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

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 400 Angstrom in the SBTN/Bi2O3/SBTN heterostructure. As the thickness of Bi2O3 films was increased from 0 to 100 Angstrom, the grain grew faster and the ferroelectric properties improved. On the other hand, when the thickness, of Bi2O3 films was thicker than 150 Angstrom, the ferroelectric properties deteriorated. In particular, when a 400 Angstrom, 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 Angstrom, 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 Angstrom, leakage current density gradually decreased because the remaining Bi2O3 layer in SBTN thin films increased.