Flexible display device and manufacturing method of the same

A flexible display device includes: a display panel including a display substrate, an organic light emitting element formed on the display substrate, and a thin film encapsulation layer covering the organic light emitting element; a first insulation layer formed under the display panel; a lower protection film formed under the first insulation layer; and a reinforcement layer formed under the lower protection film, between the lower protection film and the first insulation layer, or on the display panel, wherein the reinforcement layer is configured to prevent damage to the display panel due to bending stress.

CROSS-REFERENCE TO RELATED APPLICATIONS

This application claims priority to, and the benefit of, Korean Patent Application No. 10-2012-0127506 filed in the Korean Intellectual Property Office on Nov. 12, 2012, the entire contents of which are incorporated herein by reference.

BACKGROUND

The present disclosure relates to a flexible display device and a manufacturing method thereof.

2. Description of the Related Technology

In recent years, flexible displays having a lightweight and a shock-resistant flexible substrate made of a material such as plastic have been developed. Such a flexible display can be maximized in portability since it can be folded or rolled up, and can be applied in various fields.

A flexible display includes a display element formed on a flexible substrate. Display elements that can be used for a flexible display include an organic light emitting diode display (OLED) device, a liquid crystal display (LCD) device, and an electrophoretic display (EPD) device.

These display elements commonly include thin film transistors. Thus, in order to form a flexible display, the flexible substrate undergoes a number of thin film processes.

Also, the flexible substrate is encapsulated through a thin film process by an encapsulation substrate. The flexible substrate, the thin film transistor formed on the flexible substrate, and the encapsulation substrate form a display panel of the flexible display device.

However, when the flexible display device is bent, rolled, and folded, the display panel receives bending stress in the display device. At this time, if bending stress of more than a predetermined degree is applied to the display panel, damage such as a crack is generated in the thin film transistor or the light emitting element in the display panel.

SUMMARY OF CERTAIN INVENTIVE ASPECTS

Embodiments of the present invention provide a flexible display device in which damage to a display panel due to bending stress is prevented.

Further, embodiments of the present invention provide a manufacturing method of a flexible display device in which damage to a display panel due to bending stress is prevented.

A flexible display device according to an embodiment of the present invention includes: a display panel including a display substrate, an organic light emitting element formed on the display substrate, and a thin film encapsulation layer covering the organic light emitting element; a first insulation layer formed under the display panel; a lower protection film formed under the first insulation layer; and a reinforcement layer formed under the lower protection film, between the lower protection film and the first insulation layer, or on the display panel, wherein the reinforcement layer is configured to prevent damage to the display panel due to bending stress.

The reinforcement layer may be made of an oxide semiconductor.

The reinforcement layer may be made of an oxide semiconductor and a metal.

The metal may be one of copper, ITO, and aluminum.

The oxide semiconductor may be made of at least one of an oxide based on zinc, gallium, tin, or indium, or as a complex oxide thereof, including zinc oxide, indium-gallium-zinc oxide, indium-zinc oxide, or zinc-tin oxide.

The reinforcement layer may include a plurality of layers.

The reinforcement layer may be formed on the display panel, and the device may further include a second insulation layer formed between the display panel and the reinforcement layer.

A manufacturing method of a flexible display device according to an embodiment of the present invention includes: forming a first insulation layer on a supporting substrate; forming a display panel including a display substrate positioned on the first insulation layer, an organic light emitting element formed on the display substrate, and a thin film encapsulation layer covering the organic light emitting element; separating the supporting substrate from the first insulation layer; forming a reinforcement layer on or under the lower protection film positioned under the display panel; and adhering the lower protection film under the first insulation layer, wherein the reinforcement layer is configured to prevent damage to the display panel due to bending stress.

The reinforcement layer may be made of an oxide semiconductor.

The oxide semiconductor may be made of one of an oxide based on zinc, gallium, tin, or indium, or as a complex oxide thereof, including zinc oxide, indium-gallium-zinc oxide, indium-zinc oxide, or zinc-tin oxide.

A manufacturing method of a flexible display device according to another embodiment of the present invention includes: forming a first insulation layer on a supporting substrate; forming a display panel including a display substrate positioned on the first insulation layer, an organic light emitting element formed on the display substrate, and a thin film encapsulation layer covering the organic light emitting element; forming a second insulation layer on the display panel; forming a reinforcement layer on the second insulation layer; separating the supporting substrate from the display panel; and adhering a lower protection film under the display panel, wherein the reinforcement layer prevents damage to the display panel due to bending stress.

The reinforcement layer may be made of an oxide semiconductor.

The oxide semiconductor may be made of one of an oxide based on zinc, gallium, tin, or indium, or as a complex oxide thereof, including zinc oxide, indium-gallium-zinc oxide, indium-zinc oxide, or zinc-tin oxide.

According to the flexible display device according to an embodiment of the present invention, when bending occurs in the display device, damage to the display panel by bending stress may be prevented.

According to the manufacturing method of the flexible display device according to another embodiment of the present invention, a flexible display device that prevents damage to the display panel due to bending stress may be manufactured.

DETAILED DESCRIPTION OF CERTAIN INVENTIVE EMBODIMENTS

In addition, the size and thickness of each element in the drawings are illustrated for better understanding and ease of description, and the present invention is not limited thereto.

In the drawings, the thickness of layers, films, panels, regions, etc., may be exaggerated for clarity. In the drawings, for better understanding and ease of description, thicknesses of some layers and areas may be excessively displayed. It will be understood that when an element such as a layer, film, region, or substrate is referred to as being “on” another element, it can be directly on the other element or intervening elements may also be present.

In addition, unless explicitly described to the contrary, the word “comprise” and variations such as “comprises” or “comprising” will be understood to imply the inclusion of stated elements but not the exclusion of any other elements. Throughout this specification, it is understood that the term “on” and similar terms are used generally and are not necessarily related to a gravitational reference.

FIG. 1is a cross-sectional view of a flexible display device according to an embodiment of the present invention.

Referring toFIG. 1, a flexible display device according to an embodiment includes a display panel120, a polarizing plate110, a first insulation layer130, a lower protection film140, and a reinforcement layer150.

According to the first embodiment of the present invention, the display panel120is a constituent element displaying an image. The display panel120that is described below is a display panel120for an organic light emitting diode (OLED) display including an organic light emitting element, however it is not limited thereto, and the display panel may be a display panel for a liquid crystal display (LCD), a plasma display device (PDP), an electric field effect display device (FED), an electrophoretic display device, or the like.

Referring toFIG. 1, the display panel120is generally divided into a display substrate123, an organic light emitting element122, and a thin film encapsulation layer121. The detailed descriptions thereof will be given with reference toFIG. 2andFIG. 3.

FIG. 2is an equivalent circuit of one pixel of the display panel shown inFIG. 1, andFIG. 3is a cross-sectional view of the display panel shown inFIG. 1.

Referring toFIG. 2, the display panel120includes a plurality of signal lines21,71, and72and a pixel PX connected thereto. The pixel PX may be one of a red pixel (R), a green pixel (G), or a blue pixel (B).

The signal lines include scanning signal lines21for transmitting gate signals (or scanning signals), data lines71for transmitting data signals, and driving voltage lines72for transmitting a driving voltage. The scanning signal lines21extend substantially in a row direction and substantially parallel to each other, and the data lines71extend substantially in a column direction and substantially parallel to each other. The driving voltage lines72extend substantially in a column direction and substantially parallel to each other, however they may extend in the row direction or the column direction, and may form a mesh shape.

One pixel PX includes a switching transistor Qs, a driving transistor Qd, a storage capacitor Cst, and an organic light emitting element LD.

The switching transistor Qs has a control terminal N1, an input terminal N2, and an output terminal N3. The control terminal N1 is connected to the scan signal line21, the input terminal N2 is connected to the data line71, and the output terminal N3 is connected to the driving transistor Qd. The switching transistor Qs transmits data signals applied to the data line71to the driving transistor Qd in response to a gate signal applied to the gate line21.

The driving transistor Qd also includes the control terminal N3, the input terminal N4, and the output terminal N5. The control terminal N3 is connected to the switching transistor Qs, the input terminal N4 is connected to the driving voltage line72, and the output terminal N5 is connected to the organic light emitting element LD. The driving transistor Qd drives an output current ILDhaving a magnitude depending on the voltage between the control terminal N3 and the output terminal N5 thereof.

The capacitor Cst is connected between the control terminal N3 and the input terminal N4 of the driving transistor Qd. The capacitor Cst stores a data signal applied to the control terminal of the driving transistor Qd and maintains the data signal after the switching transistor Qs turns off.

The organic light emitting element LD as an organic light emitting diode (OLED) has an anode connected to the output terminal N5 of the driving transistor Qd and a cathode connected to a common voltage Vss. The organic light emitting element LD emits light having an intensity depending on an output current ILDof the driving transistor Qd, thereby displaying images. The organic light emitting element LD may include an organic material uniquely emitting at least one of three primary colors of red, green, and blue, and the organic light emitting device displays desired images by a spatial sum thereof.

Next, referring toFIG. 3, a cross-section of the display panel120will be described. The cross-section of the display panel120ofFIG. 3shows the display panel120ofFIG. 1in detail.

Referring toFIG. 3, a driving transistor Qd is formed on a display substrate123made of transparent glass or plastic. Also, a plurality of signal lines (not shown) and a plurality of switching transistors (not shown) may be further formed on the display substrate123. According to the one embodiment of the present invention, the display substrate123may be a flexible substrate.

A protective layer122bmade of an inorganic material or an organic material is formed on the driving transistors Qd. When the protective layer122bis made of the organic material, the surface thereof may be flat. The protective layer122bhas a contact hole122aexposing a portion of the driving transistor Qd. A pixel electrode122dis formed on the protective layer122b. The pixel electrode122dmay include a reflective electrode and a transparent electrode formed thereon. The reflective electrode may be made of a metal having high reflectance, such as silver (Ag) or aluminum (Al), an alloy thereof, or the like, and the transparent electrode may be made of a transparent conductive oxide such as ITO (indium tin oxide) or IZO (indium zinc oxide).

A pixel definition layer122ccovering a circumference of an edge of the pixel electrode122dis formed on the protective layer122b.

An organic emission layer122eis formed on the pixel electrode122d, and a common electrode122fis formed on the organic emission layer122eand the pixel definition layer122c.

The organic emission layer122emay further include organic layers (not shown) for efficiently transferring carriers of holes or electrons to the emission layer in addition to an emission layer (not shown) emitting light. The organic layers may be a hole injection layer (HIL) and a hole transport layer (HTL) positioned between the pixel electrode122dand the emission layer122e, and an electron injection layer (EIL) and an electron transport layer (ETL) positioned between the common electrode122fand the emission layer122e.

A cover layer190covering the common electrode122fto protect the common electrode122fmay be formed of the organic layer on the common electrode122f.

The thin film encapsulation layer121is formed on the cover layer190. The thin film encapsulation layer121seals and protects the organic light emitting element LD and a driving circuit portion formed on the substrate123from the outside.

The thin film encapsulation layer121includes organic encapsulation layers121aand121cand inorganic encapsulation layers121band121dalternately laminated one by one.FIG. 3shows a case where the two organic encapsulation layers121aand121cand the two inorganic encapsulation layers121band121dare alternately laminated one by one to constitute the thin film encapsulation layer121as an example, but is not limited thereto.

Referring toFIG. 1, the polarizing plate110is disposed on the display panel120. The polarizing plate110converts a light axis of the light emitted through the display panel120to the outside. In general, the polarizing plate has a structure in which a transparent protection film is deposited on both sides or one side of a polarizer made of a polyvinyl alcohol-based resin.

In detail, the polarizing plate110has a structure in which polyvinyl alcohol-based (PVA) molecule chains are arranged in a predetermined direction, and a triacetyl cellulose (TAC) film as the protection film is adhered to the polarizer including an iodine-based compound or a dichroic polarizer material. At this time, the polarizer and the protection film are adhered by an aqueous adhesive made of a polyvinyl alcohol-based solution.

However, the polarizing plate110is not limited thereto, and a polarizing plate of various structures may be used.

The first insulation layer130may be formed under the display panel120. The first insulation layer130is positioned between the display panel120and a supporting substrate160(described below), thereby allowing easy removal of the supporting substrate160after depositing the display panel120.

The first insulation layer130may be a polyimide, an acryl, a benzocyclobutene, or an epoxy. However, the first insulation layer130is not limited thereto, and it may be made of various materials having an insulation property.

Referring toFIG. 1, the lower protection film140is attached under the first insulation layer130. The lower protection film140is positioned under the display panel120thereby having a function of protecting the display panel120. An adhesion of the lower protection film140is described below.

The lower protection film140may include a carrier film (not shown) and an adhesive layer (not shown).

The carrier film may include one material selected from polyethylene terephthalate (PET), polyethylene naphthalate (PEN), polyethylene sulfide (PES), polyethylene (PE), urethane, and polycarbonate.

A thickness of the carrier film may be in a range of about 25 μm to about 300 μm. When the thickness of the carrier film is less than about 25 μm, the carrier film is excessively thin such that the function of the lower protection film protecting the lower portion of the organic light emitting display is difficult, while when the thickness of the carrier film is larger than about 300 μm, it is difficult for the organic light emitting device to be flexible when the lower protection film for the display device is attached to the organic light emitting display.

The lower protection film140is permanently adhered to the display substrate such that the carrier film of the lower protection film140is adhered under the display panel120by the adhesive layer.

The adhesive layer has a strong adhesive force. The lower protection film140may be an acryl-based strong adhesive film.

In a condition in which the lower protection film140is bent, by improving repulsion resistance of the adhesive layer, the display substrate123of the display panel120and the lower protection film140are not separated.

According to an embodiment of the present invention, the reinforcement layer150may be formed under the lower protection film140. When the display device is bent, the reinforcement layer150prevents the display panel120from being damaged by bending stress.

However, the reinforcement layer150is not limited thereto, and it may be formed between the lower protection film140and the first insulation layer130, or on the display panel120.

The bending may be generated in the flexible display device as the display device having flexibility, and in this case, the display panel120in the display device is affected by the bending stress.

In this case, if the display panel120is applied with bending stress of more than a predetermined degree, a crack may be generated in the driving transistor Qd or the organic light emitting element inside the display panel120. That is, the display panel120may be damaged, thereby causing an operation error of the display device.

Accordingly, to prevent damage to the display panel120due to the bending stress, an additional layer such as the reinforcement layer150is added under the display panel120such that the bending stress of the display panel120may be reduced.

The bending stress is a tension stress and a compression stress that are generated in the display device when a bending moment is applied to the display device. As described above, when the bending moment is applied to the display device, if the physical layer is additionally formed in the display device, the tension stress and the compression stress are reduced.

That is, if the reinforcement layer150is additionally formed under or on the display panel120, the bending stress generated in the display panel120is reduced.

FIG. 4is a cross-sectional view of a flexible display device according to another embodiment of the present invention, andFIG. 5is a cross-sectional view of a flexible display device according to yet another embodiment of the present invention.

Referring toFIG. 4, in the flexible display device according to one embodiment of the present invention, a reinforcement layer250may be formed between a first insulation layer230and a lower protection film240.

Referring toFIG. 5, in the flexible display device according to another embodiment of the present invention, a reinforcement layer350is formed on a display panel320. The reinforcement layer350may be formed on the display panel320, that is, on the thin film encapsulation layer321.

The reinforcement layer350may alternatively be formed on a second insulation layer360formed in the display panel320.

When the reinforcement layer350is directly formed on a thin film encapsulation layer321, in the process of forming the reinforcement layer350made of an oxide semiconductor, the thin film encapsulation layer321may be influenced such that the second insulation layer360may be additionally formed between the reinforcement layer350and the thin film encapsulation layer321.

The second insulation layer360may be formed with the same material as the first insulation layers130,230, and330.

The reinforcement layers150,250, and350may be made of polysilicon or the oxide semiconductor.

The reinforcement layers150,250, and350may be made of a composite material including the oxide semiconductor and the metal. The metal may include one of copper, ITO, and aluminum.

The reinforcement layers150,250, and350may be made of a plurality of layers. The reinforcement layers150,250, and350may be made of a first reinforcement layer and a second reinforcement layer.

The first and second reinforcement layers may be formed with the same material or with different materials. For example, the first and second reinforcement layers may be made of the oxide semiconductor, or may be made of the composite material including the oxide semiconductor and the metal.

Also, the first and second reinforcement layers may be formed of different materials, that is, one may be made of the oxide semiconductor, and the other may be made of the composite material of the metal or the oxide semiconductor and metal.

Next, a manufacturing method of a flexible display device according to an embodiment of the present invention will be described with reference toFIG. 6toFIG. 8.

FIG. 6toFIG. 8are views sequentially showing a manufacturing method of a flexible display device according to an embodiment of the present invention.

Firstly, referring toFIG. 6, in the manufacturing method of the flexible display device according an embodiment of the present invention, the first insulation layer130may be formed on the supporting substrate160. The supporting substrate160as a substrate supporting the display panel while forming the display panel of the flexible display device is removed after the display panel is completed.

Next, the display panel120is formed on the first insulation layer130. In detail, the display substrate123is formed on the first insulation layer130, and then the organic light emitting element122and the thin film encapsulation layer121are sequentially deposited. The process of forming the display substrate123, the organic light emitting element122, and the thin film encapsulation layer121on the first insulation layer130is applied with a disclosed display panel such that a detailed description thereof is omitted.

Next, referring toFIG. 7, the supporting substrate160is separated from the first insulation layer130. At this time, the process of separating the supporting substrate160from the first insulation layer130may be applied with a process of separating a supporting substrate from the display panel in the manufacturing process of the flexible display device.

Next, referring toFIG. 8, the reinforcement layer150is formed on or under the lower protection film140attached under the display panel120. However, sequences of the process of forming the reinforcement layer150on or under the lower protection film140and the process of separating the supporting substrate160from the first insulation layer130may be exchanged.

Next, still referring toFIG. 8, the lower protection film140is adhered under the first insulation layer130. According to an embodiment of the present invention, when the reinforcement layer150is formed under the lower protection film140, an upper surface of the lower protection film140is adhered to a lower surface of the first insulation layer130.

After forming the display panel120on the first insulation layer130, the polarizing plate110may be adhered on the display panel120, and after adhering the lower protection film140under the first insulation layer130, the polarizing plate110may be adhered on the display panel120.

According to the manufacturing method of the flexible display device according to an embodiment of the present invention, the first insulation layer330may be firstly formed on a supporting substrate (not shown). This relates to the manufacturing process of the flexible display device according to the embodiment described above.

Next, the display panel320is formed on the first insulation layer330. In detail, a display substrate323is formed on the first insulation layer330and then an organic light emitting element322and a thin film encapsulation layer321are sequentially deposited.

Next, a second insulation layer360is formed on the display panel320. Next, the reinforcement layer350is formed on the second insulation layer360.

Then, after the supporting substrate is separated from the display panel320, a lower protection film340is attached under the display panel320.

In the flexible display device according to an embodiment of the present invention, the reinforcement layer is formed on or under the display panel such that damage to the display panel due to bending stress may be prevented when the display device is bent.

Also, a manufacturing method of the flexible display device according to another embodiment of the present invention may manufacture the flexible display device in which damage to the display panel by bending stress generated in the display device is prevented.

While this invention has been described in connection with certain embodiments, it is to be understood that the invention is not limited to the disclosed embodiments, but, on the contrary, is intended to cover various modifications and equivalent arrangements included within the spirit and scope of the appended claims.