Middle Electrode in a Vertical Transistor Structure Using an Sn Layer by Thermal Evaporation

Abstract

We report a process for performing the middle electrode for a vertical field effect transistor (VOFET) by the evaporation of a tin (Sn) layer. Bare aluminum oxide (Al 2 O 3), obtained by anodization, and Al 2 O 3 covered with a polymethylmethacrylate (PMMA) layer were used as the gate dielectric. We measured the electrical resistance of Sn while the evaporation was carried out to find the best condition to prepare the middle electrode, that is, good lateral conduction associated with openings that give permeability to the electric field in a vertical direction. This process showed that 55 nm Sn thick is suitable for use in a VOFET, being easier to achieve optimal thickness when the Sn is evaporated onto PMMA than onto bare Al 2 O 3. The addition of a PMMA layer on the Al 2 O 3 surface modifies the morphology of the Sn layer, resulting in a lowering of the threshold voltage. The values of threshold voltage and electric field, V TH = − 8 V and E TH = 354.5 MV/m respectively, were calculated using an Al 2 O 3 film 20 nm thick covered with a 14 nm PMMA layer as gate dielectric, while for bare Al 2 O 3 these values were V TH = − 10 V and E TH = 500 MV/m.