Substrate Biasing Effect on the Physical Properties of Reactive RF-Magnetron-Sputtered Aluminum Oxide Dielectric Films on ITO Glasses

High dielectric constant (high-<i>k</i>) Al₂O₃ thin films were prepared on ITO glasses by reactive RF-magnetron sputtering at room temperature. The effect of substrate bias on the subband structural, morphological, electrode/Al₂O₃ interfacial and electrical properties of the Al₂O₃ films is systematically investigated. An optical method based on spectroscopic ellipsometry measurement and modeling is adopted to probe the subband electronic structure, which facilitates us to vividly understand the band-tail and deep-level (4.8–5.0 eV above the valence band maximum) trap states. Well-selected substrate biases can suppress both the trap states due to promoted migration of sputtered particles, which optimizes the leakage current density, breakdown strength, and quadratic voltage coefficient of capacitance. Moreover, high porosity in the unbiased Al₂O₃ film is considered to induce the absorption of atmospheric moisture and the consequent occurrence of electrolysis reactions at electrode/Al₂O₃ interface, as a result ruining the electrical properties