Bismuth composition control of SrBi₂TaNbO₉ thin films by heat treating Bi₂O₃-inserted heterostructure

Abstract

Ferroelectric properties of SrBi₂TaNbO₉ (SBTN) thin films were changed by the amount of Bi content in SBTN. We proposed that the addition of excess Bi to the SBTN thin films could be accomplished by heat treating the SBTN/Bi₂O₃/SBTN heterostructure fabricated by the radio frequency magnetron sputtering method. The Bi composition was controlled by changing the thickness of the inserted Bi₂O₃ from 50 to 400Å in the SBTN/Bi₂O₃/SBTN heterostructure. As the thickness of Bi₂O₃ films was increased from 0 to 100 Å, the grain grew faster and the ferroelectric properties improved. On the other hand, when the thickness, of Bi₂O₃ films was thicker than 150 Å, the ferroelectric properties deteriorated. In particular, when a 400 Å Bi₂O₃ layer was inserted between SBTN films, a Bi₂Pt phase appeared and the Bi₂O₃ films remained between SBTN films, resulting in poor ferroelectric properties. A Bi₂Pt phase was formed by the reaction between the platinum bottom electrode and Bi₂O₃ films. On the other hand, the leakage current density of SBTN thin films decreased with the increase of inserted Bi₂O₃ film thickness. As the thickness of inserted Bi₂O₃ films was increased from 0 to 50 Å, leakage current density abruptly decreased because Bi content of the SBTN thin films was increased from 8 mol% deficient to stoichiometric composition. As the thickness of inserted Bi₂O₃ films increased from 100 to 400 Å, leakage current density gradually decreased because the remaining Bi₂O₃ layer in SBTN thin films increased.