Preparation Of SrBi2Ta2O9 Thin Films Research Articles

Effects of acetoin as chelating agent on the preparation of SrBi2Ta2O9 thin films from non-hydrolyzing precursors

Ferroelectric thin films of strontium bismuth tantalate (SBT) have been fabricated by a chemical solution deposition technique using non-hydrolyzing precursors. Strontium acetate, bismuth nitrate and tantalum ethoxide were used as precursor materials, with methanol and glacial acetic as solvents. We investigate the effects of the precursor chemistry, by the selection of the chelating agent, on the elimination of residual organic compounds, thermal evolution of phase formation, and microstructure evolution of derived films. We found that the utilization of alkanolamines as chelating agent produce the segregation of metallic bismuth in as-prepared powders. On the other hand, acetoin, one of the hydroxyketones, showed the elimination of residual organics at low temperature, an earlier onset of crystallization, and no segregation of secondary phases during the whole crystallization process. A comparative investigation of the surface microstructure, grain size distribution, crystallinity, and degree of crystal orientation of films fabricated with the different chelating agents is presented. The dielectric and ferroelectric properties of films prepared with acetoin are investigated.

Characterization of low temperature preparation of SrBi2Ta2O9 thin films by ECR plasma enhanced metalorganic chemical vapor deposition

We compared a directly crystallized SrBi2Ta2O9 film prepared by ECR-metalorganic chemical vapor deposition with that transformed by solid phase reaction from fluorite phase. The distribution of two times remanent polarization (2Pr) and coercive field (Ec) against Bi/Ta mole ratio of directly crystallized film from the gas phase was narrow compared with that crystallized by the solid phase reaction. Moreover, the Bi/Ta mole ratio showing the maximum 2Pr value was different in each preparation method. The crystallinity and orientation of directly crystallized SBT phase from the gas phase were strongly influenced by those of the substrate. Consequently, direct crystallization from the gas phase is one of the important techniques for lowering the crystallization temperature of SBT phase.

Preparation of SrBi2Ta2O9 Thin Films by Liquid-Delivery Metalorganic Chemical Vapor Deposition using a Double Alcoholate Source

A liquid-delivery metalorganic chemical vapor deposition (MOCVD) apparatus for preparing SrBi2Ta2O9 (SBT) thin films was designed and set up. For the preparation of SBT thin films, a double alcoholate source, Sr[Ta(OC2H5)6]2, was used for supplying Sr and Ta atoms with a stoichiometric composition, while Bi(C6H5)3 was used for supplying Bi atoms. In the experiment, variation of the film composition with the deposition temperature and source-supply mol ratio was primarily investigated. It was found that the Bi/Ta mol ratio in the films varied with the deposition temperature and became smaller at lower deposition temperatures. It was also found that the Sr/Ta mol ratio was considerably smaller than stoichiometry above 500°C, probably because of the dissociation of Sr[Ta(OC2H5)6]2. It was ascertained that a 200-nm-thick SBT thin film with the Sr/Ta mol ratio of about 0.4, which was deposited at 350°C and subsequently annealed in O2 atmosphere at 750°C for 30 min, exhibited ferroelectricity. The dielectric constant of the film was about 120. Remanent polarization and coercive field at 10 V were 3.8 µC/cm2 and 73 kV/cm, respectively. However, the leakage current density was found to be as high as the order of 10-4 A/cm2 at 3 V. It is speculated from atomic force microscope (AFM) observation of the surface roughness of the film that the origin of the high leakage current density is the existence of local high electric field spots in the film.

Fine-Grained SrBi2Ta2O9 Thin Films by Low Temperature Annealing

A new low pressure annealing method for preparation of SrBi2Ta2O9 thin films is proposed. These thin films were prepared on Pt/TiO2/SiO2/Si substrates by the metalorganic decomposition (MOD) method, and their structural and electrical properties were investigated. Low pressure annealing was performed at 650°C for 60 min in a 2 Torr oxygen ambient per coating. The films were well crystallized and exhibited fine-grained and dense structures with grain size of about 50 nm. Pr=4.9 µC/cm2, Ec=24 kV/cm, IL=8.6×10-8 A/cm2 at a applied voltage of 3 V and breakdown voltage (VB) of over 20 V were obtained for the 200-nm-thick films. Futhermore, in the 100-nm-thick SBT film, a saturation voltage of 1 V was obtained. Pr=3.6 µC/cm2, Ec=25 kV/cm, IL=5.5×10-8 A/cm2 at 1 V and VB was over 10 V. Therefore, this method is very useful for highly integrated ferroelectric nonvolatile memory application.

Preparation of SrBi2Ta2O9 thin films with a single alkoxide sol–gel precursor

Y. Kim, H. K. Chae, K. S. Lee and W. I. Lee, J. Mater. Chem., 1998, 8, 2317 DOI: 10.1039/A806275G

New Low Temperature Processing of Sol-Gel SrBi2Ta2O9 Thin Films

A new low temperature processing method for preparation of SrBi2Ta2O9 thin films is proposed. These thin films were prepared on Pt/Ta/ SiO2/Si substrates by a sol-gel method, and their structural and electrical properties were investigated. Films were annealed before and after the top Pt electrode deposition. The 1st annealing was performed in a 760 Torr oxygen atmosphere at 600° C for 30 min, and the 2nd annealing was performed in a 5 Torr oxygen atmosphere at 600° C for 30 min. The films were well crystallized and fine grained after the 2nd annealing. The electrical properties of the 200-nm-thick film obtained using this new processing method, i.e., the remanent polarization (P r), coercive field (E c), and leakage current density (I L), were as follows: P r=8.5 µ C/cm2, E c=30 kV/cm, and I L=1×10-7 A/cm2 (at 150 kV/cm). This new processing method is very attractive for highly integrated ferroelectric nonvolatile memory applications.