  Memristors based on a double barrier design have been analysed by various
nano spectroscopic methods to unveil details about its microstructure and
conduction mechanism. The device consists of an AlOx tunnel barrier and a
NbOy/Au Schottky barrier sandwiched between Nb bottom electrode and Au top
electrode. As it was anticipated that the local chemical composition of the
tunnel barrier, i.e. oxidation state of the metals as well as concentration and
distribution of oxygen ions, have a major influence on electronic conduction,
these factors were carefully analysed. A combined approach was chosen in order
to reliably investigate electronic states of Nb and O by electron energy-loss
spectroscopy as well as map elements whose transition edges exhibit a different
energy range by energy-dispersive X-ray spectroscopy like Au and Al. The
results conclusively demonstrate significant oxidation of the bottom electrode
as well as a small oxygen vacancy concentration in the Al oxide tunnel barrier.
Possible scenarios to explain this unexpected additional oxide layer are
discussed and kinetic Monte Carlo simulations were applied in order to identify
its influence on conduction mechanisms in the device. In light of the strong
deviations between observed and originally sought layout, this study highlights
the robustness in terms of structural deviations of the double barrier
memristor device.
