Operation and design of metal-oxide tunnel transistors

The current-voltage (I-V) characteristics in the ballistic limit of metal-o xide tunnel transistors are calculated as a function of temperature, potent ial barrier height, gate insulator thickness, aspect ratio, and oxide-chann el shape. The saturation ('knee') point and three modes of current transpor t across the device are discussed. For a given aspect ratio, the output imp edance improves with increase in tunnel-oxide width, accompanied by slight decrease of gate transconductance. The net result is a significant improvem ent in the transistor gain. The gate transconductance improves with decreas e in gate-insulator thickness, while approximately maintaining the output i mpedance. The net result is also a significant improvement in the transisto r gain. Thus for a given aspect ratio, further device optimization to incre ase the transistor gain can be carried out by either increasing the tunnel oxide width or decreasing the gate insulator thickness. In practice, one pr eferably does both. A numerical study of the device performance of tapered- oxide devices is undertaken. We find that uniform-oxide channel design is g enerally superior to tapered-oxide channel designs. [S0021-8979(98)02521-3] .