Graphene Enabled Vertical Field Effect Transistors

Vertical field effect transistors (VFETs) using a carbon nanotube source electrode have recently demonstrated state-of-the-art current densities at low operating voltages from comparatively low mobility organic semiconductors. Unlike in conventional thin film transistors, transconductance arises from a gate field modulation of the contact barrier at the organic semiconductor/nanotube interface (with the performance enhanced by nanotube Fermi level shifts allowed by their low density of electronic states). Graphene's low density of states near the Dirac point similarly makes it a good candidate source electrode in VFETs. We have now demonstrated such devices, facilitated by the use of a novel transfer technique that improves areal yields while avoiding both polymeric residue and the particulates that necessitate the use of thicker channel layers in nanotube VFETs. Critical to high performance is a facile method developed for perforating the graphene sheet with holes of a tunable size and density, allowing for a direct assessment of the role of self-screening effects in VFETs. These initial graphene enabled VFETs achieve on-current densities exceeding 250mA/cm$^{2}$ at drive voltage swings of less than 4V with on/off current ratios larger than 10$^{6}$.