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Proceedings ArticleDOI

Metal contact reliability of RF MEMS switches

Qing Ma1, Quan Tran1, Tsung-Kuan A. Chou1, John Heck1, Hanan Bar1, Rishi Kant1, Valluri R. Rao1 
19 Jan 2007-Vol. 6463, pp 646305
TL;DR: In this article, a collapsing switch capable of generating large contact forces (>300μN) was shown to be less vulnerable to contamination and stiction than a simple reed switch.
Abstract: It is well-recognized that MEMS switches, compared to their more traditional solid state counterparts, have several important advantages for wireless communications. These include superior linearity, low insertion loss and high isolation. Indeed, many potential applications have been investigated such as Tx/Rx antenna switching, frequency band selection, tunable matching networks for PA and antenna, tunable filters, and antenna reconfiguration. However, none of these applications have been materialized in high volume products to a large extent because of reliability concerns, particularly those related to the metal contacts. The subject of the metal contact in a switch was studied extensively in the history of developing miniaturized switches, such as the reed switches for telecommunication applications. While such studies are highly relevant, they do not address the issues encountered in the sub 100μN, low contact force regime in which most MEMS switches operate. At such low forces, the contact resistance is extremely sensitive to even a trace amount of contamination on the contact surfaces. Significant work was done to develop wafer cleaning processes and storage techniques for maintaining the cleanliness. To preserve contact cleanliness over the switch service lifetime, several hermetic packaging technologies were developed and their effectiveness in protecting the contacts from contamination was examined. The contact reliability is also very much influenced by the contact metal selection. When pure Au, a relatively soft metal, was used as the contact material, significant stiction problems occurred when clean switches were cycled in an N 2 environment. In addition, various mechanical damages occurred after extended switching cycling tests. Harder metals, while more resistant to deformation and stiction, are more sensitive to chemical reactions, particularly oxidation. They also lead to higher contact resistance because of their lower electrical conductivity and smaller real contact areas at a given contact force. Contact reliability issues could also be tackled by improving mechanical designs. A novel collapsing switch capable of generating large contact forces (>300μN) was shown to be less vulnerable to contamination and stiction.

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Citations
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Journal ArticleDOI
TL;DR: In this article, an mN-level contact and restoring force RF microelectromechanical system metal-contact switch exhibiting high reliability, high linearity, and high power handing for dc-40 GHz applications was presented.
Abstract: This paper presents an mN-level contact and restoring force RF microelectromechanical systems metal-contact switch exhibiting high reliability, high linearity, and high power handing for dc-40-GHz applications. The device, which is insensitive to stress and temperature effects, achieves 1.2-1.5 mN of contact force (per contact) from 80 to 90 V and 1.0 mN of restoring force (per contact). The up-state capacitance is 8 fF, resulting in an isolation of 46, 31, and 14 dB at 1, 6, and 40 GHz, respectively. Measured results show switch resistances of 1-2 Ω and a reliability of >; 100 million cycles at 2-5 W under cold switching at 100 mW under hot-switching conditions, in an unpackaged and standard laboratory environment. Furthermore, the device was tested under prolonged hold-down conditions and demonstrated excellent RF power handling (>;10 W) and dc current handling (>;1 A) capability.

92 citations

Journal ArticleDOI
TL;DR: In this paper, lifetime limitations and failure analysis of many packaged RF MEMS ohmic contacting switches with Au-Au, Au-Ir, and Au-Pt contact materials operating with 100 μN of contact force per contact in hermetically sealed glass wall packages.
Abstract: We present lifetime limitations and failure analysis of many packaged RF MEMS ohmic contacting switches with Au–Au, Au–Ir, and Au–Pt contact materials operating with 100 μN of contact force per contact in hermetically sealed glass wall packages. All metals were tested using the same switch design in a controlled environment to provide a comparison between the performance of the different materials and their corresponding failure mechanisms. The switch lifetimes of the different contact materials varied from several hundred cycles to 200 million cycles with different mechanisms causing failures for different contact materials. Switches with Au–Au contacts failed due to adhesion when thoroughly cleaned while switches with dissimilar metal contacts (Au–Ir and Au–Pt) operated without adhesion failures but failed due to carbon accumulation on the contacts even in a clean, packaged environment as a result of the catalytic behavior of the contact materials. Switch lifetimes correlated inversely with catalytic behavior of the contact metals. The data suggests the path to increase switch lifetime is to use favorable catalytic materials as contacts, design switches with higher contact forces to break through any residual contamination, and use cleaner, probably smaller, packages. (Some figures may appear in colour only in the online journal)

72 citations


Cites background from "Metal contact reliability of RF MEM..."

  • ...Carbon accumulation has been reported on pure ruthenium contacts after cycling [15, 16, 20]....

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  • ...Switches with dissimilar contacts have been used to reduce failures due to adhesion and increase the maximum current carrying capability [16, 20, 23, 24, 27, 28]; however, these switches show lifetime limitations due to carbon accumulation on the contacts....

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Journal ArticleDOI
TL;DR: In this paper, the electrical contact behaviors of gold-to-gold thin-film contacts under high current conditions were investigated and the major factors that influence these contact behaviors for radio frequency microelectromechanical system switches were described.
Abstract: This paper presents the electrical contact behaviors of gold-to-gold thin-film contacts under high current conditions and describes the major factors that influence these contact behaviors for radio frequency microelectromechanical system switches. The fundamental phenomena in the contact resistance versus contact force curve were investigated with a contact measurement setup, which we devised. Based on the experimental results, the contact resistance behavior with increasing contact force can be divided into three regions: first, an unstable contact regime before the minimum contact force is reached; second, a stable contact regime where the plastic deformation of the asperities explains the behavior and, finally, a saturated regime where the thickness effect of the film on a hard substrate becomes evident. The minimum contact force required for a stable contact depended on the roughness of the surface and the current flow through the contact. The smooth surface of the Au film and the metal softening caused by a high current flow of 100 mA had the effect of lowering the minimum contact force. After the minimum contact force is exceeded, the contact resistance initially follows the asperity plastic deformation behavior, where the contact resistance is related to the resistivity and hardness of the contact material. In the higher contact force regime, the decrease in the contact resistance becomes almost negligible. With increasing contact force, the effective contact area is limited by the effect of the film thickness on a hard substrate. From these results, we found the principal factors influencing the contact behaviors of the Au-to-Au contacts to be the resistivity, hardness and softening temperature of the contact materials and the design factors such as the surface roughness, the film thickness and the substrate.

61 citations

Journal ArticleDOI
TL;DR: In this paper, the impact of device operating parameters on the ON-state resistance (RON) of microelectromechanical relays with tungsten (W) electrodes is reported.
Abstract: The impact of device operating parameters on the ON-state resistance (RON) of microelectromechanical relays with tungsten (W) electrodes is reported. Due to the susceptibility of W to oxidation, RON increases undesirably over the device operating cycles. This issue is aggravated by Joule heating when the relay is in the on state. The experimental results confirm that shorter ON time, as well as shorter off time, provides for more stable RON with respect to the number of ON/OFF switching cycles.

56 citations


Cites background from "Metal contact reliability of RF MEM..."

  • ...Although hard metals such as W are more resistant to mechanical stress and physical deformation, they are also more susceptible to chemical reaction, particularly oxidation [7]....

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Journal ArticleDOI
TL;DR: In this article, the reliability of Pt-and RuO2-coated ohmic relays in ultra-high purity gas environments was evaluated using a self-aligned shadow mask that provides electrical isolation between different traces.
Abstract: We have fabricated, tested and analyzed the reliability of Pt- and RuO2-coated ohmic microrelays in ultra-high purity gas environments. RuO2-coated relays could survive 3 × 108 contact cycles without electrical degradation, while Pt-coated devices degraded after 105 cycles. Thermally actuated microrelays were fabricated using a process that employed a polysilicon surface-micromachined substructure. After releasing the devices, just a few blanket metal depositions were required to create the different coatings. This method allowed direct comparisons between different coating materials, and was enabled by a self-aligned shadow mask that provides electrical isolation between different traces. Testing was performed in a clean environment achieved through in situ ultra-high vacuum bakeouts, chamber cooling to <5 × 10−9 Torr and chamber refill with ultra-high purity gases. The RuO2 coatings were formed by two avenues—reactive sputtering and thermal oxidation. No significant difference in contact resistance or reliability was detected for these two deposition methods. For all coatings, post-test analysis by scanning electron microscopy and Auger electron spectroscopy indicated no difference in carbon concentration on real contact versus non-contacting areas, implying that carbon did not play a role in limiting the switches’ reliability. The Pt-coated switch reliability limit was attributed to surface wear rather than to the growth of a contaminating film. For the RuO2 switches, trace resistance was reduced by ten times using an Al underlayer, so that the total device resistance was compatible with commercial device requirements. Because RuO2 is expected to be resistant to hydrocarbon contamination, this work shows that the RuO2 coating provides a promising path toward achieving ultra-high reliability ohmic microswitches.

43 citations


Cites background from "Metal contact reliability of RF MEM..."

  • ...Its incomplete removal is a major source of process-induced carbonaceous material [56, 57]....

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References
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Journal ArticleDOI
TL;DR: In this paper, a clean metal contact resistance model was used to study the contact resistance of microswitches with gold contacts, and the measured contact resistance (measured as a function of contact force) with the characteristics predicted by the model showed approximate agreement.
Abstract: Surface micromachined, electrostatically actuated microswitches have been developed at Northeastern University. Microswitches with gold contacts typically have an initial contact resistance of the order of 0.1 Ω over the first 10 5 cycles of lifetime while cold-switching 4 mA, and have a current handling capability of about 20 mA. In general, the contact resistance decreases over the first few thousand switch cycles, and degrades progressively when the switches are cycled beyond approximately 10 6 cycles. In this work, the microswitch contact resistance is studied on the basis of a clean metal contact resistance model. Comparison of the measured contact resistance (measured as a function of contact force) with the characteristics predicted by the model shows approximate agreement. The discrepancies between the model characteristics and measurements are discussed briefly.

236 citations

Proceedings ArticleDOI
TL;DR: In this paper, an interface force microscope (IFMIMM) was used to measure contact currents from 10 fA to 10 mA and forces ranging from 0.01 to 100 N. Both attractive and repulsive forces on the probe tip were found to exist at significant distances (greater than 5 nm) from the gold surface.
Abstract: Electroplated gold surfaces of the type used for MEMS switches were surveyed by atomic force microscopy (AFM) todefine the surface topographical features, and by x-ray photoelectron spectroscopy (XPS) to determine the chemicalcomposition of the contact surface. The gold surfaces were contacted with electr ochemically sharpened gold andtungsten probes using an interface force microscope (IFM), capable of simultaneously measuring contact currents from10 fA to 10 mA and forces ranging from 0.01 to 100 N. Both attractive and repulsive forces were observed, andattractive forces on the probe tip were found to exist at significant distances (greater than 5 nm) from the gold surface.The radius of the probe tip is on the order of a micron, making it a useful model system for a single-asperity contact onan actual MEMS switch-contact surface. The results of these single-contact measurement events are compared withcontact measurements made with MEMS switches of various sizes and actuation schemes to understand the origins ofcontact resistance and switch failure.Keywords: Contact, MEMS, relay, switch, Au, gold, IFM, microcontact, microrelay, reliability

25 citations

Journal ArticleDOI
TL;DR: In this paper, the contact compatibility of an organic vapor in combination with a certain contact material depends mainly on its chemical structure and its volatility, volatility, the basic structure type of the molecule (e.g., aromatic or aliphatic, length of the carbon chain), certain active groups on the other hand.
Abstract: The formation of carbon on the contact surfaces of commercial relays by thermal decomposition of organic vapors emanating from various organic materials may cause an undesirable increase of the contact resistance in the range of several Ohms. Previous investigations revealed that the contact compatibility of an organic vapor in combination with a certain contact material depends mainly on its chemical structure. There are additional correlations between the contact compatibility on the one hand and a few parameters of the vapors like volatility, the basic structure type of the molecule (e.g., aromatic or aliphatic, length of the carbon chain), certain active groups on the other hand. The contact compatibility values of a few mixtures of organic vapors investigated corresponded to those of their individual components. Humidity and oxygen concentration of the atmosphere influenced the phenomenon effectively.

14 citations


"Metal contact reliability of RF MEM..." refers background in this paper

  • ...The reliability of metal contacts was the topic of intense study for decades during the development of miniature relays for telecommunication and other applications [2-6]....

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Proceedings ArticleDOI
01 Jan 2005
TL;DR: Ceramic via wafer-level packaging of MEMS switches using eutectic gold-tin solder as well as tin-silver-copper solder combined with gold thermo-compression bonding is presented in this paper.
Abstract: We will present a novel approach to wafer level packaging for micro-electro-mechanical systems Like most common MEMS packaging methods today, our approach utilizes a wafer bonding process between a cap wafer and a MEMS device wafer However, unlike the common methods that use a silicon or glass cap wafer, our approach uses a ceramic wafer with built-in metal-filled vias, that has the same size and shape as a standard 150 mm silicon wafer This ceramic via wafer packaging method is much less complex than existing methods, since it provides hermetic encapsulation and electrical interconnection of the MEMS devices, as well as a solderable interface on the outside of the package for board-level interconnection We have demonstrated successful ceramic via wafer-level packaging of MEMS switches using eutectic gold-tin solder as well as tin-silver-copper solder combined with gold thermo-compression bonding In this paper, we will present the ceramic via MEMS package architecture and discuss the associated bonding and assembly processesCopyright © 2005 by ASME

6 citations

Journal ArticleDOI
TL;DR: The true essence of worth in any component (electrical, mechanical or solid state) can be illustrated by the length of time the particular device has been in use as discussed by the authors, which is the main reason why industry will continue to use components of proven reliability in many applications unless the new product demonstrates clearly its superiority in a number of spheres-cost, reliability, size, availability etc.
Abstract: The true essence of worth in any component (electrical, mechanical or solid state) can be illustrated by the length of time the particular device has been in use. Although the passage of time sees the introduction of many new devices, in the main, industry will continue to use components of proven reliability in many applications unless the new product demonstrates clearly its superiority in a number of spheres-cost, reliability, size, availability etc.

3 citations