2005 Fiscal Year Final Research Report Summary
Formation of multiple tunneling junctions of quantum dots using self-organized nanoholes and its application to spintronics
| Project/Area Number |
15201034
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| Research Category |
Grant-in-Aid for Scientific Research (A)
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| Allocation Type | Single-year Grants |
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| Section | 一般 |
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| Research Field |
Microdevices/Nanodevices
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| Research Institution | Kansai University (2005)
Hiroshima University (2003-2004) |
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Principal Investigator |
SHINGUBARA Shoso Kansai University, Faculty of Engineering, Professor, 工学部, 教授 (10231367)
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| Co-Investigator(Kenkyū-buntansha) |
IWABUCHI Shuichi Nara Women's University, Physics, Professor, 理学部, 教授 (40294277)
WAKAYA Fujio Osaka University, Ultimate Science research center, associate professor, 極限科学研究センター, 助教授 (60240454)
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| Project Period (FY) |
2003 – 2005
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| Keywords | porous alumina / nano ferromagnetic materials / quantum dot / tunnel junction / Coulomb blockade / spintronics |
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| Research Abstract |
We studied formation of ferromagnetic multiple tunneling junction using nano-ferromagnetic materials buried in porous alumina nanohole array and its conduction properties in aiming at new spintronics devices. For filling of ferromagnetic materials in nanoholes, we used pulsed-DC electroplating of Ni or Co, and found that ferromagnetic column diameter could be changed between 10 to 50nm by changing anodic voltage between 20 and 5V during anodic oxidation of aluminum. The unexpected problem for tunneling junction formation was that alumina thin wall between nanoholes (i.e. between nanomagnets) are too leaky even after annealing. The conduction mechanisms within alumina layer was Pool-Frenkel conduction derived from vacancies in alumina. Thus it is essential to improve quality of tunneling barrier layer, and further study such as plasma or radical oxidation would important. In order to improve switching properties of ferromagnetic nanodots, we tried to improve crystalline structure of electrodeposited materials, because they were polycrystalline and difficult to align crystalline orientation. Then we tried to remove bottom amorphous alumina layer that existed at the nanohole bottom, and succeeded in epitaxial growth of metal nanodot array on Si (100) substrate with adequate cleaning of Si surface after annealing in vacuum.
From theoretical approach, we derived analytical formalisms of tunneling conduction currents of CSET devices that was a fundamental structure to control Coulomb blockade, by taking co-tunneling effect into account. Furthermore, we expanded this formalism in order to treat with CSET and electrode systems altogether using non-equilibrium Green functions, and succeeded in developing the method to estimate an optimum condition to increase TMR (tunneling magnetoresistance) ratio.
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