Towards Vacuum-Less Operation of Nanoscale Vacuum Channel Transistors

摘要

Nanoscale Vacuum Channel Transistors (NVCTs) could potentially have superior performance compared to solid state devices of equivalent channel length owing to ballistic transport of electrons, shorter transit time and higher intrinsic breakdown voltage [1, 2]. The electron transport channel in NVCTs is free space and hence there is no scattering. Furthermore, there is no opportunity for ionization or avalanche carrier multiplication and NVCTs can have very high breakdown voltage [1]. Hence NVCTs have promise for Johnson figure of merit that could be as high as 1014 V/s. However, they need ultra-high vacuum (UHV) for reliable operation as the field emission process is sensitive to barrier height variations induced by adsorption/desorption of gas molecules. Small changes in the barrier height lead to exponential variations in current [3]. Poor vacuum also leads to generation of energetic ions that bombard the emitter tips, rendering the tips blunt and degrading electrical performance. To overcome the UHV requirement, we propose using graphene to nano-encapsulate only the field emitter either in UHV or in a gas (e.g. helium) with high ionization energy. By separating the field emission region from the acceleration region (where the electrons acquire energy), electrons can be transported in a non-ideal vacuum, if not atmospheric conditions. For mechanical strength, multiple graphene layers that are transparent to electrons while impervious to gas molecules/ions must be used [4-6]. In this work we demonstrate the electron transparency of multiple graphene layers.