On the performance limits for Si MOSFET's: A theoretical study

Performance limits of silicon MOSFET's are examined by a simple analytical theory augmented by self-consistent Schrodinger-Poisson simulations. The on-current, transconductance, and drain-to-source resistance in the ballistic limit (which corresponds to the channel length approaching zero) are examined. The ballistic transconductance in the limit that the oxide thickness approaches zero is also examined. The results show that as the channel length approaches zero (which corresponds to the ballistic limit), the on-current and transconductance approach finite limiting values and the channel resistance approaches a finite minimum value. The source velocity can be as high as about 1.5 × 10⁷ cm/s. The limiting on-current and transconductance are considerably higher than those deduced experimentally by a previous study of MOSFET's with channel lengths greater than 0.2 μm. At the same time, the transconductance to current ratio is substantially lower than that of a bipolar transistor.