Organic light-emitting display with pad area and fabricating method of same

An organic light-emitting display including a substrate, at least one thin film transistor, a pixel electrode and at least one pad electrode. The substrate is provided with a display area and a pad area spaced apart from the display area. The thin film transistor is disposed on the display area of the substrate, and includes an active layer, a gate electrode and source/drain electrodes. The pixel electrode is adjacent to the thin film transistor, and is electrically connected to the thin film transistor. The pad electrode is disposed on the pad area of the substrate, is formed of the same layer as the gate electrode or the source/drain electrodes, and is coupled with an external module.

This application claims the benefit of Korean Patent Application No. 2003-83792, filed on Nov. 24, 2003, which is hereby incorporated by reference for all purposes as if fully set forth herein.

BACKGROUND OF THE INVENTION

1. Field of the Invention

The present invention relates to a flat panel display and method of fabricating the same and, more particularly, to an organic light-emitting display and method of fabricating the same.

2. Discussion of the Related Art

Generally, organic light-emitting displays (OLED) are emissive displays that emit light by electrically exciting a fluorescent organic compound. OLEDs are considered either active matrix or passive matrix depending upon a mode for driving the pixels, which are arranged in a matrix. The active-matrix OLED has lower power consumption than the passive-matrix OLED, so it is more suitable as a large display having high resolution. OLEDs may be further divided into three types, a top emitting type, a bottom emitting type and a double-side emitting type, according to a propagation direction of light emitted from the organic compound. The top-emitting OLED, unlike the bottom-emitting OLED, is capable of emitting light in a direction opposite to the substrate on which the unit pixels are arranged, and it has a high aperture ratio.

In the top-emitting OLED, a pixel electrode may be formed with a conductive material having excellent reflectivity and a proper work function. However, no single material seems to satisfy these characteristics. Thus, the top-emitting OLED typically employs a multilayer pixel electrode.

FIG. 1is a cross-sectional view of a conventional active-matrix OLED having a multilayer pixel electrode and method of fabricating the same.

Referring toFIG. 1, a substrate10is provided with a display area A and a pad area B. An active layer20is formed on the display area A, wherein the active layer has source/drain regions23and a channel region21. A gate insulating layer25is formed on the entire surface of the substrate, and a gate electrode30, corresponding to the channel region21, is formed on the gate insulating layer25. Subsequently, an interlayer35is formed on the entire surface of the substrate, and source/drain contact holes, which expose the source/drain regions23, are formed in the interlayer35.

Next, source/drain electrodes43are formed on the interlayer35, wherein the source/drain electrodes43contact the source/drain regions23through the source/drain contact holes. Simultaneously, a pad electrode47is formed on the interlayer35of the pad area B. A planarization layer50is formed on the entire surface of the substrate and a via hole53, which exposes any one of the source/drain electrodes43, and a pad contact hole55, which exposes the pad electrode47, are formed in the planarization layer50.

Subsequently, an aluminum-neodymium (AlNd) layer and an indium tin oxide (ITO) layer are sequentially deposited and patterned on the planarization layer50. As a result, a pixel electrode60, coupled to the source/drain electrode43exposed by the via hole53, is formed on the planarization layer50of the display area A, and simultaneously, a terminal pad65, coupled to the pad electrode47through the pad contact hole55, is formed on the planarization layer50of the pad area B. Thus, the pixel electrode60and the terminal pad65are formed with the AlNd layer61,66and the ITO layer62,67. Hence, the AlNd layer61, as a reflection layer, reflects light emitted from an emission layer thereby forming a top-emitting OLED, which emits light in a direction opposite to the substrate10.

The terminal pad65is bonded with an external module after the OLED is fabricated, and it transmits an electrical signal inputted from the external module. Thus, the terminal pad65may be vulnerable to external moisture or oxygen. As set forth above, the terminal pad65is formed with the AlNd layer66and the ITO layer67. These layers may be exposed to moisture at the same time, particularly at a lateral surface P of the terminal pad65. In this case, a galvanic phenomenon may be generated between the AlNd layer66and the ITO layer67. This phenomenon appears when two materials having different electromotive force (EMF) are simultaneously exposed to a corrosive solution. The material having a greater EMF is subjected to corrosion.

Thus, when the terminal pad65corrodes, it is possible to decrease its reliability after bonding with the external module. This leads to defects in the OLED, and causes a decrease in yield. A decrease in pad reliability may also be generated when the pad electrode has a single layer structure composed of a material sensitive to external moisture or oxygen.

SUMMARY OF THE INVENTION

The present invention provides an OLED having improved pad reliability.

The present invention provides an OLED comprising a substrate provided with a display area and a pad area spaced apart from the display area. At least one thin film transistor, which includes an active layer, a gate electrode and source/drain electrodes, is disposed on the display area of the substrate. A pixel electrode, which is electrically coupled to the thin film transistor, is neighboring the thin film transistor. At least one pad electrode is disposed on the pad area of the substrate and formed of the same layer as any one of the gate electrode and the source/drain electrodes. The pad electrode is coupled with an external module.

The present invention also provides an OLED comprising a substrate provided with a display area and a pad area spaced apart from the display area. At least one thin film transistor, which includes an active layer, a gate electrode and source/drain electrodes, is disposed on the display area of the substrate. A pixel electrode, which is electrically coupled to the thin film transistor and has a layered structure of at least two conductive layers, neighbors the thin film transistor. A pad electrode, which is formed of the same layer as any one of the gate electrode and the source/drain electrodes, is disposed on the pad area. A terminal pad, which is formed of the same layer as any one of the conductive layers of the pixel electrode, is disposed on the pad electrode, and is coupled with an external module.

DETAILED DESCRIPTION OF THE INVENTION

The present invention will now be described with reference to the accompanying drawings, which show preferred embodiments of the invention. This invention may, however, be embodied in different forms and should not be construed as limited to the exemplary embodiments set forth herein. In the description and drawings, when a layer is disposed “on” another layer or a substrate, it may be directly formed on the other layer or the substrate, or it may be formed other layers or substrates that are interposed between them. Like reference numbers refer to like elements throughout the specification.

FIG. 2is a top plan view showing an OLED according to exemplary embodiments of the present invention.

Referring toFIG. 2, a display area A is positioned on a predetermined region of a substrate100for displaying images. The display area A has a unit pixel array (not shown) and a driving circuit (not shown) around the unit pixel array, wherein the unit pixel array has unit pixels arranged in a matrix, and the driving circuit drives the unit pixels. Each unit pixel is composed of at least one thin film transistor (not shown) and a pixel electrode (not shown) electrically coupled to it. The thin film transistor includes an active layer (not shown), a gate electrode (not shown) and source/drain electrodes (not shown). The pixel electrode may have at least one layered structure of conductive layers.

An encapsulation area C, which protects the unit pixels in the display area A from external moisture and oxygen, encloses the display area A. Further, a sealant that bonds the substrate100and an encapsulation substrate (not shown) is applied at the encapsulation area C.

A pad area B is located outside of the display area A and the encapsulation area C, and it is a region for coupling an external module (not shown), which applies an electrical signal, to the display area A. There are disposed various wirings (not shown) for transmitting the electrical signal between the display area A and the pad area B.

The pad area B has at least one pad electrode that is electrically coupled with these wirings. The pad electrode may be formed of the same layer as the gate electrode or source/drain electrode. When the pad electrode is formed of the same layer as the source/drain electrode, a gate pad may be disposed under the pad electrode and formed of the same layer as the gate electrode. The pad electrode or the gate pad may be electrically coupled with the wirings. A terminal pad may be disposed on the pad electrode, and formed of the same layer as any one layer of the pixel electrode. In this case, the terminal pad may be coupled with the external module. However, without the terminal pad, the pad electrode is coupled with the external module.

FIG. 3A,FIG. 3B,FIG. 3C,FIG. 3D,FIG. 3EandFIG. 3Fare cross-sectional views showing an OLED and method of fabricating the same according to a first exemplary embodiment of the present invention.FIGS. 3A to 3Fare limited to a unit pixel of the display area A and the pad area B inFIG. 2.

Referring toFIG. 3A, a substrate100has a display area A and a pad area B. The substrate100may be an insulating substrate, such as a glass or plastic substrate. A buffer layer150is formed on the entire surface of the substrate100to protect a subsequently formed thin film transistor from impurities, such as alkaline ions, which are eluted from the substrate100, and it may be formed of a silicon oxide layer or a silicon nitride layer. An active layer200, which may be formed of amorphous silicon or polycrystalline silicon, is formed on the display area A of the substrate100. A gate insulating layer250is then formed on the entire surface of the substrate100.

Referring toFIG. 3B, a gate electrode layer is deposited and patterned to simultaneously form a gate electrode300on the gate insulating layer250of the display area A, and a pad electrode330on the gate insulating layer250of the pad area B. The pad electrode330is electrically coupled with at least one wiring (not shown) connecting the pad area B with the display area A. The wiring may be a common power supply wiring or data wiring. The gate and pad electrodes300and330are preferably formed of a material that is insensitive to moisture and has excellent conductivity. More preferably, they are formed of a molybdenum alloy. Most preferably, the molybdenum alloy is a molybdenum-tungsten alloy.

Impurities may then be injected into the active layer200, using the gate electrode300as a mask to form source/drain regions230and define a channel region210between the source/drain regions230.

Referring toFIG. 3C, an interlayer350is formed to cover the gate and pad electrodes300and330. Source/drain contact holes370, which expose the source/drain regions230, are formed in the interlayer350and the gate insulating layer250. A source/drain electrode layer is then deposited and patterned on the interlayer350to form source/drain electrodes430, which are connected to the source/drain regions230exposed by the contact holes370, respectively.

Referring toFIG. 3D, a planarization layer500is formed on the entire surface of the substrate100, and a photoresist pattern (not shown) is then formed on the planarization layer500, wherein the photoresist pattern exposes predetermined regions of the display area A and the pad area B. The planarization layer500of the exposed display area A is etched, using the photoresist as an etching mask, to form a via hole530, which exposes any one of the source/drain electrodes430. Simultaneously, the planarization layer500and the interlayer350of the exposed pad area B are etched using the photoresist as an etching mask to form a pad contact hole550, which exposes the pad electrode330.

Referring toFIG. 3E, a first pixel electrode layer610may be deposited on the planarization layer500in the display area A by means of sputtering or vacuum deposition, and a second pixel electrode layer620may be deposited on the first pixel electrode layer by the same means. The first and second pixel electrode layers610,620are deposited using a high precision mask, so that the display area A, but not the pad area B, is provided with the pixel electrode layers. The pixel electrode600, which is comprised of the first and second pixel electrode layers610,620, is coupled with one of the source/drain electrodes430exposed by the via hole530.

The first pixel electrode layer pattern610may be formed of a conductive reflection layer, while the second pixel electrode layer pattern620may be formed of a conductive transparent layer. Therefore, light emitted from a subsequently formed emission layer may be reflected from the conductive reflection layer toward a direction opposite to the substrate100. Preferably, the conductive reflection layer is formed of any one selected from a group consisting of aluminum (Al), aluminum alloy, silver (Ag), silver alloy and their alloys, which have a reflectivity of at least 60%. More preferably, the conductive reflection layer is formed of aluminum-neodymium (AlNd). The conductive transparent layer is preferably formed of ITO or indium zinc oxide (IZO), which has a work function allowing holes to be easily injected into the subsequently formed organic emission layer.

Alternatively, the pixel electrode600may be formed of one conductive layer.

Referring toFIG. 3F, a pixel defining layer700is formed on the entire surface of the substrate100. Next, an opening that exposes a surface of the pixel electrode600is formed within the pixel defining layer700of the display area A, and simultaneously, the pixel defining layer700is removed from the pad area B to expose the pad electrode330. An organic functional layer730, having at least an emission layer, is then formed on the portion of the pixel electrode600exposed in the opening. The organic functional layer730may also include a charge injecting layer and/or a charge transporting layer. An opposite electrode780is formed on the organic functional layer730. The opposite electrode780may function as a cathode when the pixel electrode600functions as an anode and it may function as an anode when the pixel electrode600functions as a cathode.

A passivation insulating layer800is formed on the entire surface of the substrate, and then removed from the pad area B to expose the pad electrode330.

Subsequently, an encapsulation area C (shown inFIG. 2) of the substrate is covered with a sealant, and the substrate and an encapsulation substrate are bonded together by means of the sealant. The sealant is then cured to finish the encapsulation, which may prevent external oxygen and/or moisture from penetrating the display area A. Thus, the encapsulation may prevent the organic functional layer730and the pixel electrode600from reacting with oxygen and/or moisture, which improves characteristics of the OLED, such as its life span.

The encapsulation substrate does not encapsulate any part of the pad area B, therefore, it is exposed. The exposed pad electrode330is bonded with an external module, which may be chip on glass (COG), Flexible Printed Circuit (FPC) or other similar modules.

In this exemplary embodiment, unlike the prior art, the pad area B does not have a terminal pad (65ofFIG. 1). This structure may prevent a reduction of pad reliability resulting from corrosion of the terminal pad. Since the corrosion is responsible for a galvanic phenomenon, improvement of the pad reliability may decrease a failure rate of the OLED. Further, the pad electrode330may be formed of a material that is insensitive to moisture, which may prevent corrosion of the pad electrode330.

FIG. 4is a cross-sectional view illustrating an OLED according to a second exemplary embodiment of the present invention and method for fabricating the same.FIG. 4is limited to the unit pixel of the display area A and the pad area B shown inFIG. 2. The OLED of the present embodiment has a different pad area structure than the first exemplary embodiment. Differences from the first exemplary embodiment are discussed below.

After forming and etching the planarization layer500, a first pixel electrode layer is deposited on the planarization layer500by means of sputtering or vacuum deposition using a high precision mask, thereby providing the display area A with a first pixel electrode layer pattern610and the pad area B with a terminal pad570. Thereafter, a second pixel electrode layer is deposited on the first pixel electrode layer pattern610by means of sputtering or vacuum deposition using another high precision mask, thereby forming a second pixel electrode layer pattern620on the first pixel electrode layer pattern610, but a pattern is not formed on the terminal pad570.

The terminal pad570contacts the pad electrode330, which is exposed through the pad contact hole550.

A pixel defining layer700is then formed on the entire surface of the substrate100. Next, an opening is formed within the pixel defining layer700to expose a surface of the pixel electrode600. Simultaneously, the pixel defining layer700is removed from the pad area B to expose the terminal pad570. Next, an organic functional layer730, having at least an emission layer, is formed on the portion of the pixel electrode600exposed in the opening. An opposite electrode780is formed on the organic emission layer730.

A passivation layer800is formed on the entire surface of the substrate and then removed from the pad area B, thereby exposing the terminal pad570.

The substrate is then encapsulated using the sealant and the encapsulation substrate (not shown). The pad area B is not encapsulated by the encapsulation substrate, and the exposed terminal pad570is coupled with the external module.

In this exemplary embodiment, the terminal pad570is formed of the same, single layer as the first pixel electrode layer610, which may prevent a galvanic phenomenon caused by moisture in the air. As a result, it may be possible to prevent a decrease in pad reliability resulting from corrosion of the terminal pad (65ofFIG. 1). This improvement of the pad reliability may decrease a failure rate of the OLED.

FIG. 5is a cross-sectional view illustrating an OLED according to a third exemplary embodiment of the present invention and method for fabricating the same.FIG. 5is limited to the unit pixel of the display area A and the pad area B shown inFIG. 2. The OLED of the present embodiment has a different terminal pad structure than the second exemplary embodiment. Differences from the second exemplary embodiment are discussed below.

After forming and etching the planarization layer500, a first pixel electrode layer is deposited on the planarization layer500by means of sputtering or vacuum deposition using a high precision mask, thereby providing the display area A with a first pixel electrode layer pattern610, but a pattern is not formed on the pad area B. Next, a second pixel electrode layer is deposited on the planarization layer500, including the first pixel electrode layer pattern610, by means of sputtering or vacuum deposition using another high precision mask, thereby forming a second pixel electrode layer pattern620on the first pixel electrode layer pattern610and a terminal pad575on the pad electrode330.

The terminal pad575contacts the pad electrode330, which is exposed through the pad contact hole550.

Except as described above, the OLED of the present embodiment is the same as set forth with reference toFIG. 4.

FIG. 6AandFIG. 6Bare cross-sectional views illustrating an OLED according to a fourth exemplary embodiment of the present invention and method for fabricating the same.FIGS. 6A and 6Bare limited to the unit pixel in the display area A and the pad area B shown inFIG. 2. The OLED of the present embodiment has a different pad area structure than the first embodiment. Differences from the first exemplary embodiment are discussed below.

Referring toFIG. 6A, a substrate100is provided with an active layer200and a gate insulating layer250, which are formed by the same method as set forth with reference toFIG. 3A. A gate electrode layer is deposited and patterned on the gate insulating layer250to form a gate electrode300on the gate insulating layer250of the display area A.

Next, an interlayer350is formed on the entire surface of the substrate100. The interlayer350has source/drain contact holes370that expose the source/drain regions230. A source/drain electrode layer is then deposited and patterned on the interlayer350to simultaneously form source/drain electrodes430, which are coupled to the source/drain regions230, respectively, and a pad electrode470on the pad area B. The pad electrode470is coupled to the wiring (not shown) connecting the pad area B to the display area A. The wiring may be a common power supply wiring or data wiring. The source/drain electrodes430and the pad electrode470are preferably formed of a material that is insensitive to moisture and has excellent conductivity. More preferably, they are formed of a molybdenum alloy. Most preferably, the molybdenum alloy is a molybdenum-tungsten alloy.

Referring toFIG. 6B, a planarization layer500is formed on the entire surface of the substrate100and etched to form a via hole530, which exposes any one of the source/drain electrodes430, and a pad contact hole550, which exposes the pad electrode470.

Next, the OLED is fabricated by the same method as set forth with reference toFIG. 3EandFIG. 3F. Unlike the prior art, the OLED according to the present embodiment does not have a terminal pad (65ofFIG. 1), which may prevent a reduction of pad reliability due to corrosion of the terminal pad. Since the corrosion is responsible for the galvanic phenomenon, improvement of the pad reliability may decrease the failure rate of the OLED. Further, the pad elctrode470may be formed of a material that is insensitive to moisture, which may prevent corrosion of the pad electrode470.

FIG. 7is a cross-sectional view illustrating an OLED according to a fifth exemplary embodiment of the present invention and method for fabricating the same.FIG. 7is limited to the unit pixel of the display area A and the pad area B shown inFIG. 2. The OLED of the present embodiment has a different pad area structure than the fourth exemplary. Differences is from the fourth exemplary embodiment are discussed below.

After forming and etching the planarization layer500, a first pixel electrode layer is deposited on the planarization layer500by means of sputtering or vacuum deposition using a high precision mask, thereby providing the display area A with a first pixel electrode layer pattern610and the pad area B with a terminal pad570. Next, a second pixel electrode layer is deposited on the first pixel electrode layer pattern610by means of sputtering or vacuum deposition using another high precision mask, thereby forming a second pixel electrode layer pattern620on the first pixel electrode layer pattern610, but a pattern is not formed on the terminal pad570.

The terminal pad570contacts the pad electrode470, which is exposed through the pad contact hole550.

A pixel defining layer700is then formed on the entire surface of the substrate100. Next, an opening within the pixel defining layer700is formed exposing a surface of the pixel electrode600. Simultaneously, the pixel defining layer700is removed from the pad area B to expose the terminal pad570. Next, an organic functional layer730, having at least an emission layer, is formed on the pixel electrode600exposed in the opening. An opposite electrode780is formed on the organic emission layer730.

A passivation layer800is formed on the entire surface of the substrate and then removed from the pad area B, thereby exposing the terminal pad570.

The display area A of the substrate is encapsulated using the sealant and the encapsulation substrate (not shown), but the pad area B is left exposed. The exposed terminal pad570may be coupled with the external module.

In this exemplary embodiment, the terminal pad570is formed of the same, single layer as the first pixel electrode layer610, which may prevent a galvanic phenomenon caused by moisture in the air. This may prevent a decrease in pad reliability resulting from corrosion of the terminal pad (65ofFIG. 1), which may decrease the failure rate of the OLED.

FIG. 8is a cross-sectional view illustrating an OLED according to a sixth exemplary embodiment of the present invention and method for fabricating the same.FIG. 8is limited to the unit pixel of the display area A and the pad area B shown inFIG. 2. The OLED of the present embodiment has a different terminal pad structure than the fifth exemplary embodiment. Differences from the fifth exemplary embodiment are discussed below.

After forming and etching the planarization layer500, a first pixel electrode layer is deposited on the planarization layer500by means of sputtering or vacuum deposition using a high precision mask, thereby providing the display area A with a first pixel electrode layer pattern610, but the pad area B is not provided with an additive pattern. Next, a second pixel electrode layer is deposited the planarization layer500, including the first pixel electrode layer pattern610, by means of sputtering or vacuum deposition using another high precision mask, thereby forming a second pixel electrode layer pattern620on the first pixel electrode layer pattern610and a terminal pad575on the pad electrode470.

The terminal pad575contacts the pad electrode470, which is exposed through the pad contact hole550.

Except as described above, the OLED of the present embodiment is the same as set forth with reference toFIG. 7.

FIG. 9A,FIG. 9BandFIG. 9Care cross-sectional views explaining an OLED according to a seventh exemplary embodiment of the present invention and method for fabricating the same.FIGS. 9A through 9Care limited to the unit pixel in the display area A and the pad area B shown inFIG. 2. The OLED of the present embodiment has a different pad area structure than the previous exemplary embodiments.

Referring toFIG. 9A, a substrate100is provided with an active layer200and a gate insulating layer250, which are formed by the same method as set forth with reference toFIG. 3A.

A gate electrode layer is deposited and patterned on the gate insulating layer250to simultaneously form a gate electrode300on the gate insulating layer250of the display area A and a gate pad335on the gate insulating layer250of the pad area B. Impurities are then injected into the active layer200using the gate electrode300as the mask thereby forming source/drain regions230and defining a channel region210between the source/drain regions230.

An interlayer350is formed to cover the gate electrode300and the gate pad335. The interlayer350is simultaneously provided with source/drain contact holes370, which expose the source/drain regions230, and a gate pad contact hole390, which exposes the gate pad335.

Referring toFIG. 9B, a source/drain electrode layer is then deposited and patterned on the interlayer350to form source/drain electrodes430, which are coupled to the source/drain regions230, respectively. At the same time, a pad electrode470is formed on the gate pad335, which is exposed through the gate pad contact hole390. The pad electrode470or the gate pad335may be electrically coupled with the wiring (not shown) connecting the pad area B and the display area A. The wiring may be a common power supply wiring or data wiring. The pad electrode470and the source/drain electrodes430are preferably formed of a material that is insensitive to moisture and has excellent conductivity. More preferably, they are formed of a molybdenum alloy. Most preferably, the molybdenum alloy is a molybdenum-tungsten alloy.

Referring toFIG. 9C, a planarization layer500is formed on the entire surface of the substrate100, and etched to form a via hole530, which exposes any one of the source/drain electrodes430, and a pad contact hole550, which exposes the pad electrode470.

The OLED is then fabricated by the same method as set forth with reference toFIG. 3EandFIG. 3F. Unlike the prior art, the OLED according to the seventh exemplary embodiment does not have a terminal pad (65ofFIG. 1), which may prevent a reduction of pad reliability resulting from corrosion of the terminal pad. Since the corrosion is responsible for the galvanic phenomenon, improvement of the pad reliability may decrease the failure rate of the OLED. Further, the pad electrode470may be formed of a material that is insensitive to moisture, which may prevent corrosion of the pad electrode470.

FIG. 10is cross-sectional view illustrating an OLED according to an eighth exemplary embodiment of the present invention and method for fabricating the same.FIG. 10is limited to the unit pixel of the display area A and the pad area B shown inFIG. 2. The OLED according to the eighth exemplary embodiment has a different pad area structure than the seventh exemplary embodiment. Differences from the seventh exemplary embodiment are discussed below.

After forming and etching the planarization layer500, a first pixel electrode layer is deposited on the planarization layer500by means of sputtering or vacuum deposition using a high precision mask, thereby providing the display area A with a first pixel electrode layer pattern610and the pad area B with a terminal pad570. Next, a second pixel electrode layer is deposited on the first pixel electrode layer pattern610by means of sputtering or vacuum deposition using another high precision mask, thereby forming a second pixel electrode layer pattern620on the first pixel electrode layer pattern610, but a pattern is not formed on the terminal pad570.

A pixel defining layer700is formed on the entire surface of the substrate100. An opening within the pixel defining layer700is then formed to expose a surface of the pixel electrode600. Simultaneously, the pixel defining layer700is removed from the pad area B to expose the terminal pad570. Next, an organic functional layer730, having at least an emission layer, is formed on the pixel electrode600exposed in the opening. An opposite electrode780is formed on the organic emission layer730.

Then, a passivation layer800is formed on the entire surface of the substrate and then removed from the pad area B, thereby exposing the terminal pad570.

The substrate is encapsulated using the sealant and the encapsulation substrate (not shown), but the pad area B is left exposed. The exposed terminal pad570is coupled with the external module.

In this exemplary embodiment, the terminal pad570is formed of the same, single layer as the first pixel electrode layer610, which may prevent a galvanic phenomenon caused by moisture in the air. This may prevent a decrease in pad reliability resulting from corrosion of the terminal pad (65ofFIG. 1). The improvement in pad reliability may decrease the failure rate of the OLED.

FIG. 11is a cross-sectional view illustrating an OLED according to a ninth embodiment of the present invention and method for fabricating the same.FIG. 11is limited to the unit pixel of the display area A and the pad area B shown inFIG. 2. The OLED of the present embodiment has a different terminal pad structure than the eighth exemplary embodiment. Differences from the eighth exemplary embodiment are discussed below.

After forming and etching the planarization layer500, a first pixel electrode layer is deposited on the planarization layer500by means of sputtering or vacuum deposition using a high precision mask, thereby providing the display area A with a first pixel electrode layer pattern610, but a pattern is not added to the pad area B. Next, a second pixel electrode layer is deposited the planarization layer500, including the first pixel electrode layer pattern610, by means of sputtering or vacuum deposition using another high precision mask, thereby forming a second pixel electrode layer pattern620on the first pixel electrode layer pattern610and a terminal pad575on the pad electrode470.

The terminal pad575contacts the pad electrode470, which is exposed through the pad contact hole550.

Except as described above, the OLED of the present embodiment is the same as set forth with reference toFIG. 10.

Hereinafter, an example is described in order to help understand the present invention.

EXAMPLE

An OLED was prepared identically to that in the fourth embodiment. The pad electrode (470ofFIG. 6B) was formed of the molybdenum tungsten alloy, and was exposed through the pad contact hole (550ofFIG. 6B).

COMPARATIVE EXAMPLE

Except that a terminal pad having an AlNd layer and an ITO layer was formed on the pad electrode (470ofFIG. 6B) at the same time as the pixel electrode (600ofFIG. 6B) was formed of the same layers, an OLED was prepared identically to that of the Example.

Table 1 below shows a failure rate of ten OLEDs. Five were based on the Example and five were based on the Comparative Example. The OLEDs were maintained at 85° C. and a relative humidity of 95% for 100 hours.

Referring to Table 1, the five Example OLEDs did not generate any defects in their pads. On the other hand, all five Comparative Example OLEDs generated defects in their pads. Thus, the Example OLEDs had a 100% improvement in the failure rate as compared to the Comparative Example OLEDs.

As set forth above, according to exemplary embodiments of the present invention, the pad area B may not have a terminal pad, or if it does have a terminal pad (570ofFIGS. 4,7and10or575ofFIGS. 5,8and11), then it may be formed of the same, single layer as any one of the conductive thin layers comprising the pixel electrode600. Therefore, it may be possible to prevent a galvanic phenomenon caused by moisture in the air, which may prevent a reduction of pad reliability due to corrosion of the terminal pad. The improvement of the pad reliability may decrease a failure rate of the OLED. Furthermore, when the terminal pad is not formed, the pad electrode may be formed of a material that is insensitive to moisture, which may prevent corrosion of the pad electrode.