Requirements and restrictions in optimizing homogeneous and planar doped barrier vertical MOSFETs

Systematic simulations of ultra-short channel vertical MOSFETs and planar doped barrier MOSFETs (PDBFET) have been carried out in order to understand how to best fulfill the following requirements: high doping in order to prevent punch through, low mobility reduction due to doping, sufficiently low field in order to prevent impact ionization, a small threshold voltage and a near ideal subthreshold swing for the desired low supply voltage, and a low channel conductance. We find that the technologically more elaborate PDBFET matches these diverse requirements much better, since the i-regions forming most of the channel reduce the lateral field near source and drain, whereas the highly doped barrier prevents punch through and provides the required threshold voltage. At the same time, the scattering in the i-regions is reduced, resulting in only a low mobility reduction