Je. Lukens et al., COMPARISON OF SINGLE-ELECTRON TRAPS IN THE SUPERCONDUCTING AND NORMALSTATES, Physica. B, Condensed matter, 203(3-4), 1994, pp. 354-360
Traps, consisting of arrays of nano-scale aluminum tunnel junctions, h
ave been shown to hold single electrons for over 10(4) s (limited by o
bservation time) at 50 mK. The barrier Delta U to the change of the ch
arge state of the trap has a measured value in the range of 5-10 K (co
nsistent with calculations) for traps of seven junctions (in the norma
l state) of capacitance C approximate to 150 aF. In the superconductin
g state, the activation energy is increased by 2.6 +/- 0.4 K, equal to
the superconducting energy gap of Al. The observed escape of a single
electron from the trap is via thermal activation down to temperatures
of 50 mK (where Delta U must be reduced to observe transitions).