Valence-band Electron Tunneling Research Articles

Modeling the trends in valence-band electron tunneling in NMOSFETs with ultrathin SiO 2 and [formula omitted] dielectrics with oxide scaling

Gate oxide scaling in NMOSFETs causes electrons to tunnel from the conduction and valence bands of the silicon substrate in the direct-tunneling regime. In NMOSFETs, the tunneling of electrons from the substrate's valence band is a source of the substrate current I B and contributes to the gate current I G . Oxide thickness scaling leads to an increase in the substrate current I B and in the ratio I B I G of substrate to gate current. In this paper, we report the trends in the I B I G ratio due to oxide thickness scaling in ultrathin SiO 2 and SiO 2 Ta 2O 5 composite gate dielectrics.

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

ABSTRACTThe 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.

Two-Band Tunneling Currents and Stress-Induced Leakage in Ultra-Thin SiO2 Films

ABSTRACTThe conduction band and valence band electron tunneling currents in ultra-thin SiO2 films at the transition from direct to Fowler-Nordheim tunneling regimes are studied. The slopes of the current voltage characteristics agree well with the simulations performed. The Stress-Induced Leakage Current (SILC) behavior is quite similar for both conduction and valence band currents even if the amplitude of the valence band SILC is much lower. We show that a linear dependence exists between the stress-induced interface trap density and both valence and conduction band SILC. A new model of SILC is also proposed.

Valence band electron tunneling in metal-oxide-silicon structures

Experimental results are presented for the substrate current appearing in thin oxide metal-oxide-silicon capacitors with a shallow n/p junction beneath the gate when a positive gate voltage in the tunneling regime is applied. The analysis of the current-voltage characteristics shows that for an oxide voltage drop lower than about 5 V the substrate current is due to electron tunneling from the silicon valence band. The dispersion relation in the energy range extending 3 eV below the oxide conduction band is determined from the voltage dependence of the current in the direct tunneling regime. An effective mass of about 0.8 m e is found near the edge of the oxide conduction band, while for lower energies a strong decrease of the effective mass is observed.