CN108627969B - Bistable electrowetting structure and preparation process thereof - Google Patents

Abstract

The invention discloses a bistable electrowetting structure, which comprises a substrate layer positioned below and a packaging layer positioned above, wherein the substrate layer is provided with an array of pixel pattern blocks made of a light-transmitting insulating material, and the bistable electrowetting structure is characterized in that: an electrode layer, a hydrophobic layer, an ink layer and a water layer are sequentially arranged between the substrate layer and the packaging layer, a conductive layer is arranged on the lower surface of the packaging layer, the hydrophobic layer covers the electrode layer comprehensively, and the electrode layer continuously covers all the pixel pattern blocks. The electrowetting structure can be prepared by a full photoetching process, is easy to process on a large scale, and not only greatly reduces the working voltage of bistable electrowetting, but also is beneficial to improving the contrast and reliability of bistable electrowetting display as well as can realize transmission type and reflection type bistable electrowetting display because the special structural design reduces the distance between an electrode and a water layer.

Description

Bistable electrowetting structure and preparation process thereof

Technical Field

The invention belongs to the technical field of electrowetting display, and particularly relates to a bistable electrowetting structure and a preparation process thereof.

Background

Electrowetting is a phenomenon that a solid-liquid contact angle can be changed under the condition of an external electric field, and the position of a liquid drop can be controlled by using an electrowetting effect, so that a switching effect on reflected or transmitted light is achieved, as shown in fig. 1, and the switching control effect on light is the basis of an electrowetting display technology. Compared with other reflective display technologies, the electrowetting display technology has the advantages of high response speed (< 10ms), capability of realizing color display, high contrast and high light reflectivity.

Electrowetting devices can also be designed in a bi-stable configuration, i.e. by means of a geometric design two stable states of the droplet (display ink) are obtained in the pixel, the switching between these two states being controlled by a voltage, the state retention itself not consuming energy. The bistable electrowetting display can be realized by using a bistable structure, which is very important in the aspects of further reducing energy consumption and prolonging the working time of a display product, and the prior technical scheme has two types:

firstly, preparing a layer of ITO on a substrate through a sputtering scheme and the like, preparing a patterned planar ITO electrode through laser forming, preparing a dielectric layer on the surface of the patterned planar ITO electrode through a CVD scheme, an ALD scheme, a spin coating scheme and the like, preparing a thick SU8 square block pattern on the surface of the dielectric layer through photoetching, preparing a three-dimensional structure, and preparing a hydrophobic layer on the surface of a whole sample through pulling or spin coating of a cytop or a teflon. In the prior art, the distance between the surface of the hydrophobic layer above the SU8 square and the control electrode below the hydrophobic layer is too high, so that when an oil layer is switched from the surface of the SU8 square to the SU8 groove, the required voltage is too high, and meanwhile, a large amount of residual oil layer exists during state switching, namely, ink on the pixel electrode is not easy to completely return to the channel, the contrast is low (Journal of display technology,11,2015,175), and the method has low processing efficiency and cannot be used for large-scale preparation.

Preparing a layer of metal on a substrate through a sputtering scheme and the like, preparing a patterned electrode through a patterning technology such as photoetching, preparing a dielectric layer on the surface of the patterned electrode through a CVD (chemical vapor deposition) scheme, an ALD (atomic layer deposition) scheme, a spin-coating scheme or the like, preparing a dumbbell-shaped pattern exposed out of the dielectric layer on the surface of the dielectric layer through photoetching, preparing a hydrophobic layer through spin-coating or a Czochralski method, and realizing bistable state through movement of dyeing water drops. However, the method needs to shield a half of the area to realize the switching effect, has low aperture opening ratio and larger size, and is not beneficial to realizing miniaturization. (Journal of SID,16/2,2008,237)

Disclosure of Invention

The invention provides a special electrode structure design, which not only can realize bistable electrowetting display, but also has the advantages of low operating voltage and high contrast ratio, and can solve the problems in the prior art.

The technical scheme provided by the invention is as follows:

a bistable electrowetting structure comprising a substrate layer below and an encapsulation layer above, the substrate layer having fabricated thereon an array of pixel pattern blocks, wherein: the pixel pattern structure comprises a substrate layer, a packaging layer, an ink layer, an electrode layer, a hydrophobic layer, an ink layer and a water layer, wherein the substrate layer and the packaging layer are sequentially provided with the electrode layer, the hydrophobic layer, the ink layer and the water layer, the lower surface of the packaging layer is provided with a conductive layer, the hydrophobic layer covers the electrode layer completely, the electrode layer continuously covers all pixel pattern blocks, a channel for containing ink is reserved between the pixel pattern blocks covered with the electrode layer and the hydrophobic layer, the electrode layer part covering the pixel pattern blocks is a pixel electrode, the electrode layer part covering gaps between adjacent pixel pattern blocks is a.

Furthermore, in order to prevent electric leakage and ensure the display effect, a dielectric layer is arranged between the electrode layer and the hydrophobic layer.

The electrode pattern prepared on the electrode layer is a defect electrode pattern with two concave arc parts, and the two concave arc parts are arranged on the top surface of the pixel electrode in a diagonal mode.

Preferably, the substrate layer is made of a silicon wafer with an oxide layer, glass or PET, PEN or PI materials, the pixel pattern block is one of SU-8, silicon oxide and silicon nitride materials, the electrode layer is made of Al or ITO materials, and the conducting layer is made of ITO materials.

A preparation process of a bistable electrowetting structure is characterized by comprising the following steps:

1) preparing a plurality of pixel pattern blocks with a certain height on the surface of the substrate layer to form a pixel pattern block array, wherein gaps are reserved between adjacent pixel pattern blocks;

2) preparing a layer of uniform and continuously covered conductive film on the pixel pattern block to form an electrode layer;

3) preparing a layer of photoresist on the surface of the electrode layer;

4) preparing a corresponding photoresist pattern by optical exposure and development and fixation technology according to the required electrode pattern;

5) etching the exposed electrode layer part after exposure and development to obtain a target electrode pattern for controlling the switching of the ink between two stable states;

6) removing the photoresist, and preparing a hydrophobic layer on the electrode layer;

8) filling ink, and injecting the ink into the channels among the pixel pattern blocks;

9) and (3) packaging, namely covering a water layer on the sample after ink filling, and sealing the water and the ink between the substrate layer and the packaging layer by using a glass packaging layer with an ITO conductive layer.

On the basis of the above scheme, a further improved or preferred scheme further comprises:

in the step 1), SU-8 glue is sprayed on a substrate layer made of silicon wafers with oxide layers, glass or PET, PEN or PI materials, a pixel pattern block is obtained by utilizing a mask through an exposure and development technology, and then the pixel pattern block is baked on a hot plate at 150 ℃ for 30 minutes to be cured.

In the step 2), an Al film with the thickness of 80nm is uniformly plated on the pixel pattern block by adopting a magnetron sputtering method, and the Al film covers the top surface and the side surface of the pixel pattern block and the gap between the adjacent pixel pattern blocks.

In step 6), a 3% wt cytop solution was spin coated under 1k rpm to prepare a hydrophobic layer, and dried at 180 ℃.

In step 3), the photoresist was coated with Shipley S1813 and pre-baked at 115 ℃ for 1 minute.

In the step 6), the photoresist is removed by using a Remover PG stripper.

And the step 6) comprises the step of preparing a dielectric layer on the electrode layer after removing the photoresist and before preparing the hydrophobic layer.

Preparing Si with the thickness of 800nm by using a PECVD method in the step 6)₃N₄A dielectric layer.

The pixel electrode and the channel electrode are prepared by adopting a transparent conductive material, so that transmission type bistable electrowetting display is realized; or, the pixel electrode and the channel electrode are prepared by adopting a high-reflectivity metal conductive material, so that the reflective bistable electrowetting display is realized.

Has the advantages that:

1) in the bistable electrowetting structure, after the voltage is applied to the channel electrode, the ink moves to the position above the pixel electrode, and after the voltage is removed from the channel electrode, the ink is stably positioned above the pixel electrode; when the voltage is applied to the pixel electrode, the ink moves to the channel, and after the pixel voltage is removed, the ink is stably positioned in the channel.

2) An insulating layer medium is added between the electrode layer and the hydrophobic layer, so that electric leakage can be effectively prevented, and the display effect is ensured;

3) the distribution of the electric field is adjusted through the design of the defective electrode pattern, the moving direction of the oil layer is guided, and the reliability of bistable electrowetting display is further improved.

4) The preparation process adopts a full photoetching process, is easy for large-scale processing, and simultaneously reduces the distance between electrodes (pixel electrodes and channel electrodes) and a water layer due to special structural design, thereby not only greatly reducing the working voltage of bistable electrowetting, but also being beneficial to improving the contrast and reliability of bistable electrowetting display, and realizing two bistable electrowetting displays of a transmission type and a reflection type.

Drawings

FIG. 1 is a schematic diagram of a prior art structure;

FIG. 2 is a schematic flow diagram of a manufacturing process of the present invention;

FIG. 3 is a schematic view of ink over a pixel electrode;

FIG. 4 is a schematic view of ink on a channel electrode;

FIG. 5 is a schematic structural diagram of a defective electrode pattern according to the present invention.

Detailed Description

To further clarify the technical solution and operation principle of the present invention, the following detailed description is made with reference to the accompanying drawings and specific embodiments.

The first embodiment is as follows:

a bistable electrowetting structure, as shown in fig. 2 to 4, comprises a substrate layer 6 (lower sheet), an encapsulation layer 1 (upper sheet) and a pixel patterning layer, anelectrode layer 5, ahydrophobic layer 4, anink layer 9 and awater layer 3 sealed therebetween.

The pixel pattern layer is composed of an array ofpixel pattern blocks 7 made of light-transmitting insulating materials, an ITO conductinglayer 2 is arranged on the lower surface of the packaging layer 1, thehydrophobic layer 4 covers theelectrode layer 5 on the whole, theelectrode layer 5 continuously covers all thepixel pattern blocks 7, a channel for containing ink is reserved between thepixel pattern blocks 7 covered with theelectrode layer 5 and thehydrophobic layer 4, the electrode layer part covering thepixel pattern blocks 7 is pixel electrodes 5-1, and the electrode layer part covering gaps between adjacentpixel pattern blocks 7 is channel electrodes 5-2. As shown in fig. 3 and 4, when the voltage is applied to the channel electrode, the ink moves to the position above the pixel electrode, and when the voltage is removed from the channel electrode, the ink is stably located above the pixel electrode; when the voltage is applied to the pixel electrode, the ink moves to the channel, and after the pixel voltage is removed, the ink is stably positioned in the channel.

The preparation process of the bistable electrowetting structure specifically comprises the following steps:

1) preparing a plurality of squarepixel pattern blocks 7 with certain height on the surface of a substrate layer 6 (a silicon wafer with an oxide layer, glass, PET, PEN or PI material) to form a pixel pattern block array, wherein gaps are reserved between adjacentpixel pattern blocks 7;

2) preparing a conductive film (such as an Al film and the like) with the thickness of 80nm on thepixel pattern blocks 7 by adopting a magnetron sputtering rotation inclination coating process, and uniformly covering the top surfaces and the side surfaces of thepixel pattern blocks 7 and gaps between adjacentpixel pattern blocks 7 to form anelectrode layer 5;

3) the surface of theelectrode layer 5 is coated with a layer ofphotoresist 8, and thephotoresist 8 is a three-dimensional pattern layer, so that complete coverage can not be ensured under the condition of high-speed rotation, so that the lift coating method or low-speed spin coating can be adopted, or other suitable spraying conditions are adopted according to the required thickness, and then prebaking is carried out, wherein the photoresist adopted in the embodiment is Shipley S1813, and after spraying, the prebaking is carried out for 1 minute at the temperature of 115 ℃.

4) Preparing a corresponding photoresist pattern by optical exposure and development and fixation technology according to a preset electrode pattern;

5) etching off the exposedelectrode layer part 10 after exposure and development to obtain a target electrode pattern for controlling the switching of ink between two stable states;

6) removing thephotoresist 8 by using a Remover PG degumming agent, spin-coating a 3% wt cytop solution under the condition of 1k rpm to prepare ahydrophobic layer 4, and drying at 180 ℃;

8) filling ink, and injecting theink 9 into the channel between thepixel pattern blocks 7;

9) and (3) packaging, namely covering the sample after ink filling with awater layer 3, and sealing the water and the ink in thesubstrate layer 6 and the packaging layer 1 by using the packaging layer 1 with the ITO conductive layer.

The operating voltage of the display product prepared by the process only needs 40-60V, while the operating voltage of the bistable electrowetting product in the prior art needs 70-140V.

On the basis of the embodiment, the pixel electrode and the channel electrode are prepared by adopting a transparent conductive material, so that the transmission-type bistable electrowetting display can be realized; or, the pixel electrode and the channel electrode are prepared by adopting a high-reflectivity metal conductive material, so that the reflective bistable electrowetting display can be realized.

Example two:

on the basis of the first embodiment, in order to ensure a better display effect, in the step 6), after removing the photoresist and before preparing thehydrophobic layer 4, a dielectric layer (not shown) made of an insulating medium is additionally prepared on theelectrode layer 5, and the dielectric layer can be Si prepared by a PECVD method₃N₄Or a silicon oxide layer (e.g. 800nm thick Si)₃N₄Materials) insulating layers (e.g., aluminum oxide, hafnium oxide, etc.) that can also be grown using ALD methods.

Example three:

on the basis of the first and second embodiments, it is preferable to use the electrode pattern shown in fig. 5, and as shown by the solid line in the figure, the rectangular outline etched on the top electrode layer of thepixel pattern block 7 has a concave arc portion at the lower left corner and the upper right corner, respectively, to form the double-defect electrode. The dotted lines in fig. 5 indicate the pixel pattern block, and the solid lines represent the division lines of the pixel electrode and the channel electrode, i.e., where the electrode layer is etched away in step 5).

The invention can realize the processing and preparation of the electrode with the three-dimensional graph, the distances between the electrode and three-phase contact points of an oil layer, a water layer and a hydrophobic layer are greatly reduced under the condition, and the electrowetting theory can show that the operating voltage required by the product is greatly reduced compared with the prior art when the state is switched and controlled, the oil layer can be better controlled, the contrast is improved, and simultaneously, the design of the electrode graph with double defects is matched, and the oil layer can be better guided to shrink from the electrode graph.

The foregoing shows and describes the general principles, essential features, and advantages of the invention. It will be understood by those skilled in the art that the present invention is not limited to the embodiments described above, which are described in the foregoing description only for the purpose of illustrating the principles of the present invention, but that various changes and modifications may be made therein without departing from the spirit and scope of the invention as defined by the appended claims, specification, and equivalents thereof.

Claims (10)

1. A bistable electrowetting structure comprising a substrate layer (6) located below and an encapsulation layer (1) located above, the substrate layer (6) having an array of pixel pattern blocks (7) fabricated thereon, characterized in that: the packaging structure is characterized in that an electrode layer (5), a hydrophobic layer (4), an ink layer (9) and a water layer (3) are sequentially arranged between the substrate layer (6) and the packaging layer (1), a conducting layer (2) is arranged on the lower surface of the packaging layer (1), the hydrophobic layer (4) covers the electrode layer (5) completely, the electrode layer (5) covers all pixel pattern blocks (7) continuously, channels for containing ink are reserved between the pixel pattern blocks (7) covered with the electrode layer (5) and the hydrophobic layer (4), the electrode layer part covering the pixel pattern blocks (7) is a pixel electrode (5-1), the electrode layer part covering gaps between adjacent pixel pattern blocks (7) is a channel electrode (5-2), and the pixel pattern blocks (7) are made of light-transmitting insulating materials.

2. A bistable electrowetting structure according to claim 1, wherein a dielectric layer is provided between said electrode layer (5) and said hydrophobic layer (4).

3. A bistable electrowetting structure according to claim 1, wherein said electrode layer (5) is provided with an electrode pattern having a defect pattern with two concave arc portions diagonally disposed on the top surface of the pixel electrode.

4. A bistable electrowetting structure according to any of claims 1-3, wherein said substrate layer (6) is an oxidized silicon wafer, glass or PET, PEN or PI material, said pixel pattern block (7) is one of SU-8, silicon oxide, silicon nitride material, said electrode layer (5) is Al or ITO material, and said conductive layer (2) is ITO material.

5. A preparation process of a bistable electrowetting structure is characterized by comprising the following steps:

1) preparing a plurality of pixel pattern blocks (7) with a certain height on the surface of the substrate layer to form a pixel pattern block array, wherein gaps are reserved between adjacent pixel pattern blocks (7);

2) preparing a layer of uniform and continuously covered conductive film on the pixel pattern block to form an electrode layer (5);

3) preparing a layer of photoresist (8) on the surface of the electrode layer (5);

4) preparing a corresponding photoresist pattern by optical exposure and development and fixation technology according to the required electrode pattern;

5) etching away the exposed electrode layer part (10) after exposure development to obtain a target electrode pattern for controlling switching of ink between two stable states;

6) removing the photoresist (8), and preparing a hydrophobic layer (4) on the electrode layer;

8) filling ink, and injecting the ink (9) into a channel between the pixel pattern blocks (7);

9) and (3) packaging, namely covering a water layer (3) on the sample after ink filling, and sealing the water and the ink in the substrate layer (6) and the packaging layer (1) by using the packaging layer (1) with the ITO conductive layer.

6. A process according to claim 5, wherein the bistable electro-wetting structure is prepared by:

in the step 1), SU-8 glue is sprayed on a substrate layer made of a silicon wafer with an oxide layer, glass or PET, PEN or PI materials, a pixel pattern block is obtained by utilizing a mask through an exposure and development technology, and then the pixel pattern block is baked on a hot plate at 150 ℃ for 30 minutes to be cured;

in the step 2), an Al film with the thickness of 80nm is uniformly plated on the pixel pattern block (7) by adopting a magnetron sputtering method, and the top surface and the side surface of the pixel pattern block (7) and the gap between the adjacent pixel pattern blocks (7) are covered;

in step 6), a 3% wt cytop solution was spin-coated at 1k rpm to prepare a hydrophobic layer (4), and dried at 180 ℃.

7. The process of claim 6, wherein:

in the step 3), the photoresist is Shipley S1813, and is coated and then is pre-baked for 1 minute at 115 ℃;

in the step 6), the photoresist is removed by using a Remover PG stripper.

8. A process according to claim 5, wherein the bistable electro-wetting structure is prepared by:

in the step 6), a step of preparing a dielectric layer on the electrode layer (5) before preparing the hydrophobic layer (4) after removing the photoresist is included.

9. The process of claim 8, wherein:

preparing Si with the thickness of 800nm by using a PECVD method in the step 6)₃N₄A dielectric layer.

10. A process for the preparation of a bistable electrowetting structure according to any of claims 5 to 9, wherein:

the pixel electrode and the channel electrode are prepared by adopting a transparent conductive material, so that transmission type bistable electrowetting display is realized; or, the pixel electrode and the channel electrode are prepared by adopting a high-reflectivity metal conductive material, so that the reflective bistable electrowetting display is realized.

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