Sep 7, 2010
Tiny whiskers of carbon probed for 3D electronics role
The race towards miniaturization continues to fuel innovation in new materials, architectures and devices for pushing integration densities to unprecedented levels, from the micro- to the nanoscale regime. In this nanoscale regime, it is often difficult to measure and characterize the properties of materials, often in unusual architectures, to validate their utility in nano-devices for electronics applications.
To tackle this issue, researchers at the Jet Propulsion Laboratory and the California Institute of Technology have implemented measurement techniques to determine the suitability of materials for three-dimensional (3D) electronics, in particular 3D nano-electro-mechanical systems (NEMS). The apparatus enables scientists to probe the electrical and mechanical properties of individual carbon nanofibers (CNFs) or "whiskers", which protrude normal to the substrate. This unique 3D architecture promises a 10 times increase in integration density compared with two-dimensional (2D) planar NEMS.
The CNFs were synthesized with plasma-enhanced chemical vapour deposition (PECVD). To determine the electrical properties of the CNFs, the structures were measured using a scanning electron microscope (SEM) equipped with an electrical probe stage. These probes were manipulated with nanoscale precision to contact individual CNFs to decipher their electrical conduction characteristics. When a small gap existed between the CNF and the probe (see figure 1a, left), the application of a voltage caused the CNF to bend towards the probe (as shown in figure 1a, right), resulting in a switching event. These switching voltages were measured to be between 10 and 40 V, and the presence of stiction suggests that such structures have promise in non-volatile memory.
Mechanical properties of the individual CNFs were measured using a custom-built in situ mechanical deformation instrument in the Greer lab, the SEMentor, comprised of an SEM and a nano-mechanical module similar to a nanoindenter. While the CNF was loaded for the uniaxial compression tests (figure 1b, left), force-deflection data were gathered (figure 1b, right) from which a Young's modulus of >800 GPa was measured, which suggests that the inherent switching speeds of the CNFs should be very high for NEMS. The CNFs were also found to be very elastic and resilient in bending tests. Future work in 3D NEMS switches and resonators with monolithically integrated electrodes is currently in progress.
The researchers presented their work in the journal Nanotechnology.
About the author
Anupama B Kaul is a task manager and senior member of the technical staff at JPL. She is interested in functional micro- and nanoscale materials and integrating such materials into devices and hybrid nanosystems for applications in electronics, photonics, energy harvesting and quantum-scale devices. Krikor Megerian is involved in developing fabrication processes for a wide variety of sensors and detectors at the JPL Microdevices Laboratory. Andrew T Jennings is a PhD student in the Department of Materials Science at Caltech. His interests lie in the study of how nanoscale materials break. Julia R Greer is an assistant professor of materials science and mechanics at Caltech. Her research focus is in nano-mechanical material behaviour. We gratefully acknowledge critical support and infrastructure provided for this work by the Kavli Nanoscience Institute at Caltech. This research was carried out at the Jet Propulsion Laboratory, California Institute of Technology, under a contract with the National Aeronautics and Space Administration and was funded through the internal Research and Technology Development (R&TD) program (01STCR, R.08.023.60). Financial support for the work in the Greer lab was from JRG's NSF CAREER award (DMR-0748267).