Doping effects on the properties and microstructure of intergrowth Bi 4Ti3O12-SrBi4Ti4O 15 thin films

Undoped and La-doped intergrowth Bi4Ti3O 12-SrBi4Ti4O15 thin films were deposited on platinized silicon substrates by a modified metal-organic decomposition (MOD) method. The deposited films were crystallized at about 550-750°C in an O2 atmosphere. The microstructures of the films were investigated using X-ray diffraction and Raman spectroscopy. The ferroelectric and dielectric properties of thin films were measured using an RT66A test system. Compared with the undoped films, when crystallizing under the same temperatures, the XRD patterns of La-doped films present fewer but wider diffraction peaks. Increasing La dopant concentration results in further broadening. However, XRD and Raman spectroscopy studies show that the doping does not lead to a visible distortion of the lattice structure, which implies that La substitutes for either Bi or Sr. The hysteresis measurements show that the doped and undoped thin films have similar coercive field (Ec) and remnant polarization (2Pr). However, the polarization switching time of doped films is much shorter than that of the undoped films irrespective of film thickness. The reversible polarization was found to decrease for BIT-SBTi thin films with thicknesses greater than 210 nm while a maximum reversible polarization was found for La75BIT-SBTI intcrgrowth films at 280 nm. For a given film thickness, increasing the applied voltages resulted in increased switching times and increased reversible polarization in both cases. © 2002 Taylor & Francis.