Ferroelectric Bi _3.25 La _0.75 Ti ₃ O ₁₂ Films of Uniform a -Axis Orientation on Silicon Substrates

Abstract

The use of bismuth-layered perovskite films for planar-type nonvolatile ferroelectric random-access memories requires films with spontaneous polarization normal to the plane of growth. Epitaxially twinned a axis-oriented La-substituted Bi4Ti3O12 (BLT) thin films whose spontaneous polarization is entirely along the film normal were grown by pulsed laser deposition on yttria-stabilized zirconia-buffered Si(100) substrates using SrRuO3 as bottom electrodes. Even though the (118) orientation competes with the (100) orientation, epitaxial films with almost pure (100) orientation were grown using very thin, strained SrRuO3 electrode layers and kinetic growth conditions, including high growth rates and high oxygen background pressures to facilitate oxygen incorporation into the growing film. Films with the a-axis orientation and having their polarization entirely along the direction normal to the film plane can achieve a remanent polarization of 32 microcoulombs per square centimeter.

Wide bandgap tunability in complex transition metal oxides by site-specific substitution

“…The well-defined thickness fringes observed for most of the peaks in θ-2θ patterns together with very narrow full width at half maxima (∆w ~0.025°) in rocking curve scans indicate an atomically smooth surface and interface as well as excellent crystallinity of our thin films. (Note that the full width at half maxima in XRD rocking curves in our films reported here is drastically reduced at least by a factor of three as compared with the values from previous epitaxial films 20 .) Overall peak positions of the main peaks remain unchanged for all the samples up to 1B2L, indicating that the overall Aurivillius structure of BiT is well preserved even after the substitution.…”

“…The polarization in such non-c-axis-oriented thin films is aligned away from the film plane, so that the ferroelectric measurement can readily be performed in capacitor geometry 20 . Pt top electrodes (30-µm diameter) were deposited on the film surfaces using photolithographic lift-off to fabricate capacitors.…”

“…LaTMO 3 was our natural choice for the perovskite, as La doping is well known for stabilizing the ferroelectricity in BiT (refs. 19,20). high α originating from the Co 3d-electronic states 21 .…”

Combinatorial approach for ferroelectric material libraries prepared by liquid source misted chemical deposition method

“…1B). The crystal growth in the a and b axes is related to the intensity of the (117) (36,37). It was also reported that BLT thin film grown epitaxially in the a axis shows a P s value of 50 Ccm Ϫ2 (39).…”

Electronic structure of epitaxial SrRuO3 films studied by resonant photoemission

“…The combination of good chemical stability, metallic conductivity and easy epitaxial growth on various perovskite substrates makes it attractive for multilayer device application (Lee et al, 2002;Eom et al, 1992;Mercurio et al, 2000). The integrability of SrRuO 3 into the device fabrication process requires surface stability with respect to reduction, contamination, or loss of volatile ruthenium oxides.…”