A comparison study of symmetric ultrathin-body double-gate devices with metal source/drain and doped source/drain

We have performed a simulation study of symmetric ultrathin-body double-gate (SUTBDG) devices with metal source/drain (S/D) structures designed for low-operating-power applications. A relatively high S/D Schottky barrier strongly influences the threshold voltages of the devices. The drive current (I/sub ON/) is dominated by barrier tunneling for nonnegative SBHs. Both electrons and holes may contribute to the off-state current (I/sub OFF/). Tunneling from the drain terminal limits the minimum obtainable I/sub OFF/. Germanium channel devices with metal S/D and a given I/sub OFF/ have smaller I/sub ON/ than similar silicon devices. With low nonnegative Schottky barrier heights (SBHs), metal S/D devices can outperform doped S/D devices, if the device performance degradation due to series resistances and parasitic capacitances is taken into account. Based on realistic device design rules, we have determined the upper bounds of S/D SBHs that allow metal S/D devices to offer improved performance over doped S/D devices with different body thicknesses.