1. Field of the Invention
The present invention relates to an electro-luminescence device, and more particularly, to an electro-luminescence device that is adapted to improve thermal conductivity and have a simplified fabrication process.
2. Discussion of the Related Art
Recently, various flat panel display devices reduced in weight and bulk have been developed that are capable of reducing the disadvantages of a cathode ray tube (CRT). Such flat panel display devices include a liquid crystal display (LCD), a field emission display (FED), a plasma display panel (PDP) and an electro-luminescence device (ELD).
In particular, an ELD typically has a structure in which electrodes are attached to each side of an electro-luminescent layer consisting of a hole-transporting layer, an emitting layer and an electron-transporting layer. The ELD has been highlighted as a next generation flat panel display, owing to its characteristics of wide viewing angle, high aperture ratio and high chrominance.
Such ELDs are classified for the most part into inorganic ELDs and organic ELDs, depending on their material. An organic ELD has an advantage in that, because electrons and holes make a pair when electric charges are injected into an organic luminescent layer provided between a hole injection electrode and an electron injection electrode and emit a light upon their extinction, the organic ELD can be driven with a lower voltage than the inorganic ELD. Further, the organic ELD can be not only formed on a transparent substrate having a flexibility like a plastic, but it also can be driven with a low voltage, of less than about 10V, in comparison to the PDP or the inorganic ELD. In addition, the organic ELD has a relatively small power consumption and an excellent color sense.
ELDs can also be classified into passivation ELDs and active matrix ELDs, depending on their driving system.
Hereinafter, a conventional ELD will be described with reference to the accompanying drawings.
Generally, an ELD includes a transparent electrode formed on a transparent substrate, an electroluminescent (EL) layer provided at the upper portion of the transparent electrode, a metal electrode formed on the EL layer, and a seal cover plate joined with the transparent oppositely at the upper portion of the metal electrode.
First, a passivation ELD includes a transparent electrode having a stripe shape and arranged in a line at the transparent substrate, a protective film formed on the entire passivation ELD, including the transparent electrode, an EL layer in which a hole-transporting layer, an emitting layer and an electron-transporting layer are disposed, a cathode electrode taking a stripe shape and crossing the transparent electrode on the EL layer, a seal cover plate attached with a supporting film formed from a semi-transmitting film containing a moisture-absorbing agent, and a sealant for oppositely joining the transparent substrate with the seal cover plate.
The active matrix ELD will be described with reference to FIG. 1 below.
As shown in FIG. 1, the active matrix ELD includes scanning lines and data lines arranged on a transparent substrate 1 in a matrix including pixel areas. Switching devices 2b are provided at intersections of the scanning lines and the data lines. Pixel electrodes 2a are electrically connected to the switching devices 2b and are provided at the pixel areas. A protective film 10 is formed at the entire surface thereof, including the pixel electrodes 2a. An electro-luminescent (EL) layer 3, including a hole-transporting layer 3a, an emitting layer 3b and an electron-transporting layer 3c, is disposed on the protective film 10. A metal electrode 4 is formed on the EL layer 3. A protective film 5 is provided over the metal electrode 4. A seal cover plate 7 contains a moisture-absorbing agent 8 and is attached with a supporting film 9 formed from a semi-transmitting film. A sealant 6 joins the transparent substrate 1 and the seal cover plate 7.
Each switching device 2b consists of a thin film transistor. Herein, each pixel electrode 2a is used as an anode electrode while the metal electrode 4 is used as a cathode electrode. At this time, the seal cover plate 7 and the transparent substrate 1 are joined to each other with sealant 6, which can be, for example, an epoxy resin therebetween at a place sealed with an inactive gas such as, for example, nitrogen or argon in accordance with a general encapsulation method.
The EL layer 3 and the metal electrode 4, which are formed of a metal, react with oxygen in water or in the and are easily oxidized, thereby causing the device to deteriorate. Therefore, moisture is removed by the moisture-absorbing agent 8, and the seal cover plate 7 and the transparent substrate 1 adhere to each other by means of an adhesive 6 under an inactive gas. At this time, nitrogen N2 which is a type of inactive gas, is injected into a space defined by said adhesion of the seal cover plate 7 to the transparent substrate 1.
The seal cover plate 7 may be formed of, for example, of a glass, a plastic or a canister. The moisture-absorbing agent 8 is formed of a fine powder containing, for example, BaO, CaCO3, zeolite, silicagel or alumina. Said fine powder is put in the seal cover plate 7 and is attached with the supporting film 9, which may be, for example, paper or Teflon. Herein, it is important to form the moisture-absorbing agent 8 flatly and evenly.
However, heat is generated upon driving a panel of the ELD. Becuase it is not easy for the conventional seal cover plate 7, using a metal canister or a glass, to exhaust such heat, the characteristics of the device deteriorate. Also, because it is not easy to exhaust heat from the center of the panel if a portion of the panel is enlarged even though a metal canister is used, the characteristics of the device further deteriorate.
Moreover, a thin seal cover plate is used to manufacture a display model of more than 5 inches because the use of metal canisters is limited due to production costs. Since such thin seal cover plates have low thermal conductivity, they fail to exhaust heat generated upon driving the panel of the ELD. Further, the thin seal cover plate becomes a thermal conduction path through nitrogen N2 in a state filled with a nitrogen gas to accumulate said generated heat in the thin plate having a low thermal conductivity and to residue the heat in a state sealed fully by an adhesive. Such heat results in the deterioration of the EL device.