JPWO2001078463A1 - Organic EL display device - Google Patents

Abstract

(57) [Abstract] An organic EL display device is provided that has excellent uniformity of light emission intensity within the display area, even when the display area is relatively large. A plurality of cathode terminals (109) connected to a cathode layer (107) disposed over the entire display area are provided at different positions on a substrate (101).

Description

Detailed Description of the Invention

TECHNICAL FIELD The present invention relates to an organic EL (electroluminescence) display device having an organic EL element as a display element. BACKGROUND ART An organic EL element is a self-luminous element having a structure in which at least one light-emitting organic layer is disposed between a cathode and an anode, and has the advantage that it can be driven by a DC voltage of about 3 V and that elements with a variety of luminescent colors can be manufactured.
Organic EL elements have many advantages as display elements, such as a faster response speed and a wider viewing angle than liquid crystal display elements, and their practical use in a wide variety of applications, including display device pixels and light sources, is being considered. An organic EL panel using such organic EL elements as display elements is formed, for example, as follows: First, a transparent conductive thin film for the anode is formed on a transparent glass substrate. Next, photolithography and etching are performed on this thin film to simultaneously pattern the anodes of the organic EL elements (formed in a pattern corresponding to multiple light-emitting portions), the anode terminals, the cathode terminals, and the wiring between the anode and terminals. Next, the glass substrate surface is covered with an insulating layer except for the light-emitting portions and terminal portions of the anode. Next, a hole injection layer and a light-emitting organic layer are formed within the display region of this glass substrate surface (the region including the entire light-emitting portion but excluding the terminal portions). Next, a cathode made of a metal thin film is formed over the entire display region of this glass substrate surface. This cathode has a surface that matches the display region and a portion that protrudes from this surface outside the display region.
The pattern has four protrusions, each of which is formed so as to contact the cathode terminal. Thus, in the conventional organic EL panel, only one cathode terminal is formed on the substrate surface across the entire display area. Therefore, in organic EL panels with a relatively large display area, the cathode area is also large, and when voltage is applied, a potential difference occurs between a position close to the terminal and a position far from the terminal within the cathode surface. In other words, a voltage drop is likely to occur within the cathode. As a result, the amount of current applied to the organic EL element within the display area is likely to be non-uniform. Therefore, conventional relatively large organic EL panels have room for improvement in terms of the uniformity of light-emission intensity within the display area. The present invention has been made in response to these problems of the conventional technology, and aims to provide an organic EL display device that has excellent uniformity of light-emission intensity within the display area, even when the display area is relatively large. Disclosure of the Invention In order to solve the above-mentioned problems, the present invention provides a laminated body having an organic light-emitting layer between electrode layers formed on a substrate, one of the electrode layers being a first electrode layer formed in a pattern corresponding to a plurality of light-emitting portions, the other electrode layer being a second electrode layer disposed over the entire display area, and a first terminal connected to the first electrode layer and a second terminal connected to the second electrode layer.
In an organic EL display device in which the terminals are formed outside the display area on the substrate,
The present invention provides an organic EL display device characterized in that a plurality of terminals are formed on a substrate, and the second electrode layer is connected to the plurality of second terminals. This is referred to as the first organic EL display device of the present invention. According to the first organic EL display device of the present invention, since the second electrode layer is connected to the plurality of second terminals, voltage drop is less likely to occur within the second electrode layer compared to when the second electrode layer is connected to a single second terminal. This makes it easier to uniformize the amount of current applied to the organic EL element within the display area. The present invention also provides an organic EL display device, in which a laminate having an organic light-emitting layer between electrode layers is formed on a substrate,
The present invention provides an organic EL display device in which one electrode layer, the first electrode layer, is formed in a pattern corresponding to the plurality of light-emitting portions and has a plurality of first electrodes, and the other electrode layer, the second electrode layer, is arranged so as to cover all of the portions of the display area where the first electrodes are formed, and a first terminal connected to the first electrode layer and a second terminal connected to the second electrode layer are formed outside the display area on the substrate, the second electrode layer comprising a plurality of second electrodes, a plurality of second terminals formed on the substrate, and the plurality of second electrodes are each connected to a different second terminal. This is referred to as a second organic EL display device of the present invention. According to the second organic EL display device of the present invention, by dividing the second electrode layer into a plurality of second electrodes, a voltage drop within the second electrode layer is less likely to occur. As a result,
The amount of current applied to the organic EL elements within the plane of the display area is likely to be uniform. Furthermore, by connecting each of the multiple second electrodes to a different second terminal, it is possible to differentiate the amount of current applied to each second electrode. An embodiment of the present invention includes an organic EL display device in which the substrate is light-transmitting, the first electrode layer is a light-transmitting anode layer formed on the substrate side, and the second electrode layer is a cathode layer. An embodiment of the present invention includes an active-matrix organic EL display device in which the first electrode and the organic light-emitting layer are formed in a matrix, and the second electrode layer is formed as a common electrode, and the second electrode layer is light-transmitting. BEST MODE FOR CARRYING OUT THE INVENTION An embodiment of the present invention will now be described. FIG. 1 is a plan view showing the structure of an organic EL display panel corresponding to a first embodiment of the present invention, and FIG. 2 is a cross-sectional view taken along line A-A in FIG. 1. This display panel comprises a transparent substrate 101 and anodes (
a transparent anode layer (first electrode layer) consisting of a first electrode 102 and an anode wiring 104;
The organic light-emitting layer 106 includes an insulating layer 105, an organic light-emitting layer 106 including a hole transport layer, and a cathode layer 107. The organic light-emitting layer 106 and the insulating layer 105 are omitted in FIG.
The anode wiring 104 is omitted in Figure 2. As shown in Figure 1, this display panel is a display that displays four digital numbers, and the seven elements (light-emitting portions) that make up each digital number are composed of organic EL elements. Therefore, anodes 102 are formed directly above the substrate 101 in a pattern corresponding to each light-emitting portion. Dedicated wiring 104 is connected to each anode 102. Directly above the substrate 101, these anodes 102 and wiring 104 are also formed, along with 28 terminals 108 for the anode wiring 104 and four terminals 109 for the cathodes. These terminals are grouped together for each digital number and formed as terminal sections 103 at positions on the opposing sides outside the octagonal display area. In each terminal section 103, seven anode terminals 108 and one cathode terminal 109 are arranged in parallel. The anodes 102, wiring 104, anode terminals 108, and cathode terminals 109 are connected to the substrate 101.
The insulating layer 105 is formed by forming a transparent conductive thin film on the substrate 101 and then performing photolithography and etching on the thin film.
8 and the cathode terminal 109. This insulating layer 105 prevents light emission in areas other than the light-emitting area and electrical leakage between wirings and terminals. The organic light-emitting layer 106 is formed over the entire display area. The cathode layer 107 has an octagonal surface the same as the display area, and four protrusions 107A protruding from the sides of this octagon outside the display area. These protrusions 107A are
The anodes 102 are formed so as to contact different cathode terminals 109. In this embodiment, a soda glass substrate having a thickness of 0.7 mm is used as the substrate 101. The anodes 102 are made of ITO (Indium Tin Oxide).
The ITO thin film was made to a thickness of 150 nm. An _SiO2 layer was formed as the insulating layer 105. The organic light-emitting layer 106 was composed of, from the substrate 101 side, a hole injection layer made of N,N'-diphenyl-N,N'-dinaphthyl-1,1'-biphenyl-4,4'-diamine with a thickness of 50 nm, and an electron transport light-emitting layer made of tris(8-hydroxyquinoline)aluminum complex. The hole injection layer and the electron transport light-emitting layer were each formed to a thickness of 50 nm, and the organic light-emitting layer 15 was made to a thickness of 100 nm.
The cathode layer 107 was an alloy thin film with a composition of magnesium:silver=10:1,
The thickness of the cathode layer 107 is 200 nm. When using this display panel, each terminal 103 is connected to a corresponding terminal of the drive circuit, and the anode terminal 108 and cathode terminal 109 are connected to the corresponding terminals of the drive circuit. Then, by operating the drive circuit, a voltage is applied between the four cathode terminals 109 and the anode terminal 108 of the seven elements of each digital number that are to be illuminated. This causes the organic light-emitting layer 106 in the electrically conductive portion to emit light, thereby displaying one of the digital numbers "0" to "8." In this embodiment of the display panel, the cathode layer 107 is connected to four cathode terminals 109 equidistantly spaced along the periphery of the substrate. This reduces voltage drop within the cathode layer 107 compared to when the cathode layer 107 is connected to only one cathode terminal. As a result, even when the display area is relatively large (e.g., 4 inches or larger), the luminescence intensity across the display area is highly uniform. In a configuration in which the cathode layer is optically transparent and emits light toward the cathode side, the cathode layer must be formed with a thin film thickness, for example, approximately 200 Å, which is prone to voltage drop across the cathode layer. Therefore, even with this configuration, the display panel of this embodiment achieves the effect of improving the uniformity of light-emitting intensity across the display area. FIG. 3 is a plan view showing the structure of an organic EL display panel corresponding to a second embodiment of the present invention, and FIG. 4 is a cross-sectional view taken along line B-B in FIG. 3. The cathode layer 177 of the display panel of this embodiment consists of four cathodes (second electrodes) 171, each of which is formed by equally dividing the octagonal cathode layer 107 of the first embodiment. All other aspects are the same as those of the first embodiment. The four protrusions 107A of the cathode layer 107 of the first embodiment are distributed one per cathode 171 of this cathode layer 177. Each of the four cathodes 171 is formed to cover all of the anodes 102 that form one digital number. Each of the protrusions 107A of the four cathodes 171 is connected to a cathode terminal 109 arranged on the corresponding terminal portion 103 for the digital number. In the display panel of this embodiment, the cathode layer 177 is divided into a plurality of cathodes 171, so voltage drop in the cathode layer is less likely to occur than when the entire display area is covered with a single cathode layer. As a result, even when the area of the display area is relatively large (for example, 4 inches or more) or when the cathode layer is formed with a thin film thickness of, for example, around 200 Å to be optically transparent, the uniformity of the light emission intensity within the display area is increased. Furthermore, because each of the four cathodes 171 is connected to a different cathode terminal 109, it is also possible to differentiate the amount of current applied to each cathode 171. As a result,
By dividing the display area into multiple regions, it is possible to intentionally create a display with different light emission intensities (brightness) in each region. FIG. 5 is a plan view showing the structure of an organic EL display panel corresponding to a third embodiment of the present invention. This display panel is a panel for an active matrix organic EL display device. The transparent substrate 101 of this panel has a rectangular substrate surface, and the area excluding one short side of this rectangle and the entire periphery forms the display area 50. In this display panel, optically transparent anodes (first electrodes) and organic light-emitting layers are formed in a matrix corresponding to a large number of pixels (light-emitting portions) within the display area 50 on the substrate 101. A light-transmitting cathode layer 178 is formed on the organic light-emitting layer over the entire display area 50. This cathode layer 178 is equally divided into four cathodes 178a to 178d, which correspond to the top, bottom, left, and right regions in FIG. 5. The upper two cathodes 178a to 178d form a matrix.
A thin, light-reflective auxiliary electrode 179 is formed on the upper ends of the cathodes 178a and 178b and on the upper ends of the two lower cathodes 178c and 178d. A number of anode terminals 108 and two cathode terminals 109 are formed on the terminal section 103. An end of wiring 104A from a number of anodes formed in a matrix is connected to each anode terminal 108. Furthermore, each auxiliary electrode 179 connected to two different cathodes is connected to the two cathode terminals 109. The light-transmitting cathode layer 178 can be made of, for example, magnesium (Mg) and silver (Ag
a thin film obtained by co-evaporating lithium (Li) and aluminum (Al), a thin film obtained by co-evaporating lithium (Li) and aluminum (Al), and a first cathode layer (on the light-emitting layer side) made of a material with a small work function.
and a second cathode layer having a work function greater than that of the first cathode layer (total thickness of 140 Å or less, for example). The material for the first cathode layer may be, for example, calcium (Ca) or magnesium (Mg), and the material for the second cathode layer may be, for example, aluminum (Al), silver (Ag), or gold (Au). The anode having optical transparency may be made of ITO or IZO (I), as in the first embodiment.
In the case of using a light-reflecting anode, Pt, I, etc. can be used.
It is preferable to use a metal with a high work function such as Al, Ni, or Cd, or an oxide of such a metal.
d, voltage drop across the cathode layer is less likely to occur than when the entire display area is covered with a single cathode layer. As a result, the uniformity of light-emitting intensity across the display area 50 is enhanced. Note that the higher the pixel electrode density (the greater the number of pixel electrodes formed in a given display area), the larger the area occupied by the pixel electrode wiring and the like in the display area, resulting in a smaller area ratio of the pixel electrodes within the display area. As a result, in organic EL display panels with a relatively large display area (e.g., 4 inches or more) and a light-reflective cathode as a common electrode, the higher the density of the pixel electrode anodes, the lower the screen brightness. Therefore, in organic EL display panels with a relatively large display area (e.g., 4 inches or more) and a high density of pixel electrode anodes, it is preferable to use a light-transmitting cathode (common electrode) and configure the panel so that light is emitted from the cathode side as well. However, light-transmitting cathodes must be formed with a thinner film thickness than light-reflective cathodes, making them more susceptible to voltage drop. Therefore, in an organic EL display panel with a high density of pixel electrodes (first electrodes), it is particularly effective to form a plurality of light-transmitting electrodes (second electrodes) divided by the display area as the common electrode (second electrode layer), form a plurality of second terminals on the substrate, and connect the plurality of second electrodes to different second terminals. INDUSTRIAL APPLICABILITY As described above, the organic EL display device of the present invention reduces the occurrence of voltage drops within the second electrode layer, thereby improving the uniformity of the luminescence intensity within the display area even when the display area is relatively large. As a result, it is no longer necessary to supply a high voltage that takes into account the voltage drop within the second electrode layer, thereby enabling the organic EL display device to be driven with lower power consumption than conventional devices. In particular, the second organic EL display device of the present invention allows the display area to be divided into multiple regions by applying different amounts of current to each second electrode, thereby enabling display with intentionally different luminescence intensities within each region.

[Brief explanation of the drawings]

Fig. 1 is a plan view showing the structure of an organic EL display panel corresponding to a first embodiment of the present invention, Fig. 2 is a cross-sectional view taken along line A-A in Fig. 1. Fig. 3 is a plan view showing the structure of an organic EL display panel corresponding to a second embodiment of the present invention, Fig. 4 is a cross-sectional view taken along line B-B in Fig. 3. Fig. 5 is a plan view showing the structure of an organic EL display panel corresponding to a third embodiment of the present invention.

───────────────────────────────────────────────────── (Note) This publication is based on the publication published internationally by the International Bureau of Patents (WIPO). The effect of the international publication of the Japanese patent application (Japanese utility model registration application) related to this publication arises pursuant to Article 184-10, Paragraph 1 of the Patent Act (Article 48-13, Paragraph 2 of the Utility Model Act) and is unrelated to this publication.

Claims (4)

[Claims] [Claim 1] A laminate having an organic light-emitting layer between electrode layers is formed on a substrate, one of the electrode layers being a first electrode layer formed in a pattern corresponding to a plurality of light-emitting sections, the other electrode layer being a second electrode layer disposed over the entire display area, and a first terminal connected to the first electrode layer and a second terminal connected to the second electrode layer being
An organic EL display device formed outside a display area on a substrate, wherein a plurality of second terminals are formed on the substrate, and the second electrode layer is connected to the plurality of second terminals. [Claim 2] A laminate having an organic light-emitting layer between electrode layers is formed on a substrate, one of the electrode layers, a first electrode layer, is formed in a pattern corresponding to a plurality of light-emitting portions and has a plurality of first electrodes, the other electrode layer, a second electrode layer, is arranged so as to cover all of the portions of the display area where the first electrodes are formed, and a first terminal connected to the first electrode layer and a second terminal connected to the second electrode layer are
An organic EL display device formed outside a display area on a substrate, wherein a second electrode layer is made up of a plurality of second electrodes, a plurality of second terminals are formed on the substrate, and the plurality of second electrodes are connected to different second terminals, respectively. 3. An organic EL display device according to claim 1, wherein the substrate is light-transmitting, the first electrode layer is a light-transmitting anode layer formed on the substrate side, and the second electrode layer is a cathode layer. 4. The organic EL display device according to claim 3, wherein the first electrode and the organic light-emitting layer are formed in a matrix, and the second electrode layer is formed as a common electrode, in an active matrix organic EL display device,
The electrode layer is a light-transmitting organic EL display device.