Micro-Contact Performance Characterization of Carbon Nanotube (CNT)-Au Composite Micro-Contacts

Abstract

This paper presents the micro-contact performance comparison between contact pairs of Au/Au and composite contact pairs Au/Au-CNT. The Au/Au-CNT micro-contact's planarlower contact interface is an Au-CNT composite film with encapsulated CNTs. Micro-contact performance is affected by factors such as applied micro-contact force, temperature, current density, etc. At the micro-contact interface, asperities provide localized points for current flow. Increased temperature at these localized points may soften the contact metal and lead to bridge transfer. Prior work revealed that an Au/CNT contact pair performed poorly compared to an Au/Au contact pair, with two orders of magnitude difference in contact resistance. To maintain microcontact performance and to reduce thermal effects, a Au/Au-CNT micro-contact was designed and fabricated. This design allows the micro-contact interface to remain Au/Au with the embedded CNTs acting as a thermal conduction conduit below the lower Au contact interface. The upper micro-contact support structure is an Au micromachined fixed-fixed beam with hemisphere-shaped upper contact geometry. The micro-contacts were studied under repeated cycles using an external, calibrated load, resulted in repeatable resistance of approximately 1Ω for nearly 40 million cycles. This research revealed that including a CNT composite film in the lower contact extend the operating life and lower contact resistance as compared to similarly constructed microcontacts.

Micro-Contacts Testing using a Micro-Force Sensor Compatible with Biological Systems

“…~250µN). During CST, a constant current of 46mA and a constant contact force of 200µN were used during the individual measurement cycles [17]. This test methodology was necessary to avoid continuous, inadvertent higher power hot switching of the micro-contacts.…”

“…Au-CNT composite lower contact, hemisphere on flat, micro-contacts Figure 13 is ICT and CST data for an Au-CNT composite lower contact in a hemispherical on lower planar contact pair [17]. The ICT (Figure 13a) compares modeled values for micro-contact resistance to measured data.…”

“…During this test, the current was applied only once the contact was fully closed and it was then removed prior to breaking contact. These steps are then repeated for the desired number of cycles at a maximum frequency of 3kHz [13][14][15][16][17].…”

“…The fixed-fixed beams had a width of 150µm and a variety of lengths ranging from 350µm to 500µm. The beams were designed with a hemispherical upper contact bump of diameter 6-8µm, a lower planar contact and a gap distance between the upper and lower contacts of 2µm [16,17]. Generally, the lower contacts were evaporated Au (all except for Au-CNT composite films) while the upper contacts were sputtered or reactively sputtered Au.…”

When will MEMS Switches be Ready for Commercial Products?

“…In addition, we have studied engineered micro-contact geometries and pairs consisting of hemispherical upper contacts landing on either planar or 2D pyramid lower contacts. Additional studies in low-frequency AC, external circuit loadings, and DC polarity test have also been conducted [11][12][13][14][15]. In summary, it's the opinion of this author that MEMS switches will continue to not be commercialized until the MEMS research community fully engages with Industry to obtain realistic specifications for real applications.…”