Crystallization of sputtered lead zirconate titanate films by rapid thermal processing

Abstract

A rapid thermal annealing (RTA) technique has been employed to process lead zirconate titanate(PZT)films prepared by reactive magnetron sputtering. The films were fabricated by dc sputtering a multielement metal target in an oxygen ambient at a substrate temperature of 200 °C. A subsequent postdeposition RTA at 600 °C for 5 s crystallizes the films into a perovskite‐type structure through various intermediate phases. Due to the short postdeposition processing times inherent in the RTA method, the initial nature of the as‐grown films has a critical influence on the crystallization kinetics. The reaction sequence in the formation of perovskitePZT from the filmsdeposited at low substrate temperatures by the sputtering technique has been evaluated, and various key factors influencing the crystallization of PZT have been identified. As‐grown films are constituted of polycrystalline orthorhombic lead oxide in an amorphous matrix of titania and zirconia. During annealinglead oxide transforms into a cubic phase, and the lead oxide stoichiometry determines the processing route to PZT. In the case of lead‐rich films, intermediate compounds of lead with titania and zirconia are observed, which react during the final stage of annealing at 600 °C to form PZT. In lead‐deficient films, the formation of a pyrochlore phase has been observed, which crystallizes into perovskite at 750 °C. The Zr/Ti ratio also influences the crystallization sequence. In the case of Ti‐rich PZT, the intermediate compounds initially involve a zirconium‐rich rhombohedral PZT, with which residual titanium reacts to form tetragonal PZT. The films showed good ferroelectric and other electrical properties with a remanent polarization of 24 μC/cm2, coercive field of 32 kV/cm, ε’=950, tan δ=0.02, and σdc (300 K)=10−12 Ω−1 cm−1 with an activation energy between 0.9 and 1.4 eV.