posted on 2023-12-05, 18:33authored bySanjoy Kumar Nandi, Shimul Kanti Nath, Sujan Kumar Das, Billy J. Murdoch, Thomas Ratcliff, Dougal G. McCulloch, Robert G. Elliman
The resistive switching response
of two terminal metal/oxide/metal
devices depends on the stoichiometry of the oxide film, and this is
commonly controlled by using a reactive metal electrode to reduce
the oxide layer. Here, we investigate compositional and structural
changes induced in Nb/Nb2O5 bilayers by thermal
annealing at temperatures in the range of 573–973 K and its
effect on the volatile threshold switching characteristics of Nb/Nb2O5/Pt devices. Changes in the stoichiometry of
the Nb and Nb2O5 films are determined by Rutherford
backscattering spectrometry and energy-dispersive X-ray (EDX) mapping
of sample cross sections, while the structure of the films is determined
by X-ray diffraction, Raman spectroscopy, and transmission electron
microscopy (TEM). Such analysis shows that the composition of the
Nb and Nb2O5 layers is homogenized by interdiffusion
at temperatures less than the crystallization temperature (i.e., >773
K) but that this effectively ceases once the films crystallize. This
is explained by comparison with the predictions of a simple diffusion
model which shows that the compositional changes are dominated by
oxygen diffusion in the amorphous oxide, which is much faster than
that in the crystalline phases. We further show that these compositional
and structural changes have a significant effect on the electroforming
and threshold switching characteristics of the devices, the most significant
being a marked increase in their reliability and endurance after crystallization
of the oxide films. Finally, we examine the effect of annealing on
the quasistatic negative differential resistance characteristics and
oscillator dynamics of devices and use a lumped element model to show
that this is dominated by changes in the device capacitance resulting
from interdiffusion.