Organic light emitting diode display

An organic light emitting diode (OLED) display includes a flexible substrate, a barrier layer disposed on the flexible substrate, and an organic light emitting diode disposed on the barrier layer. The barrier layer includes a plurality of metal layers and a plurality of insulation layers in which the metal layers and the insulation layers are alternatively stacked with each other on the flexible substrate.

CROSS-REFERENCE TO RELATED APPLICATION

This application claims priority under 35 U.S.C. §119 to Korean Patent Application No. 10-2013-0122868 filed on Oct. 15, 2013, the disclosure of which is hereby incorporated by reference herein in its entirety.

TECHNICAL FIELD

The present disclosure relates to an organic light emitting diode (OLED) display. More particularly, the present disclosure relates to a flexible OLED display provided with a plastic substrate.

DISCUSSION OF THE RELATED ART

An organic light emitting diode (OLED) display includes an organic light emitting diode and a pixel circuit in each pixel area on a substrate, and displays an image using light emitted from the organic light emitting diode. As the OLED display is a self-emissive display which does not require a backlight, unlike a liquid crystal display, it is possible to reduce the thickness and the weight thereof.

In addition, the OLED display may have a flexible characteristic when a plastic film is used as the substrate. However, the plastic substrate may have a higher water vapor transmission rate (WVTR) than a glass substrate, and thus a barrier layer is provided between the plastic substrate and the pixel circuit for prevention of water transmission. The barrier layer is formed of a plurality of inorganic layers, and may have a structure, for example, in which SiOxand SiNxare alternately layered.

However, the barrier layer may be increased in thickness when assuring a predetermined level of WVTR, thereby deteriorating flexibility. Thus, when stress such as bending or torsion stress is applied to the barrier layer, cracks may be readily formed in the barrier layer, thereby deteriorating the water permeation prevention function. Further, the cracks formed in the barrier layer may spread to an upper portion where the pixel circuit and the organic light emitting diode are located, thereby causing a product failure.

SUMMARY

Exemplary embodiments of the present invention provide an OLED display that can increase a moisture transmission blocking effect by reducing a water vapor transmission rate of a barrier layer and also suppress generation of cracks while increasing flexibility by reducing the thickness of the barrier layer.

An OLED display according to an exemplary embodiment of the present invention includes: a flexible substrate, a barrier layer disposed on the flexible substrate, and an organic light emitting diode disposed on the barrier layer. The barrier layer includes a plurality of metal layers and a plurality of insulation layers in which the metal layers and the insulation layers are alternatively stacked with each other on the flexible substrate.

The metal layers may include at least one selected from a group consisting of aluminum, molybdenum, titanium, copper, nickel, chromium, tungsten, and tin. Each of the metal layers may have a thickness of about 0.01 μm to about 10 μm. A buffer layer including an inorganic layer may be disposed between the barrier layer and the organic light emitting diode, and the insulation layer may be disposed at the outermost side of the barrier layer that contacts the buffer layer.

The insulation layers may include an organic layer. The organic layer may include at least one selected from a group consisting of polyethylene terephthalate, a polyimide, a polycarbonate, an epoxy, a polyethylene, and a polyacrylate.

Alternatively, the insulation layers may include an inorganic layer. The inorganic layers may include at least one selected from a group consisting of a silicon oxide (SiOx), a silicon nitride (SiNx), alumina (Al2O3), indium tin oxide (ITO), titanium oxide (TiO2), and gallium arsenide (GaAs), and may be formed using a plasma enhanced chemical vapor deposition (PECVD) method.

The barrier layer may further include a metal oxide layer formed at one side of one of the metal layers that contacts one of the inorganic layers. The metal oxide layer may be formed using an anodization method, and has a thickness of about 2 μm to about 3 μm.

Alternatively, the inorganic layers may include at least one selected from a group consisting of a silicon oxide (SiOx), a silicon nitride (SiNx), alumina (Al2O3), indium tin oxide (ITO), titanium oxide (TiO2), and gallium arsenide (GaAs), and may be formed using an atomic layering deposition (ALD) method.

In accordance with an exemplary embodiment, an organic light emitting diode (OLED) display is provided. The OLED display includes a flexible substrate, a barrier layer disposed on the flexible substrate, a buffer layer disposed on the barrier layer, a thin film transistor disposed on the buffer layer, a capacitor disposed on the buffer layer, a passivation layer disposed on the thin film transistor and the capacitor, an organic light emitting diode disposed on the passivation layer, in which the organic light emitting diode is electrically connected with the thin film transistor, and a thin film encapsulation layer encapsulating the organic light emitting diode, in which the thin film encapsulation film includes a plurality of organic layers and a plurality of inorganic layers alternately stacked with each other on the organic light emitting diode.

The barrier layer includes a plurality of metal layers and a plurality of insulation layers which are alternatively stacked with each other on the flexible substrate, wherein an uppermost one of the insulation layers contacts the buffer layer and a lowermost one of the insulation layers contacts the flexible substrate.

According to exemplary embodiments of the present invention, the OLED display blocks moisture and oxygen entering from a flexible substrate using a barrier layer so that deterioration of the pixel circuit and the organic light emitting diode can be suppressed, and excellent flexibility and transparency can be assured. In addition, as no cracks are readily generated in the barrier layer even through stress such as bending or torsion stress is applied thereto, deterioration of the pixel circuit and the organic light emitting diode due to the cracks can be suppressed.

DETAILED DESCRIPTION OF EXEMPLARY EMBODIMENTS

Exemplary embodiments of the present invention will be described more fully hereinafter with reference to the accompanying drawings, in which exemplary embodiments of the invention are shown. As those of ordinary skill in the art would realize, the described embodiments may be modified in various different ways, all without departing from the spirit or scope of the present invention.

Unless explicitly described to the contrary, the word “comprise” and variations such as “comprises” or “comprising” will be understood to imply the inclusion of stated elements but not the exclusion of any other elements. In addition, it will be understood that when an element such as a layer, film, region, or substrate is referred to as being “on” another element, it can be directly on the other element or intervening elements may also be present. Further, in the specification, the term “˜ on” means positioning on or below the object portion, but does not essentially mean positioning on the upper side of the object portion based on a gravity direction.

Also, as used herein, the singular forms, “a”, “an”, and “the” are intended to include plural forms as well, unless the context clearly indicates otherwise.

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

Referring toFIG. 1, an OLED display100according to the present exemplary embodiment includes, for example, a flexible substrate10, a barrier layer20formed on the flexible substrate10, a thin film transistor30, a capacitor40, and an organic light emitting diode50.

The thin film transistor30and the capacitor40form a pixel circuit, and the pixel circuit and the organic light emitting diode50are provided in every pixel area on the flexible substrate10. The OLED display100displays an image using light emitted from the plurality of organic light emitting diodes50.FIG. 1illustrates one pixel area for convenience of description.

The flexible substrate10is formed of, for example, a plastic film. When the OLED display100is a bottom emission-type display and thus light emitted from the organic light emitting diode50is discharged through the flexible substrate10, the flexible substrate10is formed of, for example, a transparent plastic film. For example, in an embodiment, the flexible substrate10may be formed of, for example, at least one of polycarbonate (PC), polyester (PET), polypropylene (PP), polyethylene (PE) and polymethyl methacrylate (PMMA).

The barrier layer20is formed throughout the flexible substrate10, and has a lower moisture transmission rate and oxygen transmittance than the flexible substrate10. As the plastic film used as the flexible substrate10has a higher moisture transmission rate than a glass substrate, the barrier layer20is provided to suppress the permeation of moisture through the flexible substrate10and into the pixel circuit and the organic light emitting diode50.

A buffer layer11formed of, for example, an inorganic layer is provided on the barrier layer20. The buffer layer11may include, for example, silicon oxide (SiOx), silicon nitride (SiNx) and/or silicon oxynitride (SiONx). The buffer layer11provides a flat surface for forming the pixel circuit, and prevents permeation of moisture and foreign particles into the pixel circuit and the organic light emitting diode50.

The thin film transistor30and the capacitor40are formed on the buffer layer11. The thin film transistor30includes, for example, a semiconductor layer31, a gate electrode32, a source electrode33, and a drain electrode34. For example, the semiconductor layer31is formed of a polysilicon or oxide semiconductor, and includes a channel area311in which an impurity is not doped and a source area312and a drain area313formed at opposite ends of the channel area311and doped with an impurity. When the semiconductor layer31is formed of the oxide semiconductor, an additional protection layer may be added to protect the oxide semiconductor.

A gate insulating layer12is provided between the semiconductor layer31and the gate electrode32, and an interlayer insulating layer13is provided between the gate electrode32and the source and drain electrodes33and34. The gate insulating layer12may include, for example, at least one of silicon nitride (SiNx), silicon oxide (SiOx), silicon oxynitride (SiONx), aluminum oxide (Al2O3), zirconium oxide (ZrO2), hafnium oxide (HfO2), titanium oxide (TiO2), tantalum oxide (Ta2O5), a barium-strontium-titanium-oxygen (Ba—Sr—Ti—O) compound, a bismuth-zinc-niobium-oxygen (Bi—Zn—Nb—O) compound, an organic insulating material (e.g. benzocyclobutene (BCB)), and the like.

In an embodiment, the gate electrode32may include, for example, at least one of an aluminum-based metal, such as aluminum (Al) or an aluminum alloy, a silver-based metal, such as silver (Ag) or a silver alloy, a copper-based metal, such as copper (Cu) or a copper alloy including copper manganese (CuMn), a molybdenum-based metal, such as molybdenum (Mo) or a molybdenum alloy, chromium (Cr), tantalum (Ta), tungsten (W) and titanium (Ti).

In an embodiment, the source electrode33and the drain electrode34may each include, for example, at least one of an aluminum-based metal, such as aluminum (Al) or an aluminum alloy, a silver-based metal, such as silver (Ag) or a silver alloy, a copper-based metal, such as copper (Cu) or a copper alloy including copper manganese (CuMn), a molybdenum-based metal, such as molybdenum (Mo) or a molybdenum alloy, chromium (Cr), tantalum (Ta), tungsten (W) and titanium (Ti).

The capacitor40includes, for example, a first capacitor plate41formed on the gate insulating layer12and a second capacitor plate42formed on the interlayer insulating layer13. The first capacitor plate41may be made of, for example, the same material as the gate electrode32, and the second capacitor plate42may be made of the same material as the source and drain electrodes33and34. The second capacitor plate42may be connected with the source electrode33.

The thin film transistor30shown inFIG. 1is a driving thin film transistor, and the pixel circuit further includes a switching thin film transistor. The switching thin film transistor is used as a switching element that selects a pixel for light emission, and the driving thin film transistor applies power for light emission of the selected pixel to the corresponding pixel.

A passivation layer14is provided on the source and drain electrodes33and34and the second capacitor plate42. The passivation layer14may be formed of an organic insulating material, an inorganic insulating material, or a compound of the organic insulating material and the inorganic insulating material. For example, in an embodiment, the passivation layer14may be formed of, for example, an inorganic insulator such as silicon oxide (SiOx), silicon nitride (SiNx), silicon oxynitride (SiONx), or any combination thereof. The passivation layer14has a via hole that partially exposes the drain electrode34, and the organic light emitting diode50is formed on the passivation layer14.

The organic light emitting diode50includes, for example, a pixel electrode51, an organic emission layer52, and a common electrode53. The pixel electrode51is provided in each pixel, and is electrically connected with the drain electrode34of the thin film transistor30through the via hole. The common electrode53is formed throughout the flexible substrate10without distinction of the pixel. A pixel defining layer15partitioning the pixel areas is provided on the pixel electrode51, and the organic emission layer52is formed in an opening of the pixel defining layer15and thus contacts the pixel electrode51.

One of the pixel electrode51and the common electrode53is an anode, which is a hole injection electrode, and the other is a cathode, which is an electron injection electrode. Holes injected from the anode and electrons injected from the cathode are combined in the organic emission layer52to generate excitons, and light emission is performed while the excitons discharge energy.

At least one layer of the hole injection layer and a hole transport layer may be provided between the anode and the organic emission layer52, and at least one of the electron injection layer and an electron transport layer may be provided between the organic emission layer52and the cathode. The hole injection layer, the hole transport layer, the electron transport layer, and the electron injection layer may be formed on the entire flexible substrate10without distinction of the pixel.

One of the pixel electrode51and the common electrode53may be formed of a reflective layer, and the other may be formed of a semi-transmissive or transparent conductive layer. Light emitted from the organic emission layer52is reflected by the reflective layer and emitted to the outside through the transparent conductive layer. For example, when the OLED display is a front emission type of display, the pixel electrode51is formed of a reflective layer, and when the OLED display is a bottom emission type of display, the common electrode53is formed of a reflective layer.

A thin film encapsulation layer60is provided on the organic light emitting diode50. The thin film encapsulation layer60encapsulates the organic light emitting diode50from the external environment containing moisture and oxygen to suppress deterioration in the organic light emitting diode50due to the moisture and oxygen. The thin film encapsulation layer60may be formed of, for example, a configuration in which a plurality of organic layers and a plurality of inorganic layers are alternately stacked one by one.

The organic layer of the thin film encapsulation layer60is formed of a polymer, and may be a single layer or a stacked layer formed of any one of, for example, polyethylene terephthalate, a polyimide, a polycarbonate, an epoxy, a polyethylene, and a polyacrylate. The inorganic layer of the thin film encapsulation layer60may be a single layer or a stacked layer containing, for example, a metal oxide or a metal nitride. For example, the inorganic layer may contain at least one of silicon nitride (SiNx), aluminum oxide (Al2O3), silicon oxide (SiOx), and titanium oxide (TiO2).

FIG. 2is an enlarged view of the barrier layer20of the OLED display ofFIG. 1.

Referring toFIG. 1andFIG. 2, the OLED display100prevents rear-side water vapor transmission by arranging the barrier layer20at a rear side of the pixel circuit and the organic light emitting diode50, and prevents front-side water vapor transmission by arranging the thin film encapsulation layer60at a front side of the pixel circuit and the organic light emitting diode50. In this case, the barrier layer20includes a metal layer21having a low water vapor transmission rate and a low oxygen transmission rate (OTR).

For example, the barrier layer20is formed of a configuration in which a plurality of metal layers21and a plurality of insulation layers are alternately layered one by one, and in this case, the insulation layer is formed of an organic layer22.

For example, the metal layer21may be a single layer or a stacked layer formed of at least one of aluminum, molybdenum, titanium, copper, nickel, chromium, tungsten, and tin, and may be formed using a method such as sputtering or thermal evaporation. The organic layer22may be a single layer or a stacked layer of a polymer, and may be formed using a method such as, for example, spin coating. The polymer of the organic layer22may include, for example, at least one of polyethylene terephthalate, a polyimide, a polycarbonate, an epoxy, a polyethylene, and a polyacrylate.

The metal layer21may have a thickness of, for example, about 0.01 μm to about 10 μm. When the thickness of the metal layer21is less than about 0.01 μm, the moisture and oxygen blocking performance is deteriorated, and when the thickness of the metal layer21exceeds about 10 μm, flexibility and transparency are decreased, thereby causing deterioration of a flexible characteristic and a display characteristic of the OLED display100. That is, the metal layer21having a thickness of about 0.01 μm to about 10 μm can assure an appropriate degree of flexibility and transparency while suppressing moisture and oxygen transmission.

The metal layer21is formed by layering a plurality of metal layers21, interposing the organic layer22therebetween so that the water vapor transmission rate and the oxygen transmission rate of the entire barrier layer20can be reduced without deterioration of flexibility and transparency. The organic layer22is provided between the metal layers21to supplement the moisture and oxygen blocking function of the barrier layer20. The plurality of metal layers21are respectively made of, for example, the same material and have the same thickness as each other. In addition, the plurality of organic layers22may also be made of, for example, the same material and may have the same thickness as each other.

The organic layers22may be provided at the outermost side of the barrier layer20that contacts the buffer layer11. The buffer layer11is made of, for example, an inorganic material using a plasma enhanced chemical vapor deposition (PECVD) method because an arc may be formed when an inorganic material is deposited on the metal layer21using the PECVD method. Thus, the organic layers22is provided at the outermost side of the barrier layer20such that the buffer layer11is formed without causing the generation of the arc.

Meanwhile, inFIG. 2, the organic layers22are provided at the outermost side of the barrier layer20that contacts the flexible substrate10, but the metal layers21may be provided at the outermost side of the barrier layer20that contacts the flexible substrate10.

As described, as the barrier layer20is provided with the metal layer21having the low water vapor transmission rate and oxygen transmission rate, moisture and oxygen entering from the flexible substrate10can be effectively blocked. That is, the metal layers21perform a barrier function that substantially blocks moisture and oxygen in the barrier layer20. In addition, the barrier layer20supplements the moisture and oxygen blocking function by the organic layers22being arranged between the metal layers21, while the flexibility and the transparency are assured by forming the metal layer21as a thin film.

FIG. 3is an enlarged cross-sectional view of a barrier layer of an OLED display according to an exemplary embodiment of the present invention.

Referring toFIG. 3, an OLED display according to the present exemplary embodiment is the same as the OLED display ofFIG. 1, except that an organic layer of a barrier layer201is replaced with an inorganic layer23and a metal oxide layer24is additionally provided. The same reference numerals are used in the present exemplary embodiment to refer to the same components as those of the OLED display ofFIG. 1.

The barrier layer201is formed of, for example, a configuration in which a plurality of metal layers21and a plurality of inorganic layers23are alternatively layered one by one. In addition, the inorganic layers23are provided at the outermost side of the barrier layer201that contacts the flexible substrate10and the buffer layer11. For example, the inorganic layers23may be a single layer or a stacked layer including a metal oxide or a metal nitride, and may include any one of a silicon oxide (SiOx), a silicon nitride (SiNx), alumina (Al2O3), indium tin oxide (ITO), titanium oxide (TiO2), and gallium arsenide (GaAs).

As the inorganic layers23have a heat-resistive temperature that is significantly higher than that of the organic layer22, there may be no limit in a process temperature in a subsequent process (e.g., a process for forming a pixel circuit and an organic light emitting diode50). That is, the organic layer has a heat-resistive temperature of about 450° C., and therefore a temperature in a subsequent process may not exceed about 450° C. However, there is no temperature limitation in the subsequent process in the present exemplary embodiment because the inorganic layers23are provided between the plurality of metal layers21.

The inorganic layers23may be formed using, for example, a PECVD method. In this case, an arc may be generated in a process for deposition of the inorganic layer on the metal layer21, and therefore the metal oxide layer24is provided at an upper surface of the metal layer21that contacts the inorganic layer23to suppress generation of an arc.

That is, in the present exemplary embodiment, the barrier layer201is formed with a structure formed by, for example, layering an inorganic layer23/a metal layer21/a metal oxide layer24/an inorganic layer23/a metal layer21/a metal oxide layer24/an inorganic layer23/a metal layer21/a metal oxide layer24/an inorganic layer23. For example, the metal oxide layer24may be formed by a known anodization method, and the metal oxide layer24may be formed with a thickness of about 2 μm to about 3 μm at a surface of the metal layer21.

When the thickness of the metal oxide layer24is less than about 2 μm, an arc may be generated in a process for deposition of the inorganic layer23, and when the thickness of the metal oxide layer24exceeds about 3 μm, the metal layer21may not be able to function as a moisture transmission blocking layer.

For example, the plurality of metal layers21are respectively formed of the same material and have the same thickness as each other. In addition, the plurality of inorganic layers23are respectively formed of, for example, the same material and have the same thickness as each other.

FIG. 4is an enlarged cross-sectional view of a barrier layer of an OLED display according to an exemplary embodiment of the present invention.

Referring toFIG. 4, an OLED display according to the present exemplary embodiment is the same as the OLED display ofFIG. 3, except that a metal oxide layer of a barrier layer202is omitted and an inorganic layer23is formed using an atomic layer deposition (ALC) method. The same reference numerals are used in the present exemplary embodiment to refer to the same components as those of the OLED display ofFIG. 3.

The ALD method is a method for layering atomic layers one by one by alternately supplying an element that is required for forming a membrane. When the ALD method is used, a defect-free and flawless inorganic layer23having no impurity can be formed, and a large-sized inorganic layer23can be deposited with uniform speed. In addition, when the inorganic layer23is deposited on the metal layer21using the ALD method, no arc is generated and therefore the metal oxide layer24of the barrier layer201of the OLED display ofFIG. 3can be omitted.

The barrier layers20,201, and202of the OLED displays ofFIG. 1,FIG. 3andFIG. 4, respectively are strong against stress compared to a conventional barrier layer formed of a plurality of inorganic layers. Thus, when stress such as bending or torsion stress is applied, cracks may not be readily generated and therefore deterioration of the pixel circuit and the organic light emitting diode50due to the cracks can be suppressed.

Further, in the barrier layers20,201, and202of the OLED displays ofFIG. 1,FIG. 3andFIG. 4, respectively, the metal layer21substantially performs a barrier function and therefore the thickness of the organic layer22or the inorganic layer23included in the barrier layers20,201, and202can be minimized, and accordingly, the flexibility of the barrier layers20,201, and202can be excellent compared to a conventional barrier layer.