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

Bi
₂
Sr
₂
CaCu
₂
O
_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
/2
e
)
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.