【作者】 李颖弢；

【导师】 刘肃； 刘明；

【作者基本信息】 兰州大学 ， 微电子学与固体电子学， 2011， 博士

【摘要】 随着诸如手机、MP3、MP4、笔记本电脑等便携式个人设备的逐渐流行,以及近年来计算机技术、互联网技术以及新型大众化电子产品的高速发展,非挥发性存储器在半导体行业中扮演越来越重要的角色。非挥发性存储器最大的优点在于在无电源供应时存储的数据仍能长时间保持下来。目前市场上的非挥发性存储器以闪存(Flash)为主流,占半导体存储器市场的绝大份额。但是随着半导体技术节点不断向前推进,基于传统浮栅结构的Flash技术正遭遇到严重的技术瓶颈,其中最主要的问题就是Flash在器件尺寸缩小化过程中存在操作电压大、操作速度慢、耐久力不够好、功耗高等缺点,这在很大程度上限制了其在市场以及高科技领域的广泛应用。因此,业界对下一代非挥发性存储器技术进行了大量的研究,目前已研制出多种有望取代Flash存储器的新兴非挥发性存储器,如铁电存储器(FRAM)、磁存储器(MRAM)、相变存储器(PRAM)以及阻变存储器(RRAM)。阻变存储器由于其具有高的读写速度、低的功耗、高集成度、多值存储能力、低成本等优势,因此引起了人们极大的兴趣并一度成为现阶段研究的热点。本文将研究RRAM的注意力集中在材料组分更加简单、制备过程更加容易、制造工艺与CMOS兼容的二元金属氧化物上,主要开展了基于ZrO2、WO3以及TiO2材料RRAM器件电阻转变特性以及电阻转变机理方面的研究工作。基于ZrO2材料制备了一种ZrO2:TiOx双层结构器件,实验结果发现,当在Zr02和上电极材料之间插入一薄层的TiOx缓冲层能够改善器件的电阻转变特性,尤其是器件由高阻态向低阻态转变所需要的Set电压明显降低。其次,选择Ag作为电极材料制备了一种简单的Au/ZrO2/Ag结构器件,该器件具有更低的操作电压(<1V)、较高的电阻比率(104)、较快的操作速度(50ns)、接近100%的器件产率,并且该器件在室温以及85℃都具有很好的保持特性。此外,我们对Cu/ZrO2:Cu/Pt器件中观测到的不稳定Reset现象的物理机制进行分析。研究了不同电极材料对WO3薄膜电阻转变特性的影响,发现Cu作为上电极的Cu/WO3/Pt结构器件具有更好的电阻转变特性,通过电学测试对导致这种优良电阻转变特性的原因作了分析。其次,对Cu/WO3/Pt结构器件的多级存储特性进行了研究,采用小步长的测试方法分析了引起这种多级存储的物理机制。在基于TiO2材料的RRAM器件方面,采用退火的方法改善器件的性能。其次,制备了一种与CMOS工艺完全兼容的具有Al/TiOx/Al简单结构的RRAM器件,并对这种器件的电阻转变特性进行了研究。更多还原

【Abstract】 With the prevalent usage of portable equipments, such as mobile phone, MP3, MP4 player as well as notebook PC, the nonvolatile memory (NVM) plays an important role in the semiconductor industry. The advantage of NVM is that the stored data can be kept for a long time without power supply, and the current NVM mainstream for the semiconductor mass storage is based on the Flash technology. However, with the conventional memories approaching their scaling limits, Flash memory, which is based on the traditional floating gate concept, has encountered serious technical challenges due to the tradeoffs between the high speed, low power consumption and long retention time. It is therefore common practice to explore new memory to compensate these weaknesses. Requirements for a perfect memory would have a high capacity, fast speed, long retention time, low power consumption, and it would be also nonvolatile and scales better than existing technologies. In recent years, some emerging nonvolatile memories, such as ferroelectric random access memory (FRAM), magnetic random access memory (MRAM), phase-change random access memory (PRAM) and resistive random access memory (RRAM), are being enthusiastically studied to achieve these requirements. Among all these choices, RRAM device which shows resistive switching between a high resistance state and a low resistance state has overwhelming advantages of easy fabrication process, simple structure, excellent scalability, fast switching speed, and high integration density. Therefore, more and more research communities focus their attention on RRAM devices. This work focuses on the investigation of resistive switching characteristics in binary metal oxides-based RRAM deives due to the simple structure, easy fabrication process and compatibility with the current complementary metal oxide semiconductor (CMOS) technology. We focus our attention mainly on resistive switching characteristics and resistive switching mechanism of ZrO2、WO3 and TiO2-based RRAM deives.As for the ZrO2-based RRAM deives, we fabricated Cu/ZrO2/Pt and Cu/TiOx-ZrO2/Pt structure devices and investigated the resistive switching characteristics of these two devices. By embedding a thin TiOx layer between ZrO2 and Cu top electrode, stable and reproducible bipolar resistive switching characteristics could be observed. Especially, the set voltage obviously showed decrease compared to that in ZrO2-based RRAM device without TiOx layer. We also fabricated Au/ZrO2/Ag structure device which showed low operation voltages (<1V), high resistance ratio (about 104), fast switching speed (50ns), and reliable data retention (10 years extrapolation at both RT and 85℃). Moreover, the benefits of high yield and multilevel storage possibility made this device promising in the next generation nonvolatile memory applications. The instable reset behavior was observed in Cu/ZrO2:Cu/Pt device, and the mechanism of this instable reset behavior was investigated based on a physical model.We investigated the effect of different top electrodes on the resistive switching characteristics of WO3-based RRAM devices. Compared with the Al/WO3/Pt and Cr/WO3/Pt devices, the Cu/WO3/Pt device had much better resistive switching characteristics, such as good reproducibility, low power consumption and good data retention. In addition, the multilevel storage capability of the Cu/WO3/Pt RRAM deivce was demonstrated by setting different compliance currents during the Set process. A direct measurement by using a dc voltage sweeping mode with a smaller sweeping voltage incremental rate was employed to explore the plausible mechanism of the multilevel storage, which might be attributed to the combination of filaments radial growth and formation of more conductive filaments as applying a higher compliance current.As for the TiO2-based RRAM deives, we reported a simple method to improve uniformity of resistive switching parameters in atomic-layer-deposited titanium oxide film by nitrogen annealing. We also fabricated an Al/TiO/Al RRAM device which is fully compatible with CMOS technology.更多还原