Abstract
Most failures in micro electromechanical system (MEMS) switches can be attributed to the degradation of contact surfaces and sticking contacts. A wear-tolerant composite contact material, composed of a Au film supported by multi walled carbon nanotubes (Au/MWCNT), has been engineered to provide wear resistance and enhanced switching lifetime with conductive properties close to pure Au. Switching lifetimes of billions of cycles have been demonstrated, representing greatly increased performance over thin film Au. Below the arcing threshold (~12 V) the wear mechanism has been shown to be a combination of the fine transfer of contact material by the molten metal bridge (MMB) phenomenon and a delamination of the Au. In this study, the composite contact is hot switched at low current DC conditions (4 V DC and 20 mA) while the contact force is measured at the micro Newton scale in nanosecond resolution. The characteristic voltage waveform associated with the MMB is observed with forces detected as the contact softens, melts, and separates. The presence of a delamination event (DE) is also observed, where the contact opens abruptly with no MMB phenomenon apparent. The DE contact openings are associated with a transient peak force of 21.6 ± 2.3 µN while the MMBs are linked to a lower peak force of 18.1 ± 2.5 µN.
Highlights
The use of a metal-to-metal contact interface in a microelectromechanical system (MEMS) switch offers the advantages of a low contact resistance in the on-state while the air gap between contacts provides a high impedance in the off-state
The results show that the molten metal bridge (MMB) event can be detected by the force sensing method
The force transients are linked to the melting and boiling processes that areof linked to a transients fine transfer are wearobserved process
Summary
The use of a metal-to-metal contact interface in a microelectromechanical system (MEMS) switch offers the advantages of a low contact resistance in the on-state while the air gap between contacts provides a high impedance in the off-state These characteristics provide a low signal power loss with a radio frequency supply (insertion loss) and a large ratio between the on and off state impedance (isolation). The MEMS switch contact is typically a thin film of metal on a silicon substrate, with the moving contact formed by etching away material to form a beam or cantilever Precious metals such as gold or platinum are often used for their high conductivity and resistance to oxide formation [2]. This uses a bias electrode to attract the cantilever to close contacts
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