Wave function penetration effects in double gate metal-oxide-semiconductor field-effect-transistors: impact on ballistic drain current with device scaling

摘要

A study of the evolution of wave function penetration effects on ballistic drain current (I_D) in nanoscale double gate (DG) metal-oxide-semiconductor field-effect-transistors (MOSFET) with the downscaling of device dimensions is presented. The electrostatics of the devices is calculated through the self-consistent solution of two dimensional Schroedinger and Poisson equations. HfO_2/SiO_2 stack is considered as the gate-dielectric material. It is observed that wave function penetration increases drain current in DG MOSFETs fabricated on (110) silicon, and the off-state current is more sensitive to the penetration effects than the on-state current. Numerical results show that the magnitude of the relative increase in I_D due to wave function penetration increases sharply with the downscaling of silicon body thickness. On the other hand, the impact of the downscaling of gate length on the penetration effects depends on the gate bias. The relative increase in the off-state current due to wave function penetration decreases with the scaling of the gate length, while the variation in the relative increase in the on-state current with the gate length is insignificant. Drain-induced barrier lowering plays an important role in determining the effects of wave function penetration on the ballistic drain current with device scaling. Wave function penetration effect decreases the threshold voltage and increases the on-state transconductance. This phenomena becomes stronger with the scaling of the silicon body thickness. However, gate length scaling has little influence on these parameters. With the simultaneous scaling of the body thickness and the gate "length, wave function penetration effects on all the parameters become more dominant. Physical explanation for these observations are provided.