A second contribution is the development of an automated scheme to adaptively bias the mechanical structure, such that the sensor is operated in the mode-matched condition. Mode-matching leverages the inherently high quality factors of the microgyroscope, resulting in significant improvement in the Brownian noise floor, electronic noise, sensitivity and bias drift of the microsensor. We developed a novel architecture that utilizes the often ignored residual quadrature error in a gyroscope to achieve and maintain perfect mode-matching (i.e.0Hz split between the drive and sense mode frequencies), as well as electronically control the sensor bandwidth. A CMOS implementation is developed that allows mode-matching of the drive and sense frequencies of a gyroscope at a fraction of the time taken by current state of-the-art techniques. Further, this mode-matching technique allows for maintaining a controlled separation between the drive and sense resonant frequencies, providing a means of increasing sensor bandwidth and dynamic range. The mode-matching CMOS IC, implemented in a 0.5μm 2P3M process, and control algorithm have been interfaced with a 60μm thick M2−TFG to implement an angular rate sensor with bias drift as low as 0.1°/hr ℃ the lowest recorded to date for a silicon MEMS gyro.Ph.D.Committee Chair: Farrokh Ayazi; Committee Member: Jennifer Michaels; Committee Member: Levent Degertekin; Committee Member: Paul Hasler; Committee Member: W. Marshall Leac

High-accuracy Motion Estimation for MEMS Devices with Capacitive Sensors

With the development of micro-electro-mechanical system (MEMS) technologies, emerging MEMS applications such as in-situ MEMS IMU calibration, medical imaging via endomicroscopy, and feedback control for nano-positioning and laser scanning impose needs for especially accurate measurements of motion using on-chip sensors. Due to their advantages of simple fabrication and integration within system level architectures, capacitive sensors are a primary choice for motion tracking in those applications. However, challenges arise as often the capacitive sensing scheme in those applications is unconventional due to the nature of the application and/or the design and fabrication restrictions imposed, and MEMS sensors are traditionally susceptible to accuracy errors, as from nonlinear sensor behavior, gain and bias drift, feedthrough disturbances, etc. Those challenges prevent traditional sensing and estimation techniques from fulfilling the accuracy requirements of the candidate applications. The goal of this dissertation is to provide a framework for such MEMS devices to achieve high-accuracy motion estimation, and specifically to focus on innovative sensing and estimation techniques that leverage unconventional capacitive sensing schemes to improve estimation accuracy. Several research studies with this specific aim have been conducted, and the methodologies, results and findings are presented in the context of three applications. The general procedure of the study includes proposing and devising the capacitive sensing scheme, deriving a sensor model based on first principles of capacitor configuration and sensing circuit, analyzing the sensor’s characteristics in simulation with tuning of key parameters, conducting experimental investigations by constructing testbeds and identifying actuation and sensing models, formulating estimation schemes is to include identified actuation dynamics and sensor models, and validating the estimation schemes and evaluating their performance against ground truth measurements. The studies show that the proposed techniques are valid and effective, as the estimation schemes adopted either fulfill the requirements imposed or improve the overall estimation performance. Highlighted results presented in this dissertation include a scale factor calibration accuracy of 286 ppm for a MEMS gyroscope (Chapter 3), an improvement of 15.1% of angular displacement estimation accuracy by adopting a threshold sensing technique for a scanning micro-mirror (Chapter 4), and a phase shift prediction error of 0.39 degree for a electrostatic micro-scanner using shared electrodes for actuation and sensing (Chapter 5).PHDMechanical EngineeringUniversity of Michigan, Horace H. Rackham School of Graduate Studieshttps://deepblue.lib.umich.edu/bitstream/2027.42/147568/1/davidsky_1.pd

Inertial MEMS: readout, test and application

This thesis moves towards the investigation of Micro Electro-Mechanical Systems (MEMS) intertial sensors from different perspectives and points of view: readout, test and application. Chapter 1 deals with the state-of-the-art for the interfaces usually employed for 3- axes micromachined gyroscopes. Several architecture based on multiplexing schemes in order to extremely simplify the analog front-end which can be based on a single charge amplifier are analysed and compared. A novel solution that experiments an innovative readout technique based on a special analog-Code Division Multiplexing Access (CDMA) is presented; this architecture can reach a considerable reduction of the Analog Front-End (AFE) with reference to other multiplexing schemes. Many family codes have been considered in order to find the best trade-off between performance and complexity. System-level simulations prove the effectiveness of this technique in processing all the required signals. A case study is also analysed: a comparison with the SD740 micro-machined integrated inertial module with tri-axial gyroscope by SensorDynamics AG is provided. MEMS accelerometers are widely used in the automotive and aeronautics fields and are becoming extremely popular in a wide range of consumer electronics products. The cost of testing is a major one within the manufacturing process, because MEMS accelerometer characterization requires a series of tests that include physical stimuli. The calibration and the functional testing are the most challenging and a wide selection of Automatic Test Equipments (ATEs) is available on the market for this purpose; those equipments provide a full characterization of the Device Under Test (DUT), from low-g to high-g levels, even over temperature. Chapter 2 presents a novel solution that experiments an innovative procedure to perform a characterization at medium-g levels. The presented approach can be applied to low-cost ATEs obtaining challenging results. The procedure is deeply investigated and an experimental setup is described. A case study is also analysed: some already trimmed Three Degrees of Freedom (3DoF)-Inertial Measurement Unit (IMU) modules (three-axes accelerometer integrated with a mixed signal ASIC), from SensorDynamics AG are tested with the experimental setup and analysed, for the first time, at medium-g levels. Standard preprocessing techniques for removing the ground response from vehicle- mounted Ground Penetrating Radar (GPR) data may fail when used on rough terrain. In Chapter 3, a Laser Imaging Detection and Ranging (LIDAR) system and a Global Positioning System (GPS)/IMU is integrated into a prototype system with the GPR and provided high-resolution measurements of the ground surface. Two modifications to preprocessing were proposed for mitigating the ground bounce based on the available LIDAR data. An experiment is carried out on a set of GPR/LIDAR data collected with the integrated prototype vehicle over lanes with artificially rough terrain, consisting of targets buried under or near mounds, ruts and potholes. A stabilization technique for multi-element vehicle-mounted GPR is also presented

Design, Fabrication and Characterization of MEMS Gyroscopes Based on Frequency Modulation

Conventional amplitude modulated (AM) open loop MEMS gyroscopes experience a significant performance trade-off between having a large bandwidth or high sensitivity. It is impossible to improve both metrics at the same time without increasing the mass of the gyroscope or introducing a closed loop (force feedback) system into the device design. Introducing a closed loop system or increasing the proof mass on the other hand will surge power consumption. Consequently, it is difficult to maintain consistently high performance while scaling down the device size. Furthermore, bias stability, bias repeatability, reliability, nonlinearity and other performance metrics remain primary concerns as designers look to expand MEMS gyroscopes into areas like space, military and navigation applications. Industries and academics carried out extensive research to address these limitations in conventional AM MEMS gyroscope design. This research primarily aims to improve MEMS gyroscope performance by integrating a frequency modulated (FM) readout system into the design using a cantilever beam and microplate design. The FM resonance sensing approach has been demonstrated to provide better performance than the traditional AM sensing method in similar applications (e.g., Atomic Force Microscope). The cantilever beam MEMS gyroscope is specifically designed to minimize error sources that corrupt the Coriolis signal such as operating temperature, vibration and packaging stress. Operating temperature imposes enormous challenges to gyroscope design, introducing a thermal noise and drift that degrades device performance. The cantilever beam mass gyroscope system is free on one side and can therefore minimize noise caused by both thermal effects and packaging stress. The cantilever beam design is also robust to vibrations (it can reject vibrations by sensing the orthogonally arranged secondary gyroscope) and minimizes cross-axis sensitivity. By alleviating the negative impacts of operating environment in MEMS gyroscope design, reliable, robust and high-performance angular rate measurements can be realized, leading to a wide range of applications including dynamic vehicle control, navigation/guidance systems, and IOT applications. The FM sensing approach was also investigated using a traditional crab-leg design. Tested under the same conditions, the crab-leg design provided a direct point of comparison for assessing the performance of the cantilever beam gyroscope. To verify the feasibility of the FM detection method, these gyroscopes were fabricated using commercially available MIDIS™ process (Teledyne Dalsa Inc.), which provides 2 μm capacitive gaps and 30 μm structural layer thickness. The process employs 12 masks and hermetically sealed (10mTorr) packaging to ensure a higher quality factor. The cantilever beam gyroscope is designed such that the driving and sensing mode resonant frequency is 40.8 KHz with 0.01% mismatch. Experimental results demonstrated that the natural frequency of the first two modes shift linearly with the angular speed and demonstrate high transducer sensitivity. Both the cantilever beam and crab-leg gyroscopes showed a linear dynamic range up to 1500 deg/s, which was limited by the experimental test setup. However, we also noted that the cantilever beam design has several advantages over traditional crab-leg devices, including simpler dynamics and control, bias stability and bias repeatability. Furthermore, the single-port sensing method implemented in this research improves the electronic performance and therefore enhances sensitivity by eliminating the need to measure vibrations via a secondary mode. The single-port detection mechanism could also simplify the IC architecture. Rate table characterization at both high (110 oC) and low (22 oC) temperatures showed minimal changes in sensitivity performance even in the absence of temperature compensation mechanism and active control, verifying the improved robustness of the design concept. Due to significant die area reduction, the cantilever design can feasibly address high-volume consumer market demand for low cost, and high-volume production using a silicon wafer for the structural part. The results of this work introduce and demonstrate a new paradigm in MEMS gyroscope design, where thermal and vibration rejection capability is achieved solely by the mechanical system, negating the need for active control and compensation strategies

Development and experimental analysis of a micromachined Resonant Gyrocope

This thesis is concerned with the development and experimental analysis of a resonant gyroscope. Initially, this involved the development of a fabrication process suitable for the construction of metallic microstructures, employing a combination of nickel electroforming and sacrificial layer techniques to realise free-standing and self-supporting mechanical elements. This was undertaken and achieved. Simple beam elements of typically 2.7mm x 1mm x 40µm dimensions have been constructed and subject to analysis using laser doppler interferometry. This analysis tool was used to implement a fill modal analysis in order to experimentally derive dynamic parameters. The characteristic resonance frequencies of these cantilevers have been measured, with 3.14kHz, 23.79kHz, 37.94kHz and 71.22kHz being the typical frequencies of the first four resonant modes. Q-factors of 912, 532, 1490 and 752 have been measured for these modes respectively at 0.01mbar ambient pressure. Additionally the mode shapes of each resonance was derived experimentally and found to be in excellent agreement with finite element predictions. A 4mm nickel ring gyroscope structure has been constructed and analysed using both optical analysis tools and electrical techniques. Using laser doppler interferometry the first four out-of-plane modes of the ring structure were found to be typically 9.893 kHz, 11.349 kHz, 11.418 kHz and 13.904 kHz with respective Q-factors of 1151, 1659, 1573 and 1407 at 0.01 mbar ambient pressure. Although electrical measurements were found to be obscured through cross coupling between drive and detection circuitry, the in-plane operational modes of the gyroscope were sucessfully determined. The Cos2Ө and Sin2Ө operational modes were measured at 36.141 kHz and 36.346 kHz, highlighting a frequency split of 205kHz. Again all experimentally derived modal parameters were in good agreement with finite element predictions. Furthermore, using the analysis model, the angular resolution of the gyroscope has been predicted to be approximately 4.75º/s

Micro-Resonators: The Quest for Superior Performance

Microelectromechanical resonators are no longer solely a subject of research in university and government labs; they have found a variety of applications at industrial scale, where their market is predicted to grow steadily. Nevertheless, many barriers to enhance their performance and further spread their application remain to be overcome. In this Special Issue, we will focus our attention to some of the persistent challenges of micro-/nano-resonators such as nonlinearity, temperature stability, acceleration sensitivity, limits of quality factor, and failure modes that require a more in-depth understanding of the physics of vibration at small scale. The goal is to seek innovative solutions that take advantage of unique material properties and original designs to push the performance of micro-resonators beyond what is conventionally achievable. Contributions from academia discussing less-known characteristics of micro-resonators and from industry depicting the challenges of large-scale implementation of resonators are encouraged with the hopes of further stimulating the growth of this field, which is rich with fascinating physics and challenging problems