CN107367836B - A kind of electrowetting device and preparation method thereof - Google Patents

Abstract

The invention belongs to the field of electrowetting, and discloses an electrowetting device, comprising an upper substrate and a lower substrate, a cavity formed by the upper substrate and the lower substrate facing each other is filled with packaging liquid, and the upper substrate includes an upper support plate, A first electrode and a pixel wall, the pixel wall is provided with an oil control structure, and the lower substrate includes a lower support plate, a second electrode, and a hydrophobic insulating layer. The invention also discloses a preparation method of the electrowetting device. The invention realizes the confinement of the ink by improving the method of the pixel grid structure, thereby preventing the aggregation of the ink. The thickness of the filling ink layer is limited by the oil control structure; the occurrence of overflow problem is reduced by adjusting the relative hydrophilicity and hydrophobicity of the oil control structure and the pixel wall layer; the addition of the oil control structure improves the ink uniformity in the packaging process.

Description

A kind of electrowetting device and preparation method thereof

technical field

The invention belongs to the field of electrowetting, in particular to an electrowetting device and a preparation method thereof.

Background technique

An electrowetting display device includes a fluid chamber and an electrode structure, wherein the fluid chamber contains a non-conductive first fluid (alkane, etc.), a conductive second fluid (water or salt solution), the fluids are in contact with each other and are immiscible. For example, patent CN102792207A describes an electrowetting display device, which includes two support plates, one of which is provided with a wall pattern, that is, a pixel wall. The pixel wall is made of photoresist substances (such as SU8) through a photolithography process. It is obtained that the area formed by the pixel grid enclosed by the pixel wall is the display area, and the electrowetting display device produces a display effect on this display area. The non-conductive first fluid is filled in the display area formed by the pixel walls, and the surrounding pixel walls are used to block the flow of the first fluid to the surrounding pixel cells, thereby obtaining a stable display structure.

Another electrowetting device is described in US patent US9274331B2, in which an electrode layer and a hydrophobic insulating layer are provided on one support plate, and an electrode layer and a very high pixel wall are provided on the other support plate. The electrowetting device is encapsulated after filling with non-polar ink and polar conductive fluid.

The hydrophobic insulating layer of the first electrowetting device needs to undergo hydrophilic treatment first, and then the pixel wall can be arranged on it, and then its hydrophobicity can be restored by high temperature reflow, so that the hydrophobicity of the hydrophobic insulating layer cannot be completely restored. , and the dislocation and damage to the hydrophobic insulating layer caused by the sliding of the pixel wall on the hydrophobic insulating layer during the high temperature process. The hydrophobic insulating layer of the second electrowetting device has not undergone the hydrophobic-hydrophilic-hydrophobic treatment and recovery process, and the properties are relatively stable.

However, in the electro-wetting structure of the second type of high pixel wall, when a voltage is applied, the inks of a plurality of pixel cells are easily aggregated together to form a mass of ink, which makes the display effect very uneven. Therefore, it is necessary to develop novel electrowetting device structures to solve these problems.

SUMMARY OF THE INVENTION

The object of the present invention is to provide an electrowetting device, which can achieve the confinement of the ink by improving the structure of the pixel grid, thereby preventing the aggregation of the ink.

Another object of the present invention is to provide a method for preparing an electrowetting device.

To achieve one of the above objects, the present invention adopts the following technical solutions:

An electrowetting device includes an upper substrate and a lower substrate, a cavity formed by the upper substrate and the lower substrate facing each other is filled with a packaging liquid, the upper substrate includes an upper support plate, a first electrode, a pixel wall, and a plastic frame, The pixel wall is provided with an oil control structure, and the lower substrate includes a lower support plate, a second electrode, and a hydrophobic insulating layer.

Further, the contact angle of the oil control structure is 30-90 degrees.

Further, the oil control structure is square, rectangular, cross or cylindrical.

Further, the height of the oil control structure is 1-10 μm.

Further, the oil control structure is located at the intersection of the pixel walls.

Further, the contact angle of the pixel wall is 10-80 degrees.

Further, the height of the pixel wall is 1-100 μm.

Further, the encapsulation liquid is a polar electrolyte solution and a non-polar solution.

A method for preparing the above-mentioned electrowetting device, comprising the following steps:

S1, arranging a second electrode on the lower support plate, and arranging a hydrophobic insulating layer on the second electrode;

S2, arranging a first electrode on the upper support plate, arranging a pixel wall on the first electrode, and arranging an oil control structure on the pixel wall;

S3, filling the packaging liquid, and bonding the upper substrate and the lower substrate.

The present invention has the following beneficial effects:

The invention realizes the confinement of the ink by improving the method of the pixel grid structure, thereby preventing the aggregation of the ink. The thickness of the filled ink layer is limited by the oil control structure; the occurrence of overflow problem is reduced by adjusting the relative hydrophilicity and hydrophobicity of the oil control structure and the pixel wall layer; the addition of the oil control structure improves the ink uniformity in the packaging process.

In a previous patent application of the applicant, based on the traditional electrowetting device structure, an oil control structure is arranged on the pixel wall located on the lower substrate. The ink is gathered to the oil control structure, so as to control the movement direction of the ink during the opening process. The present invention is aimed at the problems existing in the new electrowetting structure. The pixel wall of the new electrowetting structure is on the upper substrate, the pixel wall is very high, and the ink cannot be limited, and the ink is very easy to gather during the process of filling and opening the ink, so the oil control structure is provided. to prevent ink build-up. Therefore, the functions of the oil control structure in the two schemes are completely opposite. When the oil control structure is located in the pixel wall of the traditional electrowetting device, it is to promote the ink to gather, and when the oil control structure is located in the pixel wall of the new electrowetting device , to prevent ink build-up.

Description of drawings

1 is a schematic structural diagram of an existing electrowetting device;

Fig. 2 is the schematic diagram of existing electrowetting device ink climbing wall;

Fig. 3 is the electrowetting device structure schematic diagram of the present invention;

Fig. 4 is the schematic diagram of the ink climbing wall of the electrowetting device of the present invention;

5 is a top view of a pixel wall structure;

6 is a top view of the pixel wall and the cross-shaped oil control structure;

7 is a side view of a cross-shaped oil control structure and a pixel wall obtained by two lithography methods;

8 is a side view of a cross-shaped oil control structure and a pixel wall obtained by an etching method;

9 is a top view of the pixel wall and the cylindrical oil control structure;

10 is a side view of a cylindrical oil control structure and a pixel wall obtained by two photolithography methods;

11 is a side view of a cylindrical oil control structure and a pixel wall obtained by an etching method;

Fig. 12 is the technological process of preparing pixel wall and oil control structure by two-step photolithography;

13 is a top view of the first mask;

Figure 14 is a top view of a cross-shaped mask;

Figure 15 is a top view of a cylindrical mask;

FIG. 16 is a process flow for preparing a pixel wall and an oil control structure by a resist etching method;

Figure 17 is a top view of a cross-shaped mask;

Figure 18 is a top view of a cylindrical reticle;

FIG. 19 is a schematic diagram of the protective glue after exposure and development.

Detailed ways

The present invention will be further described below with reference to specific embodiments.

Example

Fig. 1 shows the structure of the existing electrowetting device. The upper support plate 1 is provided with a first electrode 2, a pixel wall 6 and a plastic frame 9, and a second electrode 4 and a hydrophobic insulating layer 5 are arranged on the lower support plate 3. After the non-polar liquid 7 and the polar liquid 8 are pasted, the upper and lower substrates are bonded together by the glue frame 9 .

FIG. 2 is a schematic diagram of the existing electrowetting device ink climbing the wall. The electrowetting structure is prone to wetting of the ink on the high wall, that is, the situation of climbing the wall, resulting in uneven oil film in the pixel grid.

3 is the improved electrowetting device structure, the support plate 1 is provided with a first electrode 2 and a pixel wall 6, the pixel wall 6 is provided with an oil control structure 10, and the lower support plate 3 is provided with a second electrode 4 and a hydrophobic After the insulating layer 5 is filled with the non-polar liquid 7 and the polar liquid 8 , the upper and lower substrates are bonded together through the plastic frame 9 .

The oil control structure 10 is required to have a certain degree of hydrophilicity, and the contact angle is preferably 30-90 degrees.

4 is a schematic diagram of the ink climbing wall of the electrowetting device of the present invention. The improved electrowetting structure has a gradient due to the hydrophilicity and hydrophobicity of the pixel wall and the oil control structure. Therefore, the wetting of the ink across the oil control structure to the pixel wall needs to overcome certain problems. Therefore, the height of the oil film edge is controlled by the oil control structure, and the obtained oil film uniformity is better.

FIG. 5 is a top view of the pixel wall structure, and the pixel wall 6 encloses the display area 11 .

The oil control structure is preferably located at the intersection of the pixel walls.

FIG. 6 is a top view of the pixel wall and the oil control structure of the improved electrowetting device, and the oil control structure 10 is in the shape of a cross. FIG. 7 is a side view of a cross-shaped oil control structure and pixel wall obtained by two photolithography methods, and FIG. 8 is a cross-shaped oil control structure (the oil control structure is the same as the pixel wall structure material) obtained by an etching method. side view.

The oil control structure can be cylindrical, as shown in FIG. 9 . Figure 10 is a side view of a cylindrical oil control structure and pixel wall obtained by two photolithography methods, Figure 11 is a cylindrical oil control structure (the oil control structure is the same as the pixel wall structure material) and the pixel wall obtained by an etching method. side view.

The oil control structure can also be a rectangle, a square, or the like.

Electrowetting device structures were prepared as follows:

1. The layout of the lower substrate:

First, an electrode layer (second electrode), such as ITO, Al, etc., is arranged on the surface of the lower support plate. The lower support plate can be made of glass of various thicknesses, or polymer materials, such as PET, PI, etc., or a rigid substrate. , can also be a flexible substrate. The electrode layer can be a whole-layer film, can also be patterned, and can even be a TFT layer. The arrangement of the electrode layers includes vacuum coating, vapor deposition, magnetron sputtering and other methods, which are similar to the coating methods in the LCD industry.

Then, a hydrophobic insulating layer, such as AF1600, Cytop, Parylene, etc., is arranged on the surface of the electrode layer (second electrode). Specifically, the solution of the hydrophobic insulating layer material is applied to the surface of the electrode layer by screen printing, spin coating, slit coating, blade coating, etc., and then the solvent in the hydrophobic insulating layer is removed by baking at high temperature, that is, A hydrophobic insulating layer film was obtained.

Second, the layout of the upper substrate:

An electrode layer (first electrode) is arranged on the surface of the upper support plate, such as ITO, Al, etc. The upper support plate can be made of glass of various thicknesses, or polymer materials, such as PET, PI, etc., or a rigid substrate, It can also be a flexible substrate. The arrangement of electrode layers includes vacuum coating, vapor deposition, magnetron sputtering, and the like.

Then, a pixel wall layer is arranged on the surface of the electrode layer (the first electrode), and the shape of the pixel wall can be square, rectangle, or other polygons and circles. Taking a square as an example, FIG. 3 is a top view of the structure of the pixel wall. The height of the pixel wall is 1-100 μm, preferably 10-80 μm, and more preferably 30-60 μm, considering not only the support of the pixel wall between the upper and lower plates, but also the thickness of the entire device.

Next, a layer of oil control structure is arranged on the surface of the pixel wall, such as the crisscross structure shown in FIG. 6 and the cylindrical structure shown in FIG. 9 . The height of the oil control structure is preferably 1-10 μm, more preferably 2-5 μm, which is related to the thickness of the ink.

3. Filling with non-polar liquid ink and polar liquid, and bonding the upper and lower substrates through a plastic frame to obtain an improved electrowetting device with an oil-controlling structure.

The arrangement of the pixel wall and the oil control structure includes two methods: two-step photolithography and resist etching.

FIG. 12 is a process flow of preparing pixel walls and oil control structures by two-step photolithography.

First, a layer of pixel wall material 6' is arranged on the surface of the electrode layer 2 of the upper substrate. Taking negative photoresist as an example, it is exposed and baked after the pre-baking treatment to make the exposed area undergo cross-linking reaction or polymerization reaction. . The baking temperature and time, the exposure energy are related to the properties of the selected pixel wall material and the height of the pixel wall. The exposed first mask 12 is shown in FIG. 13 . Taking a square as an example, the ultraviolet light 13 passes through the illumination area of the mask 12 .

Then, another material is selected to prepare the oil control structure 10', so that the hydrophilicity and hydrophobicity of the oil control structure can be different from that of the pixel wall layer. Because the pixel wall layer has a lot of contact with water, the pixel wall layer is required to be hydrophilic, preferably the contact angle of water droplets is less than 80 degrees, more preferably less than 50 degrees. The oil control structure may be weakly hydrophilic or weakly hydrophobic, and the contact angle of water droplets is preferably 50-120 degrees, more preferably 60-100 degrees. In this way, a gradient of hydrophilicity and hydrophobicity is obtained, and the ink does not spread to the side of the pixel wall. At the same time, the ink is confined in the oil-controlling structure, preventing the accumulation of the ink. When the contact angle of the pixel wall material is between 60 and 80 degrees, the pixel wall and the oil control structure can also be made of the same material. The specific process steps are: (1) Coating the oil control structural material 10' on the surface of the pixel wall layer 6', and pre-baking. The coating method may be, but is not limited to, spin coating, screen printing, slot coating, roll coating, and the like. The baking temperature is related to the time and material properties, and the thickness of the oil control structure layer; (2) the oil control structure layer is exposed, and the exposure energy is related to the material and thickness of the oil control structure. As shown in FIG. 14 and FIG. 15 , the exposure mask 14 has a cross-shaped and a cylindrical structure respectively, and the ultraviolet light 15 passes through the illumination area of the mask 14 .

Again, the pixel wall layer 6' and the oil control structure 10' are developed. This method can be used when the developer solutions of the two are the same. When the developer solutions of the two are inconsistent, the pixel wall structure is first exposed and baked, and then developed and post-baked, and then the oil control structure layer is coated. That is, one-step development or two-step separate development is selected according to whether the development conditions of the two are consistent or not.

FIG. 16 is a process flow of preparing a pixel wall and an oil control structure by a resist etching method. The pixel wall layer obtained by this method is the same as the oil control structure material.

First, the pixel wall layer is arranged, and the height of the pixel wall is several microns higher than that of the pixel wall of the two-step lithography method, which is the sum of the height of the pixel wall of the two-step lithography method plus the oil control structure. When a negative photoresist is used to make the pixel wall layer, the process includes the steps of coating-pre-baking-exposure-middle-baking-development-post-baking. The parameters of the process are related to the properties and heights of the pixel wall material. When photoresist is used, the mask structure is the first mask. Of course, the pixel wall layer can also be other organic materials or inorganic materials, such as PE, PP, PET, PDMS, silicon materials, etc., which are arranged by a method of solution coating and baking to evaporate the solvent.

Next, a layer of protective glue material 18' is coated on the surface of the pixel wall 6', and the oil control structure and the protective glue outside the display area are removed by exposure and development, and the protective glue protects part of the pixel wall and all exposed electrode layers. The ultraviolet light 17 exposes the protective glue through the light region of the exposure mask 16 . The structure of the mask 16 is taken as an example that the protective paste is a positive photoresist, and FIG. 17 and FIG. 18 are masks with a cross-shaped structure and a cylindrical structure, respectively.

Part of the pixel wall without protective glue is etched to a certain height by physical etching, and the etched height is preferably 1-10 μm, more preferably 2-5 μm, which is related to the thickness of the ink. Finally, the remaining protective glue is developed or peeled off. Therefore, the protective adhesive is preferably a positive photoresist, so that the protective adhesive can be peeled off by exposure and development after etching. FIG. 19 is a schematic diagram of the protective glue after exposure and development.

The above are only specific embodiments of the present invention, but the protection scope of the present invention is not limited thereto. Any person skilled in the art can easily think of changes or substitutions within the technical scope disclosed by the present invention, All should be included within the protection scope of the present invention. Therefore, the protection scope of the present invention should be subject to the protection scope of the claims.

Claims (7)

1. An electrowetting device comprises an upper substrate and a lower substrate, wherein packaging liquid is filled in a cavity formed by the upper substrate and the lower substrate in an opposite direction, the electrowetting device is characterized in that the upper substrate comprises an upper supporting plate, a first electrode, a pixel wall and a rubber frame, an oil control structure is arranged on the pixel wall, the lower substrate comprises a lower supporting plate, a second electrode and a hydrophobic insulating layer, a contact angle of the oil control structure is 30-90 degrees, and the oil control structure is located at a cross point of the pixel wall.

2. An electrowetting device according to claim 1, wherein said oil control structure is square, rectangular, cross-shaped or cylindrical.

3. An electrowetting device according to claim 1, wherein the height of said oil control structure is 1-10 μm.

4. An electrowetting device according to claim 1, wherein the contact angle of the pixel wall is 10 to 80 degrees.

5. An electrowetting device according to claim 1, wherein the height of said pixel wall is 1 to 100 μm.

6. An electrowetting device according to claim 1, wherein said encapsulating liquid is a polar electrolyte solution and a non-polar solution.

7. A method of making an electrowetting device according to any one of claims 1 to 6, comprising the steps of:

s1, disposing a second electrode on the lower support plate, and disposing a hydrophobic insulating layer on the second electrode;

s2, arranging a first electrode on the upper support plate, arranging a pixel wall on the first electrode, and arranging an oil control structure on the pixel wall;

and S3, filling packaging liquid, and bonding the upper substrate and the lower substrate.

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