Design of an AC Driving Waveform Based on Characteristics of Electrowetting Stability for Electrowetting Displays

Linwei Liu,Taiyuan Zhang,Shufa Lai,Zhuoyu Wu,Li Wang,Pengfei Bai,Wei Li

doi:10.3389/fphy.2020.618752

Linwei Liu, Taiyuan Zhang + Show 5 more

Open Access

https://doi.org/10.3389/fphy.2020.618752

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Abstract

In traditional electrowetting display (EWD) drivers, direct current (DC) voltage and pulse width modulation are often used, which easily caused an electrowetting charge trapping phenomenon in a hydrophobic insulating layer. Therefore, the driving voltage must be increased for driving EWDs, and oil backflow cannot be solved. Aqueous solutions are often used as polar liquids for EWDs, and the reverse voltage of alternating current (AC) driving can cause chemical reactions between water and indium tin oxide (ITO). So, a driving waveform was proposed, which included a DC waveform and an AC waveform, to separately drive EWDs for oil rupture and open state. Firstly, a DC waveform was used when the oil was broken, and the response time was reduced by designing the DC voltage and duration. Secondly, an AC waveform was used when the oil required to be stable. Oil backflow could be suppressed by the AC waveform. The main parameters of AC waveform include reverse voltage, frequency and duty cycle. The reverse voltage of EWDs could be obtained by voltammetry. The frequency could be obtained by analyzing the rising and falling edges of the capacitance voltage curve. The experimental results showed that the proposed waveform can effectively suppress oil backflow and shorten the response time. The response time was about 86% lower than the conventional driving waveforms, and oil backflow was about 72% slower than the DC driving waveform.

Highlights

With the rapid development of display technology in the world, liquid crystal display (LCD) and electrophoretic display (EPD) have become mainstream display technologies [1,2,3]
Electrowetting display (EWD) technology is an emerging technology to enhance the user experience of electronic paper [4, 5]. It has the characteristics of fast response time, low energy consumption and so on, which can meet the requirements of high energy saving in current network terminal devices [5,6,7]
Aqueous solutions are often used as polar liquids for EWDs, and the chemical reactions between water and indium tin oxide (ITO) is caused by a reverse voltage

Summary

INTRODUCTION

With the rapid development of display technology in the world, liquid crystal display (LCD) and electrophoretic display (EPD) have become mainstream display technologies [1,2,3]. Because of the hysteresis effect, which can make charge capture and oil backflow, the driving waveform cannot be designed with EPD driver chips according to the characteristics of EWDs [20, 21]. The driving system used an unipolar PWM waveform modulation to realize the display of gray scales in EWDs. A reset frame was designed to release the trapped charge and inhibit oil backflow, and the pixel can remain stable in an open state for a longer time. In 2019, a frequency-amplitude mixed modulation driving system was proposed to improve the response speed for driving gray-scale and enhancing oil stability based on an active TFT EWD [8]. The driving mechanism of EWDs is to control contact angle between the insulator and oil by applying voltage. The imbalance between Maxwell pressure and Laplace pressure at the three-phase contact line will cause backflow

DESIGN PRINCIPLE OF ALTERNATING CURRENT WAVEFORM

EXPERIMENTAL RESULTS AND DISCUSSION

CONCLUSION

DATA AVAILABILITY STATEMENT