  Josephson junction transistors and 50-junction arrays with linear junction
dimensions from 200 nm down to 70 nm were fabricated from standard Nb/AlOx/Nb
trilayers. The fabrication process includes electron beam lithography, dry
etching, anodization, and planarization by chemical-mechanical polishing. The
samples were characterized at temperatures down to 25 mK. In general, all
junctions are of high quality and their I-U characteristics show low leakage
currents and high superconducting energy gap values of 1.35 meV. The
characteristics of the transistors and arrays exhibit some features in the
subgap area, associated with tunneling of Cooper pairs, quasiparticles and
their combinations due to the redistribution of the bias voltage between the
junctions. Total island capacitances of the transistor samples ranged from 1.5
fF to 4 fF, depending on the junction sizes. Devices made of junctions with
linear dimensions below 100 nm by 100 nm demonstrate a remarkable
single-electron behavior in both superconducting and normal state. We also
investigated the area dependence of the junction capacitances for transistor
and array samples.
