5.1.2.1 Effect of the Polysilicon Gate Doping on the Channel Tunneling

As outlined in Section 2.2.2, heavily doped polysilicon is used as material for the gate contact to allow adjustable work functions and realize CMOS circuits. Fig. 5.3 shows the electron and hole tunneling current density for different doping of the polysilicon gate contact. In the nMOS gate leakage generally increases with increasing doping of the polysilicon gate because tunneling current is dominated by electrons. In the pMOS a higher polysilicon doping leads to reduced electron tunneling current and increased hole tunneling current. The effect on the overall leakage depends on the doping and the gate bias.

Figure 5.3: Electron (left) and hole (right) current density in an nMOS (top) and a pMOS (bottom) with different doping of the polysilicon gate. Substrate doping is 1e18 cm-3, dielectric thickness is 2 nm.

A. Gehring: Simulation of Tunneling in Semiconductor Devices