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.