RF MEMS Research Articles

Contact behavior evolution induced by damage growth in radio-frequency microelectromechanical system switches

This study provides a two-contact-event model to explain the evolution of the contact behavior of microelectromechanical system (MEMS) switches through their lifetime. The succession of two dynamic contact events is carefully considered during actuation inspired by experimental observations. The contact between the MEMS switch tip and the drain can be treated as an effective contact between an elastic hemisphere and a rigid plane. If the first contact event results in elastic deformation, the effective hemisphere will fully recover. Consequently, the subsequent contact event also produces elastic deformation. If, on the other hand, the first contact event induces elastoplastic or plastic deformation, a residual depth will be produced between the hemisphere and the rigid plane. The contact force of the subsequent contact event can be significantly reduced due to this additional residual depth. With the growth of residual depth during the switch cycling process, the modeling results show three possible situations of contact radius evolution: (1) The contact radius increases to a maximum value and then decreases to zero; (2) the contact radius increases to one local maximum value; then decreases to a local minimum value; subsequently increases again to another maximum value, and finally decreases to zero; and (3) the contact radius increases to one maximum value and then decreases to zero; after an intermittent response, the contact radius increases again to another maximum value and finally decreases to zero. Furthermore, the Maxwell spreading formula is applied to determine the contact resistance which is inversely proportional to the contact radius. Three situations of contact resistance evolution corresponding to the evolution of contact radius are obtained. All three situations are also observed and validated by the experimental results.

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 new spiral frequency reconfigurable antenna with RF-MEMS switches for mobile RF front end

The full-wave analyses and design of a multiband reconfigurable antenna (MRA) using radio frequency microelec- tromechanical system (RF MEMS) switches is presented for 1.0-10.0 GHz band. Integration of spiral antenna and MEMS switches on a conventional FR4 printed circuit board (er = 4.4 and tan δ = 0.002) is designed. This paper also gives the construction and performance of low loss MEMS resistive switches and further describes the important improvements in the construction of the switches. The RF switches used here exhibit very good RF characteristics with typical values of pull-in voltages lies between 3.5 to 20.25 V. The cantilever beam structure of switch offers pull-in voltage as low as 3.5 V at air gap g0 = 0.5 μm. Further, Design-1 switch have insertion losses lower than 0.39 dB in ON position, and isolation of Design-2 switch as high as 79.83 dB in OFF position. As compared to all presented switches the Design-3 switch has opti- mized displacement time response i.e. 2 ms. The effect of optimized Design-3 switch is than study along with spiral antenna. The overall arm length of spiral is changed by activating and deactivating the three Design-3 switches and consequently its frequency reconfigured. Finally, optimization procedure using quasi Newton method is introduced for characterizing antenna by changing slot length. The wide bandwidth ranging from 200 MHz to 1.65 GHz at different multiband of proposed MRA indicates device contribution in enhancing the mobile TV and internet application speed.

A Compact L-Band Bandpass Filter with RF MEMS-Enabled Reconfigurable Notches for Interference Rejection in GPS Applications

In light of today's crowded radio spectrum and the high level of receiver sensitivity required to receive very weak signals, mitigating interference (cosite, intentional jamming, or from other sources) has become a very important topic of research. The recent controversy regarding the use of spectrum close to the global positioning system (GPS) bands is the motivation for the IEEE Microwave Theory and Techniques Society 2014 International Microwave Symposium (IMS2014) Tunable Radio-Frequency (RF) Microelectromechanical Systems (MEMS) Filter Student Design Competition, held in Tampa, Florida. Although there are frequency bands reserved for GPS,there is sometimes interference from undesired signals from a variety of sources, such as radio emissions in adjacent bands, intentional/unintentional jamming, and naturally occurring space weather. Ensuring the continuity of GPS service requires the protection of its spectrum from interference. This competition was intended to interest students in the design of innovative RF front-end solutions to address this issue. This article describes the work of the winners of the first-place award.

DESIGN AND SIMULATION OF LOW ACTUATION VOLTAGE PERFORATED RF MEMS SWITCH

DESIGN AND SIMULATION OF LOW ACTUATION VOLTAGE PERFORATED RF MEMS SWITCH

Reconfigurable metamaterial components exploiting two-hot-arm electrothermal actuators

A tunable metamaterial, derived from the combination of two-hot-arm electrothermal actuators with a split-ring resonator, is introduced in this paper. Accomplishing a reliable control of the tip displacement, the selected set of radio-frequency microelectromechanical systems (RF-MEMS) circumvent the undesired bandwidth constraints of existing structures and establish significant levels of reconfigurability. To this objective, the aforementioned actuator is realized as an integrated part of the resonator, while a modified scheme for lower-frequency operation is also developed. Moreover, a double actuated device is proposed to further reduce the bias network complexity. A multiphysics analysis is conducted to reveal the characteristics of the associated RF-MEMS components prior embedding them to any complex medium. The featured designs are numerically verified through an assortment of setups, which utilize the finite element method to extract the constitutive parameters of the proposed metamaterials. Simulation data successfully prove their bandwidth enhancement capability, as well as the controllable mu-negative performance.

Design of DC-contact RF MEMS switch with temperature stability

In order to improve the temperature stability of DC-contact RF MEMS switch, a thermal buckle-beam structure is implemented. The stability of the switch pull-in voltage versus temperature is not only improved, but also the impact of stress and stress gradient on the drive voltage is suppressed. Test results show that the switch pull-in voltage is less sensitive to temperature between -20 °C and 100 °C. The variable rate of pull-in voltage to temperature is about -120 mV/°C. The RF performance of the switch is stable, and the isolation is almost independent of temperature. After being annealed at 280 °C for 12 hours, our switch samples, which are suitable for packaging, have less than 1.5% change in the rate of pull-in voltage.

A MIM capacitor study of dielectric charging for RF MEMS capacitive switches

MIM capacitors are considered equally important devices for the assessment of dielectric charging in RF MEMS capacitive switches. Beside the obvious similarities between the down state condition of RF MEMS and MIM capacitors there are also some important differences. The paper aims to introduce a novel approach to the study of dielectric charging in MEMS with the aid of MIM capacitors by combining experimental results obtained by the application of DC, Charging Transient and Kelvin Probe techniques. The strengths and weaknesses are discussed in conjunction with experimental results obtained on SiNx based MIM capacitors and MEMS capacitive switches fabricated under the same conditions.

Radio Frequency Microelectromechanical System-Platform Based on Silicon-Ceramic Composite Substrates

In the last few years, several low-temperature coefficient of expansion of low temperature cofired ceramic (LTCC) materials have been developed for direct wafer bonding to silicon. BGK, a sodium-containing LTCC, was originally developed for anodic bonding of the sintered LTCC, whereas BCT (bondable ceramic tape) was tailored for direct silicon bonding of green LTCC tapes to fabricate a quasi-monolithic, silicon ceramic compound substrate. This so-called silicon-on-ceramic (SiCer) technique is based on homogeneous nanostructuring of a silicon substrate, a lamination step of BCT and Si, and a subsequent pressure-assisted sintering. We present a new approach for an integrated radio frequency (RF)-platform setup combining passive, active, and mechanical elements on one SiCer substrate. In this context, RF parameters of the Si-adapted LTCC tapes and the use of commercial metal pastes on BCT with respect to bondability and solderability are investigated. We show first technological results of creating cavities at the SiCer interface for SiCer-specific contacting options (e.g., exposed contact pads at the interface), as well as windows in the ceramic layer of the SiCer substrate for additional Si processing (e.g., Si backside thin-film wiring, plasma etching). A further investigated platform technology is deep reactive-ion etching of the SiCer composite substrate. The etching behavior of Si and BCT is demonstrated and discussed. With the SiCer technique, it is possible to reduce the Si content at the setup of RF microelectromechanical system to a minimum (low signal damping).

RF MEMS BASED HALF MODE BOWTIE SHAPED SUBSTRATE INTEGRATED WAVEGUIDE TUNABLE BANDPASS FILTER

A tunable planar bandpass filter based on a technique that utilizes a half mode substrate integrated waveguide (HMSIW) and novel inter-resonator coupling is presented. The tunable HMSIW based bandpass filter is implemented using two half triangle shaped cavities coupled together through inter-resonator coupling forming half mode bowtie shaped structure. The bowtie-shaped filter exhibits similar performance as found in rectangle- and circle-shaped SIW based bandpass filters. This concept reduces the circuit foot print, and miniaturization high quality factor is maintained by the structure. The tunable filter utilizes packaged RF MEMS switches; switching between different configurations of switches achieves four distinctive frequency states between 4.8-5.3 GHz. The filter maintains a constant absolute 1 dB bandwidth of 100 ± 10 MHz for all frequency states.

Analysis of RF MEMS capacitive switches by using switch EM ANN models

Artificial neural networks (ANNs) have appeared to be an alternative to the conventional models of RF MEMS switches. In this paper, neural models of an RF MEMS capacitive switch are developed and used for the electrical design of the switch. Namely, an ANN model relating the switch resonant frequency and the bridge dimensions is used to analyze efficiently the switch behavior with changes of bridge dimensions. Furthermore, it is illustrated how the developed model can be used for the determination of bridge dimensions in order to achieve the desired switch resonant frequency. In addition, application of a switch inverse ANN model for the determination of bridge dimensions is analyzed as well.

电容式RF MEMS开关膜片上边缘电场的表征

电容式RF MEMS开关膜片上边缘电场的表征

Comparative Study of Perforated RF MEMS Switch

Abstract MEMS are the Micro Electronic mechanical system or in general terms it is also known as Micro electronic mechanical switch. MEMS have classified in two types of switch that is series switch and shunt switch .The cantilever is a series type switch whereas the fixed- fixed beam is shunt type switch. Fixed- Fixed beam is the element that is fixed at both anchor ends. The electrostatic actuation process occurs on the switch due to which switch deflects from its original position. The stiction problem occurs in MEMS switches which have been reduced by the proposed design. The perforation is used to reduce the squeeze film damping by decreasing the mass of the switch. As the voltage increases the switch moves to downward z-direction .The displacement is produced in the switch as direction of movement is towards negative z-axis. When the beam contacts with electrode, pull in voltage is achieved. This paper explores the perforation and meander concept with Fixed -fixed switch, which increases the flexibility, low actuation voltage and switching speed. The various types of perforations provide discrete displacement corresponding to voltage. In this paper we represent the design and simulation of Fixed-Fixed switch using perforation of size 2 μm-5 μm. The electrostatic actuation mechanism is applied on the Fixed-fixed switch which has a serpentine meanders and perforation at different voltages. The switch is designed and simulated by using COMSOL®MULTIPHYSICS 4.3b software.

A Multiple Resonant Frequencies Circular Reconfigurable Antenna Investigated with Wireless Powering in a Concrete Block

A novel broadband reconfigurable antenna design that can cover different frequency bands is presented. This antenna has multiple resonant frequencies. The reflection coefficient graphs for this antenna are presented in this paper. The new proposed design was investigated along with RF MEMS switches and the results are also presented. Investigations were carried out to check the efficiency of the antenna in the wireless powering domain. The antenna was placed in a concrete block and its result comparison to that of a dipole antenna is also presented in this paper.

High Power Latching RF MEMS Switches

Latching RF MEMS Switches of Single-Pole-Single-Throw (SPST), Single-Pole-Double-Throw (SPDT) and Single-Pole-Triple-Throw (SP3T) types are proposed. The switches are built of a 20 μm thick nickel layer covered with a plated 2 μm gold on the top and side walls of nickel layer eliminating any potential warping due to thermal mismatch. The switches are actuated using a high stroke latching thermal actuator that exhibits a 32 μm displacement with a dc power of 250 mW under ambient pressure at 25 <sup xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">°</sup> C (298 <sup xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">°</sup> K) and 153 mW under vacuum at -193 <sup xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">°</sup> C (80 <sup xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">°</sup> K). The measured velocity for the actuator is 2.3 μm/msec. The RF measurement of the SPST switch is done under ambient and vacuum and over a wide range of temperatures from 25 <sup xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">°</sup> C (298 <sup xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">°</sup> K) to -193 <sup xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">°</sup> C (80 <sup xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">°</sup> K). The switches survived a temperature cyclic test from 25 <sup xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">°</sup> C (298 <sup xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">°</sup> K) to 85 <sup xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">°</sup> C (358 <sup xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">°</sup> K) with a total variation of 0.2 dB in insertion loss. The switch demonstrates a worst IP3 of 60.14 dBm and high power handling capabilities that exceeds 30 Watt, only tested for an hour in 1 cycle. The RF performance of the SPST, SPDT and SP3T exhibits a worst insertion loss of 0.8 dB, 1.2 dB and 1.5 dB up to 40 GHz, 40 GHz and 18 GHz, respectively.

RF MEMS/NEMS resonators for wireless communication systems and adsorption-desorption phase noise

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.

Technologies for Wafer Level MEMS Capping based on Permanent and Temporary Wafer Bonding

Further cost reduction and miniaturization of electronic systems requires new concepts for highly efficient packaging of MEMS components like RF resonators or switches, quartz crystals, bolometers, BAWs etc. This paper describes suitable base technologies for the miniaturized, low-cost wafer level chip-scale packaging of such MEMS. The approaches are based on temporary handling and permanent bonding of cap structures using adhesives or solder onto passive or active silicon wafers which are populated with MEMS components or the MEMS wafer themselves. Firstly, an overview of the possible packaging configurations based on different types of MEMS is discussed where TSV based and non-TSV based packaging solutions are distinguished in general. The cap structure for the TSV based solution can have the same size as the MEMS carrying substrate, since the electrical contacts for the MEMS can be routed either thought the cap or base substrate. Thus, full format cap wafers can be used in a regular wafer to wafer bonding process to create the wafer level cavity packages. However, if no TSVs are present in the cap or base substrate, the cap structure needs to be smaller than the base chip, so that electrical contacts outside the cap area can be accessed after the caps were bonded. Such a wafer level capping with caps smaller than the corresponding base chips can be obtained in two ways. The first approach is based on fabrication and singulation of the caps followed by their temporary face up assembly in the desired pattern on a help wafer. In a subsequent wafer to wafer bonding sequence all caps are transferred onto the base wafer. Finally the help wafer is removed from the back side of the bonded caps. This approach of reconfigured wafer bonding is especially used for uniform cap patterns or, if MEMS have an own bond frame structure. In that case no additional cap is required, since the MEMS can act as their own cap. The second approach is based on cap structure fabrication using a compound wafer stack consisting of two temporary bonded wafers. One wafer acts as carrier wafer whereas the other wafer is processed to form cap structures. Processes like thinning, silicon dry etching, deposition and structuring of polymer or metal bonding frames are performed to generate free-standing and face-up directed cap structures. The so created “cap donor wafer” is used in a wafer to wafer bonding process to bond all caps permanently to the corresponding MEMS base wafer. Finally, the temporary bonded carrier wafer is removed from the backside of the transferred caps. With that approach a fully custom specific and selective wafer level capping is possible featuring irregular cap patterns and locations on the MEMS base wafer. Examples like the selective capping process for RF MEMS switches are presented and discussed in detail. All processes were performed at 200mm wafer level.

A new MEMS based variable capacitor with wide tunability, high linearity and low actuation voltage

We have proposed a new RF MEMS variable capacitor to achieve high linearity, wide tunability and low actuation voltage. The idea is based on increasing the linear region in the gap between the plates of the capacitor. It is done by adding a fixed-fixed beam below the fixed-free beam. The fixed-free beam is one plate of the capacitor. The voltage is applied to the fixed-free beam. In the vicinity of the pull-in voltage, the fixed-free beam losses its equivalent stiffness. The fixed-fixed beam is located in the vicinity of pull in situation of the fixed-free beam. This condition increases the equivalent stiffness of the fixed-free beam and allows the beam to continue moving down linearly and consequently increases the maximum capacitance of the structure. Geometrical and material property effects of the second beam on the linearity, tunability and voltage are investigated. The governing nonlinear equation for static deflection of the beam based on the Euler–Bernoulli beam theory has been presented.

Analytical Energy Model for the Dynamic Behavior of RF MEMS Switches Under Increased Actuation Voltage

In this paper, the dynamic behavior of electrostatically actuated radio frequency-microelectromechanical system (RF-MEMS) switches is analyzed using energy considerations. An analytical model for bridge-type RF-MEMS switches is proposed and the time evolution of the system total energy is calculated numerically. Switch actuation, release times, and damped release response are derived from energy analysis with focus on the effect of increasing the actuation voltage on the RF-MEMS dynamic behavior. The dynamic and RF characteristics of different RF-MEMS ohmic-contact switches have been measured using an experimental set-up based on microwave instrumentation. The measured results show a good agreement with simulations, thus validating the proposed analytical model. It is shown (theoretically and experimentally) that the damped release response increases the effective time to reach the RF/microwave OFF-state switch isolation (up to three natural periods of the mechanical system). $\hfill{[2013\hbox{-}0222]}$

Life Lessons: Zaghloul has worn many hats [Women to Watch

An electrical engineer by trade, Mona Zaghloul wears many hats and has an impressive resume including IEEE Fellow, professor, and director at George Washington University (GWU) and the National Science Foundation (NSF). Her work has spanned decades of projects in topics such as circuits and systems, microelectronics system design, very-large-scale integration circuit design, radio frequency microelectromechanical systems (RF-MEMS), neural networks, MEMS sensor systems, and biosensors and their interface circuit design. She views engineering as a rewarding career and hopes that many women will choose it.