Improved dielectric properties and tunability of multilayered thin films of (Ba_(0.80)Sr_(0.20))(Ti_(1-x)Zr_(x))O_(3) with compositionally graded layer

摘要

Multilayered thin films of (Ba_(0.80)Sr_(0.20))(Ti_(1-x)Zr_(x))O_(3) (BSTZ) with compositionally graded layer (CGL) have been fabricated by pulsed laser deposition on Pt/TiO_(2)/SiO_(2)/Si substrate. In each CGL, four individual layers of BSTZ with x=0.36, 0.18, 0.08 and 0 are grown in series with equal thickness. Three kinds of thin-film CGL samples comprising one, two or four CGLs have been elaborated with the final same thickness, and the thickness of each CGL is accordingly varied in different samples to achieve the gradients of composition. The crystalline structures of the CGL thin films are successively characterized using x-ray diffraction and their electrical properties such as ac dielectric properties and polarizations are investigated. Improved dielectric properties and tunability of permittivity have been observed in the multilayered CGL films compared to single-layer BSTZ films prepared in the identical condition. Furthermore, with increasing gradients of compositions in the CGL multilayered films, the dielectric permittivity and its tunability increase, and the hysteresis loop of the thin films disappears. The results show that the internal stress produced by the gradient of composition could be a dominant factor to influence the dielectric properties. The improved dielectric properties and tunability for the applications of tunable devices can be obtained by the manipulation of the gradient of compositions in the multilayered films.