Comparison of valence-band tunneling in pure SiO_2, composite SiO_2/Ta_2O_5, and pure Ta_2O_5, in mosfets with 1.0 nm-thick SiO_2-equivalent gate dielectrics

摘要

The gate tunneling current in cultrathin 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 SiO_2. The large gate tunneling current can be reduced by replacing the conventional SiO_2 gate dielectric with alternative dielectrics with larger dielectric constants. This paper reports the effect of replacing SiO_2 with alternative dielectrics on the contribution of valence-band electron tunneling to the gate current. Simulations are carried out for composite SiO_2/Ta_2O_5 gate dielectric structures.