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Proceedings Paper

Metal contact reliability of RF MEMS switches
Author(s): Qing Ma; Quan Tran; Tsung-Kuan A. Chou; John Heck; Hanan Bar; Rishi Kant; Valluri Rao
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Paper 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 N2 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.

Paper Details

Date Published: 19 January 2007
PDF: 13 pages
Proc. SPIE 6463, Reliability, Packaging, Testing, and Characterization of MEMS/MOEMS VI, 646305 (19 January 2007); doi: 10.1117/12.702177
Show Author Affiliations
Qing Ma, Intel Corp. (United States)
Quan Tran, Intel Corp. (United States)
Tsung-Kuan A. Chou, Intel Corp. (United States)
John Heck, Intel Corp. (United States)
Hanan Bar, Intel Corp. (United States)
Rishi Kant, Intel Corp. (United States)
Valluri Rao, Intel Corp. (United States)

Published in SPIE Proceedings Vol. 6463:
Reliability, Packaging, Testing, and Characterization of MEMS/MOEMS VI
Allyson L. Hartzell; Rajeshuni Ramesham, Editor(s)

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