Ferroelectric property of epitaxial Bi4Ti3O12 films prepared by metalorganic chemical vapor deposition

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Abstract
The orientation dependence of the ferroelectricity of epitaxially grown Bi4Ti3O12 thin films was investigated. The (001)-, (118)-, and (104)-oriented Bi4Ti3O12 films were epitaxially grown on (100)cCaRuO3//(100)SrTiO3, (110)cSrRuO3//(110)SrTiO3, and (111)cSrRuO3//(111)SrTiO3 substrates, respectively, by metalorganic chemical vapor deposition. Ferroelectric property with different magnitude was observed for (001)- and (118)-oriented films but for (104)-oriented film due to its large leakage current. The remanent polarization and the coercive field were 1.5 mC/cm2 and 15 kV/cm, 16.5 νC/cm2 and 132 kV/cm for the (001)- and (118)-oriented thin films, respectively. The spontaneous polarization (PS) was 4.0 νC/cm2 and 27.0 νC/cm2 for (001)- and (118)-oriented films, respectively. This was different from the result of SrBi2Ta2O9 in that the ferroelectricity was not observed for (001)-oriented one, and was in good agreement with the estimation from the crystal structure. The estimated PS values along the c and a axes of Bi4Ti3O12 were 4.0 and 48.4 νC/cm2, respectively, and agreed well with the reported values for the single crystal. Furthermore, both films showed good fatigue endurance after 7.8 × 1010 switching cycles measured with 500 kHz rectangular pulses.