Structure and Electrical Behavior of Hafnium-Praseodymium Oxide Thin Films Grown by Atomic Layer Deposition

Crystal structure and electrical properties of hafnium-praseodymium oxide thin films grown by atomic layer deposition on ruthenium substrate electrodes were characterized and compared with those of undoped HfO₂ films. The HfO₂ reference films crystallized in the stable monoclinic phase of HfO₂. Mixing HfO₂ and PrO_x resulted in the growth of nanocrystalline metastable tetragonal HfO₂. The highest relative permittivities reaching 37-40 were measured for the films with tetragonal structures that were grown using HfO₂:PrO_x cycle ratio of 5:1 and possessed Pr/(Pr + Hf) atomic ratios of 0.09-0.10. All the HfO₂:PrO_x films exhibited resistive switching behavior. Lower commutation voltages and current values, promising in terms of reduced power consumption, were achieved for the films grown with HfO₂:PrO_x cycle ratios of 3:1 and 2:1 and showing Pr/(Pr + Hf) atomic ratios of 0.16-0.23. Differently from the undoped HfO₂ films, the Pr-doped films showed low variability of resistance state currents and stable endurance behavior, extending over 10⁴ switching cycles.