Active matrix organic electroluminescent display device having organic thin-film transistor and method for manufacturing the display device

An active matrix electroluminescent (OEL) display device including a p-type organic thin-film transistor (TFT) is provided. This device has a high aperture ratio, and is easily produced in an array structure. The display device includes a counter electrode, an intermediate layer including at least a light emitting layer on the counter electrode, a pixel electrode formed on the intermediate layer, a first electrode that is disposed on the pixel electrode and insulated from the pixel electrode, a second electrode that is disposed on the pixel electrode and connected to the pixel electrode, a p-type organic semiconductor layer contacting the first electrode and the first drain electrode, and a first gate electrode that is disposed on the p-type organic semiconductor layer and insulated from the first electrode, the first drain electrode, and the p-type organic semiconductor layer.

CROSS REFERENCE TO RELATED APPLICATION

This application claims priority to and benefit of Korean Patent Application No. 10-2004-0046944, filed on Jun. 23, 2004, in the Korean Intellectual Property Office, the disclosure of which is incorporated herein in its entirety by reference.

BACKGROUND OF THE INVENTION

1. Field of the Invention

The present invention relates to an active matrix organic electroluminescent (OEL) display device that has an organic thin-film transistor (OTFT), and more particularly, to an active matrix OEL display device, that has an array structure, including a p-type OTFT that has an aperture ratio of approximately 100%.

2. Description of the Related Art

FIG. 1is a plan view of a sub-pixel unit in a conventional active matrix electroluminescent (EL) display device, andFIG. 2is a cross-sectional view of the sub-pixel unit of the display device taken along line P1through P7ofFIG. 1.

Referring to the drawings, in conventional silicon thin-film transistors (TFTs)110and150that have a semiconductor layer180formed of silicon, the semiconductor layer180includes a source region and a drain region which are heavily doped by impurities. In addition, it includes a channel region formed between the above two regions. In addition, the silicon TFTs110and150include gate electrodes111and151that are insulated from the semiconductor layer180and located to correspond to the channel region, source electrodes112and152and drain electrodes113and153that contact the source region and the drain region.

The problem with these conventional silicon TFTs110or150is that they are more expensive, fragile, and cannot use a plastic substrate since that they are fabricated at high temperature of 300° C. or higher, for example.

Flat panel display devices such as liquid crystal displays (LCD) or electroluminescent displays (ELD) use TFTs as switching devices and driving devices to control and operate pixels. In order to make flat panel display devices large, thin, and flexible, researchers are trying to use plastic substrates instead of the typical glass substrate. However, manufacturing display devices with plastic substrates is difficult because the fabrication temperature is below what is necessary for conventional silicon TFTs.

Since an OTFT does not have the above manufacturing problems, active research has been performed to develop OTFTs that have an organic semiconductor layer.

FIG. 3is a schematic cross-sectional view of an OEL display device that has a conventional TFT.

Referring toFIG. 3, an OEL device210and an OTFT220are formed on a substrate200. The OEL device210includes a transparent electrode211, an organic light emitting layer212, and a metal electrode213that are sequentially formed on the substrate200. The OTFT220includes a gate electrode221formed on the substrate200, a dielectric layer222formed on the gate electrode221, an organic semiconductor layer223formed on the dielectric layer222, and a source electrode224and a drain electrode225that are disposed on both sides of the organic semiconductor layer223on the dielectric layer222. The drain electrode225is connected to the transparent electrode211and the organic light emitting layer212of the OEL device210.

However, since the OEL device210is disposed adjacent to the OTFT220, the OEL device210has low aperture ratio due to the size of the OTFT220. When the aperture ratio is low, the light emitting intensity of each unit pixel of the display device must be increased, thus reducing the lifespan of the display device.

In order to solve the above problem, Korean Patent Publication No. 2003-0017748 discloses an active matrix OEL display device, in which an OTFT and an OEL device are stacked in a vertical direction.FIG. 4is a cross-sectional view of an OEL display device that includes the OTFT disclosed in the above Patent Publication.

Referring toFIG. 4, an OEL device310and an OTFT330disposed on a substrate300are separated by a first insulating layer320. The OEL device310includes a transparent electrode311, an organic light emitting layer312, and a metal electrode313sequentially formed on the substrate300. The OTFT330includes a gate electrode331formed on the first insulating layer320, a second insulating layer332formed on the gate electrode331, a source electrode334and a drain electrode335formed on the second insulating layer332, and an organic semiconductor layer333connected to the source and drain electrodes334and335. In addition, the source electrode334is connected to the metal electrode313.

However, the above example is merely an OEL device that includes one OTFT, not an array of a plurality of OEL devices and a plurality of OTFTs. In addition, complex processes are required to fabricate the OTFT330with such a complex inverted coplanar structure. Therefore, it is difficult to form the active matrix OEL display device that can be applied in actual situation.

SUMMARY OF THE INVENTION

The present invention provides an active matrix organic electroluminescent (OEL) display device that has an organic thin-film transistor (TFT), and an aperture ratio of approximately 100%.

The present invention discloses an active matrix OEL display device that includes an organic thin-film transistor, a counter electrode, an intermediate layer including at least a light-emitting layer on the counter electrode, and a pixel electrode formed on the intermediate layer. In addition, the device includes a first electrode disposed on and insulated from the pixel electrode, a second electrode disposed on and connected to the pixel electrode, a p-type organic semiconductor layer contacting the first electrode and the first drain electrode, and a first gate electrode disposed on the p-type organic semiconductor layer that is insulated from the first electrode, the first drain electrode, and the p-type organic semiconductor layer.

The present invention also provides a method of fabricating an active matrix OEL display device including an organic thin-film transistor. The method involves forming a counter electrode on the entire surface of a substrate or in a predetermined pattern, forming an intermediate layer including at least a light emitting layer on the counter electrode, forming a pixel electrode of a predetermined pattern on the intermediate layer, and forming a protective layer covering the pixel electrode on the entire surface of the substrate. The process also includes forming a first contact hole on the protective layer so as to expose the pixel electrode, forming a second electrode connected to the pixel electrode through the first contact hole, a first electrode and a first capacitor electrode formed integrally with each other, a fourth electrode, and a third electrode on the protective layer. The process also includes forming a p-type organic semiconductor layer covering the electrodes on the entire surface of the substrate, forming a gate insulating layer on the p-type organic semiconductor layer entirely over the substrate, forming a second contact hole in the p-type organic semiconductor layer and the gate insulating layer so as to expose the fourth electrode, and forming a first gate electrode, a second capacitor electrode connected to the fourth electrode through the second contact hole, and a second gate electrode on the gate insulating layer.

DETAILED DESCRIPTION OF THE INVENTION

FIG. 5is a schematic circuit diagram of an active matrix electroluminescent (EL) display device that includes a p-type organic thin-film transistor (TFT) according to a first embodiment of the present invention.FIG. 6is a circuit diagram of part “A” inFIG. 5.FIG. 7is a schematic plan view of a sub-pixel unit of the active matrix OEL display device that includes the p-type OTFT.FIG. 8is a cross-sectional view of the sub-pixel unit of the active matrix OEL display device that includes the p-type OTFT taken along line Q5and Q6ofFIG. 7.FIG. 9is a schematic cross-sectional view of the sub-pixel unit of the active matrix OEL display device that includes the p-type OTFT taken along line Q1through Q3ofFIG. 7. In addition,FIG. 10is a schematic cross-sectional view of the sub-pixel unit of the active matrix OEL display device that includes the p-type OTFT taken along line Q1through Q5ofFIG. 7.

An EL display device includes various pixel patterns according to the color of the emitted light at a light-emitting layer. The EL device is a current-driving light-emitting device that emits red, green, or blue light depending on the current flow between both electrodes to display a predetermined image.

The EL device includes a counter electrode, an intermediate layer including at least a light emitting layer formed on an upper portion of the counter electrode, and a pixel electrode on the intermediate layer. The present invention is not limited to the above structure, however, various structures of EL devices can be applied.

A flat panel display device using the EL device of the present invention has the advantages of superior brightness, higher contrast, and wider viewing angle than those of the conventional display device.

Referring toFIG. 5andFIG. 6, each sub-pixel unit includes a second OTFT450that is driven by a driving circuit, a first OTFT410driven by the second OTFT450, and an OEL device460driven by the first OTFT410.

A third electrode452of the second OTFT450is connected to the driving circuit through a first conducting line420. A second gate electrode451of the second OTFT450is connected to the driving circuit through a second conducting line430, and a fourth electrode453of the second OTFT450is connected to a second capacitor electrode (upper electrode,442) of a storage capacitor440and a first gate electrode411of the first OTFT410.

In the above structure, the first conducting line420can be a data line and a second conducting line430can be a scan line. The second OTFT450functions as a switching transistor and the first OTFT410functions as a driving transistor. In the above selection driving circuit, two or more transistors can be used. In the following examples, a driving circuit includes two transistors, that is, a switching transistor and a driving transistor.

Referring toFIG. 6andFIG. 7, a first capacitor electrode (lower electrode441) of the storage capacitor440and the first electrode412of the first OTFT410are connected to a third conducting line470. The second electrode413of the first OTFT410is connected to the pixel electrode462of the OEL device460. As shown inFIG. 6, the counter electrode461of the OEL device460faces the pixel electrode462with a predetermined gap therebetween. An intermediate layer including at least a light emitting layer is disposed between the counter and pixel electrodes461and462.

InFIG. 7, the OTFTs410and450are disposed on right lower portion and left upper portion of the sub-pixel unit, and the storage capacitor440is disposed between the OTFTs410and450. However, the OTFTs410and450can be disposed parallel to each other on the upper or lower portion of the sub-pixel unit, and more OTFTs can be formed.

FIG. 7,FIG. 8, andFIG. 9show physical structures of part “A” shown inFIG. 5andFIG. 6.FIG. 7shows the first conducting line420and the second conducting line430that are not shown inFIG. 8andFIG. 9.FIG. 8andFIG. 9show a substrate481, a gate insulating layer483, a protective layer485, and a pixel electrode462that are not shown inFIG. 7.

Referring to the drawings, when a scan signal is applied to the second gate electrode451by the driving circuit, a conductive channel is formed on the p-type organic semiconductor layer480that connects the third electrode452and the fourth electrode453. When a data signal is supplied to the third electrode452by the first conducting line420, the data signal is transmitted to the storage capacitor440and to the first TFT410. In addition a conductive channel is formed on the p-type organic semiconductor layer that connects the first electrode412and second electrode413. Then, a signal from the third conducting line470is transmitted to the pixel electrode462.

Referring toFIG. 8,FIG. 9, andFIG. 10, detailed structure of the sub-pixel unit will be described.

Referring toFIG. 8, the counter electrode461is disposed on the entire upper surface of the substrate481and the intermediate layer487including at least the light emitting layer is formed on the counter electrode461. The pixel electrode462is disposed on the intermediate layer487. In the present invention, the p-type first OTFT410is connected to the OEL device460, and the second electrode413of the p-type first OTFT410is connected to the pixel electrode462of the OEL device460. Thus, the pixel electrode462becomes an anode, and the counter electrode461corresponding to the pixel electrode462becomes a cathode. In following descriptions, OTFT means the p-type OTFT.

When the OEL device is a backlight emission type, the substrate481and the counter electrode461are formed of a transparent material, and the pixel electrode462is formed of a metal that has a high light reflectivity. When the OEL device is a front emission type, the counter electrode461is formed of a metal that has a high light reflectivity, and the pixel electrode462, a protective layer485, an organic semiconductor layer480, and a gate insulating layer483that will be described later can be formed of a transparent material. The EL device of the present invention may be the backlight emission type, the front emission type, or the dual-emission type, where the light generated by the EL device can exit in at least one direction between the counter and pixel electrodes461and462.

If the counter electrode461is formed of a transparent material, the counter electrode461can be used as a cathode. Therefore, an auxiliary electrode or a bus electrode line is formed of a material for forming a transparent electrode such as an indium tin oxide (ITO), indium zinc oxide (IZO), ZnO, or In2O3. A metal with a small work function such as Li, Ca, LiF/Ca, LiF/Al, Al, Ag, Mg, or a compound thereof, for example, is deposited to form a metal layer of semi-permeability, thereby forming the counter electrode461with a dual structure. When the counter electrode461is used as a reflective electrode, Li, Ca, LiF/Ca, LiF/Al, Ag, Mg, or a compound thereof, for example, is deposited entirely to be thick to form the counter electrode461.

The counter electrode461can cover all of the sub-pixels, or correspond to each sub-pixel.

When the pixel electrode462is formed of the transparent material, the pixel electrode462can be formed of the ITO, IZO, ZnO, or In2O3, for example. If the pixel electrode462is used as the reflective electrode, the electrode is formed of ITO, IZO, ZnO, or In2O3, and a thick reflective layer with low resistance, including, but not limited to Ag, Mg, Al, Pt, Pd, Au, Ni, Nd, Ir, Cr, or a compound thereof is deposited thereon. When the pixel electrode462is used as the reflective layer, Au, Ni, Pt, or Pd, for example, can be used to form the electrode.

The pattern of the pixel electrode can be formed to correspond to the sub-pixel. However, the shape of pattern is not limited thereto, and an organic material such as a conductive polymer can be used as the counter and pixel electrodes.

The OEL device460includes the pixel electrode462that receives the signal from the second electrode413of the first OTFT410, the counter electrode461, and the intermediate layer487with the light-emitting layer, which is disposed between the pixel electrode462and the counter electrode461. The intermediate layer487is formed of an organic material.

The OEL device460can be a low-molecular weight organic layer or a high-molecular weight organic layer depending on the type of the organic material used. When a low-molecular weight organic layer is used to form the OEL device460, the intermediate layer can include a hole injection layer (HIL), a hole transport layer (HTL), an emission layer (EML), an electron transport layer (ETL), and an electron injection layer (EIL) that is stacked in single or multiple structure. An organic material such as copper phthalocyanine (CuPc), N,N-Di(naphthalene-1-yl)-N,N′-diphenyl-benzidine (NPB), or tris-8-hydroxyquinoline aluminum (Alq3) can be used. When an electric charge is applied to the pixel electrode and the counter electrode, the holes and electrons combine to generate excitons. When the excitons fall from an excited state to ground state, they cause the light-emitting layer to emit light.

As described above, since the pixel electrode462becomes the anode and the counter electrode461becomes the cathode, the intermediate layer487can include the HIL, HTL, EML, EIL, and ETL sequentially from the pixel electrode462. The intermediate layer487can also include additional layers.

A low-molecular weight organic layer can be formed by heating and depositing the organic material under a vacuum atmosphere. The structure of the intermediate layer is not limited to the above example, but can include various layers if necessary.

When a high-molecular weight organic layer is used as the intermediate layer487, the intermediate layer487can include the HTL and EML. As described above, since the pixel electrode462becomes the anode and the counter electrode461becomes the cathode, the intermediate layer487can include the HTL and EML sequentially from the pixel electrode462.

The high-molecular weight HTL can be formed of poly-(2,4)-ethylene-dihydroxy thiopene (PEDOT) or polyaniline (PANI) using an inkjet printing or spin coating method. The high molecular weight organic light emitting layer can be formed of a poly-phenylenevinylene (PPV), soluble PPV, Cyano-PPV, or polyfluorene, and a color pattern can be formed by a conventional method such as inkjet printing, spin coating, or a thermal transfer method using a laser. The structure of the intermediate layer is not limited to the above example, and various layers can be included.

The protective layer485is formed on the OEL device460with the above structure and a first contact hole485ais formed on the protective layer485so that the pixel electrode462can be exposed through the contact hole485a. The second electrode413is formed on a predetermined region including the region where the first contact hole485ais formed. The second electrode413is connected to the pixel electrode462of the OEL device460through the first contact hole485aformed on the protective layer485.

The first OTFT410is formed on the protective layer485, and in the OEL display device according to the present invention, the first OTFT410is the p-type OTFT.

The structure of the first OTFT410will be described with reference toFIG. 8.

The first electrode412and the second electrode413are formed on the protective layer485by sputtering, photolithography, or deposition method. Since the highest occupied molecular obit (HOMO) level of a p-type organic semiconductor layer480that will be described is about 5 eV, the work functions of the first electrode412and the second electrode413are larger than the HOMO level of the p-type organic semiconductor layer480. This allows the p-type organic semiconductor layer480and the first electrode412and the second electrode413formed of metal to ohmic contact each other. Therefore, it is desirable that the first electrode412and the second electrode413of the first OTFT410are formed of Au, Pt, Pd, Ni, Rh, Ir, or Os, and the like having large work function.

The p-type organic semiconductor layer480is formed on the first electrode412and the second electrode413. The p-type organic semiconductor layer480is formed of a-hexathienylene (a-6T), dihexyl-a-6T (DH-a-a-6T), pentacene, poly-thienylenevinylene (PTV), poly-3-hexylthiophene regioregular (P3HT), or CuPc, for example using a vacuum deposition or thermal deposition method.

The first gate electrode411is formed on the gate insulating layer483. The first gate electrode411can be formed of various conductive materials such as a metal, MoW, Al, Cr, or Al/Cu, or a conductive polymer. Possible methods of forming the electrode include sputtering, photolithography, or inkjet deposition. A part of the first gate electrode411can overlap with the first electrode412and the second electrode413as shown inFIG. 8, however, it is not limited thereto.

As described above, when the OEL device460is formed on the substrate481and the first OTFT410is formed on the OEL device460, an aperture ratio of approximately 100% can be ensured in the backlight emission displays, in which the light generated by the OEL device460exits through the substrate481. Especially, since electric charge mobility in the OTFT is low the OTFT must have a large size in order to increase the on-current level. Therefore, when the OTFT is disposed on the same plane as the OEL device, the aperture ratio may be reduced. However, when the OTFT is disposed on the OEL device according to the present invention, the aperture ratio is not reduced even when the size of the OTFT increases.

In addition, the staggered type OTFT410includes the first electrode412, the second electrode413, the p-type organic semiconductor layer480, the gate insulating layer483, and the first gate electrode411formed on the first electrode412and the second electrode413. Thus the second electrode413of the first OTFT410and the pixel electrode462of the OEL device460can be connected easily. That is, since the contact hole485ais formed on the protective layer485that is disposed between the OEL device460and the first OTFT410, the second electrode413and the pixel electrode462of the OEL device460can be connected to each other through the contact hole485a.

Structures of a second OTFT450and a storage capacitor440that are connected to the first OTFT410and the OEL device460will be described with reference toFIG. 9.

Referring toFIG. 9, the structure of the second OTFT450is the same as that of the first OTFT410. The storage capacitor440includes a first capacitor electrode441connected to the first electrode412of the first OTFT410, and a second capacitor electrode442facing the first capacitor electrode441and connected to the fourth electrode453of the second OTFT450and the first gate electrode411of the first OTFT410. The first capacitor electrode441can be formed integrally with the first electrode412, and the second capacitor electrode442can be formed integrally with the first gate electrode411.

The p-type organic semiconductor layer480and the gate insulating layer483are located between the first capacitor electrode441and the second capacitor electrode442. The p-type organic semiconductor layer480and the gate insulating layer483function as dielectrics. In addition, the second capacitor electrode442is connected to the fourth electrode453of the second OTFT450through a second contact hole483aformed in the p-type semiconductor layer480and the gate insulating layer483.

The storage capacitor440having the above structure maintains the electric current flowing toward the pixel electrode462or increases driving speed.

FIG. 10is a schematic cross-sectional view of the first OTFT410, the storage capacitor440, and the second OTFT450of the sub-pixel unit, taken along line Q1through Q5ofFIG. 7, in the active matrix OEL display device including the OTFT according to the present invention.

Referring toFIG. 10, the first electrode412and the second electrode413of the first OTFT410, the first capacitor electrode441of the storage capacitor440, and the third electrode452and the fourth electrode453of the second OTFT450are each formed in the same plane. In addition, the first gate electrode411of the first OTFT410, the second capacitor electrode442of the storage capacitor440, and the second gate electrode451of the second OTFT450are each formed in the same plane.

Since the first OTFT410, the storage capacitor440, and the second OTFT450have the above described structures, the array of the active matrix OEL display device including the switching transistor, the driving transistor, which are formed by the OTFTs, and the storage capacitor can be formed easily. In addition, referring toFIG. 10, since the OEL device460is formed under the OTFTs and the storage capacitor, an aperture ratio of approximately 100% can be ensured in the backlight emission display.

Since the OTFT can be fabricated by a low-temperature fabricating process, an OEL display device that does not affect the OEL device460and the substrate481can be fabricated. Then, the counter electrode461of the OEL device460is the transparent electrode, and the pixel electrode462is the reflective electrode.

FIG. 11is a cross-sectional view of a sub-pixel unit in an active matrix OEL display device that includes an OTFT according to a second embodiment of the present invention.

Referring toFIG. 11, the OEL device includes the counter electrode461on the substrate481, and the intermediate layer487including the light emitting layer, and the pixel electrode462. In addition, two staggered p-type OTFTs410and450, and the storage capacitor440are formed on the OEL device. The second electrode413of the first OTFT between the two p-type OTFTs410and450is connected to the pixel electrode462of the OEL device. The above structure is the same as that of the first embodiment.

A difference between the present embodiment and the above described first embodiment is that a pixel definition layer486is formed on the counter electrode461. That is, the sub-pixels formed of the OEL devices are divided by the pixel definition layer486. The pixel definition layer486increases a gap between the edge of the pixel electrode462and the counter electrode461at each sub-pixel and defines the light emitting region between the sub-pixels on the counter electrode461. Thus, the pixel definition layer486prevents the intermediate layer487including the light emitting layer from being cut around the edge of the pixel electrode462or the electric field from being concentrated at the edge of the pixel electrode462. This configuration also prevents the short circuit of the counter and pixel electrodes461and462.

FIG. 12is a schematic plan view of a part of sub-pixel units in the active matrix OEL display device including the OTFT according to a third embodiment of the present invention.

As described above, the OEL display device includes various pixel patterns for the various color of light emitted by the light emitting layer. For example, the device includes pixels that have red, green, and blue sub-pixels. Thus, the OEL device is a current-driving light emitting device that emits red, green, or blue light depending on the currents flowing between the both electrodes in order to display a predetermined image. The colors can be generated by making the light emitting layer of the intermediate layer in the OEL device emit red491, green492, or blue493light as shown inFIG. 12. The arrangement of the sub-pixels is not limited to the example shown inFIG. 12, and can also be arranged as stripes, mosaics, or delta arrangements. In addition, the OTFTs410and450and the storage capacitor440in the each sub-pixel unit are not limited to the examples shown inFIG. 12.

In order to make the light emitting layer emit red light, the sub-pixel491that has the red light emitting layer can be formed of poly(1,4-phenylenevinylene) derivative, Nile red, 4-(dicyanomethyelene)-2-methyl-6-(julolidine-4-yl-vinyl)-4H-pyran (dcm2), 2,3,7,8,12,13,17,18-octaethyl,21H,23H-porphine platinum (II) (PEOEP), and 4-(dicyanomethylene)-2-tertbuty 1-6-(1,1,7,7-tetramethyllulolidyl-9-enyl)-4H-pyran. The sub-pixel492that has the green light emitting layer can be formed of 10-(2-benzothoiazolyl)-2,3,6,7-tetrahydro-1,1,7,7-tetramethyl-1H,5H,11H-[1]benzopyrano[6,7,8-ij]quinolizine (C545T), tri(8-hydroxyquinolato)aluminum (Alq3), tris(2-(2-pyridylphenyl)-C,N))iridium(II) (Ir)ppy. In addition, the sub-pixel493that has the blue light emitting layer can be formed of fluorene-based polymer, spirofluorene-based polymer, carbazole-based low molecular weight such as dicarbazole stilbene (DCS) (also referred to as bis[carbazole-(9)]-stilbene, and 4,4′-bis(2,2′-diphenylenethen-1-yl)-N,N′-bis (phenyl)benzidine (a-NPD).

FIG. 13is a schematic cross-sectional view of a sub-pixel unit of the active matrix OEL display device that includes an OTFT according to a fourth embodiment of the present invention. Referring toFIG. 13, an OEL device including the counter electrode461, the intermediate layer487including the light emitting layer, and the pixel electrode462is disposed on the substrate481. Two staggered type p-type OTFTs410and450, and the storage capacitor440are formed on the OEL device. In addition, the second electrode413of the first OTFT410is connected to the pixel electrode462of the OEL device. The above structure is the same as those of the above embodiments.

A difference between the OEL display devices according to the present embodiment and the third embodiment is that a color filter495is disposed between the substrate481and the counter electrode461.

In the OEL display device according to the third embodiment, the light emitting layer included in the OEL device is formed of the material that emits red, green, or blue light. This allowed the full-color image to be displayed using the emitted lights. However, in the OEL display device according to the fourth embodiment, the light emitting layer is white, and the white light emitted from the light emitting layer passes through the color filter495, so that red, green, or blue light can be emitted. Here, the white-color light may include all visible wavelengths of light, or may have a spectrum, in which a peak occurs at the wavelength corresponding to red, green, or blue colors.

FIG. 14is a schematic cross-sectional view of a sub-pixel unit in the active matrix OEL display device including an OTFT according to a fifth embodiment of the present invention.

Referring toFIG. 14, an OEL device including the counter electrode461, the intermediate layer487including the light emitting layer, and the pixel electrode462is disposed on the substrate481. Two staggered type p-type OTFTs410and450, and the storage capacitor440are formed on the OEL device. In addition, the second electrode413of the first OTFT410is connected to the pixel electrode462of the OEL device. The above structure is the same as those of the above embodiments.

A difference between the fifth embodiment and the above third and fourth embodiments is that a color conversion layer496is disposed between the substrate481and the counter electrode461. In the OEL display device according to the present embodiment, the light emitting layer is formed as the blue light emitting layer, and the blue light emitted from the light emitting layer is converted into the red, green, or blue light through the color conversion layer496, thus displaying a full-color image.

FIG. 15,FIG. 16,FIG. 17, andFIG. 18are schematic cross-sectional views of processes for fabricating the active matrix OEL display device including the OTFT according to the present invention.

Referring toFIG. 15, the counter electrode461is formed on entire surface of the substrate481or at each sub-pixel on the substrate481. The intermediate layer487having the light emitting layer is formed on the counter electrode by inkjet printing, the spin coating, or the thermal transfer method. After that, the pixel electrode462is formed at each sub-pixel on the intermediate layer487. In addition, after forming the protective layer485on the pixel electrode462, the first contact hole485aexposing a part of the pixel electrode462is formed on the protective layer485of the each sub-pixel. The first contact hole485acan be formed using a laser ablation technique (LAT).

After performing the above process, the second electrode413connected to the pixel electrode462through the first contact hole485a, the first electrode412and the first capacitor electrode441formed integrally with each other, the fourth electrode453, and the third electrode452are formed as shown inFIG. 16. The second electrode413, the first electrode412, the first capacitor electrode441, the fourth electrode453, and the third electrode452can be patterned in a deposition method using a shadow mask or by inkjet printing.

Next, the p-type organic semiconductor layer480covering the above electrodes is formed on the entire surface of the substrate481by vacuum deposition or a thermal evaporation method as shown inFIG. 17. In addition, the gate insulating layer is formed on the entire p-type organic semiconductor layer480using a spin coating method. The second contact hole483ais formed in the p-type organic semiconductor layer480and the gate insulating layer483so that the fourth electrode453can be exposed. The second contact hole483acan be formed in the LAT method.

The first gate electrode411and second gate electrode451formed on the gate insulating layer483. The second capacitor electrode442connected to the fourth electrode453through the second contact hole483aand formed over the first capacitor electrode441are fabricated while being patterned in the deposition method using shadow mask or inkjet printing methods. Thus, the OEL display device including a p-type OTFT and the storage capacitor shown can be fabricated as shown inFIG. 18. A sealing member and a front substrate can be formed on the OEL devices and the OTFTs fabricated through the above processes.

The array of the OEL devices including the p-type OTFTs and the storage capacitor can be fabricated easily and thus can be mass-produced. The processes that are done after forming the OEL device460are performed by the evaporation or spin coating methods and can also be mass-produced through the above processes. For example, when the OTFT is disposed on the OEL device, the metal electrodes can be patterned by the deposition method using the shadow mask. In addition, the p-type organic semiconductor layer480can be formed by the spin coating or deposition methods, and the gate insulating layer can be formed by spin coating the surface with organic material. Therefore, the OEL display device with the above structure can be fabricated without damaging the OEL device disposed under the display device.

During fabrication, a process of forming the pixel definition layer can be further added between the process of forming the counter electrode461and the process of forming of the intermediate layer487. In this case, after forming the counter electrode461, the material of the pixel definition layer is applied on the counter electrode461over the entire substrate481, and then, the material is patterned using the photolithography method and baked. The elements formed of the organic layers are not formed yet, thus the pixel definition layer can be formed in the above process.

In addition, a process of forming color filter that filters the white light into red, green, or blue color light on the substrate481can be further included. This can be done before forming the light emitting layer (the layer emitting white light) included in the intermediate layer487and forming the counter electrode461. Otherwise, a process of forming the color conversion layer that converts the blue light into the red, green, or blue color light on the substrate481can be further included before forming the layer emitting the blue light and forming the counter electrode461.

According to the OEL display device including the OTFTs and the method of fabricating the display device of the present invention, the following effects can be obtained.

Since the p-type OTFT is formed on the OEL device, an aperture ratio of approximately 100% can be obtained.

In addition, since the aperture ratio is approximately 100%, the electric current applied to the OEL device for obtaining a predetermined brightness can be reduced, thereby reducing the power consumption and increasing the lifespan of the OEL device.

It is desirable that the size of the OTFT is large in order to increase the on-current level of the OTFT. According to the present invention, the OTFT is located on the upper portion of the OEL device, thus a sufficiently large OTFT can be formed without reducing the aperture ratio.

In addition, since the OTFT is formed in staggered configuration, the structure can be simplified and the yield can be improved.

Since an active matrix OEL device can be easily produced in the array form, the fabrication costs can be reduced by mass-producing the devices.