Conductive Carbon Nanotube Composite Microprobes

Abstract

Because of their outstanding electrical and mechanical properties, including high stiffness and mechanical resilience, ballistic electron transport at micrometer scales, and high current-carrying capacity, [1] carbon nanotubes (CNTs) could enable a new class of electrical elements ranging from transistors to interconnects. However, realizing the properties of individual CNTs in assemblies of CNTs has been a formidable challenge. Realistic applications of CNTs at the micrometer scale must employ thousands or millions of CNTs in a parallel fashion, yet, the understanding of the electromechanical behavior is still not mature enough. Most of the research so far has been either for sensing [2] or actuation applications, [3][4][5][6] whereas the potential benefits of CNTs in probing applications, where both mechanical integrity and electrical conduction is critical, have not been investigated as yet. Electromechanical probing applications continuously require smaller pitches, faster manufacturing, and lower electrical resistance. Achieving low-pitch structures without compromising elastic properties is a challenge with conventional techniques, such as in microelectromechanical systems (MEMS)-based structures. CNT-based structures present a scalable manufacturing approach, in which thousands of probes can be fabricated in very short production times and by means of a full wafer batch fabrication mode, reducing the fabrication steps currently necessary with conventional methods, all of which can have significant cost benefits.Growth of vertically aligned CNTs (VA-CNTs) by thermal chemical vapor deposition (CVD) [7,8] has created films and microstructures containing large numbers of CNTs aligned in parallel. Unfortunately, these high-temperature synthesis processes are typically optimized for growth from metal nanoclusters on silicon and ceramic substrates; whereas devices utilizing these CNTs will require a wider variety of substrates, including metals and plastics that cannot withstand the harsh processing conditions for high-yield CNT growth. To our knowledge, growth of VA-CNTs by thermal CVD with simultaneous ohmic contact on electrically conductive substrates has not yet been achieved and will remain a major challenge because of the apparent necessity of a buffer layer, such as Al 2 O 3 , SiO 2 , or MgO, for high-yield VA-CNT growth. Furthermore, weak mechanical adhesion to the substrate [7] and low bulk density [9] often prevent robust electrical and mechanical integration of CNTs under as-grown conditions. An emerging approach for device integration of VA-CNTs is to transfer the VA-CNTs from the growth substrate to a second "device" substrate. Full films of VA-CNTs have been transferred with a main emphasis on field-emission applications; however, the nature of interconnection to the CNTs and the lengthwise electrical and mechanical properties of the transferred films have not been assessed. CNTs have been previously embedded in an otherwise insulating matrix to form conducting composites, [10] but these are not al...

Transfer of patterned vertically aligned carbon nanotubes onto plastic substrates for flexible electronics and field emission devices

“…[7][8][9][10][11] The reported methods of CNT array transfer can be categorized according to the processing technique used. In the wet method, 8,12,13 CNTs soaked by the solvent, existed in adhesive paste, result in shrinkage of the CNT pattern due to capillary force. The stamp method is usually applied to transfer randomly or horizontally aligned CNTs rather than vertically aligned CNTs ͑VA-CNTs͒ because VACNTs are unable to sustain a vertical load.…”

Electroless silver plating and in-situ SEM characterization of CNT-metal hybrid contactors

“…Separable electrical contacts follow the same trends and are moving toward lower mating forces, increased working range and increased durability as well. Unique properties of vertically aligned carbon nanotubes (VA-CNT) make them attractive for use as compliant, electrically conductive structures appropriate for both permanent and separable electrical connections, and the concept of carbon nanotube based electromechanical probes has been presented previously [1][2][3][4][5]. The nonlinear elastic deformation exhibited by these structures as discussed in [6] highlights their potential for use in separable electrical connections.…”

Novel synthesis process for ceramic carbon nanotube nanocomposites with nanojunctions

“…Following CNT growth, all the support materials (MgO, catalytic metallic nanoparticles) need to be removed before harvesting the CNTs for further applications. CNTs serve as the potential building blocks for the next generation of nanoelectronic devices due to their remarkable electronic properties, such as tunable conductivity, extremely high ballistic electron mobility 10, and high charge‐storage capacity 11. Lately, their impressive electrical properties have opened a new field for the development of novel CNT‐based polymeric 12, 13 and ceramic 14 composites.…”