MEMS Relay Research Articles

Architected material analogs for shape memory alloys

Architected material analogs for shape memory alloys

Design and manufacturing of an electrostatic MEMS relay for high power applications

This paper addresses the design and manufacturing of a crab-leg based MEMS relay for a high power application. Thanks to a contact resistance lower than 100 mΩ, the relay can hold a current in the order of magnitude of an Ampere without further thermal limitation for the final application. First, an analytical model of the relay, considering its geometry and the contact resistance, is presented. The model is developed in order to focus on the contact deformation. It ensures a low bending moment due to the target contact deformation below 1 nm reducing thus the contact resistance. The design has also been done to overcome the internal resonance frequencies of the future application, i.e. electrical motor. Then, a novel manufacturing process for thicker MEMS is proposed based on micro-fabrication techniques. Finally, the performances of the relay are evaluated and a contact resistance as low as 65 mΩ (comparable to the state-of-the-art) for an applied force of 5 mN, much lower than values reported in the literature is presented.

Volatile or non-volatile switching? Establishing design parameters for metal-contact relays using ON/OFF hysteretic behavior (RT to 300 °C)

This Letter presents a systematic evaluation of the adhesion force between sub-micrometer metal (molybdenum) surfaces in microelectromechanical (MEMS) relays for a range of temperatures (RT to 300 °C). As adhesion force controls whether an electrostatic actuated MEMS relay will detach or remain in contact once the power is turned-off, therefore, it is essential to know the amount of adhesion force present between the interacting electrodes. We present a theoretical scheme that allows direct extraction of the adhesion force from experimentally measured data (ON/OFF-voltage) that can precisely determine the adhesion force from the micro- to nanoregime. Our model identified a clear correlation between the two properties, i.e., ON/OFF-voltage and adhesion force and applicable for any arbitrary material systems. The model is validated by experimental results with varying design parameters. The results confirm that the decreasing nature of pull-OFF voltage (13.9 V to 10.8 V) with increasing temperature ensures a large hysteresis window (∼4.7 V at 300 °C) for n = 3 × 6 and W/L−1 ∼ 6.67, where n is the contact-area dimension and W/L−1 is related to movable electrode geometry. The proposed method can be adopted for the precise designing of various logic relays or memory elements suitable for a wide temperature range.

Design of a MEMS relay based on SOI fabrication technology

The deployment of MEMS relay for high power switching applications requires a matrix-like arrangement of many single MEMS relay units. For consistent performance the sameness of the individual switches representing the array is crucial. We present the design, simulation and fabrication of a MEMS relay based on silicon-on-insulator (SOI) technology. The measurement results show high accordance with simulations confirming the predictability and thereby the homogeneity of SOI-based MEMS relays.

Fabrication of a flexible polyimide-based electrostatically actuated MEMS relay

A four-photomask method for fabricating a polyimide (PI)-based electrostatically actuated MEMS relay is presented. The processes for patterning the SiO2 sacrificial layer and curing the PI layer for making the movable structure were optimized. The substrate and the movable structure of the relay were all made of PI, and thus the relay exhibited excellent flexibility and could be used for flexible electronics. Moreover, using PI as the substrate of the drain electrode significantly reduced the effective hardness of the contact material. The hardness of a Au film on a PI substrate was only 42% of that of the Au film on a silicon substrate. In turn, the decrease of the hardness of the contact material contributed to obtaining a lower contact resistance. The contact resistance of the MEMS relay with a PI substrate was less than half of that of the MEMS relay with a silicon substrate.

A Low Contact Resistance 4-Terminal Mems Relay: Theoretical Analysis, Design, and Demonstration

A 4-terminal microelectromechanical systems (MEMS) relay has long been sought for signal switching applications because it allows de-coupling of the actuation (body and gate) and signal (source and drain) components unlike a 3-terminal MEMS relay. However, the contact resistance still remains a serious problem in current 4-terminal MEMS relays compared with the 3-terminal MEMS relays. In this paper, using theoretical analysis, we first determined that the two-contact design, which was the most common design in the 4-terminal MEMS relay, was the origin of the high contact resistance. We subsequently developed a 4-terminal MEMS relay with a novel single-contact design. The fabricated 4-terminal MEMS relay with the single-contact design exhibited a contact resistance of 18 $\text{m}\Omega $ . To the best of our knowledge, this result is the lowest value among 4-terminal MEMS relays. In addition, we demonstrated that the two-contacts are the origin of the high contact resistance using measurement. The relay operated up to $1.1\times 10^{6}$ cycles at 1 V / 50 mA in air and hot switching conditions. Finally, the proposed 4-terminal MEMS relay was hermetically packaged for use in commercial applications. [2017-0183]

An experimental study to investigate the micro-stereolithography tools for micro injection molding

PurposeThe use of microstereolithography (μSL) parts as micro-injection molding (μIM) tools greatly reduces the time and cost to product and offers unique solutions for complex design issues. However, they present challenges to designers because of their strength, thermal characteristics and shorter lifetimes as compared to other mold materials. The purpose of this study is to use SL to build rapid injection mold tools directly combining microfeatures for short-run production.Design/methodology/approachIn total, three tool inserts were produced. Two different μSL mold inserts were produced and evaluated in terms of different build approaches of micro features. One of the inserts includes micro features built horizontally, while the other one collaborates features built vertically, both having same geometrical dimensions. To evaluate the replication capability of prototype tools, two different thicknesses were set for micro features, that is, 30 and 120 μm. The mold inserts were assembled on a metallic mold frame and tested with polypropylene (PP).FindingsIt was observed that using inappropriate resin to fabricate the mold inserts can lead to inaccurate geometrical dimensions of the tool. Therefore, the material with high glass transition temperature (Tg) and low thermal conductivity is preferred. Also, the results of this research work showed that the processed material and technology play an important role both on part quality and tool life. After investigating the tool failure mechanisms during the injection, it was observed that tool failure occurred mainly because of excessive flexural stresses and ejection forces during the cavity filling and part ejection phases, respectively.Originality/valueThe paper describes the capability of μSL mold inserts for the production of small batches of micro-cantilevers which are used in MEMS relays.

Evolution of Voltage Transients During the Switching of a MEMS Relay With Au/MWCNT Contacts

Gold is commonly used for microelectromechanical electrical contacts due to its desirable electrical and mechanical properties; however, the lifetime of gold contacts is limited, particularly in the case of hot switching. To improve the lifetime of electrical contacts, we have developed a gold-coated multiwalled carbon nanotube bilayer composite. Experiments with these composites have shown that the switching dynamics vary over the lifetime of the switch. The change in potential across the switch contacts during the contact-break process, referred to as the transient opening voltage, has been monitored at a number of intervals throughout the switch life. The transient opening voltage shows behavior indicative of the molten metal bridge (MMB) phenomenon. While stable for most of the contact lifetime, the duration of this behavior increases sharply as the contacts approach failure. Throughout the switch lifetime, the contacts are required to survive a large number of opening and closing cycles and, therefore, it is important to understand the switching dynamics. A contact pair was investigated to failure where the experimental conditions were: load current and voltage of 50 mA and 4 V, respectively. Failure occurred after 28 million hot-switched cycles. The average energy of the MMB process was evaluated as 1.54 $\mu \text{J}$ per opening event during the stable region, this rose to 13.2 $\mu \text{J}$ shortly before failure. An experiment run under similar conditions but with a lower load current of 10 mA, which was switched for over 500 million cycles, showed a stable contact resistance and an average MMB energy of $5~\Omega $ and 57 nJ, respectively.

Total Ionizing Dose Effects in Piezoelectric MEMS Relays

This paper investigates total ionizing dose (TID) effects on the piezoelectric properties of lead zirconate titanate (PZT). The capacitance and contact voltage of thin-film, PZT-based relays were measured following incremental 60Co TID irradiations. The devices were held in several different bias conditions, during exposure. The direction of the biasing electric field during exposure, along with the polarization prior to exposure, has a measurable impact on post-irradiation operating voltage of the relay. In all cases, the switching voltage, as obtained via the peak values in a capacitance versus voltage sweep, shifted in a direction that would minimize the switching electric field in the direction of pre-exposure polarization. These effects were observed to be both significantly greater than the shifts experienced by a set of control samples, as well as reversible via aging at room temperature. The devices display remarkable robustness, operating during active TID exposure [dose rate = 855.6 rad(Si)/s], failing at a TID greater than 15 Mrad(Si).

MEMS Relay Optimization Design Algorithm Based on Particle Swarm Optimization

Mathematical model of the MEMS relay volume involves in mechanical, electrical, magnetic, thermal, etc., the MEMS relay optimization design is a constrained nonlinear function optimization problem. In this paper, aim at the disadvantages of standard Particle Swarm Optimization algorithm like being trapped easily into a local optimum, we improves the standard PSO and proposes a new algorithm to solve the overcomes of the standard PSO. The new algorithm keeps not only the fast convergence speed characteristic of PSO, but effectively improves the capability of global searching as well. Experiment results reveal that the proposed algorithm can find better solutions when compared to other heuristic methods and is a powerful optimization algorithm for MEMS relay optimization design.

The Contact Resistance Performance of Gold Coated Carbon-Nanotube Surfaces under Low Current Switching

Multi-Walled CNT (MWCNT) are synthesized on a silicon wafer and sputter coated with a gold film. The planar surfaces are mounted on the tip of a piezo-electric actuator and mated with a gold coated hemispherical surface to form an electrical contact. These switching contacts are tested under conditions typical of MEMS relay applications; 4V, with a static contact force of 1mN, at a low current between 20-50mA. The failure of the switch is identified by the evolution of contact resistance which is monitored throughout the switching cycles. The results show that the contact resistance can be stable for up to 120 million switching cycles, which are 106 orders of higher than state-of-the-art pure gold contact. Bouncing behavior was also observed in each switching cycle. The failing mechanism was also studied in relation to the contact surface changes. It was observed that the contact surfaces undergo a transfer process over the switching life time, ultimately leading to switching failure the number of bounces is also related to the fine transfer failure mechanism.

Electroplating Copper Mask for Glass Deep Wet Etching in MEMS Relay

This paper reports an electroplated copper mask technology which consists of sputtered chromium and copper seed layer with electroplated copper and gold layer, in combination with hard baked thick AZ4620 photoresist based on MEMS technology. The etching depth attains to 680μm after more than 3 hours’ immerging in the concentrated HF 48% etching solution with smooth generated surface without pinholes. In addition, undercut ratio of 0.87 could be achieved. Compared with other masks in the literature, this electroplating mask technology is characterized by lithography compatibility, simple, low cost, short time consumption, large undercut ratio as well as smooth generated surface. Thus, it can be used in MEMS fields such as: precisely assignment of permanent magnet for the electromagnetic microrelay. Keywords: Micromachining, Pyrex glass, Etching, Lithography, MEMS

The Wear Processes of Gold Coated Multi-Walled Carbon Nanotube Surfaces Used as Electrical Contacts for Micro-Electro-Mechanical Switching

An experimental investigation of gold coated, multi-walled carbon nanotube (CNT) surfaces was previously conducted, to determine the limits as electrical contacts. The results are summarized. The multi-walled CNT's (MWCNT's) were synthesized on a silicon planar and sputter coated with a gold film. The planar surfaces mounted on the tip of a piezo-electric actuator and mated with a coated Au hemispherical probe. The conditions typical of MEMS relay applications; (4 V, 1-10 mA) with an applied force of 1 mN. No failures were observed below, 10 × 106 cycles; to determine the limits, the current level was increased in stages to 50 mA. At 20 mA, the contacts were deemed to have failed due to an increased contact resistance at 70 × 106 cycles. In this paper the failure mechanism is described as a fine transfer mechanism linked to the thermodynamic processes at the contact interface as the contacts open, known as molten metal bridge transfer.

Arc extinction characteristics in power supply frequencies from 50 Hz to 1 MHz

It is well-known that arcing phenomena at the break of contacts affect seriously the reliability and lifetime of contacts. Therefore, many papers have reported arc duration, arc extinction current and other characteristics. Recently, in mobile communication application an electro-mechanical switch is said to be superior to a semiconductor switch in insertion loss and isolation, and a RF (radio frequency) MEMS relay has been intensively developed. Based on the above background it is one of important research topics how the frequency of interrupted current affects the characteristics of breaking arc. However, there are few papers on that topic. In this paper the effect of frequency on arc characteristics is investigated in range of the frequency of interrupted current from 50 Hz to 1 MHz. Consequently the followings can be made clear. At the interruption of peak current 2 A arc extinguishes in terms of arc characteristics and circuit conditions up to the frequency of 200 Hz. Above 200 Hz the arc extinguishes at current zero. The current zero extinction takes place up to 500 kHz. Therefore, arc duration decreases with high frequencies and the contact damage caused by arc is reduced with frequency. However, at frequencies higher than 600 kHz an arc is re-ignited after the current zero and failed to extinguish.

MEMS actuator and relay with horizontal actuation

A micro-electromechanical (MEMS) actuator and relay are implemented using a copper coil and a magnetic core. The magnetic core includes a base section that lies within the copper coil, and a cantilever section that lies outside of the copper coil. The presence of a magnetic field in the coil causes the cantilever section to move horizontally away from a rest position, while the absence of the magnetic field allows the cantilever section to return to the rest position.

Nanoscale Ruthenium Coatings of MEMS Switches Contacts

AbstractThe paper reports the tests results of ruthenium contacts coatings of magnetically controlled MEMS switches. During the tests the contact resistance was measured and the lifetime of MEMS switches was evaluated. After testing the analysis of the form and contact surface structure using SEM-method was carried out. The experiment results showed that the application of ruthenium nanolayers as the contact coating at slight increase of the contact resistance improves the lifetime of MEMS switches considerably.Nowadays the increase of the lifetime of all MEMS switch types (RF MEMS relays, magnetically controlled on-off MEMS switches) is the most actual problem. The work resource and operating characteristics, first of all, contact resistance, of any switching unit, the basis of the construction of which is a dry contact, are determined by the contact coating properties. This is true for MEMS switches too.The paper presents the results of the study of the operating characteristics of magnetically controlled MEMS switches with ruthenium and gold contact coatings of up to 100 nm thickness. During tests the following switching mode was used: switching voltage – 3 V, current - 10 μA. Each MEMS switch was subjected to 100 million cycles switching at the frequency of 100 Hz. After testing the contact surface investigation by SEM-method and electrical characteristics measurement was carried out. The paper presents SEM-images of the contacts surface and statistical date of electrical characteristics.After 100 million switching cycles MEMS switches with nanoscale ruthenium coating have shown 100% operating capacity; 16% of switches with gold contacts turned out to be inoperative due to electrical contacts sticking.The results of researches by SEM-method show that the contacts without nanoscale coating have the traces of strong erosion and melting; the contacts with nanoscale ruthenium coating practically did not change the form and flatness.So, the test results indicate that nanoscale ruthenium coatings of the electrical contacts provide excellent resource for the switches operation of hundred millions and more cycles.

Design and implementation of MEMS Cockcroft-Walton voltage multiplier

A design modification to the Cockcroft-Walton (CW) voltage multiplier is reported for the purpose of miniaturisation using MEMS. The configuration comprises a cascade of CW voltage-doublers connected through their outputs and supply points (Vdd). Each voltage doubler is a two-stage CW multiplier that consists of four switches and three capacitors. The classical CW voltage multiplier has voltage amplification of Ns, where Ns=2Nd (Nd is the number of voltage doublers), while the modified design has an amplification of 2Nd. Using this configuration, a novel MEMS voltage doubler has been experimentally realised with micro-relays and capacitors. The MEMS relays and capacitors were fabricated using the MetalMUMPs MEMS process. Measurements on the MEMS voltage doubler have been conducted. A voltage output of 400 V has been demonstrated, and the risetime is measured to be around 260 ms.

Laterally actuated multicontact MEMS relay fabricated using MetalMUMPS process: experimental characterization and multiscale contact modeling

Multicontact MEMS relays laterally actuated using electrostatic comb-drive actuators are reported. The relay consists of a movable main beam anchored to the substrate using two identical folded suspension springs. Multicontact RF ports consist of five movable fingers connected to the movable main beam and six fixed fingers anchored to the substrate. Comb-drive actuators located at the top and bottom ends of the main beam enable bidirectional actuation of the RF contacts. The MEMS relays were fabricated using the MetalMUMPs process, which uses 20-µm-thick electroplated nickel as the structural layer. A 3-µm-thick gold layer was electroplated at the electrical contact surfaces. An example MEMS relay with planar contacts of area 80 µm×20 µm and a spacing of 10 µm between the movable and fixed contacting surfaces is discussed. The overall size of the relay is approximately 3 mm×3 mm. "Resistance versus applied voltage" characteristics of the MEMS relay have been measured for applied DC bias voltages in the range of 172 V to 220 V. A multiscale rough surface contact model was used to estimate the actual electrical contact resistance versus applied force curve of these devices. The multiscale model showed good qualitative agreement with the experimental measurements but requires more refinement to achieve good quantitative agreement.

Design and fabrication of a magnetic bi-stable electromagnetic MEMS relay

This paper describes the principles, design, fabrication and performance of a new type of electromagnetic bistable MEMS relay. The microdevice is operated by a wiggling microactuator, which is symmetrically assembled with two integrated planar windings and one permanent rotor in the form of sandwich with coaxial sustained gaps between each other. The micromachined rotor moves to-and-fro around the axis and operates the joined brush to open or close external circuit. This hybrid MEMS relay has been provided with fast response and latching function owing to the special design. The response time is about 0.3ms and the maximum load current is 2A.

Matrix combination of elementary switches: general considerations and application to MEMS relays

This paper addresses some general aspects of switching devices consisting of a parallel-series (matrix) combination of elementary switches. The discussion is aimed at the derivation of criteria, which allow judging the potential of performance up-rating under rated current and interruption conditions. The elementary switch types considered are arcing switches and novel arc-free micro-switches. The latter are studied in some more detail in comparison with experimental data.