(Pb,La)(Zr,Ti)O3 (PLZT) thin films with various crystalline qualities, i.e., epitaxial, oriented, and polycrystalline, have been grow. These PLZT thin films cooled at various oxygen cooling pressures were found to have different asymmetric switching and imprint behaviors, depending on the crystalline quality of the PLZT thin films. It was found that the initial polarization state of as-grown PLZT thin films is an important indicator to determine further imprint behavior. Epitaxial PLZT thin-film capacitors were prepolarized in an as-grown state and further exhibited the large dependence of asymmetric switching and imprint behavior on the oxygen cooling pressure. On the other hand, oriented or polycrystalline PLZT capacitors exhibited very weak polarization and little dependence of the initial prepolarization state on the oxygen cooling pressure. Consequently, the PLZT capacitors containing polycrystalline nature had a strong resistance to the imprint failure.
We deposited epitaxial Ba 0.6 Sr 0.4 TiO 3 (BST) films having thickness of 400 nm on MgO(001) substrates, where a 10 nm thick Ba 1-x Sr x TiO 3 (x = 0.1 -0.7) interlayer was inserted between BST and MgO to manipulate the stress of the BST films. Since the main difference of those epitaxial BST films was the lattice constant of the interlayers, we were very successful in controlling the stress of the BST films. BST films under small tensile stress showed larger dielectric constant than that without stress as well as those under compressive stress. Stress relaxation was investigated using epitaxial BST films with various thicknesses grown on different interlayers. For BST films grown on Ba 0.7 Sr 0.3 TiO 3 interlayers, the critical thickness was about 600 nm. On the other hand, the critical thickness of single-layer BST film was less than 100 nm.
B. H. Park et al.
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