Microelectromechanical Systems Switches Research Articles

Piezoelectric PZT MEMS technologies for small-scale robotics and RF applications

Abstract

An electrical contact resistance model including roughness effect for a rough MEMS switch

Understanding the contact behavior of a microelectromechanical system (MEMS) switch is of great importance to reach a high-reliability level for micro-switch applications. The deformation occurring at the many a-spots produced by the mechanical contact of asperities can be elastic, elastic–plastic, fully plastic or any combination of the three types of deformation and has a strong effect on the contact resistance. This work presents an electrical contact resistance model for a rough MEMS switch. A dimensionless parameter k, which is a function of the electron mean free path and the roughness parameters of contacting surfaces, is introduced to identify the contact resistance. The results show that the dimensionless contact resistance is a strong function of the dimensionless contact load, the plasticity index ψ and the parameter k. The theoretical results are in good agreement with some of the experimental results.

Discretely tuned RF-MEMS bandstop filter with wide tuning range and uniform high rejection

A new bandstop filter is presented providing a two-state discrete wide tuning range from 20 to 30 GHz with the same high rejection level of 36 dB. In the design, metal-insulator-metal capacitors are placed on one end of the resonators and on the other end capacitive micro-electromechanical systems (MEMS) switches are used to discretely tune the centre reject band of the filter.

Microelectromechanical-Systems-Based Switches for Power Applications

A new system for switching electrical power using microelectromechanical systems (MEMS) is presented. The heart of the system utilizes custom-designed MEMS switching device arrays that are able to conduct current more efficiently and can open orders of magnitude faster than traditional macroscopic mechanical relays. Up to now, MEMS switches have been recognized for their ability to switch very quickly due to their low mass but have only been used to carry and switch very low currents at extremely low voltage. However, recent developments have enabled suppression of the arc that normally occurs when the MEMS switch is opened while current is flowing. The combination of the arc suppression with the MEMS switch arrays designed for this purpose enables a breakthrough increase in current and voltage handling capability. The resultant technology has been scaled to handle many amperes of current and switch hundreds of volts. Such current and voltage handling capability deliver improved energy efficiency and the capacity to handle fault current levels that are encountered in typical ac or dc power systems. Fault current interruption takes place in less than 10 μs, almost regardless of the prospective fault current magnitude. The properties of the MEMS switch arrays allow the switching mechanism to operate at temperatures in excess of 200 °C . The switches also have a vibration tolerance in excess of 1000 G. The combination of fast MEMS switching speed, optimized current and voltage handling capacity of the switch arrays, the arc suppression circuitry, and optimized sensing and control enables a single sensing, control, and switching system to operate in a small fraction of a millisecond. This paper will present the basic physics of the MEMS switches together with recent advances that enable the technology. Some illustrative examples of the ways that the devices may be used to provide protection and control within electrical systems will also be presented.

Analytic Modeling Of RF MEMS Shunt Connected Capacitive Switches

—This paper deals with a general analytic approach for the design of RF microelectromechanical system (MEMS) switches. The chosen configuration for these microwave devices is composed of twocoplanar transmission line sections separated by a metal membrane providing a shunt connected variable impedance. Using a bias voltage it is possible to actuate the switch. The adopted methodology for the development of the circuital model is based on the image impedance parameter representation of a two-port network. Synthesis equations are presented, and design considerations are discussed. The proposed approach is validated by means of electromagnetic simulations.

Body-Biased Complementary Logic Implemented Using AlN Piezoelectric MEMS Switches

This paper reports on the implementation of low-voltage complementary mechanical logic achieved by using body-biased aluminum nitride (AlN) piezoelectric microelectro-mechanical systems (MEMS) switches. By biasing the equivalent body of a four terminal mechanical switch with a fixed voltage, the threshold voltage of the mechanical transistor has been precisely tuned and the voltage swing used for implementing digital functionalities reduced to very low values (≤ ±2 V). Thanks to the use of a mechanical switching mechanism, the AlN MEMS switches have exhibited an extremely low subthreshold slope (0.065 mV/dec), which sets the promise for even further reduction of the voltage swing to less than 100 mV. By using opposite body biases, the same mechanical switch has been made to operate as an equivalent n-like or p-like (complementary) device. Two basic AlN mechanical switch elements have then been used to form a body-biased inverter operating at 100 Hz with a ±1.5-V voltage swing. Furthermore, low voltage and functionally complete logic elements (NAND and NOR) implemented by using body-biased complementary and thin-film (250 nm thick) AlN-based piezoelectric mechanical switches have been synthesized. Finally, scaling rules for these devices are derived, and the key challenges that will need to be addressed to achieve further miniaturization are presented.

A Physics-Based Predictive Modeling Framework for Dielectric Charging and Creep in RF MEMS Capacitive Switches and Varactors

In this paper, we develop a physics-based theoretical modeling framework to predict the device lifetime defined by the dominant degradation mechanisms of RF microelectromechanical systems (MEMS) capacitive switches (i.e., dielectric charging) and varactors (i.e., creep), respectively. Our model predicts the parametric degradation of performance metrics of RF MEMS capacitive switches and varactors, such as pull-in/pull-out voltages, pull-in time, impact velocity, and capacitance both for dc and ac bias. Specifically, for dielectric charging, the framework couples an experimentally validated theoretical model of time-dependent charge injection into the bulk traps with the Euler-Bernoulli equation for beam mechanics to predict the effect of dynamic charge injection on the performance of a capacitive switch. For creep, we generalize the Euler-Bernoulli equation to include a spring-dashpot model of viscoelasticity to predict the time-dependent capacitance change of a varactor due to creep. The new model will contribute to the reliability aware design and optimization of the capacitive MEMS switches and varactors.

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 actuation-voltage shift in MEMS switch using ramp dual-pulse

This paper proposes a ramp dual-pulse actuation-voltage waveform that reduces actuation-voltage shift in capacitive microelectromechanical system (MEMS) switches. The proposed waveform as well as two reported waveforms (dual pulse, and novel dual-pulse) are analyzed using equivalent-circuit and equation models. Based on the analysis outcome, the paper provides a clear understanding of trapped charge density in the dielectric. The results show that the proposed actuation-voltage waveform successfully reduces trapped charge and increases lifetime due to lowering of actuation-voltage shift. Using the proposed actuation-voltage waveform, the membrane reaches a steady state on the electrode faster.

Modeling RF MEMS Devices

The term radio frequency (RF) microelectromechanical systems (MEMS) refers to electronic devices with a moving submillimeter-sized part (beam, comb, disc, or ring), which provide RF functionality. Alternative definitions include bulk or surface micromachined devices, such as thin film bulk acoustic resonators (FBARs), which rely on energy transduction from the electrical energy domain to the acoustic energy domain and vice versa to provide RF functionality. Many introductory articles and textbooks have been written on MEMS and RF MEMS. This article focuses on electrostatically actuated RF MEMS devices, such as RF MEMS switches, switched capacitors and varactors, and vibrating RF MEMS resonators.

RF MEMS Switchable Slot Patch Antenna Integrated With Bias Network

The functionality of the patch antenna with switchable slot (PASS) is realized by integrating a commercially packaged MEMS (microelectromechanical system) switch and a novel bias network. The proposed antenna includes the fully integrated dc bias network capable of actuating the MEMS switch on the slot. The bias network can minimize the interference between dc bias and RF radiation mechanism with a negligible loss. By using a MEMS switch and the bias network, the patch antenna operates at 4.57 GHz and 4.88 GHz. The fabricated design shows acceptable return losses and directivities at the broadside direction when the switch is on and off. The influence of RF MEMS switch on the antenna impedance and radiation pattern is addressed.

Miniature MEMS Switches for RF Applications

This paper presents a new way to design MEMS (microelectromechanical system) metal contact switches for RF applications using miniature MEMS cantilevers. A single 25 × 25 μm switch is first demonstrated with a Au-to-Ru contact, Cu = 5 fF and Ron = 7 Ω at an actuation voltage of 55 V. The measured switching time is 2.2 μs and the release time is <;1 μs. The switch is robust to stress effects (residual and stress gradients) which increases its yield on large wafers. To reduce the effective switch resistance, 10-20 miniature RF MEMS switches have been placed in parallel and result in equal current division between the switches, an up-state capacitance of 30-65 fF and a down-state resistance of 1.4-1.5 Ω. Furthermore, 10-20 element back-to-back switch arrays are developed and result in a marked improvement in the reliability of the overall switching device. A series-shunt design is also demonstrated with greatly improved isolation. The device has a figure-of-merit of fc = 1/(2πRonCu) = 3.8 THz (RonCu = 42 fs).

MEMS-tunable composite right/left-handed (CRLH) transmission line and its application to a phase shifter

This paper reports a novel compact tunable composite right/left-handed transmission line (CRLH TL) with multi-state phase tunability using integrated microelectromechanical system (MEMS) switches and its application to a phase shifter. It is possible to select multiple states with different positive/negative phase responses. The phase states can be determined by controlling the admittance of capacitors and impedance of inductors through MEMS switch operations. The designed devices are analyzed using electromagnetic and circuit simulations. The propagation characteristics and phase lead/lag properties of the devices are investigated. The designed device can be operated as a 90°/−90° phase tunable CRLH TL at 8 GHz and a four-state phase shifter at 9.5 GHz by switch configuration. At 8 GHz, the phase responses of the device were 87° of the phase lead and −80° of the phase lag for the left-handed (LH) and right-handed (RH) states, respectively. At 9.5 GHz, the phase of each state varies among 26.7°, 14.6°, −6.7°, and −11.5°, where the first two states are in the LH region and the others are in the RH region. At 9–15 GHz, insertion losses are measured to be <2.6 dB, and return losses are >10 dB.

Investigation of anti-stiction coating for ohmic contact MEMS switches with thiophenol and 2-naphthalenethiol self-assembled monolayer

Anti-stiction coating with a conductive self-assembled monolayer (SAM) formed by π-conjugated bonds was investigated for ohmic contact microelectromechanical system (MEMS) switches with low-load contacts. SAMs of thiophenol (C 6H 5SH, TP) or 2-naphthalenethiol (C 10H 7SH, 2NT) were coated on Au samples with different surface roughness to investigate the effects of the surface asperities on the adhesion force and contact resistance. The adhesion force was measured using a silicon tipless cantilever in the relative humidity range of 10–85% and the contact resistance was measured in the contact force range of 0–70 μN using a conductive tipless cantilever coated with Au for the SAM coated samples and compared with those for a Au sample surface. The adhesion force measurements indicate that the TP and 2NT coatings can prevent a liquid meniscus from forming on device surfaces due to their hydrophobic character caused by the protruding aromatic group. In addition, it was confirmed that these coatings could reduce van der Waals forces more than Au coating. Contact resistance measurements revealed that an electric current begins to flow with smaller contact force for TP and 2NT coated samples than for Au coated samples. The measured contact resistances of the SAM and Au coated samples were comparable. Based on these results, SAMs of TP and 2NT have excellent potential as anti-stiction coating for MEMS switch contacts.

Design and Analysis of a Tunable Bandpass Filter Employing RF MEMS Capacitors

This letter presents an RF microelectromechanical systems (MEMS) tunable bandpass filter with a tuning range of 30%. An analytical process of designing a bandpass filter is also presented by using MEMS switch, series gap, and etched structure in coplanar waveguide (CPW). The designed structure of the MEMS switch and CPW is used to get a wide tuning range of the filter. The fabricated filter performances show an acceptable agreement between the measured results and the simulation results with a center frequency from 10 to 13.5 GHz.

A Ku-band Dual-SPDT RF-MEMS Switch by Double-Side SOI Bulk Micromachining

This paper presents the design, fabrication method, and measurement results of a low-loss ohmic-contact radio-frequency microelectromechanical systems (MEMS) switch. A novel bidirectional electrostatic actuation mechanism has been developed for a dual single-pole double-throw switch that could be used for an X-Ku-band low-temperature cofired ceramic switched-line-type phase shifter. A high-aspect-ratio deep reactive-ion etching process and a thick gold-plating process were used to develop low-insertion-loss air-suspended MEMS waveguides and low resistive ohmic contacts. A typical insertion loss of 0.56 dB, a return loss of 19.4 dB, and an isolation of 51.4 dB were obtained at a Ku-band frequency of 12 GHz.

Dielectric properties of thin-film ZrO2 up to 50 GHz for RF MEMS switches

The dielectric properties of zirconium dioxide (ZrO2) ceramic thin films were characterized up to 50 GHz using coplanar waveguides (CPWs) and metal–insulator–metal (MIM) capacitors with top circular electrodes. The ZrO2 films were deposited using a chemical solution onto high-resistivity Si wafers and metal layers. The real part of the dielectric constant of approximately 22 and 26 was extracted at 50 GHz for CPW and MIM structures, respectively, and the loss tangent was approximately 0.09 at 50 GHz. C–V and I–V measurements were carried out to determine low-frequency and DC dielectric properties. The measurement results indicate that ZrO2 is a promising material to be used as a dielectric layer for radio-frequency (RF) microelectromechanical systems (MEMS) capacitive switches.

Microstructure evolution of gold thin films under spherical indentation for micro switch contact applications

RF MEMS (Radio Frequency Micro Electro Mechanical System) switches are promising devices but their gold-on-gold contacts, assimilated for this study to a sphere/plane contact, represent a major reliability issue. A first step toward understanding failure mechanisms is to investigate the contact metal microstructure evolution under static and cyclic loading. After static and cyclic loading of sputtered gold thin films under spherical indentation, high-resolution Electron Back Scatter Diffraction (EBSD) is used to investigate the contact area. Grain rotation against {111} fiber texture of 1-μm-thick sputtered gold thin film is a signature of plastic deformation. Grain rotation is observed above 1.6 mN under static loading using a spherical diamond indenter with 50-μm tip radius. The heterogeneity in grain rotation observed corresponds to a greater plastic deformation in the middle of the indent than at the edge. A 30° grain rotation due to cyclic work hardening is observed for a half-million mechanical cycles under 300 μN load using a spherical gold tip (20 μm radius). The same test in hot switching mode induces a grain growth in the contact area. Therefore, thermal effects occurring during hot switching are underlined.

The low-complexity RF MEMS switch at EADS: an overview

This paper gives an overview of the low-complexity radio frequency microelectromechanical systems (RF MEMS) switch concept and technology of EADS Innovation Works in Germany. Starting in 2003, a capacitive switch concept, which is unique in several aspects, was developed to address specific needs in the aeronautic and space. Thermally grown silicon oxide as dielectric layer, the silicon substrate as actuation electrode, and a conductive zone realized by ion implantation make the EADS RF MEMS switch a very simple, low-cost, and reliable approach. In this document, data on experimental investigations are presented, which demonstrate outstanding performance figures in terms of insertion loss, isolation, frequency range, bandwidth, RF-power handling, and robustness with respect to thermal load. Based on this concept, numerous different circuits in particular single-pole single-throws (SPSTs), single-pole multi-throws (SPMTs), tunable filters, phase shifters, and electronically steerable antennas between 6 and 100 GHz have been designed, fabricated, and characterized.