Active matrix organic electroluminescent display and fabricating method thereof

An active matrix organic electroluminescent display device includes a first substrate and a second substrate facing and spaced apart from each other, a thin film transistor on an inner surface of the first substrate, a first electrode connected to the thin film transistor, an organic electroluminescent layer on the first electrode, a second electrode on the organic electroluminescent layer, a passivation layer on the second electrode, a black matrix on an inner surface of the second substrate, the black matrix includes a plurality of open portions, a color filter layer at the plurality of open portions, a color changing layer on the color filter layer, an overcoat layer on the color changing layer, and an adhesive film between the passivation layer and the overcoat layer.

The present invention claims the benefit of the Korean Patent Application No. P2001-87707 filed in Korea on Dec. 29, 2001, which is hereby incorporated by reference.

BACKGROUND OF THE INVENTION

1. Field of the Invention

The present invention relates to an organic electroluminescent display device, and more particularly, to an active matrix organic electroluminescent display device including a thin film transistor and a fabricating method thereof.

2. Discussion of the Related Art

A cathode ray tube (CRT) has been commonly used as a display screen for devices such as televisions and computer monitors. However, a CRT has the disadvantages of being large, heavy, and requiring a high drive voltage. As a result, flat panel displays (FPDs) that are smaller, lighter, and require less power have grown in popularity. Liquid crystal display (LCD) devices, plasma display panel (PDP) devices, field emission display (FED) devices, and electroluminescent display (ELD) devices are some of the types of FPDs that have been introduced in recent years.

An ELD device may either be an inorganic electroluminescent display device or an organic electroluminescent display (OELD) device depending upon the source material used to excite carriers in the device. OELD devices have been particularly popular because they have bright displays, low drive voltages, and can produce natural color images incorporating the entire visible light range. Additionally, OELD devices have a preferred contrast ratio because they are self-luminescent. OELD devices can easily display moving images because they have a short response time of only several microseconds. Moreover, such devices are not limited to a restricted viewing angle as other ELD devices are. OELD devices are stable at low temperatures. Furthermore, their driving circuits can be cheaply and easily fabricated because the circuits only require a low operating voltage. In addition, the manufacturing process of OELD devices is relatively simple.

In general, an OELD device emits light by injecting electrons from a cathode electrode and holes from an anode electrode into an emissive layer, combining the electrons with the holes, generating an exciton, and transitioning the exciton from an excited state to a ground state. Since the mechanism by which an OELD produces light is similar to a light emitting diode (LED), the organic electroluminescent display device may also be called an organic light emitting diode.

In an organic electroluminescent display device, multiple organic electroluminescent layers may be used in which each layer emits red light, green light, or blue light in order to display full color images. Because any of the organic electroluminescent layers may break down over the course of time, it may be difficult to maintain the range of all possible colors when the organic electroluminescent display device has been driven for a long period of time. To solve this problem, a method of displaying full color images by using a single organic electroluminescent layer for all pixels and a color changing medium has been suggested in U.S. Pat. No. 5,294,870, which are hereby incorporated by reference. This method will be illustrated inFIGS. 1 to 3.

FIG. 1is a plan view of an organic electroluminescent display device according to the related art. InFIG. 1, a planarization layer101is formed on a substrate, and a plurality of first electrodes R1–R5, which are spaced apart from each other, are formed on the planarization layer101along a first direction. An organic electroluminescent layer8is formed on the plurality of first electrodes R1–R5. The organic electroluminescent layer8is electrically connected to the plurality of first electrodes R1–R5. A plurality of second electrode portions C1–C6, which are spaced apart from each other, are formed on the organic electroluminescent layer8along a second direction that is substantially perpendicular to the first direction. Each second electrode portion C1–C6includes three sub-electrodes “a,” “b” and “c.” The second electrode portion C1-C6crosses the first electrode R1–R5, thereby defining pixel regions, of which a representative pixel region is “P.” The pixel region “P” includes three sub-pixel regions “Rp,” “Gp” and “Bp” of red, green and blue that are defined by the sub-electrodes “a,” “b” and “c” and the first electrodes R1–R5. External signals are applied through a peripheral portion “A” where the electroluminescent layer8is not formed.

FIG. 2is a cross-sectional view of the organic electroluminescent display device ofFIG. 1taken along II—II according to the related art.FIG. 3is a cross-sectional view of the organic electroluminescent display device ofFIG. 1taken along III—III according to the related art.

InFIGS. 2 and 3, green color changing medium “G” and red color changing medium “R” are formed on a substrate2. The green and red color changing media “G” and “R” correspond to green and red sub-pixel regions “Gp” and “Rp,” respectively. The green and red color changing media “G” and “R” may be made of a material not susceptible to a photolithographic process. Next, a planarization layer4is formed on the green and red color changing media “G” and “R” to planarize a surface of the substrate2and separate adjacent green and red sub-pixel regions “Gp” and “Rp.” The planarization layer4is made of transparent insulating material through a spin coating method or a solgel method without an additional patterning process. The planarization layer4also protects the green and red color changing media “R” and “G.” Next, a plurality of first electrodes “R1” and “R3” are formed on the planarization layer4. The plurality of first electrodes “R1” and “R3” are made of transparent conductive material such as indium-tinoxide (ITO) to transmit light.

Next, a sidewall6is formed on the plurality of first electrodes “R1” and “R3” at a boundary of the green and red sub-pixel regions “Gp” and “Rp.” The sidewall6may be formed through depositing and patterning photoresist. The sidewall6may be made of silicon oxide (SiO2), silicon nitride (SiNx) or aluminum oxide (Al2O3). Next, an organic electroluminescent layer8is formed on the sidewall6and the plurality of first electrodes “R1” and “R3.” The organic electroluminescent layer8is made of a material emitting blue light. A plurality of sub-electrodes “a,” “b” and “c,” which function in combination as a second electrode, are formed on the organic electroluminescent layer8. Preferably, the plurality of sub-electrodes “a,” “b” and “c” are made of a material having a low work function so that each is substantially efficient for proper operation of the electroluminescent display device. When the plurality of sub-electrodes “a,” “b” and “c” are formed through a sputtering method, the positioning of a target including a source material is important in order that the plurality of sub-electrodes “a,” “b” and “c” are properly spaced. If the target is close to a first surface “X” of the sidewall6, the source material is deposited on the first surface “X” of the sidewall6, but the source material is not deposited on a second surface “Y” of the sidewall6and a portion of the organic electroluminescent layer8adjacent to the second surface “Y.” Accordingly, the organic electroluminescent layer8has a gap between the adjacent sub-electrodes “a,” “b” and “c” along a first direction.

The organic electroluminescent display device ofFIGS. 1 to 3is a passive matrix organic electroluminescent display device. In the passive matrix organic electroluminescent display device, scan lines are sequentially driven so that the brightness of each pixel may be appropriately determined. Accordingly, the brightness for which a pixel is driven should be the multiple of the desired average brightness and the number of scan lines required to obtain the desired average brightness. Thus, as the number of scan lines increases, the required supply voltage and supply current increase as well. An increase in the required supply voltage and supply current accelerates the degradation of a device and increases the power consumption of the device. Although a passive matrix organic electroluminescent display device may be adequate for small display devices, it is not an adequate solution in larger display devices.

SUMMARY OF THE INVENTION

Accordingly, the present invention is directed to an organic electroluminescent display device and a fabricating method thereof that substantially obviate one or more of the problems due to limitations and disadvantages of the related art.

An object of the present invention is to provide an organic electroluminescent display device that produces color of a high quality, consumes a relatively low amount of power and permits a large display screen, and a fabricating method thereof.

An object of the present invention is to provide an organic electroluminescent display device whose elements have substantially equivalent expected life spans by forming one organic electroluminescent layer over an entire surface of a substrate and emitting light through a color changing medium and a fabricating method thereof.

Another object of the present invention is to provide an organic electroluminescent display device that can be protected from an external impact by forming a thin film transistor and a color changing medium over different substrates and attaching the respective substrates and a fabricating method thereof.

To achieve these and other advantages and in accordance with the purpose of the present invention, as embodied and broadly described, an active matrix organic electroluminescent display device includes a first substrate and a second substrate facing and spaced apart from each other, a thin film transistor on an inner surface of the first substrate, a first electrode connected to the thin film transistor, an organic electroluminescent layer on the first electrode, a second electrode on the organic electroluminescent layer, a passivation layer on the second electrode, a black matrix on an inner surface of the second substrate, the black matrix includes a plurality of open portions, a color filter layer at the plurality of open portions, a color changing layer on the color filter layer, an overcoat layer on the color changing layer, and an adhesive film between the passivation layer and the overcoat layer.

In another aspect, A method of fabricating an organic electroluminescent display device includes steps of forming a thin film transistor on a first substrate, forming a first electrode connected to the thin film transistor, forming an organic electroluminescent layer on the first electrode, forming a second electrode on the organic electroluminescent layer, forming a passivation layer on the second electroluminescent layer, forming a black matrix on a second substrate, the black matrix has a plurality of open portions, forming a color filter layer at the plurality of open portions, forming a color changing layer on the color filter layer, forming an overcoat layer on the color changing layer, and bonding the first substrate to the second substrate by interposing an adhesive film between the passivation layer and the overcoat layer.

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS

FIG. 4is a cross-sectional view of an exemplary organic electroluminescent display device according to the present invention. InFIG. 4, a first substrate100and a second substrate200may face and be spaced apart from each other. A thin film transistor (TFT) “T” including a gate electrode121, an active layer131of silicon, a source electrode122, and a drain electrode123may be formed on an inner surface of the first substrate100. A first passivation layer140may be formed on the TFT “T.” The first passivation layer140may have a drain contact hole exposing the drain electrode123and may be composed of either inorganic insulating materials or organic insulating materials. A first electrode150of an opaque conductive material may be formed on the first passivation layer140. An organic electroluminescent layer160emitting blue light may be formed on the first passivation layer140. The organic electroluminescent layer160may cover an entire surface of the first substrate100. A second electrode170composed of a transparent conductive material, such as indium-tin-oxide (ITO) or indium-zinc-oxide (IZO), may be formed on the organic electroluminescent layer160. A second passivation layer180may be formed on the second electrode170.

A black matrix220may be formed on an inner surface of the second substrate200. The second substrate200may be made of a transparent material, such as glass or plastic. The black matrix220may be placed in a position corresponding to a TFT “T” and may have a plurality of open portions225. A color filter layer230, including first, second, and third sub-color filters231,232, and233, may be formed at the plurality of open portions225. For example, the first, second, and third sub-color filters231,232, and233may correspond to red, green, and blue, respectively. Alternatively, a different combination or order of sub-color filters may be used. Each of the first, second, and third sub-color filters231,232, and233may be formed at one open portion225.

A color changing layer240, including first and second color changing mediums241and242, may be formed on the color filter layer230. InFIG. 4, the first color changing medium241, which may change color to red, may be formed on the first sub-color filter231, and the second color changing medium242, which may change color to green, may be formed on the second sub-color filter232. An overcoat layer250may be formed on the color changing layer240. Subsequently, an adhesive film300may be interposed between the second passivation layer180and the overcoat layer250. The adhesive film300may be used to bond the first and second substrates100and200together.

Accordingly, an organic electroluminescent layer that emits blue light may be formed over an entire surface of a substrate and light may be emitted using the first and second color changing mediums of red and green. Since a thin film transistor may be used to drive an organic electroluminescent display device, a larger display device producing a higher quality display with reduced power consumption may be obtained. In addition, a transparent adhesive film may be attached to the organic electroluminescent layer that may shield and protect the organic electroluminescent layer from moisture and oxygen without optical loss. As a result, reliability may be improved. Furthermore, since a first electrode is made of an opaque conductive material and a second electrode is made of a transparent conductive material, light may be emitted toward the second substrate having a color changing layer.

A method of fabricating an organic electroluminescent display device according to an embodiment of the present invention is illustrated inFIGS. 5A to 6D.

FIGS. 5A to 5Dare cross-sectional views of an exemplary method of fabricating a first substrate for an organic electroluminescent display device according to the present invention.FIGS. 6A to 6Dare cross-sectional views of an exemplary method of fabricating a second substrate for an organic electroluminescent display device according to the present invention. InFIG. 5A, a thin film transistor (TFT) “T” may be formed on a first substrate100. The TFT “T” may include a gate electrode121, an active layer131of silicon, a source electrode122, and a drain electrode123. Preferably, the active layer131is made of polycrystalline silicon. The first substrate100may be made of glass or plastic, and may have a thickness of about 0.7 mm.

InFIG. 5B, a first passivation layer140may be formed on the TFT “T” through depositing and patterning organic or inorganic insulating materials. The first passivation layer140may include a drain contact hole that exposes the drain electrode123. The organic insulating material may be composed of silicon nitride (SiNx) or silicon oxide (SiO2). The inorganic insulating material may be composed of benzocyclobutene (BCB) and photo acryl.

InFIG. 5C, a first electrode150may be formed on the first passivation layer140through depositing and patterning an opaque conductive material, such as metal. The first electrode150may be connected to the drain electrode123of the TFT “T” through the drain contact hole.

InFIG. 5D, an organic electroluminescent layer160emitting blue light may be formed on the first electrode150. A second electrode170that may be made of a transparent conductive material, such as indium-tin-oxide (ITO) or indium-zinc-oxide (IZO), may be formed on the organic electroluminescent layer160. A second passivation layer180may be formed on the second electrode170. The second passivation layer180may also be made of organic or inorganic insulating materials.

InFIG. 6A, a black matrix220may be formed on a second substrate200. The black matrix220may have a plurality of open portions225. The second substrate200may be made of a transparent material, such as a glass or a plastic, and may have a thickness of about 0.5 mm.

InFIG. 6B, a color filter layer230including first, second, and third sub-color filters231,232, and233may be formed at the plurality of open portions225. The first, second, and third sub-color filters231,232, and233, respectively corresponding to red, green and blue, may be formed sequentially through, for example, a pigment dispersion method, a dyeing method or an inkjet method. Here, each of the first, second, and third sub-color filters231,232, and233may be formed at one open portion225.

InFIG. 6C, a color changing layer240including first and second color changing mediums241and242may be formed on the color filter layer230. Here, the first color changing medium241that changes the color of light passing through it to red may be formed on the first sub-color filter231, and the second color changing medium242that changes the color of light passing through it to green may be formed on the second sub-color filter232. Preferably, a sum of the thickness of the first sub-color filter231and the thickness of the first color changing medium241may be equal to the sum of the thickness of the second sub-color filter232and the thickness of the second color changing medium242. Moreover, each of these sums may be equal to the thickness of the third sub-color filter233.

InFIG. 6D, an overcoat layer250may be formed on the color changing layer240. Subsequently, the first substrate100on which the TFT “T” and the organic electroluminescent layer160have been formed and the second substrate200on which the color changing layer240has been formed may be disposed such that the second passivation layer180faces the overcoat layer250. An organic electroluminescent display device may be completed by bonding the first and second substrates100and200together with an adhesive film300that adheres the second passivation layer180to the overcoat layer250.

In the present invention, a large organic electroluminescent display device requiring a relatively small amount of power may be obtained by using a thin film transistor to drive the device. Moreover, a high display quality and equal expected life spans for elements may be obtained by forming one organic electroluminescent layer over an entire surface of a substrate and emitting light through a color changing layer. Furthermore, the described invention may have the effect of making an organic electroluminescent display device more damage-resistant because the formation of the thin film transistor and the color changing layer on different substrates that are later attached provides an additional substrate covering the elements to shield them from an external impact.