【作者】 付永忠；

【导师】 杨继昌；

【作者基本信息】 江苏大学 ， 机械电子工程， 2010， 博士

【摘要】 当前,互联网、多媒体视频、高速计算机等技术的迅猛发展,使人们对更快速度、更大容量数据存储器的需求越来越迫切,然而传统的磁存储、光存储和半导体存储由于受到超顺磁效应、衍射现象和最小光刻单元的限制,存储密度很难进一步提高。基于扫描探针显微技术(SPM)的数据存储技术由于能够实现纳米尺度的信息存储,因此有望成为新一代的超高密度存储技术。基于此,本论文将光学存储中常用的硫系相变薄膜材料GeSb2Te4引入到SPM存储技术中,提出了基于热、电耦合效应的新型高密度数据存储方法,并对其存储机理及其它有关问题进行了详细研究。在分析硫系材料相变原理,以及作为存储介质的存储机理基础上,结合原子力显微镜(AFM)技术,提出了基于相变存储介质的探针存储系统模型,并对数据的写入、擦除、读取机理进行了阐述；自行搭建了一种新颖的基于扫描探针显微镜的相变存储实验装置,用来进行存储实验验证。发展了存储介质多层薄膜的制备方法,并通过实验对比和形貌分析,探索出薄膜制备的工艺路线和工艺参数。借助X射线衍射仪(XRD)、透射电子显微镜(TEM)、等离子发射光谱仪(ICP)等设备对GeSb2Te4薄膜的成分、状态及内部结构进行了详细分析,发现沉积态薄膜是非晶态,而随着退火温度的提高,会发生两次固体相转变,通过XRD表征可知第一次转变形成的是fcc结构,第二次形成的是hex结构,由此提出了GeSb2Te4材料的fcc结构和hex结构模型。利用经典形核理论对JMAK理论进行了优化,突破了其应用局限性,用相关公式预测了GeSb2Te4薄膜的形核时间和晶粒尺寸,以确定此种材料是否满足作为存储介质的要求；同时用优化的模型计算结果与实验结果相比较,具有较好的一致性。利用差示扫描量热(DSC)方法分析GeSb2Te4薄膜在不同退火温度,不同加热速度条件下的结构和热物性参数,并得到不同加热速度下的结晶温度和玻璃转化温度。利用四点探针测电阻方法测量了GeSb2Te4薄膜不同退火温度下的电阻率,发现沉积态薄膜的电阻率远远大于fcc结构和hex结构；另外,对薄膜的I-V特性和导电激活能也进行了比较全面的研究。应用TriboIndenter纳米力学测试系统考察了GeSb2Te4薄膜的硬度、弹性模量、粘附力和摩擦力等力学性能,并对溅射参数、薄膜厚度、相对湿度和表面粗糙度等对力学性能的影响进行了详细的分析；发现薄膜表面质量越好,硬度和弹性模量越高；相对湿度越高,探针针尖与薄膜表面的粘附力和摩擦力越大。采用ASC2000应力测试仪测量了薄膜的内应力,并研究了溅射功率和退火温度对薄膜表面残余应力的影响。基于相变探针存储系统原理,建立了用于有限元仿真的存储器结构模型以及热电耦合数学模型。在此基础上,利用多物理场耦合软件COMSOL Multiphysics模拟了施加不同宽度、幅值脉冲电压情况下的信息写入过程和擦除过程,通过分析电压对相变存储介质温度场的影响,找出合适的电压参数；并利用相变探针实验装置进行了实验验证。另外,对探针和导电层的电导率、热导率以及探针针尖直径对相变薄膜温度场的影响也进行了全面的分析,为后续工作中进一步优化存储系统结构提供了有力的支持。本论文研究成果可以应用于超高密度信息存储的设计,对于建立新型信息存储技术的理论体系具有重要意义。更多还原

【Abstract】 With the rocketing development of technologies of the Internet, multimedia video,high speed computer etc, people have been in urgent need of the more higher speed and density data storage. But traditional magnetic storage, optical storage and semiconductor storage have their own physical limitations because of the superparamagnetic effect, diffraction and minimum lithography element size, so it is very difficult to further improved the data storage density. The data storage with the aid of scanning probe microscopy (SPM) can record the nano scale information, so it is expected to be a next generation ultra-high-density storage technology. For the above-mentioned reasons, the dissertation introduced the GeSb2Te4 film into the SPM technology, which is a kind of chalcogenide materials widespread used in optical storage, and provided a novel method of ultra high density storage technology based on the effect of thermoelectricity, and described its mechanism in detail, the main work includes four aspects as follows:The dissertation analyzed the mechanism of phase change in chalcogenide materials and the principle of information storage using such materials, and established the basic scheme of SPM storage based on the phase change films and the atomic force microscopy(AFM) technology, and elaborated the writing, erasing and readout data process. As well as, a phase change storage device based on SPM is also established in the lab, which can be used to carry out some storage experiments.On this base, a direct and convenient method for preparing GeSb2Te4 film by the RF magnetron sputtering has been developed, simultaneously, the optimum producing process and parameters were explored through experimentation and comparison with surface topography of films. Then, X-ray diffraction(XRD), transmission electron microscopy(TEM) and inductive coupled plasma emission spectrometer(ICP) were carried out to analyze the composition, interior structures and state of the GeSb2Te4 films. The results indicated that the deposited GeSb2Te4 film was amorphous, but with the increment of annealing temperature, two-stage process of phase transition was discovered, the first stage was transformation between the amorphous phase and the crystalline phase with fcc structure, and the other is the fcc-hex phase transition. The Johnson-Mehl-Avrami-Kolmogorov(JMAK) kinetics was optimized combining classical nucleation theory. The incubation time and crystallite cluster size was predicted based correlation equation in order to know the GeSb2Te4 films were suitable for use the storage medium or not.Differential Scanning Calorimetry(DSC) was carried out to analyze the thermo-physical parameters and structure on different annealing temperatures and heating rate, and achieved the crystallization temperature and glass transition temperature of different heating rate. The resistivity of films after annealing treatment were measured by four--probe method, it is showed that the resistivity of as-deposited films was far larger than the fcc and hex crystal structure. Besides, the dissertation also studied comprehensive research on theⅠ-Ⅴcharacteristics and the activation energy of films. Mechanical properties of GeSbTe films, including hardness, elastic modulus, adhesive and force friction, were investigated by TriboIndenter nanomechanical test system, and the effect of sputtering parameters, thickness, roughness and relative humidity on mechanical properties of films was taken into account simultaneously. Experimental results showed that quality of the surface of GeSb2Te4film will affect the hardness and elastic modulus. The effect on the adhesion and friction between the tip and GeSb2Te4 film increased with a rise of relative humidity. Moreover, the influence of sputtering power and annealing temperature on residual stress also were studied by ADC2000 stress test instrument.Based on the principle of the data storage using phase change medium and probe, this dissertation established the thermoelectricity coupled model and the memory structure model using for finite element analysis(FEA). The COMSOL Multiphysics, a multi-physical coupling field FEA software, was used to simulated the process of writing and erasing information. In order to conclude the appropriate voltage parameters, different amplitude and width pulse was applied to calculate the temperature field changes of phase change storage medium. Besides, the probe and conductive layer parameters, including electric conductivity, thermal conductivity, probe diameter and so on, influencing on the temperature field of films were evaluated too. All these provided the strong support for further improving the storage structure in subsequent research work. These results are expected to be useful for the design of ultra high-density data storage, and of significance for establishing a framework of theory of novel data storage technology.更多还原