Preparation of bismuth layer-structured ferroelectric thin films by MOCVD and their characterization

Abstract

We have used new MOCVD source systems, Bi(CH3)3–Sr[Ta(OC2H5)6]2–O2 and Bi(CH3)3–mixture of Sr[Ta(OC2H5)6]2 and Sr[Nb(OC2H5)6]2)–O2, for the highly reproducible preparation of SrBi2Ta2O9(SBT) and SrBi2(Ta,Nb)2O9(SBTN) films, respectively. These materials are bismuth layer-structured ferroelectrics (BLSF). By using these systems, epitaxial SBT film was grown on an SrTiO3 single crystal, c-axis orientated SBT film was epitaxially grown on a (100)SrTiO3 substrate above 620°C, while a (116)-orientated one was grown on a (110)SrTiO3 substrate at 820°C. By using these orientated SBT films, we first observed the ferroelectric anisotropy of SBT film along the crystal axis; the (116)-orientated SBT film shows large ferroelectricity with a remanent polarization (Pr) of 11.4 µC/cm2, while the (001)-orientated one showed no ferro-electricity. The estimated Pr along the a-axis almost agreed with the calculated one from the SBT powder data, suggesting that there is hardly any effect of strain in the film. This strain-free character is considered to be originated from the lattice displacement along the c-axis observed by TEM. Moreover, by using this MOCVD process, we obtained an SBTN film with relatively high ferroelectricity of Pr=6.1 µC/cm2 even at the deposition temperature of 585°C on (111) orientated Pt-coated (100) Si substrate. Copyright © 2000 John Wiley & Sons, Ltd.