Atomic layer deposition of high capacitance density Ta2O5–ZrO2 based dielectrics for metal–insulator–metal structures

We have investigated electrical properties of laminated atomic layer deposited films: ZrO2–Ta2O5, ZrO2–Nb2O5–Ta2O5, ZrO2–TaxNb1−xO5 and Ta2O5–ZrxNbyOz. Even though the capacitances of laminates were often higher compared to films of constituent materials with similar thickness, considerably higher charge storage factors, Q, were achieved only when tetragonal ZrO2 was stabilized in ZrO2–Ta2O5 laminate and when the laminate thickness exceeded 50 nm. The decreased Q values in the case of most laminates were the result of increased leakage currents. In the case of thinner films only Ta2O5–ZrxNbyOz stack possessed capacitance density and Q value higher than reference HfO2. Concerning the conduction mechanisms, in the case of thinner films, the Ta2O5 or TaxNb1−xO5 apparently controlled the leakage either by Richardson–Schottky emission or Poole–Frenkel effect.