过渡族金属氧化物基阻变器件电阻转变特性及其机理研究

发布时间：2018-01-19 08:25

本文关键词： 阻变存储器电致电阻效应 ZnO CuO_x/Si WO_3　出处：《武汉理工大学》2013年博士论文　论文类型：学位论文

【摘要】：电阻型随机存储器(RRAM)是一类非常有前途的新型非易失性半导体存储器。基于过渡金属氧化物材料的RRAM器件具有“价格低,功率小,速度快,与CMOS工艺兼容性更好及物理性能更丰富”等优点,是新一代非易失性存储器的有力候选者。经过十多年地发展,相关器件的制备和新材料体系的开发上有了明显进展。然而RRAM领域中仍然存在很多问题需要解决,物理机制还不清晰,而阻变参数分散和阻变位置的不可控性等问题也困扰着RRAM的应用。本文以ZnO, CuOx/Si和WO3氧化物材料作为研究对象,在微结构、工作机理以及研究方法等方面对RRAM的关键技术进行研究,主要得到以下结果： (1)通过在Ag/Zn0.8Mg0.2O之间添加缓冲层AgOx,成功得到具有稳定阻变性能及极小转变阈值电压的双极性Ag/AgOx/Zn0.8Mg0.2O/Pt器件。该双极性器件具有非常窄的转变阈值电压和高低组态电阻值分布,σ/μ值分别为6.7%(Vset),11.8%(Vreset),9%(LRS),29.5%(HRS)。同时,该器件与其他已报道的氧化物基RRAM器件相比具有最小的转变阈值电压值(Vset:0.11V～0.19V; Vreset:-0.14V～-0.18V),大大降低了器件在使用过程中的能量消耗。同时我们在Ag/AgOx/Zn0.8Mg0.2O/Pt器件中实现了双极性和单极性两种转变方式的可控转换。研究表明Ag/AgOx/Zn0.8Mg0.20/Pt器件的电阻转变过程中焦耳热效应和电场致离子迁移运动并存,相互竞争。当离子迁移运动占主导地位时,器件表现出双极性转变行为。通过对双极性器件的高阻态进行短时脉冲处理,该器件从双极性转变转换为单极性转变。脉冲处理使Zn0.8Mg0.2O层中的丝通道发生变形,焦耳热效应起主导作用,器件表现出单极性转变行为。随后对单极性器件进行负向偏压扫描,一定条件下,器件的阻变类型转换为双极性转变。这种特性使该器件能够根据不同的需要在两种转变方式之间进行转换,扩展了器件的应用范围。 (2)利用CuOx/Si界面氧化还原反应生成结构均匀的SiOx绝缘层,成功制备了具有类均匀转变特性的Pt/CuOx/Si/Pt器件。该器件具有渐变的电形成过程(GE过程),随着电压扫描次数的增加,电阻值逐渐增加,同时电容值逐渐减小。我们通过对比试验、复阻抗谱图、I-V曲线的对称性、氧化还原反应公式、界面层有效厚度的计算及AES深度剖析逐步证实了CuOx/Si界面SiOx层的存在,并且该层对器件类均匀转变特性起了至关重要的作用。GE过程实质上是电压扫描过程中界面处发生氧化还原反应,SiOx层厚度逐渐增加导致。通过对I-V曲线和交流电导率的分析对器件的电输运特性,低阻态的弛豫行为和电阻转变机制进行了详细地研究。器件的电输运特性表现为空间电荷限制电流机制(SCLC),初始态器件中SiOx层结构较为完整,缺陷含量少,因此不存在浅陷阱控制的SCLC过程。经过电压扫描后,Cu+/Cu2+离子进入SiOx层中,成为电子跃迁的陷阱,使器件表现出浅陷阱控制的SCLC过程。在低阻态弛豫的过程中,SiOx层的厚度没有发生变化,电阻增加后,Cu+/Cu2+离子的弛豫时间和扩散系数也随之增加,离子浓度降低,即低阻态的弛豫过程由Cu+/Cu2+离子扩散出SiOx层导致。复电导率实部随频率变化的曲线高频下符合.fβ型(β～1)的交流电导行为,表明弛豫中心或跃迁势垒分布均匀,Cu+/Cu2+离子在SiO、层中分布较均匀，进而使器件表现为类均匀转变。该工作为制备均匀转变器件提供了新的思路和方法。 (3)采用C-AFM技术研究了WO3-x阻变薄膜的导电特性。发现Au/WO3-x/Au平面器件的导电通道的电阻状态分为两部分,其中靠近白色区域(与电极相连的高阻区)的弧形区域电阻最低,远离白色区域的部分电阻稍高。WO3-x/glass薄膜颗粒表现出颗粒边界导电的特性,同时边界的导电性具有不均匀性。WO3-x/Pt薄膜颗粒则表现出晶粒内部导电的特点。WO3-x/Pt薄膜颗粒存在均匀导电和不均匀导电两种导电行为。颗粒的不均匀导电是由颗粒内部氧缺陷分布不均匀造成。
[Abstract]:Resistive random access memory (RRAM) is a very promising new type nonvolatile semiconductor memory device. RRAM transition metal oxide based material has low price, small power, speed, and better physical properties and CMOS process compatibility more abundant advantages, is a new generation of non easily lost strong candidates memory. After more than 10 years of development, has been significant progress in the development of related devices and new material preparation system. However, in the field of RRAM there are still many problems to be solved, the physical mechanism is not clear, but the resistance variable parameter dispersion and resistance change position is not controllable and other problems plaguing RRAM the application of ZnO. In this paper, CuOx/Si and WO3 oxide materials as the research object, in the micro structure, the paper studies the key technology of RRAM's working mechanism and research methods, the main results are as follows:
(1) by adding AgOx buffer layer between Ag/Zn0.8Mg0.2O with bipolar Ag/AgOx/Zn0.8Mg0.2O/Pt device performance and minimal change threshold voltage stability resistance successfully. The bipolar device has a very narrow transition threshold voltage and low resistance value distribution configuration, sigma / mu = 6.7% (Vset), 11.8% (Vreset). 9% (LRS), 29.5% (HRS). At the same time, the device with other reported oxide based RRAM devices compared with the change of the minimum threshold voltage (Vset:0.11V ~ 0.19V; Vreset:-0.14V ~ -0.18V), greatly reduce the energy consumption in the process of the device in use.
At the same time we realized controllable bipolar and unipolar two mode conversion in Ag/AgOx/Zn0.8Mg0.2O/Pt devices. The results show that the Joule heat resistance transformation process of Ag/AgOx/Zn0.8Mg0.20/Pt device in the electric field induced effect and ion migration movement coexist, compete with each other. When the ion migration is dominant, the device exhibits bipolar short pulse transition behavior. By dealing with the high resistance state of bipolar devices, the device from bipolar transformation for unipolar pulse processing transformation. The wire channel in the Zn0.8Mg0.2O layer is deformed, the Joule heat effect should play a leading role, the device exhibits unipolar behavior. Then the unipolar device for negative bias scanning, certain under the condition of device type conversion for bipolar resistive transition. This feature allows the device to be according to different needs in between the two ways of transformation The conversion extends the application range of the device.
(2) the reduction reaction of uniform structure SiOx insulation layer using CuOx/Si interface oxidation, Pt/CuOx/Si/Pt device with uniform change characteristics were prepared successfully. The formation process of the electric device has a gradual (GE process), with the increase of voltage scanning frequency, the resistance value increases gradually, while the capacitance decreases. We compared test, complex impedance spectra, the symmetry of the I-V curve, the redox reaction formula, calculation and AES depth analysis of the effective thickness of interface layer gradually confirmed the CuOx/Si interface SiOx layer, and the layer of uniform change characteristics of the device class played a crucial role in the.GE process is essentially a voltage scanning process at the interface the redox reaction, the thickness of SiOx layer leads to a gradual increase.
Through the analysis of I-V curve and AC conductivity on device electrical transport properties, relaxation behavior and resistance change mechanism of the low resistance state were studied in detail. The electric performance device transport properties for the space charge limited current mechanism (SCLC), the initial state of SiOx in device layer structure is complete, the content of defects less, so there is no SCLC shallow trap control. After scanning voltage after Cu+/Cu2+ ion into the SiOx layer, become the electronic transition trap, the device showed SCLC process control. The shallow trap in the process of low resistance state relaxation, SiOx layer thickness does not change, the resistance increased after. The relaxation time and diffusion coefficient of Cu+/Cu2+ ions increases, ion concentration decreased, the low resistance relaxation process by Cu+/Cu2+ ion diffusion SiOx layer. In the real part of the complex conductivity with frequency variation curve under high frequency with.F beta (beta - 1). AC conductance behavior indicates that the distribution of relaxation centers or transition barriers is uniform. The distribution of Cu+/Cu2+ ions in SiO layer is more uniform, which makes the devices behave like homogeneous transformation. This work provides new ideas and methods for the preparation of uniform transformation devices.
(3) to study the characteristics of WO3-x conductive resistive films using C-AFM technology. It was found that the resistance state of conductive channel Au/WO3-x/Au planar device is divided into two parts, which is close to the white area (high resistance region connected with the electrodes) arc area resistance minimum, away from the white area of slightly higher resistance.WO3-x/glass film grains show conductive properties of grain boundaries, while conductivity boundary has inhomogeneity of.WO3-x/Pt thin films showed the internal characteristics of grain particles of.WO3-x/Pt thin film conductive particles exist uniform conductive and nonuniform conductive behavior. Two kinds of conductive particles by nonuniform conductive particles inside the oxygen defect distribution is not uniform.

【学位授予单位】：武汉理工大学
【学位级别】：博士
【学位授予年份】：2013
【分类号】：TP333

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