Dependence of gate control on the aspect ratio in metal/metal-oxide/metal tunnel transistors

The design criteria for large transconductance/high output impedance or high-gain operation of metal-oxide tunneling transistors is given. The dependence of the gate control on the aspect ratio of thickness to width of the tunneling oxide is investigated by computer simulation. This device structure can only operate similar to conventional semiconductor transistors for aspect ratio considerably less than one. It ceases to function as a transistor for larger aspect ratio due to insufficient penetration of the gate control field into the tunneling oxide. To demonstrate this, the current–voltage characteristics are computed for aspect ratios equal to 7/30, 1, 21/10, and the different tunneling-current behaviors compared with our experimental results on Ti/TiOx/Ti and Nb/NbOx/Nb tunnel transistors.