At critical current density of the order of 100 kA/cm(2), tunnel Josephson
junctions become overdamped and may be used in RSFQ circuits without extern
al shunting, dramatically increasing circuit density. However, the physics
of electron transport in such high-j(c) junctions differs from the usual di
rect tunneling and until recently remained unclear. We have found that the
observed de I-V curves of niobium-trilayer junctions with j(c) = 210 kA/cm(
2) can be explained quantitatively by resonant tunneling through strongly d
isordered barriers. According to this interpretation, random spread of crit
ical current in high-j(c) junctions may be rather small (below 1% r.m.s.) e
ven in deep-submicron junctions, making VLSI RSFQ circuits, with density ab
ove 10 MJJ/cm(2), feasible.