A frequency selective surface (FSS) based on switchable slots in the ground plane is presented. The switching is done using an actuating MEMS bridge over the slot. The intent is to demonstrate the control of the resonance frequency of the FSS by deflecting the bridge. It is shown that by applying a voltage between the bridge and the ground plane, the bridge displaces and changes the system capacitance which in turn changes the resonance frequency. Two analyses are presented; (1) Electromechanical analysis to show how the bridge deflects by the voltage, (2) Electromagnetic analysis to show how the resonance frequency changes by the bridge deflection. The device was fabricated and tested. The measurement results are presented for two up and down positions of the MEMS bridge to verify the correctness of the theory and design.

A frequency selective surface (FSS) based on switchable slots in the ground plane is presented. The switching is done using an actuating MEMS bridge over the slot. The intent is to demonstrate the control of the resonance frequency of the FSS by deflecting the bridge. It is shown that by applying a voltage between the bridge and the ground plane, the bridge displaces and changes the system capacitance which in turn changes the resonance frequency. Two analyses are presented; (1) Electromechanical analysis to show how the bridge deflects by the voltage, (2) Electromagnetic analysis to show how the resonance frequency changes by the bridge deflection. The device was fabricated and tested. The measurement results are presented for two up and down positions of the MEMS bridge to verify the correctness of the theory and design.

This thesis work builds on the concept of reconfiguring the antenna properties (frequency, polarization, radiation pattern) using Radio Frequency (RF) Micro Electro Mechanical Systems (MEMS). This is a part of the overall research performed at the RF Micro/Nano Electro Mechanical Systems (uNeMS) Laboratory at Utah State University, which includes design, microfabrication, test, and characterization of uNeMS integrated cognitive wireless communication systems (Appendix A). In the first step, a compact and broadband Planar Inverted F Antenna (PIFA) is designed with a goal to accommodate reconfigurability at a later stage. Then, a Frequency Reconfigurable Antenna (FRA) is designed using MEMS switches to switch between the Public Safety (PS) bands, 152-162 MHz and 406-512 MHz, while maintaining the integrity of radiation pattern for each band. Finally, robust mechanical designs of the RF MEMS switches accompanied by different analyses have been performed. These analyses are instrumental in obtaining high yield, reliable, robust microfabrication processes including thin film metal deposition and patterning.

<p>Couplers are one of the most frequently used passive devices in microwave circuitry. The main function of a coupler is to divide (or combine) a radio frequency signal into (from) two separate signals by a specific ratio and phase difference. With the need for smaller electronic devices, a reduction in the area of a distributed coupler would prove to be valuable. The purpose of this research is to develop, simulate, fabricate and test high aspect ratio microstructure couplers that are smaller in area than existing distributed couplers, and have comparable or better performance. One method used to reduce the area of a distributed coupler is to replace single or multiple transmission lines with lumped element equivalent circuits. One category of lumped elements that has not been extensively implemented is high aspect ratio lumped elements. High aspect ratio lumped elements fabricated with deep X-ray lithography are able to take advantage of using the vertical dimension, and reduce their planar area. In this thesis high aspect ratio lumped elements are used in the design of 3-dB microstructure couplers that show significant area reduction compared to equivalent distributed couplers.</p> <p>The designs of the microstructure couplers were based on the lumped element equivalent circuits of a 3-dB branch-line and a 3-dB rat-race distributed coupler. Simulations were performed to determine the lumped element values that would provide the largest 3-dB bandwidth while still maintaining close to ideal coupling and through values, return loss bandwidth, isolation bandwidth, and phase. These lumped element values were then implemented in the microstructure coupler designs as high aspect ratio microstructure lumped elements. 3-D electromagnetic simulations were performed which verified that the structures behaved electrically as couplers. The microstructure couplers were designed to be 220 &#x00B5;m tall nickel structures with capacitance gap widths of 6 µm.</p> <p>Fabrication of the microstructure couplers using deep X-ray lithography was performed by the microfabrication group at IMT/KIT in Karlsruhe, Germany. Before testing, detailed visual inspection and the etching of the structures was performed at the Canadian Light Source.</p> <p>A total of five microstructure couplers were tested. Four of the tested couplers were based on the 3-dB branch-line coupler, and the fifth coupler was based on the 3-dB rat-race coupler. The microstructure branch-line design that had the best overall results was fabricated on quartz glass substrate and had an operation frequency of 5.3 GHz. The 3-dB bandwidth of the coupler was measured to be better than 75.5% and extrapolated to be 95.0%. At the centre frequency the through and coupled values were -4.32 dB and -4.44 dB. The phase difference between the couplers output ports was designed to be 90.0° and was measured to be 95.8°. The ±5° phase bandwidth was measured to be 12.7% and the isolation bandwidth was 28.8%. The measured results from the other couplers were comparable to simulation results.</p> <p>The main advantage of the microstructure coupler designs over existing distributed couplers is that the microstructure couplers show a significant area reduction. The branch-line microstructure designs were at least 85% smaller in area than their distributed equivalent on quartz glass. The rat-race microstructure design showed an area reduction of 90% when compared to its distributed equivalent on quartz glass.</p>

<p>Couplers are one of the most frequently used passive devices in microwave circuitry. The main function of a coupler is to divide (or combine) a radio frequency signal into (from) two separate signals by a specific ratio and phase difference. With the need for smaller electronic devices, a reduction in the area of a distributed coupler would prove to be valuable. The purpose of this research is to develop, simulate, fabricate and test high aspect ratio microstructure couplers that are smaller in area than existing distributed couplers, and have comparable or better performance. One method used to reduce the area of a distributed coupler is to replace single or multiple transmission lines with lumped element equivalent circuits. One category of lumped elements that has not been extensively implemented is high aspect ratio lumped elements. High aspect ratio lumped elements fabricated with deep X-ray lithography are able to take advantage of using the vertical dimension, and reduce their planar area. In this thesis high aspect ratio lumped elements are used in the design of 3-dB microstructure couplers that show significant area reduction compared to equivalent distributed couplers.</p> <p>The designs of the microstructure couplers were based on the lumped element equivalent circuits of a 3-dB branch-line and a 3-dB rat-race distributed coupler. Simulations were performed to determine the lumped element values that would provide the largest 3-dB bandwidth while still maintaining close to ideal coupling and through values, return loss bandwidth, isolation bandwidth, and phase. These lumped element values were then implemented in the microstructure coupler designs as high aspect ratio microstructure lumped elements. 3-D electromagnetic simulations were performed which verified that the structures behaved electrically as couplers. The microstructure couplers were designed to be 220 &#x00B5;m tall nickel structures with capacitance gap widths of 6 µm.</p> <p>Fabrication of the microstructure couplers using deep X-ray lithography was performed by the microfabrication group at IMT/KIT in Karlsruhe, Germany. Before testing, detailed visual inspection and the etching of the structures was performed at the Canadian Light Source.</p> <p>A total of five microstructure couplers were tested. Four of the tested couplers were based on the 3-dB branch-line coupler, and the fifth coupler was based on the 3-dB rat-race coupler. The microstructure branch-line design that had the best overall results was fabricated on quartz glass substrate and had an operation frequency of 5.3 GHz. The 3-dB bandwidth of the coupler was measured to be better than 75.5% and extrapolated to be 95.0%. At the centre frequency the through and coupled values were -4.32 dB and -4.44 dB. The phase difference between the couplers output ports was designed to be 90.0° and was measured to be 95.8°. The ±5° phase bandwidth was measured to be 12.7% and the isolation bandwidth was 28.8%. The measured results from the other couplers were comparable to simulation results.</p> <p>The main advantage of the microstructure coupler designs over existing distributed couplers is that the microstructure couplers show a significant area reduction. The branch-line microstructure designs were at least 85% smaller in area than their distributed equivalent on quartz glass. The rat-race microstructure design showed an area reduction of 90% when compared to its distributed equivalent on quartz glass.</p>

Reconfigurable impedance matching networks are an integral part of multiband radio-frequency (RF) transceivers. They are used to compensate for the input/output impedance variations between the different blocks caused by switching the frequency band of operation or by adjusting the output power level. Various tuning techniques have been developed to construct tunable impedance matching networks employing solid-state p-i-n diodes and varactors. At millimeter-wave frequencies, the increased loss due to the low quality factor of the solid-state devices becomes an important issue. Another drawback of the solid-state tuning elements is the increased nonlinearity and noise at higher RF power levels. The objective of the research described in this thesis is to investigate the feasibility of using RF microelectromechanical systems (RF-MEMS) technology to develop reconfigurable impedance matching networks. Different types of tunable impedance matching networks with improved impedance tuning range, power handling capability, and lower insertion loss have been developed. Another objective is to investigate the realization of a fully integrated one-chip solution by integrating MEMS devices in standard processes used for RF integrated circuits (RFICs). A new CMOS-MEMS post-processing technique has been developed that allows the integration of tunable RF MEMS devices with vertical actuation within a CMOS chip. Various types of CMOS-MEMS components used as tuning elements in reconfigurable RF transceivers have been developed. These include tunable parallel-plate capacitors that outperform the available CMOS solid-state varactors in terms of quality factor and linearity. A tunable microwave band-pass filter has been demonstrated by employing the proposed RF MEMS tunable capacitors. For the first time, CMOS-MEMS capacitive type switches for microwave and millimeter-wave applications have been developed using TSMC 0.35-µm CMOS process employing the proposed CMOS-MEMS integration technique. The switch demonstrates an excellent RF performance from 10-20 GHz. Novel MEMS-based reconfigurable impedance matching networks integrated in standard CMOS technologies are also presented. An 8-bit reconfigurable impedance matching network based on the distributed MEMS transmission line (DMTL) concept operating at 13-24 GHz is presented. The network is implemented using standard 0.35-µm CMOS technology and employs a novel suspended slow-wave structure on a silicon substrate. To our knowledge, this is the first implementation of a DMTL tunable MEMS impedance matching network using a standard CMOS technology. A reconfigurable amplifier chip for WLAN applications operating at 5.2 GHz is also designed and implemented. The amplifier achieves maximum power gain under variable load and source impedance conditions by using the integrated RF-MEMS impedance matching networks. This is the first single-chip implementation of a reconfigurable amplifier using high-Q MEMS impedance matching networks. The monolithic CMOS implementation of the proposed RF MEMS impedance matching networks enables the development of future low-cost single-chip RF multiband transceivers with improved performance and functionality.

For this thesis, the use of Liquid Crystal Polymer (LCP) as a system-level substrate and packaging material is investigated. Early in the research, recipes for fabricating on LCP were developed. With this knowledge, RF components were able to be fabricated. These devices include filters, antennas, phase shifters, and RF MEMS switches. To investigate the potential of using LCP as a system-level material, packaging properties and robustness were tested. This research demonstrated that LCP could be used to package something as small and delicate as an individual switch or as large as a 4-inch wafer. In addition, it was shown that MEMS switches could survive well over a hundred million cycles. This demonstrated that LCP could be used to create reliable, high performance systems. The culmination of this research was used to create two variations of a communication module. The first device was fabricated on one layer and a multi-layer approach was taken for the other device. These modules needed to be low-cost, low-loss, flexible, and capable of beam steering. This technology can be used for communication, sensing, detection, and surveillance for a broad scope of applications. To this date, they are by far the most sophisticated SOP on LCP ever achieved. This technology can be further developed to include more functionality, smaller size, and even better performance.

Reconfigurable impedance matching networks are an integral part of multiband radio-frequency (RF) transceivers. They are used to compensate for the input/output impedance variations between the different blocks caused by switching the frequency band of operation or by adjusting the output power level. Various tuning techniques have been developed to construct tunable impedance matching networks employing solid-state p-i-n diodes and varactors. At millimeter-wave frequencies, the increased loss due to the low quality factor of the solid-state devices becomes an important issue. Another drawback of the solid-state tuning elements is the increased nonlinearity and noise at higher RF power levels. The objective of the research described in this thesis is to investigate the feasibility of using RF microelectromechanical systems (RF-MEMS) technology to develop reconfigurable impedance matching networks. Different types of tunable impedance matching networks with improved impedance tuning range, power handling capability, and lower insertion loss have been developed. Another objective is to investigate the realization of a fully integrated one-chip solution by integrating MEMS devices in standard processes used for RF integrated circuits (RFICs). A new CMOS-MEMS post-processing technique has been developed that allows the integration of tunable RF MEMS devices with vertical actuation within a CMOS chip. Various types of CMOS-MEMS components used as tuning elements in reconfigurable RF transceivers have been developed. These include tunable parallel-plate capacitors that outperform the available CMOS solid-state varactors in terms of quality factor and linearity. A tunable microwave band-pass filter has been demonstrated by employing the proposed RF MEMS tunable capacitors. For the first time, CMOS-MEMS capacitive type switches for microwave and millimeter-wave applications have been developed using TSMC 0.35-µm CMOS process employing the proposed CMOS-MEMS integration technique. The switch demonstrates an excellent RF performance from 10-20 GHz. Novel MEMS-based reconfigurable impedance matching networks integrated in standard CMOS technologies are also presented. An 8-bit reconfigurable impedance matching network based on the distributed MEMS transmission line (DMTL) concept operating at 13-24 GHz is presented. The network is implemented using standard 0.35-µm CMOS technology and employs a novel suspended slow-wave structure on a silicon substrate. To our knowledge, this is the first implementation of a DMTL tunable MEMS impedance matching network using a standard CMOS technology. A reconfigurable amplifier chip for WLAN applications operating at 5.2 GHz is also designed and implemented. The amplifier achieves maximum power gain under variable load and source impedance conditions by using the integrated RF-MEMS impedance matching networks. This is the first single-chip implementation of a reconfigurable amplifier using high-Q MEMS impedance matching networks. The monolithic CMOS implementation of the proposed RF MEMS impedance matching networks enables the development of future low-cost single-chip RF multiband transceivers with improved performance and functionality.

Permanent deformation in the form of creep is added to a one-dimensional model of a radio-frequency micro-electro-mechanical system (RF-MEMS). Due to uncertainty in the material property values, calibration under uncertainty is carried out through comparison to experiments in order to determine appropriate boundary conditions and material property values. Further uncertainty in the input parameters, in the form of probability distribution functions of geometric device properties, is included in simulations and propagated to the device performance as a function of time. The effect of realistic power-law grain size distributions on the creep response of thin RF-MEMS films is examined through the use of a finite volume software suite designed for the computational modelling of MEMS. It is seen that the use of a realistic height-dependent power-law distribution of grain sizes in the film in place of a uniform grain size has the effect of increasing the simulated creep rate and the uncertainty in its value. The effect is seen to be the result of the difference between the model with a homogeneous grain size and the model with a non-homogeneous grain size. Realistic variations in the grain size distribution for a given film are seen to have a smaller effect. Finally, in order to incorporate variations in thickness in manufactured devices, variation in the thickness of the membrane across the length and width is considered in a 3D finite element model, and variation of thickness along the length is added to the earlier one-dimensional RF-MEMS model. Estimated uncertainty in the film profile is propagated to selected device performance metrics. The effect of film thickness variation along the length of the film is seen to be greater than the effect of variation across the width.

Les microcommutateurs MEMS ohmiques comportent un contact électrique sous très faible force, très sensible à des paramètres difficiles à maîtriser. Ce contact a été l'objet d'une méthode de modélisation développée précédemment au LAAS-CNRS, dont le principe consiste à effectuer une simulation par éléments finis du contact mécanique avec les données AFM puis évaluer analytiquement la résistance électrique. Cette thèse a pour objectif d'évaluer les possibilités d'extension de cette méthode à des simulations multiphysiques.La thèse comporte une partie dédiée à la validation de la simulation mécanique par éléments finis par rapport à des résultats expérimentaux obtenus précédemment.Des simulations multiphysiques sont alors réalisées et les résultats en termes de résistance électrique sont comparés avec des résultats expérimentaux. On observe une très forte sous estimationde la résistance électrique, et donc des élévations de température. Ce constat est attribué à la présence de films isolants en surface d'une au moins des surfaces de contact.Enfin, des modèles qui incluent un film isolant sont développés avec une géométrie simplifiée d'aspérité. Les modèles les plus intéressants incluent des "nanospots": le film isolant est parsemé de zones conductrices, de très faibles dimensions. Les résultats permettent de cerner les caractéristiques typiques possibles de la géométrie dans cette configuration. / MEMS ohmic microswitches include very low force electrical contacts. These are very sensitive to parameters which reveal difficult to control. A previously developed modelization method consists in computing mechanical contact using finite elements, then estimating electrical resistance using analytical expressions. Here we focus on the possibilities of multiphysical finite element computations instead.Validation of the contact mechanical computation is first attempted, based on experimental results of previous works. Multiphysical contact computations are carried out. Resulting electrical contact resistance isfound to be much lower than experimental results. The presence of insulating surface films is supposedly the cause for that. Eventually, a simplified geometry for asperities is used to build models with insulating films.The most relevant models feature “nanospots”: some very small conductive areas are scattered on the contact area. The results allow us to determine some possible geometry configurations that could lead to contact resistance values such as those measured on real devices.