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

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Ultrathin films of oxide superconductors YBaCuO have been prepared successfully at a temperature of as low as 500^ﾟC by metalorganic chemical vapor deposition method at Tokyo Institute of Technology. Superconductivity onset was observed from a film of as thin as 3.6nm(3 unit-cell-thickness). Zero-resistivity at 30K was observed from 4.8nm-thick sample and 80K was observed from 10nm-thick YBaCuO on MgO substrate. These results suggest that we have deposited the highest quality films. We have also revealed that migration of chemical species were enhanced during the crystal growth of ultrathin films of YBaCuO by atomic layer-by-layer method. Very smooth surface of YBaCuO films with roughness of less than one unit-cell-thickness along 10 mum range was observed by atomic force microscopy. A critical current density of as high as 10^7Acm^<-2> was obtained from a microbridge structure. Josephson junctions were fabricated at Cambridge University by irradiating YBaCuO films with 350KeV electron … More beam. Magnetic field dependence of the critical current revealed that very uniform junction was obtained.Ultra-thin films of silicon were prepared by atomic layer epitaxy by using dichlorosilane and hydrogen radicals at Tokyo Institute of Ultra-thin films of Ge were also prepared by atomic layer epitaxy for the first time by using organicgerman and hydrogen radicals.Trench-oxide metal-oxide-semiconductor structure was proposed for silicon quantum wire devices from Tokyo Institute of Technology. Electron confinement by the trench MOS structure was simulated by using a supercomputer. It was then evaluated that quantum effects would be observable from the capacitance-voltage characteristics at low temperatures. Actual device of trench-MOS was fabricated by using electron beam lithography and electron cyclotron resonance reactive ion etching method. A structure due to quantum effects was observed from a sample with 28nm-wide trench at 0.5K.Digital chemical vapor deposition method was proposed for the fabrication of Si quantum dot structure from Tokyo Institute of Technology. It was found that hydrogen radicals played very important role both in the nucleation and crystal growth of nanocrystalline silicon. It turned out that hydrogen radicals were also useful for theselective etching of amorphous silicon surrounding nanocrystalline silicon for the fabrication of effective potential barrier layer.Thin film transistors of amorphous and polycrystalline silicon were investigated both at Tokyo Institute of Technology and Cambridge University. The mechanism of degradation, application of ultra-large scale integration and neural network were discussed. Less