Composition gradient optimization and electrical characterization of (Pb, Ca)TiO3 thin films

Compositionally graded (Pb, Ca)TiO3 thin films were prepared by a monoethan olamine-modified sol-gel technique on platinum-coated silicon substrates at the annealing temperature of 600 degreesC. The composition gradient of the films was greatly improved by a modified annealing method. The dielectric constants, for up-graded and down-graded films annealed at 600 degreesC for 60 min, were found to be 469 and 355, respectively. Both were larger than those reported for conventional (Pb, Ca)TiO3 thin films. The compositionall y graded films had large polarization offsets in hysteresis loops when exci ted by an alternating electric field. The more smooth the composition gradi ent of the graded film, the larger the polarization offset. This was consis tent with a theoretical model reported previously by Mantese and coworkers [Appl. Phys. Lett. 71, 2047 (1997)]. The magnitude of polarization offset d isplayed a power-law dependence on the electric field, and the direction of the offset depended on the direction of the composition gradient with resp ect to the substrate. Both up-graded and down-graded films had good leakage current characteristics. (C) 2001 American Institute of Physics.