Simulation of deep depleted SOI MOSFET's with back potential control

Abstract

We consider SOI MOSFET structures of N and P types for which a control of the back potential of the epi layer is obtained by using a back gate. The action of the interface parameters on the back and front threshold voltages is analysed in the case of a strong coupling between the front and back interface (lightly doped epi layer). This analysis is carried out by a numerical simulation of Poisson's equation throughout the structure. We thus obtain the potential profile and the electron and hole densities, as a function of front (V g1) and back (V g2) gate voltages. We also deduce the l d(V g1, V g2) characteristics in the case of low drain voltage. Experimental material is given by CMOS/SOS transistors, the sapphire substrate of which has been locally thinned down. Comparison of the experimental l d(V g2) characteristics with the simulated characteristics allows us to determine directly the fast state density and the fixed charge at the back interface.