Enhancement of the Quality of Stacked-type High-Tc Josephson Junctions by Doping and Development of the Integration Technology for These Junctions

点击翻译按钮获取中文摘要

The purpose of this research is to establish the fabrication technique of stacked-type high-Tc Josephson junctions by the new doping method and to enhance the technique for application to circuits. Following results were obtained.1.Investigation of the factors to worsen the junction properties : In addition to the suppression of pinholes by doping of Pr and Ga, we investigate the factors influencing scattering and deterioration of junction properties. It was found that the change in the surface morphology by the etching for forming the barrier was related to the junction properties, and we obtained junctions with overdamped characteristics and high critical current density at 30K. These junctions showed small scattering, and were of highest quality we ever obtained.2.Planarization of YBCO films by La doping : We confirmed that holes in YBCO films decreased by substituting part of Y or Ba in YBCO for La.3.Investigation of the barrier structure by TEM : Microstructure around the barrier layer which affects junction properties by transmission electron microscopy (TEM). Y_2O_3 phases were clearly observed around the barrier layer when the barrier was formed using high Ar ion acceleration voltage. Taking the relationship between the acceleration voltage and the junction critical current density, etc. into account, higher critical current density would correspond to thinner and more uniform barrier.4.Investigation of the material for the top electrode : In order to suppress the pinholes in the barrier layer, we tried YbBa_2Cu_3O_<7-x> (YbBCO) of which film can be obtained at lower temperature than YBCO as the top electrode. Junctions with YbBCO top electrode showed scattering smaller than those with YBCO top electrode. YbBCO may be effective to obtain good junction properties.