Low driving voltage electrowetting display and preparation method thereof

Abstract

The application relates to the technical field of materials, and particularly discloses a low-driving-voltage electrowetting display and a preparation method thereof.The electrowetting display comprises a composite material and a pixel wall; the composite material comprises a cellulose dielectric layer and a hydrophobic layer coated on the cellulose dielectric layer; and the pixel wall is above the hydrophobic layer; when the height of the pixel wall is 3.0-3.5 mu m, the equivalent capacitance of the composite material is 35-81 mu F / m 2 ; and when the height of the pixel wall is 5.0-5.5 mu m, the equivalent capacitance of the composite material is 58-81 mu F / m 2 . The thickness of the single-layer or multi-layer dielectric hydrophobic material is designed to adjust the equivalent capacitance C eq and the effective dielectric constant. When the thickness of the HF layer is reduced from 400 nm to 200 nm, V d can be reduced from 17 V to 9 V. Therefore, the enhancement of the equivalent capacitance C eq plays a decisive role in reducing the driving voltage.

Description

TECHNICAL FIELD

[0001] The present application relates to the technical field of materials, in particular to a low driving voltage electrowetting display and a preparation method thereof. BACKGROUND

[0002] Electrowetting display (EWD) technology is to change the wetting of liquid on dielectric hydrophobic material by electric drive, so that the liquid droplet spreads or shrinks, and after integration display, it can produce perceptible optical changes, which has the characteristics of fast response time, low voltage and low power consumption. At present, the driving voltage of most EWD devices is high (15-30V), and custom electrophoretic display (EPD) driving IC needs to be used. If the driving voltage of EWD device is reduced, it is possible to apply the currently widely used liquid crystal display (LCD) driving IC technology, and the lower driving voltage can further improve the service life of the device, prevent breakdown of dielectric layer and hydrophobic layer under large driving voltage, and greatly promote the update of EWD device driving IC.

[0003] The voltage range of LCD driving IC for TFT-LCD display is 3-18V, which provides the necessary voltage for larger and higher resolution screens. Therefore, the highest driving voltage of the LCD driving IC used in the direct current driving system of the EWD device is 18V, and the highest voltage of the alternating current driving system is ±9V. Therefore, it is necessary to provide a low driving voltage electrowetting display and a preparation method thereof, so as to reduce the driving voltage of the reflective electrowetting device. SUMMARY

[0004] The present application aims to at least solve one of the technical problems existing in the prior art. To this end, the present application provides a low driving voltage electrowetting display and a preparation method thereof, so as to reduce the driving voltage of the reflective electrowetting device.

[0005] The first aspect of the present application provides a low driving voltage electrowetting display.

[0006] Specifically, it comprises a composite material and a pixel wall;

[0007] The composite material comprises a cellulose-based dielectric layer and a hydrophobic layer coated on the cellulose-based dielectric layer;

[0008] The pixel wall is above the hydrophobic layer;

[0009] When the height of the pixel wall is 3.0-3.5μm, the equivalent capacitance of the composite material is 35-81μF / m 2 ;

[0010] When the height of the pixel wall is 5.0-5.5μm, the equivalent capacitance of the composite material is 58-81μF / m 2.

[0011] Preferably, when the height of the pixel wall is 3.5 μm, the equivalent capacitance of the composite material is 35-81 μF / m 2 .

[0012] Further preferably, when the height of the pixel wall is 3.5 μm, the equivalent capacitance of the composite material is 35.1-80.2 μF / m 2 .

[0013] Preferably, when the height of the pixel wall is 5.5 μm, the equivalent capacitance of the composite material is 58-81 μF / m 2 .

[0014] Further preferably, when the height of the pixel wall is 5.5 μm, the equivalent capacitance of the composite material is 58.3-80.2 μF / m 2 .

[0015] Preferably, the effective dielectric constant of the composite material is 3-8 C 2 / (N·M 2 )。

[0016] Further preferably, the effective dielectric constant of the composite material is 3.5-8 C 2 / (N·M 2 )。

[0017] More further preferably, the effective dielectric constant of the composite material is 3.5-7.9 C 2 / (N·M 2 )。

[0018] Preferably, the thickness of the cellulose-based dielectric layer is 200-1000 nm.

[0019] Preferably, when the height of the pixel wall is 3.0-3.5 μm, the thickness of the hydrophobic layer is 200-400 nm;

[0020] When the height of the pixel wall is 5.0-5.5 μm, the thickness of the hydrophobic layer is 200-205 nm.

[0021] Further preferably, when the height of the pixel wall is 3.5 μm, the thickness of the hydrophobic layer is 200-400 nm;

[0022] When the height of the pixel wall is 5.5 μm, the thickness of the hydrophobic layer is 200-205 nm.

[0023] More further preferably, when the height of the pixel wall is 3.5 μm, the thickness of the hydrophobic layer is 200-400 nm;

[0024] When the height of the pixel wall is 5.5 μm, the thickness of the hydrophobic layer is 200 nm.

[0025] Preferably, the material of the cellulose dielectric layer comprises at least one of cyanoethyl cellulose, hydroxypropyl cellulose, and cellulose acetate.

[0026] Preferably, the material of the hydrophobic layer comprises any one of amorphous polytetrafluoroethylene, perfluorocyclic polymer, and polytetrafluoroethylene.

[0027] Further preferably, the amorphous polytetrafluoroethylene is Hyflon AD 40.

[0028] Further preferably, the perfluorocyclic polymer is Cytop.

[0029] Further preferably, the polytetrafluoroethylene is Teflon.

[0030] The second aspect of the present application provides a method for preparing an electrowetting display.

[0031] Specifically, the method comprises the following steps:

[0032] (1) dissolving a material of a cellulose dielectric layer in a solvent, preparing the cellulose dielectric layer by multi-step spin coating, pre-curing, and heating; dissolving a material of a hydrophobic layer in a solvent to prepare a hydrophobic layer coating solution, spin coating the hydrophobic layer coating solution on the surface of the cellulose dielectric layer, and preparing the composite material by pre-curing and heating;

[0033] (2) performing hydrophilic treatment on the hydrophobic layer in the composite material, pre-curing by a hot plate, and performing mask exposure molding by a photolithography process to prepare a pixel wall on the hydrophobic layer;

[0034] (3) forming a pixel grid structure by the pixel wall, placing the pixel wall on a hot plate for secondary curing, developing by configuring a developing solution, cleaning, restoring the hydrophobicity of the hydrophobic layer by high-temperature reflow, filling with colored ink in a pure water environment, and packaging to prepare the electrowetting display.

[0035] Preferably, in step (2), the time for mask exposure molding is 10-50 s.

[0036] Further preferably, in step (2), the time for mask exposure molding is 10-30 s.

[0037] Preferably, in step (3), the developing solution comprises a KOH solution.

[0038] Preferably, the concentration of the KOH solution is 0.1-0.6 wt%.

[0039] Further preferably, the concentration of the KOH solution is 0.4-0.6wt%.

[0040] Further more preferably, the concentration of the KOH solution is 0.4wt%.

[0041] Compared with the prior art, the present application has the following advantages:

[0042] The present application controls the equivalent capacitance C eq and the effective dielectric constant by designing the thickness of the single-layer or multi-layer dielectric hydrophobic material, thereby providing a design criterion for the multi-layer dielectric hydrophobic material for the subsequent low driving voltage device research. When the pixel wall height is 3.5μm and the fixed CEC layer is 650nm, and the thickness of the HF layer is reduced from 400nm, 300nm to 200nm, V d can be reduced from 17V, 14V to 9V. Therefore, the enhancement of the equivalent capacitance C eq plays a decisive role in reducing the driving voltage. BRIEF DESCRIPTION OF DRAWINGS

[0043] Figure 1 is the electrowetting curve diagram of the double-layer composite material structure with different thickness combinations;

[0044] Figure 2 is the structural schematic diagram of the electrowetting display of Example 1;

[0045] Figure 3 is the corresponding aperture ratio diagram of the EWD device with different CEC layer thicknesses under the application of different voltages;

[0046] Figure 4 is the corresponding aperture ratio diagram of the EWD device with different combinations of double layers under the application of different voltages;

[0047] Figure 5 is the C-V curve diagram of the double-layer composite material structure EWD device with different pixel wall heights;

[0048] Figure 6 is the comparison diagram of the equivalent capacitance (C eq ) of the different double-layer composite material structures and the applied voltage capacitance value (C dv ) of the EWD device. DETAILED DESCRIPTION

[0049] In order to make the skilled in the art more clearly understand the technical solutions described in the present application, the following examples are listed for illustration. It should be pointed out that the following examples do not constitute a limitation on the scope of protection required by the present application.

[0050] The raw materials, reagents or devices used in the following examples, unless otherwise specified, can be obtained from conventional commercial channels or can be obtained by known methods.

[0051] Example 1

[0052] An electrowetting display with low driving voltage and a preparation method thereof.

[0053] An electrowetting display with low driving voltage, comprising a composite material and a pixel wall; the composite material comprises a cyanoethyl cellulose dielectric layer and a Hyflon hydrophobic layer coated on the cyanoethyl cellulose dielectric layer; the pixel wall is above the Hyflon hydrophobic layer. The height of the pixel wall is 3.5 μm, the equivalent capacitance of the composite material is 80.2 μF / m 2 , and the effective dielectric constant of the composite material is 3.62 C 2 / (N·M 2 ). The thickness of the cyanoethyl cellulose dielectric layer is 200 nm, and the thickness of the Hyflon hydrophobic layer is 200 nm.

[0054] Preparation method:

[0055] (1) Dissolve the cyanoethyl cellulose fibrous solid in a DMF solvent, place it in an ultrasonic magnetic stirrer at 800 rpm for 1 h, place it on a 40℃ hot plate for 10 min, let it stand for 8 h, filter it through 2 times of 1 μm organic filter membrane, and prepare a 3 wt% cyanoethyl cellulose dielectric layer coating solution;

[0056] Before spin coating, the solution can be ultrasonically treated for 10 min, and at the same time, the air dust that may be carried on the ITO glass (impurities affecting the spin coating film) can be blown away by a nitrogen gun, and the ITO glass (TP-120, thickness 0.7 mm, resistance 120 Ω) is prepared as a spin coating substrate, and a substrate pretreatment step is performed. The substrate pretreatment (the ITO glass is placed in ultrapure water / alcohol for 10 min ultrasonic cleaning twice, and after each cleaning, it is blown dry with a nitrogen gun, and after cleaning, it is transferred to an ultraviolet ozone cleaning machine for 10 min of ultraviolet light and ozone oxidation reaction cleaning (to remove organic contaminants on the ITO surface and to hydroxylate the ITO substrate surface));

[0057] The solution is prepared by multi-step spin coating (spin coating at 300 rpm for 10 s, and then spin coating at 1200 rpm for 65 s), first pre-solidification (pre-solidification treatment by placing it on a 40℃ hot plate for 3 min), and first heating (heating in a dust-free oven at 160℃ for 1.5 h) to volatilize residual organic solvents, to obtain a 200 nm cyanoethyl cellulose dielectric layer;

[0058] Hyflon AD 40 powder was dissolved in Galden D02 solvent to prepare a 3wt% hydrophobic layer coating solution. The solution was treated with ultrasound for 10 minutes, and then spin-coated on the surface of the 200nm cyanoethyl cellulose dielectric layer by multi-step spin coating (spin-coated at 300rpm for 10s, and then spin-coated at 2400rpm for 65s). The spin-coating time was 65s, and the solution was left to stand for 10 minutes after spin-coating. The composite material was prepared by second pre-curing (pre-cured on a hot plate at 85℃ for 1.5min) and second heating (heated in a dust-free oven at 185℃ for 1h) to volatilize residual organic solvents.

[0059] (2) The composite material was subjected to hydrophilic treatment by modifying the hydrophobic layer using a reactive ion etching machine (power: 5w, time: 6s). A pixel wall was prepared by spin-coating an HN-008 photoresist solution by multi-step spin coating (spin-coated at 500rpm for 10s, and then spin-coated at 1100rpm for 65s). After pre-curing on a hot plate (temperature: 110℃, time: 2.5min), the pixel wall was subjected to 18s mask exposure forming by photolithography (to prepare a pixel wall with a height of 3.5μm), and then subjected to secondary curing on a hot plate (temperature: 110℃, time: 2.5min). A 0.4wt% KOH solution was used as a developing solution, and the pixel wall was developed for 1min. The pixel wall was cleaned by the reactive ion etching machine again to remove residual photoresist and developing solution, and then developed again. After the above steps, the pixel wall was subjected to high-temperature reflow to restore the hydrophobicity of the hydrophobic layer. Finally, the pixel wall was filled with colored ink in a pure water environment, and the prepared upper substrate (ITO glass) was encapsulated with a frame to prepare an electrowetting display.

[0060] Example 2

[0061] An electrowetting display with low driving voltage and a preparation method thereof.

[0062] An electrowetting display with low driving voltage, comprising a composite material and a pixel wall. The composite material comprises a cyanoethyl cellulose dielectric layer and a Hyflon hydrophobic layer coated on the cyanoethyl cellulose dielectric layer. The pixel wall is above the Hyflon hydrophobic layer. The height of the pixel wall is 3.5μm, the equivalent capacitance of the composite material is 66.2μF / m 2 , and the effective dielectric constant of the composite material is 6.36C 2 / (N·M 2 ). The thickness of the cyanoethyl cellulose dielectric layer is 650nm, and the thickness of the Hyflon hydrophobic layer is 200nm.

[0063] Preparation method:

[0064] The difference from example 1 is that the solution in step (1) is replaced by 6wt% cyanoethyl cellulose dielectric layer coating solution, and the rotation speed of multi-step spin coating in step (1) is replaced, and the solution is prepared by multi-step spin coating (spin coating for 10s at a rotation speed of 300rpm, and then spin coating for 65s at a rotation speed of 1100rpm) to obtain a 650nm cyanoethyl cellulose dielectric layer.

[0065] Example 3

[0066] An electrowetting display with low driving voltage and a preparation method thereof.

[0067] An electrowetting display with low driving voltage, comprising a composite material and a pixel wall; the composite material comprises a cyanoethyl cellulose dielectric layer and a Hyflon hydrophobic layer coated on the cyanoethyl cellulose dielectric layer; the pixel wall is above the Hyflon hydrophobic layer. The height of the pixel wall is 3.5μm, the equivalent capacitance of the composite material is 58.3μF / m 2 , and the effective dielectric constant of the composite material is 7.90C 2 / (N·M 2 ). The thickness of the cyanoethyl cellulose dielectric layer is 1000nm, and the thickness of the Hyflon hydrophobic layer is 200nm.

[0068] Preparation method:

[0069] The difference from example 1 is that the solution in step (1) is replaced by 6wt% cyanoethyl cellulose dielectric layer coating solution, and the rotation speed of multi-step spin coating in step (1) is replaced, and the solution is prepared by multi-step spin coating (spin coating for 10s at a rotation speed of 300rpm, and then spin coating for 65s at a rotation speed of 700rpm) to obtain a 1000nm cyanoethyl cellulose dielectric layer.

[0070] Example 4

[0071] An electrowetting display with low driving voltage and a preparation method thereof.

[0072] An electrowetting display with low driving voltage, comprising a composite material and a pixel wall; the composite material comprises a cyanoethyl cellulose dielectric layer and a Hyflon hydrophobic layer coated on the cyanoethyl cellulose dielectric layer; the pixel wall is above the Hyflon hydrophobic layer. The height of the pixel wall is 3.5μm, the equivalent capacitance of the composite material is 51.8μF / m 2 , and the effective dielectric constant of the composite material is 4.1C 2 / (N·M 2 ). The thickness of the cyanoethyl cellulose dielectric layer is 400nm, and the thickness of the Hyflon hydrophobic layer is 300nm.

[0073] Preparation method:

[0074] The difference from Example 1 is that the solution in step (1) is replaced with 5wt% cyanoethyl cellulose dielectric layer coating solution, and the rotation speed of multi-step spin coating in step (1) is replaced, and the solution is prepared by multi-step spin coating (spin coating for 10s at a rotation speed of 2200rpm, and then spin coating for 65s at a rotation speed of 1500rpm) to obtain a 400nm cyanoethyl cellulose dielectric layer.

[0075] Meanwhile, the single-step rotation speed spin coating of the hydrophobic layer coating solution is replaced, and the surface of the 400nm cyanoethyl cellulose dielectric layer is spin coated at a rotation speed of 1200rpm (65s), and after standing, pre-curing and volatilizing the residual organic solvent in the dust-free oven, a 300nm Hyflon hydrophobic layer is completed, and the composite material is prepared.

[0076] Example 5

[0077] An electrowetting display with low driving voltage and a preparation method thereof.

[0078] The electrowetting display with low driving voltage comprises a composite material and a pixel wall; the composite material comprises a cyanoethyl cellulose dielectric layer and a Hyflon hydrophobic layer coated on the cyanoethyl cellulose dielectric layer; and the pixel wall is above the Hyflon hydrophobic layer. The height of the pixel wall is 3.5μm, the equivalent capacitance of the composite material is 48.2μF / m 2 , and the effective dielectric constant of the composite material is 5.17C 2 / (N·M 2 ). The thickness of the cyanoethyl cellulose dielectric layer is 650nm, and the thickness of the Hyflon hydrophobic layer is 300nm.

[0079] Preparation method:

[0080] The difference from Example 2 is that the single-step rotation speed spin coating of the hydrophobic layer coating solution is replaced, and the surface of the 650nm cyanoethyl cellulose dielectric layer is spin coated at a rotation speed of 1200rpm (65s), and after standing, pre-curing and volatilizing the residual organic solvent in the dust-free oven, a 300nm Hyflon hydrophobic layer is completed, and the composite material is prepared.

[0081] Example 6

[0082] An electrowetting display with low driving voltage and a preparation method thereof.

[0083] The electrowetting display with low driving voltage comprises a composite material and a pixel wall; the composite material comprises a cyanoethyl cellulose dielectric layer and a Hyflon hydrophobic layer coated on the cyanoethyl cellulose dielectric layer; and the pixel wall is above the Hyflon hydrophobic layer. The height of the pixel wall is 3.5μm, the equivalent capacitance of the composite material is 48.2μF / m 2, the effective dielectric constant of the composite material is 6.44C 2 / (N·M 2 ). The thickness of the cyanoethyl cellulose dielectric layer is 1000 nm, and the thickness of the Hyflon hydrophobic layer is 300 nm.

[0084] Preparation method:

[0085] The difference from Example 4 is that the solution in step (1) is replaced with a 6wt% cyanoethyl cellulose dielectric layer coating solution, and the rotation speed of the multi-step spin coating in step (1) is replaced. The solution is prepared by multi-step spin coating (spin coating for 10s at a rotation speed of 300rpm, and then spin coating for 65s at a rotation speed of 700rpm) to obtain a 1000nm cyanoethyl cellulose dielectric layer.

[0086] Example 7

[0087] A low driving voltage electrowetting display and a preparation method thereof.

[0088] The low driving voltage electrowetting display comprises a composite material and a pixel wall; the composite material comprises a cyanoethyl cellulose dielectric layer and a Hyflon hydrophobic layer coated on the cyanoethyl cellulose dielectric layer; and the pixel wall is above the Hyflon hydrophobic layer. The height of the pixel wall is 3.5μm, and the equivalent capacitance of the composite material is 37.9μF / m 2 , and the effective dielectric constant of the composite material is 4.49C 2 / (N·M 2 ). The thickness of the cyanoethyl cellulose dielectric layer is 650nm, and the thickness of the Hyflon hydrophobic layer is 400nm.

[0089] Preparation method:

[0090] The difference from Example 2 is that a hydrophobic layer coating solution is used, and the rotation speed of the single-step spin coating is replaced. The surface of the 650nm cyanoethyl cellulose dielectric layer is spin coated at a rotation speed of 720rpm (65s), and after standing, pre-curing and volatilizing the residual machine solvent in the dust-free oven, a 400nm Hyflon hydrophobic layer is completed to prepare the composite material.

[0091] Example 8

[0092] A low driving voltage electrowetting display and a preparation method thereof.

[0093] The low driving voltage electrowetting display comprises a composite material and a pixel wall; the composite material comprises a cyanoethyl cellulose dielectric layer and a Hyflon hydrophobic layer coated on the cyanoethyl cellulose dielectric layer; and the pixel wall is above the Hyflon hydrophobic layer. The height of the pixel wall is 3.5μm, and the equivalent capacitance of the composite material is 35.1μF / m 2 , and the effective dielectric constant of the composite material is 5.56C2 (N·M 2 ). The thickness of the cyanoethyl cellulose dielectric layer was 1000 nm, and the thickness of the Hyflon hydrophobic layer was 400 nm.

[0094] Preparation method:

[0095] The difference from Example 7 was that the solution in step (1) was replaced with a 6wt% cyanoethyl cellulose dielectric layer coating solution, and the rotation speed of the multi-step spin coating was replaced. The solution was prepared by multi-step spin coating (spin coating for 10s at a rotation speed of 300rpm, and then spin coating for 65s at a rotation speed of 700rpm) to obtain a 1000nm cyanoethyl cellulose dielectric layer.

[0096] Example 9

[0097] An electrowetting display with low driving voltage and a preparation method thereof.

[0098] An electrowetting display with low driving voltage, comprising a composite material and a pixel wall; the composite material comprises a cyanoethyl cellulose dielectric layer and a Hyflon hydrophobic layer coated on the cyanoethyl cellulose dielectric layer; the pixel wall is above the Hyflon hydrophobic layer. The height of the pixel wall is 5.5μm, and the equivalent capacitance of the composite material is 80.2μF / m 2 , and the effective dielectric constant of the composite material is 3.62C 2 / (N·M 2 ). The thickness of the cyanoethyl cellulose dielectric layer was 200nm, and the thickness of the Hyflon hydrophobic layer was 200nm.

[0099] Preparation method:

[0100] The difference from Example 1 was that in the preparation of the pixel wall, the rotation speed of the spin coating HN-008 photoresist solution was changed, and the solution was prepared by single-step spin coating at a rotation speed of 580rpm for 65s to prepare a thicker 5.5μm pixel wall.

[0101] Example 10

[0102] An electrowetting display with low driving voltage and a preparation method thereof.

[0103] An electrowetting display with low driving voltage, comprising a composite material and a pixel wall; the composite material comprises a cyanoethyl cellulose dielectric layer and a Hyflon hydrophobic layer coated on the cyanoethyl cellulose dielectric layer; the pixel wall is above the Hyflon hydrophobic layer. The height of the pixel wall is 5.5μm, and the equivalent capacitance of the composite material is 67.5μF / m 2 , and the effective dielectric constant of the composite material is 6.10C 2 / (N·M 2) and the thickness of the Hyflon hydrophobic layer is 200 nm.

[0104] Preparation method:

[0105] The difference from Example 9 is that the solution in step (1) is replaced by a 6wt% cyanethyl cellulose dielectric layer coating solution, and the rotation speed of multi-step spin coating in step (1) is replaced, and the solution is prepared by multi-step spin coating (spin coating for 10s at a rotation speed of 300 rpm, and then spin coating for 65s at a rotation speed of 1200 rpm) to obtain a 600nm cyanethyl cellulose dielectric layer.

[0106] Example 11

[0107] An electrowetting display with low driving voltage and a preparation method thereof.

[0108] An electrowetting display with low driving voltage, comprising a composite material and a pixel wall; the composite material comprises a cyanethyl cellulose dielectric layer and a Hyflon hydrophobic layer coated on the cyanethyl cellulose dielectric layer; the pixel wall is above the Hyflon hydrophobic layer. The height of the pixel wall is 5.5μm, the equivalent capacitance of the composite material is 58.3μF / m 2 , and the effective dielectric constant of the composite material is 7.90C 2 / (N·M 2 ). The thickness of the cyanethyl cellulose dielectric layer is 1000nm, and the thickness of the Hyflon hydrophobic layer is 200nm.

[0109] Preparation method:

[0110] The difference from Example 9 is that the solution in step (1) is replaced by a 6wt% cyanethyl cellulose dielectric layer coating solution, and the rotation speed of multi-step spin coating in step (1) is replaced, and the solution is prepared by multi-step spin coating (spin coating for 10s at a rotation speed of 300 rpm, and then spin coating for 65s at a rotation speed of 1200 rpm) to obtain a 600nm cyanethyl cellulose dielectric layer.

[0111] Comparative Example 1

[0112] An electrowetting display with low driving voltage and a preparation method thereof.

[0113] An electrowetting display with low driving voltage, comprising a composite material and a pixel wall; the composite material comprises a cyanethyl cellulose dielectric layer and a Hyflon hydrophobic layer coated on the cyanethyl cellulose dielectric layer; the pixel wall is above the Hyflon hydrophobic layer. The height of the pixel wall is 5.5μm, the equivalent capacitance of the composite material is 58.3μF / m 2 , and the effective dielectric constant of the composite material is 7.90C 2 / (N·M 2) and the thickness of the Hyflon hydrophobic layer is 400 nm.

[0114] Preparation method:

[0115] The difference from Example 9 is that the hydrophobic layer coating solution is used, and the rotation speed of single-step spin coating is changed to 720 rpm (65 s) to spin coat on the surface of the 200 nm cyanoethyl cellulose dielectric layer. After standing, pre-curing and volatilizing the residual machine solvent in the dust-free oven, a 400 nm Hyflon hydrophobic layer is completed to prepare the composite material.

[0116] Comparative Example 2

[0117] An electrowetting display with low driving voltage and a preparation method thereof.

[0118] An electrowetting display with low driving voltage, comprising a composite material and a pixel wall; the composite material comprises a cyanoethyl cellulose dielectric layer and a Hyflon hydrophobic layer coated on the cyanoethyl cellulose dielectric layer; the pixel wall is above the Hyflon hydrophobic layer. The height of the pixel wall is 5.5 μm, the equivalent capacitance of the composite material is 40.1 μF / m 2 , and the effective dielectric constant of the composite material is 3.62 C 2 / (N·M 2 ). The thickness of the cyanoethyl cellulose dielectric layer is 400 nm, and the thickness of the Hyflon hydrophobic layer is 400 nm.

[0119] Preparation method:

[0120] The difference from Comparative Example 1 is that the solution in step (1) is changed to a 5wt% cyanoethyl cellulose dielectric layer coating solution, and the rotation speed of multi-step spin coating is changed. The solution is prepared by multi-step spin coating (first spin coating for 10 s at a rotation speed of 300 rpm, and then spin coating for 65 s at a rotation speed of 1500 rpm) to prepare a 400 nm cyanoethyl cellulose dielectric layer.

[0121] Comparative Example 3

[0122] An electrowetting display with low driving voltage and a preparation method thereof.

[0123] An electrowetting display with low driving voltage, comprising a composite material and a pixel wall; the composite material comprises a cyanoethyl cellulose dielectric layer and a Hyflon hydrophobic layer coated on the cyanoethyl cellulose dielectric layer; the pixel wall is above the Hyflon hydrophobic layer. The height of the pixel wall is 5.5 μm, the equivalent capacitance of the composite material is 37.9 μF / m 2 , and the effective dielectric constant of the composite material is 4.49 C 2 / (N·M 2) and the thickness of the Hyflon hydrophobic layer is 400 nm.

[0124] Preparation method:

[0125] The difference from Comparative Example 1 is that the solution in step (1) is replaced by a 6wt% cyanethyl cellulose dielectric layer coating solution, and the rotation speed of multi-step spin coating is replaced, and the solution is prepared by multi-step spin coating (spin coating for 10s at a rotation speed of 300 rpm, and then spin coating for 65s at a rotation speed of 1100 rpm) to obtain a 650nm cyanethyl cellulose dielectric layer.

[0126] Comparative Example 4

[0127] An electrowetting display with low driving voltage and a preparation method thereof.

[0128] An electrowetting display with low driving voltage, comprising a composite material and a pixel wall; the composite material comprises a cyanethyl cellulose dielectric layer and a Hyflon hydrophobic layer coated on the cyanethyl cellulose dielectric layer; the pixel wall is above the Hyflon hydrophobic layer. The height of the pixel wall is 5.5μm, the equivalent capacitance of the composite material is 35.1μF / m 2 , and the effective dielectric constant of the composite material is 5.56C 2 / (N·M 2 ). The thickness of the cyanethyl cellulose dielectric layer is 1000nm, and the thickness of the Hyflon hydrophobic layer is 400nm.

[0129] Preparation method:

[0130] The difference from Comparative Example 1 is that the solution in step (1) is replaced by a 6wt% cyanethyl cellulose dielectric layer coating solution, and the rotation speed of multi-step spin coating is replaced, and the solution is prepared by multi-step spin coating (spin coating for 10s at a rotation speed of 300 rpm, and then spin coating for 65s at a rotation speed of 1100 rpm) to obtain a 650nm cyanethyl cellulose dielectric layer.

[0131] Comparative Example 5

[0132] An electrowetting display with low driving voltage and a preparation method thereof.

[0133] An electrowetting display with low driving voltage, comprising a Hyflon hydrophobic layer and a pixel wall; the pixel wall is above the Hyflon hydrophobic layer. The height of the pixel wall is 3.5μm, and the equivalent capacitance is 25.3μF / m 2 , and the effective dielectric constant is 2.00C 2 / (N·M 2 ). The thickness of the Hyflon hydrophobic layer is 700nm.

[0134] Preparation method:

[0135] Hyflon AD 40 powder was dissolved in Galden D02 solvent to prepare a 3wt% hydrophobic layer coating solution.

[0136] The solution was ultrasonically treated for 10 minutes before spin coating, and air dust possibly carried by the ITO glass (impurities affecting film formation by spin coating) was blown off using a nitrogen gun. The ITO glass (TP-120, thickness 0.7 mm, resistance 120 Ω) was prepared as a spin coating substrate, and a substrate pretreatment step was performed. The ITO glass was ultrasonically cleaned twice in ultrapure water / alcohol for 10 minutes each time, and after each cleaning, the ITO glass was blown dry using a nitrogen gun. After cleaning, the ITO glass was transferred to an ultraviolet ozone cleaner and subjected to ultraviolet light and ozone oxidation reaction cleaning for 10 minutes (to remove organic contaminants on the ITO surface and to hydroxylate the ITO substrate surface).

[0137] The 3wt% hydrophobic layer coating solution was ultrasonically treated for 10 minutes, and then the 3wt% hydrophobic layer coating solution was spin coated at a speed of 340 rpm on the surface of the 200 nm cyanoethyl cellulose dielectric layer. The spin coating time was 65 seconds, and after spin coating, the solution was left to stand for 10 minutes. A second pre-curing step (pre-curing treatment by placing the solution on a hot plate at 85°C for 1.5 minutes) and a second heating step (heating in a dust-free oven at 185°C for 1 hour) were performed to volatilize residual organic solvents, thereby preparing a composite material.

[0138] Comparative Example 6

[0139] A composite material.

[0140] The solution was ultrasonically treated for 10 minutes before spin coating, and air dust possibly carried by the ITO glass (impurities affecting film formation by spin coating) was blown off using a nitrogen gun. The ITO glass (TP-120, thickness 0.7 mm, resistance 120 Ω) was prepared as a spin coating substrate, and a substrate pretreatment step was performed. The ITO glass was ultrasonically cleaned twice in ultrapure water / alcohol for 10 minutes each time, and after each cleaning, the ITO glass was blown dry using a nitrogen gun. After cleaning, the ITO glass was transferred to an ultraviolet ozone cleaner and subjected to ultraviolet light and ozone oxidation reaction cleaning for 10 minutes (to remove organic contaminants on the ITO surface and to hydroxylate the ITO substrate surface).

[0141] The HN-018 solution was spin coated at a speed of 1750 rpm for 65 seconds in a single step, and a pre-curing step (pre-curing treatment by placing the solution on a hot plate at 110°C for 2.5 minutes) was performed. After pre-curing, the solution was exposed to light for 35 seconds using a photoetching machine, and a first heating step (heating in a dust-free oven at 190°C for 1.5 hours) was performed to volatilize residual organic solvents, thereby preparing a 400 nm HN-018 dielectric layer.

[0142] Hyflon AD 40 powder was dissolved in Galden D02 solvent to prepare a 3wt% hydrophobic layer coating solution. The solution was treated with ultrasound for 10 min, and then spin-coated on the surface of the 200 nm cyanoethyl cellulose dielectric layer at a speed of 720 rpm for 65 s. After standing for 10 min, the solution was pre-solidified for the second time (pre-solidification treatment was performed by placing it on a hot plate at 85°C for 1.5 min), and then heated for the second time (heating was performed by placing it in a dust-free oven at 185°C for 1 h) to volatilize the residual organic solvent, thereby completing a 400 nm Hyflon layer. Thus, a (400HN+400HF) composite material was prepared.

[0143] Comparative Example 7

[0144] A composite material.

[0145] The difference from Comparative Example 6 is that a Hyflon solution was used, and the spin-coating speed of the single-step spin-coating was changed to 1200 rpm (65 s) to spin-coat on the surface of the 400 nm HN-018 dielectric layer. After standing, pre-solidification, and volatilization of the residual organic solvent in a dust-free oven, a 400 nm Hyflon hydrophobic layer was completed, thereby preparing a (400HN+300HF) composite material.

[0146] Performance detection:

[0147] 1. Opening rate (R open ) detection:

[0148] An LCR digital bridge tester (TH2828) was used to record the capacitance-voltage (C-V) curve, and the voltage was increased at a speed of 1 V / step. A custom device composed of a microscope, a wireless power source, and a light source was used to measure the opening rate. A program created using Visual Studio 2018 was used to calculate the data to obtain the opening rate where A Oil(V) is the area occupied by the oil when V is applied on the electrowetting display device, and A Pixel is the total area of the pixel.

[0149] 2. Driving voltage (V d ) detection:

[0150] The driving voltage is the voltage at which the opening rate reaches 60%. The specific detection method is as follows: a picoammeter (model 6487, Keithley) was used as a direct current power source, the voltage was set to a linear voltage, the interval was 250 ms, and it was tested whether it could open to 60% from a low voltage. When the linear voltage applied caused the opening rate detection to exceed 60%, the voltage and opening rate data were recorded.

[0151] Table 1 Opening rate and driving voltage results of each example and comparative example

[0152] Table 1 Opening rate and driving voltage results of each example and comparative example R open (%)]] V d (V) <!-- 8 -->]]> Example 1 61.9 9 Example 2 62.1 9 Example 3 60.4 9 Example 4 61.4 14 Example 5 61.1 14 Example 6 61.2 14 Example 7 60.3 17 Example 8 61.5 17 Example 9 61.4 13 Example 10 62.7 15 Example 11 60.8 15 Comparative Example 1 60.3 23 Comparative Example 2 62.2 23 Comparative Example 3 61.3 23 Comparative Example 4 60.2 23 Comparative Example 5 60.8 25

[0153] In the electrowetting curve, Figure 1 In (a) of the present application, the electrowetting (EWOD) curves of different thicknesses of the bilayer medium were compared. When the total thickness was about 800 nm, the combination of 200 / 600 nm of the Hyflon hydrophobic layer / cyanoethyl cellulose dielectric layer (hereinafter abbreviated as HF layer / CEC layer) bilayer showed better electrowetting performance. The combination of a thinner HF layer and a thicker CEC dielectric layer improved the overall wetting performance of the bilayer structure. Under the application of a voltage of 60 V, the contact angle was modulated to 65.1°. This can be further applied to the EWOD system to achieve a θ CA (from 116.3° to 65.1°). Figure 1 (b) of the present application shows that, without changing the thickness of the HF layer, the electrowetting curves of three different thicknesses of the CEC layer were compared. The bilayer with a thinner total thickness has a lower voltage threshold for the change of the droplet, but the overall electrowetting curve is similar. The change of the CEC layer does not have as great an effect on the electrowetting curve as the change of the HF layer, but the introduction of the CEC layer significantly improves the EWOD performance, from Figure 1 (c) and (d) show that the bilayer HF / CEC structure and the bilayer HF / HN-018 (HN) have similar reversible electrowetting behavior and low hysteresis characteristics, but the optimized 200 nm HF / 600 nm CEC bilayer has a better electrowetting curve, showing better contact angle modulation.

[0154] From the comparison of the aperture ratios of the electrowetting display (EWD device) with different layer thicknesses, it can be seen that, in the case of Figure 3 In (b) of the present application, the driving voltage of the EWD device with three different thicknesses of the CEC layer changes little when the thickness of the HF layer is fixed, which also corresponds to the trend of Figure 1 (b) of the present application. And from Figure 4 It can be seen that, when the thickness of the CEC layer is kept constant, the driving voltage and the opening voltage of the bilayer EWD device are greatly reduced by reducing the thickness of the HF layer, which proves that reducing the thickness of the HF layer can effectively improve the performance. The driving voltage of the device with the optimized 200 nm HF / 600 nm CEC bilayer structure can be reduced to 9 V, which indicates that this system will be possible to apply the widely used liquid crystal display (LCD) driving IC technology, greatly promoting the update of the EWD device driving IC.

[0155] Figure 5 are C-V curve diagrams of the bilayer structure EWD devices with different pixel wall heights, showing the capacitance curve of the EWD device under the application of a voltage. Among them Figure 5The CEC thickness has less influence on the C-V curve of the double-layer EWD device when the HF thickness is normal. Figure 5 The (e) and (f) verify the importance of the HF thickness, when the CEC layer thickness is constant, the HF layer thickness plays a decisive role in the equivalent capacitance, thus affecting the driving voltage.

[0156] The present study found that by increasing the equivalent capacitance and effective dielectric constant of the double-layer dielectric hydrophobic material, the driving voltage of the electrowetting display device can be reduced, and a theoretical basis for reducing the driving voltage is proposed. The relationship between the specific dielectric constant and the capacitance can be described according to the electrowetting Young-Lippanman equation and the series equivalent capacitor equation:

[0157] As can be seen from the above formula, the ability to achieve large contact angle changes at low voltage is highly dependent on the total capacitance C eq of the dielectric multilayer. Therefore, the present application calculates the equivalent capacitance (C eq ) and effective dielectric constant (ε R ) of the double-layer structure of different thicknesses to achieve the design of the dielectric hydrophobic double-layer functional material in the low driving voltage EWD device. From the derivation of formula (2), due to the calculation of the series capacitor, the equivalent capacitance value depends more on the thickness d HF of the hydrophobic layer HF, the thicker the HF layer, the smaller the equivalent capacitance, and the influence of the CEC layer thickness is less than that of the HF layer. Therefore, in the multilayer design, the layer with a small dielectric constant often plays a larger role. Thus, the EWD can be adapted to a wider range of display technology driving ICs, while reducing the driving voltage, which can make the device work at a lower voltage and also prevent dielectric breakdown problems in electronic devices.

[0158] In Table 1, we can see the cases of different device structures, after the equivalent capacitance Ceqand the effective dielectric constant are improved, such as the double-layer equivalent capacitor of 300nm HF / 400nm CEC in Example 4, its equivalent capacitance C eq can be calculated to be 51.8μF / m 2 , which is approximately equivalent to twice the 700nm HF in Comparative Example 5 with the same thickness, and the C eq value of the 700nm HF single layer is only 25.3μF / m 2 , and after optimization, such as the double-layer of 200nm HF / 600nm CEC in Example 10, C eq can reach a higher value of 67.5μF / m 2In Comparative Example 2, increasing the HF layer thickness by only 100 nm resulted in a decrease in the Ceq of the 400 nm HF / 400 nm CEC bilayer from 51.8 μF / m. 2 Reduced to 40.1 μF / m 2 The equivalent capacitance decreases and changes significantly. In Examples 5 and 6, increasing the CEC layer thickness by 250nm and 600nm respectively revealed changes in the corresponding double-layer CEC. eq The values ​​are 48.2 and 43.9 μF / m. 2 Although there was a decrease, the change was much smaller than that of the HF layer. The above results were calculated using formula (2), and the overall capacitance C of the EWD device was also tested. dv ,See Figure 6 It also showed the same trend as the theoretical calculation, verifying that the effective capacitance of the dielectric hydrophobic material plays a key role in the overall performance of the device.

[0159] Meanwhile, the effective dielectric constant in Table 1 can also be calculated using formula (2). For example, the dielectric constant of the 700nm HF monolayer in Comparative Example 5 is only 2.00. The dielectric constant of the 300nm HF / 400nm CEC double layer in Example 4 is 4.10, and the dielectric constant of the 200nm HF / 600nm CEC double layer in Example 10 is 6.10. In Comparative Example 2, increasing the HF layer thickness by only 100nm resulted in a decrease in the dielectric constant of the 400nm HF / 400nm CEC double layer from 4.10 to 3.62, indicating a lower effective dielectric constant. In Examples 5 and 6, increasing the CEC layer thickness by 250nm and 600nm resulted in effective dielectric constants of 5.17 and 6.44 for the corresponding double layers, respectively. The increase in dielectric constant can be derived from formula (1), which allows for modulation of the same contact angle at a lower voltage, but also encounters the problem of contact angle saturation. This explains why, for the same HF thickness, a thicker CEC double layer will have a lower opening voltage, allowing the contact angle to be driven at a lower voltage. After EWD device packaging is completed, EWD devices with higher capacitance and effective dielectric constant exhibit lower driving voltage. Equation (1) shows that increasing the effective dielectric constant of the composite material can reduce the driving voltage of the electrowetting device.

[0160] The preferred embodiments of the present invention have been described in detail above. It should be understood that those skilled in the art can make numerous modifications and variations based on the concept of the present invention without creative effort. Therefore, any technical solutions obtained by those skilled in the art through logical analysis, reasoning, or limited experimentation based on the concept of the present invention and on the existing technology should be within the scope of protection defined by the claims.

Claims

1. An electrowetting display with low driving voltage, characterized in that, The composite material and the pixel wall are included; The composite material includes a cellulose dielectric layer and a hydrophobic layer coated on the cellulose dielectric layer; The pixel wall is above the hydrophobic layer; When the height of the pixel wall is 3.0-3.5 μm, the thickness of the hydrophobic layer is 200-400 nm, and the equivalent capacitance of the composite material is 35-81 μF / m 2 ; When the height of the pixel wall is 5.0-5.5 μm, the thickness of the hydrophobic layer is 200-205 nm, and the equivalent capacitance of the composite material is 58-81 μF / m 2 .

2. The electrowetting display of claim 1, wherein, The effective dielectric constant of the composite material is 3-8 C 2 / (N·M 2 ).

3. The electrowetting display of claim 1, wherein, The cellulose dielectric layer has a thickness of 200-1000 nm.

4. The electrowetting display of claim 1, wherein, The material of the cellulose dielectric layer includes at least one of cyanoethyl cellulose, hydroxypropyl cellulose, and cellulose acetate.

5. The electrowetting display of claim 1, wherein, The material of the hydrophobic layer includes any one of amorphous polytetrafluoroethylene, perfluorocyclic polymer, and polytetrafluoroethylene.

6. A process characterized in that, A method for preparing the low driving voltage electrowetting display of any one of claims 1-5, comprising the following steps: (1) dissolving the material of the cellulose dielectric layer in a solvent, and preparing the cellulose dielectric layer by multi-step spin coating, pre-curing, and heating; dissolving the material of the hydrophobic layer in a solvent to prepare a hydrophobic layer coating solution, spin coating the hydrophobic layer coating solution on the surface of the cellulose dielectric layer, and preparing the composite material by pre-curing and heating; (2) performing hydrophilic treatment on the hydrophobic layer in the composite material, pre-curing by a hot plate, and forming a pixel wall on the hydrophobic layer by mask exposure through a photolithography process; (3) forming a pixel grid structure by the pixel wall, placing the pixel wall on a hot plate for secondary curing, developing by configuring a developing solution, cleaning, restoring the hydrophobicity of the hydrophobic layer by high-temperature reflow, filling with colored ink in a pure water environment, and packaging to prepare the electrowetting display.

7. The production method according to claim 6, wherein In step (2), the mask exposure forming time is 10-50 s.

8. The preparation method according to claim 6, characterized in that, In step (3), the developing solution includes a KOH solution.

9. The production method according to claim 8, characterized by, The concentration of the KOH solution is 0.1-0.6 wt%.

Images