Driving Waveform Design of Electrowetting Displays Based on a Reset Signal for Suppressing Charge Trapping Effect

Electrowetting display (EWD) device is a new type of reflective optoelectronic equipment with paper-like display performance. Due to the oil backflow phenomenon, it is difficult for pixels to be maintained a stable aperture ratio, so the grayscale of EWDs cannot be stabilized. To reduce the oil backflow in EWDs, a driving waveform composed of a driving signal and a periodic reset signal was proposed in this paper. A direct current (DC) signal was designed as the driving signal for driving pixels. The aperture ratio of pixels was determined by the amplitude of the DC signal. The periodic reset signal was divided into a charge release phase and a driving recovery phase. During the charge release phase, the driving voltage was abruptly dropped to 0 V for a period to release trapped charges. In the driving recovery phase, the driving voltage was rapidly increased from 0 V to a maximum value. To reach the same grayscale of EWDs, the driving waveform was returned to the driving signal at the end of the driving recovery phase. Experimental results showed that the aperture ratio of EWDs was unchanged when the driving waveform was applied. However, the aperture ratio of pixels was gradually decreased with the conventional driving waveform. It was indicated that the charge trapping effect and the oil backflow phenomenon can be effectively inhibited by the proposed driving waveform. Compared with the conventional driving waveform, the speed of oil backflow was reduced by 90.4%. The results demonstrated that the proposed driving waveform is beneficial for the achievement of stable grayscale in EWDs.

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A Combined Pulse Driving Waveform With Rising Gradient for Improving the Aperture Ratio of Electrowetting Displays

Frontiers in Physics ◽

10.3389/fphy.2021.709151 ◽

2021 ◽

Vol 9 ◽

Author(s):

Lixia Tian ◽

Pengfei Bai

Keyword(s):

Charge Trapping ◽

Fast Response ◽

Driving Voltage ◽

Film Rupture ◽

Aperture Ratio ◽

Full Color ◽

Display Technology ◽

Display Performance ◽

The Stability ◽

Driving Waveform

As a reflective display technology, electrowetting displays (EWDs) have the advantages of paper-like display, low power consumption, fast response, and full color, but the aperture ratio of EWDs is seriously affected by oil dispersion and charge trapping. In order to improve the aperture ratio and optimize the display performance of EWDs, a combined pulse driving waveform with rising gradient design was proposed. First, an initial driving voltage was established by the threshold voltage of oil film rupture (Vth). And then, a rising gradient was designed to prevent oil from dispersing. At last, the oil splitting and movement were controlled to achieve the target aperture combined with the pulse waveform. Experimental results showed that the oil dispersion of EWDs can be effectively improved by using the proposed driving waveform, the aperture ratio of EWDs was increased by 3.16%, and the stability was increased by 71.43%.

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Aperture Ratio Improvement by Optimizing the Voltage Slope and Reverse Pulse in the Driving Waveform for Electrowetting Displays

Micromachines ◽

10.3390/mi10120862 ◽

2019 ◽

Vol 10 (12) ◽

pp. 862 ◽

Cited By ~ 4

Author(s):

Zichuan Yi ◽

Wenyong Feng ◽

Li Wang ◽

Liming Liu ◽

Yue Lin ◽

...

Keyword(s):

Inflection Point ◽

Charge Trapping ◽

Response Speed ◽

Driving Voltage ◽

Hysteresis Characteristic ◽

Aperture Ratio ◽

Dynamic Display ◽

Capacitance Voltage ◽

Reverse Pulse ◽

Driving Waveform

Electrowetting display (EWD) performance is severely affected by ink distribution and charge trapping in pixel cells. Therefore, a multi structural driving waveform is proposed for improving the aperture ratio of EWDs. In this paper, the hysteresis characteristic (capacitance–voltage, C-V) curve of the EWD pixel is tested and analyzed for obtaining the driving voltage value at the inflection point of the driving waveform. In the composition of driving waveform, a voltage slope is designed for preventing ink dispersion and a reverse pulse is designed for releasing the trapped charge which is caused by hysteresis characteristic. Finally, the frequency and the duty cycle of the driving waveform are optimized for the max aperture ratio by a series of testing. The experimental results show that the proposed driving waveform can improve the ink dispersion behavior, and the aperture ratio of the EWD is about 8% higher than the conventional driving waveform. At the same time, the response speed of the driving waveform can satisfy the dynamic display in EWDs, which provides a new idea for the design of the EWD driving scheme.

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Driving Waveform Design of Electrowetting Displays Based on an Exponential Function for a Stable Grayscale and a Short Driving Time

Micromachines ◽

10.3390/mi11030313 ◽

2020 ◽

Vol 11 (3) ◽

pp. 313 ◽

Cited By ~ 2

Author(s):

Zichuan Yi ◽

Zhenyu Huang ◽

Shufa Lai ◽

Wenyao He ◽

Li Wang ◽

...

Keyword(s):

Time Constant ◽

Exponential Function ◽

Waveform Design ◽

Hysteresis Curve ◽

Optimal Time ◽

Driving Voltage ◽

Aperture Ratio ◽

Driving Time ◽

Long Time ◽

Driving Waveform

The traditional driving waveform of the electrowetting display (EWD) has many disadvantages, such as the large oscillation of the target grayscale aperture ratio and a long time for achieving grayscale. Therefore, a driving waveform based on the exponential function was proposed in this study. First, the maximum driving voltage value of 30 V was obtained by testing the hysteresis curve of the EWD pixel unit. Secondly, the influence of the time constant on the driving waveform was analyzed, and the optimal time constant of the exponential function was designed by testing the performance of the aperture ratio. Lastly, an EWD panel was used to test the driving effect of the exponential-function-driving waveform. The experimental results showed that a stable grayscale and a short driving time could be realized when the appropriate time constant value was designed for driving EWDs. The aperture ratio oscillation range of the gray scale could be reduced within 0.95%, and the driving time of a stable grayscale was reduced by 30% compared with the traditional driving waveform.

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

Frontiers in Physics ◽

10.3389/fphy.2020.618752 ◽

2020 ◽

Vol 8 ◽

Author(s):

Linwei Liu ◽

Zhuoyu Wu ◽

Li Wang ◽

Taiyuan Zhang ◽

Wei Li ◽

...

Keyword(s):

Response Time ◽

Indium Tin Oxide ◽

Pulse Width Modulation ◽

Charge Trapping ◽

Driving Voltage ◽

Reverse Voltage ◽

Dc Voltage ◽

Voltage Curve ◽

Voltage Frequency ◽

Driving Waveform

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.

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Driving Waveform Design with Rising Gradient and Sawtooth Wave of Electrowetting Displays for Ultra-Low Power Consumption

Micromachines ◽

10.3390/mi11020145 ◽

2020 ◽

Vol 11 (2) ◽

pp. 145 ◽

Cited By ~ 2

Author(s):

Wei Li ◽

Li Wang ◽

Taiyuan Zhang ◽

Shufa Lai ◽

Linwei Liu ◽

...

Keyword(s):

Power Consumption ◽

Low Power ◽

Driving Voltage ◽

Ultra Low Power ◽

Sawtooth Wave ◽

Aperture Ratio ◽

Initial Stage ◽

Display Technology ◽

Three Stages ◽

Driving Waveform

As a kind of paper-like display technology, power consumption is a very important index for electrowetting displays (EWDs). In this paper, the influence of driving waveforms on power consumption of the EWDs is analyzed, and a driving waveform with rising gradient and sawtooth wave is designed to reduce the power consumption. There are three stages in the proposed driving waveform. In the initial stage, the driving voltage is raised linearly from the threshold to the maximum value to reduce the invalid power consumption. At the same time, the oil breakup can be prohibited. And then, a section of sawtooth wave is added for suppressing oil backflow. Finally, there is a section of resetting wave to eliminate the influence of charge leakage. Experimental results show that the power consumption of the ultra-low power driving waveform is 1.85 mW, which is about 38.13% lower than that of the conventional used square wave (2.99 mW), when the aperture ratio is 65%.

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A comparative study of charge trapping effect in p-type MoTe2 and WSe2 FETs using pulsed current–voltage measurements

Japanese Journal of Applied Physics ◽

10.35848/1347-4065/abd6d5 ◽

2021 ◽

Vol 60 (1) ◽

pp. 011003

Author(s):

Jeong Yong Yang ◽

Chan Ho Lee ◽

Young Taek Oh ◽

Jiyeon Ma ◽

Junseok Heo ◽

...

Keyword(s):

Comparative Study ◽

Charge Trapping ◽

Pulsed Current ◽

Trapping Effect ◽

Current Voltage ◽

P Type

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A Separated Reset Waveform Design for Suppressing Oil Backflow in Active Matrix Electrowetting Displays

Micromachines ◽

10.3390/mi12050491 ◽

2021 ◽

Vol 12 (5) ◽

pp. 491

Author(s):

Linwei Liu ◽

Pengfei Bai ◽

Zichuan Yi ◽

Guofu Zhou

Keyword(s):

Experimental Data ◽

Dielectric Layer ◽

Waveform Design ◽

Second Phase ◽

Active Matrix ◽

Two Phases ◽

Back Stage ◽

A Charge ◽

Electric Field Force ◽

Driving Waveform

The electrowetting display (EWD) is a kind of reflective paper-like display. Flicker and grayscale distortion are caused by oil backflow, which is one of the important factors restricting the wide application of EWDs. The charge embedding caused by the electric field force in the dielectric layer is the cause of oil backflow. To suppress oil backflow, a separated reset waveform based on the study of oil movement is proposed in this paper. The driving waveform is divided into two parts: a reset waveform and a grayscale waveform. The reset waveform generated by a reset circuit can be used to output various voltages. The grayscale waveform is set as a traditional PWM waveform. The reset waveform is composed of a charge-releasing stage and oil-moving back stage. Two phases are contained in the charge releasing stage. The overdriving voltage is used during the first phase to reverse the voltage of all pixels. The trapped charges can then be released from the dielectric layer during the second phase. A higher voltage is used during the oil-moving back stage to drive the oil faster in the pixel. By comparing the experimental data, the oil backflow time is extended 761 times by the reset waveform. The four grayscales can be maintained by the reset waveform after driving for 300 s.

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