  The resistive switching phenomenon in MgO-based tunnel junctions is
attributed to the effect of charged defects inside the barrier. The presence of
electron traps in the MgO barrier, that can be filled and emptied, locally
modifies the conductance of the barrier and leads to the resistive switching
effects. A double-well model for trapped electrons in MgO is introduced to
theoretically describe this phenomenon. Including the statistical distribution
of potential barrier heights for these traps leads to a power-law dependence of
the resistance as a function of time, under a constant bias voltage. This model
also predicts a power-law relation of the hysteresis as a function of the
voltage sweep frequency. Experimental transport results strongly support this
model and in particular confirm the expected power laws dependencies of
resistance. They moreover indicate that the exponent of these power laws varies
with temperature as theoretically predicted.
