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

We have used new MOCVD source systems, Bi(CH3)(3)-Sr[Ta(OC2H5)(6)](2)-O-2 a nd Bi(CH3)(3)-mixture of Sr[Ta(OC2H5)(6)](2) and Sr[Nb(OC2H5)(6)](2)-O-2, f or the highly reproducible preparation of SrBi2- Ta2O9(SBT) and SrBi2(Ta,Nb )(2)O-9(SBTN) films, respectively. These materials are bismuth layer-struct ured ferroelectrics (BLSF), By using these systems, epitaxial SET film was grown on an SrTiO3 single crystal, c-axis orientated SET film was epitaxial ly grown on a (100)SrTiO3 substrate above 620 degreesC, while a (116)-orien tated one was grown on a (110)SrTiO3 substrate at 820 degreesC. By using th ese orientated SET films, we first observed the ferroelectric anisotropy of SET film along the crystal axis; the (116)-orientated SET film shows large ferroelectricity with a remanent polarization (Pr) of 11.4 muC/cm(2), whil e the (001)-orientated one showed no ferro-electricity. The estimated Pr al ong the a-axis almost agreed with the calculated one from the SET powder da ta, suggesting that there is hardly any effect of strain in the film. This strain-free character is considered to be originated from the lattice displ acement along the c-axis observed by TEM, Moreover, by using this MOCVD pro cess, we obtained an SBTN film with relatively high ferroelectricity of P-r =6.1 muC/cm(2) even at the deposition temperature of 585 degreesC on (111) orientated Pt-coated (100) Si substrate. Copyright (C) 2000 John Wiley & So ns, Ltd.