A study of microstructures in ferroelectric Pb(Zr,Ti)O3 and KNbO3 thin films

Abstract

Oxide ferroelectric thin films are receiving considerable attention due to their potential application in a wide range of devices including ferroelectric nonvolatile memory, dynamic random access memory (DRAMs) electrooptic phase modulators, and laser light source frequency doublers. However, the complexity of the oxide materials has resulted in a relatively slow development of structureprocessing property relationships. In this paper, we review in turn how the microstructures of epitaxial KNbO3 and Pb(Zr Ti)O3 have been significantly improved over a period of time.In the case of epitaxial KNbO3 on oxide single crystal substrates, defect types which need to be controlled include 221-type misorientations, low angle boundaries, multiposition domains, and inversion domains. Several of these defect types are controlled via the substrate surface preparation. The role of lattice mismatch between film and substrate on the formation of the low angle boundaries remains an unresolved issue. We are currently comparing via TEM the KNbO3(100) films on (100)MgO, (100)MGAl2O4, (100)NdGaO3 and (100)KTaO3 substrates; these substrates covering a range of values of lattice mismatch between 0.1% and 5.0%.