Ferroelectric and pyroelectric properties of solution derived bismuth titanium oxide thin films

Ferroelectric, pyroelectric, and photovoltaic effects in the bismuth titanate (Bi₄Ti₃O₁₂, BIT) and the lanthanum bismuth titanate (La_xBi_4−xTi₃O ₁₂, LBIT) solid solution thin films were studied. Films were successfully prepared using the metalorganic spin-casting technique. The development of texture orientation in different directions in the bismuth titanate films was examined in relation to solution characteristics such as solution viscosity, Bi-content, and the heat-treatment conditions, including the sintering temperature/time. X-ray diffraction, Raman spectroscopy and electron microscopy techniques were used to structurally characterize orientation formation in the films. Experimental results indicate that Bi-excess and sintering temperature/time are the critical factors governing controlled growth of films with preferred orientation. The bismuth excess is to compensate for the Bi loss during the fabrication process. Films with high degree of c-orientation, as high as 0.95–0.97, were obtained with the heterostructure layer deposition technique.; Measurements of pyroelectric and photoelectric properties of BIT films with preferred orientation in both a- and c-directions showed significantly high responses. Indications are that these oriented films can be materials suitable for the integrated pyroelectric detector applications. The high pyroelectric response in the films was attributed to the comparatively high value of pyroelectric coefficient, relatively low dielectric constant, and low thermal time constant.; The use of lanthanum in substitution of Bi ions in the BIT lattice to form the LBIT solid solution, led to the alteration of the lattice strain, as revealed by the corresponding Raman shift spectra. Result was a lower switching field and higher spontaneous polarization in comparison with BIT and many other ferroelectric film materials. This effect was attributed to, in part, a high domain wall mobility. These results suggest that LBIT films are materials highly suitable for the ferroelectric random access memory capacitors.