Study on Spin transport Devices

为了利用隧道磁阻效应制作自旋器件，我们开展了隧道结的基本物理机制、界面结构测试仪的研制以及微结构结的微加工工艺的研究。主要研究结果总结如下：1.研究成果。基本物理性质铁/绝缘体/铁结中的隧道磁阻(TMR)效应不仅与电极(铁磁体)的自旋极化有关，而且还与绝缘体的势垒高度和宽度有关。这些依赖关系得到了系统实验的证实，并与其他小组报告的理论治疗进行了比较。详细研究了温度和外加电压对TMR比的影响。制备了具有交换偏置的自旋阀型结，其中一个磁性层使用了薄的反铁磁性FeMn或IrMn层。这些结显示了一个定义良好的开关…提高了LD、温度不敏感的TMR比，改善了TMR比的外加电压依赖性。测量装置的研制为了分析隧道结的界面结构，研制了非弹性电子隧道能谱(IETS)装置。利用该仪器对多种结的IET谱进行了测量，证明了分析的有效性。此外，还制作了用于测量隧道结小面积的克尔磁滞回线装置。实验结果表明，40×40微米~2结区的磁化过程与结的磁阻曲线吻合较好。微细加工工艺和微结构隧道结利用光刻和Ar离子研磨技术研究了小尺寸隧道结的制作工艺。通过选择最佳的Ar离子入射角和球磨深度，制备了再沉积的自由结。用CF4气体进行等离子体刻蚀，在有源结区中心形成一个小的接触孔。采用这些工艺，成功地制作出有效面积为3×3um2、隧道电阻为500Omega、TMR比为15%的结。隧道结具有用于高密度磁记录和/或磁随机存取存储器的磁读取头的高潜力。较少

In order to fabricate spin devices using tunnel magnetoresistant effect, we carried out the research on fundamental physical mechanism for tunnel junctions, on the development a measuring instrument for the interfacial structure and on the micro-fabricating process for microstructured junctions. The main results are summarized as follows.1. Fundamental physical propertiesThe tunnel magnetoresistance (TMR) effect in the Ferro/Insulator/Ferro junctions depends not only the spin-polarizations of electrodes (ferromagnets) but also on the barrier height and width of insulator. These dependences were confirmed by systematic experiments and by comparison with theoretical treatments reported by other groups. Also, the temperature and applied voltage dependence of TMR ratio were investigated in detail. Spin-valve type junctions with exchange-biasing one of the magnetic layers using a thin antiferromagnetic FeMn or IrMn layer were prepared. These junctions exhibited an well defined switching fie … More ld, temperature insensitive TMR ratio and improved the applied voltage dependence of the TMR ratio.2. Fabrication of measuring apparatus In order to analyze the interfacial structure of the tunnel junctions, inelastic electron tunnel spectroscopy (IETS) apparatus was developed. By using the apparatus IET spectrum for many kind of the junctions were examined and the usefulness of the analysis was proved. Furthermore, a Kerr hysteresis apparatus for measuring a small area of the tunnel junction was made. By using the apparatus it was shown that the magnetization process of 40*40 mum^2 junction area corresponds well to the magnetoresistance curve of the junction.3. Micro-fabrication process and microstructured tunnel junctionBy using photolithography and Ar ion milling, the process to fabricate a small tunnel junction was investigated. A redeposited free junction was made by choosing the optimum incident angle of Ar ions and milling depth. A small contact hole at the center of active junction area was well made by plasma etching with CF_4 gases. By using the processes, a junction with 3*3mum2 active area, 500OMEGA tunnel resistance and 15% TMR ratio was successfully made. The tunnel junction possesses a high potential for magnetic reading head for high density magnetic recording and/or magnetic random access memory. Less