Effect of the cooling time in YBa 2Cu 3O 7− δ film process on the electrical properties of grain boundary Josephson junctions with the tilt angle of 24°

Abstract

The effect of the cooling time at high temperature in YBa 2Cu 3O 7− δ (YBCO) film process on electrical properties of grain boundary Josephson junctions (GBJJs) on SrTiO 3 (STO) bicrystal substrates with the tilt angle of 24° has been studied. The results showed that the device parameters such as the critical current I c, the resistance R n, the I c R n product and the shape of the I– V curves changed with the increase of the cooling time from 785° to 430°C. The effect of the cooling time for 24° GBJJs was almost the same as that of 36.8° GBJJs; however, some points were different from the 36.8°-junctions. For both 24° and 36.8° GBJJs, there was an instability in T c for a shorter cooling time. However, the region of the unstable T c shrank and shifted to shorter cooling time for 24° GBJJs, and the excess conductance in high voltage is also smaller. Also, I c( T)/ I c(4.2 K) vs. (1− T/ T c) 2 was the most linear for 24°-junctions. In contrast, for 36.8° GBJJs, I c( T)/ I c(4.2 K) vs. (1− T/ T c) 1.5 was the most linear. The change of the junction properties was caused by the change of the grain boundary structure due to the change of the cooling time.