Novel Cyanoethyl Cellulose-based Bilayer Materials for Electrowetting Displays at Low Voltage

Electrowetting displays (EWD) still face the challenge of high driving voltages, provided by specialized driver ICs for electrowetting technologies. However, if the driving voltage is reduced to the threshold of widely used driver ICs of liquid crystal displays, it would significantly accelerate the revolution of driving ICs for EWD devices. Cyanoethyl cellulose (CEC) is utilized as a novel dielectric layer for electrowetting-on-dielectric systems and shows a large contact angle modulation, enabling low-voltage-driven wettability and device operation. Different combinations of bilayer Hyflon/CEC structures are systematically investigated to reduce the driving voltage. Reduction of driving voltage is revealed to be highly dependent on the enhancement of total capacitance C_eq through the link of effective dielectric constant ε_eff and a theoretical formula for reducing driving voltage is proposed. Furthermore, for the HF/CEC bilayer construction, values of C_eq largely depend on the thickness of the HF layer, while the variation in the thickness of the CEC layer has a smaller impact. Consequently, V_d can be reduced from 17, 14 to 9 V when decreasing the thickness of HF from 400, 300 to 200 nm with a CEC layer of 650 nm. Consequently, a low driving voltage of 9 V is successfully achieved for the CEC/Hyflon bilayer in the fabricated EWD, fulfilling the operating voltage for driving ICs of liquid crystal display. Therefore, capacitance values can be manipulated through tuning the thickness of CEC/Hyflon bilayers and provide a constructive strategy for designing dielectric and hydrophobic functional materials, ushering in a new era of EWD technology.