A Generalized Electrostatic Scale Length for Fully Depleted Surrounding-Gate Metal–Oxide–Semiconductor Field Effect Transistors

Abstract

On the basis of the continuity of the electric flux and potential at the interface between a Si body and a gate insulator, and of the effective insulator thickness, a generalized electrostatic scale length for two-dimensional (2D) effects in fully depleted surrounding-gate (SG) metal–oxide–semiconductor field effect transistors (MOSFETs) is derived. It is found that for the same equivalent oxide thickness, a gate insulator with a higher dielectric permittivity results in stronger 2D effects caused by an increase in electrostatic scale length. Both a thin gate insulator and a thin Si body are required to realize a small electrostatic scale length to suppress short-channel effects. Compared with conventional planar MOSFETs, high-gate-permittivity SG MOSFETs theoretically can be designed such that its insulator is thicker than its Si body without increasing its electrostatic scale length. With appropriate modification of the effective insulator layer thickness, the model also indicates an increased scale length due to quantum effects.