Scaling silicon MOSFET's for 77 K operation

Abstract

Using the gradual channel approximation and the velocity-field relationship appropriate to holes in silicon, the static characteristics of Si MOSFETs at 77 K are scaled from those at 300 K to provide similar static characteristics at the two temperatures. Compared to 300 K, the approximate scaling factors for 77 K are 1/4 for voltage, 1/3 for current, 1/12 for static power, 1/16 for dynamic power, and 1/20 for the delay-power product. At 77 K the transconductance is increased by 20% compared to room temperature. Agreement between theory and experiment on p-channel devices is good for channel lengths greater than about 5 mu m but the agreement decreases with decreasing channel length. Because the drain voltage required for current saturation decreases with decreasing temperature, circuit operation at supply voltages below 1 V appears feasible. >