CN107367836B - Electrowetting device and preparation method thereof - Google Patents

Abstract

The invention belongs to the field of electrowetting and discloses an electrowetting device which comprises an upper substrate and a lower substrate, wherein a cavity formed by the upper substrate and the lower substrate in an opposite direction is filled with packaging liquid, the upper substrate comprises an upper supporting plate, a first electrode and a pixel wall, an oil control structure is arranged on the pixel wall, and the lower substrate comprises a lower supporting plate, a second electrode and a hydrophobic insulating layer. The invention also discloses a preparation method of the electrowetting device. The invention realizes the definition of the ink by improving the pixel grid structure, thereby preventing the aggregation of the ink. Defining the thickness of the filling ink layer by the oil control structure; the 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 during the encapsulation process.

Description

Electrowetting device and preparation method thereof

Technical Field

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

Background

An electrowetting display device comprises a fluid chamber containing a first fluid (alkane, etc.) which is non-conductive, a second fluid (water or saline solution) which is conductive, the fluids being in contact and non-miscible with each other, and an electrode structure. For example, patent CN102792207A describes an electrowetting display device, which includes two support plates, one of which is provided with a wall pattern, i.e., pixel walls, which are made of a photoresist material (such as SU8) by a photolithography process, and the areas formed by pixel cells enclosed by the pixel walls are display areas, and the electrowetting display device generates a display effect on the display areas. The non-conductive first fluid is filled in the display area formed by the pixel walls, and the surrounding pixel walls are used for preventing the first fluid from flowing to the surrounding pixel grids, so that a stable display structure is obtained.

Another electrowetting device is described in US9274331B2, in which one support plate is provided with an electrode layer and a hydrophobic insulating layer, while the other support plate is provided with an electrode layer and very high pixel walls, and the two support plates are encapsulated after filling with non-polar ink and a polar conducting fluid.

The hydrophobic insulating layer of the first electrowetting device needs to be subjected to hydrophilic treatment firstly, then the pixel wall can be arranged on the hydrophobic insulating layer, and the hydrophobicity of the pixel wall is recovered in a high-temperature backflow mode, so that the hydrophobicity of the hydrophobic insulating layer cannot be completely recovered, and dislocation and damage to the hydrophobic insulating layer caused by sliding of the pixel wall on the hydrophobic insulating layer in a high-temperature process exist. The hydrophobic insulating layer of the second electrowetting device is not subjected to hydrophobic-hydrophilic-hydrophobic treatment and recovery processes, and the properties are relatively stable.

However, in the second electrowetting structure with high pixel walls, when a voltage is applied, the inks of a plurality of pixel cells are easily gathered together to form a cluster of ink, so that the display effect is very uneven. Therefore, there is a need to develop new electrowetting device structures to address these issues.

Disclosure of Invention

It is an object of the present invention to provide an electrowetting device in which ink definition is achieved by improving the pixel cell configuration, thereby preventing ink aggregation.

It is another object of the present invention to provide a method of manufacturing an electrowetting device.

In order to achieve one of the purposes, the invention adopts the following technical scheme:

the utility model provides an electrowetting device, includes upper substrate, infrabasal plate, and the cavity intussuseption that upper substrate and infrabasal plate subtend formed is filled with encapsulation liquid, upper substrate includes backup pad, first electrode, pixel wall, glues the frame, be equipped with accuse oil structure on the pixel wall, the infrabasal plate includes backup pad, second electrode, hydrophobic insulating layer down.

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

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

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

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

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

Furthermore, 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 of making an electrowetting device as described above, 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.

The invention has the following beneficial effects:

the invention realizes the definition of the ink by improving the pixel grid structure, thereby preventing the aggregation of the ink. Defining the thickness of the filling ink layer by the oil control structure; the 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 during the encapsulation process.

In the previous patent application of the applicant, based on the traditional electrowetting device structure, an oil control structure is arranged on a pixel wall positioned on a lower substrate, the pixel wall is not high, the pixel wall can play a role in limiting the height of ink, and the oil control structure enables the ink to be gathered towards the oil control structure, so that the movement direction of the ink in the opening process is controlled. The invention aims at the problems of a novel electrowetting structure, the pixel wall of the novel electrowetting structure is arranged on an upper substrate, the pixel wall is very high, ink cannot be limited, and the ink is very easy to gather in the processes of filling and opening the ink, so that the oil control structure is arranged to prevent the ink from gathering. The roles of the oil control structure in the two schemes are completely opposite, when the oil control structure is arranged on the pixel wall of the traditional electrowetting device, the oil control structure is used for promoting the ink aggregation, and when the oil control structure is arranged on the pixel wall of the novel electrowetting device, the oil control structure is used for preventing the ink aggregation.

Drawings

Fig. 1 is a schematic diagram of a prior art electrowetting device structure;

FIG. 2 is a schematic diagram of a prior art electrowetting device ink climbing a wall;

fig. 3 is a schematic diagram of an electrowetting device of the present invention;

FIG. 4 is a schematic view of an electrowetting device of the present invention showing ink climbing a wall;

FIG. 5 is a top view of a pixel wall structure;

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

FIG. 7 is a side view of a cross-shaped oil control structure and pixel wall obtained by a double photolithography method;

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

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

FIG. 10 is a side view of a cylindrical oil control structure and pixel walls obtained by a double photolithography process;

FIG. 11 is a side view of a cylindrical oil control structure and pixel walls obtained by etching;

FIG. 12 is a process flow of a two-step photolithography process for fabricating pixel walls and an oil control structure;

FIG. 13 is a top view of a first reticle;

FIG. 14 is a top view of a cross-shaped reticle;

FIG. 15 is a top view of a cylindrical reticle;

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

FIG. 17 is a top view of a cross-shaped reticle;

FIG. 18 is a top view of a cylindrical reticle;

FIG. 19 is a schematic view of the resist after exposure and development.

Detailed Description

The present invention will be further described with reference to the following specific examples.

Examples

Fig. 1 is a structure of an existing electrowetting device, in which a first electrode 2, a pixel wall 6, and a rubber frame 9 are disposed on an upper support plate 1, a second electrode 4 and a hydrophobic insulating layer 5 are disposed on a lower support plate 3, and after a non-polar liquid 7 and a polar liquid 8 are filled, an upper substrate and a lower substrate are attached to each other through the rubber frame 9.

Fig. 2 is a schematic diagram of an ink wall climbing of a conventional electrowetting device, in which an electrowetting structure is prone to ink wetting on a high wall, that is, the wall climbing condition, and thus the oil film in a pixel cell is not uniform.

Fig. 3 is an improved electrowetting device structure, a first electrode 2 and a pixel wall 6 are arranged on a support plate 1, an oil control structure 10 is arranged on the pixel wall 6, a second electrode 4 and a hydrophobic insulating layer 5 are arranged on a lower support plate 3, and after a non-polar liquid 7 and a polar liquid 8 are filled, an upper substrate and a lower substrate are attached to each other through a rubber frame 9.

The oil control structure 10 is required to have certain hydrophilicity, the contact angle is preferably 30-90 degrees, the pixel wall 6 can be made of the same material as the oil control structure, or can be made of a more hydrophilic material, and the contact angle is preferably 10-80 degrees.

Fig. 4 is a schematic view of an ink climbing wall of the electrowetting device of the present invention, and the improved electrowetting structure has a gradient in hydrophilicity and hydrophobicity of the pixel wall and the oil control structure, so that a certain energy barrier needs to be overcome when the ink crosses the oil control structure to wet the pixel wall, so that the height of the edge of the oil film is controlled by the oil control structure, and the obtained oil film has good uniformity.

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

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

Fig. 6 is a top view of a pixel wall and an oil control structure of the improved electrowetting device, wherein the oil control structure 10 is cross-shaped. Fig. 7 is a side view of a cross-shaped oil control structure and a pixel wall obtained by a double-time photolithography method, and fig. 8 is a side view of a cross-shaped oil control structure (the oil control structure and the pixel wall are made of the same material) and a pixel wall obtained by an etching method.

The oil control structure may be cylindrical, as shown in fig. 9. Fig. 10 is a side view of a cylindrical oil control structure and a pixel wall obtained by a double photolithography method, and fig. 11 is a side view of a cylindrical oil control structure (the oil control structure and the pixel wall are made of the same material) and a pixel wall obtained by an etching method.

The oil control structure can also be rectangular, square, etc.

An electrowetting device structure was prepared as follows:

firstly, arranging a lower substrate:

first, an electrode layer (second electrode) such as ITO, Al, etc. is disposed on the surface of the lower support plate, and the lower support plate may be glass of various thicknesses, or may be a polymer material such as PET, PI, etc., and may be either a rigid substrate or a flexible substrate. The electrode layer may be a full-thickness film, may be patterned, or may even be a TFT layer. The arrangement mode of the electrode layer comprises methods such as vacuum coating, vapor deposition, magnetron sputtering and the like, and is similar to the coating method in the LCD industry.

Then, a hydrophobic insulating layer, such as AF1600, Cytop, Parylene, etc., is disposed on the surface of the electrode layer (second electrode). The method comprises the following steps: and coating the solution of the hydrophobic insulating layer material on the surface of the electrode layer by screen printing, spin coating, slit coating, blade coating and other modes, and then removing the solvent in the hydrophobic insulating layer by high-temperature baking to obtain the hydrophobic insulating layer film.

Secondly, arranging an upper substrate:

an electrode layer (first electrode) such as ITO, Al, etc. is disposed on the surface of the upper support plate, which may be glass of various thicknesses, or a polymer material such as PET, PI, etc., which may be either a rigid substrate or a flexible substrate. The arrangement mode of the electrode layer comprises vacuum coating, vapor deposition, magnetron sputtering and the like.

Then, a pixel wall layer is arranged on the surface of the electrode layer (first electrode), and the shape of the pixel wall can be square, rectangle, or other polygon and circle. 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 both the support of the pixel wall between the upper and lower electrode plates and the thickness of the whole device.

Next, a layer of oil control structure, such as the cross structure shown in fig. 6 and the cylinder structure shown in fig. 9, is disposed on the surface of the pixel wall. 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.

Filling non-polar liquid ink and polar liquid, and attaching the upper substrate and the lower substrate through a rubber frame to obtain the improved electrowetting device with the oil control structure.

The pixel wall and the oil control structure are provided with two steps of photoetching and protective glue etching.

Fig. 12 is a process flow of a two-step photolithography process for fabricating pixel walls and an oil control structure.

Firstly, a layer of pixel wall material 6' is arranged on the surface of the electrode layer 2 of the upper substrate, taking a negative photoresist as an example, and after pre-baking treatment, the pixel wall material is exposed and baked to enable the exposed area to generate cross-linking reaction or polymerization reaction. The baking temperature and time, and the exposure energy are related to the properties of the selected pixel wall material and the height of the pixel wall. The exposed first reticle 12 is shown in fig. 13, and the ultraviolet light 13 is transmitted through the illuminated area of the reticle 12, taking a square as an example.

Then, another material is selected to prepare the oil control structure 10', so that the hydrophilicity and hydrophobicity of the oil control structure may be different from those of the pixel wall layer. Since the pixel wall layer is in contact with water more, the pixel wall layer is required to be hydrophilic, and the contact angle of a water drop is preferably less than 80 degrees, and more preferably less than 50 degrees. The oil control structure can be weak hydrophilic or weak hydrophobic, and the contact angle of a water drop is preferably 50-120 degrees, more preferably 60-100 degrees. Thus, a hydrophilic-hydrophobic gradient 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 control structure, preventing aggregation 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 be made of the same material. The specific process steps are as follows: (1) and coating an oil control structure 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, slit coating, roll coating, and the like. The baking temperature is related to time, material property and thickness of the oil control structure layer; (2) and exposing the oil control structure layer, wherein the exposure energy is related to the material and the thickness of the oil control structure. The exposure mask 14 has a cross-shaped structure and a cylindrical structure as shown in fig. 14 and fig. 15, respectively, and the ultraviolet light 15 penetrates 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 selected when the developing solutions are the same. When the developing solutions of the pixel wall structure and the pixel wall structure are different, the pixel wall structure is exposed and baked, then development and post-baking are carried out, and then the oil control structure layer is coated. Namely, one-step development or two-step separate development is selected according to the coincidence of the two development conditions.

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

Firstly, arranging a pixel wall layer, wherein the height of a pixel wall is higher than that of a pixel wall of a two-step photoetching method by a plurality of micrometers, namely the sum of the heights of the pixel wall and an oil control structure of the two-step photoetching method. When the negative photoresist is adopted to manufacture the pixel wall layer, the process comprises the steps of coating, pre-baking, exposing, intermediate baking, developing and post-baking, the parameters of the process are related to the property and height of the pixel wall material, and when the negative photoresist is adopted, the mask plate structure is a first mask plate. Of course, the pixel wall layer may also be other organic or inorganic materials, such as PE, PP, PET, PDMS, silicon materials, etc., and is disposed by solution coating and baking to evaporate the solvent.

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

And etching a part of the pixel wall without the protective glue by a physical etching method to form a section of height, wherein the etched height is preferably 1-10 μm, more preferably 2-5 μm, and is related to the thickness of the ink. Finally, the remaining protective gel is developed or stripped off. Therefore, the protective glue is preferably a positive photoresist, and the protective glue can be stripped by means of exposure and development after etching. FIG. 19 is a schematic view of the resist after exposure and development.

The above description is only an embodiment of the present invention, but the scope of the present invention is not limited thereto, and any changes or substitutions that can be easily conceived by those skilled in the art within the technical scope of the present invention are included in the scope of the present invention. Therefore, the protection scope of the present invention shall 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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