Subthreshold Behaviors of Nanoscale Silicon and Germanium Junctionless Cylindrical Surrounding-Gate MOSFETs

Abstract

Abstract When the traditional planar metal-oxide-semiconductor-field-effect transistors (MOSFETs) encounter insurmountable bottleneck of static power dissipation, junctionless transistor (JLT) becomes a promising candidate for sub-22 nm nanoscale devices due to its simpler fabrication process and better short-channel performances. Subthreshold behaviors dominate the standby power of nanoscale JLTs. In this chapter, a physics-based analytical model of electrostatic potential for both silicon and germanium short-channel junctionless cylindrical surrounding-gate (JLCSG) MOSFETs operated in the subthreshold regime is proposed, in which the full twodimensional (2D) Poisson’s equation is solved in the channel region by a method of series expansion. The expression of the proposed electrostatic potential is completely rigorous and explicit. Based on this result, the expressions of threshold voltage, subthreshold drain current, and subthreshold swing for JLCSG MOSFETs are derived. Subthreshold behaviors are studied in detail by changing different device parameters and bias conditions, including doping concentration, channel radius, gate length, gate equivalent oxide layer thickness, drain voltage, and gate voltage. Results predicted by all the analytical models agree well with numerical solutions from the three-dimensional simulator. These analytical models can be used to investigate the operating mechanisms of nanoscale JLCSG MOSFETs and to optimize their device performances.