A review of micro-contact physics for microelectromechanical systems (MEMS) metal contact switches

Abstract

Innovations in relevant micro-contact areas are highlighted, these include, design, contact resistance modeling, contact materials, performance and reliability. For each area the basic theory and relevant innovations are explored. A brief comparison of actuation methods is provided to show why electrostatic actuation is most commonly used by radio frequency microelectromechanical systems designers. An examination of the important characteristics of the contact interface such as modeling and material choice is discussed. Micro-contact resistance models based on plastic, elastic-plastic and elastic deformations are reviewed. Much of the modeling for metal contact micro-switches centers around contact area and surface roughness. Surface roughness and its effect on contact area is stressed when considering micro-contact resistance modeling. Finite element models and various approaches for describing surface roughness are compared. Different contact materials to include gold, gold alloys, carbon nanotubes, composite gold-carbon nanotubes, ruthenium, ruthenium oxide, as well as tungsten have been shown to enhance contact performance and reliability with distinct trade offs for each. Finally, a review of physical and electrical failure modes witnessed by researchers are detailed and examined.

Observation and Understanding of the Initial Unstable Electrical Contact Behaviors

“…4,5 However, MEMS switch reliability is a major area for improvement for large-volume commercial applications. [6][7]8,9,10 Most of these critical issues, related to reliability, are closely related to the physics of electrical contacts. Much of the underlying physics and experience gained with conventional electrical switches is described in Holm's classic book.…”

When will MEMS Switches be Ready for Commercial Products?

“…Microelectromechanical systems (MEMS) and advanced microsystem devices have matured significantly over the last 20 years and are currently used in automobiles, cellular phones, printers, and overhead projectors [1]. MEMS switches are viewed by many as paramount for next generation radio frequency (RF) circuits and applications due to their extremely low power consumption (i.e.…”

Finite element modeling of nickel oxide film for Au-Ni contact of MEMS switches

“…For MEMS switches, the contact force is very low (μN-mN), which brings only highest asperities in contact [1], and the real contact area Ar is only a very small portion of the apparent area Aa, as Ar =10…”