Detailed analysis of defect reduction in electrowetting dielectrics through a two-layer ‘barrier’ approach

• We analyze and improve upon electrowetting dielectric reliability.
• Electric field amplification for multi-layer dielectric systems must be considered.
• We show a significant decrease in dielectric failure with multi-layer systems.

Low-voltage electrowetting requires a thin dielectric capacitor and field strengths approaching 1 MV/cm. Unlike traditional metal/dielectric/metal capacitors, the conducting electrowetted liquid can electrically propagate through the smallest dielectric defects or pores, even for the best barrier polymers such as Parylenes, leading to catastrophic failure such as electrolysis. A detailed analysis of double layer dielectric systems is shown to provide > 100 times reduction in defect density, with > 10 cm2 area exhibiting no dielectric failure at > 2 times the required electrowetting voltage. An anodized-Al2O3/Parylene-HT stack provides electrowetting contact angle modulation down to saturation at 70° at < 15 V with breakdown protection to > 3 times that voltage. These results build on previous findings on the effect of ion type, liquid type, polymer dielectric choice, electrode material, and provide a next major advance in electrowetting reliability.