Impact of electron and hole inversion-layer capacitance on lowvoltage operation of scaled n- and p-MOSFET's

The influence of inversion-layer capacitance (C_inv) on supply voltage (V_dd) of n- and p-MOSFET's is quantitatively examined. The physical origin of the effect of C_inv on V_dd consists in the band bending of a Si substrate in the inversion condition due to C_inv, which is not scaled with a reduction in gate oxide thickness. The amount and the impact of the band bending is accurately evaluated on a basis of one dimensional (1-D) self-consistent calculations including two-dimensional (2-D) subband structure of inversion-layer electrons and holes. It is demonstrated that additional band bending of a Si substrate due to C_inv becomes a dominant factor to limit the lowering of V_dd for CMOS with ultrathin gate oxides. The operation at V_dd lower than 0.6 V is quite difficult even with effective T_ox less than 1 nm