RF MEMS reference oscillators platform for wireless communications

A complete platform for RF MEMS reference oscillator is built to replace bulky quartz from mobile devices, thus reducing size and cost. The design targets LTE transceivers. A low phase noise 76.8 MHz reference oscillator is designed using material temperature compensated AlN-on-silicon resonator. The thesis proposes a system combining piezoelectric resonator with low loading CMOS cross coupled series resonance oscillator to reach state-of-the-art LTE phase noise specifications. The designed resonator is a two port fundamental width extensional mode resonator. The resonator characterized by high unloaded quality factor in vacuum is designed with low temperature coefficient of frequency (TCF) using as compensation material which enhances the TCF from - 3000 ppm to 105 ppm across temperature ranges of -40˚C to 85˚C. By using a series resonant CMOS oscillator, phase noise of -123 dBc/Hz at 1 kHz, and -162 dBc/Hz at 1MHz offset is achieved. The oscillator’s integrated RMS jitter is 106 fs (10 kHz–20 MHz), consuming 850 μA, with startup time is 250μs, achieving a Figure-of-merit (FOM) of 216 dB. Electronic frequency compensation is presented to further enhance the frequency stability of the oscillator. Initial frequency offset of 8000 ppm and temperature drift errors are combined and further addressed electronically. A simple digital compensation circuitry generates a compensation word as an input to 21 bit MASH 1 -1-1 sigma delta modulator incorporated in RF LTE fractional N-PLL for frequency compensation. Temperature is sensed using low power BJT band-gap front end circuitry with 12 bit temperature to digital converter characterized by a resolution of 0.075˚C. The smart temperature sensor consumes only 4.6 μA. 700 MHz band LTE signal proved to have the stringent phase noise and frequency resolution specifications among all LTE bands. For this band, the achieved jitter value is 1.29 ps and the output frequency stability is 0.5 ppm over temperature ranges from -40˚C to 85˚C. The system is built on 32nm CMOS technology using 1.8V IO device

An Implantable Phase Locked Loop MEMS Based Readout System for Heart Transplantation

An implantable readout circuit using a MEMS pressure sensor has been designed and implemented to monitor the heart activity after heart transplant surgery. It features a time domain architecture using two identical voltage-controlled oscillators and phase locked loop circuits. The circuit was implemented in a 65 nm CMOS technology with 1 V power supply. It consumes 100 lW power and provides a digital output that is proportional to the analog sensor input with a bandwidth of up to 4 kHz. The SNR of the system is 53 dB. Measurements show the operation of the readout chip with the MEMS sensor

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

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

MICRO-ELECTRO-MECHANICAL SYSTEM OSCILLATING ACCELERAMETERS WITH CMOS READOUT CIRCUITS

Ph.DDOCTOR OF PHILOSOPH

Low Power Cmos Circuit Design And Reliability Analysis For Wireless Me

A sensor node \u27AccuMicroMotion\u27 is proposed that has the ability to detect motion in 6 degrees of freedom for the application of physiological activity monitoring. It is expected to be light weight, low power, small and cheap. The sensor node may collect and transmit 3 axes of acceleration and 3 axes of angular rotation signals from MEMS transducers wirelessly to a nearby base station while attached to or implanted in human body. This dissertation proposes a wireless electronic system-on-a-single-chip to implement the sensor in a traditional CMOS process. The system is low power and may operate 50 hours from a single coin cell battery. A CMOS readout circuit, an analog to digital converter and a wireless transmitter is designed to implement the proposed system. In the architecture of the \u27AccuMicroMotion\u27 system, the readout circuit uses chopper stabilization technique and can resolve DC to 1 KHz and 200 nV signals from MEMS transducers. The base band signal is digitized using a 10-bit successive approximation register analog to digital converter. Digitized outputs from up to nine transducers can be combined in a parallel to serial converter for transmission by a 900 MHz RF transmitter that operates in amplitude shift keying modulation technique. The transmitter delivers a 2.2 mW power to a 50 Ù antenna. The system consumes an average current of 4.8 mA from a 3V supply when 6 sensors are in operation and provides an overall 60 dB dynamic range. Furthermore, in this dissertation, a methodology is developed that applies accelerated electrical stress on MOS devices to extract BSIM3 models and RF parameters through measurements to perform comprehensive study, analysis and modeling of several analog and RF circuits under hot carrier and breakdown degradation

Microelectromechanical Systems for Wireless Radio Front-ends and Integrated Frequency References.

Microelectromechanical systems (MEMS) have great potential in realizing chip-scale integrated devices for energy-efficient analog spectrum processing. This thesis presents the development of a new class of MEMS resonators and filters integrated with CMOS readout circuits for RF front-ends and integrated timing applications. Circuit-level innovations coupled with new device designs allowed for realizing integrated systems with improved performance compared to standalone devices reported in the literature. The thesis is comprised of two major parts. The first part of the thesis is focused on developing integrated MEMS timing devices. Fused silica is explored as a new structural material for fabricating high-Q vibrating micromechanical resonators. A piezoelectric-on-silica MEMS resonator is demonstrated with a high Q of more than 20,000 and good electromechanical coupling. A low phase noise CMOS reference oscillator is implemented using the MEMS resonator as a mechanical frequency reference. Temperature-stable operation of the MEMS oscillator is realized by ovenizing the platform using an integrated heater. In an alternative scheme, the intrinsic temperature sensitivity of MEMS resonators is utilized for temperature sensing, and active compensation for MEMS oscillators is realized by oven-control using a phase-locked loop (PLL). CMOS circuits are implemented for realizing the PLL-based low-power oven-control system. The active compensation technique realizes a MEMS oscillator with an overall frequency drift within +/- 4 ppm across -40 to 70 °C, without the need for calibration. The CMOS PLL circuits for oven-control is demonstrated with near-zero phase noise invasion on the MEMS oscillators. The properties of PLL-based compensation for realizing ultra-stable MEMS frequency references are studied. In the second part of the thesis, RF MEMS devices, including tunable capacitors, high-Q inductors, and ohmic switches, are fabricated using a surface micromachined integrated passive device (IPD) process. Using this process, an integrated ultra-wideband (UWB) filter has been demonstrated, showing low loss and a small form factor. To further address the issue of narrow in-band interferences in UWB communication, a tunable MEMS bandstop filter is integrated with the bandpass filter with more than an octave frequency tuning range. The bandstop filter can be optionally switched off by employing MEMS ohmic switches co-integrated on the same chip.PhDElectrical EngineeringUniversity of Michigan, Horace H. Rackham School of Graduate Studieshttp://deepblue.lib.umich.edu/bitstream/2027.42/109069/1/zzwu_1.pd

Degree-per-hour mode-matched micromachined silicon vibratory gyroscopes

The objective of this research dissertation is to design and implement two novel micromachined silicon vibratory gyroscopes, which attempt to incorporate all the necessary attributes of sub-deg/hr noise performance requirements in a single framework: large resonant mass, high drive-mode oscillation amplitudes, large device capacitance (coupled with optimized electronics), and high-Q resonant mode-matched operation. Mode-matching leverages the high-Q (mechanical gain) of the operating modes of the gyroscope and offers significant improvements in mechanical and electronic noise floor, sensitivity, and bias stability. The first micromachined silicon vibratory gyroscope presented in this work is the resonating star gyroscope (RSG): a novel Class-II shell-type structure which utilizes degenerate flexural modes. After an iterative cycle of design optimization, an RSG prototype was implemented using a multiple-shell approach on (111) SOI substrate. Experimental data indicates sub-5 deg/hr Allan deviation bias instability operating under a mode-matched operating Q of 30,000 at 23ºC (in vacuum). The second micromachined silicon vibratory gyroscope presented in this work is the mode-matched tuning fork gyroscope (M2-TFG): a novel Class-I tuning fork structure which utilizes in-plane non-degenerate resonant flexural modes. Operated under vacuum, the M2-TFG represents the first reported high-Q perfectly mode-matched operation in Class-I vibratory microgyroscope. Experimental results of device implemented on (100) SOI substrate demonstrates sub-deg/hr Allan deviation bias instability operating under a mode-matched operating Q of 50,000 at 23ºC. In an effort to increase capacitive aspect ratio, a new fabrication technology was developed that involved the selective deposition of doped-polysilicon inside the capacitive sensing gaps (SPD Process). By preserving the structural composition integrity of the flexural springs, it is possible to accurately predict the operating-mode frequencies while maintaining high-Q operation. Preliminary characterization of vacuum-packaged prototypes was performed. Initial results demonstrated high-Q mode-matched operation, excellent thermal stability, and sub-deg/hr Allan variance bias instability.Ph.D.Committee Chair: Dr. Farrokh Ayazi; Committee Member: Dr. Mark G. Allen; Committee Member: Dr. Oliver Brand; Committee Member: Dr. Paul A. Kohl; Committee Member: Dr. Thomas E. Michael

Analog Temperature Control Circuit for a Thin-Film Piezoelectric-on-Substrate Microelectromechanical Systems Oscillator

The objective and motivation for this project is to design a low-power, low-noise oven-control circuit to optimize the stability of a MEMS oscillator. MEMS oscillators can be fabricated using conventional semiconductor manufacturing methods and can often be assembled in packages smaller than those of traditional crystal oscillators. However, one of their largest disadvantages currently is their high temperature coefficient of frequency (TCF), causing MEMS oscillators to be especially sensitive to temperature changes. Hence, this project focuses on designing a printed circuit board that will allow the user to manually tune a current passing through a resonator wire-bonded to the board to elevate the resonator temperature. This will ensure that the device\u27s resonance frequency stays largely constant and that the oscillator provides a very stable signal

Superhydrophobic BIOMEMS sensor arrays: development of actuation and readout electronic strategies

2012/2013La tecnologia dei sistemi micro-elettro-meccanici (MEMS) ha dimostrato d’avere grandi potenzialità in molti campi, in particolare nei sistemi bio-medicali. Essa si basa infatti su processi di fabbricazione ad altro volume produttivo, permettendo una considerevole riduzione dei costi per dispositivo. Un ulteriore beneficio di questa tecnologia risiede nella possibilità di dimensionare i dispositivi fino a raggiungere l’ordine del submicron, così da consentire l’integrazione e il monitoraggio in tempo reale di sistemi sensibili a biomarker di tipo medicale e biologici. Tra gli obiettivi futuri dei MEMS biomedicali (BioMEMS) vi è la realizzazione di dispositivi in grado di interfacciarsi direttamente con il paziente e definirne lo stato di salute grazie alla rilevazione del livello di centinaia di diversi biomarker (siano essi chimici o fisici). La medicina assumerebbe in questa visione una configurazione ad personam nella quale al paziente verrebbe prontamente somministrato un quantitativo di medicinale adatto alle risposte del suo organismo. A tale scopo i dispositivi MEMS devono essere in grado di effettuare analisi multiple operando in un ambiente liquido. Tuttavia è proprio l’ambiente liquido a comportare la riduzione di sensibilità e, quindi, di performance dei sensori MEMS. La presente ricerca si pone lo scopo di sviluppare nuovi sistemi elettronici di misurazione e attuazione di due distinte tipologie di BioMEMS risonanti operanti in liquido, i cantilever e i pillar. In particolare verrano trattati tre argomenti: la realizzazione di setup ottici per applicazione dei MEMS in liquido ed in aria, la progettazione di sistemi elettronici di attuazione e lettura di singoli pillar nel loro comportamento in frequenza e lo sviluppo di un software LabVIEW in grado di programmare un FPGA ed ottenere un PLL digitale da impiegarsi nell’analisi in tempo reale del comportamento in frequenza di RF-MEMS. Il primo progetto è stato sviluppato in collaborazione l'Università di Kaiserslautern (Germania) e prevedeva la realizzazione di sistemi microfluidici e setups ottici, interfacciati in modo tale da permettere la rilevazione della risposta in frequenza di molteplici MEMS operanti in parallelo. Nel secondo progetto l’obiettivo era la realizzazione di un sistema elettronico in grado di integrare in un unico dispositivo i sistemi di attuazione e lettura dei pillar. In particolare siamo stati in grado di modulare l’ampiezza di risonanza dei nostri dispositivi risonanti mediante l’applicazione della forza di polarizzazione Kelvin mentre lo sviluppo del sistema di lettura richiede ulteriore lavoro di indagine. Infine, nell'ultimo progetto è stato realizzato un sistema PLL digitale con 10 MHz di banda passante utilizzando la tecnologia della National Instruments (FlexRIO NI5781R). Mediante questo PLL si è potuto identificare la frequenza di risonanza di diverse tipologie di MEMS e se ne è seguite le variazioni in tempo reale . Le attività di ricerca sperimentale sono state eseguite presso il laboratorio CNR- IOM a Trieste.XXVI Ciclo198