Interest in high-permittivity oxide films has grown mainly due to the replacement of silicon oxide in transistors and memory capacitors. Besides single metal oxides, attempts have also been made to tailor useful properties of different oxides, combined as mixed materials of variable stoichiometry, or by deposition of stacked layers of different oxides in the form of nanolaminates. Oxides exhibiting good insulating properties, such as Al₂O₃, may be combined with oxides of high polarizability, such as TiO₂. ALD processes are established, enabling conformal growth of dense oxide layers. However, combination of different materials induces additional amounts of bulk defects as well as multiple interfaces, possibly degrading the electrical properties of these insulators. In addition, different materials exhibit variable stability in contact to semiconductor substrates and metal electrodes, affecting the quality of contact charge barriers.

The Al_1-xTi_xO_y mixtures and Al₂O₃-TiO₂-Al₂O₃ nanolaminates with variable composition and thicknesses were grown to investigate the electrical quality of such films. Several samples were annealed in N₂ or O₂ at 700 °C to study the effect of thermal post-deposition treatment. At similar capacitance values, films containing TiO₂ remained inferior to Al₂O₃ films in terms of insulating properties. The analysis of current-voltage characteristics revealed strong influence on defects and impurities. However, the modeling of electron emission into layered high-k stacks has first suggested the preferred exploitation of insulating materials with wider band gap even in defect-free cases. Further, the modeling suggested superiority of higher k films (TiO₂) when electrodes with higher work function were used, especially when EOT value of stack became smaller than 2 nm. In such films, the leakage in stack containing higher-k film (TiO₂) remained smaller even when a discrete impurity level was included to take into account trap assisted currents.

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