Large-Area High-Contrast Hydrophobic/Hydrophilic Patterned Surface for Robust Electrowetting Devices

Abstract

Hydrophobic/hydrophilic patterned surfaces (HHPS) are found in nature and are highly desired for practical applications as well. Building hydrophilic patterns firmly on low free energy hydrophobic coatings has been a long-term challenge. The conventional process of reactive ion etching combined with a thermal reflow (RIE-reflow) process results in degradation of both the hydrophobicity and dielectric strength of the hydrophobic coatings. In this work, we propose a reconstructive approach by encapsulating the “damaged” hydrophobic Teflon AF 1600 (AF) surface with a fresh one to keep its hydrophobicity the same as that of a virgin AF surface and, at the same time, enhance the hydrophilicity of patterned microstructures by a local plasma etching method with a self-assembled protection mask. In this way, the extremely high wettability contrast with a large oil/water contact angle difference (Δθo/w) of 175° is reached between the hydrophobic and hydrophilic surfaces. Comparing to the conventional RIE-reflow process, the AF films prepared by this reconstruction process show superior dielectric strength and surface hydrophobicity. Electrowetting display devices constructed by this process demonstrate improved optical and electrical performance, presenting a more uniform pixel aperture ratio, higher voltage tolerance, and less leakage current compared to those made using the conventional “RIE-reflow” process.