An investigation of the thermal cycling stability of Bi2Sr2CaCu2Ox stacks fabricated by self-planarizing process

Abstract

We have investigated the thermal cycling properties of Bi2Sr2CaCu2Ox (Bi-2212) stacks since the thermal stability is one of the most important factors in determining successful applications of the Josephson effect. The stacks with an area of 30×40cm2 or 15×40cm2 were fabricated by self-planarizing process. The surfaces of the device with or without a 100nm-thick overlying SiO2 layer were coated by AZ-5206E photoresist to protect from water vapor in the air. The current–voltage (I–V) characteristics of the stacks exhibited large hysteresis and multiple branches, which can be explained by a series connection of highly capacitive Josephson junctions. The observed critical currents (Ic) for the surface junctions in the stacks did not change with thermal cycling up to 150 cycles repeated between 77 and 300K. This suggests that the self-planarized Bi-2212 stacks have sufficient stability for thermal cycling.