Electrical reliability of metal-organic chemical vapor deposited high permittivity TiO₂ dielectric metal-oxide-semiconductor field effect transistors

The reliability of high permittivity films as a gate insulator is a serious concern due to small bandgaps (3.0 to approximately 4.0 eV). Ramped voltage, time dependent dielectric breakdown, and capacitance-voltage measurements were done on 190 angstroms layers of high permittivity TiO₂ which were deposited through the metal-organic chemical vapor deposition 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 hot carrier effects was also measured at V_d = 3.5 V and V_g EQ 2 V, but the threshold voltage shift and transconductance were clearly improved rather than degraded. Most of this increase in leakage upon electrical stress may be due to holes stored at the TiO₂/SiO₂ interface. The stored charge at the interface changes the shape of the bands, allowing a Fowler-Nordheim like tunneling mechanism to occur.