The electrowetting display (EWD) device is a new type of electrowetting-on-dielectric (EWOD) equipment that can achieve a paper-like display effect under the control of an electric field. In this microfluidic system, the stability of grayscale can be affected by various factors, such as the physicochemical properties of the materials, the device structure, and electric field distribution. To improve the grayscale stability of active matrix electrowetting displays (AM-EWDs), the impact of different polarities of driving voltage on oil backflow was investigated in this study. Based on the driving principles of AM-EWD, an optimized inter-frame bipolar reset driving waveform was designed to overcome oil backflow. The proposed driving waveform maintained the stability of the oil state by periodically and rapidly releasing trapped charges in the dielectric layer through a reverse driving voltage. Additionally, the effect of feed-through voltage on pixel driving voltage was eliminated by compensating for the driving voltage on a common electrode. Finally, the performance of the designed driving waveform was evaluated with a 6-inch AM-EWD driving platform. Compared to the conventional unipolar reset driving waveform, the backflow speed decreased by 2.70 a.u./s. The standard deviation of the display luminance was also reduced by 11.24 a.u. Experimental results indicated that both the oil backflow speed and the fluctuation range of luminance were effectively suppressed by the proposed driving waveform.
Keywords: active matrix; driving waveform; electrowetting display; grayscale stability; oil backflow.