Driving method for inhibiting ink splitting of electrowetting display device

Abstract

The invention provides a driving method for inhibiting ink splitting of an electrowetting display device. A combined driving scheme of an over-starting stage and a stable display stage is adopted. In the over-opening stage, the problem of ink splitting can be effectively weakened by improving voltage amplitude distribution in the stage. In the stable display stage, a section of asymmetric alternating current driving scheme is adopted to reduce brightness oscillation and suppress the charge accumulation effect, so that the purpose of improving the display stability of the electrowetting display is achieved. The driving scheme provided by the invention has the advantages that the EWD can restrain ink splitting, meanwhile, high gray scale display stability can be kept, and the display state of the ink is more stable. Besides, the optimal value of the influence of different sine-oriented driving schemes on the brightness value in the over-opening stage is determined by analyzing the dispersion motion after the ink is broken in the over-opening stage, so that better display performance is obtained, and an experimental platform is developed to verify the effectiveness of the driving scheme.

Description

Technical Field

[0001] The invention relates to the field of display devices, in particular to a driving method for suppressing ink splitting of an electrowetting display device. Background Art

[0002] Electrowetting theory is a technology that uses electric fields to manipulate liquid movement. By applying an electric field on the surface of a dielectric to change the contact angle, the liquid can move, deform, and split according to certain rules. The electrowetting theory was first discovered in 1981. After 22 years of development and change, Robert A. Hayes realized high-quality electrowetting display (EWD). Compared with EPD display technology, EWD display technology has the characteristics of millisecond response speed, rich display colors, and high reflectivity.

[0003] like Figure 1 As shown in the figure, the EWD structure consists of two layers of indium tin oxide (ITO) electrode plates wrapped with polar liquid (NaCl solution) and color ink. A hydrophobic insulating layer is coated on the bottom ITO glass substrate, and the color ink is separated by photoresist. Each pixel in the EWD is composed of a hydrophobic insulating layer, color ink, polar liquid, pixel wall, and ITO glass electrode plate. Some pixels are also equipped with columns to prevent pixel deformation.

[0004] From the EWD structure and its pixel composition, it can be seen that the pixel unit is equivalent to an optical switch. By giving different driving schemes to the upper and lower ITO electrode plates, continuous opening and closing can be achieved, and finally the EWD grayscale conversion effect is achieved. Therefore, the display performance of EWD is mainly affected by the driving scheme. The electrowetting effect can be described by the Young-Lippmann equation containing an external electric field term. The specific equation is:

[0005]

[0006] Where θ is the contact angle after applying voltage, θ0 is the equilibrium contact angle between the color ink and the hydrophobic insulating layer, ε0 is the vacuum dielectric constant, and ε d is the dielectric constant, d is the thickness of the insulating layer, V is the driving voltage, and γ is the interfacial tension between water and color ink.

[0007] The suitability of the driving scheme greatly affects the display effect of EWD. The measurement indicator of EWD display effect is the aperture ratio, which refers to the ratio of the opening area to the area of ​​a single pixel after removing the area occupied by the color ink. The aperture ratio calculation formula is:

[0008]

[0009] Among them, W A (V) is the aperture ratio, S oil(V) is the area occupied by the color ink in the pixel, S pixel Indicates the area of ​​a single pixel. After the ink is split, the opening ratio decreases.

[0010] like Figure 2 As shown in the figure, the DC driving solution cannot stabilize the EWD at the target grayscale. The charge accumulation phenomenon will cause the ink to flow back, which will eventually lead to a decrease in display brightness. Using the traditional PWM waveform to drive the pixel unit can improve the ink backflow problem, but there are still problems such as slow EWD opening response speed and excessive ink splitting. Therefore, the EWD display effect cannot meet the needs of market applications.

[0011] In summary, this application suppresses ink splitting and improves the stability of EWD based on asymmetric AC drive and polarity-dependent drive scheme. In addition, as an application scenario of microfluidic technology, the research on EWD in this paper can be extended to the field of microfluidics research. Summary of the invention

[0012] In view of the above problems in the prior art, the present application proposes a driving method for suppressing ink splitting of an electrowetting display device. The driving method includes an over-opening stage and a stable display stage. The over-opening stage adopts a sinusoidal guided drive, and the stable display stage adopts an asymmetric AC drive. In the over-opening stage, after a time T1, the driving voltage increases from a negative threshold voltage V thn The driving voltage is increased to twice the maximum driving voltage V0; after time T2, the driving voltage is reduced from V0 to a stable voltage V1, and the stable voltage V1 lasts for T3; the voltage-time equation of the sinusoidal guided driving scheme is specifically:

[0013]

[0014] Among them, V st1 is the real-time voltage during the over-opening phase, t is the time, T1 and T2 are the driving time values, k1 and k2 are constants to ensure that the driving scheme is continuous; during the charge release phase of duration T4, the driving voltage is V2.

[0015] In one embodiment, the total duration of T3 and T4 is 20 milliseconds, T1 = 10 ms, T2 = 10 ms. V1 is -6V, and the release voltage V2 is 7V. The negative threshold voltage V thn is the threshold voltage for ink rupture.

[0016] The above technical features can be combined in various suitable ways or replaced by equivalent technical features as long as the purpose of the present invention can be achieved.

[0017] The driving method for suppressing ink splitting of an electrowetting display device provided by the present invention has at least the following beneficial effects compared with the prior art:

[0018] It was determined that the sinusoidal guided driving scheme in the over-opening stage can effectively suppress the ink splitting phenomenon. The optimal value of the asymmetric AC driving scheme on the EWD brightness value in the stable display stage was determined. The brightness oscillation of the ink during the driving process was reduced, and the stability of the grayscale display was improved. The driving scheme is divided into the over-opening stage and the stable display stage. In the over-opening stage, a sinusoidal guided driving scheme with an initial voltage of 2 times the threshold voltage of ink rupture is applied, which effectively suppresses the ink dispersion. By testing the response time of EWD, the influence of different asymmetric AC driving schemes on the brightness value in the stable display stage is analyzed. By testing the brightness of EWD, the advantages of the proposed driving scheme compared with the combined driving scheme with sinusoidal guidance and asymmetric AC, the traditional PWM driving scheme, and the driving scheme that suppresses ink reflux are analyzed. An experimental platform is developed to verify the effectiveness of the driving scheme. BRIEF DESCRIPTION OF THE DRAWINGS

[0019] The present invention will be described in more detail below based on embodiments and with reference to the accompanying drawings, wherein:

[0020] Figure 1 A schematic diagram of a pixel unit of the present invention is shown;

[0021] Figure 2 A diagram showing the ink splitting state of the present invention is shown;

[0022] Figure 3 A schematic diagram of the driving scheme of the present invention is shown;

[0023] Figure 4 A schematic diagram comparing the first 60ms of three waveforms of the present invention is shown;

[0024] Figure 5 A comparison chart of the waveform test results of the present invention is shown. DETAILED DESCRIPTION

[0025] The present invention will be further described below in conjunction with the accompanying drawings.

[0026] like Figure 3 As shown, the present invention provides a driving method for suppressing ink splitting of an electrowetting display device. The overall goal of the driving waveform design is to improve the grayscale stability of the EWD display and reduce the aperture ratio fluctuation problem caused by ink splitting. This patent optimizes the driving scheme for the ink splitting problem and proposes corresponding optimization schemes for the problems in different driving stages. First, the driving scheme is divided into an over-opening stage and a stable display stage. The proposed driving scheme consists of a sinusoidal guided driving scheme and an asymmetric AC driving scheme. In the over-opening stage, the driving voltage is increased from the negative threshold voltage V thnThe driving voltage is then increased to the maximum driving voltage V0 by twice of the voltage V0, and the duration is T1 = 10ms. Then, the driving voltage is reduced from V0 to the stable voltage V1, and the duration is T2 = 10ms. The total driving time of 20ms is sufficient to play a 50Hz video. In summary, the voltage-time equation of the sinusoidal steering driving scheme is:

[0027]

[0028] Among them, V st1 is the real-time voltage during the on-state phase, t is the time, T1 and T2 are the driving time values, and k1 and k2 are constants to ensure that the driving scheme is continuous. In the stable display phase, an asymmetric AC driving scheme is adopted. The target brightness is set to 500. V1 is -6V, while the release voltage V2 is 7V. V2 is introduced in the charge release phase of T4. The total duration of T3 and T4 is 20 milliseconds.

[0029] First, we use professional software to design and generate a driving scheme on a computer (Pro G6, HP, China). The characteristics of this driving scheme will be described by a binary file and stored in a signal generator (AFG1022, Tektronix, USA). Since the output voltage of the signal generator has certain limitations, in order to effectively drive the external working device (EWD) we use, we need to use a voltage amplifier (Agilent 33502A, Agilent, USA) to amplify the driving scheme. During the driving process, we use a colorimeter (Arges-45, Admesy, the Netherlands) to measure and record the brightness changes of the EWD. Through the split experimental platform, we can comprehensively and accurately control and monitor the changes in brightness and response time values ​​during the experiment, thereby providing a more reliable data basis for physical experiments.

[0030] Comparison experiments with other driving schemes prove that the driving scheme design in this patent can effectively ensure the aperture ratio and display stability. The traditional PWM square wave driving scheme, gradient rising AC driving scheme and the driving scheme proposed in this article are selected for comparative testing. The waveform diagram is shown in the figure below. Figure 4 shown.

[0031] This application proposes a driving scheme to suppress ink splitting, and compares it with the traditional pulse width modulation (PWM) driving scheme and the ink backflow suppression driving scheme. The test results are as follows: Figure 5As shown. When the EWD is driven by the PWM driving scheme, the aperture ratio of the pixel is high and the average brightness is 528.6. However, the occurrence of ink splitting is high, resulting in unstable display performance with an average brightness variance of 4.87. Meanwhile, when the EWD is driven by the ink backflow suppression driving scheme, the average brightness is 520.6. In this case, the ink splitting is weakened and the average brightness variance is 2.31. In contrast, when the EWD is driven by the driving scheme of this patent, the average brightness is 516.9, the ink splitting is effectively suppressed, and the average brightness variance is reduced to 1.35. Therefore, the driving scheme proposed in this letter leads to a 2.2% reduction in brightness compared to the PWM driving scheme. The reduction in brightness is because an optimal duty cycle of 80% is required to effectively suppress ink backflow, which limits the achievable brightness to 516.9. However, this adjustment significantly reduces brightness fluctuations, thereby improving overall display stability. In addition, when the EWD is driven by the proposed driving scheme, the brightness stability is improved by 41.6% compared to the driving scheme that suppresses ink backflow, with an average maximum brightness fluctuation of 7.1.

[0032] Edit the voltage amplitude, frequency, driving cycle and other performance parameters of the driving scheme in Matlab software and output them as a waveform file in txt format. Then convert the format through Arbexpress Application software, save the file as a tfw file and save it in a USB flash drive.

[0033] Insert the U disk into the function signal generator, then select the arbitrary waveform output mode on the function generator, find the waveform file in the U disk and adjust the high and low levels and drive frequency for output.

[0034] The output terminal of the function generator is connected to the input terminal of the voltage amplifier through an adapter cable. The input resistance of the voltage amplifier is adjusted to 50Ω and the amplification factor is 10 times.

[0035] The positive output terminal of the voltage amplifier is connected to the common electrode of the EWD, and the negative output terminal is connected to the pixel electrode of the EWD.

[0036] Connect the colorimeter to the computer, open the Admesy software in the computer, and then calibrate the colorimeter with a standard reference white board. At the same time, set the delay to 7 so that the brightness value of the EWD can be fully and correctly collected.

[0037] Place the colorimeter steadily on the EWD, then turn on the output of the function signal generator and the voltage amplifier to provide input signals, and start measuring the brightness value of the EWD in real time.

[0038] Finally, the brightness value measured by the colorimeter and the corresponding image were saved as an EXCEL document and a jpg picture on the Admesy software, and then the performance of the two was analyzed to obtain the final result.

[0039] Compared with the traditional driving scheme, the traditional driving scheme has problems such as long response time, ink splitting and brightness oscillation. This patent adopts a combined driving scheme of the over-opening stage and the stable display stage. In the over-opening stage, the ink splitting problem can be effectively reduced by improving the voltage amplitude distribution in this stage. In the stable display stage, an asymmetric AC driving scheme is adopted to reduce brightness oscillation and suppress the charge accumulation effect, so as to achieve the purpose of improving the display stability of the electrowetting display. The advantage of this invention is that the proposed driving scheme can enable EWD to suppress ink splitting while maintaining a high grayscale display stability, making the display state of the ink more stable. In addition, by analyzing the dispersed movement after the ink breaks in the over-opening stage, the optimal value of the influence of different sinusoidal guided driving schemes on the brightness value in the over-opening stage is determined to obtain better display performance, and an experimental platform is developed to verify the effectiveness of the driving scheme.

[0040] Although the present invention is described herein with reference to specific embodiments, it should be understood that these embodiments are merely examples of the principles and applications of the present invention. It should therefore be understood that many modifications may be made to the exemplary embodiments and that other arrangements may be devised without departing from the spirit and scope of the present invention as defined by the appended claims. It should be understood that the various dependent claims and features described herein may be combined in a manner different from that described in the original claims. It should also be understood that features described in conjunction with individual embodiments may be used in other described embodiments.

Claims

1. A driving method for suppressing ink splitting of an electrowetting display device, characterized in that: The driving method includes an over-opening stage and a stable display stage. The over-opening stage adopts a sinusoidal guided drive, and the stable display stage adopts an asymmetric AC drive. In the over-opening stage, after a time T1, the driving voltage changes from a negative threshold voltage V thn The driving voltage is increased to twice the maximum driving voltage V0; after time T2, the driving voltage is reduced from V0 to a stable voltage V1, and the stable voltage V1 lasts for T3; the voltage-time equation of the sinusoidal guided driving scheme is specifically: Among them, V st1 is the real-time voltage during the over-opening phase, t is the time, T1 and T2 are the driving time values, k1 and k2 are constants to ensure that the driving scheme is continuous; during the charge release phase of duration T4, the driving voltage is V2.

2. The driving method for suppressing ink splitting of an electrowetting display device according to claim 1, characterized in that: The total duration of T3 and T4 is 20 milliseconds.

3. The driving method for suppressing ink splitting of an electrowetting display device according to claim 1, characterized in that: T1=10ms.

4. The driving method for suppressing ink splitting of an electrowetting display device according to claim 1, characterized in that: T2=10ms.

5. The driving method for suppressing ink splitting of an electrowetting display device according to claim 1, characterized in that: V1 is -6V, and the release voltage V2 is 7V.

6. The driving method for suppressing ink splitting of an electrowetting display device according to claim 1, characterized in that: Negative threshold voltage V thn is the threshold voltage for ink rupture.

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