Experimental study on the reliability of water/fluoropolymer/ITO contact in electrowetting displays

The practicability of using DI water in electrowetting displays with a thick layer of fluoropolymer and the reliability of water/fluoropolymer/indium tin oxide contact was investigated experimentally. Electrowetting performances of DI water on a fluoropolymer coating of indium tin oxide surface were tested via sessile droplet test, compared with that of ionic solutions. A platform with a camera system was built to study the electrical property and breakdown phenomenon in water/fluoropolymer/indium tin oxide contact under a DC voltage sweep up to 200 V. The I-V characteristics and synchronized video were used to analyze the charge transport mechanism and anodic/cathodic reactions in the failure process. DI water was proved to be conducting enough for electrowetting displays and liquid conductivity had very little influence on the electrowetting performance. The failure processes of samples with fluoropolymer coating of different thicknesses were studied. Samples with relatively thin fluoropolymer coating showed a rapid increasing leakage current after certain voltage threshold and severe gas evolution, ITO corrosion and fluoropolymer delamination were observed via the camera system. Samples with fluoropolymer coating thicker than 800 nm showed good insulating property in the I-V test and only a few gas bubbles and pitting corrosion dots were observed. The sample with a fluoropolymer coating of 1000 nm showed a maximum leakage current density of 13.6 µA/cm2 at the voltage of 200 V, which is promising for a single layer electrowetting display device. Keywords: Reliability, Fluoropolymer, Water, ITO, EF