Study on Spin transport Devices

为了利用隧道磁阻效应制作自旋器件，我们开展了隧道结基本物理机制的研究、界面结构测量仪器的研制和微结构结的微加工工艺的研究。主要研究结果如下：1. Ferro/Insulator/Ferro结的隧道磁电阻（TMR）效应不仅与电极（铁磁体）的自旋极化有关，还与绝缘层的势垒高度和宽度有关。这些依赖性证实了系统的实验，并通过与其他团体报告的理论治疗比较。此外，温度和外加电压的TMR比的依赖关系进行了详细的研究。自旋阀型结与交换偏置的磁性层之一，使用薄的反铁磁FeMn或IrMn层制备。这些结表现出一个明确的开关场 关于我们 ld，温度不敏感的TMR比，并改善了TMR比的施加电压依赖性.测量装置的制作为了分析隧道结的界面结构，开发了非弹性电子隧道能谱（IETS）装置。用该装置对多种结的IET谱进行了测试，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装置。实验结果表明：40 × 40 mm^2结面积的磁化过程与结的磁电阻曲线相吻合.微加工工艺与微结构隧道结研究了利用光刻和氩离子刻蚀技术制作小型隧道结的工艺。通过选择最佳的Ar离子入射角和铣削深度，制备了再沉积自由结。用CF_4气体等离子体刻蚀在有源区中心形成了一个小的接触孔。采用该工艺成功地制作出有源区面积为3 × 3 mum ~ 2、隧道电阻为500 Ω、TMR比为15%的结。该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阅读头的高电势。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