Solid State Electronic Devices, 7th Edition

6.6 Advanced Mosfet Structures

6.6.1 Metal Gate-High-k

As described above, the Si MOSFET with thermally grown SiO₂ gate dielectric with its high-quality interface, and heavily doped polysilicon gate electrode has been the workhorse in this field for decades. However, due to the problems of tunneling leakage currents in ultra-thin SiO₂ gate dielectrics, in recent years there has been a shift to high-k gate dielectrics such as HfO₂ which can be made physically thicker without sacrificing gate capacitance, C_i = ϵ_i/d. Generally, higher dielectric constant materials have lower band gaps than SiO₂. Hence, the band offsets in the conduction and valence bands may also be lower between these high-k gate dielectrics and Si. Thus, while the gate dielectric ...