We have measured the low frequency critical current noise in Nb/AlO$_{ \mathrm{ x}}$/Nb Josephson junctions. Unshunted junctions biased above the gap voltage and resistively shunted junctions biased near the critical current, $I_{ c}$, have been measured. For both, the spectral density of $\delta I_{ c}/I_{ c}$, $S_{ i_{ c}}(f)$, is proportional to $1/f$, scales inversely as the area, $A$, and is independent of $J_{ c} \equiv I_{ c}/A$ over a factor of nearly 20 in $J_{ c}$. For all devices measured at 4.2 K, $S_{ i_{ c}}$(1 Hz)$= 2.0 \pm 0.4 \cdot 10^{ -12}$/Hz when scaled to A=1 $\mu$m$^{ 2}$. We find that, from 4.2 K to 0.46 K, $S_{ i_{ c}}(f)$ decreases linearly with temperature.
Categories: cond-mat.supr-con