Study of Ultra-Thin-Film/Ultra-Fine-Structure Devices

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Ultrathin films of oxide superconductors YBaCuO have been prepared successfully by atomic layr-by-layr metalorganic chemical vapor deposition. Precursors of betadiketonate complex have been supplied sequentially according to a computer program. Since migration of species on the growth surface is enhanced, a very smooth surface is obtained with a terrace length of 330nm for SrTiO3 substrate and 660nm for NdGaO3 substrate. A high superconductivity critical current has been obtained from an ultrathin film of even 12nm thick.Josephson junctions were fabricated by irradiating YBaCuO films with 350keV electron beam. Magnitic field depedence of the critical current revealed that a very uniform junctions were obtained. Annealing at 400K improvedthe degradation problem with junctions. Fabrication of junctions using scanning probe microsccopes has also been investigated.Ultrathin films of silicon and germaniuim were prepared by atomic layr epitaxy using atomic hydrogen as reducer. A new method w … More as developed in which Si source gas of high pressure was confined in a reaction chamber. A conditionof ALE with one monomolecular layr per cycle was established. Atomic layr deposition of silicon oxide and nitride has also been investigated.Trench-oxide metal-oxide-semicconductor structure was proposed for silicon quantum wire devices. Electron confinement by trench MOS structure was simulated using a supercomputer. A sample device was fabricated using electron beam lithography and electron-cyclotron-resonance reactive ion etching method. A signal due to quantum effects is obtained in capacitance-voltage characteristics measured at ultralow temperature.Nanoccrystalline silicon with diameter less than 10nm was fabricated in a plasma cell of silane and hydrogen. Monodispersed particles were ontained by an idea of separating nucleation and crystal growth. Structure of nanocrystalline silicon was evaluated by atomic force microscopy and electron microscopy. Visible photoluminescence was observed at room temperature. Coulomb staircase phenomena, single electron tunneling effects, were observed in current-voltage characteristics from a nanocrystalline silicon at room temperature.Thinfilm transistors of amorphous and polycrystalline silicon were investigated. The mechanism of degradation, application of ultralarge scale integration and neural network were discussed. Less