219 research outputs found

    MEMS switches having non-metallic crossbeams

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    A RF MEMS switch comprising a crossbeam of SiC, supported by at least one leg above a substrate and above a plurality of transmission lines forming a CPW. Bias is provided by at least one layer of metal disposed on a top surface of the SiC crossbeam, such as a layer of chromium followed by a layer of gold, and extending beyond the switch to a biasing pad on the substrate. The switch utilizes stress and conductivity-controlled non-metallic thin cantilevers or bridges, thereby improving the RF characteristics and operational reliability of the switch. The switch can be fabricated with conventional silicon integrated circuit (IC) processing techniques. The design of the switch is very versatile and can be implemented in many transmission line mediums

    Design, fabrication and characterisation of silicon carbide resonators

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    Micro-electro-mechanical systems (MEMS) are integrated mechanical and electrical elements realised with micro-fabrication technology and employed as sensors and actuators. The integration of reliable MEMS switches and resonators into transceiver devices is a challenging and attractive solution to increase the efficiency and reduce the power consumption. Silicon carbide (SiC) is an excellent candidate for developing robust and reliable high frequency MEMS for transceivers applications due to its unique mechanical properties.This thesis presents the design, fabrication and characterisation of 3C-SiC micromechanical vertical resonators. New device architectures have been developed for the study of the electro-mechanical behaviour of the devices with the aim of optimising the actuation efficiency, increasing the resonant frequency and obtaining new device functions.A process for the fabrication of single or poly-crystalline 3C-SiC cantilevers, bridges and rings has been developed with the option of integrating top electrodes made of aluminium (Al) or lead zirconium titanate (PZT). The crystal structure and quality of the SiC layers have been evaluated with X-ray diffraction and Raman spectroscopy. A Young's Modulus of ~ 440 GPa has been calculated for the single crystalline SiC from the mechanical resonant frequency of the fabricated single material cantilevers. The fabricated Al/SiC bridges and rings have been actuated and driven into resonance electro-thermally. It has been found that wide Al electrodes applied close to the beams' anchor can maximise the induced displacement and vibration amplitude thus improving the actuation efficiency. Resonant frequencies in the MHz range have been obtained with the ring architectures therefore achieving higher frequencies compared to beam architectures. In addition, electro-thermal mixing of two input frequencies has been demonstrated and performed with the fabricated Al/SiC structures. Furthermore, piezo-electric transduction has been used for actuating the PZT/SiC cantilevers and for sensing the devices' resonance electrically. The design of the PZT piezo-electric active layer has been shown to influence strongly the devices' resonant frequency and has been optimised to enhance the electrical output by decreasing the electrodes length thus decreasing the feedthrough capacitance.The results obtained in this work can be used for the implementation of SiC MEMS mixer-filters with electro-thermal actuation and piezo-electric sensing for transceiver applications

    Radio Frequency Microelectromechanical Systems in Defence and Aerospace

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    For all onboard systems applications, it is important to have very low-loss characteristics and low power consumption coupled with size reduction. The controls and instrumentation in defence and aerospace continually calls for newer technologies and developments. One such technology showing remarkable potential over the years is radio frequency microelectromechanical systems (RF MEMS) which have already made their presence felt prominently by offering replacement in radar and communication systems with high quality factors and precise tunability. The RF MEMS components have emerged as potential candidates for defence and aerospace applications. The core theme of this paper is to drive home the fact that the limitations faced by the current RF devices can be overcome by the flexibility and better device performance characteristics of RF MEMS components, which ultimately propagate the device level benefits to the final system to attain the unprecedented levels of performance.Defence Science Journal, 2009, 59(6), pp.568-567, DOI:http://dx.doi.org/10.14429/dsj.59.156

    DEVELOPMENT OF NANO/MICROELECTROMECHANICAL SYSTEM (N/MEMS) SWITCHES

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    Ph.DDOCTOR OF PHILOSOPH

    A micromachined zipping variable capacitor

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    Micro-electro-mechanical systems (MEMS) have become ubiquitous in recent years and are found in a wide range of consumer products. At present, MEMS technology for radio-frequency (RF) applications is maturing steadily, and significant improvements have been demonstrated over solid-state components.A wide range of RF MEMS varactors have been fabricated in the last fifteen years. Despite demonstrating tuning ranges and quality factors that far surpass solid-state varactors, certain challenges remain. Firstly, it is difficult to scale up capacitance values while preserving a small device footprint. Secondly, many highly-tunable MEMS varactors include complex designs or process flows.In this dissertation, a new micromachined zipping variable capacitor suitable for application at 0.1 to 5 GHz is reported. The varactor features a tapered cantilever that zips incrementally onto a dielectric surface when actuated electrostatically by a pulldown electrode. Shaping the cantilever using a width function allows stable actuation and continuous capacitance tuning. Compared to existing MEMS varactors, this device has a simple design that can be implemented using a straightforward process flow. In addition, the zipping varactor is particularly suited for incorporating a highpermittivity dielectric, allowing the capacitance values and tuning range to be scaled up. This is important for portable consumer electronics where a small device footprint is attractive.Three different modelling approaches have been developed for zipping varactor design. A repeatable fabrication process has also been developed for varactors with a silicon dioxide dielectric. In proof-of-concept devices, the highest continuous tuning range is 400% (24 to 121 fF) and the measured quality factors are 123 and 69 (0.1 and 0.7 pF capacitance, respectively) at 2 GHz. The varactors have a compact design and fit within an area of 500 by 100 µm

    A micromachined zipping variable capacitor

    No full text
    Micro-electro-mechanical systems (MEMS) have become ubiquitous in recent years and are found in a wide range of consumer products. At present, MEMS technology for radio-frequency (RF) applications is maturing steadily, and significant improvements have been demonstrated over solid-state components. A wide range of RF MEMS varactors have been fabricated in the last fifteen years. Despite demonstrating tuning ranges and quality factors that far surpass solid-state varactors, certain challenges remain. Firstly, it is difficult to scale up capacitance values while preserving a small device footprint. Secondly, many highly-tunable MEMS varactors include complex designs or process flows. In this dissertation, a new micromachined zipping variable capacitor suitable for application at 0.1 to 5 GHz is reported. The varactor features a tapered cantilever that zips incrementally onto a dielectric surface when actuated electrostatically by a pulldown electrode. Shaping the cantilever using a width function allows stable actuation and continuous capacitance tuning. Compared to existing MEMS varactors, this device has a simple design that can be implemented using a straightforward process flow. In addition, the zipping varactor is particularly suited for incorporating a highpermittivity dielectric, allowing the capacitance values and tuning range to be scaled up. This is important for portable consumer electronics where a small device footprint is attractive. Three different modelling approaches have been developed for zipping varactor design. A repeatable fabrication process has also been developed for varactors with a silicon dioxide dielectric. In proof-of-concept devices, the highest continuous tuning range is 400% (24 to 121 fF) and the measured quality factors are 123 and 69 (0.1 and 0.7 pF capacitance, respectively) at 2 GHz. The varactors have a compact design and fit within an area of 500 by 100 μm

    Are diamonds a MEMS\u27 best friend?

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    Next-generation military and civilian communication systems will require technologies capable of handling data/ audio, and video simultaneously while supporting multiple RF systems operating in several different frequency bands from the MHz to the GHz range [1]. RF microelectromechanical/nanoelectromechanical (MEMS/NEMS) devices, such as resonators and switches, are attractive to industry as they offer a means by which performance can be greatly improved for wireless applications while at the same time potentially reducing overall size and weight as well as manufacturing costs

    RF MEMS/NEMS RESONATORS FOR WIRELESS COMMUNICATION SYSTEMS AND ADSORPTION-DESORPTION PHASE NOISE

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    During the past two decades a considerable effort has been made to develop radio-frequency (RF) resonators which are fabricated using the micro/nanoelectro-mechanical systems (MEMS/NEMS) technologies, in order to replace conventional large off-chip components in wireless transceivers and other high-speed electronic systems.The first part of the paper presents an overview of RF MEMS and NEMS resonators, including those based on two-dimensional crystals (e.g. graphene). The frequency tuning in MEMS/NEMS resonators is then analyzed. Improvements that would be necessary in order for MEMS/NEMS resonators to meet the requirements of wireless systems are also discussed.The analysis of noise of RF MEMS/NEMS resonators and oscillators is especially important in modern wireless communication systems due to increasingly stringent requirements regarding the acceptable noise level in every next generation. The second part of the paper presents the analysis of adsorption-desorption (AD) noise in RF MEMS/NEMS resonators, which becomes pronounced with the decrease of components' dimensions, and is not sufficiently elaborated in the existing literature about such components. Finally, a theoretical model of phase noise in RF MEMS/NEMS oscillators will be presented, with a special emphasize on the influence of the resonator AD noise on the oscillator phase noise

    MEMS Demodulator Based on Electrostatic Actuator

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    This thesis provides analysis and modeling for one of the Micro-Eletro-Mechanical System (MEMS) electrostatic actuator that consists of a micro-plate at the end of a cantilever beam, and introduces different type of MEMS electrostatic actuator; a paddle structure, which is a micro-plate suspended by two cantilever beams on each side. An electrode plate is placed right under the micro-plate to apply an actuation voltage. A step-by-step analysis explains how to obtain each parameter used for the simulations. Static and dynamic models are presented with governing equations for the paddle-shaped MEMS electrostatic actuator. The key findings are that the proposed electrostatic MEMS demodulator architecture taking advantage of the resonance circuit principle not only theoretically work in analytical model, and numerical simulations, but also work in real life. For the Amplitude Modulations (AM) demodulations, simulations with various damping factors are provided, and experimental data are discussed. By measuring the displacement using the phase detector circuit and vibrometer, as a proof of versatility of the demodulation architecture based on the MEMS electrostatic actuator, the results from Frequency Modulations (FM), Amplitude Shift Keying (ASK), and Frequency Shift Keying (FSK) demodulation scheme experiments that are conducted with the physically identical dimensions and configuration are provided. The future plan for further analysis and experiment is discussed at the end
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