2007 NSTI Nanotechnology Conference and Trade Show - Nanotech 2007 - 10th Annual

Transition Point Consideration for Velocity Saturating Four-terminal DG MOSFET Compact Model

T. Nakagawa, T. Sekigawa, T. Tsutsumi, M. Hioki, S. O’uchi and H. Koike
AIST, JP

Keywords:
compact model, MOSFET, double-gate

Abstract:
We have proposed a compact model for four-terminal DG MOSFETs based on double charge-sheet model, with the velocity saturation effect as a function of carrier density profile inside the channel, with explicit handling of drain electric field, and with the introduction of the transition point that separates the transport-equation dominating region and the drain electric field dominating region. Although this model describes transistor ON-state and near-threshold behaviors excellently, it sometimes failed in deep-subthreshold region. We found that the transition point where the quasi-Fermi level gradient of the source side is smoothly connected with the lateral electric field of the drain side gives better behavior. Still the equation gave the drain current significantly larger than qnvSAT, where vSAT is the saturation velocity. To solve this problem, we tested a new transport equation that guarantees that the current is always smaller than qnvSAT. Although the new model behaves well in ON state, it gave too small drain current at near-threshold condition and below, when the channel length was very short. Further refinement of the model, such as including channel length shortening by the source-side built-in voltage, will be necessary for the model to achieve better agreement with real devices.

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