Direct measurement of field transistor threshold voltages using inversion layer fed transistors in deep submicron processes

Polysilicon field transistors are traditionally overlapped onto thin oxide regions to connect to the source and drain of a transistor. Submicron processes have gate oxides with breakdown voltages below the field threshold and the traditional layout is not suitable. It is however necessary to maintain a channel to the source and drain, but this can be accomplished using a field plate device. By placing a metal gate over the poly gate, and biasing the metal gate into strong inversion, it is possible for the polysilicon gate to control the transistor current. In fact with this one structure both the polysilicon and metal field threshold voltages can be ascertained.