Thermal stability of aluminum-tin-oxide thin-film interface

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Abstract
Thermal stability of an Al/SnO2 contact was investigated in the temperature range of 120–166 °C. Contact resistance measurements showed that the degradation in a neutral ambient or in clean and dry air follows two different regime. At early stages contact resistance increases exponentially with the square root of time, possibly indicating the presence of a tunneling type of current flow through the interface. Activation energy for this process was found to be 0.91 eV. At later stages the contact resistance increases proportionally to the square root of time. In humid air catastrophic failure of the contact was observed. The degradation in this case was found to be more than two orders of magnitude higher compared to the degradation in dry or neutral ambient. In all cases, a 100-Å Ti barrier layer was found to virtually stop the degradation under the circumstances investigated in the present work. Auger electron spectroscopy analysis showed that the degradation of the contact is due to the diffusion of Al into the SnO2 film and the subsequent reduction of SnO2, resulting in the formation of Al2O3/metallic Sn mixture at the interface. The Ti barrier layer prevents the degradation process by acting as a diffusion barrier for Al.