Bismuth composition control of SrBi 2 TaNbO 9 thin films by heat treating Bi 2 O 3 -inserted heterostructure
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Bismuth composition control of SrBi2TaNbO9 thin films by heat treating Bi2O3-inserted heterostructure Yoon-Baek Park,a) Jeon-Kook Lee,b) and Hyung-Jin Jung Thin Film Technology Research Center, Korea Institute of Science and Technology, Seoul 136-791, Korea
Jong-Wan Park Department of Metallurgical Engineering, Hanyang University, Seoul 133-791, Korea (Received 3 September 1998; accepted 13 April 1999)
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.
I. INTRODUCTION
There has been considerable interest in ferroelectric materials for nonvolatile random access memory application. For these applications, thin films of various Pb(Zr1−xTix)O3 (PZT) compositions have been widely studied. However, ferroelectric fatigue, in which the remanent polarization (Pr) decreased with an increase of switching cycles, is the predominant problem for the microelectronics device application. Research is being conducted to improve the fatigue properties of PZT materials by using conductive oxide electrodes such as (La,Sr)CoO3 (LSCO) and doping La donors into the films.1–8
a)
Present address: Department of Analysis, Division of Memory Product and Technology Development, Hyundai Electronics Industries Co., Ltd. b) Address all correspondence to this author. e-mail: [email protected] 2986
J. Mater. Res., Vol. 14, No. 7, Jul 1999
Another candidate ferroelectric material to control the fatigue problem in the ferroelectric capacitor is SrBi 2 Ta 2 O 9 (SBT). It has been demonstrated that Pt–SBT–Pt capacitors were found to exhibit no fatigue up to 1012
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