Flexible display apparatus

A flexible display apparatus includes: a flexible substrate including a first surface and a second surface which is opposite to the first surface; a first display unit which displays an image with light and is on the first surface of the flexible substrate, the first display unit including a transmission area at which light from the flexible substrate passes through the first display unit to outside the first display unit; and a second display unit which displays an image with light and is on the second surface of the flexible substrate, the second display unit disposed corresponding to the transmission area of the first display unit on the first surface of the flexible substrate.

This application claims priority to Korean Patent Application No. 10-2016-0044260, filed on Apr. 11, 2016, and all the benefits accruing therefrom under 35 U.S.C. § 119, the content of which in its entirety is herein incorporated by reference.

BACKGROUND

One or more embodiments relate to a flexible display apparatus, and more particularly, to a flexible display apparatus that is relatively easily bent.

2. Description of the Related Art

Among display apparatuses, an organic light-emitting display apparatus has advantages such as relative wide viewing angles, a high contrast ratio and fast response rates and thus has drawn attention as a next-generation display apparatus.

In general, when the organic light-emitting display apparatus is manufactured, thin film transistors and organic light-emitting devices are formed on a substrate, and the organic light-emitting devices generate and emit light during operation of the organic light-emitting apparatus. The organic light-emitting display apparatus is used as a display unit of a relatively small product such as a cell phone or a display unit of a relatively large product such as a television (“TV”).

Light-emitting diodes (“LED”s) convert electrical signals into light such as infrared rays or visible rays based on characteristics of a compound semiconductor and are used in home appliances, remote controls, electric display boards, various automatic devices, or the like. LEDs have been used in an increasing number of areas from relatively small hand-held electronic devices to relatively large display devices.

SUMMARY

In a conventional flexible display apparatus, an insulating layer and a light-emitting element are disposed on a flexible substrate at a bending area of the flexible display apparatus. Due to bending of the flexible display apparatus at the bending area, the insulating layer may be damaged such as by cracking, and defects may occur in the light-emitting element due to the cracking of the insulating layer.

One or more embodiments of the invention include a flexible display apparatus that is relatively easily bent so as to solve problems including the problem described above. However, this is an example and does not pose a limitation on the scope of the present disclosure.

According to one or more embodiments, a flexible display apparatus includes: a flexible substrate including a first surface and a second surface which is opposite to the first surface; a first display unit which displays an image with light and is on the first surface of the flexible substrate, the first display unit including a transmission area at which light from the flexible substrate passes through the first display unit to outside the first display unit; and a second display unit which displays an image with light and is on the second surface of the flexible substrate, the second display unit disposed corresponding to the transmission area of the first display unit on the first surface of the flexible substrate.

The flexible substrate may include a bending area at which the flexible display apparatus is bent and a non-bending area at which the flexible display apparatus is not bent. The transmission area of the first display unit may be disposed at the bending area of the flexible substrate.

The first display unit may include a first light-emitting element which generates light of the first display unit. The first light-emitting element includes: a pixel electrode, an opposite electrode opposite to the pixel electrode, and an intermediate layer between the pixel electrode and the opposite electrode and comprising an emission layer.

The second display unit may include a second light-emitting element which is disposed at the transmission area of the first display unit and generates light of the second display unit.

The light emitted by the second light-emitting element may transmit through the flexible substrate at the transmission area of the first display unit and pass through the first display unit at the transmission area thereof to the outside of the first display unit.

At the transmission area of the first display unit, the first display unit may include an insulating layer disposed on the first surface of the flexible substrate, and a first opening may be defined in the insulating layer of the first display unit, the first opening defining a transparent window of the transmission area at which the light from the flexible substrate passes through the first display unit to the outside of the first display unit.

The second light-emitting element on the second surface of the flexible substrate may be disposed at the first opening of the first display unit disposed on the first surface of the flexible substrate.

The flexible substrate may further include a bending area at which the flexible display apparatus is bent and a non-bending area at which the flexible display apparatus is not bent, the second display unit may be disposed at the bending area of the flexible substrate and the flexible display apparatus may further include a protection film on the second surface of the flexible substrate at the non-bending area of the flexible substrate.

The protection film on the second surface of the flexible substrate may be disposed non-overlapping the second display unit on the second surface of the flexible substrate.

The flexible display apparatus may further include an adhesive layer between the second display unit and the second surface of the flexible substrate. The adhesive layer may have transparency.

DETAILED DESCRIPTION

As the present disclosure allows for various changes and numerous embodiments, particular embodiments will be illustrated in the drawings and described in detail in the written description. The attached drawings for illustrating embodiments of the present disclosure are referred to in order to gain a sufficient understanding of the present disclosure, the merits thereof, and the objectives accomplished by the implementation of the present disclosure. The present disclosure may, however, be embodied in many different forms and should not be construed as being limited to the embodiments set forth herein.

Hereinafter, the present disclosure will be described in detail by explaining embodiments of the present disclosure with reference to the attached drawings. Like reference numerals in the drawings denote like elements.

It will be understood that when a layer, region, or component is referred to as being “formed on” another layer, region, or component, it can be directly or indirectly formed on the other layer, region, or component. That is, for example, intervening layers, regions, or components may be present. In contrast, when an element is referred to as being “directly on” another element, there are no intervening elements present.

Due to a growing interest in flexible display apparatuses among organic light-emitting display apparatuses, research into flexible organic light-emitting display apparatuses has been actively conducted. Glass substrates are generally used as a base substrate to manufacture flexible display apparatuses. However, flexible substrates including, for example, synthetic resin, have been recently used as the base substrate to implement flexible display apparatuses.

FIG. 1is a schematic perspective view of an embodiment of a flexible display apparatus1according to the invention.FIG. 2is a schematic cross-sectional view taken along line II-II′ of the flexible display apparatus1ofFIG. 1. The flexible display apparatus1is shown in a bent state inFIG. 1. The bent flexible display apparatus1ofFIG. 1is shown in an unbent state thereof inFIG. 2.

Referring toFIG. 1, the flexible display apparatus1includes a flexible (base) substrate100having or defining a first surface100a, a second surface100b, a first display unit200(or layer) on the first surface100aof the flexible substrate100and including a transparent (or transmission) area TA, and a second display unit (or layer)300on the second surface100bof the flexible substrate100. An upper surface of the first display unit200may form an outermost surface of the flexible display apparatus1at a viewing side thereof.

The flexible substrate100having flexibility may be in a board form and have the first surface100aand the second surface100bwhich is opposite to the first surface100a. The flexible substrate100may be extended in a plane defined by two directions, and have a thickness extended in a direction which crosses each of the two plane-directions. The flexible substrate100may include various materials, for example, metals, plastics such as polyethylene terephthalate (“PET”), polyethylene naphthalate (“PEN”) or polyimide, or the like. The flexible substrate100may be extended to be flat (e.g., unbent state) or may be deformed (e.g., bent state).

The flexible substrate100may include a bending area BA at which the flexible display apparatus1is bent and a non-bending area NBA at which the flexible apparatus1is not bent (e.g., disposed in a respective plane).FIG. 1shows that the bending area BA is between plural non-bending areas NBA. However, the bending area BA may be at an edge of a panel so as to not be between plural non-bending areas NBA. The bending area BA of the flexible substrate100(and/or the flexible display apparatus1) is disposed adjacent to a non-bending area NBA thereof.

In addition, referring toFIG. 1, both of the non-bending areas NBA substantially form a right angle with respect to the bending area BA. However, the present disclosure is not limited thereto. An angle formed by the non-bending areas NBA with respect to the bending area BA may vary. According to an embodiment, the flexible substrate100may be completely folded such that the non-bending areas NBA are disposed to overlap each other in a top plan view (e.g., thickness direction of the flexible display substrate100and/or flexible display apparatus1).

The first display unit200may be on the first surface100aof the flexible substrate100. As shown inFIG. 1, the first display unit200may be on the entire surface100aof the flexible substrate100.FIG. 1shows opposing y-axis direction edges of the first display unit200disposed coplanar with opposing y-axis edges of the flexible substrate100in the y-axis direction. While not shown inFIG. 1, opposing x-axis direction edges of the first display unit200may similarly disposed coplanar with opposing x-axis edges of the flexible substrate100in the x-axis direction.

The first display unit200generates and displays an image with light. The first display unit200may include a display layer or optical medium layer, and a driving (or switching) layer which respectively controls the display or optical medium layer to generate light or to not generate light and/or to transmit light or block light. In an embodiment, the display unit200may include a thin film transistor (“TFT”) as a switching or control element. The thin film transistor TFT may be provided in plurality within the display unit200. The display unit200may be an organic light-emitting display unit including the TFTs and pixel electrodes which are connected to the TFTs to be controlled or driven thereby. In another embodiment, the display unit200may be a liquid crystal display unit having liquid crystal as the optical medium layer. In the illustrated embodiment, the first display unit200may be an organic light-emitting display unit. The first display unit200as the organic light-emitting display unit may include a pixel P provided in plurality such as an organic light-emitting diode (“OLED”) provided in plurality. The OLED may generate and emit light of the first display unit200.

Although not shown, a touch screen panel (“TSP”) and/or a cover window may be further disposed on an upper surface of the first display unit200which is furthest in the thickness direction thereof from the flexible substrate100.

The first display unit200may include the transparent area TA through which external light from outside the first display unit200(and the flexible display apparatus1) penetrates. The external light may penetrate through an entirety of the transparent area TA or through a portion thereof. The transparent area TA may be at a location corresponding to the bending area BA of the flexible substrate100. In the transparent area TA, a transparent window TW may be disposed. The transparent window TW may be an opening in a layer of the first display unit200, such as a first opening OP1. The external light may penetrate through the transparent window TW portion of the transparent area TA and may not penetrate through portions thereof at which the transparent window TW is not disposed.

In the transparent area TA, an insulating layer may be placed. It may be understood that the insulating layer may collectively refer to all or some of a buffer layer211, a gate insulating layer213, an interlayer insulating layer215, a planarization layer217and a pixel-defining layer219. In this case, the collective insulating layer may include or define the first opening OP1, and at least one of individual layers among those of the insulating layer may include or define the first opening OP1. The first opening OP1may be provided in plurality within the transparent area TA. The first opening OP1may correspond to the transparent window TW of the transparent area TA. Therefore, there may be plural transparent windows TW in the overall transparent area TA. In an embodiment, one single transparent window TW may correspond to the entire transparent area TA, depending on a size of the transparent window TW. In particular, the first display unit200may include the planarization layer217and the pixel-defining layer219as individual insulating layers, and the transparent window TW may be formed or defined in or by the planarization layer217and the pixel-defining layer219.

FIG. 2shows that the transparent window TW is formed in and by the planarization layer217and the pixel-defining layer219. However, in another embodiment, the transparent window TW may be formed in one or more individual insulating layer among the buffer layer211, the gate insulating layer213, the interlayer insulating layer215, the planarization layer217and the pixel-defining layer219.

Within the overall transparent area TA, there may be multiple transparent windows TW. Where the transparent window TW is provided in plurality, the transparent windows TW in the bending area BA may have sizes substantially the same as those of pixel areas PA in the non-bending area NBA (refer to the solid line rectangles inFIG. 1). As shown inFIG. 2, the pixel-defining layer219includes a second opening OP2defining a pixel area PA of a pixel P. Light may be generated and/or transmitted at the pixel area PA of the pixel P, while light may not be generated at and/or transmitted by a portion of the pixel P other than the pixel area PA. The second opening OP2may be provided in plurality to define the pixel area PA in plurality at the non-bending area NBA. The second opening OP2(e.g., the pixel area PA) of the pixel P of the non-bending area NBA may have a same planar size as the first opening OP1the transparent window TW of the transparent area TA.

As another embodiment, as shown inFIGS. 3 and 4, a single one of the transparent window TW in the transparent area TA of the bending area BA may have a planar size greater than that of the pixel area PA in the non-bending area NBA. InFIGS. 3 and 4, a planar size of the transparent windows TW ofFIGS. 1 and 2are shown in dotted line for reference. The planar size of the single one transparent window TW as shown inFIGS. 3 and 4may correspond to essentially an entirety of an overall planar size of the transparent area TA.

A first light-emitting element of the first display unit200, such as the OLED, may not be placed in the transparent area TA. That is, the OLED or other non-light transmitting or generating members may not be placed in the transparent window TW in the transparent area TA. The transparent window TW may function as a window through which light emitted from the second display unit300towards the first display unit200penetrates through the flexible substrate100to be disposed at the upper surface of the first display unit200. In this case, it may be understood that a transparent window has transparency or functions to have transparency to function as a light-transmitting area at which light may penetrate.

The second display unit300may be on the second surface100bof the flexible substrate100. The second display unit300may be a display unit including a TFT provided in plurality and a light-emitting device provided in plurality and connected to the TFTs. In the illustrated embodiment, the second display unit300may include a second light-emitting element such as a light-emitting diode (“LED”) as a light-emitting device. The LED may be provided in plurality within the second display unit300. The LEDs in the illustrated embodiment may be micro LEDs. Although the term ‘micro’ herein may indicate a size of about 1 micrometer (μm) to about 100 μm, the present disclosure is not limited thereto. The term ‘micro’ may be a size smaller or greater than the above-described sizes.

The first display unit200may be on the first surface100aof the flexible substrate100, and the second display unit300may be on the second surface100bthereof to dispose the flexible substrate100therebetween. Each of the first and second display units200and300may include a discrete light-emitting element, such as an OLED or LED. As shown inFIG. 1, the flexible substrate100may include or define the bending area BA and the non-bending areas NBA, and the second display unit300may be at a location corresponding to the bending area BA of the flexible substrate100. That is, the second display unit300may be on only a portion of the second surface100bof the flexible substrate100. InFIGS. 1 and 2, the second display unit300is at a location corresponding to the transparent area TA of the first display unit200and not corresponding to the non-bending area NBA. The light emitted from the second display unit300may penetrate the flexible substrate100and may be discharged through the transparent area TA of the first display unit200such as through the transparent window TW thereof.

Referring toFIGS. 1 and 2, one or more embodiment of the flexible display apparatus1according to the invention includes the first display unit200on the first surface100aof the flexible substrate100and the second display unit300on the second surface100bof the flexible substrate100.

As described above, the first display unit200may be on the entire surface100aof the flexible substrate100. That is, the flexible substrate100may include the bending area BA and the non-bending areas NBA. The first display unit200may be overlapping the bending area BA and the non-bending areas NBA of the flexible substrate100. The first display unit200in the non-bending areas NBA may include the pixels P each including an OLED.

On the flexible substrate100, the buffer layer211may be placed to flatten a surface of the flexible substrate100or to reduce or effectively prevent penetration of impurities or the like into a semiconductor layer212of a TFT. The semiconductor layer212may be on the buffer layer211. The buffer layer211may include silicon oxide or silicon nitride.

A gate electrode214is over the semiconductor layer212and may be electrically connected to a source electrode216aand a drain electrode216baccording to signals transmitted to the gate electrode214. The gate electrode214may be a single layer or collectively multiple layers. The gate electrode214may include, for example, at least one of aluminum (Al), platinum (Pt), palladium (Pd), silver (Ag), magnesium (Mg), gold (Au), nickel (Ni), neodymium (Nd), iridium (Ir), chromium (Cr), lithium (Li), calcium (Ca), molybdenum (Mo), titanium (Ti), tungsten (W) and copper (Cu) by taking into account adhesion with adjacent layers, surface flatness of stacked layers, workability, and the like.

In this case, the gate insulating layer213may be between the semiconductor layer212and the gate electrode214in order to insulate the semiconductor layer212and the gate electrode214from each other. The gate insulating layer213may include silicon oxide and/or silicon nitride.

The interlayer insulating layer215may be on the gate electrode214and may be a single layer or collectively multiple layers including silicon oxide, silicon nitride, or the like.

The source electrode216aand the drain electrode216bare on the interlayer insulating layer215. The source electrode216aand the drain electrode216bmay respectively connected to the semiconductor layer212through contact holes formed in the interlayer insulating layer215and the gate insulating layer213. The source electrode216aand the drain electrode216bmay each be a single layer or collectively multiple layers including, for example, at least one of Al, Pt, Pd, Ag, Mg, Au, Ni, Nd, Ir, Cr, Li, Ca, Mo, Ti, W, and Cu by taking conductivity, etc. into account.

Although not shown, a protection layer (not shown) may cover the TFT to protect the TFT. The protection layer may include, for example, an inorganic material such as silicon oxide, silicon nitride or silicon oxynitride. The protection layer may be between the TFT and the planarization layer217, but not being limited thereto.

The planarization layer217may be over the flexible substrate100. In this case, the planarization layer217may be a planarization layer or a protection layer. The planarization layer217substantially flattens an upper surface of the TFT and protects the TFT and various devices when the OLEDs are over the upper surface of the TFT. The planarization layer217may include, for example, an acryl-based organic material or benzocyclobutene (“BCB”). In this case, the buffer layer211, the gate insulating layer213, the interlayer insulating layer215and the planarization layer217may be over the entire flexible substrate100. However, as shown inFIG. 2, the planarization layer217may not be placed at the transparent window TW. In another example, some of the buffer layer211, the gate insulating layer213and/or the interlayer insulating layer215may not be in the transparent window TW in order to increase light transparency at the transparent window TW.

The pixel-defining layer219may be over the upper surface of the TFT. The pixel-defining layer219may be over the entire flexible substrate100and on the planarization layer217described above. The pixel-defining layer219may define boundaries of the transparent window TW as the first opening OP1in the bending area BA. The pixel-defining layer219may also define a pixel area PA as the second opening OP2in the non-bending area NBA.

The pixel-defining layer219may be, for example, an organic insulating layer. The organic insulating layer may include an acryl-based polymer such as polymethyl methacrylate (“PMMA”), polystyrene (“PS”), a polymer derivative having a phenol group, an imide-based polymer, an aryl ether-based polymer, an amide-based polymer, a fluorine-based polymer, a p-xylene-based polymer, a vinyl alcohol-based polymer or any combination thereof.

The OLED may be in the non-bending area NBA. The OLED may be on the planarization layer217and may include a pixel electrode220, an intermediate layer230including an emission layer (“EML”), and an opposite electrode240.

The intermediate layer230may be in the pixel area PA defined by the pixel-defining layer219. The intermediate layer230includes an EML which emits light due to electrical signals and may further include a hole injection layer (“HIL”) and a hole transport layer (“HTL”), which are between the EML and the pixel electrode220, and an electron transport layer (“ETL”) and an electron injection layer (“EIL”), which are between the EML and the opposite layer240, in addition to the EML. The intermediate layer230may have a single-layer structure or multilayer structure in which at least one of the HIL, the HTL, the ETL and the EIL is stacked. However, the intermediate layer230is not limited thereto and may have various structures.

The opposite electrode240that covers the intermediate layer230including the EML and is opposite to the pixel electrode220may be over the entire flexible substrate100. That is, the opposite electrode240may be commonly disposed with plural pixel areas PA. The opposite electrode240may be a (translucent) transparent electrode or a reflective electrode. The opposite electrode240in the non-bending area NBA may extend therefrom to be disposed in the bending area BA

When the opposite electrode240is a (translucent) transparent electrode, the opposite electrode240may include a layer including a metal, for example, Li, Ca, lithium fluoride (LiF)/Ca, LiF/Al, Al, Ag, Mg, or a combination thereof, which has a relatively small work function and a (translucent) transparent conductive layer including ITO, IZO, ZnO, In2O3, or the like. When the opposite electrode240is a reflective electrode, the opposite electrode240may include a layer including Li, Ca, LiF/Ca, LiF/Al, Al, Ag, Mg, or a combination thereof. However, a structure and materials of the opposite electrode240are not limited thereto and may vary.

A thin film encapsulation layer250may be on the opposite electrode240. The thin film encapsulation layer250may be over the entire first display unit200and may be a single layer or collectively multiple layers. When the thin film encapsulation layer250has a multilayer structure, the thin film encapsulation layer250may have a structure in which organic layers and inorganic layers or organic/inorganic combination layers are alternately stacked. The thin film encapsulation layer250may protect the first display unit200from penetration of external moisture.

The transparent area TA of the first display unit200may be in the bending area BA of the flexible substrate100. As described above, the OLED may not be placed in the transparent area TA. Instead, the transparent area TA may include at least one transparent window TW, and light emitted from the second display unit300may penetrate the flexible substrate100to be finally emitted from the first display unit200through the transparent window TW thereof.

As shown inFIG. 2, at the transparent window TW, the buffer layer211, the gate insulating layer213, the interlayer insulating layer215, the opposite electrode240and the thin film encapsulation layer250may be arranged. In another example, at the transparent window TW, only the opposite electrode240or the thin film encapsulation layer250may be placed and the buffer layer211, the gate insulating layer213, the interlayer insulating layer215may not be placed. In still another example, at the transparent window TW, the opposite electrode240or the thin film encapsulation layer250may not be placed and portions of the buffer layer211, the gate insulating layer213or the interlayer insulating layer215may be place and exposed at the transparent window TW by an opening of the first display unit200. In another example, no layers among the buffer layer211, the gate insulating layer213, the interlayer insulating layer215, the opposite electrode240and the thin film encapsulation layer250may be at the transparent window TW of the transparent area TA, and the flexible substrate100may be exposed at the transparent window TW by an opening of the first display unit200.

For the illustrated embodiment, in an embodiment of manufacturing a flexible display apparatus, the transparent window TW of the transparent area TA that is in the bending area BA may be patterned to have substantially the same size as each pixel area PA in the non-bending area NBA. AlthoughFIG. 2shows only one single transparent window TW, there may be multiple transparent windows TW in the transparent area TA in the bending area BA (refer toFIG. 1).

As shown inFIG. 2, some insulating layers may be at the transparent window TW of the transparent area TA. In order for the light, which is emitted from the second display unit300, to penetrate through the transparent window TW of the transparent area TA, the buffer layer211, the gate insulating layer213and the interlayer insulating layer215at the transparent window TW of the transparent area TA including a transparent or translucent material. Also, the thin film encapsulation layer250at the transparent window TW includes a same material as above, that is, a transparent or translucent material. As shown inFIG. 2, when the opposite electrode240is formed over the entire flexible substrate100and placed at the transparent window TW of the transparent area TA, the opposite electrode240also includes a transparent or translucent material.

The second display unit300may be on the second surface100bof the flexible substrate100. The second display unit300may be in the bending area BA of the second surface100bof the flexible substrate100. That is, it will be understood that the second display unit300may be at a location corresponding to the transparent area TA of the first display unit200on the first surface100aof the flexible substrate100. That is, instead of placing the light-emitting OLEDs in the transparent area TA of the first display unit200to provide light at the bending area BA, the light, which is emitted from the second display unit300placed on the second surface100bof the flexible substrate100to correspond to the transparent area TA at the bending area BA, may be emitted towards the first display unit200through the flexible substrate100. As such, light is emitted from the flexible display apparatus1at each of the bending and non-bending areas BA and NBA, merely from discrete light-generating and emitting elements disposed at different sides of the flexible substrate100.

The second display unit300includes a flexible substrate310different from the base flexible substrate100of the overall flexible display apparatus1, a TFT provided in plurality on the flexible substrate310, and a LED provided in plurality and electrically connected to the TFTs.

AlthoughFIG. 2shows that a semiconductor layer312of the TFT is directly on the flexible substrate310, in some cases, a buffer layer (not shown) may be between the semiconductor layer312and the flexible substrate310. A gate electrode314above the semiconductor layer312may overlap at least some portions of the semiconductor layer312, and a gate insulating layer313may be between the semiconductor layer312and the gate electrode314in order to insulate the semiconductor layer312and the gate electrode314from each other. A source electrode316(or a drain electrode) and a drain electrode318(or a source electrode) may be on an interlayer insulating layer315placed on the gate electrode314. The source electrode316and the drain electrode318may each be electrically connected to the semiconductor layer312through contact holes respectively formed or defined in the interlayer insulating layer315and the gate insulating layer313.

The TFT of the second display unit300is substantially the same as the TFT of the first display unit200, and thus repeated descriptions thereof will be omitted.

In addition, in the illustrated embodiment, the TFTs of the first display unit200and the second display unit300are of a top gate type in which a gate electrode is on an upper surface of an active layer. However, the invention is not limited thereto. The gate electrode may be under a lower surface of the active layer to define a bottom gate type TFT.

A first insulating layer330may be on the TFT and thus may protect and flatten an upper surface of the TFT. The first insulating layer330may include or define a concave portion330a. A first electrode319and a second electrode320placed on the interlayer insulating layer315may be exposed to outside the first insulating layer330at and by the concave portion330a. An LED350may be mounted in the concave portion330aand may be electrically connected to the first electrode319and the second electrode320which are exposed at the concave portion330a. The LED350may generate and emit light of the second display unit300. The LED350and/or the concave portion330amay be provided in plurality within the second display unit300. The LEDs350may be in one-to-one correspondence with the concave portions330a, or in multiple-to-one correspondence with the concave portions330a. In the illustrated embodiment, the first electrode319may be an extension of the drain electrode318(or the source electrode) of the TFT. In another embodiment, the first electrode319may be a separate layer from the layers forming the TFT of the second display unit300.

The first electrode319may be a reflective electrode and may include at least one layer. In an embodiment, for example, the first electrode319may include a metal material layer such as Al, Mo, Ti, Ti/W, Ag, Au, or a combination thereof. The first electrode319may include a reflective layer and a transparent conductive layer including a transparent conductive oxide (“TCO”) such as ITO, IZO, ZnO, or In2O3, or a conductive material such as a carbon nano tube film or a transparent conductive polymer. In an embodiment, the first electrode319may be a trilayer including an upper transparent layer and a lower transparent layer with a reflective layer therebetween.

The second electrode320may be a transparent or translucent electrode. In an embodiment, for example, the second electrode320may include the aforementioned transparent conductive material and at least one material selected from among Ag, Al, Mg, Li, Ca, Cu, LiF/Ca, LiF/Al, MgAg, and CaAg.

The LED350may be a micro LED. Although the term ‘micro’ herein indicates a size of about 1 μm to about 100 μm, but the present disclosure is not limited thereto. The term ‘micro’ may indicate a size smaller or greater than the above size. In an embodiment of manufacturing a flexible display apparatus, the LEDs350may be individually or collectively picked up and transported by a transport device on a wafer to the flexible substrate310with layers of the second display unit300thereon on which the LEDs350are to be disposed, and mounted in respectively the concave portion330adefined on the flexible substrate310. The LED350may be a red, green, blue or white LED or an ultraviolet (“UV”) LED.

The LED350may include a p-n diode (not shown), a first contact electrode (not shown) and a second contact electrode (not shown). The first contact electrode and/or the second contact electrode may include at least one layer and various conductive materials, for example, metals, conductive oxides, and conductive polymers. Each of the first contact electrode and the second contact electrode may selectively include a reflective layer, for example, an Ag layer. The first contact electrode is electrically connected to the first electrode319, and the second contact electrode is electrically connected to the second electrode320. In an embodiment, the p-n diode may include a p-doping layer, at least one quantum well layer, and an n-doping layer.

FIG. 2shows a horizontal micro LED. However, the present disclosure is not limited thereto. The LED350may be a flip-type LED in which the first contact electrode and the second contact electrode are arranged in the same direction, a vertical micro LED, or the like. In this case, locations of the first electrode and the second electrode may correspond to locations of the first contact electrode (not shown) and the second contact electrode (not shown) of the LED350.

Although not shown, the LED350may further include a reflective layer, etc. between the flexible substrate310and the LED350in order to reflectively emit light towards the flexible substrate100.

A second insulating layer340may be on the LED350to protect the LED350and flatten an upper surface of the LED350. The second insulating layer340and the first insulating layer330described above may be organic insulating layers. The organic insulating layers may include an acryl-based polymer such as PMMA, PS, a polymer derivative having a phenol group, an imide-based polymer, an aryl ether-based polymer, an amide-based polymer, a fluorine-based polymer, a p-xylene-based polymer, a vinyl alcohol-based polymer, or any combination thereof.

An adhesive layer510may be between the second display unit300and the second surface100bof the flexible substrate100. That is, the second display unit300may be adhered to the second surface100bof the flexible substrate100through the adhesive layer510. In this case, the adhesive layer510may include a transparent adhesive material since the adhesive layer510is placed in a direction in which light is emitted from the second display unit300. The adhesive layer510may include, for example, an optically clear adhesive (“OCA”), optically clear resin (“OCR”), or the like.

A protection film400may be on the second surface100bof the flexible substrate100. As shown inFIG. 2, the protection film400may be on a portion of the second surface100bon which the second display unit300is not placed. That is, when the second display unit300is at the location corresponding to the bending area BA of the flexible substrate100, the protection film400may be at a location corresponding to the non-bending area NBA of the flexible substrate100. An adhesive layer520may be between the protection film400and the flexible substrate100. Materials of the adhesive layer520and the adhesive layer510may be the same or different from each other. The protection film400may include a flexible plastic material, for example, PET.

The protection film400and the second display unit300may be spaced apart from each other by a certain interval such as by a groove530that may be formed therebetween. The groove530may be disposed at a boundary (dotted line inFIG. 2) where the bending area BA and the non-bending area NBA meet. In another embodiment, the protection film400and the second display unit300may contact each other at an interface of the bending and non-bending areas BA and NBA. In this case, one of the adhesive layer510or520may extend to define the other one of the adhesive layer510and520.

Referring toFIGS. 1 and 2, the first display unit200may include OLEDs, and the second display unit300may include LEDs. Referring to the unbent state of the flexible display apparatus1inFIG. 2, the flexible substrate100may be disposed in an x-y plane defined by the x-axis direction and the y-axis direction. In the plane of the flexible substrate100, the OLEDs may be spaced apart from one another by a first interval in a direction (an x-axis direction and/or a y-axis direction), and the LEDs are spaced apart from each other by a second interval in a direction (an x-axis direction and/or a y-axis direction). In an embodiment, the OLEDs correspond to pixel areas PA and the LEDs correspond to transparent windows TW, such that the pixel areas PA are spaced apart from one another by the first interval in a direction (an x-axis direction and/or a y-axis direction), and the transmission windows TW are spaced apart from each other by the second interval in a direction (an x-axis direction and/or a y-axis direction). In the illustrated embodiment, the first interval may be the same as the second interval. In another embodiment, the first interval may be different from the second interval.

In a conventional flexible display apparatus having OLEDs disposed on a same surface at both a bending area and a non-bending area, the yield and reliability of the entire flexible display apparatus decreases due to the frequent occurrence of defects in the OLEDs in the bending area.

In one or more embodiment of the flexible display apparatus1, the first display unit200on the first surface100aof the flexible substrate100includes the transparent area TA to correspond to the bending area BA, and through the transparent area TA, light emitted from the second display unit300that is on the opposing second surface100bof the flexible substrate100may pass through the flexible substrate100to be disposed at the first surface100athereof. In the illustrated embodiment, the LEDs350at the opposing second surface100bare included in the second display unit300in a micro unit such that the reliability of the flexible display apparatus1including light-emitting elements in the bending area BA may be improved.

In addition, as the first display unit200of the flexible display apparatus1includes the transparent window TW, images may be freely displayed at the bending area BA through an image generated by the second display unit300. In particular, even when the first display unit200does not emit light and an image is not generated by the first display unit200, certain information, etc. may still be displayed on the bending area BA through image-generation by the second display unit300using light.

FIG. 3is a schematic perspective view of another embodiment of a flexible display apparatus2according to the invention, andFIG. 4is a schematic cross-sectional view taken along line IV-IV′ of the flexible display apparatus2ofFIG. 3. The flexible display apparatus2is shown in a bent state inFIG. 3. The bent flexible display apparatus2ofFIG. 3is shown in an unbent state thereof inFIG. 4.

Referring toFIG. 3, the flexible display apparatus2includes the flexible substrate100having the first surface100aand the second surface100b, the first display unit200arranged on the first surface100aof the flexible substrate100and including the transparent area TA, and the second display unit300on the second surface100bof the flexible substrate100and generating and emitting light at the transparent area TA.

The flexible substrate100of the flexible display apparatus2according to the embodiment ofFIG. 3includes the bending area BA and the non-bending area NBA, and a structure corresponding to the bending area BA of the flexible display apparatus2is different from that corresponding to the flexible display apparatus1ofFIG. 1. Thus, a difference between the structures corresponding to the bending areas BA will be mainly described. Descriptions regarding the pixels P, pixel areas PA, the protection film400, and the like, which are at locations corresponding to the non-bending area NBA, are the same as those provided with reference toFIG. 1and thus are not repeated.

Referring toFIG. 3, in the flexible display apparatus2, the first display unit200may include the transparent (or transmission) area TA at a location corresponding to the bending area BA.

The transparent area TA may include the transparent window TW, and the transparent window TW may be understood as defined by or at the first opening OP1in a collective insulating layer. In particular, the first display unit200may include the individual planarization layer217and pixel-defining layer219as the collective insulating layer, and the transparent window TW defined with the first opening OP1may be formed or defined in the collective insulating layer planarization layer217and pixel-defining layer219.FIG. 4shows that the transparent window TW may be formed or defined in or by the planarization layer217and the pixel-defining layer219. However, in another embodiment, the transparent window TW may be formed in only one of the planarization layer217and the pixel-defining layer219.

The transparent window TW may be provided singularly in the transparent area TA. The single transparent window TW may have substantially a same planar size as that of the overall non-bending area NBA. That is, as shown inFIGS. 3 and 4, the single transparent window TW in the transparent area TA may have a greater planar size than each pixel area PA in the non-bending area NBA or a planar size corresponding to the entire transparent area TA.

In the illustrated embodiment, the transparent area TA may include the transparent window TW corresponding to the first opening OP1. Unlike the transparent window TW of the first flexible display apparatus1that is patterned to have a planar size substantially the same to that of the pixel area PA, the transparent window TW of the embodiment inFIGS. 3 and 4may expose the entire bending area BA of the flexible substrate100. That is, light-transmitting properties of layers at the single transparent window TW may allow light to be transmitted at an entire of the bending area BA. In another embodiment, a side or the other side of the transparent window TW may be open. In other words, a portion of the first display unit200, in which the transparent window TW of the transparent area TA is placed, may correspond to the bending area BA of the flexible substrate100.

Referring toFIG. 4, the first display unit200may include the transparent area TA including the transparent window TW, and the transparent window TW may correspond to the entire bending area BA of the flexible substrate100. Thus, in the second display unit300on the second surface100bof the flexible substrate100, plural LEDs350may correspond to the single transparent window TW of the transparent area TA.

Referring toFIG. 4, the first insulating layer330, in which the concave portion330aare formed or defined in plurality, may be on the flexible substrate310, and a plurality of LEDs350may be respectively mounted in the concave portions330a.FIG. 4shows that the LEDs350are directly on the flexible substrate310. However, various layers may be disposed on the flexible substrate310, and the LEDs350may be on any of these layers (refer toFIG. 2, for example). In an embodiment, for example, a TFT may be on the flexible substrate310, a planarization layer may cover the TFT, and an electrode electrically connected to the TFT may be on the planarization layer.

In the illustrated embodiment, the LED350may be a micro LED. Although the term ‘micro’ herein indicates a size of about 1 μm to about 100 μm, but the present disclosure is not limited thereto. The term ‘micro’ may indicate a size smaller or greater than the above size. In an embodiment of manufacturing a flexible display apparatus, the LEDs350may be individually or collectively picked up and transported by a transport device on a wafer to the flexible substrate310and thereby respectively mounted in the concave portions330a. Each LED350may be a red, green, blue or white LED or a UV LED.

Descriptions regarding the LEDs350and a structure of the second display unit300including the same are the same as those provided with reference toFIG. 2and thus are not repeated.

In a conventional flexible display apparatus having OLEDs disposed on a same surface at both a bending area and a non-bending area, the yield and reliability of the entire flexible display apparatus decreases due to the frequent occurrence of defects in the OLEDs in the bending area.

In one or more embodiment of the flexible display apparatus2, the first display unit200on the first surface100aof the flexible substrate100includes the transparent area TA at the location corresponding to the bending area BA, and the light emitted from the second display unit300on the opposing second surface100bof the flexible substrate100through the transparent window TW of the transparent area TA may penetrate the flexible substrate100to be disposed at the first surface100athereof. In the illustrated embodiment, the second display unit300includes the LEDs350at the opposing second surface100bin a micro unit such that the reliability of the flexible display apparatus2including the bending area BA may be improved.

In addition, as the first display unit200of the flexible display apparatus2includes the transparent window TW, images may be freely displayed at the bending area BA through an image generated by the second display unit300, and in particular, even when the first display unit200does not emit light and an image is not generated by the first display unit200, certain information, etc. may be displayed only on the bending area BA through image-generation by the second display unit300using light.

According to the one or more embodiments of the present disclosure, a flexible display apparatus that is relatively easily bent may be implemented. However, the scope of the present disclosure is not limited thereto.

It should be understood that embodiments described herein should be considered in a descriptive sense only and not for purposes of limitation. Descriptions of features or features within each embodiment should typically be considered as available for other similar features in other embodiments.