Toward Suppressing Charge Trapping Based on a Combined Driving Waveform with an AC Reset Signal for Electro-Fluidic Displays

High-Performance Multi-Level Grayscale Conversion by Driving Waveform Optimization in Electrowetting Displays

As a new type of reflective display, electrowetting display (EWD) has excellent dynamic display performance, which is based on polymer coatings. However, there are still some issues which can limit its performance, such as oil backflow and the hysteresis effect which reduces the stability and response speed of EWDs. Therefore, an effective driving waveform was proposed to overcome these drawbacks, which consisted of grayscale conversions between low gray levels and high gray levels. In the driving waveform, to stabilize the EWD at any initial grayscale (low gray levels/high gray levels), an exponential function waveform and an AC signal were used. Then, the grayscale conversion was performed by using an AC signal with a switching voltage to quickly achieve the target grayscale. Finally, another AC signal was used to stabilize the EWD at the target grayscale. A set of driving waveforms in grayscale ranging across four levels was designed using this method. According to the experimental results, oil backflow and the hysteresis effect could be effectively attenuated by the proposed driving waveforms. During conversion, the response speed of EWDs was boosted by at least 9.37% compared to traditional driving waveforms.

Stability Study of Multi-Level Grayscales Based on Driving Waveforms for Electrowetting Displays

Electrowetting Display (EWD) is a new reflective display with an outstanding performance of color video playback. However, some problems still exist and affect its performance. For instance, oil backflow, oil splitting, and charge trapping phenomena may occur during the driving process of EWDs, which would decrease its stability of multi-level grayscales. Therefore, an efficient driving waveform was proposed to solve these disadvantages. It consisted of a driving stage and a stabilizing stage. First, an exponential function waveform was used in the driving stage for driving the EWDs quickly. Then, an alternating current (AC) pulse signal waveform was used in the stabilizing stage to release the trapped positive charges of the insulating layer to improve display stability. A set of four level grayscale driving waveforms were designed by using the proposed method, and it was used in comparative experiments. The experiments showed that the proposed driving waveform could mitigate oil backflow and splitting effects. Compared to a traditional driving waveform, the luminance stability was increased by 8.9%, 5.9%, 10.9%, and 11.6% for the four level grayscales after 12 s, respectively.

Design of Multi-DC Overdriving Waveform of Electrowetting Displays for Gray Scale Consistency

Gray scale consistency in pixels was extremely important for electrowetting displays (EWDs). However, traditional electrowetting display driving waveforms could not obtain a pixel aperture ratio consistency, which led to the occurrence of gray inconsistency even if it was the same driving waveform. In addition, the oil backflow caused by charge trapping could not be sustained. Therefore, a multi-direct current (DC) overdriving waveform for gray scale consistency was proposed in this paper, which could effectively improve the performance of EWDs. The driving waveform was divided into a start-up driving phase and a stable driving phase. The stable driving phase was composed of a square wave with a duty cycle of 79% and a frequency of 43 Hz. Subsequently, an overdriving pulse was also introduced in the stable driving phase. The multi-DC driving waveform for gray scale consistency was applied to a thin film transistor-electrowetting display (TFT-EWD). The average difference between increasing driving voltage and decreasing driving voltage was only 2.79%. The proposed driving waveform has an aperture ratio of 3.7 times at low voltages compared to DC driving.