A Chemical Approach Using Liquid Sources Tailored to Bi-Based Layer-Structured Perovskite Thin Films

Abstract

The electrical properties of Bi-based layer-structured perovskite compounds strongly depend on their anisotropic crystal structure. Because of this dependence, the properties are expected to be designed or controlled through two kinds of crystallographic approaches: the choice of cations in both the A and B sites of the perovskite layers between the Bi-O layers; and adjustment of the number, n, of oxygen octahedra along the c-axis. Chemical solution deposition is superior to other deposition techniques in precise compositional control and a low processing temperature for multi-component oxide thin films. In particular, it would be a promising technique for control of the crystal structure when the molecules in the precursor solutions are tailored to have optimum structures for easy transformation to the functional oxides. In this chapter, discussions are focused on the effects of the choice of Ca$^{2+}$ as the A site cation and adjustments of n in the range of 2 to 5 on the properties of thin films. Namely, thin films of CaBi$_{2}$Ta$_{2}$O$_{9}$ ($n=2$), CaBi$_{3}$Ti$_{3}$O$_{12 - \delta }$ ($n=3$), CaBi$_{4}$Ti$_{4}$O$_{15}$ ($n=4$), and Ca$_{2}$Bi$_{4}$Ti$_{5}$O$_{18}$ ($n=5$) were deposited using precursor solutions which were synthesized by chemical reactions of metal alkoxides on the basis of the original concept. The properties of the novel thin films were primarily investigated. The relationship between the crystallographic and electronic properties is fundamentally considered and then the potential for application to FeRAMs is addressed.