|Budget Amount *help
¥3,300,000 (Direct Cost : ¥3,300,000)
Fiscal Year 1998 : ¥900,000 (Direct Cost : ¥900,000)
Fiscal Year 1997 : ¥2,400,000 (Direct Cost : ¥2,400,000)
Bismuth layer-structured ferroelectric (BLSF) materials such as SrBi_2Ta_2O_9, SrBi_2Nb_2O_9, SrBi_4Ti_4O_<15> have attracted great interest as a promising nonvolatile random access memory (NvRAM) applications. Among them, SrBi_2Ta_2O_9 (SBT) is the most promising candidate for nonvolatile memory applications, because of non-fatigue nature and possibility of low polarization switching voltage.
This paper describes the preparation of SBT thin films from precursor solutions. Crystal orientation, surface morphology and dielectric properties of SBT thin films were investigated. Strontium di-n-butoxide and bismuth tri-i-propoxide were mixed together in 2-methoxyethanol at room temperature for lh, and then the solution was added to tantalum ethoxide, and finally stirred for 2h at room temperature. In some SBT solutions, acac was added as a chelating agent to Sr, Bi and Ta-containing solutions. SBT gel thin films were prepared by spin-coating technique on Pt(111)/ Ti /SiO_2 /Si substrates. Gel
thin films were dried at 150ﾟC for 5min and heated at400ﾟC for 30min and then heated at 500-750ﾟC.The above-mentioned process was repeated several times.
Ferroelectric Sr_<0.7>Bi_<2.2>Ta_2O_9 (SBT) thin films were prepared at 600ﾟC and 750ﾟC for lh using SBT precursor solutions of metal alkoxides with and without an addition of acethylacetone (acac), respectively. Crystalline SBT thin films were successfully prepared at 600ﾟC from precursor solutions without an addition of acac. SBT thin films prepared at 750ﾟC exhibited a high (105) diffraction intensity with random orientation, and exhibited a bimodal grain structure consisting of stone wall-like grains of 500-860nm and small grains of 100-300nm. The addition of acac to precursor solutions promoted a c-axis preferred orientation of SBT.SBT thin films with a c-axis preferred orientation showed a bimodal microstructure which consisted of large grains of 200-300nm and small grains of about SOnm.
SBT thin films prepared at 750ﾟC from precursor solutions without an addition of acac exhibited epsilon of 119, P, of 3.1 muC/cm_2 andE_c of 65.1 kV/cm, while those prepared at 750ﾟC from precursor solutions containing acac exhibited epsilon of 205, P of 7.2 mu C/cm_<2c> andEs of 53.3 kV/cm. Less