TEM STUDIES OF RF MAGNETRON-SPUTTERED THIN-FILMS

Lead scandium tantalate (PST) thin films sputtered onto sapphire substrates have been studied by using transmission electron microscopy. Samples in transverse section were used to characterize the microstructure of the thin films as a function of distance from the PST-sapphire interface whereas samples in plan section allowed a more detailed, structural investigation of the PST. A liquid nitrogen cold stage was used to induce the paraelectric-ferroelectric phase transition in situ and to perform heating and cooling experiments on the thin films. In general, samples which had the lowest dielectric constants were found to have a layer of unreacted ScTaO4 at the film-substrate interface, whereas the highest dielectric constants were associated with fully perovskite-structured films. Films prepared by the sequential deposition of ScTaO4 and PbO, followed by heat treatment, readily spalled from the sapphire. They also exhibited an increase in the Sc and Ta cation order with distance from the film-sapphire interface. A sample prepared by the simultaneous deposition of ScTaO4 and PbO did not spall and showed an increase in structural order at both the PST-sapphire interface and at the film surface.