Organic light emitting diode display

An OLED display includes a substrate on which OLEDs are formed, a TFE layer formed on the substrate so as to cover the OLEDs, and absorbers disposed at a distance from each other and preventing or inhibiting penetration of external foreign materials.

CROSS-REFERENCE TO RELATED APPLICATIONS

This application claims priority to and the benefit of Korean Patent Application No. 10-2009-0010099 filed in the Korean Intellectual Property Office on Feb. 9, 2009, the disclosure of which is incorporated herein by reference in its entirety.

BACKGROUND

The present disclosure relates to an organic light emitting diode (OLED) display. More particularly, it relates to an OLED display with application of a thin film encapsulation (TFE) structure.

2. Description of the Related Technology

An organic light emitting diode (OLED) display typically includes a plurality of OLEDs formed of a hole injection electrode, an organic emission layer, and an electron injection electrode. Each OLED can emit light by energy from excitons generated when electrons and holes that are combined drop from an excited state to a ground state, and the OLED display displays an image by using the light.

Accordingly, the OLED display has self-luminance characteristics, and unlike a liquid crystal display (LCD), its thickness and weight can be reduced since a separate light source is not required. Further, because the OLED display has certain desirable characteristics such as low power consumption, high luminance, and high reaction speed, the OLED display may be suitable for use in a mobile electronic device.

The OLED may be deteriorated due to internal and external factors. With the internal factors, the organic emissive layer may be deteriorated under the atmosphere of oxygen if indium tin oxide (ITO) is the electrode material, or under the interfacial reaction between organic layer components of the organic emissive layer. The external factors may include external moisture and oxygen, and ultraviolet rays. In particular, because the external oxygen and moisture can influence the life span of the OLED, it is very important to package the OLED such that it is sealed from the outside in a vacuum tight manner.

A thin film encapsulation (TFE) technique may be introduced in packaging the organic light emitting diode, which is well known to those skilled in the art. With the thin film encapsulation technique, one or more of inorganic and organic layers can be alternately stacked on the OLEDS formed at the display area of the substrate, thereby covering the display area with a TFE layer. For an OLED display with such a TFE layer, a substrate formed with a flexible film can be bent easily, and can be advantageous in forming a slim structure.

However, a typical TFE layer can have a weak edge compared to a center portion, such that external moisture and oxygen can penetrate through the edge of the TFE layer. That is, the external moisture and oxygen may penetrate through a side of an externally exposed organic layer or an interface between an inorganic layer and an organic layer. Accordingly, the OLEDs disposed at the edge of the display area can be deteriorated such that display failures may occur.

The above disclosure is only provided to enhance understanding of the background and does not necessarily reflect prior art that was known to a person of ordinary skill in the art.

SUMMARY

Embodiments of the invention provide OLED displays that can prevent or reduce deterioration of OLEDs by inhibiting penetration of external moisture and oxygen into a TFE layer.

An OLED display according to an exemplary embodiment of the present invention includes a substrate on which OLEDs are formed, a thin film encapsulation (TFE) layer formed on the substrate while covering the OLEDs, and absorbers disposed at a distance from each other inside the TFE layer and inhibiting penetration of external foreign materials.

The substrate may include a display area where the OLEDs are provided, and the absorbers may be disposed outside the display area.

The absorbers may be disposed to form at least one row along the edge of the display area. In this case, the absorbers may be disposed at a constant distance from each other.

On the other hand, the absorbers may be formed at random in an irregular pattern along the edge of the display area.

The absorbers may be formed as a dot shape.

The TFE layer may include a plurality of inorganic layers and a plurality of organic layers, and the inorganic layers and the organic layers may be alternately stacked.

The absorbers may be disposed on a bottom surface of at least one of the plurality of inorganic layers, or may be disposed on a bottom surface of at least one of the plurality of organic layers.

On the other hand, the absorbers may be disposed on a bottom surface of at least one of the plurality of inorganic layers and a bottom of at least one of the plurality of organic layers.

The absorbers may be made of at least one selected from a group of calcium, calcium oxide, barium oxide, aluminum, aluminum oxide, magnesium, and magnesium oxide.

According to embodiments of the invention, penetration of foreign material can be inhibited by the TFE layer in the OLED display, and the external foreign material entered in the TFE layer can be absorbed by the absorbers. Accordingly, deterioration of OLEDs can be prevented or reduced.

Accordingly, OLED displays according to embodiments of the invention can minimize display failures and increase durability and life-span.

DETAILED DESCRIPTION OF THE EMBODIMENTS

FIG. 1is a perspective view of an organic light emitting diode (OLED) display according to a first embodiment of the invention, andFIG. 2is a cross-sectional view ofFIG. 1, taken along the line I-I.

Referring toFIG. 1andFIG. 2, an OLED display101according to the illustrated embodiment can include a panel assembly12and a printed circuit board16. The panel assembly12typically has a display area A10and a pad area A20, and displays a predetermined image in the display area A10. The printed circuit board16is typically electrically connected to the panel assembly12through a flexible circuit board14.

The panel assembly12can include a substrate18having the display area A10and the pad area A20defined on an upper surface thereof and a thin film encapsulation (TFE) layer20formed on the substrate18, covering the display area A10. The TFE layer20can be formed larger than the display area A10so that it covers not only the display area A10but also the upper surface of the substrate18outside of the display area A10for protection. The pad area A20can be exposed rather than being covered by the TFE layer20.

A plurality of sub-pixels can be arranged in a matrix format in the display area A10of the substrate18, and a scan driver (not shown) and a data driver (not shown) for driving the sub-pixels are provided outside the display area A10. A plurality of pad electrodes (not shown) can be provided in the pad area A20of the substrate18for transmitting an electric signal to the scan driver and the data driver.

FIG. 3is a schematic view of a sub-pixel circuit structure of the panel assemble ofFIG. 1, andFIG. 4is a partially enlarged cross-sectional view of the panel assembly ofFIG. 1.

Referring toFIG. 3andFIG. 4, a sub-pixel of the panel assembly12can be formed of an OLED L1and a driving circuit unit. The OLED L1can include an anode (hole injection electrode)22, an organic emission layer24, and a cathode (electron injection electrode)26.

The organic emission layer24may further include an emission layer (not shown) that substantially emits light and organic layers (not shown) for efficient transmission of holes or electrons to the emission layer. The organic emission layer24may include at least one of a hole injection layer (HIL) and a hole transport layer (HTL) interposed between the anode22and the emission layer, and an electron injection layer (EIL) and an electron transport layer (ETL) interposed between the cathode26and the emission layer.

Referring toFIG. 3, the driving circuit unit can include at least two thin film transistors T1and T2and at least one storage capacitor C1. The thin film transistors typically include a switching transistor T1and a driving transistor T2.

The switching transistor T1can be connected to a scan line SL1and a data line DL1, and can transmit a data voltage input from the data line DL1according to a switching voltage input to the scan line SL1to the driving transistor T2. The storage capacitor C1can be connected to the switching transistor T1and a power source line VDD, and can store a voltage that corresponds to a difference between a voltage transmitted from the switching transistor T1and a voltage supplied to the power source line VDD.

The driving transistor T2can be connected to the power source line VDD and the storage capacitor C1and supplies an output current IOELDthat is proportional to the square of a difference between the voltage stored in the storage capacitor C1and a threshold voltage to the OLED L1, and the OLED L1can emit light by the output current IOLED. The driving transistor T2can include a source electrode28, a drain electrode30, and a gate electrode32, and the anode22of the OLED L1may not be connected to, the drain electrode30of the driving transistor T2. The configuration of the sub-pixel is not limited thereto, and may be variously modified.

Referring toFIG. 2andFIG. 4, the TFE layer20can be formed directly on the OLEDs and driving circuit units can be formed on the substrate18to seal the OLEDs and the driving circuit units from the external environment for protection.

The TFE layer20can be formed on two or more inorganic layers201, and two or more organic layers202, and the inorganic layers201and the organic layers202can be alternately stacked. InFIG. 2andFIG. 4, the TFE layer20can be formed, for example, of two alternately stacked inorganic layers201and two organic layers202.

The inorganic layer201may be made of aluminum oxide or silicon, and the organic layer202may be made of epoxy, acrylate, and urethane acrylate. The inorganic layer201can reduce or suppress penetration of external moisture and oxygen, and the organic layer202can ease internal stress of the inorganic layer201or fill micro-cracks and pinholes of the inorganic layer201.

Referring back toFIG. 1andFIG. 2, an integrated circuit (IC) chip34and a flexible circuit board14can be mounted on the pad area A20of the panel assembly12by respectively using a chip-on-glass (COG) method and a chip-on-film (COF) method. A protective layer36can be formed around the IC chip34and the flexible circuit board14to cover pad electrodes formed in the pad area A20for protection. In the flexible circuit board16, electrons are typically provided for processing driving signals and a connector38is provide for transmitting an external signal to the flexible circuit board16.

In a rear side of the panel assembly12, a buffering tape (not shown) or a bezel (not shown) may be provided for increasing internal impact intensity of the panel assembly12. The flexible circuit board14may be fixed to the pad area A20and bent to the rear side of the panel assembly12to make the printed circuit board16face the rear side of the panel assembly12.

In the illustrated embodiment, the TFE layer20can include absorbers40that absorb foreign materials such as moisture and oxygen. Thus, in one embodiment the absorbers include materials that can react with moisture and/or oxygen. For example, the absorbers40may include or be entirely formed of a metal or an inorganic material that reacts with moisture and oxygen. For example, the metal or inorganic material of the absorbers40may be selected from a group of calcium, calcium oxide, barium oxide, aluminum, aluminum oxide, magnesium, and magnesium oxide.

Although the TFE layer20may itself inhibit penetration of external moisture and oxygen, foreign materials may still enter inside the TFE layer20through an externally exposed edge of the TFE layer20. In this case, the absorbers40can absorb foreign materials that have entered inside the TFE layer20to prevent or reduce deterioration of the OLED. Thus, in one embodiment, the absorbers40may surround the display area A10so as to absorb foreign materials entering through the exposed edge of the TFE layer20.

The absorbers40may be separated by a distance from each other, that is, they may be formed in a pattern of individual members that are separated from each other rather than in a line to maximize a surface area for increasing the absorbing function of the foreign materials. Thus, for example, each absorber40may be formed as a short bar shape or a dot, of which the width and the length may be the same, or other various shapes. InFIG. 1andFIG. 2, the absorber40may for example be formed as a dot shape. The dot-shaped absorber40can maximize the surface size thereof. The width of the absorber40may be less than 5 mm. When this condition is satisfied, excessive extension of the width of an external dead space of the display area A10can be avoided.

The absorbers40may be formed on a bottom surface of one inorganic layer201, for example, a bottom surface of an inorganic layer210positioned in the lowest portion of the TFE layer20. For example, the absorbers40may be formed on an upper surface of the substrate18.

The absorbers40may be disposed at a distance from each other, and each of the absorbers40may be disposed at an intended position so that the absorbers40can form a specific pattern. In one particular example, the absorbers40may form at least one row that surrounds the display area A10.

InFIG. 1andFIG. 2, the first absorbers401for example form an inner row along the edge of the display area A10, and second absorbers402form an outer row along the edge of the display area A10outside of the first absorbers401. In this case, the absorbers40absorb the foreign materials having entered from the edge of the TFE layer20through two steps so that the foreign material can be effectively eliminated.

Through the above-described configuration, in the OLED display101according to an embodiment, penetration of foreign material can be inhibited by the TFE layer20and the foreign material having entered in the TFE layer20can be absorbed by the absorbers40. Accordingly, deterioration of OLEDs and display failures can be minimized.

FIG. 5is a partially enlarged cross-sectional view of an OLED display according to a second embodiment of the invention.

Referring toFIG. 5, an OLED display102according to the illustrated embodiment can have the same configuration as the OLED display of the first described embodiment, except that absorbers403may be formed on a bottom surface of one of an organic layer202among a plurality of organic layers202. That is, the absorbers403may be formed on an upper surface of an inorganic layer201. Like reference numerals are used for like elements of the first described embodiment.

FIG. 6is a partially enlarged cross-sectional view of an OLED display according to a third embodiment of the invention.

Referring toFIG. 6, an OLED display103according to the illustrated embodiment has the same configuration as the OLED display of the first described embodiment, except that absorbers404may be formed on a bottom surface of one of a plurality of inorganic layers201and on a bottom surface of one of a plurality of organic layers202. Like reference numerals are used for like elements of the first described embodiment.

FIG. 7is a partially enlarged cross-sectional view of an OLED display according to a fourth embodiment of the invention.

Referring toFIG. 7, an OLED display104according to the illustrated embodiment has the same configuration as the OLED display of the first described embodiment, except that absorbers405may be formed on bottom surfaces of a plurality of inorganic layers201. Like reference numerals are used for like elements of the first described embodiment.

FIG. 8is a partially enlarged cross-sectional view of an OLED display according to a fifth embodiment of the invention.

Referring toFIG. 8, an OLED display105according to the illustrated embodiment has the same configuration as the OLED display of the fourth described embodiment, except that absorbers406may be formed on bottom surfaces of a plurality of organic layers202. Like reference numerals are used for like elements of the fourth described embodiment.

FIG. 9is a partially enlarged cross-sectional view of an OLED display according to a sixth embodiment of the invention.

Referring toFIG. 9, an OLED display106according to the illustrated embodiment has the same configuration as the OLED display of the fourth described embodiment, except that absorbers407may be formed on bottom surfaces of a plurality of organic layers202and on bottom surfaces of a plurality of inorganic layers201. Like reference numerals are used for like elements of the fourth described embodiment.

As the number of inorganic layers201and organic layers202that form the TFE layer20and the number of absorbers405,406, and407are increased, penetration of foreign materials to the OLEDs can be effectively inhibited.

FIG. 10is a top plan view of an OLED display according to a seventh embodiment of the invention.

Referring toFIG. 10, an OLED display107according to the illustrated embodiment has the same configuration as the OLED display of one of the first to sixth described embodiments, except that absorbers408may be formed at random in an irregular pattern along the edge of a display area A10. As described, when the absorbers408are formed in the irregular pattern, precise consideration of an alignment characteristic of the absorbers408is not necessary during a manufacturing process so that the process can be simple and easy.

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