Charge trapping model for investigating oil backflow mechanism in electrowetting display pixels

Area of Science:

• Materials Science
• Display Technology
• Physics

Background:

• Electrowetting displays (EWDs) offer excellent performance but suffer from charge trapping effects.
• Charge trapping in the hydrophobic insulating layer causes oil backflow and contact angle saturation, limiting aperture ratio and grayscale stability.

Purpose of the Study:

• To investigate the charge trapping behavior within an electrowetting display pixel.
• To establish a quantitative correlation between pixel aperture and trapped charge potential.
• To analyze the mechanism of oil backflow caused by trapped charges.

Main Methods:

• Constructed an equivalent pixel model based on electrowetting-on-dielectric principles.
• Developed a method to calculate trapped charge potential, surface charge density, and electrowetting force using pixel aperture ratio measurements.
• Analyzed the influence of trapped charges on surface charge density and electrowetting force.

Main Results:

• The potential of trapped charges showed a linear relationship with direct current (DC) driving time (up to 120 seconds).
• Higher driving voltages resulted in a greater average growth rate of trapped charge potential.
• At 30V, the average growth rate of trapped charge potential reached 0.053 V/s.

Conclusions:

• Charge trapping significantly influences electrowetting display performance, particularly oil backflow.
• The study provides a method to quantify trapped charges and their impact on display parameters.
• Understanding charge trapping is crucial for improving EWD stability and performance.