Effect of the cooling time in YBa 2Cu 3O 7− δ film process on the electrical properties of grain boundary Josephson junctions on SrTiO 3 (100) bicrystal with the misorientation angle of 36.8°

Abstract

We have studied the effect of the cooling time at high temperature in YBa 2Cu 3O 7− δ film process on electrical properties of grain boundary junctions on SrTiO 3 bicrystal substrates. 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 were changed by the increase of the cooling time at high temperature from 785 to 430°C. The electrical properties could be divided into three regions. For the cooling time from 5 to 6 min, the junctions showed high T c and high J c. The junctions with the cooling time from 10 to 30 min showed poor T c, a spread of the junction parameters, and remarkable parabolic type I– V curves. For the cooling time from 30 to 120 min, the junctions showed stable parameters on the cooling time, and the parameters were enough for the device application at 77 K. Since the YBa 2Cu 3O 7− δ films on SrTiO 3 bicrystal substrates have very high quality, the change of the junction properties occurred in the vicinity of a grain boundary. On the other hand, magnetic field and temperature dependence of the critical current has the same characteristics in each region. As a result, the cooling rate at high temperature in YBCO film process is one of origins of a spread of the device parameters such as T c and I c.