In this work I apply state of the art analysis techniques and develop new measure- ment methodologies to investigate the role of oxygen diffusion, impurities, and microstructure in ReRAM operation.
To test models of oxygen movement in ReRAM devices beyond what has previously been possible I present a new nanoscale analysis method. Harnessing the power of secondary ion mass spectrometry, the most sensitive surface analysis technique, for the first time, I observe the movement of 16O across electrically biased silicon oxide (SiOx) ReRAM stacks. This enables the measurement of bulk concentration changes in a continuous profile with unprecedented sensitivity. Applying this to three devices, a clear link is revealed between the thermodynamics and microstructure of the electrode material with the scale and nature of the oxygen diffusion across the oxide- metal interface. Through further tuning the microstructure and thermodynamics of the electrode material I suggest how the stability and longevity of resistance switching can be further improved. At the surface of the SiOx the measurements revealed oxygen injection into devices from the ambient, which can be controlled through changing the porosity of the SiOx.
Combining conductive atomic force microscopy, scanning electron microscopy and energy dispersive X-ray spectroscopy revealed the connection between the compositional changes induced during operation and the columnar microstructure of the SiOx which is porous, with conductive column boundaries between the grains.
Quantitative measurements of the thin film compositions in ReRAM devices revealed oxidised electrodes and high concentrations of impurities, in particular hydrogen, through every device analysed, even those manufactured industrially. This provides further compelling evidence that hydrogen is involved in ReRAM operation. I make several suggestions for reducing this contamination, demonstrating the potential of a TiO2 thin film barrier layer, preventing the diffusion of hydrogen and other impurities into devices.