INVERSION CHARGE MODELING OF SIGE PMOS AND APPROACHES TO INCREASING THE HOLE DENSITY IN THE SIGE CHANNEL

A physical model of SiGe PMOS is presented. The condition for proper design ensuring the onset of strong inversion in the SiGe channel is modeled as a function of device structure. The threshold voltages and the inversion charge densities for both channels are also obtained. We show that the key to increasing the hole density in the SiGe channel lies in the reducing of the vertical electric field across the bottom Si/SiGe hetero-interface. Based on the modeling, a new bulk SiGe PMOS with a back pn junction sharing the depletion charge with the gate is proposed. Numerical simulation shows that the hole density in the SiGe channel of the back junction SiGe PMOS is comparable to that of the thin film SOI SiGe PMOS.