Ultrasonic Nanowelding Technology Between Carbon Nanotubes and Metal Electrodes

Abstract

Carbon nanotubes (CNTs) exhibit a great prospect as a nanoscale building block for future nanoelectronics due to their unique one-dimensional nanostructure and properties [1]. To explore their potential in various domains, an essential prerequisite is to build reliable interconnections between the CNTs and the external electrical circuits and mechanical systems. To address this need, various chemical and physical processes have been explored to build such interconnections. For example, Burghard et al. reported “controlled adsorption of CNTs on chemically modified electrodes” for interconnection of CNTs [2,3]. However, a stronger bonding instead of a weak chemical adsorption is mandatory for constructing reliable nanodevices. Ruoff et al. showed that focused electron beam in a scanning electron microscope (SEM) can be used to deposit a small amount of hydrocarbon contamination so as to attach nanotubes on an AFM tip [4, 5]. Such a “spot welding” technique has also been used for connecting CNTs and polysilicon surface electrically and mechanically [6]. Madsen et al. presented an in situ method for highly conductive attachment of multiwalled carbon nanotubes (MWCNTs) onto microelectrodes by depositing a gold–carbon composite using a focused electron beam system [7]. Although robust contacts can be obtained by the these methods, limited access to a focused electron beam system and the small-scale spot-treatment nature prevent their large-scale industrial applications. To meet the needs of future large-scale applications, simpler, less capital intensive and more scalable processes are highly desirable. In this chapter, we introduce a novel ultrasonic nanowelding process, with which one can fabricate reliable bonding between single-wall carbon nanotubes (SWCNTs) and metal electrodes. Contacts formed by the present process are found to have low contact resistance and good long-term stability and mechanical strength. A low resistance of around 15 k Ω for a 1- µm-long metallic SWCNT at room temperature can be achieved. After nanowelding, the effective Schottky barrier height between semiconducting SWCNT and Ti electrode is as low as ~6:6 meV in the ON-state and the barrier width is ~0:9 nm at Vg = 0. The performance of the CNT field-effect transistors (FETs) fabricated by this method has also been demonstrated to have greatly improved.