Electroluminescence Display

Abstract

The electroluminescent display device according to this application comprises a substrate, a low potential pad, a bank, a mushroom structure, an under-cut region, a first cathode electrode layer, a second cathode electrode layer, and a third cathode electrode layer. The low potential pad comprises a first electrode layer and a second electrode layer laminated on the first electrode layer. The bank comprises a cathode contact hole exposing the central portion of the low potential pad and covers the edge of the low potential pad. The mushroom structure is disposed in the central portion of the low potential pad. An under-cut region is formed below the edge of the bank and the mushroom structure. The first cathode electrode layer is applied to the upper surface of the bank and the mushroom structure, the upper surface of the low potential pad exposed to the cathode contact hole, and the under-cut region. The second cathode electrode layer is applied on the first cathode electrode layer excluding the under-cut region. The third cathode electrode layer contacts the upper surface of the second cathode electrode layer and contacts the first cathode electrode layer in the under-cut region.

Description

Technology Field

[0001] This application relates to an electroluminescent display device equipped with a low-reflection cathode electrode. In particular, it relates to an electroluminescent display device having a connection structure for lowering contact resistance in the connection between a low-potential pad that applies a low potential voltage and a low-reflection cathode electrode. Background Technology

[0002] Recently, various types of display devices, such as CRTs (Cathode Ray Tubes), LCDs (Liquid Crystal Displays), PDPs (Plasma Display Panels), and Luminescent Displays, have been developed and are advancing. These diverse display devices are utilized to display image data in a wide range of products, including computers, mobile phones, ATMs, and vehicle navigation systems, each tailored to its unique characteristics.

[0003] In order to resolve the degradation of display quality caused by the reflection of external light in electroluminescent display devices, it is required to apply a low-reflection structure to the cathode electrode. Furthermore, when applying the low-reflection structure, structural improvements are required to prevent a voltage rise from occurring in the low potential voltage applied to the cathode electrode. In particular, a connection structure is required to reduce contact resistance at the connection point between the cathode electrode having a low-reflection structure and the low potential pad applying the low potential voltage. The problem to be solved

[0004] The purpose of this application is to overcome the problems of the prior art and to provide an electroluminescent display device equipped with a low-reflection cathode electrode that can prevent external light from reflecting from the cathode electrode and thereby degrading the display quality. Another purpose of this application is to provide an electroluminescent display device having a structure for lowering the connection resistance between the cathode electrode and the low-potential pad in a low-potential pad portion for applying a low-potential voltage to a cathode electrode having a low-reflection structure. means of solving the problem

[0005] To achieve the above objective, the electroluminescent display device according to this application comprises a substrate, a low potential pad, a bank, a mushroom structure, an under-cut region, a first cathode electrode layer, a second cathode electrode layer, and a third cathode electrode layer. The substrate has a display region and a non-display region disposed around the display region. The low potential pad is disposed in the non-display region and has a first electrode layer and a second electrode layer laminated on the first electrode layer. The bank has a cathode contact hole exposing the central portion of the low potential pad and covers the edge of the low potential pad. The mushroom structure is disposed in the central portion of the low potential pad. An under-cut region is formed below the edge of the bank and the mushroom structure. The first cathode electrode layer is applied to the upper surface of the bank and the mushroom structure, the upper surface of the low potential pad exposed by the cathode contact hole, and the under-cut region. The second cathode electrode layer is applied on the first cathode electrode layer excluding the under-cut region. The third cathode electrode layer contacts the upper surface of the second cathode electrode layer and contacts the first cathode electrode layer in the under-cut region.

[0006] For example, the first electrode layer comprises any one of a transparent conductive material including indium-tin oxide and indium-zinc oxide. The second electrode layer comprises at least one of aluminum (Al), copper (Cu), molybdenum (Mo), chromium (Cr), titanium (Ti), tantalum (Ta), and any one of alloys formed by various combinations thereof.

[0007] For example, the thickness of the first cathode electrode layer is 100 Å to 200 Å. The thickness of the second cathode electrode layer is 500 Å to 900 Å. The thickness of the third cathode electrode layer is 2,000 Å to 3,000 Å.

[0008] For example, the first cathode electrode layer is in direct contact with a portion of the side of the second metal layer that is over-etched in the under-cut region. The third cathode electrode layer is in direct contact with the side of the first cathode electrode layer and the over-etched second metal layer in the under-cut region.

[0009] For example, multiple mushroom structures are placed on a low-potential pad exposed in the cathode contact hole.

[0010] For example, it further includes a pixel disposed in a display area. The pixel includes an anode electrode, a bank, an organic light-emitting layer, and a cathode electrode. The anode electrode is disposed on a substrate. The bank covers the edges of the anode electrode and exposes the central portion. The organic light-emitting layer is disposed on the bank and the anode electrode exposed to the bank. The cathode electrode comprises a first cathode electrode layer disposed on the organic light-emitting layer, a second cathode electrode layer disposed on the first cathode electrode layer, and a third cathode electrode layer disposed on the second cathode electrode layer.

[0011] For example, the first cathode electrode layer and the third cathode electrode layer comprise at least one of a metallic material including aluminum (Al), silver (Ag), molybdenum (Mo), magnesium (Mg), calcium (Ca), and barium (Ba). The second cathode electrode layer comprises a conductive resin material.

[0012] For example, a conductive resin material comprises a domain material and a dopant. The domain material comprises any one of Alq3, TmPyPB, Bphen, TAZ, and TPB. The dopant comprises at least one of an alkali metal material including Li, Cs, Cs2O3, CsN3, and Rb2, and C60, which are dispersed within the domain material. Effects of the invention

[0013] The electroluminescent display device according to this application has a structure in which three conductive layers are sequentially stacked on a cathode electrode constituting an organic light-emitting element. In particular, a thin metal layer is stacked in the lower layer to ensure transmittance, a transparent resin layer made of a conductive resin material is stacked in the middle layer, and a thick metal layer having high reflectivity is stacked in the upper layer. Accordingly, external light incident on the lower layer is partially reflected by the lower layer, and the remaining portion passes through the lower layer and the transparent resin layer and is reflected by the upper layer. At this time, by ensuring that the light reflected from the lower layer has a phase opposite to the phase of the light reflected from the upper layer, the reflection of external light can be suppressed to 2% or less due to destructive interference. Furthermore, when connecting a cathode electrode having a low-reflection structure to a low-potential pad that applies a low potential voltage, the thick metal layer, which is the upper layer, is directly connected to the low-potential pad by a mushroom structure, thereby ensuring low contact resistance. Accordingly, this application can provide an electroluminescent display device having excellent display quality by having a cathode electrode that suppresses external light reflection while maintaining a constant low potential voltage. Brief explanation of the drawing

[0014] FIG. 1 is a diagram showing the schematic structure of an electroluminescent display device according to this application. FIG. 2 is a diagram showing the circuit configuration of a pixel constituting an electroluminescent display device according to this application. FIG. 3 is a plan view showing the structure of pixels arranged in an electroluminescent display device according to this application. FIG. 4 is a cross-sectional view showing the structure of an electroluminescent display device according to the first embodiment of this application, taken along I-I' of FIG. 2. FIGS. 5a and 5b are enlarged cross-sectional views showing the stacked structure of the pad portion and pixel portion in FIG. 4, respectively. FIG. 6 is a cross-sectional view showing the structure of an electroluminescent display device according to a second embodiment of this application, taken along I-I' of FIG. 2. Figure 7 is an enlarged cross-sectional view showing the laminated structure of the pad portion in Figure 6. FIG. 8 is an enlarged plan view showing the arrangement of mushroom structures placed in the pad portion in FIG. 6. Specific details for implementing the invention

[0015] The advantages and features of this application and the methods for achieving them will become clear by referring to the examples described below in detail together with the accompanying drawings. However, this application is not limited to the examples disclosed below but may be embodied in various different forms; the examples of this application are provided merely to ensure that the disclosure of this application is complete and to fully inform those skilled in the art of the scope of the invention to which the invention of this application belongs, and the invention of this application is defined only by the scope of the claims.

[0016] Shapes, sizes, proportions, angles, quantities, etc. disclosed in the drawings for illustrating examples of this application are examples and are not limited to the matters depicted herein. Throughout the specification, the same reference numerals refer to the same components. Furthermore, in describing the examples of this application, detailed descriptions of related prior art are omitted if it is determined that such detailed descriptions would unnecessarily obscure the essence of the application.

[0017] Where terms such as 'includes,' 'have,' and 'consists of' mentioned in this application specification are used, other parts may be added unless 'only' is used. Where a component is expressed in the singular, it includes cases where it is in the plural unless specifically stated otherwise.

[0018] In interpreting the components, they are interpreted to include a margin of error even in the absence of a separate explicit statement.

[0019] In the case of describing a positional relationship, for example, when the positional relationship between two parts is described using expressions such as 'on,' 'upper,' 'lower,' or 'next to,' one or more other parts may be located between the two parts unless 'immediately' or 'directly' is used.

[0020] In the case of an explanation of a temporal relationship, for example, when a temporal sequence is explained using 'after', 'following', 'next', 'before', etc., it may include cases where the sequence is not continuous unless 'immediately' or 'directly' is used.

[0021] The terms first, second, etc. are used to describe various components, but these components are not limited by these terms. These terms are used merely to distinguish one component from another. Accordingly, the first component mentioned below may be the second component within the technical scope of this application.

[0022] The term “at least one” should be understood to include all combinations that can be presented from one or more related items. For example, the meaning of “at least one of the first item, the second item, and the third item” may mean not only the first item, the second item, or the third item individually, but also all combinations of items that can be presented from two or more of the first item, the second item, and the third item.

[0023] The features of each of the various examples of this application may be combined or combined with one another, either partially or wholly, and may technically enable various interlocking and operation. Each example may be implemented independently of one another or may be implemented together in an interlocking relationship.

[0024] Hereinafter, an example of an organic light-emitting display device according to this application will be described in detail with reference to the attached drawings. In assigning reference numerals to the components of each drawing, the same components may have the same reference numeral as much as possible, even if they are shown in different drawings.

[0025] Hereinafter, this application will be described in detail with reference to the attached drawings. FIG. 1 is a drawing showing the schematic structure of an electroluminescent display device according to this application. In FIG. 1, the X-axis represents a direction parallel to the scan wiring, the Y-axis represents a direction parallel to the data wiring, and the Z-axis represents the height direction of the display device.

[0026] Referring to FIG. 1, the electroluminescent display device according to this application includes a substrate (110), a gate (or scan) driving unit (200), a data pad unit (300), a source driving integrated circuit (410), a flexible wiring film (430), a circuit board (450), and a timing control unit (500).

[0027] The substrate (110) may include an insulating material or a material having flexibility. The substrate (110) may be made of glass, metal, plastic, etc., but is not limited thereto. If the electroluminescent display device is a flexible display device, the substrate (110) may be made of a flexible material such as plastic. For example, it may include a transparent polyimide material.

[0028] The substrate (110) may be divided into a display area (DA) and a non-display area (NDA). The display area (DA) is an area where an image is displayed and may be defined in most of the area including the central part of the substrate (110), but is not limited thereto. Scan lines (or gate lines), data lines, and pixels (P) are formed in the display area (DA). A plurality of pixels (P) are arranged in a matrix manner in the display area (DA).

[0029] The non-display area (NDA) is an area where no image is displayed and may be defined at the edge portion of the substrate (110) to surround all or part of the display area (DA). A gate driver (200) and a data pad portion (300) may be formed in the non-display area (NDA).

[0030] The gate driver (200) supplies scan (or gate) signals to the scan lines according to the gate control signal input from the timing control unit (500). The gate driver (200) may be formed in a non-display area (NDA) outside one side of the display area (DA) of the base substrate (110) in a GIP (gate driver in panel) manner. The GIP method refers to a structure in which the gate driver (200) is formed directly on the substrate (110).

[0031] The data pad section (300) supplies data signals to the data wires according to a data control signal input from the timing control section (500). Data pads (not shown) placed at one end of the data wire (DL) may be arranged side by side in the data pad section (300). The data pads placed in the data pad section (300) may be connected to a source driving integrated circuit (410). For example, the source driving integrated circuit (410) may be manufactured as a driving chip, mounted on a flexible wiring film (430), and attached to a non-display area (NDA) outside one side of the display area (DA) of the substrate (110) using a tape automated bonding (TAB) method. The pads placed on the flexible wiring film (430) may be connected in a one-to-one correspondence with the data pads placed in the data pad section (300).

[0032] In the data pad section (300), low voltage pad terminals (ESPs) may be disposed between the flexible wiring films (430). Preferably, in the data pad section (300), one low voltage pad terminal (ESP) may be disposed between groups of data pads (D) arranged by group, where multiple data link wires (LK) are gathered. For example, one low voltage pad terminal (ESP) may be disposed between the flexible wiring films (430). When the link wires (LK) connecting the data pads (DP) to the data wires (DL) are arranged in a fan shape toward the display area (DA) in the flexible wiring film (430), the low voltage pad terminal (ESP) may have a trapezoidal shape.

[0033] The source driving integrated circuit (410) receives digital video data and a source control signal from the timing control unit (500). The source driving integrated circuit (410) converts the digital video data into analog data voltages according to the source control signal and supplies them to the data wires. When the source driving integrated circuit (410) is manufactured as a chip, it can be mounted on a flexible wiring film (430) using a COF (chip on film) or COP (chip on plastic) method.

[0034] In the flexible wiring film (430), wirings connecting the data pad section (300) and the source driving integrated circuit (410), and wirings connecting the data pad section (300) and the circuit board (450) may be formed. The flexible wiring film (430) is attached to the data pad section (300) using an anisotropic conducting film, thereby allowing the wirings of the data pad section (300) and the flexible film (430) to be connected.

[0035] The circuit board (450) can be attached to flexible wiring films (430). The circuit board (450) may have a number of circuits implemented with driving chips mounted on it. For example, a timing control unit (500) may be mounted on the circuit board (450). The circuit board (450) may be a printed circuit board or a flexible printed circuit board.

[0036] The timing control unit (500) receives digital video data and timing signals from an external system board through a cable of the circuit board (450). Based on the timing signals, the timing control unit (500) generates a gate control signal for controlling the operation timing of the gate driver (200) and a source control signal for controlling the source driver integrated circuits (410). The timing control unit (500) supplies the gate control signal to the gate driver (200) and supplies the source control signal to the source driver integrated circuits (410). Depending on the product, the timing control unit (500) may be formed with the source driver integrated circuit (410) and a single driver chip and mounted on the substrate (110).

[0037] <1st Embodiment>

[0038] Hereinafter, a first embodiment of the present application will be described with reference to FIGS. 2 to 4. FIG. 2 is a diagram showing the circuit configuration of a pixel constituting an electroluminescent display device according to the present application. FIG. 3 is a plan view showing the structure of pixels according to the present application. FIG. 4 is a cross-sectional view showing the structure of an electroluminescent display device according to the present application, cut along I-I' of FIG. 1 and II-II' of FIG. 3. In FIGS. 2 to 4, an organic light-emitting display device, which is a type of electroluminescent display device, is described as an example.

[0039] Referring to FIGS. 2 through 4, a pixel (P) of an organic light-emitting display is defined by a scan line (SL), a data line (DL), and a driving current line (VDD). Inside a pixel (P) of an organic light-emitting display, there is a switching thin-film transistor (ST), a driving thin-film transistor (DT), an organic light-emitting diode (OLE), and an auxiliary capacitance (Cst). A high potential voltage is applied to the driving current line (VDD) to drive the organic light-emitting diode (OLE).

[0040] For example, a switching thin-film transistor (ST) may be placed at the intersection of a scan line (SL) and a data line (DL). The switching thin-film transistor (ST) includes a switching gate electrode (SG), a switching source electrode (SS), and a switching drain electrode (SD). The switching gate electrode (SG) is connected to the scan line (SL). The switching source electrode (SS) is connected to the data line (DL), and the switching drain electrode (SD) is connected to a driving thin-film transistor (DT). The switching thin-film transistor (ST) functions to select a pixel to be driven by applying a data signal to the driving thin-film transistor (DT).

[0041] The driving thin-film transistor (DT) functions to drive the organic light-emitting diode (OLE) of a pixel selected by the switching thin-film transistor (ST). The driving thin-film transistor (DT) includes a driving gate electrode (DG), a driving source electrode (DS), and a driving drain electrode (DD). The driving gate electrode (DG) is connected to the switching drain electrode (SD) of the switching thin-film transistor (ST). For example, the switching drain electrode (SD) is connected through a drain contact hole (DH) that penetrates the intermediate insulating layer (ILD) covering the driving gate electrode (DG). The driving source electrode (DS) is connected to the driving current wiring (VDD), and the driving drain electrode (DD) is connected to the anode electrode (ANO) of the organic light-emitting diode (OLE). An auxiliary capacitance (Cst) is placed between the driving gate electrode (DG) of the driving thin-film transistor (DT) and the anode electrode (ANO) of the organic light-emitting diode (OLE).

[0042] The driving thin-film transistor (DT) is placed between the driving current wiring (VDD) and the organic light-emitting diode (OLE). The driving thin-film transistor (DT) adjusts the amount of current flowing from the driving current wiring (VDD) to the organic light-emitting diode (OLE) according to the magnitude of the voltage of the gate electrode (DG) connected to the drain electrode (SD) of the switching thin-film transistor (ST).

[0043] An organic light-emitting diode (OLE) comprises an anode electrode (ANO), an organic light-emitting layer (EL), and a cathode electrode (CAT). The organic light-emitting diode (OLE) emits light according to a current controlled by a driving thin-film transistor (DT). In other words, since the amount of light emitted by the organic light-emitting diode (OLE) is controlled according to the current controlled by the driving thin-film transistor (DT), the brightness of the electroluminescent display device can be controlled. The anode electrode (ANO) of the organic light-emitting diode (OLE) is connected to the driving drain electrode (DD) of the driving thin-film transistor (DT), and the cathode electrode (CAT) is connected to a low-potential wiring (VSS) to which a low potential voltage is supplied. That is, the organic light-emitting diode (OLE) is driven by the potential difference between the low potential voltage and the high potential voltage controlled by the driving thin-film transistor (DT).

[0044] A protective film (PAS) is laminated on the surface of a substrate (110) on which thin-film transistors (ST, DT) are formed. It is preferable that the protective film (PAS) be formed from an inorganic film such as silicon oxide or silicon nitride. A planarization film (PL) is laminated on the protective film (PAS). The planarization film (PL) is a thin film intended to flatten the surface of the substrate (110) on which thin-film transistors (ST, DT) are formed, as the surface may not be uniform. To make the height difference uniform, the planarization film (PL) may be formed from an organic material. Pixel contact holes (PH) are formed in the protective film (PAS) and the planarization film (PL) to expose a portion of the drain electrode (DD) of the driving thin-film transistor (DT).

[0045] An anode electrode (ANO) is formed on the upper surface of the planarization film (PL). The anode electrode (ANO) is connected to the drain electrode (DD) of the driving thin-film transistor (DT) through a pixel contact hole (PH). The components of the anode electrode (ANO) may vary depending on the light-emitting structure of the organic light-emitting diode (OLE). For example, in the case of a bottom-emitting type that provides light toward the substrate (110), it can be formed from a transparent conductive material. As another example, in the case of emitting light toward the top facing the substrate (110), it can be formed from a metallic material with excellent light reflectivity. Here, the case of the bottom-emitting type is described. In the case of the bottom-emitting type, it is preferable to form the anode electrode (ANO) from a transparent conductive material. For example, it may include an oxidized conductive material such as indium zinc oxide or indium tin oxide.

[0046] An organic light-emitting layer (EL) is laminated on the anode electrode (AN0). The organic light-emitting layer (EL) may be formed over the entire display area (DA) of the substrate (110) to cover the anode electrode (ANO) and the bank (BA). An organic light-emitting layer (EL) according to one example may include two or more vertically laminated light-emitting parts to emit white light. For example, the organic light-emitting layer (EL) may include a first light-emitting part and a second light-emitting part for emitting white light by mixing a first light and a second light.

[0047] As another example, the organic light-emitting layer (EL) may include any one of a blue light-emitting part, a green light-emitting part, and a red light-emitting part for emitting light corresponding to the color set in the pixel. Additionally, the organic light-emitting diode (OLE) may further include a functional layer to improve the luminous efficiency and / or lifespan of the organic light-emitting layer (EL).

[0048] A cathode electrode (CAT) is laminated to make surface contact with an organic light-emitting layer (EL). The cathode electrode (CAT) is formed across the entire substrate (110) to be commonly connected to the organic light-emitting layer (EL) formed in all pixels. In the case of a bottom-emitting type, the cathode electrode (CAT) comprises a metallic material with excellent light reflection efficiency. For example, the cathode electrode (CAT) may be made of any one material selected from silver (Ag), aluminum (Al), molybdenum (Mo), gold (Au), magnesium (Mg), calcium (Ca), or barium (Ba), or an alloy of two or more of these materials.

[0049] In the bottom-emitting electroluminescent display device according to this application, the cathode electrode (CAT) comprises three cathode electrode layers. For example, the cathode electrode (CAT) comprises a first cathode electrode layer (100), a second cathode electrode layer (200), and a third cathode electrode layer (300) sequentially stacked on an organic light-emitting layer (EL). The first cathode electrode layer (100) is stacked first to make direct surface contact with the organic light-emitting layer (EL). The first cathode electrode layer (100) may comprise a metal material having low surface resistance. For example, it may be formed from a metal material selected from aluminum (Al), silver (Ag), molybdenum (Mo), gold (Au), magnesium (Mg), calcium (Ca), or barium (Ba). Considering the manufacturing process and manufacturing cost, the case where the first cathode electrode layer (100) is formed from aluminum is described as the most preferred example.

[0050] When the first cathode electrode layer (100) is made of aluminum, it is preferable to form it with a thickness of 100 Å to 200 Å. Metal materials such as aluminum are opaque and have a very high reflectivity. However, if the aluminum is formed very thin, it can transmit light. For example, at a thin thickness of 200 Å or less, some of the incident light (40% to 50%) is reflected, and the remainder (50% to 60%) is transmitted.

[0051] The second cathode electrode layer (200) may include a conductive resin material. The conductive resin material may include a domain material composed of a resin material with high electron mobility and a dopant that lowers the barrier energy of the domain material. The resin material with high electron mobility may include any one selected from Alq3, TmPyPB, Bphen, TAZ, and TPB. Alq3 is an abbreviation for Tris(8-hydroxyquinoline) Aluminum, which is a complex having the chemical formula Al(C9H6NO)3. TmPyPB is an organic material that is an abbreviation for 1,3,5-tri(m-pyrid-3-yl-phenyl)benzene. Bphen is an organic material that is an abbreviation for Bathophenanthroline. TAZ is an organic material, and TPB is an organic material that is an abbreviation for triphenyl bismuth. These organic materials have high electron mobility and can be used in organic light-emitting diodes.

[0052] Dopant materials may include alkaline doping materials. For example, they may include any one of lithium (Li), cesium (Cs), cesium oxide (Cs2O3), cesium nitride (CsN3), rubidium (Rb), and rubidium oxide (Rb2O). Other dopant materials may include fullerenes, which possess high electron mobility characteristics. Fullerene is a general term for molecules in which carbon atoms are arranged in spherical, ellipsoidal, or cylindrical shapes. For example, Buckminsterfullerene (C), in which 60 carbon atoms are bonded in a soccer ball shape, is a type of fullerene. 60 ; May include Buckminster-fullerene). In addition, C 70 , C 76 , C 78 , C 82 , C 90 , C 94 and C 96 It may also include higher-order fullerenes such as.

[0053] The second cathode electrode layer (200) may be made of the same material as the electron transport layer or electron injection layer included in the organic light-emitting layer (EL). However, unlike the electron transport layer or electron injection layer, it is desirable that the electron mobility be higher. For example, in the case of the electron transport layer or electron injection layer, the electron mobility is 5.0 x 10 -4 (S / m) to 9.0X10 -1 (S / m), whereas the second cathode electrode layer (200) has an electron mobility of 1.0×10 -3 (S / m) to 9.0X10 +1 It is preferable that (S / m) is used. To this end, it is preferable that the conductive resin material constituting the second cathode electrode layer (200) has a higher dopant content than the electron transport layer or electron injection layer.

[0054] For example, it is preferable that the electron transport layer or electron injection layer has a dopant doping concentration of 2% to 10%, while the second cathode electrode layer (200) is a conductive resin material having a dopant doping concentration of 10% to 30%. The domain material itself, having a dopant doping concentration of 0%, has an electrical conductivity of 1.0×10 -4 (S / m) to 5.0X10 -3 (S / m) may be. By injecting 10% to 30% of a dopant into the domain material, the second cathode electrode layer (200) has an electrical conductivity of 1.0×10 -3 (S / m) to 9.0X10 +1 It is improved to (S / m) and can be used as a cathode electrode.

[0055] In some cases, the second cathode electrode layer (200) may have the same conductivity as the electronic functional layer (electron transport layer and / or electron injection layer) of the organic light-emitting layer (EL). In this case, the sheet resistance can be maintained at a sufficiently low value by the first cathode electrode layer (100) made of aluminum.

[0056] The third cathode electrode layer (300) can be formed from the same metal material as the first cathode electrode layer (100). It is desirable for the third cathode electrode layer (300) to have a sufficient thickness so that it does not transmit light but reflects it entirely, and so that the sheet resistance of the cathode electrode (CAT) can maintain a constant value regardless of the position of the substrate (SUB). For example, it is desirable for the third cathode electrode layer (300) to be formed with a metal material having low sheet resistance and a thickness relatively thicker than that of the first and second cathode electrode layers (CAT1, CAT2) in order to lower the sheet resistance of the entire cathode electrode (CAT). As an example, the third cathode electrode layer (300) can be formed from aluminum having a thickness of at least 2,000 Å. If the thickness of the third cathode electrode layer (300) is made too thick, the manufacturing process may be prolonged or the cost may increase. Accordingly, it is preferable that the third cathode electrode layer (300) be formed of aluminum having a thickness of 2,000 Å to 3,000 Å.

[0057] A cathode electrode layer (CAT) having such thickness and stacked structure can minimize the reflectivity of light incident from the lower direction (first cathode electrode layer (100)). The portion suppressing external light reflection may be primarily a display area that can affect image information. Therefore, it is desirable to implement a low-reflection structure in the cathode electrode (CAT) that is applied commonly over the entire display area (DA). Below, the explanation will be made with reference to the arrows indicating the light paths shown in FIG. 5a. FIG. 5a and 5b are enlarged cross-sectional views showing the stacked structure of the pad portion and the pixel portion in FIG. 4, respectively.

[0058] Looking at the structure of the cathode electrode (CAT) of the pixel section, incident light (①) entering from the bottom of the cathode electrode (CAT) passes through the transparent anode electrode (ANO) and the organic light-emitting layer (EL), and is partially reflected from the bottom surface of the first cathode electrode layer (100) to proceed toward the substrate (SUB) as primary reflected light (②). Since the first cathode electrode layer (100) has a thin thickness of 200 Å or less, it cannot reflect all of the incident light (①). For example, only about 40% of the incident light (①) is reflected as primary reflected light (②), and the remaining 60% passes through the first cathode electrode layer (100). The transmitted light (③) that passes through the first cathode electrode layer (100) passes through the transparent second cathode electrode layer (200) as is. After that, the transmitted light (③) is reflected by the third cathode electrode layer (300). Since the third cathode electrode layer (300) has a thickness of 2,000 Å or more, all of the transmitted light (③) is reflected and travels toward the substrate (SUB) as secondary reflected light (④).

[0059] At this time, the thickness of the second cathode electrode layer (200) can be adjusted so that the phases of the first reflected light (②) and the second reflected light (④) cancel each other out. As a result, the luminance of the reflected light, which is the intensity of the reflected light incident and reflected from the bottom of the cathode electrode (CAT), can be reduced to 2%.

[0060] Meanwhile, among the light emitted from the organic light-emitting layer (EL), the light radiated in the direction of the cathode electrode (CAT) may also be reduced to about 2% as it is emitted in the direction of the substrate (SUB) through the same light path. However, since the light emitted from the organic light-emitting layer (EL) is emitted in all directions, the amount of light reduced by the cathode electrode (CAT) is only about 50% of the total amount of light, and the remaining 50% is emitted in the direction of the substrate (SUB).

[0061] The electroluminescent display device according to the first embodiment may be a bottom-emitting type having a cathode electrode with a triple-layer stacked structure. In addition, the reflectivity of external light can be suppressed to the maximum extent by the structure of the cathode electrode with a triple-layer stacked structure. Therefore, there is no need to place a polarizing element to reduce external light reflection outside the substrate (SUB). Although the polarizing element has a positive effect of suppressing external light reflection, it has a negative effect of reducing the amount of light emitted from the organic light-emitting layer (EL) by at least 50%.

[0062] In the electroluminescent display device according to the first embodiment, the amount of light emitted from the organic light-emitting layer (EL) is reduced by about 50% due to the cathode electrode of the triple-layer stacked structure, but this is almost the same as the reduction in light amount caused by the polarizing element. Therefore, the electroluminescent display device according to this application can provide the same level of organic light-emitting layer (EL) luminous efficiency without using a significantly expensive polarizing element, while simultaneously minimizing external light reflection.

[0063] Meanwhile, referring to FIG. 5b, the structure of the cathode electrode (CAT) of the pad portion (300) is such that the cathode electrode (CAT) is in contact with the low potential pad (ESP) disposed in the pad portion. For example, the low potential pad (ESP) can be formed on a flattening film (PL) that is in the same plane as the anode electrode (ANO). In the case of a bottom-emitting type, the anode electrode (ANO) includes a transparent conductive material. Since the transparent conductive material has higher sheet resistance and contact resistance than the metal material, it may be disadvantageous for uniformly transmitting the low potential voltage.

[0064] To prevent this, in the electroluminescent display device according to this application, the low potential pad (ESP) may have a structure in which a first electrode layer (E1) containing the same material as the anode electrode (ANO) and a second electrode layer (E2) containing a metal material with low resistance are sequentially stacked. For example, the first electrode layer (E1) may include indium-tin oxide or indium-zinc oxide. The second electrode layer (E2) may be formed from any one of at least one of aluminum (Al), copper (Cu), molybdenum (Mo), chromium (Cr), titanium (Ti), tantalum (Ta), and alloys of various combinations thereof. Here, the second electrode layer (E2) is disposed only in the pad portion and is not disposed in the display area (DA).

[0065] A low potential pad portion disposed in a non-display area comprises a low potential pad (ESP), a bank (BA), a cathode contact hole (CHC), and a cathode electrode (CAT) formed on a planarization film (PL). The low potential pad (ESP) comprises a first electrode layer (E1) and a second electrode layer (E2) sequentially stacked on the planarization film (PL). The bank (BA) covers the edge of the low potential pad (ESP). Thus, the cathode contact hole (CHC) is a contact hole formed in the bank (BA) and exposes most of the central portion of the low potential pad (ESP). The cathode electrode (CAT) extends from the display area (DA) to cover the bank (BA) and makes surface contact with the surface of the low potential pad (ESP).

[0066] To explain in more detail, the structure has a first cathode electrode layer (100) of a cathode electrode (CAT) and a second electrode layer (E2) containing a metal material stacked on top of a low potential pad (ESP) in direct surface contact. Then, a second cathode electrode layer (100) is stacked on top of the first cathode electrode layer (100), and a third cathode electrode layer (300) is stacked on top of it.

[0067] The current density applied to the low potential pad (ESP) to supply a low potential voltage to the cathode electrode (CAT) in the pad portion (300) is about 800 to 2,000 times greater than the current density of the entire cathode electrode (CAT) applied to the entire display area. Therefore, it is very important to keep the contact resistance of the pad portion as low as possible. However, since the first cathode electrode layer (100) is very thin with a thickness of 200 Å or less, it is difficult to lower the contact resistance between the cathode electrode (CAT) and the low potential pad (ESP).

[0068] In the following second embodiment, a connection structure is proposed to further lower the contact resistance between the cathode electrode (CAT) and the low potential pad (ESP) in the electroluminescent display device according to the first embodiment of this application.

[0069] <Second Embodiment>

[0070] Hereinafter, a second embodiment of this application will be described with reference to FIGS. 6 to 8. FIG. 6 is a cross-sectional view showing the structure of an electroluminescent display device according to the second embodiment of this application, taken along I-I' of FIG. 2. FIG. 7 is a plan view showing the structure of a low-potential pad disposed in a pad portion according to the second embodiment of this application. FIG. 8 is an enlarged cross-sectional view showing the stacked structure of a pad portion, taken along the cutting line III-III' in FIG. 7. Since the structure of the display area (DA) in the second embodiment is the same as that of the first embodiment, the structure of the display area shown in FIG. 6 is depicted identically to the display area shown in FIG. 5, and a redundant description is omitted.

[0071] Referring to FIGS. 6 and 7, in an electroluminescent display device according to a second embodiment, the pad portion comprises a low potential pad (ESP), a bank (BA), a mushroom structure (MS), a cathode contact hole (CHC), and a cathode electrode (CAT) formed on a planarization film (PL). The low potential pad (ESP) comprises a first electrode layer (E1) and a second electrode layer (E2) sequentially stacked on the planarization film (PL). The bank (BA) covers the edge of the low potential pad (ESP). Thus, the cathode contact hole (CHC) is a contact hole formed in the bank (BA) that exposes most of the central portion of the low potential pad (ESP). The mushroom structure (MS) is formed on the surface of the low potential pad (ESP) exposed by the cathode contact hole (CHC). At least one mushroom structure (MS) may be disposed. The cathode electrode (CAT) extends from the display area (DA) to cover the bank (BA) and makes surface contact with the surface of the low potential pad (ESP) exposed to the cathode contact hole (CHC) and the mushroom structure (MS). Here, the term 'mushroom structure' is used to mean a structure having a mushroom shape with a wide upper width and a narrow lower width.

[0072] With reference to FIGS. 7 and 8, the detailed structure of the low potential pad (ESP) is described. The low potential pad (ESP) is covered at the edge portion by a bank (BA) and a portion of the central portion is covered by a mushroom structure (MS). The mushroom structure (MS) can be formed from the same material as the bank (BA). A second electrode layer (E2) containing a metallic material, which is the upper layer of the low potential pad (ESP), is disposed below the mushroom structure (MS) and the bank (BA). The second electrode layer (E2) is not disposed in the display area (DA).

[0073] The second electrode layer (E2) exposed by the mushroom structure (MS) and the bank (BA) is etched to expose the first electrode layer (E1). In this process, the second electrode layer (E2) may be over-etched to form an under-cut region (UC) at the lower edge of the mushroom structure (MS) and the bank (BA). An under-cut region refers to an area formed in a shape where the lower layer is indented inward from the lower part of the upper layer, as a result of using an etching solution in which the etching rate for the upper layer is low and the etching rate for the lower layer is high, causing the lower layer to be etched more than the upper layer. Meanwhile, since there is no second electrode layer (E2) in the display area (DA), the anode electrode (ANO) is made only of a transparent conductive material. Therefore, an under-cut region is not formed at the lower part of the bank (BA) covering the edge of the anode electrode (ANO) in the display area (DA).

[0074] After the mushroom structure (MS) and bank (BA) are formed and an under-cut region (UC) is formed in the pad portion, an organic light-emitting layer (EL) is applied to the display region (DA). At this time, it is preferable to apply the organic light-emitting layer (EL) using an open mask that covers the non-display region (NDA) and exposes the entire display region (DA).

[0075] After that, a cathode electrode (CAT) connected across the entire display area (DA) and non-display area (NDA) is stacked. As a result, in the display area (NDA), an organic light-emitting diode (OLE) is completed in which an anode electrode (ANO), an organic light-emitting layer (EL), and a cathode electrode (CAT) are stacked for each pixel (P) area.

[0076] At the same time, a cathode electrode (CAT) is also laminated on the pad portion located in the non-display area (NDA). Looking at the process of forming the cathode electrode (CAT), a first cathode electrode layer (100) is first applied. The first cathode electrode layer (100), formed from aluminum, is also laminated on the under-cut area (UC) formed on the mushroom structure (MS) in the pad portion. In particular, the first cathode electrode (100) is laminated while contacting the etched side (SW) of the second metal layer (E2) exposed in the under-cut area (UC) and the surface of the exposed first metal layer (E1).

[0077] Next, a second cathode electrode layer (200) is applied. Since the second cathode electrode layer (200) is formed from a conductive organic material, it is laminated only on the portion of the upper surface of the first cathode electrode layer (100) exposed to the bank (BA) and the mushroom structure (MS). That is, the second cathode electrode layer (200) is not laminated on the under-cut region (UC).

[0078] Finally, a third cathode electrode layer (300) is applied. Since the third cathode electrode layer (300) is formed of aluminum, it is also laminated into the under-cut region (UC) formed in the mushroom structure (MS) at the pad portion. As a result, the first cathode electrode layer (100) and the third cathode electrode layer (300) can have a structure in which they are in direct contact at the under-cut region (UC) of the mushroom structure (MS). Therefore, the contact resistance between the cathode electrode (CAT) and the low potential pad (ESP) can be stably maintained at a low value by the mushroom structure (MS). In order to secure more low-resistance connection structures by the mushroom structure (MS), it is preferable to form multiple mushroom structures (MS) on the surface of the low potential pad (ESP) exposed by the cathode contact hole (CHC), as shown in FIG. 7.

[0079] The features, structures, effects, etc. described in the examples of this application described above are included in at least one example of this application and are not necessarily limited to only one example. Furthermore, the features, structures, effects, etc. exemplified in at least one example of this application may be combined or modified and implemented in other examples by a person skilled in the art to which this application pertains. Therefore, matters related to such combinations and modifications should be interpreted as being included within the scope of this application.

[0080] It will be obvious to those skilled in the art to which this application pertains that the above-described application is not limited to the embodiments and attached drawings described above, and that various substitutions, modifications, and changes are possible within the scope of the technical details of this application. Therefore, the scope of this application is defined by the claims set forth below, and all modifications or variations derived from the meaning and scope of the claims and equivalent concepts should be interpreted as being included within the scope of this application. Explanation of the symbols

[0081] OLE: Organic Light Emitting Diode ANO: Anode Electrode EL: Organic Light-emitting Layer CAT: Cathode Electrode CAT1: First cathode electrode layer CAT2: Second cathode electrode layer CAT3: Third cathode electrode layer ESP: Low potential pad E1: First electrode layer E2: Second electrode layer MS: Mushroom structure CHC: Cathode contact hole

Claims

Claim 1 A substrate having a display area and a non-display area disposed around the display area; a low potential pad disposed in the non-display area and having a first electrode layer and a second electrode layer laminated on the first electrode layer; a bank covering the edge of the low potential pad and having a cathode contact hole exposing the central part of the low potential pad; a mushroom structure patterned such that the bank is disposed in an island shape in the central part of the low potential pad; an under-cut area formed by over-etching the second electrode layer below the edge of the bank and the mushroom structure; a first cathode electrode layer applied to the upper surface of the bank and the mushroom structure and the upper surface of the low potential pad exposed to the cathode contact hole and the under-cut area; and a second cathode electrode layer applied on the first cathode electrode layer excluding the under-cut area. An electroluminescent display device comprising a third cathode electrode layer that contacts the upper surface of the second cathode electrode layer and contacts the first cathode electrode layer in the under-cut region. Claim 2 An electroluminescent display device according to claim 1, wherein the first electrode layer comprises any one of a transparent conductive material including indium-tin oxide and indium-zinc oxide, and the second electrode layer comprises any one of at least one of aluminum (Al), copper (Cu), molybdenum (Mo), chromium (Cr), titanium (Ti), tantalum (Ta) and any one of alloys formed by various combinations thereof. Claim 3 An electroluminescent display device according to claim 1, wherein the thickness of the first cathode electrode layer is 100 Å to 200 Å, the thickness of the second cathode electrode layer is 500 Å to 900 Å, and the thickness of the third cathode electrode layer is 2,000 Å to 3,000 Å. Claim 4 An electroluminescent display device according to claim 1, wherein the first cathode electrode layer is in direct contact with a portion of the side of the second electrode layer that is over-etched in the under-cut region, and the third cathode electrode layer is in direct contact with the side of the first cathode electrode layer and the over-etched second electrode layer in the under-cut region. Claim 5 In claim 1, the mushroom structure is an electroluminescent display device having a plurality of structures arranged on the low potential pad exposed to the cathode contact hole. Claim 6 An electroluminescent display device according to claim 1, further comprising a pixel disposed in the display area, wherein the pixel comprises: an anode electrode disposed on the substrate; a bank covering the edge of the anode electrode and exposing the central portion; an organic light-emitting layer disposed on the bank of the display area and on the anode electrode exposed to the bank; and a cathode electrode having a first cathode electrode layer disposed on the organic light-emitting layer, a second cathode electrode layer disposed on the first cathode electrode layer, and a third cathode electrode layer disposed on the second cathode electrode layer. Claim 7 In claim 1, the first cathode electrode layer and the third cathode electrode layer comprise at least one of the same metallic materials including aluminum (Al), silver (Ag), molybdenum (Mo), magnesium (Mg), calcium (Ca), and barium (Ba), and the second cathode electrode layer comprises a conductive resin material, an electroluminescent display device. Claim 8 An electroluminescent display device according to claim 7, wherein the conductive resin material comprises a domain material comprising any one of Alq3, TmPyPB, Bphen, TAZ, and TPB; and a dopant comprising at least one of an alkali metal material comprising Li, Cs, Cs2O3, CsN3, Rb2, and C60 dispersed within the domain material.

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