CN114974141A - Driving method for inhibiting leakage current of electrowetting display - Google Patents
Driving method for inhibiting leakage current of electrowetting display Download PDFInfo
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- CN114974141A CN114974141A CN202210612023.2A CN202210612023A CN114974141A CN 114974141 A CN114974141 A CN 114974141A CN 202210612023 A CN202210612023 A CN 202210612023A CN 114974141 A CN114974141 A CN 114974141A
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- 238000000034 method Methods 0.000 title claims abstract description 18
- 230000002401 inhibitory effect Effects 0.000 title abstract description 11
- 230000000087 stabilizing effect Effects 0.000 claims abstract description 10
- 230000008859 change Effects 0.000 claims abstract description 9
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- 238000011105 stabilization Methods 0.000 claims description 6
- 230000001629 suppression Effects 0.000 claims description 3
- 238000003776 cleavage reaction Methods 0.000 claims description 2
- 230000007017 scission Effects 0.000 claims description 2
- 230000000452 restraining effect Effects 0.000 claims 3
- 230000000694 effects Effects 0.000 abstract description 5
- 238000013467 fragmentation Methods 0.000 abstract description 4
- 238000006062 fragmentation reaction Methods 0.000 abstract description 4
- 238000005516 engineering process Methods 0.000 abstract description 3
- 230000004044 response Effects 0.000 abstract description 3
- 238000002310 reflectometry Methods 0.000 abstract 1
- 230000008602 contraction Effects 0.000 description 4
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- AMGQUBHHOARCQH-UHFFFAOYSA-N indium;oxotin Chemical compound [In].[Sn]=O AMGQUBHHOARCQH-UHFFFAOYSA-N 0.000 description 1
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- G—PHYSICS
- G09—EDUCATION; CRYPTOGRAPHY; DISPLAY; ADVERTISING; SEALS
- G09G—ARRANGEMENTS OR CIRCUITS FOR CONTROL OF INDICATING DEVICES USING STATIC MEANS TO PRESENT VARIABLE INFORMATION
- G09G3/00—Control arrangements or circuits, of interest only in connection with visual indicators other than cathode-ray tubes
- G09G3/20—Control arrangements or circuits, of interest only in connection with visual indicators other than cathode-ray tubes for presentation of an assembly of a number of characters, e.g. a page, by composing the assembly by combination of individual elements arranged in a matrix no fixed position being assigned to or needed to be assigned to the individual characters or partial characters
- G09G3/34—Control arrangements or circuits, of interest only in connection with visual indicators other than cathode-ray tubes for presentation of an assembly of a number of characters, e.g. a page, by composing the assembly by combination of individual elements arranged in a matrix no fixed position being assigned to or needed to be assigned to the individual characters or partial characters by control of light from an independent source
- G09G3/3433—Control arrangements or circuits, of interest only in connection with visual indicators other than cathode-ray tubes for presentation of an assembly of a number of characters, e.g. a page, by composing the assembly by combination of individual elements arranged in a matrix no fixed position being assigned to or needed to be assigned to the individual characters or partial characters by control of light from an independent source using light modulating elements actuated by an electric field and being other than liquid crystal devices and electrochromic devices
- G09G3/348—Control arrangements or circuits, of interest only in connection with visual indicators other than cathode-ray tubes for presentation of an assembly of a number of characters, e.g. a page, by composing the assembly by combination of individual elements arranged in a matrix no fixed position being assigned to or needed to be assigned to the individual characters or partial characters by control of light from an independent source using light modulating elements actuated by an electric field and being other than liquid crystal devices and electrochromic devices based on the deformation of a fluid drop, e.g. electrowetting
Abstract
The application relates to a driving method for inhibiting leakage current of an electrowetting display. The electrowetting display is a novel reflection type display prepared based on the electrowetting technology, and is expected to replace the traditional electrophoretic display due to the advantages of high reflectivity, high response speed, easiness in realizing color display and the like. The driving waveform is one of the key factors affecting the performance of the display, and the conventional driving waveform has the problems of ink splitting caused by abrupt voltage change and ink backflow caused by leakage current, which not only cause the brightness of the display to be reduced and the accurate gray scale to be displayed to be difficult to control, but also cause the insulating layer to be broken down to damage the pixels. The driving waveform provided by the invention comprises a fragmentation inhibiting stage, a direct current stage, an ink stabilizing stage and a resetting stage. The aperture ratio of the pixel is improved by suppressing the ink splitting, the ink is stabilized in a contracted state by canceling out a voltage generated by a leakage current, and the driving effect is excellent in repeatability by releasing the captured charges in the reset stage.
Description
Technical Field
The invention belongs to the technical field of electrowetting displays (EWDs), and particularly provides a driving method for inhibiting ink splitting and leakage current of an electrowetting display.
Background
Electrowetting displays (EWDs) are a novel reflective display prepared based on electrowetting technology, and compared with the traditional reflective display (electrophoretic display), the EWDs have the advantages of high response speed, easy realization of color display and the like, and are a new generation of electronic paper technology with the most development potential. The structure is shown in fig. 1, and it is composed of a top plate, a bottom plate, two Indium Tin Oxide (ITO) glass plates, color ink, conductive solution (sodium chloride aqueous solution), an insulating layer, pixel walls, and an additional pinning structure (EPS). Wherein, two ITO glass plates are respectively a common electrode plate and a pixel electrode plate, the pixel wall is used for separating the color ink between different pixels, and EPS is used for inducing the direction of ink shrinkage.
In this technique, the threshold voltage is the minimum voltage required for the ink to start shrinking, and when the voltage applied to the two electrode plates is less than the threshold voltage, the ink spreads on the insulating layer, and the color ink reflects incident light, and the display displays the color of the ink, as shown in fig. 2 (a). As the voltage is increased, the insulating layer gradually changes from hydrophobic to oleophobic, the color ink is pushed away by the conductive solution to shrink at the corners of the pixel, at which time the backplane reflects the incident light and the display displays the color of the backplane, as shown in fig. 2 (b). The ratio of the exposed area of the bottom plate to the total area of the pixels is called the aperture ratio, and is shown in formula (1). The opening ratio is proportional to the contact angle of the oil-solid interface, and the Lippmann-Young equation can be used to describe the relationship between the contact angle and the applied voltage in EWDs, as shown in equation (2).
cosθ V -cosθ 0 ＝KV 2 #(2)
Wherein R is A Is the aperture ratio of the pixel, S u Is the area of the exposed base plate, S p Is the total area of one pixel, θ V Is the contact angle after application of a voltage, theta 0 Is the contact angle in the absence of an applied voltage, K is a constant associated with the EWDs material and structure, and V is the two electrodesThe voltage applied to the plate shows that the contact angle is proportional to the square of the voltage, with the larger the voltage, the larger the contact angle.
The driving waveform is a sequence of voltages applied across the two electrode plates that control the turning on and off of the pixels. The traditional driving waveform is a Pulse Width Modulation (PWM) square wave, the voltage amplitude is related to the material and structure of the display, and the waveform is prone to ink splitting and leakage current problems. The ink break-up is a phenomenon that the ink shrinks to two or more corners of the pixel after the voltage is applied, and as shown in fig. 3, the relationship between the area occupied by the ink and the volume of the ink and the voltage is shown in formula (3).
Wherein S is oil Is the area occupied by the ink, V oil Is the volume of ink. It can be seen that the splitting of the ink will result in an increase in the area occupied by the ink for the same volume, and therefore the defect will result in a decrease in the aperture ratio of the pixel. The leakage current is caused because charges are trapped in the insulating layer during driving to form leakage current, and this defect causes ink to flow back and makes it difficult to stabilize the luminance of the pixel.
Disclosure of Invention
The present invention is directed to suppressing ink cracking and reducing the effect of leakage current on a display. The driving waveform is divided into a fragmentation inhibiting stage, a direct current stage, an ink stabilizing stage and a resetting stage. In the splitting inhibition phase, the voltage waveform of a power function starts to rise from a threshold voltage, and the voltage does not change suddenly so as to inhibit the ink splitting. The direct current phase is used to drive the ink to contract rapidly. In the ink stabilization stage, a linear voltage sequence is adopted, and the voltage can effectively offset the voltage generated by leakage current, so that the ink is stabilized. The reset phase is used to discharge the charge in the insulating layer.
The method specifically comprises the following steps:
the design of the driving waveform directly affects the performance of the EWD, and the driving waveform proposed by the present invention consists of a crack suppression stage, a direct current stage, an ink stabilization stage, and a reset stage. The voltage sequence in the splitting inhibition stage is a power function waveform, as shown in formula (4), wherein a power constant a is 3, the formula (4) is derived to obtain a formula (5), and V' is 0 when t is 0, so that the voltage slope is increased from 0, and the ink splitting caused by voltage mutation is effectively avoided. The dc stage is a dc voltage with an amplitude that is the voltage required by the pixel to reach the target gray level. The ink stabilizing stage is a linear voltage sequence, the slope of the voltage is 50mV/s, and the voltage generated by leakage current can be offset, so that the ink is stabilized. The reset phase is a section of square wave with the polarity opposite to that of the driving voltage, and the amplitude of the square wave is threshold voltage, so that voltage generated by leakage current is released. The driving waveforms are shown in fig. 4.
Wherein, V M Voltage required for target gray scale, V th Is a threshold voltage, T s To suppress the duration of the cleavage phase, V vth Threshold voltages of opposite polarity.
The aperture ratio of the EWD can be characterized by the brightness and the response time can be characterized by the change in brightness, thus, a platform is constructed to test the brightness value of the EWD. The experimental platform consisted of a computer (H430, associative, china), a function generator (AFG3022C, Tektronix, usa), a voltage amplifier (ATA-2022H, Agitek, china), a colorimeter (Arges-45, Admesy, the netherlands), and a microscope (SZ680, Cnoptec, china). In the test process, the driving waveform can be edited by Matlab on a computer, then a file of the generated driving waveform is transmitted to a function generator through a Universal Serial Bus (USB) interface, the amplitude value is amplified by 10 times through a voltage amplifier, and finally the output voltage is applied to the EWD. The colorimeter was placed on the EWD to record the brightness value thereof, and the shrinkage state of the ink was observed with a microscope.
The invention has the following advantages and beneficial effects:
the traditional electrowetting display driving waveform has the problems of ink splitting caused by sudden voltage change and ink backflow caused by leakage current, and the defects seriously affect the display effect of the EWD. The driving waveform provided by the invention comprises a fragmentation inhibiting stage, a direct current stage, an ink stabilizing stage and a resetting stage. In the stage of inhibiting the split, a power function waveform is raised from a threshold voltage to a voltage required by a target gray, and the ink split problem can be effectively solved because the slope of the voltage is gradually increased from 0. In the ink stabilization phase, a linear voltage sequence is used to stabilize the ink, and the increasing voltage can counteract the voltage generated by the leakage current, thereby inhibiting ink backflow. A dc voltage is used to drive the pixel quickly to the target gray level during the dc phase interposed between the inhibit break-up phase and the ink stabilization phase. In the reset phase, the square wave of the opposite polarity can discharge the electric charges trapped to the insulating layer due to the leakage current, the magnitude of which is the threshold voltage, and thus the ink oscillation can be prevented. The invention has the advantages that the aperture ratio of the pixel is improved by inhibiting the ink from splitting, in addition, the ink is stabilized in a contraction state by offsetting the voltage generated by the leakage current, and the captured charges are released in the reset stage, so that the driving effect has excellent repeatability.
1. The effectiveness of the power function waveform rising from the threshold voltage for suppressing ink splitting was determined.
2. The optimal drive time for each phase and the optimal power constant are determined.
3. It was determined that a linear voltage sequence could counteract the voltage generated by the leakage current to stabilize the ink.
Drawings
FIG. 1 is a three-dimensional block diagram of an electrowetting display pixel;
FIG. 2 is a schematic diagram of the "off" and "on" states of a pixel (a) and (b) of an electrowetting display;
FIG. 3 is a schematic view of ink dispersion;
fig. 4 shows the driving waveforms proposed herein. The method comprises a fission inhibiting stage, a direct current stage, an ink stabilizing stage and a resetting stage;
FIG. 5 is a diagram of two conventional drive waveforms for an electrowetting display used for comparison;
FIG. 6 is a contrast of brightness during ink shrinkage;
FIG. 7 shows the contrast of brightness of ink in steady state.
Detailed Description
The invention is further illustrated by the following examples, which are not intended to limit the scope of the invention.
The method includes the steps of editing a designed driving waveform through Matlab and Arbexpress, and storing a generated file in a USB flash disk.
Secondly, a driving waveform file is transmitted into the function generator through the USB flash disk, and then the function generator is used for adjusting the waveform to be the required amplitude and frequency.
Thirdly, transmitting the driving waveform signal output by the function generator into a voltage amplifier, amplifying the amplitude of the waveform by 10 times and applying the amplified waveform signal to the EWD.
A colorimeter is placed on the EWD to test the luminance thereof, and the Admesy software can record the variation curve of the luminance.
And fifthly, observing the shrinking state of the ink through a microscope.
The waveforms presented herein are compared to conventional drive waveforms. The conventional driving waveforms used for comparison are shown in fig. 5, where the red curve represents a linear driving waveform, the black curve represents a PWM square wave, and they are composed of an ink contraction phase and a dc driving phase, the time of the ink contraction phase is 100ms, and the dc driving phase is 30 s. For the designed driving waveform, the fragmentation suppressing stage is 100ms, the direct current stage is 40ms, the ink stabilizing stage is 30s, and the reset stage is 5 ms. The change in brightness of the EWD under the three-waveform driving is shown in fig. 6 and 7, fig. 6 shows the change in brightness during the ink contraction process, fig. 7 shows the change in brightness during the ink steady state, the driving waveform provided achieves a brightness of 600.025, the linear function driving waveform achieves a brightness of 579.523, and the exponential function achieves a brightness of 552.763. It can be seen that we propose that the brightness of the drive waveform is highest, i.e. ink splitting is suppressed, and the brightness value is stabilized at a maximum value, demonstrating that the leakage current effect is suppressed.
Claims (7)
1. A driving method for restraining leakage current of an electrowetting display is characterized in that a driving waveform is divided into a division restraining stage, a direct current stage, an ink stabilizing stage and a reset stage, wherein a voltage sequence of the driving waveform in the division restraining stage is a power function waveform, the direct current stage is a direct current voltage, the ink stabilizing stage is a linear voltage sequence, the reset stage is a square wave with polarity opposite to that of the driving voltage, and the amplitude of the square wave is threshold voltage.
2. A driving method for suppressing leakage current of an electrowetting display as claimed in claim 1, wherein in the splitting suppression phase, a voltage waveform of an exponential function is raised from a threshold voltage, the voltage does not change abruptly so as to suppress ink splitting, the dc phase is used to drive ink to shrink rapidly, in the ink stabilization phase, a linear voltage sequence is used, the voltage is effective to cancel a voltage generated by the leakage current so as to stabilize the ink, the reset phase is used to discharge charges in the insulating layer, and the design of the driving waveform improves an aperture ratio of the pixel.
3. The driving method for suppressing leakage current of electrowetting display according to claim 2, wherein the voltage sequence for suppressing the splitting stage is a power function waveform, and the driving waveform is of the formula
Wherein the power constant a is 3, V M Voltage required for target gray scale, V th Is a threshold voltage, T s To suppress the duration of the cleavage phase.
4. A driving method for suppressing leakage current of an electrowetting display according to claim 2, wherein the dc stage is a dc voltage having an amplitude of a voltage required for the pixel to reach a target gray level.
5. The driving method for suppressing leakage current of an electrowetting display according to claim 2, wherein the ink stabilizing period is a linear voltage sequence having a slope of 50mV/s, which can counteract a voltage generated by the leakage current, thereby stabilizing the ink.
6. The driving method for suppressing leakage current of an electrowetting display according to claim 2, wherein the optimal parameters of each stage of the driving waveform are that the splitting suppression stage is 100ms, the dc stage is 40ms, the ink stabilization stage is 30s, and the reset stage is 5 ms.
7. The driving method for suppressing the leakage current of the electrowetting display as claimed in claim 1, wherein the generating and applying method of the driving waveform is firstly editing the designed driving waveform through Matlab and Arbexpress, storing the generated file in a U-disk, secondly transmitting the driving waveform file into a function generator through the U-disk, then adjusting the waveform to a required amplitude and frequency by using the function generator, thirdly transmitting a driving waveform signal output by the function generator into a voltage amplifier, amplifying the amplitude of the waveform by 10 times and applying the amplified waveform to the EWD, and finally placing the colorimeter on the EWD to test the brightness, wherein Admesy software can record a change curve of the brightness, and finally, the ink shrinkage state can be observed through a microscope.
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| CN202210612023.2A CN114974141A (en) | 2022-05-31 | 2022-05-31 | Driving method for inhibiting leakage current of electrowetting display |
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| CN202210612023.2A CN114974141A (en) | 2022-05-31 | 2022-05-31 | Driving method for inhibiting leakage current of electrowetting display |
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