Academic literature on the topic 'MEMS Coriolis Vibrating Gyroscopes'

A MEMS Gyroscope is a micromachined inertial sensor that can measure the angle of orientation or the angular rate of rotation. These devices have the potential to be used in high precision navigation, safety and consumer electronics applications. Due to their complexity, MEMS Gyroscopes are prone to have imperfections that inhibit their full potential. By deeply characterizing these sensors, it is possible to validate fabrication methodologies, apply control circuit mechanisms, and design alternative mechanical structures that improve the performance. In this project, a streamlined methodology for testing and characterizing these devices is presented and executed. Analysis to the obtained results is given. Aditionally, a prototype circuit was designed to operate the sensors in a closed-loop mode. Two families of gyroscopes with different thickness were characterized - 40 m and 100 m. The devices presented low sensitivity thresholds due to the presence of a large quadrature error. A phase sensitive demodulation solution was provided to eliminate this noise source. The 40 m presented an overall better performance. A Python Script to extract key noise performance parameters was also displayed.<br>Giroscópios MEMS são micro sensores inerciais que conseguem medir o ângulo de orientação ou a variação ângular de uma rotação. Estes dispositivos têm o potencial de ser usados em aplicações de alta precisão para sistemas de navegação, segurança e para eletrónica comercial. Devido à sua complexidade, os Giroscópios MEMS são propensos a imperfeições que inibem o seu potencial máximo. Através da caracterização extensa destes sensores, é possível validar as metodologias de fabricação, aplicar circuitos de controlo e projetar estruturas mecânicas alternativas que melhorem a sua performance. Neste projeto é apresentada uma metodologia substanciada para testar e caracterizar estes dispositivos. Os resultados obtidos foram analisados. Adicionalmente, foi desenhado um protótipo de um circuito que opera os sensores em circuito fechado. Duas famílias de giroscópios com diferentes espessuras foram caracterizadas - 40 m e 100 m. Os dispositivos apresentaram baixos graus de sensibilidade devido a uma forte influência do erro de quadratura. Foi aplicada uma demodulação sensível à fase para melhoramento da performance. Um programa em Python para extrair parâmetros de ruído na resposta é apresentado.

碩士<br>國立清華大學<br>動力機械工程學系<br>104<br>This study implements a MEMS gyroscope by TSMC 0.18μm 1P6M standard CMOS process. The structure which fabricates by this process must encounter the problem of residual stress warping. In order to reduce the deformation of the residual stress, this study integrates several structure design method in existing literatures. The design methods which be implemented in this research including symmetric stack structure and pure oxide structure are expected to achieve a structure of low residual stress warping. By this way, the fabrication parameter of this standard platform would not be modified to fit the demand of structure and the advantage of this platform would also be kept include monolithic integration capability and the good ability of electrical routing. However, for the gyroscope, the problem of low signal response may have chance to be compensated by the advantage of this platform which could make sub-micron sensing gaps.

MEMS vibratory gyroscopes are used to measure the angular rate of a body by sensing the Coriolis force induced motion of the sensing element vibrating in a rotating frame of reference. MEMS gyroscopes find use in a wide variety of applications such as smartphones, automobiles, navigation, bio medical instruments, industrial systems, etc. A considerable amount of research has been done over the past two decades towards the improvement of MEMS gyroscope performance in terms of its scale factor, resolution, dynamic range, temperature sensitivity and bandwidth, with a goal of using them in high performance applications. Industrial report published about a year ago predicted the advent of inertial grade MEMS gyroscopes into the market by 2030. Towards this goal, active research is being pursued across the world by solving various issues towards the improvement of signal to noise ratio in MEMS gyroscopes stretching them into the ultimate performance regime at par with their optical counterparts. This work focuses on the complete development of a MEMS gyroscope suitable for high-performance applications. This involves the thorough study of specifications, meticulous design of the sensing structure to extract the required performance parameters, incorporation of fabrication related non-idealities into the design, precise fabrication of the sensor structure with tight tolerance, complete die-level characterization of the sensor, vacuum sealed packaging and integration with electronics to extract the sensor response to applied angular rates. The technique of sensitivity analysis is used to optimize the design and the same is demonstrated on three different designs of MEMS gyroscopes. DRIE process related non-idealities like the slanting and scalloping profiles are incorporated into the modelling of gyroscope structures. Extensive simulations are carried out to study the dependence of the etch profiles on different performance criteria of the MEMS gyroscope. Two designs are finalized and carried forward for fabrication. Combined wet and dry bulk micromachining technique is used to fabricate the sensor chips. Two different fabrication process flows are optimized to realize the two different designs. Novel findings in the area of TMAH based wet bulk micromachining for long duration etching and NH2OH added KOH based wet bulk micromachining at low temperatures for faster etch rates are reported. DRIE is used for precise controlled etching of the 100 μm device layer to realize the gyroscope structure. The fabricated sensor chips are subsequently characterized mechanically to extract the drive and sense resonant frequencies. A novel mechanical characterization set up for multiple sensor chips is discussed. The experimental observations are compared with FEM simulation values. Electrical characterization of the sensor chip involving C-V measurements and drive voltage optimization is also reported. The packaging of the sensor chip is carried out using an 84 pin quad flat leadless ceramic package. This package is sealed in vacuum of a few mTorr. The sealed sensor package is then used for further electronic integration. The electronic integration is carried out in two different ways. The sensor is directly integrated with AD7746 24-bit capacitance-to-digital converter for extracting the sense capacitance variation with angular rate. In the second method, a Trans-Impedance Amplifier circuit and a Lock-in Amplifier are used for real time measurements of sensor response to angular rate variation. A sensitivity of about 9.27 mV/(deg/s) is obtained with a non-linearity of about 0.5% over the entire range of ±440 deg/s. Further, raw data is continuously recorded for about 7 hrs with gyroscope in drive excitation mode and without application of angular rate. This data is used to plot Allan deviation curve which shows a bias instability of <5 deg/hr. The values of the specifications achieved, point towards a high- performance gyroscope even with the sensor packaged separately. The integration of the sensor chip with a C-V conversion ASIC is also briefly discussed for hybrid packaging to achieve even better performance. This thesis therefore presents some novel findings in the area of design, fabrication and characterization of high-performance MEMS gyroscopes