Device design consideration for V_th-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 (φ_m) 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 φ_ms 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 (5) 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.