A systematic study on structural and dielectric properties of lead zirconate titanate/(Pb,La)(Zr(1−x)Ti(x))O3 thin films deposited by metallo-organic decomposition technology

Abstract

Pin-hole free ferroelectric (Pb,La)(Zr1−xTix)O3 thin films with uniform composition have been fabricated using the metallo-organic precursor compounds, which were carefully home synthesized. The structural development, spectroscopic, and dielectric properties of these films have been systematically investigated using atomic force microscopy (AFM), x-ray diffraction, Fourier transform infrared spectroscopy, Raman scattering, and dielectric measurements. It has been found from our experimental results of PZT 40/60 thin films that the overlapping of (h00) and (00l) peaks of these films in x-ray diffraction patterns, mainly due to the small grain sizes in films, makes it very difficult to distinguish individual diffraction peaks and to identify the phases. However, Raman measurements undoubtedly reveal the Raman spectra of these films in the tetragonal phase field, demonstrating that Raman spectroscopy is an effective tool to identify structures, especially in the case of thin films having very small grains. AFM results show that the PZT perovskite structure in films may grow radially by rosettes and that microcracks appear in the three-dimensional AFM pictures at grain boundaries, which may be the cause for easy dielectric breakdown. A striking feature of the AFM observation is that three polycrystalline perovskite regions intersect symmetrically at a point with 120° to each other, and a rosette growth model for the perovskite structure in PZT films is thus proposed to explain this new phenomenon. The excellent ferroelectric properties of these films, such as the high fatigue resistance and low leakage current, are attributed to the high quality of the metallo-organic solutions and to reduce the amount of oxygen vacancies in the films by optimizing the annealing conditions and by doping a suitable amount of La ions to minimize the charge blocking of oxygen vacancy at the interface by Pt electrode. It seems that the rhombohedral PZT films with softer hysteresis loops are suitable for nonvolatile random access memory application.