Abstract

The proper selection of electrical contact materials is one of the critical steps in designing a metal contact microelectromechanical system (MEMS) switch. Ideally, the contact should have both very low contact resistance and high wear resistance. Unfortunately this combination cannot be easily achieved with the contact materials currently used in macroswitches because the available contact force in microswitches is generally insufficient (less than 1 mN) to break through nonconductive surface layers. As a step in the materials selection process, three noble metals, platinum (Pt), rhodium (Rh), ruthenium (Ru), and their alloys with gold (Au) were deposited as thin films on silicon (Si) substrates. The contact resistances of these materials and their evolution with cycling were measured using a specially developed scanning probe microscope test station. These results were then compared to measurements of material hardness and resistivity. The initial contact resistances of the noble metals alloyed with Au are roughly proportional to their resistivities. Measurements of contact resistance during cycling of different metal films were made under a contact force of 200–250 μN in a room air environment. It was found that the contact resistance increases with cycling for alloy films with a low concentration of gold due to the buildup of contamination on the contact. However, for alloy films with a high gold content, the contact resistance increase due to contamination is insignificant up to 108 cycles. These observations suggest that Rh, Ru, and Pt and their gold alloys of low gold content are prone to contamination failure as contact materials in MEMS switches.

Notes

Originally published in Journal of Applied Physics v.102, 074910 (2007); doi:10.1063/1.2785951

Keywords

contact resistance, gold alloys, hardness, microswitches, platinum alloys, rhodium alloys, ruthenium alloys, scanning probe microscopy, semiconductor-metal boundaries, surface contamination, thin films, wear resistance

Subject Categories

Microelectromechanical systems, Electric switchgear

Disciplines

Electrical and Electronics | Nanoscience and Nanotechnology

Publisher

American Institute of Physics

Publication Date

10-8-2007

Rights Information

Copyright 2007

Rights Holder

American Institute of Physics

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Fig1.zip (772 kB)
Figure 1 - high resolution image

Fig2.zip (172 kB)
Figure 2- high resolution image

Fig3.zip (89 kB)
Figure 3 - high resolution image

Fig4.zip (30 kB)
Figure 4 - high resolution image

Fig5.zip (90 kB)
Figure 5 - high resolution image

Fig6.zip (16 kB)
Figure 6 - high resolution image

Fig7.zip (97 kB)
Figure 7 - high resolution image

Fig8.zip (2160 kB)
Figure 8 - high resolution image

Fig9.zip (2967 kB)
Figure 9 - high resolution image

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