Organic light emitting display

An organic light emitting display is capable of reducing or preventing IR drop in a cathode electrode. An organic light emitting display includes a first substrate and a second substrate. The first substrate has a plurality of pixels located thereon, each of the pixels comprising an organic light emitting diode, wherein a cathode electrode of the organic light emitting diode including a transparent material is located on substantially an entire area of the pixels. The second substrate has a mesh type auxiliary electrode located thereon at a side facing the pixels, the mesh-type auxiliary electrode corresponding to non-emission regions between the pixels and electrically connected to the cathode electrode.

CROSS-REFERENCE TO RELATED APPLICATION

This application claims priority to and the benefit of Korean Patent Application No. 10-2008-0101947, filed on Oct. 17, 2008, in the Korean Intellectual Property Office, the entire content of which is incorporated herein by reference.

BACKGROUND OF THE INVENTION

1. Field of the Invention

The present invention relates to an organic light emitting display, and more particularly, to an organic light emitting display in which IR drop (i.e., voltage drop) in a cathode electrode is prevented or reduced.

2. Description of the Related Art

Recently, various flat panel displays (FPDs) that are light and thin in comparison to cathode ray tubes (CRTs) have been developed. Among the FPDs, organic light emitting displays using organic compound as phosphor to have excellent brightness and color purity are in the spotlight.

Since the organic light emitting displays are thin and light and capable of being driven with low power consumption, they are suitable for portable displays in addition to applications in larger size FPDs.

The organic light emitting displays are typically classified as a top emission organic light emitting display or a bottom emission organic light emitting display according to light emission directions. Further, a dual-side emission organic light emitting display has combined features of the top emission organic light emitting display and the bottom emission organic light emitting display.

A conventional bottom emission organic light emitting display has disadvantages of a low aperture ratio because thin film transistors for driving OLEDs cannot be positioned at light emitting regions.

On the contrary, the top emission organic light emitting display can achieve a desired aperture ratio regardless of whether or not the thin film transistors are located under the OLEDs.

However, in the top emission organic light emitting display, as light generated from an emission layer of the OLED is emitted out through a cathode electrode, the cathode electrode is required to be transparent. Therefore, the cathode electrode is made of a transparent conductive material such as ITO, or MgAg having a sufficiently small thickness to be transparent.

However, the transparent conductive material such as ITO has a high resistance, and MgAg can only have a limited thickness. Thus, resistance of the cathode electrode is high so that a relatively high IR drop (i.e., voltage drop) occurs. Particularly, as a display panel becomes larger in size, IR drop in the cathode electrode is greatly increased so that image quality and display characteristics may not be uniform.

SUMMARY OF THE INVENTION

Accordingly, it is an aspect according to embodiments of the present invention to provide an organic light emitting display in which IR drop in a cathode electrode can be reduced or prevented.

In order to achieve the foregoing and/or other aspects of the present invention, according to a first embodiment of the present invention, an organic light emitting display including a first substrate and a second substrate is provided. The first substrate has a plurality of pixels located thereon, each of the pixels including an organic light emitting diode, wherein a cathode electrode of the organic light emitting diode including a transparent material is located on substantially an entire area of the pixels. The second substrate has a mesh type auxiliary electrode located thereon at a side facing the pixels, the mesh-type auxiliary electrode corresponding to non-emission regions between the pixels and electrically connected to the cathode electrode.

Here, the auxiliary electrode may include a conductive black matrix material.

The auxiliary electrode may include a material with a lower specific resistance than a material for the cathode electrode.

The organic light emitting display further includes a transparent conductive layer on substantially an entire area of the auxiliary electrode and contacting the cathode electrode to electrically connect the auxiliary electrode to the cathode electrode. The transparent conductive layer contacts the cathode electrodes at the non-emission regions between the pixels.

Accordingly, in organic light emitting displays according to embodiments of the present invention, since an auxiliary electrode, electrically connected to a cathode electrode on a lower substrate and having resistance lower than the cathode electrode, is on an upper substrate, IR drop in the cathode electrode can be reduced or prevented.

DETAILED DESCRIPTION

Hereinafter, exemplary embodiments of the present invention will be described in detail with reference to the accompanying drawings, namely,FIGS. 1 to 3.

FIG. 1is an exploded perspective view illustrating an organic light emitting display according to an embodiment of the present invention, andFIG. 2is a sectional view illustrating main parts of the organic light emitting display as shown inFIG. 1.

Referring toFIG. 1, an organic light emitting display according to an embodiment of the present invention includes a lower substrate100on which a plurality of pixels110respectively including organic light emitting diodes (OLEDs) are formed, an upper substrate200on which a mesh-type auxiliary electrode210is located at the side facing the pixels110. A transparent conductive layer220is formed on substantially an entire area of the auxiliary electrode210at the side facing the pixels110. While the auxiliary electrode210is primarily described herein as a single electrode formed as a mesh as shown inFIG. 1, the auxiliary electrode can also be viewed as a plurality of auxiliary electrodes that are electrically connected together in a form of a mesh.

Each of the pixels110, as illustrated inFIG. 2, includes a thin film transistor112and an OLED116which are formed on the lower substrate100.

Each of the thin film transistors112includes a semiconductor layer112aformed on a buffer layer111, which is on the lower substrate100, a gate electrode112bformed on the semiconductor layer112a, where an insulating layer113is interposed between the gate electrode112band the semiconductor layer112a, and source/drain electrodes112cformed on the gate electrode112b, where an interlayer insulating layer114is interposed between the source/drain electrodes112cand the gate electrode112b. The source/drain electrodes112care electrically connected to the semiconductor layer112a.

An insulating planarization layer115is formed on the thin film transistor112. An OLED116connected to the thin film transistor112through a via-hole is formed on the planarization layer115.

The OLED116is formed on the planarization layer115. The OLED116includes an anode electrode116aelectrically connected to the thin film transistor112through the via-hole formed in the planarization layer115, a light emission layer116bformed on the anode electrode116aat an area exposed by a pixel definition layer117which is formed on the planarization layer115to overlap with an upper portion of an edge of the anode electrode116a, and a cathode electrode116cformed on the light emission layer116band made of transparent material. The cathode electrode layer116cis formed over substantially an entire upper side of the pixels110.

Here, the light emission layer116bmay be formed in the form of a red light emission layer R, a green light emission layer G, or a blue light emission layer B, independently deposited using a fine metal mask (FMM). According to kind of the light emission layer116b, the pixels110may be classified as a red pixel110R, a green pixel110G, or a blue pixel110B.

Each of the pixels110includes the cathode electrode116cmade of a transparent material to emit light toward the cathode electrode116c. Accordingly, the organic light emitting display may be implemented as a top emission (or a dual-side emission) organic light emitting display. In the described embodiment, the cathode electrode is a common electrode shared by all of the pixels. However, each pixel can also be viewed as having its own cathode electrode that is electrically connected to cathode electrodes of other pixels.

Since the cathode electrode116cshould transmit light in a top emission or dual-side emission organic light emitting display, the cathode electrode116cis made of a transparent conductive layer. To this end, the cathode electrode116cis made of a transparent conductive material such as ITO, or MgAg having a thickness that is small enough to be transparent. Here, the thickness of MgAg is determined within a range of guaranteeing transparency greater than a predetermined transparency with respect to light. The term transparency or transparent in the present application refers to translucency greater than a desired transparency (e.g., predetermined transparency) or substantial transparency, as well as a transparency of 100%.

In non-emission regions120between the pixels110, spacers118are provided to maintain a gap (e.g., a predetermined gap) between the first substrate100and the second substrate200.

Each of the spacers118is formed between the pixel definition layer117of the non-emission region120and the cathode electrode116c. In other words, the cathode electrode116cis formed in a region including an upper portion of the spacer118of the non-emission region120, that is, is positioned on the top of the lower substrate100.

The auxiliary electrode210is formed at a side of the upper substrate200facing the pixels110to correspond to the non-emission region120between the pixels110in the form of a mesh, and is electrically connected to the cathode electrode116cof the lower substrate100by a transparent conductive layer220.

The auxiliary electrode210may function as a black matrix containing conductive black matrix material. The conductive black matrix material may be at least one selected from the group consisting of chrome (Cr), chrome alloys, molybdenum (Mo), molybdenum alloys, oxides thereof (CrOx, MoOx), and combinations thereof. For example, the auxiliary electrode210may be formed of a single chrome layer, or may include a dual chrome layer/chrome oxide layer or a dual molybdenum layer/molybdenum oxide layer for effective light interception.

Moreover, even if the auxiliary electrode210does not completely function as a black matrix, since it is formed in the non-emission region120, it does not necessarily have to be transparent. Thus, the thickness of the auxiliary electrode210has less restriction than that of the cathode electrode116c. Therefore, the auxiliary electrode210may be formed with a thickness relatively greater than that of the cathode electrode116c.

When the cathode electrode116cis formed as a transparent electrode made of ITO, for example, the auxiliary electrode210may be made of one of a variety of materials having a specific resistance lower than the material for the cathode electrode116c.

That is, the auxiliary electrode210has a resistance lower than that of the cathode electrode116cand is electrically connected thereto so as to prevent or reduce IR drop in the cathode electrode116c.

The transparent conductive layer220is formed on substantially an entire area of the auxiliary electrode210and contacts the cathode electrode116cat the non-emission regions120between the pixels110to electrically connect the auxiliary electrode210to the cathode electrode116c.

The transparent conductive layer220performs a function of preventing or reducing IR drop in the cathode electrode116ctogether with the auxiliary electrode210, and may be made of indium tin oxide (ITO) such that light can be transmitted therethrough. In other embodiments of the present invention, the transparent conductive layer220may not be provided, and the auxiliary electrode210may directly contact the cathode electrode116cwhen the transparent electrode220is not used.

As described above, according to embodiments of the present invention, the auxiliary electrode210and/or the transparent conductive layer220to be electrically connected to the cathode electrode116con the lower substrate100, are formed on the upper substrate200. Then, the two substrates100and200are bonded to each other. Accordingly, IR drop in the cathode electrode116ccan be prevented or reduced.

FIG. 3is a sectional view illustrating main parts of an organic light emitting display according to another embodiment of the present invention. InFIG. 3, same reference numerals are assigned to the same elements as those inFIG. 2and their description will be omitted.

Referring toFIG. 3, in an organic light emitting display according to another embodiment of the present invention, each of OLEDs116′ or a red pixel110R′, a green pixel110G′, and a blue pixel110B′ includes white light emitting layer W.

Between the auxiliary electrode210of the upper substrate200, color filters230corresponding to the pixels110R′,110G′, and110B′ are provided. Here, color filters are located at openings of the mesh-type auxiliary electrode210. That is, red color filters R C/F, green color filters G C/F, and blue color filters B C/F are formed on the red pixels110R′, the green pixels110G′, and the blue pixels110B′, respectively. Using the color filters, the organic light emitting display displays an image with full colors.

Although not shown in the drawings, when unit pixels include a red pixel, a green pixel, a blue pixel, and a white pixel to display an image with full colors, the white pixel may not include a color filter or may include a filter for adjusting the amount of transmitted light.

This way, in another embodiment, the transparent conductive layer220is formed on substantially an entire area of the auxiliary electrode210and color filters230and contacts the cathode electrodes116cto electrically connect the auxiliary electrode210to the cathode electrodes116c.