CALIBRATED MODEL FOR THE SUB-THRESHOLD OPERATION OF A SHORT CHANNEL MOSFET INCLUDING SURFACE-STATES

A knowledge of subthreshold behavior in short channel MOSFET's is important in very large-scale integration circuits with low leakage current requirements. This paper will describe a simple two-dimensional subthreshold model for short channel MOSFET's. The effects of surface state density are also included in the model. A regional charge density approximation was used in the solution of Poisson's equation and an analytical solution of the continuity equation in two dimensions was derived. Excessive computations are avoided in the present model; this was made possible by the use of a valid regional charge approximation. The model was experimentally verified by performing measurements on short channel devices (L = 0.95 µm; L = 1.05 µm; L = 1.75 µm). The model was calibrated from measurements on a long channel device (L = 9.0 µm) which was present on the same silicon chip. Results are presented in this paper for the subthreshold leakage current as a function of substrate bias, polysilicon gate length, diffusion depth and surface state density. The present two-dimensional model can be used for short channel device design and for the estimation of subthreshold leakage current in MOSFET dynamic random access memories. Particularly, the use of this model should be directed towards minimizing the sensitivity of the device's physical properties and fabrication tolerances. Copyright © 1979 by The Institute Of Electrical And Electronics Engineers, Inc.