Electrical properties of Tantalum based composite oxide films

Tantalum oxide is a widely used insulator in electronic applications requiring high permittivity. When deposited at low temperature, tantalum oxide films, however, often exhibit large leakage current. A common way to reduce leakage is to anneal the films in an ambient containing extremely reactive oxygen species, or at high temperature in dry oxygen. A different approach is to use composite oxide materials. We have studied layered tantalum based oxide films deposited by Atomic Layer Epitaxy, and observed that the leakage current is decreased by several orders of magnitude when a fraction of tantalum oxide is replaced by another oxide, such as aluminum or hafnium oxide. Leakage current density of 40 nA/cm² in the electric field of 1 MV/cm is attained for unannealed Ta-Hf-O film deposited at 300°C. Layered composite insulators are an interesting new class of materials, and ALE proves to be a useful method for depositing them.