Enabling Atmospheric Operation of Nanoscale Vacuum Channel Transistors

A vacuum channel transistor is the ultimate wide band-gap structure with potential for high Johnson figure of merit (~10 14 V/s) due to no electron scattering and no impact ionization/breakdown [1] , [2] . Hence, nanoscale vacuum channel transistors (NVCTs) can possibly outperform solid-state transistors in terms of speed, breakdown voltage and reliability in harsh environments [1] . Carriers are injected into the channel by electron tunneling across a barrier narrowed by an electric field. Such electron sources can be realized using nanoscale gated Si field emitter arrays (FEAs) with high packing densities (≥10 8 /cm 2 ) and self-aligned apertures which have low turn-on voltage (8.5 V), low operating voltage, high current density (150 A/cm 2 ) and long lifetime (>300 hours) [3] . The barrier height is nonetheless sensitive to adsorption/desorption of gas molecules, resulting in large current variations in poor vacuum, which can also generate energetic ions that erode the emitter. Hence FEAs require costly and bulky ultra-high vacuum (UHV) systems for reliability [4] . Using multi-layers of graphene (Gr) that withstand high pressure gradients and, are transparent to electrons, but impervious to gas molecules, can enable operation of these FEAs in poor vacuum [5] , [6] . In this paper, Gr layers are used to encapsulate such FEAs with two self-aligned gates ( Fig. 1 ); this structure allows an independent control of the bias applied to the Gr layer, and significantly reduces the volume to be encapsulated.