Organic electroluminescent display device

An organic electroluminescent display device can compensate for voltage drop of power supply voltage line by asymmetrically arranging a plurality of contact hole for connecting cathode electrodes and cathode power supply line. The organic electroluminescent display device may include first power supply line for supplying power supply voltage to pixels, and second power supply line for supplying voltage to an electrode on the upper side of the pixel (the supply line can include a region superposed on the electrode). The second power supply line may include a plurality of contact holes through which the second power supply line is connected to the electrode. The plurality of contact holes may be asymmetrically arranged with respect to a bisector of the superposition region of the second power supply line and electrode.

CROSS REFERENCE

This application claims the benefit of Korean Patent Application No. 2004-431, filed on Jan. 5, 2004, the disclosure of which is hereby incorporated herein by reference in its entirety.

BACKGROUND OF THE INVENTION

1. Field of the invention

The present invention relates to an organic electroluminescent display device, more particularly, to an organic electroluminescent display device capable of compensating voltage drop of power supply voltage lines by asymmetrically forming a plurality of contact holes for connecting a cathode electrode and a cathode power supply line.

2. Description of Related Art

FIG. 1is a plane figure for showing a conventional organic electroluminescent display device.

As shown inFIG. 1, an organic electroluminescent display device100may include a pixel region160equipped with a plurality of pixels and an upper power supply voltage line110arranged at an upper side and left and right sides of the pixel region160for power supply voltage. It may also include a lower power supply voltage line130arranged at a lower side of the pixel region160for power supply voltage and a pixel power supply voltage line111arranged correspondingly to the pixel region160to connect the upper power supply voltage line110and the lower power supply voltage line130. It may further include a scan driver140for outputting selection signals and a data driver150for outputting data signals.

Furthermore, the organic electroluminescent display device100may additionally include a cathode electrode122arranged correspondingly to the pixel region160, and a cathode power supply line120(not shown inFIG. 1) formed at one side of the pixel region160. The cathode power supply line120may be equipped with contact holes for connecting the cathode power supply line120to the cathode electrode122.

FIG. 2illustrates a plane structure of a cathode power supply line equipped with one contact hole for connecting the cathode power supply line to the cathode electrode in a conventional organic electroluminescent display device.

As shown inFIG. 2, one contact hole121may be arranged on a cathode power supply line120so that the cathode power supply line120is connected to a cathode electrode122through the contact hole121. A cathode voltage supplied to the cathode power supply line120from an external terminal may be supplied to the cathode electrode122through the contact hole121.

In a conventional organic electroluminescent display device having the foregoing structure, if selection signals and data signals are provided to the pixel region160from the scan driver140and data driver150, power supply voltage may be provided to the pixel power supply voltage line111from the power supply voltage lines110and130. The cathode voltage may be provided to the cathode electrode122from the cathode power supply line120. Switching transistor and driving transistor (not shown inFIG. 2) composing pixels arranged on the pixel region160may be driven so that electroluminescent elements (not shown inFIG. 2) emit lights.

FIG. 3illustrates conventional distribution of power supply voltage supplied to the pixel region160from the power supply voltage lines110and130in an organic electroluminescent display device illustrated onFIG. 1.

As shown inFIG. 3, the distribution of the power supply voltage in the pixel region160may be divided into a region to which a relatively lower power supply voltage is provided, and one in which a relatively higher power supply voltage is provided. These may be selected based on the distance from the power supplying component, because the farther away the pixel region160is from a power supply voltage supplying component, the greater the voltage drop is. This voltage drop may be attributed to resistance loss (IR loss) in the line. Furthermore, the same effect can be observed in the cathode power supply lines.

That is, a relatively higher power supply voltage may be supplied to a part adjacent to the power supply voltage supplying side of the circuit, than to the remainder of the line. Similarly, a relatively higher cathode voltage may be supplied to a part adjacent to an external terminal, than to the more distant parts.

There have been conventional problems with non-uniformity of luminance in the pixel region. These problems may be further worsened because the part that experiences the voltage drop of the cathode electrode may also be the part having a high voltage drop of power supply voltage in the pixel region. Thus the two regions may overlap. Furthermore, there also have been conventional problems that emission luminance of the pixel region may become even less uniform because the cathode power supply line may be only at one side of the pixel region.

SUMMARY OF THE INVENTION

Therefore, in order to solve the foregoing problems of the prior art, the present invention provides an organic electroluminescent display device capable of improving luminance uniformity by arranging cathode bus lines at least at both sides of the pixel region, thereby compensating for the voltage drop of the power supply voltage.

The present invention also provides an organic electroluminescent display device capable of compensating to avoid non-uniformity of luminance due to voltage drop of the power supply voltage by asymmetrically forming a plurality of contact holes for connecting cathode electrode and cathode power supply line.

The present invention provides, for example, an organic electroluminescent display device that may include a pixel region on which a plurality of pixels respectively comprising first and second electrodes and an organic thin film layer interposed between the first and second electrodes. It may also include a first power supply line for supplying voltage of first level to the pixels of the pixel region and a second power supply line for supplying voltage of a second level to the second electrode. It may also include at least a region superposed on the second electrode, wherein the second power supply line include a plurality of contact holes through which the second power supply line are connected to the second electrode. The plurality of contact holes may be asymmetrically arranged with respect to a bisector of the superposition region of the second power supply line and second electrode.

The contact holes may be arranged on at least two or more superposition regions. The area of the contact holes in a region having a high voltage drop may be larger than that of the contact holes in a region having a low voltage drop.

Furthermore, at least two or more of the contact holes may be arranged in a direction of long axis of the second power supply line, and lengths of the contact holes may differ from each other in the direction of the long axis of the second power supply line. Length of the contact holes in the long axis direction of the second power supply line in a region having high voltage drop may be longer than that of the contact holes in the long axis direction of the second power supply line in a region having low voltage drop.

Furthermore, at least three or more of the contact holes may be formed in a long axis direction of the second power supply line. A gap between two adjacent contact holes arranged in the long axis direction of the second power supply line in the region having high voltage drop may differ from a gap between two adjacent contact holes arranged in the long axis direction of the second power supply line in the region having low voltage drop. The gap between two adjacent contact holes arranged in the long axis direction of the second power supply line in the region having high voltage drop may be shorter than the gap between two adjacent contact holes arranged in the long axis direction of the second power supply line in the region having low voltage drop.

Furthermore, at least two or more of the contact holes may be arranged in a short axis direction of the second power supply line. The lengths of the contact holes arranged in the long axis direction of the second power supply line may differ from each other. The total length of the contact holes on the short axis direction of the second power supply line in the region having high voltage drop may surpass that of the contact holes on the short axis direction of the second power supply line in the region having low voltage drop.

The number of contact holes arranged in the short axis direction of the second power supply line may be different from the number of the contact holes arranged in the long axis direction of the second power supply line in regions having high and low voltage drops respectively. The contact holes may be arranged such that a gap between adjacent holes at a part having high voltage drop is equal to a gap between the adjacent contact holes at a part having low voltage drop.

Furthermore, the contact holes may be arranged such that a gap between adjacent holes at a part having high voltage drop is different from a gap between the adjacent contact holes at a part having low voltage drop. The contact holes may be arranged such that the gap between the adjacent contact holes decreases at the part having higher voltage drop compared to the part having lower voltage drop. Sizes of the contact holes may be equal to each other.

The number of contact holes arranged in the short axis direction of the second power supply line may be equal to the number of the contact holes arranged in the long axis direction of the second power supply line in regions having high and low voltage drops respectively. The contact holes may be arranged such that a gap between adjacent holes at a part having high voltage drop is different from a gap between the adjacent contact holes at a part having low voltage drop. The contact holes may be arranged such that the gap between the adjacent contact holes may decrease at the part having high voltage drop compared to the part having low voltage drop.

Furthermore, sizes of contact holes arranged in a long axis direction or short axis direction of the second power supply line may be different from each other, and a plurality of the contact holes may be arranged such that the total length of the contact holes decreases from a part having high voltage drop to a part having low voltage drop.

Furthermore, the present invention may also include an organic electroluminescent display device having a pixel region on which a plurality of pixels respectively comprising first and second electrodes and an organic thin film layer interposed between the first and second electrodes. The display device may also include first power supply line for supplying voltage of first level to the pixels of the pixel region and second power supply line for supplying voltage of a second level to the second electrode and comprising at least a region superposed on the second electrode.

The second power supply lines are arranged on at least two side surfaces in a plurality of side surfaces of the pixel region, at least one second power supply line in second power supply lines arranged on the two side surfaces comprises a plurality of contact holes through which the second power supply lines are connected to the second electrode, and the plurality of contact holes are asymmetrically arranged with respect to a bisector of the superposition region of the second power supply lines and second electrode.

Furthermore, the present invention may include an organic electroluminescent display device with a pixel region on which a plurality of pixels respectively comprising first and second electrodes and an organic thin film layer interposed between the first and second electrodes. It may also include a first power supply line for supplying voltage of a first level to the pixels of the pixel region; and a second power supply line for supplying voltage of a second level to the second electrode. It may also include at least a region superposed on the second electrode. The second power supply line may be arranged on at least one side surface in a plurality of side surfaces of the pixel region and equipped with a plurality of contact holes. The total circumference of the plurality of contact holes may be longer than a circumference of the superposition region of the second electrode and the second power supply line. At least two or more of the contact holes may be arranged in a direction of long axis of the second power supply line. The lengths of the contact holes may differ from each other in the direction of the long axis of the second power supply line. The area of the contact holes in a region having high voltage drop may be larger than that of the contact holes in a region having low voltage drop.

Furthermore, at least three or more of the contact holes may be formed in a long axis direction of the second power supply line, and a gap between two adjacent contact holes arranged in the long axis direction of the second power supply lines in the region having high voltage drop may be different from a gap between two adjacent contact holes arranged in the long axis direction of the second power supply line in the region having low voltage drop.

The number of contact holes arranged in the short axis direction of the second power supply line may differ from the number of the contact holes arranged in the long axis direction of the second power supply line in regions having high and low voltage drops respectively. The contact holes may be arranged such that a gap between adjacent holes at a part having high voltage drop differs from a gap between the adjacent contact holes at a part having low voltage drop. Furthermore, the contact holes may be arranged such that the gap between the adjacent contact holes is less at the part having higher voltage drop. The numbers of contact holes arranged in each column may be equal to each other. Sizes of contact holes arranged in each column and row may be equal to each other. Sizes of contact holes arranged in each column and row may differ from each other, and a plurality of the contact holes may be arranged such that the total length of the contact holes decreases from a part having high voltage drop to a part having low voltage drop.

DETAILED DESCRIPTION OF THE INVENTION

The present invention will now be described in detail in connection with preferred embodiments with reference to the accompanying drawings. Like reference characters designate corresponding parts throughout several views.

In general, the drawing include depictions of organic electroluminescent display device200, upper power supply voltage line210, pixel power supply voltage line211, cathode electrode220, first cathode power supply line221, second cathode power supply line222, contact holes223,224,225,226,227aand227b,228a,228b, and228c, lower power supply voltage line230, scan driver240, and data driver250.

As shown inFIG. 5, an organic electroluminescent display device200may include a pixel region260on which a plurality of pixels are arranged, upper power supply voltage lines210arranged at an upper side and left and right sides of the pixel region260to supply power supply voltage to the pixel region260, and lower power supply voltage lines230arranged at a lower side of the pixel region260to supply power supply voltage to the pixel region260. It may also include pixel power supply voltage lines211arranged in correspondence to the pixel region260such that the pixel power supply voltage lines211are connected to the upper power supply voltage lines210and the lower power supply voltage lines230. It may also include a scan driver240for outputting selection signals to the pixel region260and a data driver250for outputting data signals to the pixel region260.

Furthermore, the organic electroluminescent display device may also include a cathode electrode220arranged on an upper part of the pixel region260, first cathode power supply lines221arranged at one side of the pixel region260such that the first cathode power supply lines221overlap the cathode electrode220to supply cathode voltage to the cathode electrode220, and second cathode power supply lines222arranged at other side of the pixel region260such that the second cathode power supply lines222overlap the cathode electrode220to supply cathode voltage to the cathode electrode220.

Each of the first and second cathode power supply lines221and222may include a plurality of contact holes223through which the first and second cathode power supply lines221and222are connected to the cathode electrode220. The plurality of contact holes223of the first and second cathode power supply lines221and222may be asymmetrically arranged. At least two or more of the contact holes may be asymmetrically arranged to compensate voltage drop generated through the cathode power supply lines as illustrated inFIGS. 6,7,8,9,10,11, and12.

FIG. 6illustrates a plane structure of cathode power supply lines in an organic electroluminescent display device according to a first preferred embodiment of the present invention.FIG. 6illustrates only a region overlapping the cathode electrode220.

As shown inFIG. 6, a plurality of contact holes may be asymmetrically arranged on a region where the respective cathode power supply lines221and222overlap the cathode electrode220. The plurality of contact holes223may be asymmetrically arranged with respect to a bisector in a long axis direction of a superposition region of the cathode power supply lines221and222with the cathode electrode. That is, the contact holes223may not be arranged on a part adjacent to an external terminal to which cathode voltage is supplied in the region superposed on the cathode electrode220, but a plurality of contact holes223may be arranged on a part spaced apart from the external terminal to which the cathode voltage is supplied.

A plurality of contact holes223may be arranged in a matrix shape of columns and rows with the same pitch being maintained between adjacent contact holes, the size of the respective contact holes may be equal to each other, and the number of contact holes arranged in each column and row (i.e., in long and short axial directions) may be equal.

In an organic electroluminescent display device, a power supply voltage supplied to the pixel region260from the upper and lower power supply voltage lines210and230through the pixel power supply voltage line211may be distributed differently according to the position of the power supply voltage lines210and230. That is, power supply voltage may be higher due to a relatively smaller voltage drop at a part that is close to an external terminal while power supply voltage may be lower due to a relatively larger voltage drop at a part that is far from the external terminal.

As illustrated inFIG. 3, when a power supply voltage is supplied to the pixel region260through the power supply voltage lines210and230, low power supply voltage may be supplied to pixels arranged at an upper side of the pixel region260that is far from the external terminal because voltage drop of the power supply voltage lines210and230is relatively larger. Similarly, high power supply voltage may be supplied to pixels arranged at a lower side of the pixel region260because voltage drop of the power supply voltage lines210and230is relatively smaller.

As shown inFIG. 6, therefore, a plurality of contact holes223may be formed at a part having a large voltage drop of power supply voltage lines in the cathode power supply lines221and222, and the contact holes223may not be formed at a part having a small voltage drop of the power supply voltage lines210and230in the cathode power supply lines221and222in an organic electroluminescent display device. That is, in the contact holes223arranged on the cathode power supply lines221and222, the same number of at least two or more of the contact holes223may be formed on a part having a large voltage drop in long and short axial directions (distances t53and t54between adjacent contact holes223in a short axial direction may be equal to each other and distances t51and t52between adjacent contact holes223in a long axial direction are equal to each other). Therefore, current density at the cathode power supply lines221and222may be concentrated on the circumferential part of the contact holes223, and current density at the central part of the contact holes223may be reduced.

Therefore, the total length of the contact holes obtained by summing up the circumference of the respective contact holes may increase so that current mobility of the cathode power supply lines may increase. Also the voltage drop of cathode bus lines may accordingly be prevented if a plurality of contact holes are formed as in an organic electroluminescent display device. It may be preferable that the sum of the circumference of a plurality of contact holes arranged on a region where the cathode electrode and cathode power supply lines overlap each other is larger than the circumference of the superposition region of the cathode electrode and cathode power supply lines.

Therefore, the voltage drop of the cathode power supply lines may be large because contact holes are not formed at a part having a small voltage drop of power supply lines in the cathode power supply lines221and222as in the present invention (e.g., a part that is close to an external terminal). The voltage drop of the cathode power supply lines may be small because a plurality of contact holes may be formed at a part having a large voltage drop of the power supply lines (e.g., a part that is far from the external terminal).

Voltage drop of the cathode power supply lines221and222may decrease by arranging a plurality of contact holes223on the cathode power supply lines221and222correspondingly to a part having a large voltage drop of the power supply voltage lines210and230on a pixel region260in a region overlapping the cathode electrode220. Thus, current provided to the cathode through the anode of an organic electroluminescent device (not illustrated on drawings) may be concentrated on a plurality of contact holes223arranged on the cathode power supply lines221and222while voltage drop of the cathode power supply lines221and222increases by not forming the contact holes corresponding to a part having a small voltage drop of the power supply voltage lines210and230.

Therefore, in a first preferred embodiment of the present invention, voltage drop of the cathode power supply lines may be compensated by forming cathode power supply lines at both sides of the pixel region, and power supply voltage distribution may be obtained as inFIG. 4Cby asymmetrically forming a plurality of contact holes on the cathode power supply lines. This may prevent voltage drop along the cathode power supply lines. It can be seen fromFIG. 4Cthat equipotential lines may be formed in a horizontal symmetrical structure by arranging the cathode voltage lines at both sides of the pixel region and asymmetrically forming a plurality of contact holes on the cathode power supply lines. A distance ΔV4between the equipotential lines may be larger than a distance ΔV1between conventional equipotential lines illustrated inFIG. 3.

Although cathode power supply lines may be arranged at both sides of a pixel region, distribution of power supply voltage as illustrated inFIG. 4Bcan be obtained even if the contact holes are arranged only at one side of the pixel region as inFIG. 1, so long as a plurality of the contact holes are asymmetrically arranged. Voltage drop of the power supply voltages can be compensated because a distance ΔV2between equipotential lines of the cathode power supply lines is greater than the distance ΔV1between conventional equipotential lines illustrated inFIG. 3.

Furthermore, if the cathode power supply lines are arranged at both sides of the pixel region, a plurality of contact holes may be symmetrically arranged. As illustrated inFIG. 4A, the equipotential lines of power supply voltages may be horizontally symmetrically arranged, and a distance ΔV3between the equipotential lines of the power supply voltages may be larger than the distance ΔV1between the conventional equipotential lines illustrated inFIG. 3. Therefore, voltage drop of the power supply voltages can be compensated by asymmetrically arranging a plurality of contact holes on at least one side surface among a plurality of side surfaces of pixels in the present invention to prevent voltage drop of the cathode power supply lines.

It can be seen that distances ΔV2, ΔV3, and ΔV4between equipotential lines of the present invention are larger than the distance ΔV1between the conventional equipotential lines because voltage drop of the cathode power supply lines is reduced. CompareFIGS. 4A,4B, and4C toFIG. 3. That is, a distance ΔV3or ΔV4when a plurality of contact holes are asymmetrically arranged may be larger than a distance ΔV2when a plurality of contact holes are symmetrically arranged. Moreover, the distance ΔV2may be larger than the distance ΔV1between the conventional equipotential lines.

Therefore, voltage drop in power supply voltage lines can be compensated by guiding voltage drop in cathode power supply lines opposite to voltage drop of the power supply voltage lines. Luminance non-uniformity because of voltage drop of the power supply lines can thus be improved.

FIG. 7illustrates a plane structure of cathode power supply lines comprising contact holes for connecting the cathode power supply lines to cathode electrode in an organic electroluminescent display device according to a second preferred embodiment of the present invention.

As shown inFIG. 7, a plurality of contact holes224may be asymmetrically arranged in a region overlapping cathode electrode220in the cathode power supply lines221and222. The plurality of contact holes224may be asymmetrically arranged with respect to an equipotential line in a long axial line of a region overlapping the cathode electrode in the cathode power supply lines221and222. That is, the contact holes224may not be arranged at a part adjacent to an external terminal to which cathode voltage is supplied, but the contact holes224may be arranged a certain distance spaced apart from the external terminal to which cathode voltage is supplied.

At least two or more contact holes may be arranged in each column and row so that the number of contact holes in each row is equal, and the number of contact holes in each column is equal. This may be achieved by arranging the plurality of contact holes224in a matrix shape of columns and rows.

The farther the contact holes224are from an external terminal of cathode power supply lines221and222, the larger the contact holes224may be. The distances t61and t62between adjacent contact holes in a long axial direction may be equal. A distance t63between the contact holes224in a short axial direction adjacent to a region231having a large voltage drop of power supply voltage in the cathode power supply lines overlapping the cathode electrode may be shorter than a distance t64between contact holes224in a short axial direction adjacent to a region232having a small voltage drop. Therefore, the area of contact holes224included in each row may be larger in the region231having a large voltage drop compared to the region232having a small voltage drop as described in the above.

That is, the total circumference and total area of the contact holes in a region231having a large voltage drop may be larger than the total circumference and total area of the contact holes in a region232having a small voltage drop. This may be because two contact holes adjacent to a region231having a large voltage drop and a distance L61between the two contact holes may be larger than two contact holes adjacent to a region232having a small voltage drop and a distance L62between the two contact holes.

Therefore, voltage drop according to deviation of size and distance between contact holes224arranged may be generated because current density may increase from a part having a small voltage drop to a part having a large voltage drop. Therefore, voltage distribution of the cathode power supply lines221and222may offset voltage drop of the power supply voltage lines210and230because the cathode power supply lines221and222may have voltage distribution directly opposite the voltage distribution of the power supply voltage lines210and230. The total circumference of a plurality of contact holes224arranged on a region where cathode electrode and cathode power supply lines overlap each other may be larger than the circumference of the superposition region of the cathode electrode and cathode power supply lines.

As shown inFIG. 8, a plurality of contact holes225may be asymmetrically arranged in a region overlapping cathode electrode220in the cathode power supply lines221and222. The plurality of contact holes225may be asymmetrically arranged with respect to an equipotential line in a long axial line of a region overlapping the cathode electrode in the cathode power supply lines221and222. That is, the contact holes225may not be arranged at a part adjacent to an external terminal to which cathode voltage is supplied in the region overlapping the cathode electrode220, but a plurality of the contact holes225may be arranged at a distance from the external terminal to which cathode voltage is supplied.

According to a third preferred embodiment of the present invention, a plurality of contact holes225may be arranged in a matrix shape of columns and rows so that the number of contact holes arranged at each row is equal, and the number of contact holes arranged at each column is equal, and sizes of the contact holes are equal to each other.

Three or more contact holes may be arranged in a long axial direction of cathode power supply lines, and a distance t73between contact holes in a region233having a large voltage drop may be smaller than a distance t74between contact holes in a region234having a small voltage drop.

Therefore, the distance difference between contact holes225may generate a voltage drop because current density increases from a part having a small voltage drop to a part having a large voltage drop. Therefore, voltage distribution of the cathode power supply lines221and222may offset voltage drop of the power supply voltage lines210and230. This may be because the cathode power supply lines221and222have voltage distribution directly opposite to the voltage distribution of the power supply voltage lines210and230. The total circumference of a plurality of contact holes225arranged on a region where cathode electrode and cathode power supply lines overlap each other may be larger than the circumference of the superposition region of the cathode electrode and cathode power supply lines.

As shown inFIG. 9, a plurality of contact holes226may be asymmetrically arranged in a region overlapping cathode electrode220in the cathode power supply lines221and222. The contact holes226may be asymmetrically arranged with respect to an equipotential line in a long axial line of a region overlapping the cathode electrode in the cathode power supply lines221and222. That is, the contact holes226may not be arranged at a part adjacent to an external terminal to which cathode voltage is supplied, but the contact holes226may be arranged at a distance from the external terminal to which cathode voltage is supplied.

Although the distance between adjacent contact holes226may be equal between a part having a large voltage drop and a part having a small voltage drop, the number of contact holes225arranged in each column may be different according to the voltage drop of the power supply voltage lines210and230. The size of contact holes arranged on each column may be equal. At least two or more contact holes may be arranged in a short axial direction of the cathode power supply lines, and different numbers of contact holes may be arranged in a long axial direction of the cathode supply lines.

Therefore, the sum of lengths C1, C2, C3, C4, C5, and C6of the contact holes226of an AA′ region having a large voltage drop may be larger than the sum of lengths C1, C2and C3of the contact holes226of a BB′ region having a small voltage drop. This may be because the number of contact holes arranged in a long axial direction of the cathode power supply lines according to voltage drop of power supply voltage may be different if the sizes of contact holes arranged in each column in a short axial direction of cathode power supply lines are C1, C2, C3, C4, C5and C6.

Therefore, current density may increase, because the larger the voltage drop of the power supply voltage lines210and230is, the greater the number of the contact holes226arranged in a short axial direction of cathode power supply lines may be. Thus the current density may be reduced to offset the voltage drop of the power supply voltage lines210and230. This may be because the smaller the voltage drop is, the fewer the number of the contact holes226. The total circumference of a plurality of contact holes226arranged a region where the cathode electrode overlaps the cathode power supply lines may be larger than the circumference of a superposition region of the cathode electrode and cathode power supply lines.

As shown inFIG. 10, a plurality of contact holes227aand227bmay be asymmetrically arranged in a region overlapping cathode electrode220in the cathode power supply lines221and222. The plurality of contact holes227aand227bmay be asymmetrically arranged with respect to an equipotential line in a long axial line of a region overlapping the cathode electrode in the cathode power supply lines221and222. That is, the contact holes227aand227bmay not be arranged at a part adjacent to an external terminal to which cathode voltage is supplied in the region overlapping the cathode electrode220, but a plurality of the contact holes227aand227bmay be arranged at a distance from the external terminal to which cathode voltage is supplied.

The contact holes may be arranged in a row in a long axial direction of the cathode power supply lines221and222. Distances t91and t92between adjacent contact holes may be equal to each other. The sizes of the contact holes may be different from each other. At least two or more of the contact holes may be arranged in a long axial direction of the cathode power supply lines. Length L66in a long axial direction of the cathode power supply lines221and222of the contact hole227bin a region having a small voltage drop may be shorter than length L65in a long axial direction of the cathode power supply lines221and222of the contact hole227ain a region having a large voltage drop.

Furthermore, the area of the contact hole227ain the region having a large voltage drop may be larger than area of the contact hole227bin the region having a small voltage drop. This may be the case if the area of the contact hole227ain the region having a large voltage drop is S1, and the area of the contact hole227bin the region having a small voltage drop is S2. The total circumference of a plurality of contact holes arranged in a region where the cathode electrode and cathode power supply lines overlap may be longer than the circumference of a superposition region of the cathode electrode and cathode power supply lines.

Therefore, voltage drop may be generated according to the size of contact holes227aand227b. This is because current density may increase from a part having a small voltage drop to a part having a large voltage drop. Therefore, voltage distribution of the cathode power supply lines221and222may offset voltage drop of the power supply voltage lines210and230. This may be because the cathode power supply lines221and222have voltage distribution directly opposite to voltage distribution of the power supply voltage lines210and230.

As shown inFIG. 11, a plurality of contact holes228a,228b, and228cmay be asymmetrically arranged in a region overlapping cathode electrode220in the cathode power supply lines221and222. The plurality of contact holes228a,228b, and228cmay be asymmetrically arranged with respect to an equipotential line in a long axial line of a region overlapping the cathode electrode in the cathode power supply lines221and222. That is, the contact holes228a,228b, and228cmay be arranged such that distances between adjacent contact holes in a plurality of contact holes228a,228b, and228care different from each other. The contact holes may be at a distance from a part adjacent to an external terminal to which cathode voltage is supplied in a region overlapping the cathode electrode220.

Three or more of the contact holes may be arranged in a row in a long axial direction of the cathode power supply lines221and222. The contact holes may all be the same size. A distance t16in a long axial direction of the cathode power supply lines221and222between contact holes228band228cin a region having a small voltage drop may be shorter than a distance t15in a long axial direction of the cathode power supply lines221and222between contact holes228a,228badjacent to a region having a large voltage drop. The total circumference of a plurality of contact holes228a,228b, and228carranged in a region where the cathode electrode and cathode power supply lines overlap may be longer than the circumference of a superposition region of the cathode electrode and cathode power supply lines.

Therefore, voltage drop may be generated according to size of contact holes228a,228b, and228carranged because current density increases from a part having a small voltage drop to a part having a large voltage drop. Therefore, voltage distribution of the cathode power supply lines221and222may offset voltage drop of the power supply voltage lines210and230because the cathode power supply lines221and222may have voltage distribution directly opposite to voltage distribution of the power supply voltage lines210and230.

As shown inFIG. 12, a plurality of contact holes229may be asymmetrically arranged in a region overlapping cathode electrode220in the cathode power supply lines221and222. The plurality of contact holes229may be asymmetrically arranged with respect to an equipotential line in a long axial line of a region overlapping the cathode electrode in the cathode power supply lines221and222.

Two or more of the contact holes229may be arranged in a short axial direction of the cathode power supply lines221and222. The lengths of the contact holes229at least in a long axial direction may differ from each other. The sizes of the contact holes229and distances between adjacent contact holes in a short axial direction of the cathode power supply lines can be equal to or different from each other. The total circumference of a plurality of contact holes229arranged in a region where the cathode electrode and cathode power supply lines overlap may be longer than the circumference of a superposition region of the cathode electrode and cathode power supply lines.

The sum of lengths C7, C8, C9, C10, C11and C12of contact holes229of a CC′ region having a large voltage drop may be larger than the sum of lengths C7, C8and C9of contact holes229of a DD′ region having a small voltage drop. This may be because lengths of contact holes arranged in a long axial direction of the cathode power supply lines according to voltage drop of power supply voltage may differ from each other if the sizes of the contact holes arranged in each column in a short axial direction of cathode power supply lines are C7, C8, C9, C10, C11and C12. Therefore, the total area of the contact holes229of the CC′ region having a large voltage drop may also be larger than the total area of the contact holes229of the DD′ region having a small voltage drop.

Therefore, voltage density of the cathode power supply lines221and222may offset voltage drop of the power supply voltage lines210and230. This may be because the voltage density of the cathode power supply lines221and222has voltage distribution directly opposite to the voltage drop of the power supply voltage lines210and230.

Although the cathode power supply lines may be formed at both sides of pixel region, and a plurality of contact holes may be asymmetrically arranged at the cathode power supply lines arranged at both sides of the pixel region, the cathode power supply lines may alternatively be formed at the pixel region as well as at least one side of the pixel region, and a plurality of the contact holes may be asymmetrically arranged the cathode power supply lines.

Asymmetrically arranging contact holes may cause voltage drops of cathode power supply lines offset voltage drop of power supply voltages. In addition, voltage drop of the power supply voltages can be compensated by varying the size and alignment states of the contact holes. These beneficial results may occur because current density at the cathode power supply lines is concentrated toward the perimeter of the contact holes.

The present invention may make the luminance of a pixel region uniform, particularly in an organic electroluminescent display. Additionally, the current provided may be controlled by arranging cathode power supply lines to counter voltage drop with voltage drop in the opposite direction. The voltage drop may be controlled by adjusting the distances between the contact holes. Power supply lines may include cathode power supply lines arranged on both sides of the pixel region. A plurality of contact holes may be asymmetrically formed at the cathode power supply voltage lines.

Although the invention has been particularly shown and described with reference to certain embodiments thereof, changes may be made without departing from the scope of the invention.