基于氧化铪的阻变存储器性能及机理的研究

发布时间：2018-06-06 23:29

本文选题：氧化铪 + 阻变存储器　；参考：《复旦大学》2012年硕士论文

【摘要】：随着集成电路工艺技术结点的不断缩小,不挥发存储器领域里,占市场主流的传统Flash存储器,由于其自身结构问题导致的栅极漏电等一系列难以克服的问题,使得其应用面临严峻的挑战。因此,基于各种材料、机制以及操作方式的下一代新型非挥发存储器开始进入研究领域,包括铁电存储器(FeRAM)、相变存储器(PRAM)、磁存储器(MRAM)以及阻变存储器(RRAM),并得到了迅速的发展。在这些新型不挥发存储器中,阻变存储器被认为是成为下一代“通用”存储器的强有力候选者之一,因为它具有结构简单、读写速度快、保持时间长、存储密度高、操作电压低、非破坏性读取、可缩小能力强、功耗低和与传统CMOS工艺兼容等优点。而在所有的具有阻变特性的材料中,又以基于过渡金属二元氧化物的阻变存储器因其成本低、成分简单、易于制备且性能稳定,成为最有前景的一种存储器。但是,有关其电阻变特性的物理机制尚不完全清楚,仍需做大量的研究工作。本论文从基于原子层淀积工艺制备氧化铪(HfO2)材料的阻变存储器性能的电学和材料特性测试出发,做了一系列的研究。首先从ALD工艺出发,讲了ALD工艺的原理、分类以及系统简介。其次,根据RCB模型对金属氧化物材料中filaments的通断与电场强度关系之间的模拟,提出采用薄low k/厚high k堆叠结构来改善单一high k材料阻变存储器的开关电压的稳定性和减小开关电压数值。由于两种材料介电常数不同,施加外部电压时,根据高斯定理,穿过两层介质的电位移矢量是连续的,使得low k介质中的电场强度是high k材料中的好几倍,从而使得RRAM器件在开关过程中filament的通断都被控制在接近阳极的较薄的1ow K A12O3层内,而不是随机的发生在整个阻变功能层里,从而可以改善器件的SET电压与RESET电压的离散性以及减小SET电压与RESET电压的数值,改善稳定性和减小功耗。实验结果成功实现了这一目的,并对比了当lowk薄膜A1203材料厚度不同时的两种情况,发现当low k薄膜更薄的时候,稳定性更好,开关电压值更小,器件的高低阻阻值窗口更大。之后,对基于氧化铪的阻变存储器,从材料特性和电学性能上做了了氧化铪氮化与非氮化后的器件特性分析与对比,发现氮化后,材料特性上上,薄膜中有N元素掺进去；电学特性上器件的阻变特性消失,分析其阻变机理是跟薄膜中的氧空位和缺陷有关的,氮化前后,电流漏电特性从空间电荷限流效应转变为普尔—法兰克效应。最后,对本论文的实验工作进行了总结并对RRAM的前景做出了展望。
[Abstract]:With the continuous reduction of the technical nodes of IC process, the traditional Flash memory, which dominates the market in the field of non-volatile memory, has a series of insurmountable problems such as gate leakage caused by its own structure problem. It makes its application face severe challenge. Therefore, the next generation of nonvolatile memory, which is based on various materials, mechanisms and modes of operation, has come into the research field, including ferroelectric memory (FeRAM), phase change memory (PRAM), magnetic memory (MRAM) and resistive memory (RRAM), and has been developed rapidly. Among these new types of nonvolatile memory, resistive memory is considered to be one of the most powerful candidates for the next generation of "universal" memory because of its simple structure, fast reading and writing speed, long retention time, high storage density. Low operating voltage, non-destructive reading, high power reduction, low power consumption and compatibility with traditional CMOS process. Among all the materials with resistance properties, the transition-metal binary oxide based resistive memory is the most promising memory because of its low cost, simple composition, easy preparation and stable performance. However, the physical mechanism of its resistive properties is not completely clear, and a lot of research work is needed. In this paper, a series of studies have been done on the electrical and material properties of the resistive memory based on the atomic layer deposition process for the fabrication of hafnium oxide (HfO _ 2) materials. The principle, classification and system introduction of ALD process are introduced from the point of view of ALD process. Secondly, according to the RCB model, the relationship between filaments's on-off and electric field strength in metal oxide materials is simulated. A thin low k / thick high k stack structure is proposed to improve the switching voltage stability and reduce the switching voltage value of a single high k resistive memory. Because the dielectric constants of the two materials are different, when the external voltage is applied, according to the Gao Si theorem, the electric displacement vectors passing through the two layers of dielectric are continuous, so that the electric field intensity in the low k medium is several times higher than that in the high k material. As a result, the switching of filament in RRAM devices is controlled in the thin 1ow K A12O3 layer near the anode, rather than in the whole resistive function layer. It can improve the dispersion of SET voltage and RESET voltage, reduce the value of SET voltage and RESET voltage, improve stability and reduce power consumption. The experimental results successfully achieve this goal, and compare the two cases when the thickness of lowk thin film A1203 is different. It is found that when the low k film is thinner, the stability is better, the switching voltage is smaller, and the high and low resistance window of the device is larger. After that, the characteristics of Hafnium oxide nitrided and non-nitrided devices are analyzed and compared in terms of material properties and electrical properties. It is found that after nitridation, N elements are added to the films. The electrical characteristics of the devices disappear. The resistance mechanism is related to the oxygen vacancies and defects in the films. Before and after nitriding, the current leakage characteristics change from the space charge current limiting effect to the Poor-Frank effect. Finally, the experimental work of this paper is summarized and the prospect of RRAM is prospected.
【学位授予单位】：复旦大学
【学位级别】：硕士
【学位授予年份】：2012
【分类号】：TP333

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