Mobility Degradation Mechanisms of MOSFETs with a High-k Dielectric Layer

The electrical characteristics of MOSFETs with a high-k dielectric layer were simulated by using a full three-dimensional technology computer-aided design simulator. The MOSFETs leakage current increased when their size decreased. The mobility variation mechanisms due to the polarization variation with the positive fixed charges in the high-k dielectric layer and with the negative trap charges in the SiO₂ layer were clarified by using a modified mobility model of the universal model taking into account remote phonon scattering effects. The induced polarization in the high-k dielectric layer was dominantly attributed to the magnitude and the polarity of the charges in an interfacial layer. The mobility degradation was dominantly attributed to the polarization effects. The mobility values of the channel region in the MOSFETs, calculated by using the modified mobility model, were in reasonable agreement with their real mobility magnitudes. This result improves the enhancement of the electrical characteristic of the MOSFETs with a high-k layer.