Compositionally graded ba1-xsrxtio3 ferroelectric thin films layer-by-layer deposited by pulsed laser abalation

Abstract

Compositionally graded (Ba1-xSrx)TiO3 (BST) (x: 0.0∼ 0.25) thin films were layer-by-layer grown on Pt(111)/Ti/SiO2/Si(100) substrates by pulsed laser ablation at oxygen pressures between 50 ∼ 400 mTorr. The influence of ambient gas pressure on the film preferred orientation and dielectric properties of graded films were systematically investigated. For up-graded films with Ba/Sr ratios varying from 75/25 at the substrate to 100/0 at the top surface, the preferred orientation evolved in the sequences of (100)+(110)→(110)+(111)→(100) as increasing the ambient gas pressure, whereas for the down-graded films with Ba/Sr ratios varying from 100/0 at the substrate to 75/25 at the top surface, the preferred orientation varied in the order of (100)+(110)→(100). The related driving force for orientation evolution was presumably changed from minimization of surface energy to minimization of energy loss per unit area as increasing ambient gas pressure. An enhanced dielectric behavior was observed in the down-graded films, which may be mainly attributed to the large strain fields built in the down-graded films and at the down-graded film/substrate interface.