1. Field of the Invention
The present invention relates to an organic light emitting display (LED) device and a method for fabricating the same, and more particularly, to an organic LED device structured to prevent decomposition of organic layers caused by moisture, and a method for fabricating the same.
2. Discussion of the Related Art
With developments in the information-oriented society, demands for a new type of image displaying device to overcome shortcomings of the related art cathode ray tubes (CRT), such as its great weight and volume, have been increasing. In order to meet such demands, a variety of flat panel displays have been developed and spotlighted, including a liquid crystal display (LCD), an organic light emitting diode (OLED) display device, a plasma display panel (PDP) device, and a surface-conduction electron-emitter display (SED) device.
Among the above, the OLED device adopts an organic LED which is a self-emitting element that forms exciton through recombination of an electron and a hole, and generates light of a specific wavelength by energy from the exciton. Having excellent display properties such as a contrast ratio and a response time, and being efficient to implement a flexible display, the OLED device is considered as an ideal next-generation display device.
In general, the OLED is equipped with a cathode electrode for injecting the electron and an anode electrode for injecting the hole. The electron and the hole are injected into an emission layer respectively from the cathode electrode and the anode electrode. The OLED device emits light as the exiton formed by combination of the electron and the hole is turned from an excited state to a ground state.
Through such a principle, the OLED device does not require a dedicated light source, which is different from a related art thin film LCD device and therefore is capable of reducing the volume and the weight of the device. In addition, the OLED device achieves high-quality panel characteristics, that is, a low voltage, a high brightness, a fast response time and a low weight.
Owing to such advantageous characteristics, the OLED device is being applied to various portable digital devices including a mobile terminal, a car navigator system (CNS), a camcorder, and a digital camera, and further applied even to a TV screen. That is, the OLED device gaining popularity as the next-generation display device.
Moreover, the OLED device can considerably reduce fabricating costs compared to related art LCD devices since the fabricating process is relatively simple.
The OLED devices may be classified into a passive matrix type and an active matrix type based upon the driving method.
The passive matrix type OLED device is simply structured and fabricated. However, much power is consumed, and it is difficult to implement a large-area display. In addition, the numerical aperture (NA) is deteriorated as the number of lines increases.
On the other hand, the active matrix type OLED device is capable of supplying a high emission efficiency and a high image quality.
FIG. 1 schematically shows the structure of an active matrix type OLED device including red, green and blue emission layers according to a related art. FIG. 2 explains a problem of a case where an inorganic passivation layer is applied in the related art OLED device.
As shown in FIG. 1, the OLED device 10 comprise a first substrate 12 having pixel regions P arranged in a matrix form, thin film transistors (TFT) T formed in each of the pixel regions P, first electrodes 14 electrically connected with the TFTs T provided in the respective pixel regions P, organic layers 18 formed at an upper part of the respective first electrodes 14, second electrodes 20 formed at an upper part of the respective organic layers 18, a second substrate 28 encapsulating and sealing an upper part of the first substrate 12 with a sealant 26, and a moisture absorbent 22 attached to the second substrate 28.
The organic layers 18 comprise organic emission layers 18c made of a dedicated organic material that emits red R, green G, and blue B lights.
In order to enhance the emission efficiency, a hole injection layer 18a and a hole transport layer 18b may be further provided. The injection layer 18a may be formed between the organic emission layer 18c and the first electrode 14, and the hole transport layer 18b may be formed between the organic emission layer 18c and the second electrode 20.
The moisture absorbent 22 prevents entry of moisture to the inside. The second substrate 28 is partly etched and the moisture absorbent 22 in a powder form is attached to the etched portion and fixed by an adhesive tape 25.
Additionally, although not shown, a partition may be further provided to prevent interference between adjoining pixel regions.
As described above, an organic light emitting display (OLED) device comprises thin film transistors (TFTs) for driving respective pixel regions, and the TFTs are electrically insulated from other layers by a passivation layer formed on the whole surface of a substrate including the TFTs.
Generally, the passivation layer comprises an inorganic insulating material such as SiNx or SiOy, being formed through a chemical vaporized deposition (CVD).
Such a passivation layer 92 formed of the inorganic insulating material, however, has a morphologically uneven surface, thereby partially generating protrusions Pr as shown in FIG. 2.
When the protrusions Pr are generated, an anode electrode 94, an organic emission layer 96, and a cathode electrode 98 deposited on the upper part of the protrusions Pr are influenced in sequence. Accordingly, a short circuit may be caused between the anode electrode 94 and the cathode electrode 98 as shown by a part A in FIG. 2.
Thus, the short circuit part of the anode electrode 94 and the cathode electrode 98 is indicated by dark spots in the drawing.
In the OLED device, additionally, various layers including the organic emission layer are formed of organic materials. Such organic layers are subject to decomposition due to moisture from the outside and moisture outgassed from the inside. Therefore, it is difficult to guarantee a sufficient lifespan of the device as a display device.
To this end, a technology that removes the moisture existing in the encapsulated inside is required as an essential factor for commercializing the OLED device.