A nano-indentation study of the contact resistance and resistivity of a bi-layered Au/multi-walled carbon nanotube composite

Abstract

A bi-layer metal-carbon nanotube composite has been developed as a potential low-force electrical contact surface, for application in micro-electromechanical systems switching devices. The samples consist of a vertically aligned forest of multi-walled carbon nanotube (MWCNT), sputter coated with a layer of Au. The effect of varying the components and composition are investigated by means of a modified nano-indenter. By measuring the contact resistance of the composites under various loading conditions, the electrical properties and performance can be evaluated. The composites are shown to have homogenous properties, with each of the layers influencing the total electrical characteristics of the samples. The internal structure of the sample, the MWCNT height and penetration of gold into the forest is shown to directly influence the performance and characteristics of the samples. By analyzing the samples as bulk, the effective resistivities of the composites are also determined to have values from 303 nΩ m down to 54 nΩ m, depending on the composition of the samples.

The Relationship between Contact Resistance and Roughness (Sq) of a Bi-layered Surface using a Finite Element Model

“…4. The data was used to determine the effective resistivity using Eq (1), [9,11]. The effective resistivity for the 505 surface is shown in Fig.…”

“…1&2 are for a composite surface of 50 µm high, vertically aligned, carbon nanotubes partially shown in Fig. 2 and coated with a 500 nm nominal layer of Au (referred to as a 505 surface) [8,9]. The measured rough surface is shown over a measured area of 0.15 mm x 0.15 mm with a sample length of (δ) 0.25 µm.…”

“…As already noted, a fundamental parameter for the calculation of the contact resistance (or in this case the constriction resistance as there is no significant contribution from film contamination or oxide film formation); is the effective resistivity of the surfaces. It was shown in [9], based on the modified nano-indentation test used in [6], for a 1mm ball; that the effective resistivity was a function of the composite mixture, and related to a ratio of the metallic film thickness over the CNT growth height. Further to this it was observed that at higher force levels (>1.2 mN), the effective resistivity increased for a given surface (e.g.…”

“…5). In [9] the effective resistivity (ρ e), was determined from the measured contact resistance (Rc) using Eq. (1).…”

Transient Contact Opening Forces in a MEMS Switch Using Au/MWCNT Composite

“…The carbon nanotubes provide a mechanically compliant sublayer, allowing the conductive Au to conform to the incoming contact ( Figure 2). This provides reduced contact pressure, increased contact area, and a mechanism to absorb the kinetic energy of contact closure [18], when compared to thin film Au-Au contacts. The vertical alignment of the nanotubes is crucial in achieving the extended lifetime as random or non-vertical alignments provide negligible benefit [19].…”