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To achieve spin accumulation in ferronmagnetic single electron transitor
Dawei Wang The recognition of spin as a binary variable analogous to electrons and holes in semiconductors opened new fields of science and technology that have already led to commercial devices, called spin electronics holding great promise for nanoscale science and information technology. By combining the recent advances of single electron transistor and magnetic tunnel junctions, polarized spins are injected into nanosized Al thin film, and various phenomena such as spin accumulation, enhanced magnetoresistance and superconducting gap suppression are predicted. In this paper, we first present the calculations made to understand the variations of accumulated spin ensity in the island of a ferromagnetic single electron transistor (FMSET). Results show that large spin accumulation on the island can be achieved in the case of short island lengths and small junction resistances. These results provide a guideline for the design and fabrication of devices in order to study spin dependent transport across the tunnel junctions. Based on this, a method for fabricating ferromagnetic single electron transistors using electron beam lithography and shadow mask evaporation technique is presented. In our experiment, bi-layer ebeam resist is used. The ebeam lithography machine operates at 100 kV accelerating voltage. Such high voltage is crucial for obtaining a fine linewidth, but unfavorable for getting a large undercut for angle evaporation. To circumvent this, we employ both UV flooding method and double dose exposures to optimize the desirable linewidth and undercut. The standard high dose exposes both the top and bottom layers, and the application of low dose results in further exposure of the more sensitive bottom layer. Furthermore, the resist is developed in two stages in order to get larger undercut without affecting the top layer resist. The advantage of this method is that a fine linewidth can be easily obtained and the size of the undercut can be controlled. Using this method, a top linewidth of ~40 nm with an undercut of more than 600 nm has been obtained, and FMSET with different coercivities has been fabricated. From the current transport measurements, spin accumulation in the island has been observed when the electrodes are in antiparallel configuration.
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Presented at the International Congress
of Nanotechnology, November 7-10, 2004 San Francisco, USA
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