Fixing a pixel defect in a display device

A display device that lends itself to easy repair of a defective pixel is presented. The device includes: a thin film transistor formed having a first electrode and a second electrode, the second electrode having a first part facing the first electrode, a second part that protrudes from the first part and having a first width, and a third part that extends from the second part and having a second width which is different from the first width. The device also includes a wall encompassing the pixel electrode and a common electrode formed on the wall.In one version of the repairing process, the second part of the second electrode is coupled to the common electrode. This coupling causes electric current from the second electrode to flow to the common electrode instead of to a light emitting diode, thereby converting a white spot to a black spot.

CROSS-REFERENCE TO RELATED APPLICATIONS

This application claims the benefit of Korean Patent Application No. 2005-0113611 filed on Nov. 25, 2005, in the Korean Intellectual Property Office, the disclosure of which is incorporated herein by reference.

BACKGROUND OF THE INVENTION

1. Field of the Invention

The present invention relates to a display device, and more particularly to a display device that lends itself to easy repair of a defective pixel.

2. Description of the Related Art

Recently, an organic light emitting diode (OLED), among flat panel displays, has become popular due to its low driving voltage, slim shape, light weight, a wide viewing angle, and short response time, among other advantages.

In an active-matrix OLED, a thin film transistor thin film transistor is connected to each pixel area to control the organic light-emitting layer's emission by pixel areas. A pixel electrode is disposed in each pixel area and electrically separated from the adjacent pixel electrodes in order to be driven independently. A hole-injecting layer and the organic light-emitting layer are formed sequentially on the pixel electrodes.

In the OLED, each pixel area has a plurality of thin film transistors, generally a switching thin film transistor connected to a data line and a driving thin film transistor connected to a voltage supply line. In addition, extra transistors may be included, for example for a compensation circuit or the like.

Due to the complicated configuration of each pixel, an OLED often gets a defective pixel. One of the common defects is the formation of a white spot caused by the light-emitting layer being supplied with an electric current continuously. The white spot degrades the display quality, as it may easily be recognized by a viewer.

SUMMARY OF THE INVENTION

The present invention provides a display device that is easily repaired and a method of manufacturing such display device.

The foregoing and/or other aspects of the present invention are also achieved by providing a display device that includes: an insulating substrate; a thin film transistor formed on the insulating substrate and including a first electrode and a second electrode, the second electrode having a first part facing the first electrode, a second part protruding from the first part and having a first width, and a third part extending from the second part and having a second width that is different from the first width; a pixel electrode connected to the second electrode; a wall encompassing the pixel electrode; an organic layer formed on the pixel electrode; and a common electrode formed on the wall and the organic layer.

The foregoing and/or other aspects of the present invention are also achieved by providing a display device comprising: an insulating substrate; a thin film transistor formed on the insulating substrate; a pixel electrode connected to the thin film transistor; a wall encompassing the pixel electrode; an organic layer formed on the pixel electrode; and a common electrode formed on the wall and the organic layer. The thin film transistor has a repair region that is not covered by the pixel electrode, the repair region being located for removal during pixel repair.

The foregoing and/or other aspects of the present invention are also achieved by providing a method of manufacturing a display device including: forming a thin film transistor that has a first electrode and a second electrode on an insulating substrate, the second electrode including a first part facing the first electrode, a second part protruding from the first part and having a first width, and a third part extending from the second part and having a second width that is different from the first width. The method also includes forming a pixel electrode connected to the second electrode; forming a wall encompassing the pixel electrode; forming an organic layer on the pixel electrode; and forming a pixel by forming a common electrode on the wall and the organic layer.

In another aspect, the invention is a method of manufacturing a display device that includes: forming a thin film transistor on an insulating substrate; forming a pixel electrode connected to the thin film transistor; forming a wall encompassing the pixel electrode; forming an organic layer on the pixel electrode; forming a pixel by forming a common electrode on the wall and the organic layer; detecting whether the pixel is defective; and repairing a defective pixel by blocking an electric current applied from the thin film transistor to the pixel electrode in the defective pixel.

DETAILED DESCRIPTION OF THE EMBODIMENT(S)

In the following description, if a layer is said to be formed “on” another layer, then a third layer may be disposed between the two layers or the two layers may be contacting each other. In other words, 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 be present.

FIG. 1is an equivalent circuit diagram of a pixel in a display device according to a first embodiment of the present invention.

A pixel has a plurality of signal lines. The signal lines include a gate line transmitting a scan signal, a data line transmitting a data signal, and a voltage supply line transmitting a driving voltage. The data line and the voltage supply line are disposed parallel to each other, and the gate line extends perpendicularly to the data line and the voltage supply line.

Each pixel comprises a light emitting diode element LD, a switching thin film transistor Tsw, a driving thin film transistor Tdr, and a capacitor C.

The driving thin film transistor Tdr has a control terminal, an input terminal, and an output terminal. The control terminal is connected to the switching thin film transistor Tsw, the input terminal is connected to the voltage supply line, and the output terminal is connected to the light emitting diode element LD.

The light emitting diode element LD comprises an anode connected to the output terminal of the driving thin film transistor Tdr and a cathode connected to a common voltage Vcom. The light emitting diode element LD emits light with varying intensity depending on the electric current outputted from the driving thin film transistor Tdr to display an image. The electric current from the driving thin film transistor Tdr varies in its intensity according to voltage between the control terminal and the output terminal.

The switching thin film transistor Tsw has a control terminal, an input terminal, and an output terminal. The control terminal is connected to the gate line, the input terminal is connected to the data line, and the output terminal is connected to the control terminal of the driving thin film transistor Tdr. The switching thin film transistor Tsw transmits the data signal applied to the data line to the driving thin film transistor Tdr according to the scan signal applied to the gate line.

The capacitor C is connected between the control terminal and the input terminal of the driving thin film transistor Tdr. The capacitor C charges and maintains the data signal inputted to the control terminal of the driving thin film transistor Tdr.

Hereafter, a configuration of the display device1according to the first embodiment of the present invention will be described with reference toFIGS. 2 and 3.

FIG. 2is an arrangement view of the display device according to the first embodiment of the present invention, andFIG. 3is a section view, taken along the line111-111inFIG. 2.

As shown inFIGS. 2 and 3, a gate line assembly is formed on an insulating substrate110made of transparent glass. The “gate line assembly” is herein refers collectively to the gate line211extending in a first direction, a switching gate electrode212extending from the gate line211in a second direction, and a driving gate electrode222separated from the gate line211. The gate line assembly is made of a metal layer and may have a single-layered structure or a multi-layered structure.

The gate line211transmits the scan signal and extends in the first direction, perpendicularly to the data line511. The gate line211may have a wide end portion (not shown) for connection to another layer or an external device. If a gate driving circuit (not shown) generating the scan signal is integrated into the insulating substrate110, the gate line211may directly be connected to the gate driving circuit.

The switching gate electrode212is connected to the gate line211and functions as the control terminal of the switching thin film transistor Tsw. The driving gate electrode222is the control terminal of the driving thin film transistor Tdr and is connected to a switching drain electrode513of the switching thin film transistor Tsw.

A gate insulating layer310, which contains silicon nitride (SiNx), is formed on the insulating substrate110and the gate line assembly.

A semiconductor layer containing amorphous silicon is formed on the gate insulating layer310. The “semiconductor layer” herein refers to a switching semiconductor layer411disposed on the switching thin film transistor Tsw and a driving semiconductor layer412disposed on the driving thin film transistor Tdr. The switching semiconductor411is an island and the driving semiconductor412extends in the second direction along the driving gate electrode222. the switching semiconductor layer411and the driving semiconductor layer412may be formed at an intersection of the gate line211and the data line511and an intersection of the gate line211and the voltage supply line521.

An ohmic contact layer450comprising n+ hydrogenated amorphous silicon highly doped with n-type dopant is formed between the semiconductor layer and a data line assembly. The “data line assembly” refers collectively to a data line511, a switching source electrode512, a switching drain electrode513, a voltage supply line521, a driving source electrode522, and a driving drain electrode523. The data line assembly is formed on the ohmic contact layer450and the portion of the gate insulating layer310that is not covered with the ohmic contact layer450.

The data line511and the switching source electrode512are formed in a single body, and the voltage supply line521and the driving source electrode522are formed in a single body.

The data line511transmits the data signal and extends in the second direction to cross the gate line211. The data line511may have a wide end portion (not shown) for connection to another layer or an external device. If a data driving circuit (not shown) generating the data signal is integrated into the insulating substrate110, the data line511may directly be connected to the data driving circuit. The switching source electrode512is formed in a single body with the data line511and functions as the input terminal of the switching thin film transistor Tsw.

The switching drain electrode513of the switching thin film transistor Tsw is connected to the driving gate electrode222of the driving thin film transistor Tdr.

The voltage supply line521is disposed parallel to the data line511and supplies the driving voltage to the driving source electrode522of the driving thin film transistor Tdr. The driving source electrode522is formed in a single body with a voltage supply line521and extends in a second direction.

The driving drain electrode523has a first part523aformed parallel to the driving source electrode522, a second part523bprotruding from the first part523a, and a third part523cextending from the second part523band connected to a pixel electrode713.

The width d1of the second part523bis larger than the width d2of the third part523c. In more detail, the width d1of the second part523bis about 110% to about 200% of the width d2of the third part523c. The second part523bhas about 0.1% to about 20% of the area of the pixel electrode713exposed by a wall810, or is in the range of about 10 μm2and about 40 μm2. The second part523belectrically couples with the common electrode830upon being irradiated with a laser beam during the repair process for the defective pixel. If the second part523bhas a small area, it is not easy to aim the laser beam properly. On the other hand, if the second part523bhas a large area, the aperture ratio undesirably decreases.

A passivation layer610is formed on the data line assembly (511,512,513,521,522and523) and the portion of the semiconductor layer (411and412) that is not covered with the data line assembly (511,512,513,521,522and523). The passivation layer610includes silicon nitride (SiNx).

The passivation layer610is partially removed to form a contact hole611exposing the switching drain electrode513, a contact hole612exposing the driving gate electrode222, and a contact hole613exposing the third part523cof the driving drain electrode523. Here, the gate insulating layer310is also removed from the contact holes612and613.

Transparent electrodes are formed on the passivation layer610. The “transparent electrodes” herein refer to a bridge711, a capacity forming part712, and a pixel electrode713. The transparent electrodes are made of a transparent conductive material such as indium tin oxide (ITO) or indium zinc oxide (IZO).

The bridge711connects the switching drain electrode513of the switching thin film transistor Tsw to the driving gate electrode222of the driving thin film transistor Tdr. For the connection using the bridge711, the switching drain electrode513and the driving gate electrode222are exposed through the contact holes611and612, respectively.

The capacity forming part712is formed in a single body with the bridge711and extends under the voltage supply line521. Storage capacity is formed in the passivation layer610where the capacity forming part712and the voltage supply line521overlap each other.

The pixel electrode713, which functions as an anode, provides holes to an organic layer820. The pixel electrode713is connected to the third part523cof the driving drain electrode523through the contact hole613.

A wall810is formed between the adjacent pixel electrodes713. The wall810divides the pixel electrodes713to define a pixel area and is formed on the thin film transistors Tsw and Tdr. The wall810may contain photoresist having thermal resistance and solvent-resisting property, such as acrylic resin, polyimide resin and etc., an inorganic material, such as SiO2and TiO2, or a double-layered structure having an organic layer and an inorganic layer.

A caved-in part811is formed on the wall810covering the second part523bof the driving drain electrode523. The thickness d3of the wall810where the caved-in part811is not formed is in the range of about 3 μm to 5 μm, and the thickness d4of the wall810where the caved-in part811is formed is in the range of about 0.5 μm to 2 μm. If the thickness d4is smaller than 0.5 μm, the distance between the common electrode830and the driving drain electrode523becomes too short and parasitic capacitance is generated. If the thickness d4is larger than 2 μm, it is not easy to electrically couple the second part523bof the driving drain electrode523to the common electrode830using the laser beam.

The organic layer820is formed on a portion of the pixel electrode713not covered with the wall810. The organic layer820comprises a hole-injecting layer821and a light-emitting layer822.

The hole injecting layer821contains a hole injecting material, such as poly-3,4-ethylenedioxythiophene (PEDOT) and poly styrenesulfonate (PSS) and is formed by ink-jetting the hole injecting material in an aqueous suspension state.

Holes transmitted from the pixel electrode713and electrons transmitted from the common electrode830combine with each other in the light-emitting layer822to become excitons, and then the excitons generate light while inactivated.

The common electrode830is disposed on the wall810and the light-emitting layer822. The common electrode830functions as a cathode and provides electrons to the light-emitting layer822. The common electrode830includes a calcium layer and an aluminum layer. In this case, a layer having low work function is preferably disposed close to the light-emitting layer822.

Lithium fluoride may enhance the light-emitting efficiency depending on the material that makes up the light-emitting layer822, and thus a lithium fluoride layer may be formed between the light-emitting layer822and the common electrode830. If the common electrode830is made of a non-transparent material such as aluminum or silver, light emitted from the light-emitting layer822exits to the insulating substrate110. This is called a bottom emission method.

The display device1may further comprise an electron transfer layer (not shown) and an electron injection layer (not shown) between the light-emitting layer822and the common electrode830. Moreover, the display device1may further comprise an additional passivation layer to protect the common electrode830and an encapsulation member bag to prevent moisture and air from penetrating into the organic layer820. The encapsulation member may comprise sealing resin and a sealing can.

Hereinafter, a manufacturing method of a display device according to the first embodiment of the present invention will be described with reference toFIGS. 2,3, and4A through4G.

Referring toFIG. 4A, a gate metal layer is formed on the insulating substrate110and patterned to form the gate line assembly (211,212and222). The gate metal layer is formed across the insulating substrate110by sputtering. Then, the gate insulating layer310is formed on the gate line assembly211,212and222. The gate insulating layer310comprises silicon nitride and is formed by chemical vapor deposition (CVD).

Referring toFIG. 4B, the semiconductor layer411and412and the ohmic contact layer450are formed on the gate insulating layer310. The gate insulating layer310, the semiconductor layer (411and412), and the ohmic contact layer450may be formed sequentially.

Referring toFIG. 4C, a data metal layer is formed and patterned to form the data line assembly (511,512,513,521,522and523). The data metal layer is formed across the insulating substrate110by sputtering. In this process, a portion of the ohmic contact layer450which is not covered with the data line assembly (511,512,513,521,522and523) is removed. Thereafter, oxygen plasma is preferably performed to stabilize the surface of the semiconductor layer411and412which is exposed. The ohmic contact layer450may be etched by dry etching using plasma. When forming the data line assembly (511,512,513,521,522and523), the second part523bof the driving drain electrode523is formed more widely than the third part523cthereof.

Referring toFIG. 4D, the passivation layer610and the transparent electrodes (711,712and713) are formed. The passivation layer610contains silicon nitride and is formed by CVD. The passivation layer610is patterned to form the contact holes611,612and613. Here, the contact hole613exposing the driving drain electrode523is formed to correspond to the third part523c.

A transparent conductive layer comprising ITO or IZO is deposited and etched by photolithography to form the transparent electrodes711,712and713. Preferably, nitrogen gas is used in a pre-heating process before the ITO or IZO is deposited. The pixel electrode713is formed so as not to overlap with the second part523bof the driving drain electrode523.

Referring to4E, a photoresist layer815is formed and exposed using a mask10. The photoresist layer815is a positive type in which an exposed area is resolved, and may be formed by a slit coating method or a spin coating method.

The mask10includes a base substrate11made of quartz and a light shield layer formed on the base substrate11. The light shield layer does not transmit ultraviolet rays and contains chrome oxide.

The light shield layer has a first sub-layer12corresponding to an area A where the caved-in part811of the wall810is formed and a second sub-layer13corresponding to an area B where the caved-in part811is not formed. There is a slit pattern in the first sub-layer12.

The area A of the photoresist layer815corresponding to the first sub-layer12is exposed to be partially resolved. The area B corresponding to the second sub-layer13is not resolved by exposure to the light. The area C corresponding to a portion of the mask10where the light shield layer12and13is not formed is completely resolved. Then, the photoresist815is developed and a resolved area is removed, thereby forming the wall810where the caved-in part811is formed on the second part523bof the driving drain electrode523.

FIG. 4Fshows that a hole-injecting solution825, which is a polymer solution containing a hole-injecting material, is dropped onto the pixel electrode713by ink-jetting. The hole-injecting solution825may contain poly thiophene derivatives such as poly-3,4-ethylenedioxythiophene (PEDOT), poly styrenesulfonate (PSS) and a polar solvent. The polar solvent, for example, may be isopropyl alcohol (IPA), n-butanol, γ-buthylolactone, N-methylpyrrolidone (NMP) and 1,3-dimethyl-2-imidazolidinon (DMI) and derivatives thereof and glycolether such as cabitol acetate, buthyl cabitol acetate or the like.

The hole-injecting solution825is dried to form the hole-injecting layer821. A drying process is performed under nitrogen atmosphere at room temperature at a pressure of 1 Torr. If the pressure is too low, the hole-injecting solution825may rapidly boil. Also, if the temperature is more than the room temperature, the evaporation speed of the solvent increases, making it hard to form a layer having a uniform thickness.

After completing the drying process, heat treatment may be performed under nitrogen atmosphere, or preferably in a vacuum, and at about 200° C. for 10 minutes, so that any solvent or water remaining in the hole-injecting layer821is removed.

FIG. 4Gshows that a light-emitting solution826, which is a polymer solution containing a light-emitting material, is dropped onto the pixel electrode613.

The light-emitting solution826may contain a nonpolar solvent in which the hole-injecting layer821is insoluble. This way, the re-dissolving of the hole-injecting layer is prevented. The nonpolar solvent may contain cyclohexylbenzene, dihydrobenzofuran, trimethylbenzene, tetramethylbenzene and etc.

A problem with the hole-injecting layer821is that it has low chemical affinity to the nonpolar solvent. As a result, the light-emitting layer826may not adhere closely to the hole-injecting layer821or may have a non-uniform thickness where the light-emitting solution826that is used contains a nonpolar solvent.

To increase the chemical affinity of the hole-injecting layer821to the nonpolar solvent, a surface reforming process is performed on the hole-injecting layer821before dropping the light-emitting solution826.

In the surface reforming process, a surface reforming agent is applied to the hole-injecting layer821, and then dried and evaporated. The surface reforming agent may contain cyclohexylbenzene, dihydrobenzofuran, trimethylbenzene and tetramethylbenzene, which are the solvent of the light-emitting solution826, or toluene and xylene which are similar to the aforementioned solvent. The surface reforming agent may be applied by ink-jetting, spin coating or dipping.

A surface of the hole-injecting layer821becomes chemically attractive to the nonpolar solvent through the surface reforming process, allowing the light-emitting solution826to be uniformly applied.

A drying process of the light-emitting solution826is similar to that of the hole-injecting solution825.

Thereafter, the light-emitting solution826is dried to form the light-emitting layer822, and then the common electrode830is formed on the light-emitting layer822, thereby completing the display device1as shown inFIGS. 2 and 3.

FIGS. 5A and 5Bare sectional views that illustrate how to repair a defective pixel in the display device according to the first embodiment of the present invention.

When manufacturing the display device1, each pixel is inspected for defect through an automatic optical inspection (AOI) or the like. The display device1may be inspected while or after being manufactured. Further, the display device1may be inspected under a practical condition with a driving circuit mounted thereon.

A pixel that is determined to be defective, especially a pixel that causes the formation of a white spot, is repaired by a laser beam. Upon repair, the white spot is changed to a black spot.

FIG. 5Ashows that the second part523bof the driving drain electrode523is irradiated with laser during a pixel repair process, andFIG. 5Bshows that the second part523bbecomes electrically coupled to the common electrode830by laser irradiation.

The distance between the second part523band the common electrode830is short since the wall810disposed over the second part523bis thin, and the second part523bis wide in comparison to the thickness of the wall810between the second part523band the common electrode830. Accordingly, the electrical-coupling of the second part523bwith the common electrode830can be easily obtained. Further, the pixel electrode813is not disposed between the second part523band the common electrode830, and thus the second part523bdirectly contacts the common electrode830. Additionally, the wall810over the second part523bhas a particular configuration, so that a manufacturer may easily find where to aim the laser beam.

FIG. 6is an equivalent circuit diagram of a repaired pixel in the display device according to the first embodiment of the present invention. in the diagram, the switching thin film transistor Tsw and the driving thin film transistor Tdr are assumed to be defective.

An electric current supplied from the voltage supply line is adjusted in its intensity through the driving thin film transistor Tdr and supplied to a light emitting diode element LD. However, a bypass line is formed between the output terminal of the driving thin film transistor Tdr and the common electrode through repair. Most of the electric current from the output terminal of the driving thin film transistor Tdr flows in the common electrode having a relatively low contact resistance rather than the light emitting diode element LD, which has a relatively high contact resistance. Accordingly, the electric current from the driving thin film transistor Tdr is not supplied to the light emitting diode element LD, and the repaired pixel becomes a black spot.

Hereinafter, a display device according to a second embodiment of the present invention will be described with reference toFIGS. 7 and 8.

FIG. 7is an arrangement view of the display device according to the second embodiment of the present invention, andFIG. 8is a sectional view taken along the line VIII-VIII inFIG. 7.

In the second embodiment, the width d5of a second part523bof a driving drain electrode523is shorter than the width d2of a third part523cthereof. In detail, the width d5of the second part523bmay be in the range of 50% and 90% of the width d2of the third part523c. The second part523bin the second embodiment is to be irradiated with laser when repairing a pixel.

FIGS. 9A and 9Bare sectional views to illustrate how to repair a defective pixel in the display device according to the second embodiment of the present invention.

FIG. 9Ashows that the second part523bof the driving drain electrode523is irradiated with laser to repair the pixel, andFIG. 9Bshows that the first part523ais disconnected from a third part523cby laser irradiation.

The second part523bis comparatively narrow, so that the disconnection of the first part523afrom the third part523cmay be easily performed. The wall810disposed over the second part523babsorbs impurities generated during the laser irradiation process for disconnecting the second part523b. Further, the pixel electrode713is not disposed between the second part523band the common electrode830. Thus, any short-circuiting of the second part523bwith the common electrode830is prevented.

FIG. 10is an equivalent circuit diagram of a repaired pixel in the display device according to the second embodiment of the present invention. The switching thin film transistor Tsw and the driving thin film transistor Tdr shown in the equivalent circuit diagram are defective.

An electric current supplied from a voltage supply line is adjusted in its intensity through the driving thin film transistor Tdr and supplied to a light emitting diode element LD. However, the output terminal of the driving thin film transistor Tdr is disconnected from the light emitting diode element LD due to the repair. Thus, the electric current from the driving thin film transistor Tdr is not supplied to the light emitting diode element LD, so that the repaired pixel becomes a black spot. This method does not affect the electrical function of the common electrode or neighboring pixels.