Low-temperature Preparation and Evaluation of Ferroelectric Thin Films for FeRAM by Chemical Solution Process

近年来，Bi4Ti3O12、SrBi2Ta2O9和SrBi2Nb2O9等双层钙钛矿薄膜在非易失性随机存取存储器(NVRAM)器件中的应用引起了人们的极大关注。其中，由于SrBi2Ta2O9(SBT)薄膜具有优异的抗疲劳性能和较小的矫顽场EC，因此在NVRAM中具有特别大的应用潜力。Sol-Gel法主要是以金属醇盐为原料制备SBT薄膜。为了获得优异的铁电性能，控制SBT薄膜的结构和结晶度是至关重要的。SBT薄膜的低温制备是其在硅器件中应用的需要。在这项工作中，我们主要研究了准分子紫外光照射下SBT薄膜的制备和性能。以SBT前驱体的醇盐溶液为原料，采用旋涂技术在PI(200 Nm)/Ti(50 Nm)/SiO_2/Si衬底上制备了SBT凝胶薄膜。用Xe准分子紫外灯在不同温度下照射凝胶薄膜5min。经UV处理的薄膜在500℃下焙烧30min，然后在氧气气氛中750℃下热处理1h。SBT薄膜呈随机取向，具有较强的(115)取向。薄膜的微观结构由0.1~0.2μm的细小颗粒组成，与在O2气氛中辐照相比，准分子紫外光照射下的薄膜具有较强的C-H基团红外吸收。在200℃的紫外光照射下，薄膜的结晶度有所提高。SbT薄膜具有饱和的P-E磁滞曲线，剩余极化为4.1μC/cm~2，矫顽场为88.7KV/cm。SBT薄膜具有致密的微结构，晶粒度为500~600 nm

Recently, Bi-layered perovskite thin films such as Bi_4Ti_3O_<12>, SrBi_2Ta_2O_9 and SrBi_2Nb_2O_9 have been attracting much attention for use in nonvolatile random access memory (NvRAM) devices. Among them, SrBi_2Ta_2O_9 (SBT) thin films have an especially high potential for NvRAM applications, because SBT has superior fatigue-free properties and small coercive fields, Ec. SBT thin films have been fabricated predominantly by Sol-Gel method with metal alkoxides. It is very important to control the structure and crystallinity of SBT thin films in order to obtain the excellent ferroelectric properties. Low-temperature preparation of SBT thin films is desired for the application to silicon device. In this work, we focussed on the preparation and properties of SBT thin films using Excimer UV irradiation. Thin films of SBT gels were prepared on Pi (200nm)/Ti (50nm)/SiO_2/Si substrates by a spin-coating technique from alkoxide solutions of SBT precursors. The gel thin films were irradiated using Xe excimer UV lamp at various temperatures for 5min. The UV-processed films were calcined at 500℃ for 30min, and then annealed at 750℃ for 1h in an O_2 atmosphere. The SBT thin films exhibited random orientation with strong (115) orientation. The microstructure of the films consisted of fine grains of 0.1〜0.2μm. Strong IR absorption assigned to C-H group was observed in SBT gel films with Excimer UV irradiation in N_2 atmosphere, in contrast with the irradiation in O_2 atmosphere. The crystallinity of the prepared films was improved by the UV irradiation at 200℃. SBT thin films showed well-saturated P-E hysteresis curve with a remanent polarization of 4.1μC/cm^2 and coercive field of 88.7kV/cm. SBT thin films showed a dense microstructure with grain sizes of 500〜600nm