Organic light emitting diode display device and method of fabricating the same

An organic light emitting diode display device having a frit which can improve mechanical strength and adhesion between the upper substrate and the lower substrate, and a method of fabricating the same are disclosed. The organic light emitting diode display device includes a lower substrate, an organic light emitting diode disposed on the lower substrate, an upper substrate to be coupled to the lower substrate, and a frit disposed between the lower substrate and the upper substrate to couple both the lower substrate and the upper substrate to each other where the frit has a plurality of pores.

CROSS-REFERENCE TO RELATED APPLICATIONS

This application claims the benefit of Korean Patent Application No. 2008-13277, filed Feb. 14, 2008, the disclosure of which is hereby incorporated herein by reference in its entirety.

BACKGROUND

The field relates to an organic light emitting diode (OLED) display device and a method of fabricating the same, and more particularly, to an OLED display device and a method of fabricating the same, where the display device has improved mechanical strength because of a plurality of pores formed in a frit to absorb external impact, and has improved adhesion between the upper substrate and the lower substrate because a small height difference between the frit and an upper or lower substrate is filled.

2. Description of the Related Technology

Generally, in an OLED display device, a lower substrate having a pixel region and a non-pixel region is disposed to face an upper substrate for encapsulation, and is coupled to the upper substrate by a sealant such as epoxy.

A plurality of organic light emitting diodes are formed between a scan line and a data line in the pixel region of the lower substrate, and each of the organic light emitting diodes includes an anode electrode, a cathode electrode, and an organic layer having an organic light emitting layer formed between the anode electrode and the cathode electrode.

Since the organic light emitting diode described above includes an organic material, it is vulnerable to hydrogen and oxygen, and since the organic light emitting diode includes the cathode electrode formed of a metallic material as an upper electrode, it is easily oxidized by moisture in the air, and as a result, its electrical and emitting characteristics are degraded. For these reasons, to protect the organic light emitting diode, a powder-type desiccant is disposed on the upper substrate formed of metal, glass or plastic, or a film-type desiccant is attached to the upper substrate, thereby removing moisture permeated from outside.

However, when the powder-type desiccant is used, the process becomes complicated, and the number of materials, production costs and a thickness of the display device are increased. Particularly, the powder-type desiccant is difficult to apply to a top-emission structure. On the other hand, when the film-type desiccant is used, there is a limitation in removing moisture and durability and reliability are reduced, and thus it is difficult to use in mass-production.

To solve these problems, a frit having an excellent encapsulation characteristic due to very low permeability may be formed between the lower substrate and the upper substrate to effectively protect the organic light emitting diode without using a desiccant separately.

However, the frit has poor flexibility and malleability and thus is very vulnerable when it is deformed. Therefore, when the frit is exposed to external impact, a crack may be generated in the frit, so that the organic light emitting diode display device may be damaged or delaminate.

SUMMARY OF THE CERTAIN INVENTIVE ASPECTS

One aspect is an organic light emitting diode (OLED) display device. The device includes a lower substrate, an organic light emitting diode disposed on the lower substrate, an upper substrate coupled to the lower substrate, and a frit disposed between the lower substrate and the upper substrate coupling the lower substrate to the upper substrate, where the frit includes a plurality of pores.

Another aspect is a method of fabricating an organic light emitting diode display device. The method includes providing a lower substrate, forming an organic light emitting diode on the lower substrate, providing an upper substrate, and forming a frit between the lower substrate and the upper substrate, wherein the frit couples the lower substrate to the upper substrate, and wherein the frit comprises a plurality of pores.

DETAILED DESCRIPTION OF CERTAIN INVENTIVE EMBODIMENTS

The present invention will now be described more fully with reference to the accompanying drawings, in which various embodiments are shown.

FIG. 1is a cross-sectional view of an organic light emitting diode (OLED) display device according to an embodiment.

Referring toFIG. 1, a lower substrate100is used. The lower substrate100may comprise a glass, plastic or conductive substrate. When the lower substrate100is formed of glass, it can have a more excellent adhesion characteristic to a frit.

An organic light emitting diode110is disposed on the lower substrate100. The organic light emitting diode110includes a first electrode101, an organic layer102including a light emitting layer, and a second electrode103. The first electrode101may be an anode, which may be formed of indium thin oxide (ITO) or indium zinc oxide (IZO). In a top-emission structure, a reflective layer may be further formed under the ITO or IZO layer.

The organic layer102may include at least a light emitting layer, and may further include at least one of a hole injection layer, a hole transport layer, a hole blocking layer, an electron transport layer, an electron injection layer and an electron blocking layer.

The second electrode103may be a cathode, which may be formed of at least one of magnesium (Mg), silver (Ag), aluminum (Al), calcium (Ca), and an alloy thereof having a low work function.

The organic light emitting diode110may further include a thin film transistor including a semiconductor layer, a gate electrode, and source and drain electrodes.

The thin film transistor may be a top gate thin film transistor having a gate electrode formed on a semiconductor layer, or a bottom gate thin film transistor having a gate electrode formed under a semiconductor layer.

An upper substrate120is disposed on the organic light emitting diode110. The upper substrate120may comprise at least one of glass, plastic, and a conductive material. When the upper substrate120is formed of glass, it can have a more excellent adhesion characteristic to a frit.

Between the lower substrate100and the upper substrate120, a frit130is disposed to couple the lower substrate100to the upper substrate120and thus encapsulate the organic light emitting diode110, which can prevent permeation of moisture from outside. The frit130is disposed along edges of the substrates100and120.

The frit130according to the present invention has a plurality of pores131. Generally, a frit has poor flexibility and malleability, and thus is susceptible to mechanical failure when it is deformed. Therefore, when exposed to external impact, the frit does not absorb the external impact well, and easily cracked. However, in this embodiment, because the frit130has the plurality of pores131, the frit130can absorb at least some of the external impact. Accordingly, mechanical strength of the OLED display device using a porous frit is greatly improved. Moreover, a small gap may exist between the frit130and the lower substrate100or upper substrate120and, in some embodiments, the gap is filled as the pores131in the frit130expand, and thus adhesion between the lower substrate100and the upper substrate120may be also improved.

The pores131may have a size of about 0.21 μm to about 10 μm. The pores131may have a size of about 0.2 μm or more to effectively absorb external impact and effectively improve adhesion between the substrates100and120. The pores131may have a size of about 10 μm or less to maintain bearing strength of the upper substrate120and lower substrate100. Pores131of less than about 0.2 μm and/or greater than about 10 μm may also be used.

A porosity of the frit130may be about 5% to about 95%. The frit may have a porosity of about 5% or more to effectively absorb external impact and improve adhesion between the substrates100and120, and may have a porosity of about 95% or less to maintain the bearing strength of the upper substrate120and the lower substrate. Due to characteristics of the material for the frit130, moisture from outside does not permeate the frit130, and in some embodiments, the frit130has a porosity of 70% or less to effectively prevent any possible permeation of moisture from the outside through the pores131.

In some embodiments, the frit130may further include a filler. When the frit130includes the filler, a pore may be more easily formed compared to the frit without a filler. Thus, the filler is preferably added to the frit130. The filler may be at least one of a zirconium-tungsten-phosphate based filler, a zirconium-phosphate based filler (e.g., zirconium phosphate), a zirconium based filler (e.g., zirconium), an eucryptite based filler (e.g., beta-eucryptite), a cordierite based filler, alumina, silica, zinc silicate, and aluminum titanate. The filler may be added to the frit130at between about 3 wt % to about 30 wt %. When the filler is added in this range, pores are formed more easily.

The frit130may further include an absorber for absorbing laser or infrared radiation.

FIGS. 2A and 2Bare photographs of an OLED display device including a frit with pores according to one embodiment and an OLED display device including a frit without pores, respectively, which have each been dropped from a height of 1.5 m

FIG. 2Ais a photograph of a section of a frit after the OLED display device including the frit with pores according to an exemplary embodiment is dropped from 1.5 m. Referring toFIG. 2A, it can be seen that pores having various sizes, 0.2 to 10 μm, are formed in the frit, and no crack is found in the frit after the drop of the OLED display device. On the other hand,FIG. 2Bis a photograph of a section of a frit after the OLED display device including the frit without pores is dropped. Unlike the exemplary embodiment of the frit ofFIG. 2A, it can be seen that no pores are formed in the frit and a crack is generated therein by the drop of the OLED display device. As shown in these Figures, when a plurality of pores are formed in the frit, the pores absorb external impact, so that the organic light emitting diode is effectively protected from external impact and mechanical strength of the OLED display device can be greatly improved, while effectively preventing moisture permeated from outside.

FIGS. 3A,3B and3D are cross-sectional views illustrating a method of fabricating an OLED display device according to an embodiment, andFIG. 3Cis a plan view ofFIG. 3B.

Referring toFIG. 3A, a lower substrate300is provided. The lower substrate300may comprise at least one of a glass, a plastic, and a conductive material. When the lower substrate300is formed of glass, the lower substrate300may have a more excellent adhesion characteristic to a frit.

An organic light emitting diode310is formed on the lower substrate300. The organic light emitting diode310includes a first electrode301, an organic layer302having at least a light emitting layer, and a second electrode303.

In the organic light emitting diode310, the first electrode301may be an anode, which may be formed of ITO or IZO. In a top-emission structure, a reflective layer may be further formed under the ITO or IZO layer.

The organic layer302includes a light emitting layer, and may further include at least one of a hole injection layer, a hole transport layer, a hole blocking layer, an electron transport layer, an electron injection layer, and an electron blocking layer.

The second electrode303may be a cathode, which may be formed of at least one of Mg, Ag, Al, Ca and an alloy thereof having low work functions.

The organic light emitting diode310may be formed to further include a thin film transistor including a semiconductor layer, a gate electrode, and source and drain electrodes.

Subsequently, referring toFIGS. 3B and 3C, an upper substrate320facing the lower substrate300is provided. The upper substrate320may comprise at least one of a glass, a plastic, and a conductive material. When the upper substrate320is formed of glass, the upper substrate320may have a more excellent adhesion characteristic to a frit.

A frit330is applied along an edge of the upper substrate320. The frit330is formed by melting glass formed of at least one selected from the group consisting of MgO, CaO, BaO, Li2O, Na2O, K2O, B2O3, V2O5, ZnO, TeO2, Al2O3, SiO2, PbO, SnO, P2O5, Ru2O, Rh2O, Fe2O3, CuO, TiO2, WO3, Bi2O3, Sb2O3, lead-borate glass, tin-phosphate glass, vanadate glass and borosilicate glass, grinding the melted glass to form fine glass powder, and mixing the powder with an organic binder, so that a paste is formed. The paste may be applied by a screen-printing or dispensing method.

A filler for controlling a thermal expansion coefficient or an absorber for absorbing laser or infrared ray may be further added to the frit330. When the filler is included in the frit330, pores may be easily formed compared to when the filler is not included in the frit. The filler may be at least one of a zirconium-tungsten-phosphate based filler, a zirconium-phosphate based filler (e.g., zirconium phosphate), a zirconium based filler (e.g., zirconium), an eucryptite based filler (e.g., beta-eucryptite), a cordierite based filler, alumina, silica, zinc silicate, and aluminum titanate. The filler may be added to the frit at about 3 wt % to 30 wt %.

Subsequently, the upper substrate320to which the frit330is applied is injected into a furnace to fire the frit330. The firing of the frit330may be performed at a temperature of about 300° C., to about 500° C., thereby removing moisture or an organic binder from the frit, and hardening the frit. When the material, the firing temperature, and other firing conditions are controlled, pores having a size of about 0.1 μm or less may be formed in the frit330after the firing.

Subsequently, referring toFIG. 3D, the upper substrate320is disposed over the lower substrate300having the organic light emitting diode310. Heat is applied along the frit330formed on the upper substrate320. The heat source may be laser or infrared ray. When the heat is applied to the frit330, the frit330melts and becomes sticky, thereby attaching the upper substrate to the lower substrate.

When conditions of the heat source applied to the frit330are determined to achieve desired frit characteristics, depending on the material of the frit330, pores may be formed in the frit330of a desired size, or may increase in size because of expansion and/or through clustering of the pores formed in the firing process. It is preferable that the pores331formed in the frit330have a size of about 0.2 μm to about 10 μm, and that the temperature applied to the frit330be at about 400° C. to about 700° C.

The frit330may have a porosity of about 5% to about 95%. The porosity of the frit330may be adjusted by controlling the material of the frit330, the amount of added filler and/or conditions of the heat source applied to the frit330.

When the pores331are formed with the desired sized in the frit330or the formed pores are expanded by applying the heat source to the frit330, the frit330melts, and the frit330expands to fill the gap which may exist between the frit330and the upper substrate320or the lower substrate300. As a result, adhesion between the upper substrate320and the lower substrate300is further improved. In addition, since the pores331can absorb external impact, mechanical strength of the OLED display device is improved.

When a plurality of pores are formed in a frit to absorb external impact, the mechanical strength of an OLED display device can be improved. In addition, by the expansion of the frit caused by the expansion of the pores, a small gap between the frit and an upper or lower substrate can be filled, so that adhesion between the upper and lower substrates is improved.

Although certain inventive aspects have been described with reference to specific exemplary embodiments, it will be understood by those skilled in the art that a variety of modifications and variations may be made without departing from the spirit or scope of the present invention.