Electron-beam and ion-beam-induced deposited tungsten contacts for carbon nanofiber interconnects.

Ion-beam-induced deposition (IBID) and electron-beam-induced deposition (EBID) with tungsten (W) are evaluated for engineering electrical contacts with carbon nanofibers (CNFs). While a different tungsten-containing precursor gas is utilized for each technique, the resulting tungsten deposits result in significant contact resistance reduction. The performance of CNF devices with W contacts is examined and conduction across these contacts is analyzed. IBID-W, while yielding lower contact resistance than EBID-W, can be problematic in the presence of on-chip semiconducting devices, whereas EBID-W provides substantial contact resistance reduction that can be further improved by current stressing. Significant differences between IBID-W and EBID-W are observed at the electrode contact interfaces using high-resolution transmission electron microscopy. These differences are consistent with the observed electrical behaviors of their respective test devices.

Carbon nanofiber interconnect RF characteristics improvement with deposited tungsten contacts.

Carbon nanotubes (CNTs) and carbon nanofibers (CNFs) are potential materials for high-performance electronic devices and circuits due to their light weight and excellent electrical properties such as high current capacity and tolerance to electromigration. In addition, at high frequencies, these materials exhibit transport behavior which holds special promise for applications as on-chip interconnects. Contact resistance at CNF-metal interface is a major factor in limiting the electrical performance of CNF interconnects at all frequencies. In this paper, it is demonstrated that the contact resistance can be minimized and the high-frequency characteristics much enhanced by depositing tungsten on CNF-metal electrode contacts.

The effect of catalysts and underlayer metals on the properties of PECVD-grown carbon nanostructures.

The growth behaviors and contact resistances of vertically aligned carbon nanotubes (CNTs) and carbon nanofibers (CNFs) grown on different underlayer metals are investigated. The average diameter, diameter distribution, density, growth rate and contact resistance exhibit strong correlation with the choice of catalyst/underlayer combination. These observations are analyzed in terms of interactions between the catalyst and the underlayer metal. The CNT via test structure has been designed and fabricated to make current-voltage measurements on single CNTs using a nanomanipulator under scanning electron microscopy (SEM) imaging. By analyzing the dependence of measured resistance on CNT diameter, the CNT-metal contact resistance can be extracted. The contact resistances between as-grown CNTs and different underlayer metals are determined. Relationships between contact resistances and various combinations of catalysts and underlayer metals are investigated.

Functionalization of carbon nanotubes via nitrogen glow discharge.

We have exposed single-wall carbon nanotubes (SWCNTs) to microwave-generated N2 plasma with the aim to functionalize the nanotubes. The results strongly depend on the distance between the discharge source and the sample, since nitrogen atoms generated can be lost due to recombination. No functionalization was observed when this distance was 7.0 cm. At intermediate distances (2.5 cm), the incorporation of nitrogen and oxygen onto the SWCNT was observed, while, at short distances (1 cm), products containing CN were also observed.