Dielectric and ferroelectric properties of compositionally graded (Pb,La)TiO3 thin films on Pt/Ti/SiO2/Si substrates

Compositionally graded (Pb,La)TiO3 thin films were prepared on platinum-coated silicon substrates by a sol-gel technique. The crystalline orientation and surface morphology of the graded films were closely related to the deposition sequence of the film layer. The dielectric constants, for up-graded and down-graded films annealed at 600 degrees C for 60 min, were found to be 765 and 374, respectively. The compositionally graded films had large polarization offsets in hysteresis loops when driven by an alternating electric field. The magnitude of polarization offsets displayed a power-law dependence on the electric field, and the direction of the offsets depended on the direction of the composition gradient with respect to the substrate. The offset, 250 mu C/cm(2) at the driving electric field of 250 kV/cm, was obtained. These results showed that the sol-gel technique was a very promising route for the realization of compositionally graded ferroelectric thin films and the compositionally-graded (Pb,La)TiO3 thin films had excellent dielectric properties and abnormal ferroelectric properties which can be used in various microelectronic devices. (C) 2000 American Institute of Physics. [S0003-6951(00)00334-X].