基于标准逻辑工艺的阻变存储器性能及存储结构研究

发布时间：2018-07-24 21:19

【摘要】：以Flash为代表的传统非挥发存储器已经取得了巨大的成功,但是随着工艺尺寸的不断减小,Flash即将到达它的物理极限。为替代Flash引领新一代的非挥发存储器,近些年新型非挥发存储器得到了广泛研究。阻变存储器(RRAM)因结构简单、可微缩化、读写速度快、功耗低、与标准逻辑工艺良好兼容、成本低等优点,被认为是最有前途的新型存储技术之一,然而阻变存储器在性能参数均匀性、高密度应用、数据保持特性和操作成品率方面还存在不足,需要进一步改善。具有RRAM特性的材料体系和存储结构很多,而具体选择哪种材料作为RRAM,同时又要满足与CMOS标准逻辑工艺兼容性及集成成本等要求则是一个相当困难的议题。金属钽在阻挡层工艺中广泛应用,TaOx基阻变存储器无需引入污染性元素,具有成本和CMOS工艺兼容的优势。但从目前国际上的报道来看,TaOx基RRAM高低阻态偏低,器件功耗高,器件性能并不是非常理想。对此,本文提出引入Ta205/TaOx双层结构,增大了高低阻窗口、降低了功耗,并控制阻变发生位置一致,使得电学特性呈现出重复性和集中化。另外,给出了分别面向高密度和嵌入式应用的Ta2O5/TaOx双层结构三维器件集成和平面工艺集成方案。本文基于SMIC0.18um工艺制备得128kbit AlOx/WOy RRAM芯片,给出了阻变特性阵列结果,如高低阻分布、置位复位电压统计等,并分析各层薄膜在阻变过程中充当的角色和器件转换机理。通过对比不同AlOx/WOy RRAM的制备条件以及操作算法研究AlOx/WOy双层结构数据保持特性,发现经过还原气氛退火后的器件数据保持特性失效率大幅降低,而操作算法越强,器件数据保持特性失效率则越高,这样从工艺和设计的角度分别给出了器件数据保持特性改善的方法。本文研究了AlOx/WOy双层结构对于不同Forming极性时呈现出来的阻变特性差异,并基于薄膜结构成分提出了基于能带角度的机理解释。梯度氧空位在AlOx层的分布对Forming电压极性反应明显,当采用正向Forming时,器件表现出了良好的阻变转换特性、疲劳特性以及抗读干扰性；负向Forming时由于氧空位进一步移开AlOx/Al2O3界面,使得势垒变得更高更宽,表现出极低的操作成品率和直接击穿。
[Abstract]:The traditional nonvolatile memory, represented by Flash, has achieved great success, but with the decrease of process size, it is about to reach its physical limit. In order to replace Flash, a new type of nonvolatile memory has been widely studied in recent years. Resistive memory (RRAM) is considered to be one of the most promising new storage technologies because of its simple structure, miniaturization, fast reading and writing speed, low power consumption, good compatibility with standard logic technology and low cost. However, resistive memory has some shortcomings in performance parameter uniformity, high density application, data retention characteristics and operating yield, which need to be further improved. There are many material systems and storage structures with RRAM characteristics, but it is a very difficult issue to select which materials as RRAM, and to meet the requirements of CMOS standard logic process compatibility and integration cost at the same time. Tantalum is widely used in the barrier layer process without the introduction of polluting elements in the TaOx based resistive memory. It has the advantages of cost compatibility and CMOS process compatibility. However, according to the international reports, the low resistance state of TaOx-based RRAM is low, the device power consumption is high, and the device performance is not very ideal. In this paper, we propose the introduction of Ta205/TaOx double-layer structure, which increases the high and low resistive window, reduces the power consumption, and controls the same position of resistive change, which makes the electrical characteristics present repeatability and centralization. In addition, the scheme of 3D device integration and planar process integration of Ta2O5/TaOx bilayer structure for high density and embedded applications are presented. In this paper, 128kbit AlOx/WOy RRAM chip is fabricated based on SMIC0.18um process. The array results of resistive characteristics, such as high and low resistive distribution, position reset voltage statistics, etc., are given. The roles of each layer of thin films in the resistance process and the mechanism of device conversion are analyzed. By comparing the preparation conditions and operation algorithms of different AlOx/WOy RRAM, the data retention characteristics of AlOx/WOy bilayer structure are studied. It is found that the failure rate of the device data retention characteristics after annealing in reducing atmosphere is greatly reduced, and the stronger the operation algorithm is, the stronger the operation algorithm is. The higher the failure rate of device data retention characteristics is, the better the method of improving device data retention characteristics is given from the point of view of process and design. In this paper, the resistance characteristics of AlOx/WOy bilayer structure for different polarity of Forming are studied, and the mechanism based on the energy band angle is proposed based on the composition of the thin film structure. The distribution of the gradient oxygen vacancy in the AlOx layer has obvious response to the polarity of the Forming voltage. When the positive Forming is used, the device exhibits good resistance to conversion, fatigue and anti-reading interference, and the negative Forming is further removed from the AlOx/Al2O3 interface due to the oxygen vacancy. The barrier becomes higher and wider, showing extremely low operating yield and direct breakdown.
【学位授予单位】：复旦大学
【学位级别】：硕士
【学位授予年份】：2013
【分类号】：TP333

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