Hirohiko Kitsuki

Length dependence of current-induced breakdown in carbon nanofiber interconnects

Current-induced breakdown is investigated for carbon nanofibers (CNF) for potential interconnect applications. The measured maximum current density in the suspended CNF is inversely proportional to the nanofiber length and is independent of diameter. This relationship can be described with a heat transport model that takes into account Joule heating and heat diffusion along the CNF, assuming that breakdown occurs when and where the temperature reaches a threshold or critical value.

Temperature Modeling for Carbon Nanofiber Breakdown

Carbon nanofibers (CNF) are proposed for electrical interconnect applications because of their relatively large current capacity and ability to form well-aligned one-dimensional structures. It is experimentally determined that nanofibers that are suspended between two electrodes breakdown at or near the nanofiber center. Based on published property values a simple model is used to calculate the temperature and quantify the effect of heat generation at the CNF/electrode interface on the nanofiber temperature. The model has the capability to separately account for the substrate temperature and the temperature at the CNF/electrode junction. It is determined that the CNF reaches a temperature at which carbon oxidation is likely to occur.Copyright

Bright-field transmission imaging of carbon nanofibers on bulk substrate using conventional scanning electron microscopy

The authors present scanning transmission electron microscopy (STEM) of carbon nanofibers (CNFs) on a bulk substrate using conventional scanning electron microscopy (SEM) without specimen thinning. By utilizing the electron beam tilted >85° from the substrate normal, bright-field STEM contrast is obtained for the CNFs on substrate with conventional SEM. Analysis of the observed contrast using Monte Carlo simulation shows that the weakly scattered electrons transmitted from the CNF are selectively enhanced by the largely tilted substrate and result in the observed STEM contrast. This mechanism provides a useful STEM imaging technique to investigate the internal structure of materials on bulk substrates without destructive specimen thinning.

Image Formation Mechanisms in Scanning Electron Microscopy of Carbon Nanofibers on Substrate

Nanostructures fabricated on thick substrates (typically a silicon wafer) are building blocks for high-performance electronic devices. While detailed structural analysis using high-resolution electron microscopy usually requires a thinning process to obtain an electron transparent specimen, a non-destructive approach is also required to analyze the structure. A recent study showed that heat dissipation into the substrate from a nanotube device governs its electronic transport characteristics [1]. In such a system, structural analysis that can be performed without any sample modification is favorable since imaging can be performed before, after, and even during the electrical operation of devices to investigate structural change. In this paper, we present two kinds of imaging techniques using conventional scanning electron microscopy (SEM) developed for the characterization of carbon nanofiber (CNF) devices fabricated on a thick Si substrate without any sample modification.

Electron Transport Across Interfaces in Horizontal Carbon Nanofiber Interconnects

In a carbon nanofiber (CNF) metal contact such as a bridge between two metallic electrodes, passing high current (current stressing) reduces the total resistance of the system (CNF resistance RCNF and contact resistance Rc) by orders of magnitude. The role of current stressing is modeled as a reduction in the interfacial tunneling gap with transport characteristics attributed to tunneling between Au and CNF. The model predicts a reduction in Rc and the nonlinearity in the current-voltage (I-V) characteristics gradually disappears as Rc decreases. These results are consistent with I-V behavior measured experimentally.

Current-induced breakdown of carbon nanofiber interconnects

Current-induced breakdown phenomena of carbon nanofibers (CNFs) for future on-chip interconnect applications are presented. The effect of heat dissipation via the underlying substrate is studied using different experimental configurations. Scanning electron microscopy (SEM) techniques are utilized to study the structural damage by current stress. While the measured maximum current density in the suspended CNF in air is inversely proportional to nanofiber length and independent of diameter, SiO2-supported CNFs improves their current capacity, which implies effective heat dissipation to the oxide. The correlation between maximum current density and electrical resistivity confirms the importance of local Joule heating, showing strong coupling between electrical and thermal transport in CNFs.

Current-induced breakdown of carbon nanofibers for interconnect applications

Current-induced breakdown phenomena of carbon nanofibers (CNFs) for future on-chip interconnect applications are presented. Scanning transmission electron microscopy (STEM) techniques are developed to study the structural damage by current stress, including in situ electrical measurement with STEM, and sample-preparation-free STEM imaging. The analysis shows that the breakdown occurs along graphitic layers comprising the CNF and that the maximum current density has strong correlation with electrical resistivity. The effect of heat dissipation into the underlying substrate is also studied using different experimental configurations.

High-Current Reliability of Carbon Nanofibers for Interconnect Applications

We present a high-current reliability study of carbon nanofibers (CNFs) for interconnect applications. In situ scanning transmission electron microscopy (STEM) reveals structural damage to CNFs after current stress. The effect of heat dissipation on the current capacity is also discussed by using different experimental configurations. Long-time reliability tests are performed with a vertical via interconnect structure, showing promising high reliability of CNF interconnects for future electronic devices.

Current-carrying Capacity of Carbon Nanofiber Interconnects

Current-carrying capacity of carbon nanofibers (CNF) is investigated for potential interconnect applications. The measured maximum current density in the suspended CNF in air is inversely proportional to nanofiber length and independent of diameter. This relationship can be described with a heat transport model that takes into account Joule heating and heat diffusion along the CNF, assuming that breakdown occurs when and where the temperature reaches a threshold or critical value. Supporting the CNFs with SiO2 improves their current capacity, which implies effective heat dissipation to the oxide.

Analysis of carbon-based interconnect breakdown

Current-induced breakdown phenomena of carbon nanofibers (CNFs) for future on-chip interconnect applications are presented. The effect of heat dissipation via the underlying substrate is studied using different experimental configurations. Scanning electron microscopy (SEM) techniques are utilized to study the structural damage by current stress. While the measured maximum current density in the suspended CNF in air is inversely proportional to nanofiber length and independent of diameter, SiO2-supported CNFs improves their current capacity, which implies effective heat dissipation to the oxide. The correlation between maximum current density and electrical resistivity confirms the importance of local Joule heating, showing strong coupling between electrical and thermal transport in CNFs.