Charge trapping and degradation in high-permittivity TiO₂ dielectric films

Suitable replacement materials for ultrathin SiO₂ in deeply scaled MOSFET's such as lattice polarizable films, which have much higher permittivities than SiO₂, have bandgaps of only 3.0 to 4.0 eV. Due to these small bandgaps, the reliability of these films as a gate insulator is a serious concern. Ramped voltage, time dependent dielectric breakdown (TDDB), and capacitance-voltage (C-V) measurements were done on 190 Å layers of TiO₂ which were deposited through the metal-organic chemical vapor deposition (MOCVD) of titanium tetrakis-isopropoxide. Measurements of the high- and low-frequency capacitance indicate that virtually no interface states are created during constant current injection stress. The increase in leakage current upon electrical stress may be due to the creation of uncharged, near interface states in the TiO₂ film near the SiO₂ interfacial layer that give rise to increased tunneling leakage.