Electromechanical investigation into the influence of MWCNT height on the performance of Au/MWCNT composites for electrical contacts
Au/MWCNT composites have been shown to be a useful contact material for electrical contacts. In this work we have investigated the influence of the MWCNT forest height on both the electrical and mechanical properties. Three heights of MWCNT forest have been investigated (30, 50 and 80 μm, all a sputtered 500 nm Au layer). It is shown that the electrical and mechanical behavior of the 30 and 50 μm composites is quite comparable, whereas there is a large change in the performance where the height is increased to 80 μm. As the MWCNT height is increased the effective hardness of the composite reduces which means that for a given contact pressure, the resultant contact area will be larger for taller MWCNT forests. A larger area combined with a higher resilience to impact is expected to result in larger lifetimes. A consequence of the softer composite with larger contact area is that the molten-metal bridge phenomenon has been shown to increase with MWCNT height. Experimental data is discussed to identify the optimum MWCNT height where the sputtered Au thickness is 500 nm. By analyzing the Au:MWCNT thickness ratio, it is possible to infer the optimum value for other thickness of Au. Combining this data with our model, it is also possible to estimate optimum thicknesses with other contact materials.
The Relationship Between Contact Resistance and Contact Force on Au-Coated Carbon Nanotube Surfaces Under Low Force Conditions
Carbon nanotube (CNT)-coated surfaces are investigated to determine the electrical contact performance under low force conditions. The surfaces under investigation are vertically aligned multiwalled CNTs formed on a silicon substrate and coated with an Au film. These planar surfaces are mated with a hemispherical Au plated probe mounted in a nanoindentation apparatus. The maximum contact force used is 1 mN. The contact resistance of these surfaces is investigated as a function of the applied force and is also studied under repeated loading cycles. The surfaces are compared with a reference Au-Au contact under the same experimental conditions and the results compared to established contact theory. The results show that the vertically aligned multiwalled CNT surface provides a stable contact resistance. This paper shows the potential for the application of CNT surfaces as an interface in low force electrical contact applications.
Mechanical characterization of a Au coated carbon nanotube multi-layered structure
Multiwalled Carbon Nanotube (MWCNT)-coated surfaces have been proved to be able to provide stable resistance for the electrical contact under low force conditions since they can offer a compliant support for the conducting gold layer. However, the contact mechanics of the Au/MWCNTs composite have not been understood. In this study, a finite element multilayered contact model was developed, in which the top layer was modeled as a composite and under layer was modeled as CNT forest. The study shows that this complex surface is best modeled as a multi-layered structure. The model is optimized and validated with nano-indenter data. The model can help to better understand the configuration and material properties of Au/CNTs surfaces, and can provide guidance to optimize the surface in terms of contact resistance performance in MEMS switches.