  We present results of a study of tunnel junction aging in which the early
time dynamics are captured by in situ monitoring of electrical properties of
Al-AlOx-Al planar tunnel junctions beginning when the deposition of the
counterelectrode is complete. The observed stretched exponential dependences of
the conductance and the capacitance manifest hierarchically constrained
dynamics imposed by correlated relaxations of interface traps. Bias voltage is
used as a control parameter to create bias-dependent aging trajectories that
exhibit memory and age-dependent relaxations. Simple tunnel barrier and
equivalent circuit modeling provide a comprehensive understanding of this novel
and unexpected glassy behavior that appears to be unique to tunnel junctions
and has important implications for technical applications.
