Ferroelectric thin films have been studied extensively due to their various applications in a number of microelectronic and optoelectronic devices such as ferroelectric memories, infrared pyroelectric sensors, micro-electro-mechanical systems, optical waveguides. Ferroelectric multilayers and thin films with composition gradient across the film through thickness are recently well known for their striking properties that were not observed in conventional ferroelectric layers. The compositionally graded structures were reported to have a higher tunability, polarization and flatter temperature characteristics because of their enhanced chemical heterogeneity. The Curie temperature of compositionally graded Ba_1-xSr_xTiO3 (BST) thin films can be tailored by the composition gradients to meet the requirements of enhanced ferroelectric properties near room temperature, which is very interest from application point of view.

In this work a set of BST thin films and graded structures of composition 100/0, 80/20 and 60/40 were produced by pulsed laser deposition technique on a (111)Pt/TiO₂/SiO₂/Si substrate. A KrF excimer laser with a wavelength of 248 nm and pulse duration of 10 ns was used. The deposition was performed with an oxygen pressure of 0.20 mbar at the substrate temperature of 650 ^oC. After deposition the films were annealed at 700 ^oC for 30 min in ambient air that resulted in formation of pure perovskite phase and good crystallinity. The films are characterized with XRD, SEM and Raman spectroscopy. The dielectric and ferroelectric properties were studied in the frequency window 10-10⁶ Hz and temperature range 10-200 ^oC. The comparable analysis of physical properties of homogenous BST films and graded structures has been carried out and the results are presented.

Acknowledgement. The Authors (D.C. and A.L-C) acknowledge the support of Polish Ministry of Education and Science within a research project N507 098 31/2319 funded from the funds for science in 2006-2009.

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