Device Design Consideration for Vth-Controllable Four-Terminal Double-Gate Metal-Oxide-Semiconductor Field-Effect Transistor

The optimum device design for a threshold-voltage (V th)-controllable four-terminal double-gate metal-oxide-semiconductor field-effect transistor (4T-DGFET) has been investigated by device simulation. The effects of the device parameters, e.g., workfunction (φm) of the double gate, gate oxide thickness (T ox), effective gate length (L eff), and the range of the second gate voltage (V g2) on 4T-DGFET performance have been systematically examined. Simulation results show that lowering φms and increasing the second gate oxide thickness (T ox2) are preferable for the improvement of 4T-DGFET performance. The short channel effects (SCEs) for the 4T-DGFET have also been investigated in terms of V th roll-off, degradation in subthreshold slope (S) and back-gate-effect factor (γ). It is shown that all the SCEs become severer with increasing T ox2. As a result, in the case of the ultrashort L eff regime, a thick T ox2 is not so preferable. In particular, under the limited V g2 condition, a thin T ox2 is advantageous for enhancing the drive current due to the high V th controllability and SCE immunity.