A 1 µm Cross-Line Junction Process
A new fabrication process for all refractory Josephson tunnel junctions with dimensions less than 2.5 µm-square is proposed, in which junctions are formed by reactively ion etching a full wafer junction sandwich using a cross-line patterning method. As a mask of the junction patterning process, a two-layer resist system has been employed for improving the patterning accuracy. The cross-line patterning method has made it possible to fabricate small area junction with small spreads of the maximum critical currents. All niobium nitride (NbN) Josephson junctions with dimensions from 1.25 µm-square to 0.5 µm-square have been integrated on a chip by this method. The standard deviation of the maximum critical currents for 1024 1 µm-square junctions has been measured to be about 4%.
KeywordsJosephson Junction Tunnel Junction Scanning Electron Microscope Photograph Small Spread Niobium Nitride
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