Yap et al. Nanoscale Research Letters 2012, 7:105 http://www.nanoscalereslett.com/content/7/1/105 Page 7 of 8 Figure 6 Two-point probe DC measurement across two interconnection bumps measured across the carrier substrate’s input and output. The CNT bump dimensions were 150 × 150 μm. (a) Similar I-V characteristics were observed to demonstrate the concept of reworkable process using this form of joining methodology. (b) Equivalent electrical circuit for the measured resistances and CNT interconnection bump. identical as they share the same graphene band structure [21]. For MWCNTs, majority of the current only passes through the outermost layer of MWCNTs, and a metallic behavior is expected [23]. Even if the MWCNT is not metallic, the bandgap of semiconducting CNTs can be estimated as Eg = 0.9 eV/diameter, approximating a band- gap of 9 meV for a CNT diameter of 100 nm [16]. In this case, the Fermi level of the CNT in contact with another CNT will align within the bandgap of the semiconducting CNT. The resulting band structures have a negligible Schottky barrier height due to the small bandgap. Thus, the metal-to-CNT and CNT-to-CNT interfaces are similar to the metal-to-metal junctions. The major transport mechanism for electron transport is through tunneling across atomic thick air gap, resulting in an ohmic and lin- ear I-V behavior observed in Figure 6a[22]. From the literature, a typical resistance between indi- vidual metallic CNT to metallic CNT separated by van der Waals distance of 0.34 nm is 200 kΩ [21]. In our work, the gap may be much larger than 0.34 nm, result- ing in a huge tunneling resistance through the air gap and absorbents [24]. Nevertheless, the results obtained from other experiments involving CNT-to-CNT con- tacts displayed positive results and outlook for use as alternatives to solve the high contact resistance between the CNT tip and metal [11,20]. More work will be required to study the formation of reliable and high- performance small-scale CNT interconnection bumps for use as vertical interconnects in the future. Conclusion The feasibility to use the PECVD approach to achieve CNT bump pitches smaller than 150 μm has been stu- died. The introduction of the TiN barrier layer between the Ni catalyst and Au metallization allows an efficient growth of CNT bumps directly on Au while maintaining