Fundamental Research of Single-Atomic Memories

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This research project aims fundamental research for developing a new type memory which enables to memorize a unit of digital information in an atomic size. In this fiscal year, development of a manufacturing process for Si tips which can be used for electron emission by the tunneling phenomenon and development of a micron-size field emitters. For characterization of Si tips, we have developed a unique "in-situ" measurement system by which we are able to reveal effects of annealing, environment, etc. The following summarize results of this fiscal year.(1) Ar ion sputtering is effective in sharpening of Si tips which have been prepared by anisotropic wet chemical etching using such chemicals as KOH. As a result, we can fabricate tip with tip radius of about 10nm.(2) The surface of Si tips fabricated by Ar ion sputtering is damaged. But it can be annealed out at 600ﾟC or above, and it results in a field emission of electrons superior to Si tips fabricated by other processes. The field emission characteristic is improved with increasing annealing temperature up to about 800ﾟC. This is because of surface cleaning. But annealing at 900ﾟC results in degradation of the field emission characteristic due to restructuring of the tip apex.(3) The field emission current from Si tips can be drastically improved by operating in bydrogen ambient. This is due to change in surface state density distribution.(4) Noise of emission current from a Si tip in vacuum shows the 1/f characteristic, while that of a tip in hydrogen depends on 1/f^n (n>1). This sggests that the noise originates from the combination of surface migration and adsorption/desorption of atoms.(5) A new self-aligned process for fabrication of micron size field emitter by usingsputter evaporation has been developed.