Effect of passive film on electrochemical surface treatment for indium tin oxide

Changes in indium tin oxide (ITO) film surface during electrochemical treatment in oxalic acid, tartaric acid, and citric acid were investigated. Controlling the voltage applied on ITO film allows the formation of a passive layer, effectively protecting the film surface. X-ray photoelectron spectrometry showed that the passive layer composition was predominantly SnO2 in tartaric acid, while a composite of tin oxide and tin carboxylate in citric or oxalic acid. Even though the passive films on ITO surface generated in these organic acids, the indium or tin could complex with the organic acid anions, enhancing the dissolution of ITO films. The experimental results show that the interaction between the dissolution and passivation could assist to planarize the ITO surface. We found that the optimal treatment at 0.5 V in 3 wt.% tartaric acid could provide the ITO surface with root-mean-squared roughness less than 1.0 nm, due to the weak complexing characteristics of tartaric acid.

► Oxalic, tartaric, and citric acid baths accompanying with applied voltages were used to treat the ITO surface.
► We investigated the changes in ITO surfaces by examining the potentiodynamic behavior of ITO films.
► AFM analysis showed the formation of a passive layer could assist to planarize surface.
► XPS analysis indicated this passive layer was mainly composed of SnO2.
► A better planarization was obtained by treating in 3.0 wt.% tartaric acid at 0.5 V due to weak complexation strength.