Conduction mechanisms in amorphous and crystalline Ta2O5 thin films

Electrical properties and leakage current mechanisms of amorphous and polycrystalline tantalum pentoxide (Ta2O5) films were studied. Ta2O5 thin films were deposited on Pt/SiO2/n-Si substrate by reactive magnetron sputtering and then annealed at temperatures ranging from 500 to 800 °C for 30 min in O2. The as-deposited films were amorphous and showed good electrical properties in terms of a dielectric constant of about 31 and leakage current density of 10−10 A/cm2 at 100 kV/cm. The leakage current flowing through Ta2O5 film increases from 10−10 to 10−7 A/cm2 following the annealing. The conduction mechanism at low electric fields (100 kV/cm) is due to Ohmic conduction. On the other hand Schottky mechanism dominates at the intermediate fields (100–350 kV/cm) and Poole–Frenkel becomes predominant at high fields (>350 kV/cm). The increase in leakage current density in the crystallized film is due to Si penetrated into the Ta2O5 grain and grain boundary from the underlying SiO2/n-Si substrate.