Trap-assisted tunneling in high permittivity gate dielectric stacks

摘要

The electrical characteristics of SiO_(x)/ZrO_(2) and SiO_(x)/Ta_(2)O_(5) gate dielectric stacks are investigated. The current-density J_(G) in these dielectric stacks is shown to be strongly temperature dependent at low voltage (below about 2 V), the more so in the ZrO_(2) stack. On the other hand, J_(G) is much less temperature dependent at higher voltage. These results are consistent with a model which takes into account the direct tunneling of electrons across the SiO_(x) layer and the trap-assisted tunneling of electrons through traps with energy levels below the conduction band of the high permittivity dielectric layer. The energy levels and densities of these electron trapping centers are estimated by fitting this trap-assisted tunneling model to the experimental results.