Organic light-emitting diode display having improved adhesion and damage resistance characteristics, an electronic device including the same, and method of manufacturing the organic light-emitting diode display

Provided is an organic light-emitting diode (OLED) display including: first and second plastic layers; a first barrier layer and a first intermediate layer each positioned between the first and second plastic layers; and an OLED layer formed on the second plastic layer. The first barrier layer comprises silicon nitride.

BACKGROUND

One or more embodiments of the present invention relate generally to an organic light-emitting diode (OLED) display. More specifically, one or more embodiments of the present invention relate to an OLED display including a flexible substrate, an electronic device including the OLED display, and a method of manufacturing the OLED display.

2. Description of the Related Art

An organic light-emitting diode (OLED) display is a self-emission type display that includes a hole injection electrode, an electron injection electrode, and an organic emission layer disposed therebetween, wherein a light is emitted as holes injected from the hole injection electrode and electrons injected from the electron injection electrode are recombined in the organic emission layer. The OLED display has been attracting attention as a potential next generation display due to its high quality characteristics, such as low power consumption, excellent luminance, and high response speed.

SUMMARY

One or more embodiments of the present invention include an organic light-emitting diode (OLED) display including a flexible substrate that has a low water vapor transmission rate and high adhesive strength, and a method of manufacturing the OLED display.

In one embodiment, an organic light-emitting diode (OLED) display includes first and second plastic layers; a first barrier layer and a first intermediate layer each positioned between the first and second plastic layers; and an OLED layer formed on the second plastic layer. The first barrier layer may include silicon nitride.

The silicon nitride may be present within the first barrier layer at a density of equal to or more than 2.2 g/cm3and less than or equal to 2.4 g/cm3.

The OLED display may further include a second barrier layer formed on the second plastic layer. The second barrier layer may include silicon nitride.

A density of the silicon nitride in the first barrier layer may be lower than a density of the silicon nitride in the second barrier layer.

A refractive index of the first barrier layer may be lower than a refractive index of the second barrier layer.

The OLED display may further include a third plastic layer formed over the second plastic layer, and a third barrier layer formed between the second and third plastic layers. The third barrier layer may include silicon nitride.

A density of the silicon nitride in the first barrier layer may be lower than a density of the silicon nitride in the third barrier layer.

A refractive index of the first barrier layer may be lower than a refractive index of the third barrier layer.

The silicon nitride may be present within the first barrier layer at a density of equal to or more than 2.2 g/cm3and less than or equal to 2.4 g/cm3.

In another embodiment, a method of manufacturing an OLED display may include forming a mother flexible substrate, the mother flexible substrate including first and second plastic layers, and a first barrier layer and a first intermediate layer each positioned between the first and second plastic layers. Also included may be forming a plurality of OLED layers on the mother flexible substrate; and dividing the mother flexible substrate into a plurality of display units each including one of the OLED layers. The first barrier layer may include silicon nitride.

The method may further include receiving a carrier substrate, wherein the forming a mother flexible substrate further includes forming the mother flexible substrate on the carrier substrate; and separating the carrier substrate from the mother flexible substrate.

In the method, the silicon nitride may be present within the first barrier layer at a density of equal to or more than 2.2 g/cm3and less than or equal to 2.4 g/cm3.

The method may further include forming a second barrier layer on the second plastic layer. The second barrier layer may include silicon nitride.

In the method, a density of the silicon nitride in the first barrier layer may be lower than a density of the silicon nitride in the second barrier layer.

In the method, a refractive index of the first barrier layer may be lower than a refractive index of the second barrier layer.

The method may further include forming a third plastic layer over the second plastic layer; and forming a third barrier layer between the second and third plastic layers. The third barrier may include silicon nitride.

In the method, a density of the silicon nitride in the first barrier layer may be lower than a density of the silicon nitride in the third barrier layer.

In the method, a refractive index of the first barrier layer may be lower than a refractive index of the third barrier layer.

In the method, the silicon nitride may be present within the first barrier layer at a density of equal to or more than 2.2 g/cm3and less than or equal to 2.4 g/cm3.

DETAILED DESCRIPTION

The present invention will now be described more fully with reference to the accompanying drawings for those of ordinary skill in the art to be able to perform the present invention without any difficulty. The invention may, however, be embodied in many different forms and should not be construed as being limited to the embodiments set forth herein.

Also, parts in the drawings unrelated to the detailed description are omitted to ensure clarity of the present invention. Like reference numerals in the drawings denote like elements, and thus their description will not be repeated.

The same elements denoted by the same reference numerals will be explained in a representative first embodiment and other embodiments will be explained by focusing on elements other than the elements in the first embodiment.

In the drawings, sizes and thicknesses of elements are arbitrarily shown for convenience of explanation, and thus the present invention is not limited thereto.

Thicknesses of various layers and regions in the drawings are expanded for clarity. Thicknesses of some layers and regions are exaggerated for convenience of explanation. It will be understood that when a layer, film, region, or plate is referred to as being “on” another layer, film, region, or plate, it may be directly on the other layer, film, region, or plate or intervening layers, films, regions, or plates elements may be present.

It will be further understood that the terms “includes” and/or “including” used herein specify the presence of stated features, integers, steps, operations, members, components, and/or groups thereof, but do not preclude the presence or addition of one or more other features, integers, steps, operations, members, components, and/or groups thereof. When an element is referred to as being disposed “on” another element, the term “on” may encompass both orientations of “over” and “under”, that is, not only “over” in a gravity direction.

FIG. 1is a cross-sectional view of an organic light-emitting diode (OLED) display100according to an embodiment of the present invention.

The flexible substrate FS includes a first plastic layer1PL, a first barrier layer1BL, a first intermediate layer1IL, a second plastic layer2PL, and a second barrier layer2BL.

The first and second plastic layers1PL and2PL may be formed of a plastic material having excellent thermal resistance and excellent durability, such as polyimide, polyiminde, polyethylene naphthalate, polyethylene terephthalate (PET), polyarylate, polycarbonate, polyether imide (PEI), or polyethersulfone.

Since moisture or oxygen easily penetrates through the first and second plastic layers1PL and2PL formed of the plastic material as compared to a glass substrate, the OLED layer120, which is vulnerable to moisture or oxygen, may deteriorate, and thus a lifespan of the OLED display100may be reduced.

Accordingly, the first barrier layer1BL is formed on the first plastic layer1PL and the second barrier layer2BL is formed on the second plastic layer2PL.

The first and second barrier layers1BL and2BL may be formed of an inorganic material, such as a metal oxide, a silicon nitride, or a silicon oxide. For example, the first and second barrier layers1BL and2BL may each be a single layer or multilayer of an inorganic material, such as AlO3, SiO2, or SiNx. A water vapor transmission rate (WVTR) of the first and second barrier layers1BL and2BL formed as single layers or multilayers may be lower than or equal to 10-5 (g/m2/day).

The first intermediate layer1IL may be formed between the first barrier layer1BL and the second plastic layer2PL in order to increase an adhesive strength between the first barrier layer1BL and the second plastic layer2PL, as will be described in detail later.

The TFT layer110and the OLED layer120are formed on the flexible substrate FS.

FIG. 2is an enlarged view of a region II ofFIG. 1, illustrating parts of the TFT layer110and the OLED layer120of the OLED display100.

Referring toFIG. 2, a TFT including a semiconductor layer111, a gate electrode113, a source electrode115, and a drain electrode116may be formed on the second barrier layer2BL. A gate insulation film112may be formed between the semiconductor layer111and the gate electrode113, and an interlayer insulation film114may be formed between the gate electrode113and the source electrode115and between the gate electrode113and the drain electrode116. Here, the semiconductor layer111may be amorphous silicon, an organic layer, or a conductive oxide. InFIG. 2, a top gate type TFT is shown, but the present invention is not limited thereto. In other words, a TFT having any one of various structures including a bottom gate type TFT may be used.

Meanwhile, inFIG. 2, the TFT is directly formed on the second barrier layer2BL, but the present invention is not limited thereto. A buffer layer (not shown) may be further disposed between the second barrier layer2BL and the TFT.

The buffer layer flattens the flexible substrate FS and prevents impure elements from penetrating into the semiconductor layer111from the flexible substrate FS. In the buffer layer, a silicon nitride and/or silicon oxide may be arranged as a single layer or a plurality of layers. Also, although not shown inFIG. 2, at least one capacitor may be connected to the TFT.

A passivation layer117may be formed on the TFT, and a pixel-defining layer122may be formed on the passivation layer117. The passivation layer117may protect the TFT and flatten or planarize a top surface of the TFT.

An OLED may be connected to one of the source and drain electrodes115and116of the TFT. The OLED may include a pixel electrode121, a counter electrode124, and a layer123including at least an organic emission layer disposed between the pixel and counter electrodes121and124. The layer123may be formed of a low molecular or high molecular organic material. When a low molecular organic material is used, the layer123may have a single or complex structure of a hole injection layer (HIL), a hole transport layer (HTL), an emission layer (EML), an electron transport layer (ETL), and an electron injection layer (EIL). When a high molecular organic material is used, the layer123may have a structure including an HTL and an EML. The layer123may form one unit pixel by using sub-pixels emitting red, green, and blue lights. The layer123may be formed as separate layers each including emission materials emitting one of red, green, and blue light and each being perpendicularly stacked on each other, or may be formed as layers each having a mix of differently-colored emission materials. Of course, any other combination of colors may be used as long as a white light is emitted. In addition, the OLED display100may further include a color changing layer or color filter that changes the white light to a predetermined color.

The counter electrode124may be variously modified, for example, may be commonly formed throughout or across a plurality of pixels.

The pixel electrode121may operate as an anode and the counter electrode124may operate as a cathode, or vice versa. Also, at least one of the pixel electrode121and the counter electrode124may be a transparent electrode through which a light emitted from the EML penetrates.

InFIGS. 1 and 2, the OLED layer120is formed on the TFT layer110for convenience of description. Thus, for example, parts of the TFT layer110and OLED layer120may be formed on the same layer. For example, the gate electrode113of the TFT and the pixel electrode121of the OLED may be formed on the same layer.

The thin-film encapsulation layer130encapsulating the OLED is formed on the flexible substrate FS. The thin-film encapsulation layer130may be formed of a plurality of inorganic layers or a combination of an inorganic layer and an organic layer.

The organic layer may be formed of a polymer, and for example, may be a single layer or a multilayer formed of any one of polyethylene terephthalate, polyimide, polycarbonate, epoxy, polyethylene, and polyacrylate. The organic layer may be formed of polyacrylate, and in detail, may include a polymerized monomer composition including a diacrylate-based monomer and a triacrylate-based monomer. A monoacrylate-based monomer may be further included in the polymerized monomer composition. Also, the polymerized monomer composition may include a well known photoinitiator, such as TPO, but is not limited thereto.

The inorganic layer may be a single layer or a multilayer including a metal oxide or a metal nitride. In detail, the inorganic layer may include any one of SiNx, Al2O3, SiO2, and TiO2.

An uppermost layer of the thin-film encapsulation layer130, which is externally exposed, may be formed of an inorganic layer in order to prevent water vapor transmission to the OLED.

The thin-film encapsulation layer130may include at least one sandwich structure, wherein at least one organic layer is inserted between at least two inorganic layers. Alternatively, the thin-film encapsulation layer130may include at least one sandwich structure, wherein at least one inorganic layer is inserted between at least two organic layers.

The thin-film encapsulation layer130may include a first inorganic layer, a first organic layer, and a second inorganic layer sequentially stacked from a top of the OLED. Alternatively, the thin-film encapsulation layer130may include a first inorganic layer, a first organic layer, a second inorganic layer, a second organic layer, and a third inorganic layer sequentially stacked from the top of the OLED. Alternatively, the thin-film encapsulation layer130may include a first inorganic layer, a first organic layer, a second inorganic layer, a second organic layer, a third inorganic layer, a third organic layer, and a fourth inorganic layer sequentially stacked from the top of the OLED. It should be noted that embodiments of the invention are not strictly limited to this configuration of layers, and any other suitable combination or order of layers is contemplated.

A halogenated metal layer including LiF may be further disposed between the OLED and the first inorganic layer. The halogenated metal layer may prevent the OLED from being damaged while forming the first inorganic layer via a sputtering method or a plasma deposition method.

The first organic layer may have a smaller area than the second inorganic layer, and the second organic layer may have a smaller area than the third inorganic layer. Also, the first organic layer may be completely covered by the second inorganic layer, and the second organic layer may be completely covered by the third inorganic layer.

Meanwhile, inFIGS. 1 and 2, the thin-film encapsulation layer130is directly formed on the counter electrode124, but alternatively, another component, such as a filler or an adhesive material, may be further disposed between the counter electrode124and the thin-film encapsulation layer130.

FIG. 3is a cross-sectional view of an OLED display101according to a comparative example.

Referring toFIG. 3, the OLED display101includes a flexible substrate FS-1the TFT layer110, the OLED layer120, and the thin-film encapsulation layer130.

The flexible substrate FS-1includes the first plastic layer1PL and the first barrier layer1BL. In other words, the flexible substrate FS-1includes one plastic layer and one barrier layer.

As shown in the comparative example, when the flexible substrate FS-1is formed only of one plastic layer and one barrier layer, the first barrier layer1BL may be damaged, for example, cracked, due to impurities or retraction defects formed on the first plastic layer1PL and/or the first barrier layer1BL. Moisture or oxygen may penetrate through such a damaged surface, in turn damaging the OLED.

FIG. 4is a cross-sectional view of an OLED display102according to another embodiment of the present invention.

Referring toFIG. 4, the OLED display102includes a flexible substrate FS-2, the TFT layer110, the OLED layer120, and the thin-film encapsulation layer130.

The flexible substrate FS-2includes the first plastic layer1PL, the first barrier layer1BL, the second plastic layer2PL, and the second barrier layer2BL. In other words, in the flexible substrate FS-2, a structure of a plastic layer and a barrier layer formed on the plastic layer is repeatedly formed twice.

Impurities or retraction defects may be randomly formed not only in the first plastic layer1PL and the first barrier layer1BL, but also in the second plastic layer2PL and the second barrier layer2BL. However, since an average water vapor transmission path from a defected region to an OLED is longer in the OLED display102than the OLED display101, the OLED may be prevented from being damaged even if the first barrier layer1BL and/or the second barrier layer2BL are damaged, for example, cracked.

Here, dark spot defects may be reduced as the flexible substrate FS-2has a low water vapor transmission rate, but since an adhesive strength between the first barrier layer1BL that is an inorganic film and the second plastic layer2PL that is an organic film is relatively weak, the first barrier layer1BL and the second plastic layer2PL may be detached from each other during manufacturing processes.

However, according to the OLED display100, the first barrier layer1BL and the second plastic layer2PL are not detached from each other since the first intermediate layer1IL improving the adhesive strength between the first barrier layer1BL and the second plastic layer2PL is formed between the first barrier layer1BL and the second plastic layer2PL.

The first intermediate layer1IL may include an amorphous material. The first intermediate layer1IL may include amorphous silicon as an example of the amorphous material.

Alternatively, the first intermediate layer1IL may include a metal thin film. The metal thin film may include at least one selected from among indium tin oxide (ITO), aluminum (Al), titanium (Ti), and molybdenum (Mo). However, a material of the first intermediate layer1IL is not limited to any of these materials, and any material is contemplated as long as the adhesive strength between the first barrier layer1BL and the second plastic layer2PL is improved.

Also, the first intermediate layer1IL may have a UV light transmittance of at least 10% so that the second plastic layer2PL is smoothly separated from a glass substrate GS during a process of separating a mother flexible substrate MFS and the glass substrate GS, which is described later with reference toFIGS. 11A and 11B. Accordingly, the first intermediate layer1IL may have a thickness that is less than or equal to 100 Å.

Table 1 below shows detachment evaluation results between the first barrier layer1BL and the second plastic layer2PL before a structure that does not include the first intermediate layer1IL on the flexible substrate FS-2is divided into display units. Sample 1 uses a SiO2 single layer, Sample 2 uses a SiNx single layer, Sample 3 uses a SiO2/SiNx/SiO2 complex layer, and Sample 4 uses a SiNx/SiO2/SiNx complex layer, as the first and second barrier layers1BL and2BL.

Table 2 below shows detachment evaluation results between the first barrier layer1BL and the second plastic layer2PL in a unit of a display, after the structure that does not include the first intermediate layer1IL on the flexible substrate FS-2is divided into display units. Sample 5 uses a SiNx/SiO2 complex layer and Sample 6 uses a SiNx/SiO2/SiNx complex layer as the first and second barrier layers1BL and2BL.

Table 3 below shows detachment evaluation results between the first barrier layer1BL and the second plastic layer2PL before a structure that includes the first intermediate layer1IL on the flexible substrate FS is divided into display units. Sample 7 uses ITO, Sample 8 uses Ti, and Sample 9 uses Al, as the first intermediate layer1IL. Also, Sample 10 forms the first intermediate layer1IL for 5 seconds by using a-Si, and Sample 11 forms the first intermediate layer1IL for 10 seconds by using a-Si. In Samples 7 through 11, the first and second barrier layers1BL and2BL are formed by using a SiNx/SiO2 complex layer respectively in thicknesses of 600 Å and 1500 Å.

Table 4 below shows detachment evaluation results between the first barrier layer1BL and the second plastic layer2PL in a display unit after the structure that includes the first intermediate layer1IL on the flexible substrate FS is divided into display units. Samples 7 through 11 are the same as those in Table 3.

Referring to Table 1, before the structure that does not include the first intermediate layer1IL is divided into display units, an average adhesive strength between the first barrier layer1BL and the second plastic layer2PL is from about 60 to about 200 gf/inch, and referring to Table 2, an average adhesive strength between the first barrier layer1BL and the second plastic layer2PL in a display unit after the structure is divided into display units is from about 35 to about 40 gf/inch, i.e., low.

However, referring to Table 3, before the structure that includes the first intermediate layer1IL is divided into display units, i) an average adhesive strength between the first barrier layer1BL and the second plastic layer2PL with an a-Si first intermediate layer1IL is from about 100 to about 300 gf/inch and ii) the first barrier layer1BL and the second plastic layer2PL are undetachable in the metal thin films. Referring to Table 4, the first barrier layer1BL and the second plastic layer2PL are undetachable in a display unit after the structure that includes the first intermediate layer1IL is divided into display units, and thus an average adhesive strength is not measurable. In other words, when the first intermediate layer1IL is disposed between the first barrier layer1BL and the second plastic layer2PL, an adhesive strength between the first barrier layer1BL and the second plastic layer2PL significantly increases.

Accordingly, in the OLED display100of the embodiment of the present invention, not only is an average water vapor transmission path increased, but also an adhesive strength between a lower barrier layer and an adjacent upper plastic layer is increased so as to improve detachment defects of a display, by alternately stacking two plastic layers and two barrier layers and disposing an intermediate layer between the adjacent plastic and barrier layers to form the flexible substrate FS.

FIG. 17is a view of an example of the flexible substrate FS of the OLED display100ofFIG. 1.

Referring toFIG. 17, the flexible substrate FS includes the first plastic layer1PL, the first barrier layer1BL, the first intermediate layer1IL, the second plastic layer2PL, and the second barrier layer2BL.

In the current embodiment, the first and second barrier layers1BL and2BL respectively include at least one silicon nitride film1SN and at least one silicon nitride film2SN. The density of a silicon nitride in the at least one silicon nitride film1SN of the first barrier layer1BL may be less than the density of a silicon nitride of the at least one silicon nitride film2SN of the second barrier layer2B. For example, the density of the silicon nitride of the at least one silicon nitride film1SN of the first barrier layer1BL may be equal to or more than 2.2 g/cm3and less than or equal to 2.4 g/cm3.

In order to prevent water vapor transmission through a plastic substrate, at least one layer of the first and second barrier layers1BL and2BL is formed of a silicon nitride, but a hydrogen content of the silicon nitride may affect a device characteristic of a TFT.

FIG. 18is a graph showing the gate voltage and drain current of an OLED, when a flexible substrate having a structure A, in which a silicon nitride film is formed in the first barrier layer1BL and a silicon nitride film is not formed in the second barrier layer2BL, is used, and when a flexible substrate having a structure B, in which silicon nitride films having the same density are formed in the first and second barrier layers1BL and2BL, is used.

Referring toFIG. 18, the slope of the leftmost portion of the curve is higher for the structure B than for the structure A. However, a change in the slope of the curve generated when the structure B does not occur in all OLEDs, but only in some OLEDs. Thus, in the structure B, a compensation design of a current is desired such that the device characteristic is more uniform. However, when a driving voltage is reduced according to the compensation design, a low grayscale off defect, wherein insufficient brightness occurs for low grayscales, may be generated.

Table 5 below shows a low grayscale off defect generated based on 20 cd, when the flexible substrates having the structures A and B are used.

As shown in Table 5, in the structure B, the prevalence of low scale off defects significantly increases because a device characteristic of a TFT is disunified by hydrogen that is randomly generated in the silicon nitride film of the second barrier layer2BL.

However, when the structure A is employed so as to decrease the number of such low grayscale off detects, a water vapor transmission rate that is an important characteristic of a barrier may be increased.

However, when the density of the silicon nitride of the at least one silicon nitride film1SN of the first barrier layer1BL is lower than the density of the silicon nitride of the at least one silicon nitride film2SN of the second barrier layer2BL, as is the case with the flexible substrate FS of the current embodiment, a deviation of a water vapor transmission rate of an OLED display may be reduced and characteristics of its TFTs may be improved.

FIG. 19is a graph showing a relationship between density of an initial silicon nitride film and hydrogen content.

Referring toFIG. 19, the hydrogen content increases as the density of the initial silicon nitride film decreases. As in the current embodiment, the density of the silicon nitride of the at least one silicon nitride film1SN of the first barrier layer1BL may be less than or equal to 2.4 g/cm3so that the at least one silicon nitride film1SN is formed to be porous. Here, it is difficult to form the at least one silicon nitride film1SN such that the density of the silicon nitride is lower than 2.2 g/cm3due to process reasons. When the at least one silicon nitride film1SN is porous, hydrogen content may be equal to or greater than 1×1017at./cm2, thereby increasing an amount of hydrogen generated during a thermal process of the at least one silicon nitride film1SN. Here, it is difficult to form the at least one silicon nitride film1SN such that the hydrogen content is greater than 10×1018at./cm2due to process reasons. The increased hydrogen amount may cure a defect site of a TFT, thereby improving a device characteristic of the TFT. In addition, by including the at least one silicon nitride film1SN in the first barrier layer1BL, a water vapor transmission rate may also be improved.

Meanwhile, the density of the silicon nitride of the at least one silicon nitride film1SN of the first barrier layer1BL may be formed to be lower than the density of the silicon nitride of the at least one silicon nitride film2SN of the second barrier layer2BL, so that a refractive index of the at least one silicon nitride film1SN of the first barrier layer1BL is formed to be smaller than a refractive index of the at least one silicon nitride film2SN of the second barrier layer2BL.

Meanwhile, inFIG. 17, one silicon nitride film1SN is formed on a silicon oxide film in the first barrier layer1BL, but embodiments of the present invention are not limited thereto. For example, one silicon nitride film may be formed somewhere else in the first barrier layer1BL, or in a different layer. Alternatively, a plurality of silicon nitride films may be formed in the first barrier layer1BL. Alternatively, a plurality of silicon oxide films and a plurality of silicon nitride films may be formed in the first barrier layer1BL.

FIGS. 5A through 10are views for describing a method of manufacturing the OLED display100, according to an embodiment of the present invention.

FIG. 5Ais a plan view for describing a process of forming the mother flexible substrate MFS on the glass substrate GS, andFIG. 5Bis a cross-sectional view taken along a line VB-VB ofFIG. 5A.

Referring toFIGS. 5A and 5B, the mother flexible substrate MFS is formed on the glass substrate GS.

The mother flexible substrate MFS formed of a plastic material bends or is stretched when heat is applied, and thus it is difficult to precisely form thin film patterns, such as various electrodes or conductive wires, on the mother flexible substrate MFS. Accordingly, several thin film patterns are formed while adhering the mother flexible substrate MFS to the glass substrate GS that is a carrier substrate.

First, a first plastic layer1PS is formed on the glass substrate GS. The first plastic layer1PS may be formed by coating and hardening a plastic polymer solution including at least one of polyimide, polyethylene naphthalate, polyethylene terephthalate, polyarylate, polycarbonate, polyether imide, and polyethersulfone on the glass substrate GS, or by laminating a polymer film on the glass substrate GS. Here, examples of a hardening method include a heat hardening method, a UV hardening method, and an electronic beam hardening method.

Then, the first barrier layer1BL is formed on the first plastic layer1PS. The first barrier layer1BL may be formed in a single layer or a multilayer by using an inorganic material, such as AlO3, SiO2, or SiNx, via chemical vapor deposition (CVD), plasma enhanced chemical vapor deposition (PECVD), or atomic layer deposition (ALD).

Then, the first intermediate layer1IL is formed on the first barrier layer1BL. The first intermediate layer1IL may be formed in a single layer or a multilayer by using an amorphous material, such as amorphous silicon, or a metal thin film, such as ITO, Al, Ti, or Mo, via CVD, PECVD, or ALD.

Then, the second plastic layer2PL is formed on the first intermediate layer1IL. The second plastic layer2PL may be formed of the same material as the first plastic layer1PL via the same method.

Meanwhile, the second plastic layer2PL may have lower viscosity than the first plastic layer1PL. When the first and second plastic layers1PL and2PL are formed via coating, a high viscosity coating solution includes many impurities, and the impurities may also be coated. Accordingly, the second plastic layer2PL may have lower viscosity than the first plastic layer1PL so that filtering is performed while coating the second plastic layer2PL. Here, impurities may be reduced by forming the second plastic layer2PL using a filtered material, and since a coating material forming the second plastic layer2PL has low viscosity, impurities generated in the first plastic layer1PL and the first barrier layer1BL may be covered.

Meanwhile, the first plastic layer1PL and the second plastic layer2PL have the same thickness inFIGS. 1 and 5A, but an embodiment of the present invention is not limited thereto. Penetration times of oxygen and moisture penetrating from outside the flexible substrate FS are affected more by the thickness of the second plastic layer2PL closer to the OLED layer120than by that of the first plastic layer1PL. Accordingly, by forming the second plastic layer2PS closer to the OLED layer120to be thicker than the first plastic layer1PL, the penetration times are delayed, thereby preventing deterioration of an OLED.

Then, the second barrier layer2BL is formed on the second plastic layer2PL. The second barrier layer2BL may be formed of the same material as the first barrier layer1BL via the same method.

FIG. 6Ais a plan view for describing a process of forming a plurality of units of OLED displays100on the mother flexible substrate MFS, andFIG. 6Bis a cross-sectional view taken along a line VIB-VIB ofFIG. 6A.

Referring toFIGS. 6A and 6B, the plurality of units of OLED displays100including the TFT layer110and the OLED layer120are formed on the mother flexible substrate MFS.

Various methods may be applied according to the semiconductor layer111(refer toFIG. 2) forming the TFT layer110. For example, when crystalline silicon, amorphous silicon, or conductive oxide is used as the semiconductor layer111, the semiconductor layer111may be formed via a deposition method, such as a PECVD method, an atmospheric pressure CVD (APCVD) method, or a low pressure CVD (LPCVD) method, and when an organic TFT is applied as the semiconductor layer111, a coating method or a printing method may be used. Alternatively, when polycrystalline silicon is used as the semiconductor layer111, amorphous silicon may be crystallized by using any one of various crystallization methods, such as rapid thermal annealing (RTA), solid phase crystallization (SPC), excimer laser annealing (ELA), metal induced crystallization (MIC), metal induced lateral crystallization (MILC), and sequential lateral solidification (SLS).

The gate electrode113(refer toFIG. 2), the source electrode115(refer toFIG. 2), the drain electrode116(refer toFIG. 2), a capacitor (not shown), and various wires (not shown) may be deposited on the TFT layer110via CVD, PECVD, or ALD, and the TFT layer110may be patterned via a photolithography process.

The layer123(refer toFIG. 2) including the organic emission layer of the OLED layer120may be formed via any one of various methods, such as a deposition method, a coating method, a printing method, and a light-heat transfer method.

Although not shown inFIG. 6B, a buffer layer (not shown) may be further disposed between the second barrier layer2BL and the TFT layer110.

FIG. 7is a cross-sectional view for describing a process of forming the thin-film encapsulation layer130for encapsulating a plurality of the OLED layers120on the mother flexible substrate MFS.

As described above, the thin-film encapsulation layer130may be formed of a plurality of inorganic layers or a combination of an inorganic layer and an organic layer. The inorganic layer and the organic layer may be formed via any one of various methods, such as a CVD method, a PECVD method, and a sputtering method.

Meanwhile, inFIG. 7, the thin-film encapsulation layer130commonly covers the entire plurality of units of OLED displays100, but an embodiment of the present invention is not limited thereto. In other words, the thin-film encapsulation layer130may individually cover the units of OLED displays100.

FIGS. 8 and 9are cross-sectional views for describing a process of separating the glass substrate GS and the mother flexible substrate MFS.

Referring toFIG. 8, in order to separate the mother flexible substrate MFS from the glass substrate GS, a laser beam is irradiated onto a surface of the glass substrate GS opposite to where the mother flexible substrate MFS is formed.

The laser beam may be a UV light irradiated by using an excimer laser. The irradiated UV light penetrates through the glass substrate GS, and is absorbed by the first and second plastic layers1PL and2PL. A binding force between the first and second plastic layers1PL and2PL and the glass substrate GS is weakened by absorbed energy. Also, the first and second barrier layers1BL and2BL are easily broken by external tension. Accordingly, by suitably applying the external tension to the mother flexible substrate MFS and the glass substrate GS in directions indicated by arrows ofFIG. 9, the mother flexible substrate MFS may be separated from the glass substrate GS.

Meanwhile, a first protection film140may be applied to the thin-film encapsulation layer130before the process of separating the mother flexible substrate MFS and the glass substrate GS. The first protection film140may be an optical member, such as a polarization film.

FIG. 10is a cross-sectional view for describing a process of dividing the OLED layer120formed on the mother flexible substrate MFS into the plurality of units of OLED displays100.

After separating the mother flexible substrate MFS from the glass substrate GS, a second protection film150is adhered to a rear surface of the mother flexible substrate MFS, and then the mother flexible substrate MFS may be divided into the plurality of units of OLED displays100. The second protection film150may be an optical member, such as a polarization film.

The OLED layer120formed on the mother flexible substrate MFS may be divided into the plurality of units of OLED displays100by cutting the mother flexible substrate MFS along a cutting line CL in a non-display region between the OLED displays100by using a cutting wheel or a laser cutter.

A method of manufacturing a mother flexible substrate MFS-1of the OLED display100according to another embodiment of the present invention will now be described with reference toFIGS. 11A and 11B.

FIG. 11Ais a plan view for describing a process of forming the mother flexible substrate MFS-1on the glass substrate GS, andFIG. 11Bis a cross-sectional view taken along a line XIB-XIB ofFIG. 11A.FIGS. 11A and 11Bparticularly illustrate in detail an outer region of bonding surfaces of the glass substrate GS and the mother flexible substrate MFS-1.

The first plastic layer1PL and the second plastic layer2PL formed on the glass substrate GS are respectively covered by the first barrier layer1BL and the second barrier layer2BL.

If an organic coating solution flows outside the glass substrate GS while forming the first and second plastic layers1PL and2PL on the glass substrate GS via a coating process, the organic coating solution that flowed outside the glass substrate GS generates a defect. Accordingly, the first and second plastic layers1PL and2PL are coated in a region smaller than the glass substrate GS. On the other hand, since the first and second barrier layers1BL and2BL are formed via a deposition method, such as CVD or PECVD, the first and second barrier layers1BL and2BL are formed closer to an end of the glass substrate GS than the first and second plastic layers1PL and2PL.

The second plastic layer2PL slightly covers, or extends beyond one or more outer edges of, the first plastic layer1PL. Even if the second plastic layer2PL is formed at the same location as the first plastic layer1PL, the second plastic layer2PL flows to an outer region of the first plastic layer1PL due to fluidity of a coating solution. The first intermediate layer1IL has the same size as the first and second barrier layers1BL and2BL. Accordingly, the outer region of the mother flexible substrate MFS-1has an overlapping region OA where a first intermediate layer1IL-1and the second plastic layer2PL overlap each other.

While separating the mother flexible substrate MFS-1and the glass substrate GS, an irradiated UV light has to penetrate through the glass substrate GS and be absorbed into the first and second plastic layers1PL and2PL, but in the overlapping region OA, the first intermediate layer1IL-1absorbs the UV light, and thus the UV light is prevented from being absorbed in the second plastic layer2PL. Accordingly, it may be difficult to separate the mother flexible substrate MFS-1from the glass substrate GS.

Accordingly, the first intermediate layer1IL-1may be formed such that the UV light suitably penetrates therethrough. For example, the first intermediate layer1IL-1may have UV light transmittance of at least 10%. The first intermediate layer1IL-1may have the UV light transmittance of at least 10% by suitably adjusting a thickness of the first intermediate layer1IL-1by adjusting a time of forming the first intermediate layer1IL-1. For example, the thickness of the first intermediate layer1IL-1may be lower than or equal to about 100 Å.

FIG. 12is a cross-sectional view for describing a method of manufacturing the OLED display100ofFIG. 1, according to an embodiment of the present invention.

Referring toFIG. 12, a first intermediate layer1IL-2is formed to be smaller than or equal in area to the first plastic layer1PL while forming a mother flexible substrate MFS-2.

InFIGS. 11A and 11B, the UV light transmittance of the first intermediate layer1IL-1is adjusted by adjusting the thickness of the first intermediate layer1IL-1in the overlapping region OA of the outer region of the mother flexible substrate MFS-1, whereas inFIG. 12, the first intermediate layer1IL-2is formed to be smaller than or equal in area to the first plastic layer1PL so that the overlapping region OA is fundamentally not formed in the outer region. In other words, an end of the second plastic layer2PL and an end of the first barrier layer1BL directly contact each other at an end of the glass substrate GS. Accordingly, the mother flexible substrate MFS-2may be smoothly separated from the glass substrate GS.

FIG. 13is a cross-sectional view for describing a method of manufacturing the OLED display100ofFIG. 1, according to another embodiment of the present invention.

Referring toFIG. 13, a second plastic layer2PL-3is formed to be smaller than or equal in area to the first plastic layer1PL while forming a mother flexible substrate MFS-3.

By forming the second plastic layer2PL-3to be smaller than or equal in area to the first plastic layer1PL, the overlapping region OA of the second plastic layer2PL-3and the first intermediate layer1IL is fundamentally not formed in the outer region as described above with reference toFIG. 12. Accordingly, the mother flexible substrate MFS-3and the glass substrate GS may be more readily separated from each other. Here, since the second plastic layer2PL-3flows on the first plastic layer1PL during a coating process, an area of the second plastic layer2PL-3may be designed smaller than an actual area to be formed during a designing process.

FIG. 14is a cross-sectional view of an OLED display200according to another embodiment of the present invention.

Referring toFIG. 14, the OLED display200includes the flexible substrate FS-2, the TFT layer110, the OLED layer120, and the thin-film encapsulation layer130. The current embodiment will be described mainly based on differences between the OLED display200and the OLED display100, and like reference numerals shall be understood based on the above descriptions thereof.

The flexible substrate FS-2of the OLED display200includes the first plastic layer1PL, the first barrier layer1BL, a first intermediate layer1IL-4, the second plastic layer2PL and the second barrier layer2BL.

The first intermediate layer1IL-4of the current embodiment is patterned to be located in a region where the OLED layer120is formed.

FIGS. 15A and 15Bare respectively a plan view and a cross-sectional view for describing a method of manufacturing the OLED display200ofFIG. 14, according to an embodiment of the present invention.

FIG. 15Ais a plan view for describing a process of forming a mother flexible substrate MFS-4on the glass substrate GS, andFIG. 15Bis a cross-sectional view taken along line XVB-XVB ofFIG. 15A.

Referring toFIGS. 15A and 15B, the first plastic layer1PL and the first barrier layer1BL are sequentially formed on the glass substrate GS, and then the first intermediate layer1IL-4is formed.

Here, the first intermediate layer1IL-4is formed only in regions corresponding to units of OLED displays200, and is not formed in a non-display region between the OLED displays200. Accordingly, in dividing of the mother flexible substrate MFS-4into the plurality of units of OLED displays200, an inorganic layer, such as the first intermediate layer1IL-4, is formed without reaching a cutting line so that a crack or contamination generated by the inorganic layer during cutting is reduced.

Also, since the first intermediate layer1IL-4is not formed at the end of the glass substrate GS, the first intermediate layer1IL-4and the second plastic layer2PL do not overlap at the end of the glass substrate GS. In other words, the end of the second plastic layer2PL and the end of the first barrier layer1BL directly contact each other at the end of the glass substrate GS. Accordingly, the mother flexible substrate MFS-4and the glass substrate GS may be more readily separated from each other.

FIG. 16is a cross-sectional view of an OLED display300according to another embodiment of the present invention.

Referring toFIG. 16, the OLED display300includes a flexible substrate FS-3, the TFT layer110, the OLED layer120, and the thin-film encapsulation layer130. The current embodiment will be described mainly based on differences between the OLED display300and the OLED display100, and like reference numerals shall be understood based on the above descriptions thereof.

The flexible substrate FS-3of the OLED display300includes the first plastic layer1PL, the first barrier layer1BL, the first intermediate layer1IL, the second plastic layer2PL, a second intermediate layer21L, the second barrier layer2BL, a third plastic layer3PL, and a third barrier layer3BL.

In other words, the flexible substrate FS-3of the OLED display300is formed by alternately stacking three plastic layers and three barrier layers, and disposing intermediate layers between adjacent plastic and barrier layers. Since an average water vapor transmission path is longer in the OLED display300than in the OLED display100, penetration of oxygen and moisture may be further prevented.

Although not shown in detail inFIG. 16, the first through third barrier layers1BL through3BL of the flexible substrate FS-3may each include at least one silicon nitride film (not shown).

The density of silicon nitride of the silicon nitride film of the first barrier layer1BL may be lower than the density of silicon nitride of the silicon nitride film of the third barrier layer3BL. For example, the density of the silicon nitride of the silicon nitride film of the first barrier layer1BL may be less than or equal to 2.4 g/cm3. Here, it is difficult to form the first barrier layer1BL such that the density of the silicon nitride is less than 2.2 g/cm3due to process reasons. Similarly, a refractive index of the silicon nitride film of the first barrier layer1BL may be smaller than a refractive index of the silicon nitride film of the third barrier layer3BL.

As such, by forming the silicon nitride film of the first barrier layer1BL to have a density of silicon nitride less than or equal to 2.4 g/cm3, such that the silicon nitride film is porous, a hydrogen amount generated during a thermal process of the silicon nitride film may be increased. The increased hydrogen amount may cure a defect site of a TFT, thereby improving a device characteristic of the TFT. In addition, by including the silicon nitride film1SN in the first barrier layer1BL, a water vapor transmission rate may also be improved.

Meanwhile, inFIG. 16, three plastic layers and three barrier layers are alternately stacked on each other, but a greater number of plastic and barrier layers may be stacked if required. Here, an intermediate layer is further disposed between adjacent plastic and barrier layers if required.

The first and second intermediate layers1IL and2IL may be patterned as described above with reference toFIG. 14.

Also, the above embodiments are described based on a structure of an OLED display, but the embodiments of the present invention may also be applied to various flexible displays. For example, the embodiments of the present invention may be applied to various electronic devices, such as mobile devices, navigations, video cameras, lap tops, tablet PCs, flat TVs, and beam projectors.

As described above, according to the one or more of the above embodiments of the present invention, a flexible substrate is formed by alternately stacking two plastic layers and two barrier layers and then disposing an intermediate layer between adjacent plastic and barrier layers, thereby increasing an average water vapour transmission path so as to prevent deterioration of an OLED.

An adhesive strength between a lower barrier layer and an adjacent upper plastic layer is increased, and thus a detachment defect of an OLED display may be improved.

By forming barrier layers to include a silicon nitride, where the density of silicon nitride in a barrier layer disposed far from an OLED is less than the density of silicon nitride in a barrier layer disposed closer to the OLED, a TFT characteristic may be improved and the water vapor transmission rate of a flexible substrate may be decreased.

While one or more embodiments of the present invention have been described with reference to the figures, it will be understood by those of ordinary skill in the art that various changes in form and details may be made therein without departing from the spirit and scope of the present invention as defined by the following claims. Various features of the embodiments shown can be mixed and matched in any manner, to produce further embodiments contemplated by the invention.