Operation and design of metal-oxide tunnel transistors

Abstract

The current–voltage (I–V) characteristics in the ballistic limit of metal-oxide tunnel transistors are calculated as a function of temperature, potential barrier height, gate insulator thickness, aspect ratio, and oxide-channel shape. The saturation (‘knee’) point and three modes of current transport across the device are discussed. For a given aspect ratio, the output impedance improves with increase in tunnel-oxide width, accompanied by slight decrease of gate transconductance. The net result is a significant improvement in the transistor gain. The gate transconductance improves with decrease in gate-insulator thickness, while approximately maintaining the output impedance. The net result is also a significant improvement in the transistor gain. Thus for a given aspect ratio, further device optimization to increase the transistor gain can be carried out by either increasing the tunnel oxide width or decreasing the gate insulator thickness. In practice, one preferably does both. A numerical study of the device performance of tapered-oxide devices is undertaken. We find that uniform-oxide channel design is generally superior to tapered-oxide channel designs.