Characterization of ${\rm Bi}_{2}{\rm Sr}_{2}{\rm CaCu}_{2}{\rm O}_{8+\delta }$ Stacks Fabricated by Acid Treatment Process

Bi₂Sr₂CaCu₂O_8+δ (Bi-2212) stacks of intrinsic Josephson junctions were fabricated by an acid-treatment process from inside a single crystal. The surrounding acid-treated product is a transparent material, BiOCl. During the process, an optical adhesive (NOA-61) was used to fix a piece of the crystal on a glass substrate and to coat the surface of the sample. The current-voltage characteristics of the stacks at T = 77 K exhibited large hystereses and multiple branches with voltage spacings of approximately 2-3 mV. Under an external microwave field in the frequency range of 2-18 GHz, clear Shapiro steps were observed at voltages with multiples of (h/2e)f_rf. In addition, the thermal cycling properties of the critical current (I_c) were investigated. No apparent degradation of the I_c was observed during repeated thermal cycling between 300 and 77 K.