Preparation and Dielectric Properties of SrBi_2 Ta_2 O_9 Thin Films by Sol-Gel Method

铋层结构铁电（BLSF）材料SrBi_2Ta_2O_9， SrBi_2Nb_2O_9, SrBi_4Ti_4O_<15>作为一种有前途的非易失性随机存取存储器（NvRAM）应用引起了人们的极大兴趣。其中，SrBi_2Ta_2O_9 （SBT）由于其非疲劳特性和低极化开关电压的可能性，是最有希望应用于非易失性存储器的候选材料。本文介绍了用前驱体溶液制备SBT薄膜的方法。研究了SBT薄膜的晶体取向、表面形貌和介电性能。将二正丁醇锶和三正丙醇铋在2-甲氧基乙醇中室温混合1h，然后加入氧化钽，室温搅拌2h。在一些SBT溶液中，acac作为螯合剂加入到含Sr、Bi和ta的溶液中。采用旋涂技术在Pt(111)/ Ti /SiO_2 /Si基底上制备了SBT凝胶薄膜。在150℃下干燥5min，在400℃下加热30min，然后在500 ~ 750℃下加热。上述过程重复了几次。采用添加和不添加乙酰丙酮（acac）的金属醇氧化物SBT前体溶液，分别在600和750℃的温度下制备了Sr_<0.7>Bi_<2.2>Ta_2O_9 （SBT）薄膜。在不添加acac的前提下，在600℃的温度下成功制备了SBT晶体薄膜。在750℃下制备的SBT薄膜具有高（105）衍射强度和随机取向，晶粒结构为500 ~ 860nm的石壁状晶粒和100 ~ 300nm的小晶粒组成的双峰结构。前驱体溶液中加入acac促进了SBT的c轴优先取向。c轴择优取向的SBT薄膜呈现200 ~ 300nm的大晶粒和SOnm左右的小晶粒的双峰结构。不添加acac的前驱体溶液在750 C下制备的SBT薄膜的ε ε为119，P为3.1 μ C/cm_2， de_c为65.1 kV/cm，而含有acac的前驱体溶液在750 C下制备的SBT薄膜的ε ε为205，P为7.2 μ C/cm_<2c>， ε ε为53.3 kV/cm。少

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 … More 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