Recent results have demonstrated that metal-insulator-Si-field-effect transistors (MOSFET's) can be made narrow enough that the electronic conduction process in them changes in a fundamental way. At low temperature, large, nonmonotomic variations of the conductance are observed when the voltage on the gate is varied. Recent results on devices with 70nm wide inversion layers indicate that the current is limited by electron tunneling through localized states in the inversion layer of the MOSFET. These are apparently caused by the random potential resulting from ions on the surface of the oxide or variations in the width of the gate wire. This represents an unusual situation in which the current is limited by electronic transitions through just one electronic state. New fabrication methods are being developed with the goals of reducing the disorder caused by impurities on the oxide surface and localized electronic states in the oxide, and making the gate wires narrower and more uniform. Devices are being fabricated in the MIT Submicron Structures Laboratory, and they are being characterized at temperatures above 2;soK at MIT.
