MEMS TECHNOLOGY FOR ADVANCED TELECOMMUNICATION APPLICATIONS

RF MEMS (radio frequency micro electro mechanical systems) technology holds great promise for wireless communication and sensor systems. Excellent MEMS switching devices have recently been developed, but because of packaging problems, no commercial integrated product exists. The objective of the ongoing work at CFD Research Corporation (CFDRC) and Morgan Research Corporation (MORGAN) is to develop novel packaging concepts, design tools, and demonstrated RF MEMS packaged devices for high frequency applications.

A novel eight-mask fabrication process for the integration of low-temperature-superconducting niobium (Nb) RF circuits with gold-based RF microelectromechanical system (MEMS) switches is proposed. DC-contact and capacitive-contact RF MEMS switches integrated with Nb-based transmission lines are presented for the first time. A comparison of the RF performance of the switches at room and cryogenic temperatures indicate that the proposed gold-based MEMS fabrication process did have a major impact on the superconducting characteristics of Nb. A switched capacitor bank is also designed, implementing a dc-contact RF MEMS switch. The measured results of the capacitor bank show the variation of the capacitance value from 0.22 to 5.25 pF at 4 K. A thermal analysis of the devices under test (DUTs) is also performed, and an investigation is carried out to minimize the thermal loss between the chuck and the DUT.

Micro-Electromechanical Systems (MEMS) has been regarded as one of the most promising technologies for the 21st Century. Recently, some highlight areas attract great attention including Inertial MEMS, Optic MEMS, RF MEMS, BioMEMS, Power MEMS, and NEMS. The state of arts on MEMS research in China is briefly introduced and research activities in Northwestern Polytechnical University such as MEMS CAD tool, inertial MEMS devices, flexible substrate for MEMS integration, micro mirror, micro battery and three dimension measurement are demonstrated.

Over the past three decades, Micro-Electro-Mechanical Systems (MEMS) have provided advancements in different fields of electronics. MEMS technology also enabled microwave and antenna engineers to produce some existing and novel radio-frequency components resulting as a new research field, namely RF MEMS. The use of MEMS technology for RF and microwave applications promises to solve many limitations, RF MEMS can reduce manufacturing cost, size, weight, and improve performance and battery life. In terms of performance, MEMS can provide low-loss switching and tuning of microwave circuits with higher dynamic range, lour cost, and greater flexibility than the competing techniques. In this paper we proposed a reconfigurable patch Antenna structures using MEMS switches. This concept leads to reduction in space and multiple functionality from a single antenna structure.

This paper presents a high-performance substrate-integrated-waveguide RF microelectromechanical systems (MEMS) tunable filter for 1.2-1.6-GHz frequency range. The proposed filter is developed using packaged RF MEMS switches and utilizes a two-layer structure that effectively isolates the cavity filter from the RF MEMS switch circuitry. The two-pole filter implemented on RT/Duroid 6010LM exhibits an insertion loss of 2.2-4.1 dB and a return loss better than 15 dB for all tuning states. The relative bandwidth of the filter is 3.7 ± 0.5% over the tuning range. The measuredQuof the filter is 93-132 over the tuning range, which is the best reportedQin filters using off-the-shelf RF MEMS switches on conventional printed circuit board substrates. In addition, an upper stopband rejection better than 28 dB is obtained up to 4.0 GHz by employing low-pass filters at the bandpass filter terminals at the cost of 0.7-1.0-dB increase in the insertion loss.

In this paper, a fully integrated CMOS and high voltage compatible RF MEMS (radio frequency microelectromechanical systems) technology is proposed and demonstrated for the first time. The high performance RF MEMS switch, high voltage MOSFET, and CMOS devices are all obtained using a simple process. The fabricated high voltage device has a breakdown voltage of over 35V. The MEMS capacitive switch fabricated on a high resistivity SOI substrate and with high-k dielectric (HfO/sub 2/) exhibits a low insertion loss (0.14dB at 5GHz) and a good isolation (9.5dB at 5GHz). This technology demonstrates the feasibility of building fully integrated RF systems for wireless communication applications.

<para xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink"> A self-aligned fabrication process for capacitive fixed-fixed beam RF microelectromechanical system (MEMS) components is disclosed. It enables the scaling of the critical dimensions and reduces the number of processing steps by 40% compared with a conventional RF MEMS fabrication process. RF MEMS varactors with beam lengths of 30 <formula formulatype="inline"><tex>${\rm \mu}\hbox{m}$</tex></formula> are demonstrated by using the self-aligned fabrication process, and the performance of a four-by-four RF MEMS varactor bank is discussed as well. At 20 GHz, the measured capacitance values range between 180.5 and 199.2 fF. The measured capacitance ratio is 1.15 when a driving voltage of 35 V is applied, and the measured loaded <formula formulatype="inline"> <tex>${Q}$</tex></formula> -factor ranges between 14.5 and 10.8. The measured cold-switched power handling is 200 mW. <formula formulatype="inline"><tex>$\hfill$</tex> </formula>[2008-0018] </para>

Micro Electro Mechanical Systems (MEMS) Switches have become very popular in the Electronics industry and we need to carefully select beam material and structural parameters for reliability and better performance. A variety of materials can be used as beam material in RF MEMS switches. The cantilever beam is used to change the state of RF switch and for actuation is made mostly using aluminum, copper, gold, molybdenum, nickel and platinum. This paper investigates which is the best material to be used for beam for achieving lower pull-in voltage and also represents the effect of structural parameters such as air gap and beam thickness on the performance of MEMS series switches. Characterization of cantilever MEMS switches is carried out with 3D simulation using COMSOL Multiphysics based on Finite Element Method [FEM]. Reduction of Pull-in voltage can be done by carefully selecting beam material and it can further be reduced by decreasing air gap and beam thickness.

This paper explores the usefulness of RF MEMS and reconfigurable antennas in the context of modern communication systems and other applications. Simulation studies on a fractal antennas with switches and phase shifters provide beam steering and beam scanning characteristics. A brief description of the design aspects of two MEMS based coplanar waveguide (CPW) phase shifters for microwave and millimeter wave antenna applications are also provided here. One phase shifter design consists of a unique bilateral interdigital structure on a silicon substrate deposited with a thin film of electrically tunable barium strontium titanate. The dielectric constant of the thin film, and hence the effective permittivity of the transmission line changes by the application of a bias voltage. The second device is a distributed microelectromechanical system (MEMS) phase shifter fabricated on a high resistivity silicon substrate using microstereolithography technique is presented here. The distributed MEMS phase shifter consists of a high-impedance CPW transmission line and several MEMS bridges of uniform height. By applying a voltage the height of these bridges can be adjusted. This results in a variation in the distributed capacitance of the segment of the transmission line, which manifests in the phase shift at the output terminal. The fabrication procedure described here shows significant promise for the use of microstereolithography techniques for RF MEMS devices.

In this paper, rectification methods for micro-energy harvesting systems are proposed and estimated. We present introduce two methods. The first is a mechanical rectification. The second is semiconducting rectification which is fabricated through MEMS technology. Vibration-driven micro-energy harvesting by micro electro mechanical systems (MEMS) technology is needed because the electrical power consumption of our society is increasing. But most of the vibration-driven generators supply alternating-current and intermittent electro energy. For using, it is necessary to construct the micro energy system supplying direct current. Therefore, we present the micro energy system that is composed of vibration-driven micro-energy harvesting, rectification and energy storage. In particular, we consider the rectification in this paper. In designing, we consider that vibration-driven micro-energy harvestings are developed through MEMS technology. Compatibility between semiconductor process and MEMS process is hard to achieve in materials, temperature, contamination and so on.

This paper reports on the experimental and theoretical characterization of RF microelectromechanical systems (MEMS) switches for high-power applications. First, we investigate the problem of self-actuation due to high RF power and we demonstrate switches that do not self-actuate or catastrophically fail with a measured RF power of up to 5.5 W. Second, the problem of switch stiction to the down state as a function of the applied RF power is also theoretically and experimentally studied. Finally, a novel switch design with a top electrode is introduced and its advantages related to RF power-handling capabilities are presented. By applying this technology, we demonstrate hot-switching measurements with a maximum power of 0.8 W. Our results, backed by theory and measurements, illustrate that careful design can significantly improve the power-handling capabilities of RF MEMS switches.

In this paper, we report monolithic integration of MEMS (micro electro mechanical systems) actuators and high-voltage driver circuits into a silicon chip. Driver circuits of up to 40 V were prepared on an 8-/spl mu/m-thick SOI (silicon-on-insulator) wafer by the DMOS (double-diffused metal oxide semiconductor) processes, after which MEMS electrostatic actuators were integrated into an identical SOI layer by post-processing using DRIE (deep reactive ion etching). This technique opens up a new way of high-voltage ASIC (application specific integrated circuit) for MEMS designer. As a prototype application model, we have developed microlens optical scanners and other elementary MEMS electrostatic actuators with multi-channel driver circuits.

Design, fabrication and characterization of miniature RF MEMS switched capacitor based phase shifter

The water condensation is important for wide range of industrial systems such as condensers and heat exchangers of steam power plants and refrigerators. The condensation generally has two patterns; filmwise condensation (FWC) and drop-wise condensation (DWC). DWC has one-tenth higher heat transfer coefficient than that of FWC. It has been pointed out by many investigators that DWC occurs on the hydrophobic surface and FWC occurs on hydrophilic surface. However, the durability of those hydrophobic effects was not clear enough. In order to maintain a sufficiently long DWC, it is important to understand the effect of the surface property and structure on the condensation surface in more detail. The recent advancement of MEMS (Micro Electro Mechanical System) technology enables us to change the physical nature the surface in the micro scale. It is expected that the hydrophobic surface by the MEMS technology may kept DWC for a longer time. In the present paper, we experimentally investigate the effects of thin metal film and micro structured surface on condensation pattern. Especially, our condensation experiments were performed with the micro structured surfaces by using etching and the metal thin film surfaces by sputtering for approximately 24 hours. Silicon (Si) wafer was used as a basic surface. For the metal thin films surface, we used sputtered Lead (Pb) and Titanium (Ti) on Si surface. For the micro structured surfaces, micro-structured grid was etched on Si surface with several conditions. In order to obtain the relation between the condensation pattern and surface condition, the surface conditions were measured by laser micro-scope, contact angle meter and atomic force microscope (AFM). For the metal thin films surface, condensation patterns on thin Pb film surface showed DWC. Meanwhile, condensation patterns on thin Ti surfaces showed FWC. From our results, the adsorption forces decreased with increasing contact angle on DWC for Pb. On the other hand, the adsorption forces increased with decreasing contact angle on FWC for Ti. For the micro structured surfaces, condensation pattern was FWC and contact angle decreased in our experimental results. This is because that the condensed water is accumulated in the groove on the micro structure surface.

Optical MEMS (micro electro mechanical systems) have been used to reduce size, weight and costs of any kind of optical systems very successfully starting in the last decades. Scientists at Fraunhofer IPMS invented a resonant drive for 1-d and 2-d MEMS scanning mirror devices. Besides mirrors also scanning gratings have been realized. Now, rapidly growing new applications demand for enhanced functions and further miniaturization. This task cannot be solved by simply putting more functionality into the MEMS chip, for example grating and slit structures, but by three dimensional hybrid integration of the complete optical system into a stack of several functional substrates. Here we present the optical system design and realization strategy for a scanning grating spectrometer for the near infrared (NIR) range. First samples will be mounted from single components by a bonder tool (Finetech Fineplacer Femto) but the option of wafer assembly will be kept open for future developments. Extremely miniaturized NIR spectrometer could serve a wide variety of applications for handheld devices from food quality analysis to medical services or materials identification.