Abstract:
An electro-luminescent display and a method of manufacturing thereof prevents the formation of a barrier interface between the anode electrode and the electro-luminescent layer by placing the electro-luminescent layer directly on the anode electrode so that there is no need to etch a subsidiary layer so that the electro-luminescent layer and the anode electrode have excellent electrical contact. The elimination of this etching step prevents damage to the anode electrode caused by collision of ions with the anode electrode during the etching process. Further, etch remainders or contaminant particles that exist in the etchant gas are prevented from accumulating on the anode electrode. Thus, the charge carriers of the anode are easily transported across the interface between the anode electrode and the electro-luminescent layer so as to greatly improve the expected life span, the brightness, and the efficiency of the electro-luminescent display.

Description:
BACKGROUND OF THE INVENTION 
     1. Field of the Invention 
     The present invention relates to an electro-luminescent display (ELD) and a method of manufacturing thereof. More specifically, the present invention relates to an active ELD including an organic luminescent layer. 
     2. Discussion of the Related Art 
     An ELD is a luminescent device that emits light when electrons and holes that are injected into a luminescent layer recombine. The emission of light by the recombination of electrons and holes eliminates the need for a back-light in the ELD. Thus, it is easy to manufacture a very thin panel using an ELD. Further, the ELD has the added advantage of low power consumption. Additionally, an organic ELD, having a light-emitting layer with an organic electro-luminescent (EL) substance, is characterized by a low driving voltage, high light-emitting efficiency, and low process temperature. However, organic EL substances are vulnerable to moisture so that the patterns are defined by a method that prevents the organic EL substance from contacting moisture directly, unlike conventional photolithography. 
     In an active ELD, a plurality of pixels are defined by providing a plurality of scanning lines that cross with a plurality of signal lines, and also such that a power supply line is arranged in the same direction as the signal line in each of the pixels. Each pixel includes a storage capacitor, an EL portion, and at least one switching device such as a thin film transistor (TFT). 
     When the pixel includes two TFTs, an excitation signal for the EL portion is distinguished from the scanning signal. The EL portion is selected by a logic TFT which is the first TFT, and the excitation signal for the EL portion is controlled by the second TFT. The storage capacitor then maintains the excitation power in the EL portion of the selected cell. 
     FIGS. 1A to FIGS. 1D illustrate a method of manufacturing an ELD according to a related art method. Referring to FIG. 1A, polysilicon is deposited on an insulating substrate  11  having a switching part and a pixel part, via a chemical vapor deposition (CVD) process. Then an active layer  13  is formed by patterning the polysilicon via a photolithography process. An insulating substance such as silicon oxide, silicon nitride, or other similar substances are then deposited on the insulating substrate  11  to cover the active layer  13 . Next, an electrically-conductive substance is deposited on the insulating substance. Then, a gate insulating layer  15  and a gate electrode  17  is formed by sequentially patterning the electrically-conductive substance and the insulating substance so that they remain on the middle portion of the active layer  13 . Note that a scanning line (not shown in the drawing) that is connected to the gate electrode  17  may be provided as soon as the gate electrode  17  is formed. A source region  19  and a drain region  21  are then formed by heavily doping the exposed portions of the active layer  13  with either n type or p type impurities with the gate electrode  17  functioning as a mask. Note that the middle portion of the active layer  13 , which is not doped with impurities, becomes a channel region. 
     Referring to FIG. 1B, a first insulating interlayer  23  is then provided and covers the active layer  13 , the gate electrode  17 , and the scanning line by depositing an insulating substance such as silicon oxide, silicon nitride, or other similar substances on the insulating substrate  11 . Next, the first insulating interlayer  23  is patterned to expose the source region  19  and the drain region  21 , and a source electrode  25  and a drain electrode  27  are connected electrically with the exposed source region  19  and exposed drain region  21 , respectively, by depositing and then patterning a known conductive substance. Thus, a TFT that functions as a switching device is manufactured. Note that a signal line (not shown in the drawing) may be defined on the insulating interlayer  23  at the same time the source electrode  25  and the drain electrode  27  are provided. 
     Referring to FIG. 1C, a second insulating interlayer  29  is provided and covers the source electrode  25  and the drain electrode  27  and the signal line by depositing silicon oxide or silicon nitride on the first insulating interlayer  23 . A contact hole  30  exposes the drain electrode  27  and is provided by patterning the second insulating interlayer  29 . Next, a transparent conductive substance is deposited so as to contact the exposed portion of the drain electrode  27  through the contact hole  30  that is provided in the second insulating interlayer  29 . Then, an anode electrode  31  is formed by patterning via a photolithography process the transparent conductive substance so that the anode electrode  31  remains in the pixel portion of the second insulating interlayer  29 . Note that the anode electrode  31  is electrically connected to the drain electrode  27 , and is isolated electrically from other anode electrodes in adjacent pixel cells. 
     Referring to FIG. 1D, a passivation layer  33  covers the anode electrode  31  by the deposition of silicon oxide or silicon nitride on the second insulating interlayer  29 . Alternatively, the passivation layer  33  may be formed with an organic substance such as BCB (benzocyclobutene), SOG(spin-on glass), and other similar substances. Note that the passivation layer  33  made of an organic substance may be relatively thick in order to provide an even surface. Next, the passivation layer  33  is patterned via a photolithography process, including a dry etching process, so as to expose the anode electrode  31 . An organic EL layer  35 , which emits a predetermined color such as red, blue, or green, is provided on the passivation layer  33  by an evaporation process. Note that the organic EL layer  35  just contacts the anode electrode  31  and the exposed pixel portion. Next, a cathode electrode  37 , which functions as a common electrode, is disposed on the organic EL layer  35 . 
     As mentioned in the above description, the ELD of the related art carries out the switching operation by selecting a TFT that has an n-type channel in a certain pixel, which has a predetermined signal line (not shown in the drawing) crossing with a predetermined scanning line (not shown in the drawing), such that a ‘high’ signal is applied to the predetermined scanning line while a ‘high’ signal is applied to the predetermined signal line. Thus, the selected TFT turns on and transfers the signal of the predetermined signal line to the drain electrode by which holes are injected into the organic EL layer via the anode electrode and electrons are injected into the organic EL layer via the cathode electrode. Thus, the pixel achieves light-emission through the recombination of electrons and holes. 
     Unfortunately, in the structure and method of the related art, the exposed portion of the anode electrode is easily damaged by the collision of the ions when dry-etching the passivation layer for exposing the anode electrode. Further, contaminant particles, albeit a small amount, remain on the exposed portion of the anode electrode after the etching process. Thus, the damage to the anode electrode caused by the collision of the ions during the etching process and the remaining contaminant particles on the anode electrode after the etching process creates a barrier interface between the anode electrode and the EL layer that hinders the efficient transport of charge carriers such as holes. Therefore, the expected life span, brightness, and efficiency of the ELD suffers greatly from the structure and method of the related art. 
     SUMMARY OF THE INVENTION 
     To overcome the problems described above, preferred embodiments of the present invention provide an ELD and a method of manufacturing the ELD that improves the expected life span, brightness, and efficiency of the ELD by preventing the generation of a barrier interface between the anode electrode and the organic EL layer, which hinders the transport of charge carriers such as holes across the interface. 
     A preferred embodiment of the present invention includes a substrate having a pixel portion and a switching portion, an active layer on the switching portion of the substrate including a source region on a first end of the active layer, a drain region on a second end of the active layer, and a channel region at a middle portion of the active layer and in between the drain region and the source region, a gate insulating layer on the channel region, a gate electrode on the gate insulating layer such that the gate insulating layer is disposed between the gate electrode and the active layer, an insulating interlayer on the substrate covering the gate electrode, wherein the insulating interlayer does not substantially cover the source and drain regions so that substantial portions of the source and drain regions are exposed, a source electrode and a drain electrode in contact electrically with the exposed portions of the source and drain regions, respectively, a passivation layer on the insulating interlayer, wherein the passivation layer covers the source electrode and the drain electrode, a connect hole in the passivation layer, wherein the connect hole substantially exposes the drain electrode, an anode electrode on the passivation layer, wherein the anode electrode is in contact electrically with the drain electrode through the connect hole, an organic electro-luminescent layer on the passivation layer and covering the anode electrode, and a cathode electrode on the organic electro-luminescent layer. 
     Another preferred embodiment of the present invention includes a substrate, a plurality of layers on the substrate, wherein the plurality of layers includes source and drain electrodes, a passivation layer on the substrate and covering the source and drain electrodes, a connect hole in the passivation layer and exposing the drain electrode, an anode electrode on the passivation layer and in contact with the drain electrode, and an organic electro-luminescent layer on the passivation layer covering the anode electrode. 
     In another preferred embodiment of the present invention, a method of manufacturing an ELD includes the steps of providing a substrate, separating the substrate into a switching portion and a pixel portion, forming an active layer on the switching portion, forming a gate insulating layer and a gate electrode on a middle portion of the active layer, forming a source region and a drain region on exposed portions of the active layer by doping the exposed portions of the active layer heavily with impurities while using the gate electrode as a mask, disposing an insulating interlayer on the substrate and covering the active layer and the gate electrode, patterning the insulating interlayer so as to expose the source and drain regions, forming a source electrode and a drain electrode that is in contact with the exposed portions of the source and drain regions, forming a passivation layer on the insulating interlayer, defining a contact hole in the passivation layer for exposing the drain electrode, defining an anode electrode on the passivation layer, and covering the drain electrode so as to be in contact with the drain electrode, forming an organic electro-luminescent layer on the passivation layer and covering the anode electrode, defining a cathode electrode on the organic electro-luminescent layer. 
     Therefore, preferred embodiments of the present invention provide an ELD structure and method of manufacturing an ELD which achieve the advantages of increasing the expected lifespan, increasing the brightness, and improving the efficiency of the ELD by preventing the generation of a barrier interface between the anode electrode and a electro-luminescence layer by eliminating a subsidiary layer between the anode electrode and the electro-luminescence layer thereby removing the need to etch the subsidiary layer for allowing the anode electrode and the electro-luminescence layer to have excellent contact therebetween. 
     Other features, elements and advantages of the present invention will be described in detail below with reference to preferred embodiments of the present invention and the attached drawings. 
    
    
     BRIEF DESCRIPTION OF THE ATTACHED DRAWINGS 
     The present invention will become more fully understood from the detailed description given herein below and the accompanying drawings which are given by way of illustration only, and thus do not limit the present invention and wherein: 
     FIGS. 1A to FIGS. 1D illustrate a method of manufacturing an ELD according to a related art; 
     FIG. 2A is a general diagram of an ELD according to a preferred embodiment of the invention; 
     FIG. 2B is a cross-sectional view of a portion of an ELD according to a preferred embodiment of the present invention; and 
     FIG. 2A is a general diagram of an ELD and FIG. 2B is a cross-sectional view of an ELD according to a preferred embodiment of the present invention. As shown in FIG. 2A, the ELD includes a plurality of pixels each pixel  100  including: a switching TFT (Qs) having a gate electrode connected to a gate line  120  and a source electrode connected to a data line  140 ; a driving TFT (Qd) having a gate electrode connected to a drain of the switching TFT, a source electrode connected to a power line Vdd, and a drain electrode connected to an electro-luminescent diode Ed; and a capacitor C connected between the gate electrode and the source electrode of the driving TFT. 
     Referring to FIG. 2B, each pixel of the ELD according to the present invention includes an active layer  43  preferably made of polysilicon and preferably having a thickness of about 500 Å to about 1000 Å disposed on a predetermined portion of a switching portion of an insulating substrate  41  made of a transparent substance such as quartz, glass, or other similar substance, and having a switching portion and a pixel portion. A source region  49  and a drain region  51 , which are doped heavily with either n-type impurities such as P or, As, or p-type impurities such as B, are provided at both ends of the active layer  43 . The approximate central portion of the active layer  43  is not doped with impurities and defines a channel region. A gate insulating layer  45 , which is preferably made of an insulating substance such as silicon oxide, silicon nitride and other similar substances and preferably about 800 Å to 1500 Å thick, is provided on the channel region of the active layer  43 . A gate electrode  47 , which is made of an electrically-conductive substance such as Al, Al alloy or other similar substances having a low resistance and preferably about 4000 Å to 5000 Å thick, is provided on the gate insulating layer  45 . 
     FIG. 3A to FIG. 3D illustrate a method of manufacturing an ELD according to another preferred embodiment of the present invention. 
    
    
     DETAILED DESCRIPTION OF PREFERRED EMBODIMENTS 
     FIG. 2 is a cross-sectional view of an ELD according to a preferred embodiment of the present invention. Referring to FIG. 2, an ELD includes an active layer  43  preferably made of polysilicon and preferably having a thickness of about 500 Å to about 1000 Å disposed on a predetermined portion of a switching portion of an insulating substrate  41  made of a transparent substance such as quartz, glass, or other similar substance, and having a switching portion and a pixel portion. A source region  49  and a drain region  51 , which are doped heavily with either n-type impurities such as P or, As, or p-type impurities such as B, are provided at both ends of the active layer  43 . The approximate central portion of the active layer  43  is not doped with impurities and defines a channel region. A gate insulating layer  45 , which is preferably made of an insulating substance such as silicon oxide, silicon nitride and other similar substances and preferably about 800 Å to 1500 Å thick, is provided on the channel region of the active layer  43 . A gate electrode  47 , which is made of an electrically-conductive substance such as Al, Al alloy or other similar substances having a low resistance and preferably about 4000 Å to 5000 Å thick, is provided on the gate insulating layer  45 . 
     In the present preferred embodiment, the gate electrode  47  may have two layers such that a refractory metal such as Cr, Mo, Ti, Ta, or other similar metals are deposited on a low resistance metal such as Al, Al alloy or other similar metals. Also, the gate electrode  47  may be formed as soon as a scanning line (not shown in the drawing), which is connected to the gate electrode  47 , is provided. 
     Next, an insulating interlayer  53  that exposes the source region  49  and the drain region  51  are defined on the insulating substrate  41  and covers the gate electrode  47 . The insulating interlayer  53  which is preferably about 4000 Å to 5000 Å thick is defined preferably by depositing an insulator such as silicon oxide, silicon nitride and other similar substances. Then, a source electrode  55  and a drain electrode  57 , which are preferably in contact electrically with the exposed portions of the source region  49  and the drain regions  51 , respectively, are provided on the insulating interlayer  53 . The source electrode  55  and the drain electrode  57  are preferably made of a single layer of conductive metal such as Al, Al alloy, or other similar substances having a low resistance. Note that a signal line (not shown in the drawing) that is connected to the source electrode  55  may be formed on the insulating interlayer  53  at the same time that the source electrode  55  is formed. A passivation layer  59  that covers the source electrode  55  and the signal line, but which exposes the drain electrode  57  through a hole  60 , is provided on the insulating interlayer  53 . The passivation layer  59  is provided preferably by depositing silicon oxide or silicon nitride and having a thickness preferably about 4000 Å to about 5000 Å, and then coating the deposited silicon oxide or silicon nitride with an organic substance such as BCB (Benzocyclobutene), SOG(Spin On Glass), or other similar substances, wherein the coating is preferably about 1 μm to 3 μm thick. Note that in preferred embodiments of the present invention, the degradation from steps in the layers is less since the passivation layer  59  is relatively thick and includes the organic substance to provide a smooth surface thereon. 
     Next, an anode electrode  61  that is in contact electrically with the exposed portion of the drain electrode  57  through the hole  60  is provided on the passivation layer  59  of the pixel portion. Note that the anode electrode  61 , which is defined preferably by depositing a transparent conductive substance such as an ITO (Indium Tin Oxide), TO(TiN Oxide), or other similar substances and is preferably about 1000 to 2000 Å 0  thick, is isolated electrically from the other anode electrodes in the neighboring pixels. An organic EL layer  63  is then provided on the passivation layer  59  and preferably covers the anode electrode  61 . Note that the organic EL layer  63  is preferably about 1000 to 2000 Å thick, and is defined by depositing a substance that emits a light having a red, blue, or green color as electrons and holes recombine. Then, a cathode electrode  65 , which is preferably used as a common electrode connected to ground, is defined on the organic EL layer  63 . The cathode electrode  65  is defined preferably by depositing a metal having a low work function, such as Al, Al alloy, Ka, Na, Ca, Li, or other similar substances, to make it easy for electrons to be injected into the organic EL layer  63 , and is preferably about 1000 Å to about 3000 Å thick. Note that the organic EL layer  63  also includes a hole injecting and transporting region that is in contact with the anode electrode  61 , and an electron injecting and transporting region that is in contact with the cathode electrode  65 , and a luminescent layer that emits light. The hole or electron injecting/transporting regions may be provided with a single substance or with multiple substances. The light emission occurs in the hole and electron injecting/transporting region as the transported electrons and holes recombine in the luminescent layer. 
     Note that in preferred embodiments of the present invention, the organic EL layer  63  is defined on the entire anode electrode  61  and is in contact with the entire anode electrode without a subsidiary layer (e.g., layer  33  in FIG. 1) located in between. Therefore, the surface of the anode electrode  61  is not damaged since an etching process is not necessary for the organic EL layer  63  to contact the anode electrode  61 . Further, the etch remainders or the contaminant particles that are contained in etchant do not exist on the anode electrode  61 . 
     Therefore, the expected life span, brightness, and efficiency of the ELD is improved dramatically as charge carriers such as holes are transported with ease at the interface between the anode electrode  61  and the organic EL layer  63 . 
     FIG. 3A to FIG. 3D illustrate a method of manufacturing an ELD according to a preferred embodiment of the present invention. Referring to FIG. 3A, an active layer  43  is provided preferably by depositing a polysilicon layer preferably about 500 Å to 1000 Å thick on an insulating substrate  41  having a switching portion and a pixel portion preferably via a CVD process and then patterning the polysilicon layer preferably via a photolithography process. The insulating substrate  41  is preferably made of a transparent substance such as quartz, glass, or other similar substances. An insulating substance preferably about 800 Å to 1500 Å thick such as silicon oxide, silicon nitride, and other similar substances is deposited on the insulating substrate  41  preferably via a CVD process and preferably covers the active layer  43 . Next, a conductive metal preferably about 4000 Å to 5000 Å thick, and preferably having low resistivity, such as Al, Al alloy, or other similar metals is deposited on the insulating substance preferably via a sputtering method. Next, a gate electrode  47  and a gate insulating layer  45  are then provided by patterning, preferably via a photolithography process, the conductive metal and the insulating substance so that they remain on the middle portion of the active layer  43 . In the above-described method, the gate electrode  47  may preferably have two layers such that a refractory metal, which is made of Cr, Mo, Ti, Ta, or other similar substances, is disposed preferably on a low resistance metal such as Al, Al alloy or other similar substances. Note that the gate electrode  47  may be provided as soon as a scanning line (not shown in the drawing) that is connected to the gate electrode  47  is formed. A source region  49  and a drain region  51 , both of which are preferably doped heavily with either n-type impurities such as P, As, or p-type impurities such as B, are defined preferably at the two exposed ends of the active layer  43 . The middle portion of the active layer  43 , which is not doped with impurities, defines a channel region of the active layer  43 . 
     Referring to FIG. 3B, an insulating interlayer  53  is provided on the insulating substrate  41  and preferably covers the gate electrode  47 , the active layer  43 , and the scanning line by dispersing an insulating substance preferably about 4000 Å to 5000 Å thick such as silicon oxide, silicon nitride and other similar substances. The insulating interlayer  53  is then preferably patterned so as to expose the source region  49  and the drain region  51 . Next, a source electrode  55  and a drain electrode  57 , which are in contact electrically with the exposed portions of the source region  49  and the drain region  51 , respectively, are defined on the insulating interlayer  53 . The source electrode  55  and the drain electrode  57  are formed preferably by depositing and then patterning the conductive metal having a low resistance such as Al, Al alloy, or other similar substances preferably via a sputtering method and then preferably via a photolithography process, respectively. The resultant structure is a thin film transistor that functions as a switching device. Note that the source electrode  55  and the drain electrode  57  are preferably made from a single layer of a conductive metal such as Al, Al alloy, or other similar substances having a low resistance. Also, a signal line (not shown in the drawing) is connected to the source electrode  55 , and may be defined on the insulating interlayer  53  at the same time as the source electrode  55  and the drain electrode  57  are formed. 
     FIGS. 3A to FIGS. 3D illustrate a method of manufacturing an ELD having the configuration as shown in FIG. 2 according to a preferred embodiment of the present invention. Referring to FIG. 3A, an active layer  43  is provided preferably by depositing a polysilicon layer preferably having a thickness of about 500 Å to about 1000 Å on an insulating substrate  41  having a switching portion and a pixel portion preferably via a CVD process and then patterning the polysilicon layer preferably via a photolithography process. The insulating substrate  41  is preferably made of a transparent substance such as quartz, glass, or other similar substances. An insulating substance, preferably having a thickness of about 800 Å to about 1500 Å, such as silicon oxide, silicon nitride, and other similar substances is deposited on the insulating substrate  41  preferably via a CVD process and preferably covers the active layer  43 . Next, a conductive metal preferably having a thickness of about 4000 Å to about 5000 Å, and preferably having low resistivity, such as Al, Al alloy, or other similar metals is deposited on the insulating substance preferably via a sputtering method. Next, a gate electrode  47  and a gate insulating layer  45  are then provided by patterning, preferably via a photolithography process, the conductive metal and the insulating substance so that they remain on a portion (e.g., middle portion) of the active layer  43 . In the above-described method, the gate electrode  47  may preferably have two layers such that a refractory metal, which is made of Cr, Mo, Ti, Ta, or other similar substances, is disposed preferably on a low resistance metal such as Al, Al alloy or other similar substances. Note that the gate electrode  47  may be provided as soon as a scanning line (not shown in the drawing) that is connected to the gate electrode  47  is formed. A source region  49  and a drain region  51 , both of which are preferably doped heavily with either n-type impurities such as P, As, or p-type impurities such as B, are defined preferably at the two exposed ends of the active layer  43 . The middle portion of the active layer  43 , which is not doped with impurities, defines a channel region of the active layer  43 . 
     Referring to FIG. 3D, an organic EL layer  63  is provided and preferably covers the anode electrode  61 . Next, a cathode electrode  65 , which functions as a common electrode, is provided on the organic EL layer  63 . The cathode electrode  65  is preferably about 1000 Å to 3000 Å thick, and is provided by depositing a metal with a low work function such as Al, Al alloy, Ka, Na, Ca, Li, or other similar metals for easier injection of electrons into the organic EL layer  63 . The organic EL layer  63  is preferably about 1000 Å to 2000 Å thick, and is provided by depositing a substance that emits light as electrons and holes recombine, the light being either red, blue, or green. The organic EL layer  63  preferably includes a hole injecting and transporting region that is in contact with the anode electrode  61 , an electron injecting and transporting region that is in contact with the cathode electrode  65 , and a luminescent layer that emits light. Note that the hole and electron injecting/transporting regions may be defined with a single substance or with multiple substances. Light-emission occurs in the hole and electron injecting/transporting regions as the transported electrons and holes recombine in the luminescent layer. 
     Note that in the ELD of preferred embodiments of the present invention, the organic EL layer  63  is provided on the anode electrode  61  and in contact with the anode electrode without a subsidiary layer disposed in between. Thus, the surface of the anode electrode  61  is not damaged because an etching step is not performed to allow the organic EL layer  63  to be in contact with the anode electrode  61 . Further, etch remainders or contaminant particles contained in the etch gases do not accumulate on the surface of the anode electrode  61 . Accordingly, there does not exist a barrier interface between the anode electrode and organic EL layer which would hinder the transport of carriers such as holes. Therefore, the expected life span, the brightness, and the efficiency of the ELD are greatly improved as the holes are transported through the interface between the anode electrode and organic EL layer with ease. 
     While the invention has been particularly shown and described with reference to preferred embodiments thereof, it will be understood by those skilled in the art that the foregoing and other changes in form and details may be made therein without departing from the spirit and scope of the present invention.