4 research outputs found
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
Energy efficient control of electrostatically actuated MEMS
Plenty of Micro-electro-mechanical Systems (MEMS) devices are actuated using electrostatic forces, and specially, parallel-plate actuators are extensively used, due to the simplicity of their design. Nevertheless, parallel-plate actuators have some limitations due to the nonlinearity of the generated force. The dissertation analyzes the dynamics of the lumped electrostatically actuated nonlinear system, in order to obtain insight on its characteristics, define desired performance goals and implement a controller for energy efficient robustly stable actuation of MEMS resonators.
In the first part of the dissertation, the modeling of the electromechanical lumped system is developed. From a complete distributed parameters model for MEMS devices which rely on electrostatic actuation, a concentrated parameters simplification is derived to be used for analysis and control design.
Based on the model, energy analysis of the pull-in instability is performed. The classic approach is revisited to extend the results to models with a nonlinear springs. Analysis of the effect of dynamics is studied as an important factor for the stability of the system. From this study, the Resonant Pull-in Condition for parallel-plate electrostatically actuated MEMS resonators is defined and experimentally validated.
Given the importance of the nonlinear dynamics and its richness in behaviors, Harmonic Balance is chosen as a tool to characterize the steady-state oscillation of the resonators. This characterization leads to the understanding of the key factors for large and stable oscillation of resonators. An important conclusion is reached, Harmonic Balance predicts that any oscillation amplitude is possible for any desired frequency if the appropriate voltage is applied to the resonator. And the energy consumption is dependent on this chosen oscillation frequency.
Based on Harmonic Balance results, four main goals are defined for the control strategy:
Stable oscillation with large amplitudes of motion; Robust oscillation independently of MEMS imperfections; Pure sinus-like oscillation for high-grade sensing; and Low energy consumption.
The second part of the dissertation deals with the controller selection, design and verification.
A survey of prior work on MEMS control confirms that existing control approaches cannot provide the desired performance. Consequently, a new three-stage controller is proposed to obtain the desired oscillation with the expected stability and energy efficiency. The controller has three different control loops. The first control loop includes a Robust controller designed using on µ-synthesis, to deal with MEMS resonators uncertainties. The second control loop includes an Internal-Model-Principle Resonant controller, to generate the desired control action to obtain the desired oscillation. And the third control loop handles the energy consumption minimization through an Extremum Seeking Controller, which selects the most efficient working frequency for the desired oscillation.
The proposed controller is able to automatically generate the needed control voltage, as predicted by the Harmonic Balance analysis, to operate the parallel-plate electrostatically actuated MEMS resonator at the desired oscillation. Performance verification of stability, robustness, sinus-like oscillation and energy efficiency is carried out through simulation.
Finally, the needed steps for a real implementation are analyzed. Independent two-sided actuation for full-range amplitude oscillation is introduced to overcome the limitations of one-sided actuation. And a modification of standard Electromechanical Amplitude Modulation is analyzed and validated for position feedback implementation. With these improvements, a MEMS resonator with the desired specifications for testing the proposed control is designed for fabrication. Based on this design, testing procedure is discussed as future work.Molts microsistemes (MEMS) són actuats amb forces electrostàtiques, i especialment, els actuadors electrostàtics de plaques paral.leles són molt usats, degut a la simplicitat del seu disseny. Tot i això, aquests actuadors tenen limitacions degut a la no-linealitat de les forces generades. La tesi analitza el sistema mecànic no-lineal actuat electrostàticament que forma el MEMS, per tal d'entendre'n les característiques, definir objectius de control de l'oscil.lació, i implementar un controlador robust, estable i eficient energèticament. A la primera part de la tesi es desenvolupa el modelat del sistema electromecànic complert. A partir de la formulació de paràmetres distribuïts aplicada a dispositius MEMS amb actuació electrostàtica, es deriva una formulació de paràmetres concentrats per a l'anàlisi i el disseny del control. Basat en aquest model, s'analitza energèticament la inestabilitat anomenada Pull-in, ampliant els resultats de l'enfocament clàssic al model amb motlles no-lineals. Dins de l'anàlisi, l'evolució dinàmica s'estudia per ser un factor important per a l'estabilitat. D'aquest estudi, la Resonant Pull-in Condition per a actuadors electrostàtics de plaques paral.leles es defineix i es valida experimentalment. Donada la importància de la dinàmica no-lineal del sistema i la seva riquesa de comportaments, s'utilitza Balanç d'Harmònics per tal de caracteritzar les oscil.lacions en estacionari. Aquesta caracterització permet entendre els factors claus per a obtenir oscil.lacions estables i d'amplitud elevada. El Balanç d'Harmònics dóna una conclusió important: qualsevol amplitud d'oscil.lació és possible per a qualsevol freqüència desitjada si s'aplica el voltatge adequat al ressonador. I el consum energètic associat a aquesta oscil.lació depèn de la freqüència triada. Llavors, basat en aquests resultats, quatre objectius es plantegen per a l'estratègia de control: oscil.lació estable amb amplituds elevades; robustesa de l'oscil.lació independentment de les imperfeccions dels MEMS; oscil.lació sinusoïdal sense harmònics per a aplicacions d'alta precisió; i baix consum energètic. La segona part de la tesi tracta la selecció, disseny i verificació dun controlador adequat per a aquests objectius. La revisió dels treballs existents en control de MEMS confirma que cap dels enfocaments actuals permet obtenir els objectius desitjats. En conseqüència, es proposa el disseny d'un nou controlador amb tres etapes per tal d'obtenir l'oscil.lació desitjada amb estabilitat i eficiència energètica. El controlador té tres llaços de control. Al primer llaç, un controlador robust dissenyat amb µ-síntesis gestiona les incertes es dels MEMS. El segon llaç inclou un controlador Ressonant, basat en el Principi del Model Intern, per a generar l'acció de control necessària per a obtenir l'oscil.lació desitjada. I el tercer llaç de control gestiona la minimització de l'energia consumida mitjançant un controlador basat en Extremum Seeking, el qual selecciona la freqüència de treball més eficient energèticament per a l'oscil.lació triada. El controlador proposat és capaç de generar automàticament el voltatge necessari, igual al previst pel Balanç d'Harmònics, per tal d'operar electrostàticament amb plaques paral.leles els ressonadors MEMS. Mitjançant simulació se'n verifica l'estabilitat, robustesa, inexistència d'harmònics i eficiència energètica de l'oscil.lació. Finalment, la implementació real és analitzada. En primer lloc, un nou esquema d'actuació per dos costats amb voltatges independents es proposa per aconseguir l'oscil.lació del ressonador en tot el rang d'amplituds. I en segon lloc, una modificació del sensat amb Modulació d'Amplitud Electromecànica s'utilitza per tancar el llaç de control de posició. Amb aquestes millores, un ressonador MEMS es dissenya per a ser fabricat i validar el control. Basat en aquest disseny, es proposa un procediment de test plantejat com a treball futur.Postprint (published version
A modular approach to high throughput microsystems
A modular high throughput microsystem was developed using microfabrication technology and nucleic acid analysis. The purpose of developing this microsystem is to identify acute infectious disease and prevent contagious outbreak in a matter of time. This microsystem included three major components, a reagent distribution device, a 96 CFPCR array, and a multi-zone thermal system, to efficiently amplify specific DNA fragments to determine the disease status or precisely pinpoint a disease from multiple patients. Polymerase chain reaction (PCR) is the key component in the nucleic acid analysis for disease because it can be used to amplify interested DNA fragments by repeatedly thermal cycles. Temperature distribution is critical to the PCR reaction, and thermal management was studied; the approaches which reached good biochemical results were applied to the design of a 96 CFPCR array and a multi-zone thermal system. Protein adsorption is another issue when PCR is realized in a micro device because of the increased surface-to-volume ratio, which might terminate the biochemical reaction. A series of experiments were carried out to understand the protein adsorption in the microchannels with different geometries. A disposable 96 CFPCR was designed and fabricated on a polycarbonate substrate by double-sided hot embossing and its requirement of multiple temperature zones was fulfilled by building a multi-zone thermal system. Their thermal performance was characterized by numerical simulations and validated by infrared camera experiments. To evenly distribute the analyte with reducing pipetting steps, a reagent distribution device was designed to assemble with the 96 CFPCR array by using passive alignment structures to perform a systematic performance. The passive alignment structures including three pairs of v-groove and hemisphere-tipped post was studied and modified to ensure a smooth passage for mass, momentum, and energy of chemical analyte. Biochemical experiments demonstrated parallel amplifications of both identical and different DNA fragments from the multiple CFPCRs on the multi-zone thermal system, which implied the potential to detect acute infectious disease with acceleration, accuracy, specificity, and high throughput
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