Fully Integrated High-Performance MEMS Lumped Element Filters for Reconfigurable Radios.

In this research, we present RF MEMS filters which address the most challenging performance requirements of modern RF front-end systems, namely multi-band processing capability, low energy consumption, and small size. These filters not only provide a wide tuning range for multiple-band selection, but also offer low loss, high power handling capability, fast tuning speed, and temperature stability. Two different technologies are considered for tunable lumped element filter targeting UHF range. The first technology is a tunable RF MEMS platform based on surface micromachining, enabling fabrication of continuously tuned capacitors, capacitive and ohmic switches, as well as high-Q inductors, all on a single chip. The filter is in a third-order coupled resonator configuration. Continuous electrostatic tuning is achieved using three tunable capacitor banks each consisting of one continuously tunable capacitor and three switched capacitors with pull-in voltage of less than 40V. The center frequency of the filter is tuned from 1GHz to 600MHz while maintaining a 3dB-bandwidth of 13 to 14% and insertion loss of 2%. The filter occupies a small size (1.5 cm x 1.0 cm). This filter shows the best published performance yet in terms of insertion loss, out-of-band rejection, temperature stability, and tuning range. The second technology is based on a new tuning mechanism utilizing phase-change (PC) materials. PC technology has been investigated and adopted in memory industry due to its fast transition time in nano second range, small size, and high resistance change ratio. Although PC materials offer several benefits, they have not been considered for RF applications because of their limited power handling capability and relatively higher on-resistance in their current form. In this work, germanium tellurium (GeTe) is considered as it offers a low on-resistivity and pronounced resistance change ratio of up to 106. To characterize RF properties of GeTe, different types of RF switches have been fabricated and compared. Such PC switches can be monolithically integrated with other micromachined components to implement reconfigurable front-end modules, potentially offering high tuning speed, low loss, high linearity, and small size.PHDElectrical EngineeringUniversity of Michigan, Horace H. Rackham School of Graduate Studieshttp://deepblue.lib.umich.edu/bitstream/2027.42/98038/1/yhshim_1.pd

Novel MEMS Tunable Capacitors with Linear Capacitance-Voltage Response Considering Fabrication Uncertainties

Electrostatically actuated parallel-plate MEMS tunable capacitors are desired elements for different applications including sensing, actuating and communications and RF (radio frequency) engineering for their superior characteristics such as quick response, high Q-factor and small size. However, due to the nature of their coupled electrostatic-structural physics, they suffer from low tuning range of 50% and have nonlinear capacitance-voltage (C-V) responses which are very sensitive to the voltage change near pull-in voltage. Numerous studies in the literature introduce new designs with high tunability ranging from 100% to over 1500%, but improvement of the nonlinearity and high sensitivity of the capacitor response have not received enough attention. In this thesis, novel highly tunable capacitors with high linearity are proposed to reduce sensitivity to the voltage changes near pull-in. The characteristic equations of a perfectly linear capacitor are first derived for two- and three-plate capacitors to obtain insight for developing linear capacitance-voltage responses. The devices proposed in this research may be classified into three categories: designs with nonlinear structural rigidities, geometric modifications and flexible moving electrodes. The concept of nonlinear supporting beams is exploited to develop parallel-plate capacitors with partially linear C-V curves. Novel electrodes with triangular, trapezoidal, butterfly, zigzag and fishbone shapes and structural/geometric nonlinearities are used to increase the linearity and tuning ratio of the response. To investigate the capacitors' behavior, an analytical approximate model is developed which can drastically decrease the computation time. The model is ideal for early design and optimization stages. Using this model, design variables are optimized for maximum linearity of the C-V responses. The results of the proposed modeling approach are verified by ANSYS FEM simulations and/or experimental data. When the fabrication process has dimensional limitations, design modifications and geometric enhancements are implemented to improve the linearity of the C-V response. The design techniques proposed in this thesis can provide tunabilities ranging from 80% to over 350% with highly linear regions in resulting C-V curves. Due to the low sensitivity of the capacitance to voltage changes in new designs, the entire tuning range is usable. Furthermore, the effect of fabrication uncertainties on parallel-plate capacitors performance is studied and a sensitivity analysis is performed to find the design variables with maximum impact on the C-V curves. An optimization method is then introduced to immunize the design against fabrication uncertainties and to maximize the production yield for MEMS tunable capacitors. The method approximates the feasible region and the probability distribution functions of the design variables to directly maximize the yield. Numerical examples with two different sets of design variables demonstrate significant increase in the yield. The presented optimization method can be advantageously utilized in design stage to improve the yield without increasing the fabrication cost or complexity

Substrate Integrated Coaxial Filters with Fixed and Tunable Responses

Wireless and mobile communications are already playing an important role in our lives, and this will can only grow more and more due to the predominant importance and use of modern smartphones, tablets and any kind of connected devices. With this is mind, the spectrum for wireless and mobile communications is becoming incredibly overcrowded, leading to increasing requirements for RF front-end filters. This progress has encouraged an impressive need for developing low-cost, high performance, mass-producible, small footprint, and highly integrated front-end solutions for microwave and millimeter-wave systems and applications including emerging 5G and future wireless platforms. In this context, high quality factor resonators are usually typical basic building blocks of many high performance passive and active circuits, and its design has become even more challenging in the last decade. As a result, Substrate Integrated Waveguide (SIW) technology has attracted scientific community and industry attention as a very good candidate for developing such desired high-Q planar microwave devices. Recently, SIW is demonstrating to be a successful approach for implementing microwave and mm-wave filters with high Q-factor, easy integration with other planar circuits, and for mass-production manufacturing processes in many technologies (i.e. Printed Circuit Board (PCB) and Low Temperature Co-fired Ceramics (LTCC) technologies among them). Its enormous similarity with waveguides is probably one of the main reasons why the development of SIW-based components and circuits is rapidly growing among the research community. Other potential features that, combined with the former advantages, could be of huge interest in a wide range of wireless and mobile applications are a lively set of research subjects, such as compactness, advanced filtering responses, and recently frequency-agility capabilities. These key features have been recently introduced in the design of microwave filters for the next-generation wireless systems. Taking into account the above-mentioned background, the work carried out during the course of this PhD Thesis has been directed towards a further study of SIW technology to propose, analyze and develop an innovative and original resonator topology. The proposed topology is based on the extension of the classical coaxial waveguide resonator to SIW technology, and must take advantage of the characteristics of SIW devices to allow the design of improved and innovative microwave resonator filters for advanced wireless systems. This PhD Thesis includes the latest improvements made on this topic, from the working principles of the basic coaxial SIW block, until different applications for the design of compact quasi-elliptic and reconfigurable microwave filters. The results are promising and demonstrate the validity of the proposed topology for the design of high-Q microwave filters, as well as its potential application to implement complex designs. The general knowledge gained from these cases of study can be considered a good base for further developing this technology, which can help to improve its EM performance, and also contribute to a more general use in the market.Las comunicaciones inalámbricas y móviles juegan un papel importante en nuestras vidas, y esto sólo puede ir a más debido a su enorme importancia y al uso de los modernos teléfonos inteligentes (del inglés, smartphones), tabletas y toda clase de dispositivos inalámbricos. Con todo esto en mente, el espectro electromagnético para comunicaciones inalámbricas y móviles se está saturando cada día más, lo que conlleva un constante aumento de los requisitos para los filtros de radio-frecuencia usados en las cabeceras de dichos sistemas. Este progreso ha llevado a un creciente interés en desarrollar componentes de microondas de bajo coste, alto rendimiento, pequeño tamaño, que permitan implementar soluciones altamente integradas para sistemas de alta frecuencia (i.e. microondas y ondas milimétrica) y sus aplicaciones, incluyendo entre ellas la emergente conexión 5G y las futuras plataformas inalámbricas. En este contexto, los resonadores de elevado factor de calidad constituyen generalmente los bloques básicos para el diseño de muchos circuitos pasivos (entre ellos filtros) y activos de alto rendimiento. Su diseño se ha convertido por tanto en un reto aún mayor en la última década. Como resultado de ello, la tecnología de guía de ondas integradas en substrato (Substrate Integrated Waveguide, SIW) ha atraído la atención de la comunidad científica e industrial, al revelarse como una buena aproximación para el desarrollo de dispositivos planares de microondas con excelentes prestaciones eléctricas, y en particular para la implementación de filtros de microondas y onda milimétrica de bajas pérdidas y elevada integración con circuitos en tecnología planar. Además, su flexibilidad se caracteriza también por su adecuación a diferentes procesos de fabricación y producción en masa, en tecnologías tales como los circuitos impresos (Printed Circuit Board, PCB) o la tecnología de materiales cerámicos multi-capa co-sinterizados a baja temperatura (Low Temperature Co-fired Ceramics, LTCC) entre otras. Su enorme similitud con las ya largamente estudiadas guías de onda es, probablemente, una de las principales razones por las cuales el desarrollo de dicho circuitos está creciendo rápidamente entre la comunidad de investigadores. Cabe mencionar como, además de las anteriores ventajas, otras características de la tecnología SIW que podrían ser de gran interés en una amplia gama de aplicaciones inalámbricas y móviles son la miniaturización, la posibilidad de implementar respuestas avanzadas de filtrado y, recientemente, las capacidades de sintonía en frecuencia de los componentes de microondas. De este modo, el trabajo desarrollado a lo largo de esta Tesis Doctoral se ha orientado hacia el planteamiento, análisis y desarrollo de una topología de resonador innovadora y original. Dicha topología se basa en una extensión de las cavidades coaxiales en guía de onda metálica a una implementación integrada en substrato inspirada en la tecnología SIW. Esta Tesis Doctoral recapitula los últimos avances que se han producido sobre este tema, empezando desde la descripción de los principios fundamentales de funcionamiento de las estructuras, hasta la demostración de varias aplicaciones concretas útiles para el diseño de filtros de microondas muy compactos, con respuestas filtrantes avanzadas y reconfigurables. Los resultados que se van a mostrar a continuación son prometedores, y demuestran la validez de la topología propuesta. El conocimiento general obtenido de los diferentes prototipos fabricados y caracterizados experimentalmente puede considerarse una buena base para seguir desarrollando esta tecnología, lo que puede ayudar a mejorar su rendimiento electromagnético, así como a contribuir a un uso más extendido de estos dispositivos en el mercado.Les comunicacions sense fils i mòbils juguen un paper important en les nostres vides, i això només pot anar a més a causa de la gran importància i l'ús dels moderns telèfons intel·ligents (de l'anglès, smartphones), tablets i tota classe de dispositius sense fil. Tenint en compte tot açò, l'espectre electromagnètic per a comunicacions sense fils i mòbils s'està saturant cada dia més, el que comporta un constant augment dels requisits per als filtres de radiofreqüència usats en les capçaleres d'aquests sistemes. Aquest progrés ha portat a un creixent interès en desenvolupar components de microones de baix cost, alt rendiment, volum reduït, que permeten implementar solucions altament integrades per a sistemes d'alta freqüència (ie. microones i ones mil·limètriques) i les seves aplicacions, incloent l'emergent connexió 5G i les futures plataformes sense fils. En aquest context, els ressonadors d'elevat factor de qualitat constitueixen generalment els blocs bàsics per al disseny de molts circuits passius (entre ells filtres) i actius d'alt rendiment. El seu disseny s'ha convertit per tant en un repte encara més gran en l'última dècada. Com a resultat d'això, la tecnologia de guia d'ones integrades en substrat (Substrate Integrated Waveguide, SIW) ha atret l'atenció de la comunitat científica i industrial, al revelar-se com una bona aproximació per al desenvolupament de dispositius planars de microones amb excel·lents prestacions elèctriques , i en particular per a la implementació de filtres de microones i ones mil·limètriques de baixes pèrdues i elevada integració amb circuits en tecnologia planar. A més, la seua flexibilitat es caracteritza també per la seua adequació a diferents processos de fabricació i producció en massa, en tecnologies com ara els circuits impresos (Printed Circuit Board, PCB) o la tecnologia de materials ceràmics multicapa co-sinteritzats a baixa temperatura (Low Temperature Co-Fired Ceramics, LTCC) entre d'altres. La seua enorme similitud amb les ja llargament estudiades guies d'ona és, probablement, una de les principals raons per les quals el desenvolupament d'aquests circuits està creixent ràpidament entre la comunitat d'investigadors. Cal destacar com, a més de les anteriors avantatges, altres característiques de la tecnologia SIW que podrien ser de gran interès en una àmplia gamma d'aplicacions sense fils i mòbils són la miniaturització, la possibilitat d'implementar respostes avançades de filtrat i, recentment, les capacitats de sintonia en freqüència dels components de microones. Aquestes característiques clau s'han introduït recentment en el disseny de filtres microones per als sistemes sense fils de pròxima generació, convertint-se en objecte prioritari d'estudi per part de la comunitat científica. D'aquesta manera, el treball desenvolupat al llarg d'aquesta tesi doctoral s'ha orientat cap al plantejament, anàlisi i desenvolupament d'una topologia de ressonador innovadora i original. Aquesta topologia es basa en una extensió de les cavitats coaxials en guia d'ona metàl·lica a una implementació integrada a substrat inspirada en la tecnologia SIW. Aquesta tesi doctoral recapitula els últims avanços que s'han produït sobre aquest tema, començant des de la descripció dels principis fonamentals de funcionament de les estructures, fins a la demostració de diverses aplicacions concretes útils per al disseny de filtres i microones molt compactes, amb respostes de filtrat avançades i reconfigurables. Els resultats que es mostraran a continuació són prometedors, i demostren la validesa de la topologia proposada. El coneixement general obtingut dels diferents prototips fabricats i caracteritzats experimentalment es pot considerar com una bona base per seguir desenvolupant aquesta tecnologia, el que pot ajudar a millorar el seu rendiment electromagnètic, així com a contribuir a un ús més estès d'aquests dispositius en el merSirci, S. (2017). Substrate Integrated Coaxial Filters with Fixed and Tunable Responses [Tesis doctoral no publicada]. Universitat Politècnica de València. https://doi.org/10.4995/Thesis/10251/78838TESI

Vertically aligned carbon based varactors

This paper gives an assessment of vertically aligned carbon based varactors and validates their potential for future applications. The varactors discussed here are nanoelectromechanical devices which are based on either vertically aligned carbon nanofibers or vertically aligned carbon nanotube arrays. A generic analytical model for parallel plate nanoelectromechanical varactors based on previous works is developed and is used to formulate a universal expression for their voltage-capacitance relation. Specific expressions for the nanofiber based and the nanotube based varactors are then derived separately from the generic model. This paper also provides a detailed review on the fabrication of carbon based varactors and pays special attention to the challenges in realizing such devices. Finally, the performance of the carbon based varactor is assessed in accordance with four criteria: the static capacitance, the tuning ratio, the quality factor, and the operating voltage. Although the reported performance is still far inferior to other varactor technologies, our prognosis which stems from the analytical model shows a promise of a high quality factor as well as a potential for high power handling for carbon based varactors

Adaptive Sliding Mode Control of MEMS AC Voltage Reference Source

The accuracy of physical parameters of a tunable MEMS capacitor, as the major part of MEMS AC voltage reference, is of great importance to achieve an accurate output voltage free of the malfunctioning noise and disturbance. Even though strenuous endeavors are made to fabricate MEMS tunable capacitors with desiderated accurate physical characteristics and ameliorate exactness of physical parameters’ values, parametric uncertainties ineluctably emerge in fabrication process attributable to imperfections in micromachining process. First off, this paper considers applying an adaptive sliding mode controller design in the MEMS AC voltage reference source so that it is capable of giving off a well-regulated output voltage in defiance of jumbling parametric uncertainties in the plant dynamics and also aggravating external disturbance imposed on the system. Secondly, it puts an investigatory comparison with the designed model reference adaptive controller and the pole-placement state feedback one into one’s prospective. Not only does the tuned adaptive sliding mode controller show remarkable robustness against slow parameter variation and external disturbance being compared to the pole-placement state feedback one, but also it immensely gets robust against the external disturbance in comparison with the conventional adaptive controller. The simulation results are promising

Stretching the limits of dynamic range, shielding effectiveness, and multiband frequency response

In this dissertation, an RF MEMS variable capacitor suitable for applications requiring ultrawide capacitive tuning ranges is reported. The device uses an electrostatically tunable liquid dielectric interface to continuously vary the capacitance without the use of any moving parts. As compared to existing MEMS varactors in literature, this device has an extremely simple design that can be implemented using simple fabrication methods that do not necessitate the use of clean room equipment. In addition, this varactor is particularly suited for incorporating a wide range of liquid dielectric materials for specific tuning ratio requirements. Additionally, the shielding effectiveness performance of graphene-doped ABS thin films is investigated. The use of graphene as a replacement for metal fillers in composite EMI shielding materials is quickly becoming a widely-investigated field in the electromagnetic compatibility community. By replacing conventional metal-based shielding methods with graphene-doped polymers, low-weight, field-use temporary shielding enclosures can be implemented that do not suffer from mechanical unreliability and corrosion/oxidation like a traditional metal enclosure. While the performance of composite EMI shielding materials has not yet surpassed metals, the advantages of polymer-based shielding methods could find usage in a variety of applications. Finally, mutliband pre-fractal antennas fabricated via 3D printing are reported. These devices are the first to incorporate the advantages of 3D printing (rapid prototyping, fabrication of complex geometries otherwise unobtainable) with the advantages of self-similar antennas (increased gain and multiband performance) in a single device. The Sierpinski tetrahedron-based antenna design was both computationally modeled and physically realized to illustrate its potential as a solution to enable true multiband communication platforms

Low Temperature Superconducting RF MEMS Devices

Abstract Superconducting microelectronics technology (SME) has the potential of realizing high speed digital receivers capable of performing direct digitization of radio frequency signals with very low power consumption. An SME receiver is implemented on a single chip using low-temperature superconducting (LTS) Josephson junctions (JJs). The technology provides ultrafast digital switches and logic circuits along with high linearity analog-to-digital converters (ADCs). However, SME technology offers limited choices for realizing reconfigurable analog front-ends. While a tunable inductor using a string of JJs or superconducting quantum interference devices (SQUIDs) can be realized using the SME technology, the main problems with these tuning inductor elements are poor linearity performance and low power handling. RF MEMS technology has the capability to offer highly linear and high power handling tuning elements such as switches and varactors. To integrate a receiver with radio frequency (RF) front-end on a single chip, MEMS devices need to be fabricated using the same fabrication process as SME technology. In this study, a post-processing technique is developed and optimized to release the MEMS parts of the SME chip while keeping the SME electronics intact. Another challenge is to design MEMS structures that can handle extreme low-temperature working environments. For the first time, superconducting niobium-based RF MEMS dc-contact switches, capacitive-contact switches and varactors are developed employing the SME technology, operating at 4K. The loss in all of the devices is extremely low and the quality factor is quite high when niobium superconducts. The mechanical performance of the MEMS structures are investigated at liquid nitrogen and liquid helium temperatures of 77k and 4K, respectively. The deformation of the MEMS structures and material stiffness at cryogenic temperature are also investigated. Additionally, more advanced tunable RF circuits are developed, fabricated and characterized, implementing the primary devices. Two types of MEMS capacitor banks are designed, post-processed and characterized using the dc-contact and capacitive-contact RF MEMS switches. The capacitor banks show a very high quality factor at 4K. As well, a single-port-double-throw switch is developed and measured as the building block for switch matrices, showing extremely low insertion loss, and tunable resonators are presented that implement both varactors and dc-contact RF MEMS switches as the tuning elements. The resonators are extremely miniaturized, with a size of o/1600, and tunable filters are developed and characterized using these resonators. While niobium-based RF MEMS can be integrated within the niobium-layers of the SME technology, designers often do not have the flexibility to select the thickness of the MEMS structural layers. Also, since the fabrication process of SME technology is not specifically designed for MEMS technology, there are limitations in designing more reliable RF MEMS devices. A novel niobium-based micro-fabrication process is developed to integrate gold-based MEMS structures with niobium-based RF circuits. This method benefits from the very low-loss characteristic of superconducting metal niobium while implementing a more matured technology for MEMS structures. An 8-mask fabrication process is developed that allows the monolithic integration of superconducting niobium-based RF circuits with gold-based MEMS structures. By developing this fabrication method, many low-loss and high quality factor tunable RF devices can be achieved. The challenge is to maintain the quality of the niobium metal layer so that there is no degradation in the critical temperature of the niobium after going through all of the 8-mask process steps. Niobium RF devices integrated with gold-based dc-contact and capacitive-contact RF MEMS switches are fabricated and characterized on alumina substrates using the proposed fabrication process. All devices demonstrate insertion loss reduction due to the superconducting nature of niobium. The measurements of coplanar waveguide transmission lines and low-pass filters demonstrate that the critical temperature of the niobium metal layer is not degraded during the process steps. A capacitor bank is designed, fabricated and characterized showing a very high quality factor. Finally, two types of niobium tunable bandpass filters are presented that employ gold-based dc-contact RF MEMS switches as the tuning elements

Low power strain sensor based on MOS tunneling current.

Sensors, such as pressure sensors, accelerometers and gyroscopes, are very important components in modern portable electronics. A limited source of power in portable electronics is motivating research on new low power sensors. Piezoresistive and capacitive sensing technologies are the most commonly utilized technologies, which typically consume power in the µW to mW range. Tunneling current sensing is attractive for low power applications because the typical tunneling current is in the nA range. This dissertation demonstrates a low power strain sensor based on the tunneling current in a metal-oxide-semiconductor (MOS) structure with a power consumption of a couple of nano-Watts (nW) with a minimum detectable strain of 0.00036%. Both DC and AC measurements were used to characterize the MOS tunneling current strain sensor. The noise level is found to be smallest in the inversion region, and therefore it is best to bias the device in the inversion region. To study the sensitivity in the inversion region, a model is developed to compute the tunneling current as a function of strain in the semiconductor. The model calculates the tunneling current due to electrons tunneling from the conduction band of the semiconductor to the gate (ECB tunneling current) and the tunneling current due to electrons tunneling from the valence band of the semiconductor to the gate (EVB tunneling current). It is found that the ECB tunneling current is sufficient to explain experimental gate leakage current results reported in the literature for MOSFETs with low substrate doping concentration. However, for the tunneling current strain sensor with a higher substrate doping concentration reported here, a model using both ECB and EVB tunneling current is required. The model fits our experiments. During both DC and AC measurements, the MOS tunneling current is found to drift with time. The drift could arise from the trap states within the oxide. The current drift makes it difficult to obtain an absolute measurement of the strain. Combining the tunneling current strain sensor with a resonant sensor may be a good choice because it measures changes in the mechanical resonant frequency, independent of a drift of the tunneling current amplitude

A COMPREHENSIVE OVERVIEW OF RECENT DEVELOPMENTS IN RF-MEMS TECHNOLOGY-BASED HIGH-PERFORMANCE PASSIVE COMPONENTS FOR APPLICATIONS IN THE 5G AND FUTURE TELECOMMUNICATIONS SCENARIOS

The goal of this work is to provide an overview about the current development of radio-frequency microelectromechanical systems technology, with special attention towards those passive components bearing significant application potential in the currently developing 5G paradigm. Due to the required capabilities of such communication standard in terms of high data rates, extended allocated spectrum, use of massive MIMO (Multiple-Input-Multiple-Output) systems, beam steering and beam forming, the focus will be on devices like switches, phase shifters, attenuators, filters, and their packaging/integration. For each of the previous topics, several valuable contributions appeared in the last decade, underlining the improvements produced in the state of the art and the chance for RF-MEMS technology to play a prominent role in the actual implementation of the 5G infrastructure