Chemical solution deposition of layer-structured ferroelectric thin films

Ferroelectric rare-earth-doped Bi4Ti3O12 thin films have been successfully prepared on Si-based substrates by using metallo-organic precursor solutions. The pyrolysis behavior of (Bi,R)(4)Ti3O12 precursors depends upon the starting rare earth source, which strongly affects the surface morphology of the synthesized film. Among the (Bi,R)(4)Ti3O12 films, BNT thin films reveal the most homogeneous and smooth surfaces. Single-phase (Bi,R)(4)Ti3O12 films of Bi-layered perovskite have been crystallized on Si-based substrates. Rare-earth-doped BIT thin films show different crystal orientations dependent upon the substituent ion. BIT and BLT thin films exhibit strong (00l) peaks, while BNT, BST and BGT thin films have a marked (117) preferred orientation. Among the rare-earth-doped BIT thin films, BNT thin films show the best saturation properties of the ferroelectrics with a large P-r and small E-c for low applied voltages. However, low-temperature-processed BNT films do not exhibit enough ferroelectricity. From further investigation of BNT films, the surface morphology and ferroelectric properties can be improved by optimization of the Ge doping in the BNT, particularly in the case of BNT-based thin films prepared at low temperatures. Furthermore, excimer UV irradiation of as-deposited films is very effective in removing the residual organic groups in the precursor film and in improving the microstructure and ferroelectric properties of the resultant BNT thin film. The use of excimer UV irradiation, further, leads to the easy formation of single-phase BIT-based thin films exhibiting excellent ferroelectric properties and a homogeneous microstructure with uniform fine grains at low temperatures. The layer-structured ferroelectric (Bi,R)(4)Ti3O12 films developed in this study, especially the BNT-based films, axe found to have potential for application in several electric thin-film devices utilizing ferroelectricity, such as the FeRAM.