Nonlinear mechanisms in passive microwave devices

Premi extraordinari doctorat curs 2010-2011, àmbit d’Enginyeria de les TICThe telecommunications industry follows a tendency towards smaller devices, higher power and higher frequency, which imply an increase on the complexity of the electronics involved. Moreover, there is a need for extended capabilities like frequency tunable devices, ultra-low losses or high power handling, which make use of advanced materials for these purposes. In addition, increasingly demanding communication standards and regulations push the limits of the acceptable performance degrading indicators. This is the case of nonlinearities, whose effects, like increased Adjacent Channel Power Ratio (ACPR), harmonics, or intermodulation distortion among others, are being included in the performance requirements, as maximum tolerable levels. In this context, proper modeling of the devices at the design stage is of crucial importance in predicting not only the device performance but also the global system indicators and to make sure that the requirements are fulfilled. In accordance with that, this work proposes the necessary steps for circuit models implementation of different passive microwave devices, from the linear and nonlinear measurements to the simulations to validate them. Bulk acoustic wave resonators and transmission lines made of high temperature superconductors, ferroelectrics or regular metals and dielectrics are the subject of this work. Both phenomenological and physical approaches are considered and circuit models are proposed and compared with measurements. The nonlinear observables, being harmonics, intermodulation distortion, and saturation or detuning, are properly related to the material properties that originate them. The obtained models can be used in circuit simulators to predict the performance of these microwave devices under complex modulated signals, or even be used to predict their performance when integrated into more complex systems. A key step to achieve this goal is an accurate characterization of materials and devices, which is faced by making use of advanced measurement techniques. Therefore, considerations on special measurement setups are being made along this thesis.Award-winningPostprint (published version

Microelectromechanical Systems and Devices

The advances of microelectromechanical systems (MEMS) and devices have been instrumental in the demonstration of new devices and applications, and even in the creation of new fields of research and development: bioMEMS, actuators, microfluidic devices, RF and optical MEMS. Experience indicates a need for MEMS book covering these materials as well as the most important process steps in bulk micro-machining and modeling. We are very pleased to present this book that contains 18 chapters, written by the experts in the field of MEMS. These chapters are groups into four broad sections of BioMEMS Devices, MEMS characterization and micromachining, RF and Optical MEMS, and MEMS based Actuators. The book starts with the emerging field of bioMEMS, including MEMS coil for retinal prostheses, DNA extraction by micro/bio-fluidics devices and acoustic biosensors. MEMS characterization, micromachining, macromodels, RF and Optical MEMS switches are discussed in next sections. The book concludes with the emphasis on MEMS based actuators

Piezoelectric Fused Silica Resonators for Timing References.

MEMS resonators have the capability to match or exceed the performance of state-of-the-art quartz timing references at a fraction of the size, power, and cost. To enable this capability, this work investigates the use of fused silica as a substrate for piezoelectrically actuated resonators for applications in timing references. This thesis presents the design and fabrication of a piezoelectrically actuated fused silica resonator. The fabricated resonators show a quality factor (Q) of 19,671 at 4.96 MHz with an insertion loss of 16.9 dB, and is the first reported example of a piezoelectrically actuated fused silica resonator in literature. An in-depth investigation into loss mechanisms in fused silica is performed in order to identify and address the major losses in the device and maximize potential performance. Multiple experimental and analytical investigations are presented, with a new form of loss, known as charge redistribution, presented as a possible dominant loss in these piezoelectric resonators. This loss mechanism is analytically modeled and simulated to have a Q of 25,100, within 20% of the experimentally measured devices. The temperature sensitivity of fused silica is also addressed; as fused silica shows a temperature coefficient of elasticity almost three times higher than that shown in uncompensated silicon. Both active and passive methods of temperature compensation are implemented, including a fused silica ovenized platform and nickel-refilled trenches for temperature compensation. The nickel-refilled trenches are shown to reduce temperature sensitivity in piezoelectrically actuated fused silica resonators from 78 ppm/K to 50 ppm/K, with larger compensation possible but complete compensation infeasible from passive techniques alone. From this, a dual-mode system is proposed for use in ovenized systems where two modes are simultaneously activated in a single device volume. In this system, one mode acts as a stable reference frequency and the second mode acts as a temperature sensor, allowing for extremely accurate ovenization. A silicon-based prototype is developed, showing a +14 ppm/K temperature difference between the two modes, with additional temperature differential possible through the addition of material-based passive compensation.PHDElectrical EngineeringUniversity of Michigan, Horace H. Rackham School of Graduate Studieshttp://deepblue.lib.umich.edu/bitstream/2027.42/135878/1/peczalsk_1.pd

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

RF MEMS technology for millimeter-wave radar sensors

The dissertation discusses RF MEMS technology for millimeter-wave radar sensors. RF MEMS, which stands for radio frequency micro-electromechanical system, and radar sensor fundamentals are briefly introduced. Of particular interest are: Firstly, a self-aligned fabrication process for capacitive fixed-fixed beam RF MEMS components is disclosed. It enables scaling of the critical dimensions and reduces the number of processing steps by 40% as compared with a conventional RF MEMS fabrication process. Scaling of the critical dimensions of RF MEMS components offers the potential of submicrosecond T/R switching times. RF MEMS varactors with beam lengths of 30 μm are demonstrated using the self-aligned fabrication process, and the performance of a 4 by 4 RF MEMS varactor bank is discussed as well. At 20 GHz, the measured capacitance values range between 180.5 fF and 199.2 fF. The measured capacitance ratio is 1.15, when a driving voltage of 35 V is applied, and the measured loaded Q factor ranges between 14.5 and 10.8. The measured cold-switched power handling is 200 mW. The simulated switching time is 354.6 ns. Secondly, an analog RF MEMS slotline TTD phase shifter is disclosed, for use in conjunction with ultra wideband (UWB) tapered slot antennas, such as the Vivaldi aerial and the double exponentially tapered slot antenna. It is designed for transistor to transistor logic (TTL) bias voltage levels and exhibits a measured phase shift of 28.2°/dB (7.8 ps/dB) and 59.2°/cm at 10 GHz, maintaining a 75 Ω; differential impedance match (S11dd ≤ -15.8 dB). The input third-order intercept point (IIP3) is 5 dBm at 10 GHz for a Δf of 50 kHz, measured in a 100 Ω differential transmission line system.Ph.D.Electrical EngineeringUniversity of Michiganhttp://deepblue.lib.umich.edu/bitstream/2027.42/61348/1/vcaeken.pd

Surpassing Fundamental Limits through Time Varying Electromagnetics

Surpassing the fundamental limits that govern all electromagnetic structures, such as reciprocity and the delay-bandwidth-size limit, will have a transformative impact on all applications based on electromagnetic circuits and systems. For instance, violating principles of reciprocity enables non-reciprocal components such as isolators and circulators, which find application in full-duplex wireless radios, radar, biomedical imaging, and quantum computing systems. Overcoming the delay-bandwidth-size limit enables ultra-broadband yet extremely-compact devices whose size is not fundamentally related to the wavelength at the operating frequency. The focus of this dissertation is on using time-variance as a new toolbox to overcome these fundamental limits and re-imagine circuit and system design. Traditional non-reciprocal components are realized using ferrite materials that loose their reciprocity under the application of external magnetic bias. However, the sheer volume, cost and weight of these magnet based non-reciprocal components coupled with their inability to be fabricated in conventional semiconductor processes, have limited their application to bulky and large-scale systems. Other approaches such as active-biased and non-linearity based non-reciprocity are compatible with semiconductor processes, however, they suffer from other poor linearity and noise performance. In this dissertation, using passive transistor switch as the modulating element, we have proposed the concept of spatio-temporal conductivity modulation and have demonstrated a gamut of non-reciprocal devices ranging from gyrators to isolators and circulators. Through novel circuit topologies, for the first time, we have demonstrated on-chip circulators with multi-watt input power handling, operation at high millimeter-wave frequencies, and tailor made circulators for emerging technologies such as simultaneous-transmit-and-receive MRI and quantum computing. Delay-bandwidth-size trade-off is another fundamental electromagnetic limit, that constrains the delay imparted by a medium or a device within a fixed footprint to be inversely proportional to the signal bandwidth. It is this limit that governs the size of any microwave passive devices to be inversely proportional to its operating frequency. As a part of this dissertation, through intelligent clocking of switched capacitor networks we overcame the delay-bandwidth-size limit, thus resulting in infinitesimal, yet broadband microwave devices. Here we proposed a new paradigm in wave propagation where the properties such as the propagation delay and characteristic impedance does not depend on the constituent elements/materials of the medium, but rather heavily rely on the user-defined modulation scheme, thereby opening huge opportunities for realizing highly-reconfigurable passives. Leveraging these concepts, we demonstrated wide range of reciprocal an non-reciprocal devices including ultra-compact delay elements, highly-reconfigurable microwave passives, ultra-wideband circulators with infinitesimal form-factors and dispersion-free chip scale floquet topological insulators. Application of these devices have also been evaluated in real-world systems through our demonstrations of wideband, full-duplex receivers leveraging switched capacitors based true-time-delay interference cancelers and floquet topological insulator based antenna interfaces for full-duplex phased-arrays and ultra-wideband beamformers. Furthermore, to cater the growing RF and microwave needs of future, large-scale quantum computing systems, we demonstrated a low-cryogenic, wideband circulator based on time modulation of superconducting devices. This superconducting circulator is expected to operate alongside the superconducting qubits, inside a dilution refrigerator at 10mK-100mK, thus enabling a tightly integrated quantum system. We also presented the design and implementation of a cryogenic-CMOS clock driver chip that will generate the clocks required by the superconducting circulator. Finally, we also demonstrated the design and implementation of a low-noise, low power consumption, 6GHz - 8GHz cryogenic downconversion receiver at 4K for cryogenic qubit readout

Development of III-nitride-based waveguides for application in all-optical integrated circuits at 1.55 [my]m

El desarrollo de una nueva tecnología todo-óptica para el procesado de datos en las futuras redes de telecomunicación está generando un gran interés desde hace una década. Esta tecnología está encaminada al total aprovechamiento del gran ancho de banda que proporciona la fibra óptica, evitando la conversión entre los dominios óptico y eléctrico necesaria en cada nodo de las redes de comunicaciones actuales. Esta nueva tecnología todo-óptica requiere de diferentes componentes ópticos que puedan ser controlados ópticamente. Estos dispositivos se obtienen a partir de distintos materiales semiconductores y se implementan de forma miniaturizada en un circuito todo-óptico integrado operando a 1.55 [my]m, mejorando de esta forma la fiabilidad del sistema y reduciendo su coste. Teniendo en cuenta que los nitruros del grupo III son materiales que han demostrado un gran potencial para aplicaciones en comunicaciones ópticas a 1.55 [my]m, el objetivo de este trabajo es el desarrollo de nuevos dispositivos todo-ópticos basados en éstos para su futura implementación en circuitos fotónicos integrados ultrarrápidos operando a longitudes de onda de telecomunicación. Durante esta Tesis se han desarrollado varios dispositivos de guía de onda basados en diferentes estructuras de nitruros del grupo III sobre substratos de zafiro y funcionando a 1.55 [my]m. En primer lugar, se han optimizado diferentes guías de onda ópticas basadas en pozos y puntos cuánticos de GaN/AlN para trabajar como absorbentes saturables a través de sus transiciones intersubbanda. Estas guías de onda podrían utilizarse en procesos de conmutación todo-óptica. En segundo lugar, se ha optimizado el crecimiento de AlN por sputtering de radiofrecuencia permitiendo su uso para la fabricación de guías de onda pasivas. El comportamiento óptico lineal de las guías de AlN por sputtering muestra su idoneidad para actuar como interconectores pasivos de bajo coste en un circuito todo-óptico integrado. Por último, se han optimizado dos tipos de guías de onda basadas en InN por sputtering para funcionar como absorbentes saturables inversos mediante procesos de absorción de dos fotones. La respuesta óptica no lineal de ambas guías abre la posibilidad de utilizar estos dispositivos para aplicaciones en limitación todo-óptica a longitudes de onda de telecomunicación