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-coa ted silicon substrates by a sol-gel technique. The crystalline orientation and surface morphology of the graded films were closely related to the depo sition 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 b e 765 and 374, respectively. The compositionally graded films had large pol arization offsets in hysteresis loops when driven by an alternating electri c field. The magnitude of polarization offsets displayed a power-law depend ence on the electric field, and the direction of the offsets depended on th e 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 obta ined. These results showed that the sol-gel technique was a very promising route for the realization of compositionally graded ferroelectric thin film s and the compositionally-graded (Pb,La)TiO3 thin films had excellent diele ctric properties and abnormal ferroelectric properties which can be used in various microelectronic devices. (C) 2000 American Institute of Physics. [ S0003-6951(00)00334-X].