Studying the Barrier Quality of ALD Oxide Layers

The usage of an electrical device in an aqueous medium requires a sealing which keeps the water and the ionic components out of the isolation. Thus, the quality of a passivation does not only depend on the chemical inertness and the bulk resistance of a material, but also on the extent of material transfer through the passivation layers. Impedance spectroscopy belongs to the best techniques to qualify this property. However, in many cases the knowledge of an equivalent circuit and a parameter fit are necessary, sometimes leading to ambiguous results. To circumvent these difficulties an alternative concept has been evaluated. Theoretical investigations of Bisquert et al. propose that mass transfer into a sealing layer can also be indicated by the Nyquist plot in the electrical impedance spectroscopy (EIS). A parameter fit could therefore be omitted. To evaluate this approach several oxide films on comb electrodes have been investigated. The studies include aluminum, titanium and tantalum oxides which were deposited using atomic layer deposition (ALD). The influence of the film thickness and process temperature were investigated. The results indicate that a significant transfer of ionic species occurs in all cases.