High-k HfO2–Ta2O5 mixed layers: Electrical characteristics and mechanisms of conductivity

Electrical properties of mixed HfO2–Ta2O5 films (10;15 nm) deposited by rf sputtering on Si have been studied from the view point of their applications as high-k layers, by standard capacitance–voltage and temperature dependent current–voltage characteristics. The effect of HfO2 addition to the Ta2O5 is thickness dependent and the thicker layers exhibit advantages over the pure Ta2O5 (higher dielectric constant, enhanced charge storage density and improved interface quality). The process of HfO2 and Ta2O5 mixing introduces negative oxide charge, tends to creates shallow bulk traps and modifies the dominant conduction mechanisms in the stack capacitors as compared to the Ta2O5-based one (a contribution of tunneling processes through traps located below the conduction band of mixed layers to the leakage current in the HfO2–Ta2O5 stacks is observed). The traps involved in both Poole–Frenkel and tunneling processes are identified.