Efficient layout generation and evaluation of vertical channel devices

Abstract

Vertical gate-all-around (VGAA) has been shown to be one of the most promising devices for the scaling beyond 10nm for its reduced delay, large driving current, and good gate control. Moreover, emerging devices such as heterojunction tunneling FETs are more amenable to vertical fabrication. However, past studies of vertical channel devices focused more on regular memory architectures and simple standard cells like inverter. Since naive migration of regular FinFET layouts to vertical FETs yields little benefits, we identify several vertical efficient layout structures and propose novel layout generation heuristics for vertical channel devices. We also compare VGAA with symmetric and asymmetric source/drain architectures. The layout efficiencies of several VGAA structures, vertical double gate (VDG), lateral gate-all-around (LGAA), and FinFET are presented in our experiments. We observe that even though most vertical channel standard cells have more diffusion gaps than lateral cells do, they still benefit from vertical architectures in area because of the elimination of diffusion contacts. For asymmetric architectures, the area is larger than symmetric architectures because of the extra diffusion gaps needed, but our experiments indicate that for both symmetric and asymmetric architectures, vertical channel devices are likely to have a density advantage over lateral channel devices assuming that current drive strengths of both are similar.