Hydrothermally Grown TiO₂ Nanorod Array Memristors with Volatile States

In the present study, the memristive characteristics of hydrothermally grown TiO₂ nanorod arrays, particularly, the difference in the retention time of the resistance state, are investigated in dependence of the array growth temperature. A volatile behavior is observed and related to a redistribution of oxygen vacancies over time. It is shown that the retention time increases for increasing array growth temperatures from several seconds up to 20 min. The relaxation behavior is also seen in the current-voltage characteristics, which do not show the common unipolar, bipolar, or complementary switching behavior. Instead, the temporal evolution depends on the duration of the applied voltage and on the nanowire growth temperature. Therefore, electronic measurements are combined with scanning electron and scanning transmission electron microscopy, so that the amount of oxygen defect-rich grain boundaries in the upper part of the nanowires can be linked to the differences in the current-voltage behavior and retention time.