Preferred crystal orientation of sol-gel-derived Bi4-xLaxTi3O12 thin films on silicon substrates

Polycrystalline thin films of La-substituted bismuth titanate (BLT) were formed directly on p-type Si(100) substrates by using sol-gel and spin coat methods. The BLT film and interfacial layer between BLT and Si were quantitatively investigated by the X-ray reflectivity method. Also, crystal orientations of sub-100-nm-thick BLT thin films were confirmed by X-ray diffraction using a synchrotron radiation source. The preferred c-axis orientation normal to the surface depended on the crystallization temperature. The difference in the preferred c-axis orientations of the BLT films caused the difference in the hysteresis voltage width in the capacitance-voltage characteristics of Au/BLT/p-Si structures. Furthermore, the c-axis of the Bilayered structure was preferentially oriented and aligned in the in-plane direction.