过渡金属氧化物阻变存储器动态特性的蒙特卡洛仿真.docx

过渡金属氧化物阻变存储器动态特性的蒙特卡洛仿真


摘要

　　　随着集成电路工艺技术的发展，以FLASH存储器为代表的传统非易失性存储器在集成电路特征尺寸不断减小的情况下遇到越来越多的问题。新型非易失性阻变存储器(RRAM)因其表现出的特征尺寸可缩小性良好、存储单元结构简单、与现代半导体工艺相兼容等特点，引起国内外业界与学术界的广泛研究。RRAM器件工作过程中功能层的微观效应和阻变机理尚未完全明确，影响了RRAM器件的进一步研发与应用。
　　　本文中采用动力学Monte Carlo方法，首先对基于电化学原理的双极型RRAM的阻值变化过程进行了仿真，并根据功能层厚度等因素对RRAM器件的电特性进行了模拟和分析，从而完善了已有的双极型RRAM模型。
　　　在准确模拟阻变功能层转变过程的基础上，以RRAM器件二维尺寸变化为评价标准，分别从电学性质变化、参数均匀性变化和局域热效应的角度，对双极RRAM的工作性能变化进行了分析。从模拟结果可以看出，通过调整优化RRAM器件的二维尺寸，可以得到较为理想的器件性能，从而应用于未来的存储器生产中。
　　　其次，通过对一维氧空位模型电子占有率的计算，确定了基于VCM原理的RRAM器件中氧空位产生和复合发生的几率。运算所得到的氧空位电子占有率在代入二维动力学Monte Carlo模型后，对VCM原理的RRAM器件进行了电学转变过程的仿真。
　　　最后，为了同仿真结果进行对比讨论，验证建模仿真工作的准确性，制备了W/VOx/Cu阻变存储单元结构，从而以实验与建模仿真结合的方式对阻变存储器存储机理进行了探索。
　　　本文探讨了过渡金属氧化物RRAM在未来作为新一代非易失存储器的电学特性，尤其是工作过程中的动态特征，所得到的分析结果对将来RRAM器件的建模理论分析有一定的指导意义，并且对RRAM器件制备及应用也具有一定的指导意义。

关键词： 阻变存储器 电化学原理 Monte Carlo仿真 氧空位导电

Abstract

　　With fast development of modern integrated circuit design and technology, conventional non-volatile memory such as FLASH memory is faced with more issues as it is reaching its physical limitation when critical dimension is scaling down. The emerging resistive RAM (RRAM) is attracting much attention from both manufactures and colleges for its great scalability, simple memory cell structure and good compatibility with IC process. However, the switching mechanism of RRAM device is not thoroughly studied so far, and the local effect in the functional layer of RRAM device is still under debate, all of which hinder further research and fabrication of RRAM.
　　In this paper, we adopted kinetic Monte Carlo method to model the resistive switching process of the device. The electrical characteristics of RRAM device are analyzed with device thickness scaling down, and the current is improved through the simulation.
　　Besides the prediction on switching process of RRAM functional layer, we analyzed the two dimensional impact on the electrical characteristics, parameter uniformity and local heat effect of bipolar RRAM device. From the simulation results it is concluded that through optimizing the device size of RRAM, the switching characteristics of device can be controlled, and RRAM memory with better performances could be expected in further application.
　　With calculation on electron occupancy of one dimensional oxygen vacancy chain, the formation probability of oxygen vacancy (VOs) is obtained. The switching process of valance change RRAM is simulated based on above parameters.
　　In order to discuss with the simulation results to verify the accuracy of the modeling simulation work, the resistive switching device of Si substrate W/VOx/Cu structure was fabricated, and the experiment and modeling simulation are combined for deeper exploration of the resistance change storage mechanism
　　 Above all, the switching process of transitional metal oxide based RRAM were studied in this paper. Switching properties and the aspects of dynamic process of RRAM were systematically studied, which contributes to the further studies of RRAM and its application.
　　
　　Key words：RRAM, Electrochemical Metallization, Monte Carlo method, Oxygen Vacancy Conduction

目    录
第一章 绪论  1
1.1 引言  1
1.2 阻变存储器的工作机理  3
1.2.1 熔丝-反熔丝模型  4
1.2.2 电化学原理（ECM）模型  5
1.2.3 离子价变（VCM）模型  6
1.3 阻变存储器模拟的国内外研究现状  7
1.4 Monte Carlo方法模拟  8
1.5 本论文的研究意义与内容  9
第二章 基于电化学原理RRAM的Monte Carlo仿真分析  11
2.1电化学导电细丝RRAM的Monte Carlo模拟仿真流程  11
2.2 基于阴极导电细丝的ECM RRAM的KMC模拟仿真步骤  13
2.3 阴极导电细丝机理的RRAM仿真结果与分析  15
2.3.1仿真I-V曲线及导电细丝生长的非均匀性  15
2.3.2 阻变层厚度对阻变转变时间的影响  17
2.3.3 导电细丝的形貌分析  18
2.4 本章小结  19
第三章 双极型RRAM器件二维尺寸因素影响的模拟分析  20
3.1 双极型RRAM结构仿真计算方法  20
3.2 二维尺度效应：器件电学特性变化  20
3.3二维尺度效应：均匀性的改善  21
3.4二维尺度效应：局域热效应  22
第四章 VCM原理RRAM的仿真模拟  24
4.1基于势阱辅助隧穿效应的电子占有率计算  24
4.2电子占有率计算模型的建立  26
4.3电子占有率模拟仿真结果分析  27
4.4双极型氧空位器件阻变过程描述与建模 29
4.5 Forming阻变过程的模拟仿真 30
4.6 Reset阻变过程的模拟仿真  31
4.7本章总结  33
第五章 Cu/VOx/W结构阻变存储器的制备与表征  34
5.1 VOx阻变器件的制备  34
5.2 VOx阻变器件物理特性表征  35
5.3 VOx器件的电学性能表征与分析  37
5.4 Cu/VOx/W结构器件电学性质与电化学模型仿真的比较与分析  40
第六章 总结与展望  41
参考文献  43
发表论文和科研情况说明  48
致   谢  50