Potential-Based Modeling of Depletion-Mode MOSFET Applicable for Structural Variations

The additional implanted channel-dopant layer of depletion-mode (DM) MOSFETs induces, at the same time, two main currents, namely, an accumulation current at the channel surface and a neutral-region current flowing deep in the implanted buried layer. In particular, the neutral-region current causes the normally-on condition of DM MOSFETs. These two currents dominate drain-source current alternatively depending on the bias conditions. To model the measured features of a DM MOSFET, a compact model is developed by considering also the complete vertical potential distribution from the surface to the bottom of the additional implanted channel-dopant layer. The potential distribution is self-consistently obtained by solving the Poisson equation. It is further demonstrated that a major development task is the correct coupling between V_ds and V_bs contributions, which is needed to describe the specific features of the DM MOSFET accurately.