Crystallization process of perovskite type oxide thin films deposited by PLD without substrate heating: Influence of sputtering rate and densification-driven high tensile strain

Abstract

Crystallization process in non-heating pulsed laser deposition (PLD) and the following post-annealing route for perovskite oxide thin film fabrication has been studied. Remarkable influence of sputtering rate on crystallization temperatures is demonstrated for BaZrO3 and SrZrO3 thin films in this process. Crystalline nuclei formation occurs randomly in the thin films deposited at a high sputtering rate which leads to the faster crystallization at a lower temperature, while it occurs predominantly at the substrate or interlayer interface at a higher temperature when the sputtering rate is very low, which is also reinforced by the atomic oxygen irradiation upon deposition. It should be noted that crystalline thin film synthesis of BaZrO3 is possible at a post-annealing temperature below 200°C when the sputtering rate is relatively high. On the other hand, obtained thin films show high tensile strain which is not related to the difference in thermal expansion coefficient between substrate and thin film, but is found to be due to the densification upon crystallization. The tensile strain is relaxed when the thin films are annealed at 750°C or above, while the strain is very stable at a temperature as low as 600°C for 1week.