【作者】 钟超荣；

【导师】 林德华； 何豫生；

【作者基本信息】 重庆大学 ， 凝聚态物理， 2005， 硕士

【摘要】 自1986 年高温超导体出现以来,超导量子干涉器件的应用日益受到重视。本文就如何改进中科院物理所SC6 组研制成功的扫描SQUID 显微镜的空间分辨率进行了有益的探讨,同时也在扫描SQUID 显微镜在无损检测的应用,尤其是在检测微弱电流上做了一些原理性的工作。本文首先介绍了Josephson 效应及超导量子干涉仪(SQUID)的工作原理,然后介绍了扫描SQUID 显微镜的发展。扫描SQUID 显微镜是一种弱磁信号测量仪器。中科院物理所SC6 组研制成功的扫描SQUID 显微镜由高温超导材料YBCO制作的SQUID 器件及其电子学系统,低温维持系统,真空隔离系统,样品装载系统,数据采集及控制系统组成,其磁场灵敏度约为46pT/Hz1/2,空间分辨率约为400um。其中空间分辨率较差,约为400um,离最好的100um 空间分辨率(检测室温样品)相差较大,因此本文作者和乌克兰Bondenranko 教授合作,通过一种磁聚焦方法进行改进,并取得了进展。本文首先从室温模拟出发,研究了代表磁聚焦器聚焦能力的磁聚焦参数K 和磁聚焦器几何尺寸之间的重要关系。然后,根据磁聚焦参数和实际的扫描SQUID 显微镜,设计出了初步的磁聚焦器。具体的测试实验正在进行中。本文在SQUID 无损检测方面的应用也做了某些原理性方面的探讨,结合微电子工业的无损检测需求,我们使用载流导线模拟微电子器件,在检测微弱电流上做了原理性的研究,即从微弱电流产生的磁场分布中反演得到微弱电流的分布。通过加载10mA 的微弱电流到(0.1mm)小直径的漆包线模拟微型电路,然后使用扫描SQUID 显微镜检测由微弱电流激发的磁场。随后,本文从Biot-Savart 定律出发,结合电流与磁场之间的傅立叶转换关系,建立了一个二平面模型来描述磁场反演电流的过程,结果成功得到了原始的漆包线形状,即电流的分布。更多还原

【Abstract】 Since the discovery of high temperature superconductors in 1986, the applications of Superconducting Quantum Interference Device (SQUID) have drawn increasing attention. This dissertation contains the main results of the research work for the Master’s degree of Sciences, including the efforts for improving the spatial resolution of the Scanning SQUID Microscope (SSM ) designed and constructed by the SC6 group of Institute of Physics Chinese Academy of Sciences (IOP, CAS) and the work for applications of the SSM in the Non-destructive Testing (NDT), especially in detecting weak current. To start with, fundamental concepts and main theories of Josephson effect and SQUID were briefly introduced in the dissertaion. Attention was paid to the development of the SSM, which is a new type of magnetic imaging instrument, being able to detect extremely small fields or currents with unparalleled sensitivity. The SSM designed by the SC6 group of IOP, CAS consists a SQUID made by YBCO, the electronics system, the cryogenics maintain system, the vacuum system, the sample mounting and moving system, the data collection system and the control system. The magnetic sensitivity of the microscope is 46pT/Hz1/2 and the spatial resolution is about 400um. The spatial resolution is worse than the best spatial resolution of other type SSMs, of which the reason is that the sample of ours being in room temperature whereas the sample of others lying inside the low temperature dewar, the unavoidable vacuum layer of the dewar leading to the deterioration of spatial resolution. Therefore it is very important to find a technique being able to improve the spatial resolution of SSM for room temperature samples, which is the main task of this dissertation. As a potential candidate of such technology, magnetic concentration device (i.e. concentrator) was systematically studied and a special parameter (i.e., concentration parameter K), for characterizing the feature of the concentrator, was proposed. A simple model was then developed, of which K is dependent on the magnetic permeability of the material and the demagnetization factor of the device. Experimental results of dependences of the concentration parameter on device length and excited field (current) were obtained, respectively. It was established that the magnetic concentrator should be able to improve the spatial sensitivity of the SSM. A real device containing a concentrator for the present SSM in IOP, CAS has been designed and constructed and the experiments of the SSM with this magnetic concentrator device is being carried out. The applications of SSM in NED were also discussed in the dissertation. One of them is the detection of weak currents inside a sample (e.g. short circuit current inside a IC chip). Effort has been concentrated on the inverse process of obtaining two-dimension images of the weak current from the magnetic field measured by the SSM. Considering that what being detected by the SQUID is the vertical component of the magnetic field on a plan where the SQUID lies, whereas the current which produces the magnetic field is actually located in a plan below the SQUID, a TWO PLAN model has been developed. In this model Biot-Savart force laws and Fourier transformation were used to inverse the detected magnetic field into the underneath weak current. It has been shown that the distance between the current and the SQUID, which is important parameter for the spatial resolution, and the noise ratio of the experimental data, which is related to another important parameter of the microscope, i.e., magnetic field sensitivity, have significant effects on the quality of the inverse process.更多还原