Sputtered lead scandium tantalate thin films: crystallization behaviourduring post-deposition annealing

Abstract

Lead scandium titanate (PST) thin films were deposited by RF dualmagnetron sputtering and then annealed either by vacuum furnace or combinedrapid thermal annealing (RTA) and furnace anneal. The film structure wasinvestigated by x-ray diffraction, scanning electron microscopy andtransmission electron microscopy (TEM) and energy dispersive x-rayspectroscopy techniques. Lead loss was more severe using furnace annealingthan the combined RTA and furnace anneal. The annealed films werecharacterized by the presence of voids and exhibited relaxor ferroelectriccharacteristics. PST perovskite crystal grains were found to co-exist withpyrochlore matrix in the furnace-only annealed films, whilst in RTA annealedfilms no apparent pyrochlore morphology was observed in the TEM image. Leadwas found to diffuse through the bottom electrode Pt layer during theannealing. Films treated by combining RTA and furnace annealing have shownpyroelectric coefficients under field of up to 500 µC m-2 K-1,a dielectric loss of below 0.007 and a merit figure for thermal detection of2.5×10-5 Pa-1/2.