Structural, dielectric, and ferroelectric properties of compositionally graded (Pb,La)TiO3 thin films with conductive LaNiO3 bottom electrodes

We report structural, dielectric, and ferroelectric properties of compositi onally graded (Pb,La)TiO3 thin films on LaNiO3/SiO2/Si substrates, where al l the films were prepared by the sol-gel technique. The crystalline orienta tion and surface morphology of the graded films were closely related to the deposition sequence of film layer. Upgraded film exhibited (100) preferent ially oriented growth, whereas downgraded film showed a randomly oriented g rowth, where the films with La content increasing or decreasing gradually a long film thickness from the substrate to the top surface are called "upgra ded" or "downgraded" films, respectively. The dielectric constants, for upg raded and downgraded films annealed at 650 degrees C for 60 min, were found to be 659 and 641, respectively. The thin films had large polarization off sets in hysteresis loops when driven by an alternating electric field. The magnitude of the offsets displayed a power law dependence on the electric f ield, and the direction of the offsets depended on the direction of the com position gradient with respect to the substrate. The leakage current of the upgraded film was 3.43 x 10(-8) A/cm(2) at the voltage of 3 V. These resul ts showed that the compositionally graded (Pb,La)TiO3 thin films had excell ent dielectric properties and abnormal ferroelectric properties which can b e used in various microelectronic devices. (C) 2000 American Institute of P hysics. [S0003-6951(00)04233-9].