Cofabrication of Vacuum Field Emission Transistor (VFET) and MOSFET

Co-fabrication of a nanoscale vacuum field emission transistor (VFET) and a metal-oxide-semiconductor field effect transistor (MOSFET) is demonstrated on a silicon-on-insulator wafer. The insulated-gate VFET with a gap distance of 100 nm is achieved by using a conventional 0.18-μm process technology and subsequent photoresist ashing process. The VFET shows a turn-on voltage of 2 V at a cell current of 2 nA and a cell current of 3 μA at the operation voltage of 10 V with an ON/OFF current ratio of 10⁴. The gap distance between the cathode and anode in the VFET is defined to be less than the mean free path of electrons in air, and consequently, the operation voltage is reduced to be less than the ionization potential of air molecules. This allows the relaxation of the vacuum requirement. The present integration scheme can be useful as it combines the advantages of both structures on the same chip.