【作者】 赵钢；

【导师】 褚家如；

【作者基本信息】 中国科学技术大学 ， 精密仪器及机械， 2007， 博士

【摘要】 传统的磁存储、光存储和半导体存储受到超顺磁效应、衍射现象和最小光刻单元的限制而存在各自的物理极限，基于扫描探针显微术(SPM)的信息存储技术能够突破传统存储技术的物理极限，有望成为下一代的高密度存储技术，但目前存在读取速率低和探针寿命短等问题。针对上述问题，本论文将压电功能材料锆钛酸铅(PZT)薄膜应用于SPM技术中，提出了新型的“热-压电-机械”数据存储方法，并对其机理进行了详细论述。用于“热-压电-机械”数据存储的读写头是由压电悬臂梁探针组成的阵列，论文中用减小几何尺寸的方法设计了一种低刚度高谐振频率的悬臂梁式压电探针，以非矩形不等截面多层复合结构的悬臂梁作为探针的力学模型，通过理论推导获得探针的弹性常数为4N／m，谐振频率为245kHz。以探针自由端部集成的微型加热器为中心研究了探针的热学特性，研究表明加热器热量散失的主要方式为通过梁体传导到基体，次要方式为传导到空气中，而对流和辐射对热量散失带来的影响可以忽略。数据写入过程是针尖和介质相互作用的过程，结合存储介质聚甲基丙烯酸甲酯(PMMA)的材料特性和数据写入机理，建立了包含力学接触分析、热传导分析、粘弹性分析以及运动流体界面追踪分析在内的六步模型来描述整个数据写入过程，并用该模型对单个数据写入过程进行了数值模拟，模拟结果显示在加热和加载力共同作用下最终形成中央凹陷50nm周围凸起十几纳米的数据斑。模拟同时表明数据斑周围的凸起是将介质在流体状态挤出所致，而介质受热膨胀的影响很小。从电荷灵敏度的角度研究了数据读出，通过增加悬臂梁弹性层厚度、剥离部分钝化层以及为PZT加直流偏压等方法可提高电荷灵敏度，并以此优化了探针结构和数据读出过程。利用微加工方法加工和制备了存储系统的部分关键结构和材料。通过各向异性刻蚀法获得了高宽比为1.56，尖端曲率半径小于50mm的单晶硅针尖结构，通过旋涂法获得了厚度为200nm左右表面粗糙度低于2nm的PMMA薄膜，通过等离子体增强化学气相沉积法(PECVD)获得了低应力的氮化硅薄膜以及非晶硅薄膜。对上述内容进行深入研究的结果表明“热-压电-机械”的存储方式在保证高密度的前提下，具有更高的读写速率，更长的探针寿命和更低的器件功耗，能够解决目前存在的读取速率低、探针寿命短等问题，在推动超高密度信息存储技术实用化方面具有重要意义。更多还原

【Abstract】 Traditional magnetic storage, optical storage and semiconductor storage have their own physical limitations because of the superparamagnetic effect, diffraction and minimum lithography element size. Scanning probe microscopy (SPM) based data storage technology is an ideal high-density data storage technology, which can break through the physical limitations of the traditional storage technology. But low data rate and short probe lifetime are the problems faced nowadays. This dissertation applies piezoelectric material, lead zirconate titanate (PZT), into SPM technology, brings up the novel "thermo-piezoelectric-mechanical" method for data storage and describes its mechanism in detail.Piezoelectric cantilevers array is the key part in the storage system for "thermo-piezoelectric-mechanical" storage. In this dissertation, a novel piezoelectric cantilever probe with low stiffness and high resonance frequency was structural designed by decreasing its geometric dimensions. A multi-layered cantilever with non-rectangle and unequal sections is abstracted as the mechanics model of the probe. By theoretical analysis, the spring constant and the resonance frequency of the cantilever probe was calculated as 4 N/m and 245 kHz respectively. The microheater integrated on the free end of the cantilever is the main object of thermal analysis. The results show that heat dissipation is mainly by conduction along the cantilever body to the substrate, partly by conduction into air, while convection and radiation could be neglected.Data writing process is the interaction between tip and storage medium. Based on the material properties of polymethyl methacrylate (PMMA) and data writing mechanism, a six-stepped model was set up to describe the whole data writing process. This model includes mechanical contact analysis, thermal conduction analysis, viscoelasticity analysis and tracing of moving interface integrated with volume of fluid analysis. The result of numerical simulation for the single data pit writing process shows that under the thermal and mechanical loading, a 50nm depth center-depressed and more than 10nm peripheral-heaved data pit was formed. The pilling up around the pit is caused by extruding fluid status media instead of thermal expanding.The research of data reading out is concentrated on the piezoelectric charge sensitivity. The charge sensitivity could be better through the following ways: increasing the thickness of the elastic layer of the cantilever, peeling off part of passivation layer and applying DC bias to PZT. The probe structure and data reading out process were also optimized.Some experimental researches were executed on the fabrication and preparation for the key structures and main materials involved in the storage system. Anisotropic wet etching was used to fabricate single-crystalline silicon tip, which has an aspect ratio of 1.56 and curvature radius of less than 50nm. Spin coating was used to prepare 200nm-thick PMMA thin film, which roughness is less than 2nm of Ra value. Plasma enhanced chemical vapor deposition (PECVD) was used to prepare low-stressed silicon nitride thin films and amorphous silicon thin films.All above research results show that besides high storage density, "thermo-piezoelectric-mechanical" storage has higher data access rate, longer probe lifetime and lower power consumption. This storage method could resolve the problems of low data rate and short probe lifetime and promote the utilization of ultra-high-density data storage technology.更多还原