Radio Frequency Microelectromechanical Switch Research Articles

Design of high performances electronically reconfigurable antenna arrays by means of parasitic structures and RF-MEMS switches

AbstractThis work explores the development of smart array antennas, able to electronically change their beam patterns through reconfigurable linear, planar, or conformal parasitic structures controlled by mean of a set of electronic switches namely the radio frequency micro-electromechanical switches (RF-MEMS). The motivation of this study is to extend and make competitive the use of reconfigurable antenna arrays in areas such as the Internet of Things (IoT) and wireless sensor networks. These hot research areas require a capillary distribution of sensors characterized by compact dimensions and limited cost. The radiating systems play a key role in such applications since the improvement of the radiating properties can dramatically reduce the power consumption of such sensors and extend their operative range. Standard smart antenna arrays such as phased, or fully adaptive arrays are extremely expensive, expensive and difficult to control. In this work, the use of smart reconfigurable antenna arrays that do not require expensive digital variable phase shifters and attenuators has been considered. The proposed antenna structures are based on reconfigurable parasitic structures, that thanks to suitable RF-MEMs switches are able to obtain a desired beam pattern, by steering the main beam in a given direction, removing eventually interfering signals and maximizing the signal-to-noise ratio SNR. The versatility, simplicity, and low cost of such antennas make them particularly suitable for the emergent wireless sensor networks and IoT applications. Theoretical background, design guidelines, and suggestions for their fabrication are detailed in this work. Some antenna models for different practical applications are designed, optimized, numerically assessed with commercial electromagnetic simulators, and commented to provide a valid alternative to researchers involved in antenna design for IoT applications.

Recent development in reconfigurable dielectric resonator antenna and microwave filter: design and application

SummaryDeveloping wireless communication systems depends on reconfigurable microwave filters (MF) and dielectric resonator antenna (DRA) because the functionality of the various filters and antennas available for a wireless communication system is limited, and reconfigurable DRA and MF are utilized to overcome these limitations. The throughput of a multiantenna system can be achieved with reconfigurable DRA and filter. Various switching strategies and classifications of reconfigurable DRA and MF are presented. The electrical reconfiguration technique is most suitable for developing a reconfigurable DRA and filter among all the switching techniques. In this approach, reconfigurability may be accomplished by utilizing a PIN diode, a varactor diode, and a radio‐frequency microelectromechanical switch (RF‐MEMS). These switches are more reliable, highly efficient, and easily integrated with the microwave circuit. Reconfigurable DRA with machine learning is demonstrated. The application of reconfigurable DRA and filters in cognitive radio (CR) is also demonstrated. Also, the review article focused on the performance parameters, design, and challenges of reconfigurable antenna and MF.

Investigation and Research of High-Performance RF MEMS Switches for Use in the 5G RF Front-End Modules

In this article, based on the developed methodology, the stages of designing two designs of high-performance radio-frequency single-pole single-throw microelectromechanical switches are investigated. These radio-frequency microelectromechanical switches are designed to operate at a central resonant frequency of 3.6 GHz and 3.4 GHz, respectively, as well as to work both in mobile communication devices and in the design of the architecture of 5G mobile networks, in particular in arrays of integrated antennas and radio-frequency interface modules. The manufacture and study of two designed structures are researched. For the first manufactured experimental sample in the open state the insertion loss is no more than -0.69 dB and the reflection loss is -28.35 dB, and in the closed state the isolation value is at least -54.77 dB at a central resonant frequency of 3.6 GHz. For the second in the open state the value of the insertion loss is no more than -0.67 dB and the reflection loss is -20.7 dB, and in the closed state the isolation value is not less than -52.13 dB at the central resonant frequency of 3.4 GHz. Both manufactured experimental samples are characterized by high linearity, as well as a small value of contact resistance in the closed state.

Spectrum-Aware Compact Reconfigurable UHF Antenna for Interweave Cognitive Radio

This paper presents a compact ultra-high frequency (UHF) folded antenna design that relies on a single radio frequency micro-electro-mechanical switch (RF-MEMS) to reconfigure its frequency of operation between 575 MHz and 760 MHz. The reconfigurable multi-layered antenna design has a volumetric folded topology with total dimensions of 40×40mm2; equivalent to 0.11λx0.11λ at 575 MHz. The antenna is fabricated and tested where the measurements agree well with the simulation results. The antenna exhibits a radiation efficiency of 40% at 575 MHz and 62% at 760 MHz. Furthermore, the proposed antenna is tested in a cognitive radio environment to validate its ability to adapt to cognitive input and tune its performance across white space within the UHF band. This is achieved by relying on a trained classifier model that is embedded within a microcontroller to autonomously control the state of the integrated switch based on which channel is idle.

Optimized vertical RF-MEMS switch design with a small actuation voltage

A vertical RF-MEMS (Radio Frequency Micro ElectroMechanical Switch) switch design is proposed in this work that features a shunt capacitive configuration and can operate at a very low actuation voltage. Besides operating on a low switching voltage, the switch behold a small value of insertion loss in Up (ON) state and offers a towering isolation factor in Down (OFF) state. A horizontal structure of bridge membrane is used in the proposed design and the switch function (with ON and OFF operating states) is provided by the vertical movement of this membrane structure that is controlled by the electrostatic actuation technique. The actuation pad is centrally fed by a Coplanar Waveguide structure. The switch performance has been analysed over a wide frequency range from 1 to 40 GHz. For obtaining a 1.5 μm vertical displacement of the bridge membrane, a sheer 3.0 Volts of pull-in voltage (VPI) is required. CoventorWare and HFSSv13 tools are used in this work for designing and analysing the proposed switch. The use of fixed-fixed flexure beam configuration is chosen for switch design. Simulation results showcase excellent RF characteristics with isolation factor of −47 dB (at 32.5 GHz) and insertion loss in range of −0.01 to −1.10 dB (for 1−40 GHz frequency).

Isolation enhanced MIMO PIFA system with multiple reconfiguration techniques

In this study, a reconfigurable, two-element, multiple-input multiple-output (MIMO) printed inverted-F antenna (PIFA) is presented with an enhanced isolation ability. The MIMO antenna system is designed using three different reconfiguration techniques that are based on positive-intrinsic-negative diodes, radio frequency micro-electromechanical switches and varactors. Their impact on the performance of the PIFA and the MIMO system is evaluated in terms of radiation characteristics, gain, power dissipated, radiation efficiency, linearity, biasing requirements and MIMO performance. Isolation between the two MIMO antenna elements is enhanced by integrating a reconfigurable band-reject filter within the ground plane between the radiating elements. The band-reject filter is reconfigured simultaneously with the radiating elements, hence resulting in less coupling and better isolation. The MIMO system along its various components is fabricated for the three different reconfiguration techniques and the comparison with predicted data shows great agreement.

Analytical Approach in the Development of RF MEMS Switches

Currently, the technology of microelectromechanical systems is widely used in the development of high-frequency and ultrahigh-frequency devices. The most important requirements for modern and advanced devices of the ultra-high-frequency range are the reduction of weight and size characteristics, power consumption with an increase in their functionality, operating frequency and level of integration. Radio frequency microelectromechanical switches are developed using the technology of the manufacture of CMOS-integrated circuits. Integrated radio frequency control circuits require low control voltages, the high ratio of losses to the isolation in the open and closed condition, high performance and reliability. This review is devoted to the analytical approach based on the knowledge of materials, basic performance indices and mechanisms of failure, which can be used in the development of radio-frequency microelectromechanical switches.

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.

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.

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.

A novel comprehensive approach to feedback control of membrane displacement in radio frequency micro-electromechanical switches

In this work, a novel feedback control technique for MEMS switch membrane is presented. Due to difficulties associated with measurement of membrane displacement, the capacitor current is used as the controller feedback signal. System identification is utilized to construct a transfer function relating Membrane displacement to capacitor current. Accelerating electrostatic pulse is utilized to accelerate the membrane at the start of the closing stage while a two degree-of-freedom, proportional-integral-derivative control is implemented and tuned to attain soft landing of the membrane on the electrode. The proposed technique eliminates membrane impact bouncing, reduces switch closing time, and improves the durability and reliability of the switch. The technique also improves the membrane transient response during pull-in and release stages. Simulation of the structural model dynamics shows good agreement with experimental results. The proposed technique achieved 200% increase in switch closing speed, 100% reduction in impact bouncing, 75% reduction in release overshoot, and an average of 55% reduction in membrane settling time at zero electrostatic voltage. The proposed model is benchmarked against experimental data, while the control technique is validated via simulation.

Impact of the Surface Roughness Description on the Electrical Contact Resistance of Ohmic Switches Under Low Actuation Forces

At the present time, the insertion of radio frequency microelectromechanical switches into real architecture requires reduced actuation voltages, reduced dimensions, and better control of the electrical and electromechanical behavior that gives more importance to surface effects, their understanding, and modeling. The use of such devices requires the development of methods for estimating the contact performances as a function of surface roughness, contact materials, and contact topologies. With increase in computation capabilities, the rough surface topography can be implemented in the finite element model but implies long calculation times or even calculation overloading if a high definition of the roughness is desired. To reduce these limitations, assumptions on the microgeometry are required. This paper treats, by use of finite element modeling, the influence of the definition of roughness of contacting switch members on the electrical contact resistance of resistive switches, and investigates the error introduced by using a minimum defined atomic force microscope sampling interval of 10 nm. The present numerical analysis is implemented for switch test structures.

Analysis of fluid-structure interaction for predicting resonant frequencies and quality factors of a microcantilever on a squeeze-film

The dynamic behavior of a flexible microcantilever vibrating above a substrate such as the cantilever-based structure of a radio frequency microelectromechanical switch is strongly affected by the motion of gas between the microcantilever and the substrate. In this paper, parameter studies to investigate the effects of geometry, material properties of a microcantilever, and ambient pressure on the resonant frequencies and quality factors of the microcantilever are described. A Reynolds-equation-based continuum model is used to derive the gas force reflecting the gas rarefaction effect due to the size effect of MEMS packed at low ambient pressure. The frequency response function of an inertially-excited microcantilever is developed using the mode superposition method. One interaction parameter, including information on geometry, material properties of a microcantilever, and ambient pressure, is defined to investigate the fluidstructure interaction in a microcantilever vibrating on a squeeze-film. The quality factors of the first three bending modes increase with the decreasing interaction parameter. The changing trend of associated resonant frequencies depends on the order of the bending mode.

Charging and discharging in ion implanted dielectric films used for capacitive radio frequency microelectromechanical systems switch

In this work, metal-insulator-semiconductor (MIS) capacitor structure was used to investigate the dielectric charging and discharging in the capacitive radio frequency microelectromechanical switches. The insulator in MIS structure is silicon nitride films (SiN), which were deposited by either low pressure chemical vapor deposition (LPCVD) or plasma enhanced chemical vapor deposition (PECVD) processes. Phosphorus or boron ions were implanted into dielectric layer in order to introduce impurity energy levels into the band gap of SiN. The relaxation processes of the injected charges in SiN were changed due to the ion implantation, which led to the change in relaxation time of the trapped charges. In our experiments, the space charges were introduced by stressing the sample electrically with dc biasing. The effects of implantation process on charge accumulation and dissipation in the dielectric are studied by capacitance-voltage (C-V) measurement qualitatively and quantitatively. The experimental results show that the charging and discharging behavior of the ion implanted silicon nitride films deposited by LPCVD is quite different from the one deposited by PECVD. The charge accumulation in the dielectric film can be reduced by ion implantation with proper dielectric deposition method.