Abstract:
Shadow masks capable of full-color process of display elements are provided. An exemplary embodiment of a shadow mask comprises a main body having a plurality of openings formed therethrough. A plurality of recesses formed over the main body, located adjacent to the openings. In an exemplary embodiment, the recesses are respectively defined by a trench formed in the main body and the trench is integrated with the main body. In another exemplary embodiment, the recesses are defined by a plurality of ribs protruding over a surface of the main body.

Description:
BACKGROUND OF THE INVENTION  
       [0001]     1. Field of the Invention  
         [0002]     The present invention relates to electroluminescent display device fabrication, and more particularly to a shadow mask for full-color process of display elements of an electroluminescent display.  
         [0003]     2. Description of the Related Art  
         [0004]     Recently, research and development of electroluminescent techniques has been undertaken in the field of self-emissive display devices. Compared with other emissive display devices, such as plasma display devices, electroluminescent display devices have advantages such as lower power consumption, reduced size and provides images of higher brightness and sharpness. Typically, a plurality of pixel arrays are defined over an electroluminescent display device by a plurality of intercrossing scan lines and data lines formed therein and may be coupled with light-emitting devices. The light-emitting devices can be, for example, organic light-emitting devices (OLEDs) and are driven by a driving circuit corresponding to each thereof.  
         [0005]     Typically, an OLED is formed by a stacked film structure, comprising an organic material layer which is sandwiched by two electrodes, named as cathode and anode. The organic material layer further comprises a hole transport layer, a light-emitting layer, and an electron transport layer. When voltages are applied between the cathode and the anode, positive and negative charges emitted by these layers will recombine in the light-emitting layer to thereby emit light.  
         [0006]     The color of the light emitted by an OLED depends on the organic light-emitting material used therein. Conventional full-color OLED displays include a plurality of pixels for emitting lights mainly comprising red, green, and blue (RGB) colors and is formed in a manner of pixel array. Full-color spectrum can be achieved by the mixing of these lights of different colors during operation.  
         [0007]     Such an organic light-emitting layer for emitting light of a certain color is formed by a vacuum evaporation incorporating a shallow mask. Use of the shadow mask selectively reveals regions over an array substrate of an OLED device for vacuum evaporation processing, thereby forming organic light-emitting layers for emitting different colors, for example green, red and blue.  
         [0008]     Nevertheless, during the vacuum evaporation process, the shadow mask directly contacts some structures over an array substrate, such as spacers formed thereon, to precisely control regions of vacuum evaporation. Particles from the clean room or a previously contacted containment substrate may possibly remain on the surface of the shadow mask and therefore ruin device elements formed over the array substrate due to direct contact therebetween.  
         [0009]      FIG. 1  is a schematic diagram illustrating display devices formed over a substrate of an electroluminescent device damaged by particles remaining on a shadow mask in a related art vacuum evaporation.  
         [0010]     Referring now to  FIG. 1 , during the vacuum evaporation, a substrate, for example an array substrate  100 , is first provided, having components such as gate lines and data lines for functioning signal lines, and thin film transistors (TFTs) formed thereon. The array substrate  100  in  FIG. 1  is illustrated as a planar substrate merely for simplicity. As shown in  FIG. 1 , a plurality of spaces  110  are formed over the array substrate  100 , defining a plurality display regions  120 ,  130  and  140  thereon, wherein the display regions  120 ,  130  and  140  are regions for forming display units of emitting lights of different colors.  
         [0011]     As shown in  FIG. 1 , a transparent electrode  150  is respectively formed over the array substrate  100  in each of the display regions  120 ,  130  and  140 . The vacuum evaporation (not shown) is repeatedly performed incorporation with a shadow mask  200  to form an organic light-emitting layer for emitting a light of a predetermined color in each of the display regions  120  and  140 , such as the organic light-emitting layer  160  for emitting a light of red color in the display region  120  and the organic light-emitting layer  170  for emitting a light of green color in the display region  140 , respectively.  
         [0012]     Still referring to the  FIG. 1 , the shadow mask  200  is used again to form an organic light-emitting layer  170  for emitting a light of blue color by another vacuum evaporation (not shown). As illustrated, the shadow mask  200  is now exposed with an opening  210  substantially aligning to the display region  130  and a main body  205  thereof directly contacts the spacers  110  formed over the array substrate  100 .  
         [0013]     Nevertheless, the shadow mask  200  directly contacts the array substrate  100  at a side having a planar surface thereof, therefore particles came from the ambient of the clean room or a contaminant substrate which previously contacted with the shadow mask inevitably remains on the shadow mask and protrudes over the surface thereof. The particles are now illustrated as a particle  300  in  FIG. 1  for illustration, the particle  300  now remains on the surface of the array substrate  100  that directly contacts the shadow mask  200 . As shown in  FIG. 1 , since the particle  300  protrudes over the main body  205  of the shadow mask  200  at a side directly contacting the array substrate  100 . Thus, the particle  300  directly contacts the organic light-emitting layer  170  previously formed in the display region  140  during the formation of the organic light-emitting layer  180  for emitting a light of blue color in the vacuum evaporation and thereby damages the planar surface in the display region  140 , such that the device reliability in the display region  140  is affected.  
         [0014]     Thus, the particles remaining and protruding over the shadow mask may repeatedly damage display units in certain display regions during the vacuum evaporation, thereby affecting the image performance of an ultimately formed display device. Therefore, an improved shadow mask design is needed to prevent the above mentioned image performance issues generated by the undesired particles which may remain on the shadow mask.  
       BRIEF SUMMARY OF THE INVENTION  
       [0015]     Shadow masks capable of full-color process of display elements are provided. An exemplary embodiment of a shadow mask comprises a main body having a plurality of openings formed therethrough. A plurality of recesses formed over the main body, located adjacent to the openings.  
         [0016]     A detailed description is given in the following embodiments with reference to the accompanying drawings. 
     
    
     BRIEF DESCRIPTION OF THE DRAWINGS  
       [0017]     The present invention can be more fully understood by reading the subsequent detailed description and examples with references made to the accompanying drawings, wherein:  
         [0018]      FIG. 1  is a schematic diagram illustrating a display device over an array substrate ruined by a particle remaining over a surface of a shadow mask in a related art vacuum evaporation;  
         [0019]      FIG. 2  is a schematic top view showing a part of a shadow mask according to an embodiment of the invention;  
         [0020]      FIG. 3  is a schematic cross section taken along line  3 - 3  of  FIG. 2 ;  
         [0021]      FIG. 4  is a schematic view showing the shadow mask of  FIG. 2  performed in a fall-color process;  
         [0022]      FIG. 5  is a schematic top view showing a part of a shadow mask according to another embodiment of the invention;  
         [0023]      FIG. 6  is a schematic cross section taken along line  6 - 6  of  FIG. 5 ; and  
         [0024]      FIG. 7  is a schematic view showing the shadow mask of  FIG. 5  performed in a fall-color process. 
     
    
     DETAILED DESCRIPTION OF THE INVENTION  
       [0025]     The following description is of the best-contemplated mode of carrying out the invention. This description is made for the purpose of illustrating the general principles of the invention and should not be taken in a limiting sense. The scope of the invention is best determined by reference to the appended claims.  
         [0026]      FIGS. 2-7  illustrate exemplary embodiments of the invention. Referring now to  FIG. 2 , a top view of a part of a shadow mask  600  is illustrated. The shadow mask  600  includes a main body  605  comprised of, for example, Invar alloy, stainless steel (e.g. SUS  304 ,  420 ,  430 ), nickel or alloys of nickel and cobalt. A plurality of openings  700  is formed in the main body  605 . The openings  700  are arranged with a predetermined spacing over the shadow mask  600  and formed through the main body  605 , exposing regions for vacuum evaporation. The arrangement of the openings  700  can be modified and is not limited to the arrangement illustrated in  FIG. 2 . In  FIG. 2 , a plurality of recesses  620  are formed in portions of the main body  605  between the openings  700  to thereby accommodatr particles which may remain on a surface of the main body  605 , thus preventing particle issues of the related art.  
         [0027]     Referring now to  FIG. 3 , a cross section taken along line  3 - 3  of  FIG. 2  is illustrated. As shown in  FIG. 3 , the recesses  620  are formed in a part within the main body  605  by trenches  630  formed by methods such as dry etching. Therefore, the main body  605  of the shadow mask  600  is now formed with an uneven surface which is different to the planar surface of the related art shadow mask illustrated in  FIG. 1 . The surface of the main body  605  is now formed with a plurality of recesses  620 . As shown in  FIG. 3 , the trenches  630  have a depth of about 2-10 μm from the top surface of the main body  605 . As observed by the inventors, particles from the ambient of a clean room and a previously contacted contaminated array substrate typically have a diameter of not more than 2 μm, the trenches  630  formed in the main body  605  can thus accommodate particles and thereby prevent protrusion thereof over the surface of the main body  605 .  
         [0028]      FIG. 4  is a schematic diagram showing the shadow mask  600  of  FIG. 2  performed in a full-color process.  
         [0029]     Referring now to  FIG. 4 , the fall-color process is illustrated as a vacuum evaporation and the substrate being performed with the vacuum evaporation is an array substrate of an electroluminescent device, such as the array substrate  500  but are not limited thereto. Other full-color processes and substrates can be also adopted. The substrate  500  is provided with components such as gate lines and data lines for functioning signal lines, and thin film transistors (TFTs) formed thereon. However, the array substrate  500  in  FIG. 4  is illustrated as a substrate with a planar surface merely for simplicity. As shown in  FIG. 4 , a plurality of spacers  510  are formed over the array substrate  500 , defining a plurality display regions  520 ,  530  and  540  thereon, wherein the display regions  520 ,  530  and  540  are regions for forming display units of emitting lights of different colors.  
         [0030]     As shown in  FIG. 4 , a transparent electrode  550  is respectively formed over the array substrate  500  in each of the display regions  520 ,  530  and  540 . The vacuum evaporation (not shown) is repeatedly performed in corporation with the shadow mask  600  to form an organic light-emitting layer for emitting a light of a predetermined color in each of the display regions  520  and  540 , such as the organic light-emitting layer  560  for emitting a light of red color in the display region  520  and the organic light-emitting layer  570  for emitting a light of green color in the display region  540 , respectively.  
         [0031]     Still referring  FIG. 4 , a full-color process for forming an organic light-emitting layer  580  for emitting light of blue color over a transparent electrode  550  in a display region  530  by incorporating the shadow mask  600  is illustrated. As shown in  FIG. 4 , the main body  605  the shadow mask  600  is now exposed with an opening  700  substantially aligning to the display region  530  and the main body  605  is now directly contacts the spacers  510  formed over an array substrate  500 . The recesses  620  formed in the main body  605  now substantially align to adjacent display units, such as the display regions  520  and  540 , respectively.  
         [0032]     Since the recesses  620  are formed in the main body  605  adjacent to the opening  700 , a side of the shadow mask  600  for directly contacting the array substrate  500  is now formed with an uneven surface. Thus, particles came from the ambient of the clean room or a contaminant substrate, such as the particle  750  here, which previously contacted the shadow mask inevitably remains on the shadow mask  600  are now properly accommodated by the recesses  620 . The particle  750  is now remains on a top surface of the main body  605  and protrudes therefrom. Thus, the particle  750  does not contact the organic light-emitting layer  570  previously formed in the display region  540  during the formation the organic light-emitting layer  580  for emitting red light during the vacuum evaporation and thereby reliability of the display device formed in the display region  540  is ensured.  
         [0033]     Referring now to  FIG. 5 , a top view of a part of a shadow mask  800  according to another exemplary embodiment is illustrated. The shadow mask  800  includes a main body  805  comprised of, for example, Invar alloy, stainless steel (e.g. SUS  304 ,  420 ,  430 ), nickel or alloys of nickel and cobalt. A plurality of openings  700  is formed in the main body  805 . The openings  700  are arranged with a predetermined spacing over the shadow mask  800  and formed through the main body  605 , exposing regions for vacuum evaporation. Arrangements of the openings  700  can be modified and is not limited to the situation illustrated in  FIG. 5 . In  FIG. 5 , a plurality of recesses  820  are defined over portions of the main body  805  between the openings  700  by forming a plurality of ribs  830  on both sides of the openings  700 . The recesses  820  are capable of accommodating particles which may remain on a surface of the main body  805 , thus preventing the shadow mask from particle issues of the related art.  
         [0034]     As shown in  FIG. 5 , the recess  620  are formed over the main body  805  and are defined by the ribs  830  protruding over the surface of the main body adjacent to both sides of the openings  700 . The side of the main body  805  for directly contacting the array substrate is now an uneven surface comprising a plurality of recesses and is different to the planar surface of the related art shadow mask illustrated in  FIG. 1 .  
         [0035]     Referring now to  FIG. 6 , a cross section taken along line  6 - 6  of  FIG. 5  is illustrated. As shown in  FIG. 6 , the recesses  620  have a depth d′ of about 2-10 μm and are substantially equal to a thickness of the ribs  830 . As observed by the inventors, particles from the ambient of a clean room and a previously contacted contaminated array substrate typically have a diameter not more than 2 μm, the ribs  830  formed over the main body  805  can therefore define spaces for accommodating particles and thereby preventing protrusion thereof over the surface of the main body  805 . Materials for forming the ribs  830  can be photosensitive materials such as resist and photosensitive polyimide and the ribs can be formed by method such as photolithography.  
         [0036]      FIG. 7  is a schematic diagram showing the shadow mask  800  of  FIG. 5  performed in a full-color process.  
         [0037]     Referring now to  FIG. 7 , the full-color process is illustrated as a vacuum evaporation here and the substrate being performed with the vacuum evaporation is an array substrate of an electroluminescent device, such as the array substrate  900  but are not limited thereto. Other full-color processes and substrates can be also adopted. The substrate  900  is provided with components such as gate lines and data lines for functioning signal lines, and thin film transistors (TFTs) formed thereon. However, the array substrate  900  in  FIG. 7  only illustrates a substrate with a planar surface, for simplicity. As shown in  FIG. 7 , a plurality of spacers  910  are formed over the array substrate  900 , defining a plurality display regions  920 ,  930  and  940  thereon, wherein the display regions  920 ,  930  and  940  are regions for forming display units of emitting lights of different colors.  
         [0038]     As shown in  FIG. 7 , a transparent electrode  950  is respectively formed over the array substrate  900  in each of the display regions  920 ,  930  and  940 . The vacuum evaporation (not shown) is repeatedly performed in corporation with the shadow mask  800  to form an organic light-emitting layer for emitting a light of predetermined color in each of the display regions  920  and  940 , such as the organic light-emitting layer  960  for emitting a red light in the display region  920  and the organic light-emitting layer  970  for emitting a green light in the display region  940 , respectively.  
         [0039]     Still referring  FIG. 7 , a full-color process for forming an organic light-emitting layer  980  for emitting lights of blue color over a transparent electrode  950  in a display region  930  by incorporating the shadow mask  800  is illustrated. As shown in  FIG. 7 , the main body  805  the shadow mask  800  is now exposed with an opening  700  substantially aligning to the display region  930  and the ribs  830  formed over the main body  805  now directly contacts the spacers  910  formed over an array substrate  900 . The recesses  820  formed in the main body  805  now substantially align to adjacent display units, such as the display regions  820  and  840 , respectively.  
         [0040]     Since the recesses  820  are defined over the main body  805  adjacent to the opening  700  by the ribs  830  formed thereon, a side of the shadow mask  800  for directly contacting the array substrate  900  is now formed with an uneven surface. Thus, particles from the ambient of the clean room or a contaminant substrate, such as the particle  750  here, which previously contacted the shadow mask and inevitably remained on the shadow mask  800  are now properly accommodated by the recesses  820 . The particle  750  now remains on a top surface of the main body  805  and protrudes thereof. Thus, the particle  750  does not contact the organic light-emitting layer  970  previously formed in the display region  940  during the formation the organic light-emitting layer  980  for emitting red light during the vacuum evaporation and thereby reliability of the display device formed in the display region  940  is ensured.  
         [0041]     While the invention has been described by way of example and in terms of the preferred embodiments, it is to be understood that the invention is not limited to the disclosed embodiments. To the contrary, it is intended to cover various modifications and similar arrangements (as would be apparent to those skilled in the art). Therefore, the scope of the appended claims should be accorded the broadest interpretation so as to encompass all such modifications and similar arrangements.