Investigation of gate oxide traps effect on NAND flash memory by TCAD simulation

The effects of gate oxide traps on gate leakage current and device performance of metal–oxide–nitride–oxide–silicon(MONOS)-structured NAND flash memory are investigated through Sentaurus TCAD. The trap-assisted tunneling(TAT)model is implemented to simulate the leakage current of MONOS-structured memory cell. In this study, trap position, trap density, and trap energy are systematically analyzed for ascertaining their influences on gate leakage current, program/erase speed, and data retention properties. The results show that the traps in blocking layer significantly enhance the gate leakage current and also facilitates the cell program/erase. Trap density ~10¹⁸ cm^-3 and trap energy ~ 1 eV in blocking layer can considerably improve cell program/erase speed without deteriorating data retention. The result conduces to understanding the role of gate oxide traps in cell degradation of MONOS-structured NAND flash memory.     

原子层沉积制备Ta_2O_5薄膜的光学特性研究

以乙醇钽[Ta(OC2H5)5]和水蒸气为前驱体,采用原子层沉积(ALD)方法分别在基板温度为250℃和300℃的K9和石英衬底上制备了Ta2O5光学薄膜。采用分光光度计、X射线光电子能谱(XPS)、X射线衍射(XRD)、扫描电子显微镜(SEM)和原子力显微镜(AFM)等手段对薄膜的光学特性、微结构和表面形貌进行了研究。结果表明,用ALD方法制备的Ta2O5薄膜在刚沉积和350℃退火后均为无定形结构,而250℃温度下沉积的薄膜其表面粗糙度低,聚集密度很高,光学均匀性优,在中紫外到近红外均表现出很好的光学特性,可以作为高折射率材料很好地应用于光学薄膜中。