Comparison of Valence-Band Tunneling in Pure SiO₂, Composite SiO₂ /Ta₂O₅, and Pure Ta₂O₅, in Mosfets with 1.0 nm-Thick SiO₂-Equivalent Gate Dielectrics

Abstract

The gate tunneling current in ultrathin gate dielectric NMOSFETs with positive gate bias is due to the tunneling of electrons from the conduction and valence bands of the substrate. Valence-band electrons tunnel from the substrate of NMOS devices when the valence-band edge in the substrate rises above the conduction-band edge in the substrate. This paper reports experimental trends in the contribution of valence-band electrons tunneling to the gate current of NMOSFETs with gate oxides composed of pure SiO₂. The large gate tunneling current can be reduced by replacing the conventional SiO₂ gate dielectric with alternative dielectrics with larger dielectric constants. This paper reports the effect of replacing SiO₂ with alternative dielectrics on the contribution of valence-band electron tunneling to the gate current. Simulations are carried out for composite SiO₂/Ta₂O₅ gate dielectric structures.