Radio Frequency Microelectromechanical Research Articles

Comprehensive Review of RF MEMS Switches in Satellite Communications.

The miniaturization and low power consumption characteristics of RF MEMS (Radio Frequency Microelectromechanical System) switches provide new possibilities for the development of microsatellites and nanosatellites, which will play an increasingly important role in future space missions. This paper provides a comprehensive review of RF MEMS switches in satellite communication, detailing their working mechanisms, performance optimization strategies, and applications in reconfigurable antennas. It explores various driving mechanisms (electrostatic, piezoelectric, electromagnetic, thermoelectric) and contact mechanisms (capacitive, ohmic), highlighting their advantages, challenges, and advancements. The paper emphasizes strategies to enhance switch reliability and RF performance, including minimizing the impact of shocks, reducing driving voltage, improving contacts, and appropriate packaging. Finally, it discusses the enormous potential of RF MEMS switches in future satellite communications, addressing their technical advantages, challenges, and the necessity for further research to optimize design and manufacturing for broader applications and increased efficiency in space missions. The research findings of this review can serve as a reference for further design and improvement of RF MEMS switches, which are expected to play a more important role in future aerospace communication systems.

Implementation of Highly Reliable Contacts for RF MEMS Switches.

A contact is the key structure of RF MEMS (Radio Frequency Microelectromechanical System) switches, which has a direct impact on the switch's electrical and mechanical properties. In this paper, the implementation of highly reliable contacts for direct-contact RF MEMS switches is provided. As a soft metal material, gold has the advantages of low contact resistance, high chemical stability, and mature process preparation, so it is chosen as the metal material for the beam structure as well as the contacts of the switch. However, a Pt film is used in the bottom contact area to enhance the reliability of the contact. Three kinds of contacts with various shapes are fabricated using different processes. Particularly, a circular-shaped contact is obtained by dry/wet combined processes. The detailed fabrication process of the contacts as well as the Pt film on the bottom contact area are given. The experimental test shows that the contact shape has little effect on the RF performance of the switches. However, the circular contact shows better reliability than other contacts and can work well even after 1.2 × 109 cycles.

Low-Voltage and High-Reliability RF MEMS Switch with Combined Electrothermal and Electrostatic Actuation.

In this paper, we report a novel laterally actuated Radio Frequency (RF) Microelectromechanical Systems (MEMS) switch, which is based on a combination of electrothermal actuation and electrostatic latching hold. The switch takes the advantages of both actuation mechanisms: large actuation force, low actuation voltage, and high reliability of the thermal actuation for initial movement; and low power consumption of the electrostatic actuation for holding the switch in position in ON state. The switch with an initial switch gap of 7 µm has an electrothermal actuation voltage of 7 V and an electrostatic holding voltage of 21 V. The switch achieves superior RF performances: the measured insertion loss is −0.73 dB at 6 GHz, whereas the isolation is −46 dB at 6 GHz. In addition, the switch shows high reliability and power handling capability: the switch can operate up to 10 million cycles without failure with 1 W power applied to its signal line.

Finite element based contact analysis of radio frequency MEMs switch membrane surfaces

Finite element simulations were performed to determine the contact behavior of radio frequency (RF) micro-electro-mechanical (MEM) switch contact surfaces under monotonic and cyclic loading conditions. Atomic force microscopy (AFM) was used to capture the topography of RF-MEM switch membranes and later they were analyzed for multi-scale regular as well as fractal structures. Frictionless, non-adhesive contact 3D finite element analysis was carried out at different length scales to investigate the contact behavior of the regular-fractal surface using an elasto-plastic material model. Dominant micro-scale regular patterns were found to significantly change the contact behavior. Contact areas mainly cluster around the regular pattern. The contribution from the fractal structure is not significant. Under cyclic loading conditions, plastic deformation in the 1st loading/unloading cycle smooth the surface. The subsequent repetitive loading/unloading cycles undergo elastic contact without changing the morphology of the contacting surfaces. The work is expected to shed light on the quality of the switch surface contact as well as the optimum design of RF MEM switch surfaces.

Approaching attometer laser vibrometry.

The heterodyne two-beam interferometer has been proven to be the optimal solution for laser-Doppler vibrometry (LDV) regarding accuracy and signal robustness. The theoretical resolution limit for a two-beam interferometer of laser class 3R (up to 5 mW visible measurement-light) is in the regime of a few femtometer per square-root Hertz and well suited to study vibrations in microstructures. However, some new applications of radio-frequency microelectromechanical (RF-MEM) resonators, nanostructures, and surface-nano-defect detection require resolutions beyond that limit. The resolution depends only on the photodetector noise and the sensor sensitivity to specimen displacements. The noise is already defined in present systems by the quantum nature of light for a properly designed optical sensor and more light would lead to an inacceptable influence like heating of the tiny specimen. Noise can only be improved by squeezed-light techniques which require a negligible loss of measurement light which is impossible to realize for almost all technical measurement tasks. Thus, improving the sensitivity is the only path which could make attometer laser vibrometry possible. Decreasing the measurement wavelength would increase the sensitivity but would also increase the photon shot noise. In this paper, we discuss an approach to increase the sensitivity by assembling an additional mirror between interferometer and specimen to form an optical cavity. A detailed theoretical analysis of this setup is presented and we derive the resolution limit, discuss the main contributions to the uncertainty budget, and show a first experiment proving the sensitivity and resolution improvement of our approach.

Viscoelasticity Recovery Mechanism in Radio Frequency Microelectromechanical Switches

Radio frequency microelectromechanical system (RF MEMS) switches require a lifetime of 20 years, during which the devices must operate without failure. During operation, the RF MEMS switches are subjected to prolonged actuation which may induce the problems of charge trapping and mechanical relaxation leading to stiction of the moving membrane. In this paper, we suggest an innovative recovery procedure that allows to avoid the stiction. At regular intervals, the switch is opened and an electrical current forced through the suspended membrane can effectively fully recover the switch. Using the topography analysis, we show that the restoring mechanism is based on the recovery of the mechanical properties of the moving bridge during the current flow. The validity of the procedure is demonstrated with the application of the recovery system on several devices for 20 consecutive cycles.

Design and Simulation of Radio Frequency Micro Electro Mechanical Capacitive Shunt Switches

Radio Frequency Micro ElectroMechanical (RFMEM) switches play an important role in microwave switching. The demand for low voltage, low insertion loss, high Isolation RF MEMS capacitive switches for high frequency (10-40GHz) applications has led to the development of MEMS based switching devices in the RF domain. This work reports the design and simulation of RF MEMS capacitive shunt switches for K and Ka bands. The switching element consists of a thin gold membrane which gets actuated over a transmission line under an applied bias. The dc simulation is carried out in CoventorWare and the designed switch is found to actuate at 18.75 volts. HFSS simulation results demonstrate an acceptable RF performance with an insertion loss of 0.25 dB in the range 20-35GHz and an isolation better than 20dB beyond 20GHz.

Control of Bouncing in MEMS Switches Using Double Electrodes

This paper presents a novel way of controlling the bouncing phenomenon commonly present in the Radio Frequency Microelectromechanical Systems (RF MEMS) switches using a double-electrode configuration. The paper discusses modeling bouncing using both lumped parameter and beam models. The simulations of bouncing and its control are discussed. Comparison between the new proposed method and other available control techniques is also made. The Galerkin method is applied on the beam model accounting for the nonlinear electrostatic force, squeeze film damping, and surface contact effect. The results indicate that it is possible to reduce bouncing and hence beam degradation, by the use of double electrodes.

A Novel Technique to Alleviate the Stiction Phenomenon in Radio Frequency Microelectromechanical Switches

Radio frequency (RF) microelectromechanical system (MEMS) switches subject to long term actuation suffer from narrowing of the actuation and release voltages. This can lead to the failure of the device when the device remains actuated without external biasing due to stiction effects. The stiction phenomenon is one of the most challenging problems in RF MEMS switches, especially in applications where these devices have to remain actuated for an extended period of time (months or even years). In this letter, we show a novel recovery technique to alleviate the stiction phenomenon significantly increasing the device lifetime. In particular, we show how the flowing of a small current through the suspended membrane can be used to fully restore the device properties to its fresh conditions in just a few seconds.

Effects of thermally induced packaging stress on a distributed RF MEMS phase shifter

This paper presents an experimental study of the influence of thermally induced packaging stress from a die-attaching process on the behavior of a distributed Radio Frequency Microelectromechanical Systems (RF MEMS) phase shifter. The phase shifter consists of a high-impedance coplanar waveguide transmission line periodically loaded with 16 shunt capacitive MEMS switches. It shows that the thermal stress has an apparent effect on the phase shift characteristic of the device. Up to 13 GHz, the variation of the phase shift before and after the packaging process can be as large as about 160°. Nonuniformity of the stress across the chip is used to explain this behavior. The results presented here suggest that the stress nonuniformity has to be considered during the package design of the distributed RF MEMS device.

RF MEMS switches for smart antennas

In this paper novel V-shaped and Z-shaped thermally actuated radio frequency (RF) MicroElectroMechanical Systems (MEMS) switches are designed and fabricated for the application of smart antennas. The switches are driven by a metal electrothermal actuator, which is able to generate large displacement and high contact force at lower temperatures. The MEMS switches utilizing the parallel beam actuator achieved 8 μm displacement. RF performances are improved by suspending the switching structures 25 μm above the substrate, thereby reducing the loss in the substrate. ON state insertion loss of −0.42 dB at 10 GHz, OFF state isolation of −40 dB at 10 GHz and return loss better than of −20 dB at 10 GHz for bidirectional Z-shaped thermally actuated RF MEMS switch are achieved on the low resistivity silicon substrate.

Modular Ka-band switch matrices using two RF MEMS technologies

This paper presents the design and measurement of two different switch matrix modules based on Radio Frequency Microelectromechanical System (RF MEMS) switches. The operational frequency range is between 25.5 GHz and 26.5 GHz for data links between a Geostationary Earth Orbit (GEO) relay satellite and Low Earth Orbit (LEO) satellites. The switch matrix implements a key functionality for tracking the incident signals of the LEO satellites on the receive feed antenna array of the GEO satellite's reflector antenna. Two different technologies are used to build simplified switch matrix modules suitable for realizing the full functionality switching matrix. Rogers RT/Duroid 5880 with commercially available RF MEMS is used to build the first module, while EADS in house RF MEMS are integrated in Rogers Ultralam 3850 Liquid Crystal Polymer (LCP) for the second module. Maximum insertion losses of 8.5 dB and 10.2 dB have been measured for the Rogers RT/Duroid 5880 and the LCP module, respectively. Isolation is higher than 45 dB and a minimum return loss of 15 dB is shown. Finally, the measured losses in the LCP module are analyzed and suitable improvements are discussed.

Analytical design of polymer-encapsulated radio frequency microelectromechanical devices

An analytical design of radio frequency microelectromechanical (RF MEMS) devices and fabrication and encapsulation results is discussed. The encapsulated MEMS device is an in-plane variable capacitor (varactor), continuously tuned up to 115% at 3.25 V, showing a Q factor of 49 at 1 GHz at zero bias and self-resonance frequency above 5 GHz. The 60-μm-thick device measures 0.6 mm×0.6 mm and is fabricated using high-aspect ratio single-crystal and polysilicon technology, having an air gap of 0.8 μm for tuning and 2 μm for actuation. The effect of gap size, substrate doping, and gold coating on Q is studied. The wafer-level encapsulation is done by the thermal decomposition of a sacrificial polymer through a polymer overcoat at 130°C-150°C, followed by gold evaporation to provide a degree of hermeticity. The overcoat polymer is patterned instead of screen printed, which defines the package boundary, providing a small amount of interconnection. The encapsulated device measures 0.7 mm×0.7 mm, which is only 35% larger than the MEMS device. The insertion loss of the 1 μm/20 μm gold/Avatrel package is measured to be 1.4 dB at 1 GHz and 1.51 dB at 5 GHz, and the calculated nitrogen permeability is less than 1 Barrer. The temperature stability of the rest and the maximum capacitance is better than 7%, in the range of −30-50 °C.

RF MEMS Switch and Its Applications

RF MEMS (Radio Frequency Microelectromechanical System) has seen an amazing growth in the past 20 years. It has immense commercial and defense potential due to its low loss, low power consumption and superior RF performances. In this article, RF MEMS and its applications are reviewed. Special emphasis is on the RF MEMS switches and MEMS phase shifters investigated in IMETU (Institute of Microelectronics of Tsinghua University). A variety of RF MEMS switches with different configurations are introduced. The MEMS switch present unique properties for the application in future miniaturized antenna and radar system. The prototype illustrates the RF MEMS switch as a fundamental structure in signal path control, structural optimization, and match circuits is very promising to be used in future reconfigurable radar and antenna system, which will address to the application not only in the mobile terminal but also the high end wireless sensor network.

An output error algorithm for piecewise affine system identification

Within Hybrid systems, piecewise affine systems are a common class to be identified from input/output data. In this paper an improved algorithm for identifying piecewise affine systems is developed. The algorithm stems from clustering-based system identification. An affine output error algorithm is used to identify final models. The performance of the new Piecewise Affine Output Error (PWA-OE) algorithm is demonstrated using experimental data from a Radio Frequency MicroElectroMechanical Systems switch. Compared to the existing state-of-the-art, the PWA-OE algorithm generates a potential 62% improvement in model coefficient accuracy. Furthermore the PWA-OE algorithm is less sensitive to two additional input parameter selections.

Low power digital TTL command for 1 bit 60 GHz RF MEMS phase shifter

This paper presents a circuit used to actuate Radio Frequency MicroElectroMechanical Systems (RF MEMS) based phase shifters for 60GHz beam forming. Wireless transmission in the 60GHz band show a dramatic free space loss, thus making it mandatory to use antennas with high gain in a desired direction. Beam forming is then necessary to optimize the link budget between communicating nodes. Antenna arrays can be used for beam forming. The work done at LAAS was aiming to provide RF MEMS based phase shifters working with a standard digital command. RF MEMS commonly have high actuation voltages usually obtained with charge pumps. This paper presents a full 1bit phase shifter with a digital translation part, an analog DC–DC converter, and an RF MEMS based loaded line phase shifter for 60GHz signals. This converter is built using boost converters as an alternative to the use of charge pumps for driving RF MEMS in the field of wireless communications. Boost converters, despite relatively high current peaks, allow shorter settling times compared to charge pumps.

Interconnection Characteristics of Rivet Packaging for Radio Frequency Microelectromechanical Systems Applications

Interconnection Characteristics of Rivet Packaging for Radio Frequency Microelectromechanical Systems Applications

Characterization and Adhesion of Interacting Surfaces in Capacitive RF MEMS Switches Undergoing Cycling

The performance and reliability of capacitive-type Radio Frequency Microelectromechanical Systems (RF MEMS) switches are affected by interfacial interactions such as strong attractive adhesion forces that could cause the switch to get temporarily or permanently stuck, thus rendering the device nonfunctional. Such adhesion forces could be induced and progressively increase during cycling by mechanical surface changes, such as increased real contact area or electrical effects such as increased electrostatic forces by dielectric charging. Both effects can occur simultaneously, which makes the characterization of capacitive switch behavior more complex than metal-to-metal switches. In this work, capacitive RF MEMS switches with Ti-on-silicon nitride contact surfaces were fabricated and tested for different numbers of cycles. After cycling, the Ti beam and Si3N4 dielectric contact surfaces were exposed and examined topographically (using Atomic Force Microscopy), chemically (using Time-Of-Flight Secondary Ion Mass Spectrometry) and nanomechanically (using nanoindentation) to measure surface changes induced by cycling. Such surface changes could explain adhesion behavior and failure of capacitive RF MEMS switches. Topographical roughness analysis showed that physical surface changes occurred early (during the first few hundred cycles). Chemical and nanomechanical analyses also showed surface property changes with cycling, in agreement with the roughness analysis. Therefore, RF MEMS switch surface changes occur with cycling and such changes are readily detectable and could adversely affect (increase) interactive adhesion forces and thus render the switch inoperable.

CMOS Compatible RF MEMS Switches with Serpentine Springs

This paper describes a serpentine flexure spring design and fabrication process development for radio frequency microelectromechanical (RF MEMS) capacitive switches with coplanar waveguide (CPW) lines. Sputtered tungsten is employed as the CPW line conductor instead of Au, a non-Si compatible material. The bridge membrane is fabricated from Al. The materials and fabrication process can be integrated with CMOS and SOI technology to reduce cost. Results show the MEMS switch has excellent performance with insertion loss 0.3dB, return loss -27dB at 30GHz and high isolation -30dB at 40GHz. The process developed promises to simplify the design and fabrication of RF MEMS on silicon.

직접접촉식 RF MEMS 스위치에서의 미소용접 현상 억제

본 연구에서는 고 전력의 RF 신호용 직접 접촉식 스위치에서 문제가 되고 있는 접촉부위에서의 미소용접에 의한 점착 현상을 감소시키기 위해, 고 융점 금속인 텅스텐(W)과 몰리브덴(Mo)을 스위치 접촉 부위에 코팅하여 스위치의 성능을 분석하였다. 스위치의 삽입손실과 신호격리도, 전력 손실 등의 변화를 네트워크 분석기, 전력 측정기 등을 통하여 측정하였다. 측정결과로부터 RF 신호 전송에 있어서 낮은 입력 전력에서는 고융점 금속이 금(Au)보다 접촉저항이 더 크지만 입력 전력이 커지면 비교적 낮은 비저항의 고융점 금속을 사용하는 것이 고전력 전송 및 수명 연장에 있어서 유리함을 밝혀냈다. In this paper, a new method for suppressing microwelding on the RF MEMS (Radio Frequency Microelectromechanical System) direct contact switches is introduced. Two kinds of refractory metals, tungsten and molybdenum were coated onto the contact point of the switches and the effect of the coating was examined. The changes in insertion loss and isolation at the switch were measured by using network analyzer and power loss was evaluated by power measurement. The results revealed that while tungsten and molybdenum showed higher contact resistance than gold in low input power range, they enhanced the power handling capability and reliability of the switches in high input power region.