Abstract:
A method of fabricating a pixel structure for use in an electroluminescent panel includes the following steps. A substrate is provided. Three shadow masks having a plurality of first, second, and third openings patterned in an array of T shaped are respectively provided, and three evaporation processes using the three shadow masks are subsequently performed to form a plurality of first subpixel units, second subpixel units and third subpixel units respectively. One first subpixel of the first subpixel unit, one second subpixel of the second subpixel unit adjacent to the first subpixel unit, and one third subpixel of the third subpixel unit adjacent to the first subpixel unit form a display pixel unit.

Description:
CROSS REFERENCE TO RELATED APPLICATIONS 
     This application is a division of application Ser. No. 11/469,464 filed on Aug. 31, 2006. 
    
    
     BACKGROUND OF THE INVENTION 
     1. Field of the Invention 
     The present invention relates to pixel structures for use in electroluminescent panels, and more particularly, to a pixel structure having high precision and a related fabrication method. 
     2. Description of the Prior Art 
     An electroluminescent display, such as an organic light emitting diode (OLED) display, is growing in popularity as a mainstream type of thin, flat display, due to characteristics of small size, high resolution, high contrast ratio, low power consumption and active luminescence. 
     A color image frame of the electroluminescent display is primarily provided by a plurality of display pixels comprising red, green and blue subpixels, and the color image frame is composed of different combinations of grey level color values displayed by the red, green and blue subpixels of each display pixel while the image frame is being displayed. 
     A pixel structure of the electroluminescent display is an arrangement of the red, green and blue subpixels, and a resolution of the electroluminescent display is heavily influenced by a design of the pixel structure. Recently, the most popular pixel structure for use in the electroluminescent display is a stripe. Please refer to  FIG. 1 , which is a schematic diagram of a prior art stripe pixel structure. As shown in  FIG. 1 , the stripe pixel structure  10  comprises a plurality of red subpixels R, a plurality of green subpixels G, and a plurality of blue subpixels B, wherein the red subpixels R, the green subpixels G, and the blue subpixels B are arranged in respective stripe formations. In other words, each column of the stripe pixel structure  10  comprises subpixels of one color, and the columns are arranged in an order of red, green, then blue. The stripe pixel structure  10  comprises a plurality of display pixel units  12 , and each display pixel unit  12  comprises a red subpixel R, a green subpixel G, and a blue subpixel B adjacent to each other and in a same row. 
     Although the pattern arrangement of the stripe pixel structure  10  is simple, a limitation exists when making a shadow mask used in an evaporation deposition process. Please refer to  FIG. 2 , which is a schematic diagram of the shadow mask utilized to make the stripe pixel structure of  FIG. 1 . As shown in  FIG. 2 , the shadow mask  14  comprises a plurality of rectangular openings  16 , and each rectangular opening  16  corresponds to the plurality of subpixels of a single color, such as the plurality of red subpixels. However, because the shadow mask  14  is made of a metallic material, a gap between adjacent rectangular openings  16  must be sufficiently large (as indicated by an arrow of  FIG. 1 ) to allow the shadow mask  14  to maintain structural strength, which establishes a lower limit on a density of the subpixels, affecting a maximum resolution achievable in the electroluminescent display. 
     Please refer to  FIG. 3 , which is a schematic diagram of another prior art pixel structure  20 . The pixel structure  20  comprises a plurality of red subpixel units  22 R, a plurality of green subpixel units  22 G and a plurality of blue subpixel units  22 B, wherein each subpixel unit has four subpixels of a same color arranged in a matrix, and the red subpixel unit  22 R, the green subpixel unit  22 G and the blue subpixel unit  22 B are arranged in an alternating formation, as shown in  FIG. 3 . A display pixel unit  24  of pixel structure  20  consists of four subpixels (represented by a dotted line) from four adjacent subpixel units, respectively. In other words, the display pixel unit  24  at least comprises a red subpixel R, a green subpixel G, and a blue subpixel B, and further comprises another subpixel that may be a red subpixel R, a green subpixel G, or a blue subpixel B. 
     Although the arrangement of  FIG. 3  exhibits better color performance than the stripe pixel structure of  FIG. 1 , the resolution cannot be further increased because of process limitations. The pixel structure of the electroluminescent panel generally utilizes an evaporation deposition process with a shadow mask having different opening patterns to fabricate the red subpixel unit, the green subpixel unit, and the blue subpixel unit, respectively. However, the arrangement of the red subpixel unit  22 R, the green subpixel unit  22 G and the blue subpixel unit  22 B in the pixel structure  20  will similarly encounter the process limitation of the evaporation deposition process. 
     Please refer to  FIG. 4 , which is a schematic diagram of the shadow mask used to fabricate the pixel structure  20  of  FIG. 3 . As shown in  FIG. 4 , the shadow mask  30  comprises a plurality of rectangular openings  32 , and each rectangular opening  32  corresponds to the subpixel units of a single color, such as the red subpixel units. The subpixel unit can be deposited onto a substrate of the electroluminescent panel through use of the shadow mask  30  by evaporation. As mentioned above, because the shadow mask  30  is made of a metallic material, a distance between adjacent rectangular openings  32  must be sufficiently large (as shown by an arrow in  FIG. 4 ) to maintain a structural strength of the shadow mask  30 . Thus, a lower limit on a density of the subpixels will be unable to decrease, which affects a resolution of the display. 
     SUMMARY OF THE INVENTION 
     A pixel structure for use in an electroluminescent panel comprises a substrate and a plurality of display pixel units disposed on the substrate. Each display pixel unit comprises a first subpixel, a second subpixel, and a third subpixel. The first subpixel, the second subpixel, and the third subpixel are arranged in a delta formation. The first subpixel of each display pixel unit is adjacent to the first subpixels of two adjacent display pixel units. The second subpixel of each display pixel unit is adjacent to the second subpixels of two adjacent display pixel units. The third subpixel of each display pixel unit is adjacent to the third subpixels of two adjacent display pixel units. 
     A method of fabricating a pixel structure for use in an electroluminescent panel according to the present invention starts with providing a substrate. Then, a first shadow mask having a plurality of first openings patterned in an array of T shapes is provided. The first shadow mask is utilized to evaporate a plurality of first subpixel units comprising three first subpixels in a delta formation onto the substrate, each first subpixel unit corresponding to one of the plurality of first openings. Then, a second shadow mask having a plurality of second openings patterned in an array of T shapes is provided. The second shadow mask is utilized to evaporate a plurality of second subpixel units comprising three second subpixels in a delta formation onto the substrate, each second subpixel unit corresponding to one of the plurality of second openings and without overlapping the plurality of first subpixel units. A third shadow mask having a plurality of third openings patterned in an array of T shapes is provided. The third shadow mask is utilized to evaporate a plurality of third subpixel units comprising three third subpixels in a delta formation onto the substrate, each third subpixel unit corresponding to one of the plurality of third openings and without overlapping the plurality of first subpixel units or the plurality of second subpixel units. One first subpixel of the first subpixel unit, one second subpixel of the second subpixel unit adjacent to the first subpixel unit, and one third subpixel of the third subpixel unit adjacent to the first subpixel unit form a display pixel unit. 
     These and other objectives of the present invention will no doubt become obvious to those of ordinary skill in the art after reading the following detailed description of the preferred embodiment that is illustrated in the various figures and drawings. 
    
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS 
         FIG. 1  is a schematic diagram of a stripe-shaped pixel structure according to the prior art. 
         FIG. 2  is a schematic diagram of a shadow mask utilized to fabricate the stripe-shaped pixel structure of  FIG. 1 . 
         FIG. 3  is a schematic diagram of another pixel structure according to the prior art. 
         FIG. 4  is a schematic diagram of a shadow mask utilized to fabricate another pixel structure of  FIG. 3 . 
         FIG. 5  is a schematic diagram of a pixel structure according to a preferred embodiment of the present invention. 
         FIG. 6  is a schematic diagram of a display pixel unit of the pixel structure of  FIG. 5 . 
         FIG. 7  is a flow chart of a method of fabricating a pixel structure according to the present invention. 
         FIGS. 8 to 10  are schematic diagrams of shadow masks utilized to fabricate the pixel structure shown in  FIG. 5  according to the present invention. 
     
    
    
     DETAILED DESCRIPTION 
     Please refer to  FIG. 5 , which is a schematic diagram of a pixel structure for use in an electroluminescent panel according to a preferred embodiment of the present invention. As shown in  FIG. 5 , the pixel structure  50  comprises a substrate  52 , a plurality of first subpixel units  54  disposed on the substrate  52 , a plurality of second subpixel units  56  disposed on the substrate  52 , and a plurality of third subpixel units  58  disposed on the substrate  52 . In the preferred embodiment, the first subpixel units  54 , the second subpixel units  56 , and the third subpixel units  58  are red, green, and blue subpixel units, respectively, and therefore each first subpixel unit  54  comprises three first subpixels (red subpixels) R arranged in a delta formation, each second subpixel unit  56  comprises three second subpixels (green subpixels) G arranged in a delta formation, and each third subpixel unit  58  comprises three third subpixels (blue subpixels) B arranged in a delta formation. 
     In the pixel structure  50  of the preferred embodiment, the first subpixel unit  54 , the second subpixel unit  56  and the third subpixel unit  58  are arranged in an alternating formation. As shown in  FIG. 5 , according to a direction of a row of subpixel units, the subpixel units disposed in each row are arranged in a repeating sequence of one first subpixel unit  54  followed by one second subpixel unit  56  followed by one third subpixel unit  58 . In adjacent rows, the first subpixel unit  54 , the second subpixel unit  56 , and the third subpixel unit of a row are disposed in a mismatched arrangement relative to the first subpixel unit  54 , the second subpixel unit  56  and the third subpixel unit  58  of an adjacent row. Further, any two adjacent subpixel units are upside-down relative to each other, such as an obverse triangle and a reverse triangle. 
       FIG. 5  shows an arrangement of the subpixel units of the pixel structure  50 , but the pixel structure  50  forms a display frame by combining display pixel units when displaying an image. Please refer to  FIG. 6 , which is a schematic diagram of the display pixel unit  60  of the pixel structure  50  shown in  FIG. 5 . As shown in  FIG. 6 , the pixel structure  50  comprises a plurality of display pixel units  60 . Each display pixel unit  60  comprises a first subpixel R, a second subpixel G, and a third subpixel B. The first subpixel R, the second subpixel G, and the third subpixel B of each display pixel unit  60  respectively belong to one first subpixel unit  54 , one second subpixel unit  56  and one third subpixel unit  58  that are adjacent to each other. 
     As can be seen in  FIG. 6 , a characteristic of a structure of the display pixel unit  60  of the preferred embodiment is that the first subpixel R of each display pixel unit  60  is next to the first subpixels R of two adjacent display pixel units  60 , the second subpixel G of each display pixel unit  60  is next to the second subpixels G of two adjacent display pixel units  60 , and the third subpixel B of each display pixel unit  60  is next to the third subpixels B of two adjacent display pixel units  60 . Additionally, in each display pixel unit  60 , the first subpixel R, the second subpixel G and the third subpixel B are arranged in a delta formation, such that each display pixel unit  60  forms a similar triangle structure. In addition, each display pixel unit  60  in a same row is oriented differently from an adjacent pixel unit in the same row. In other words, any two adjacent display pixel units  60  are upside-down (such as an obverse triangle and a reverse triangle) relative to each other. 
     As designed, in the aforementioned display pixel unit  60 , the first subpixel R, the second subpixel G, and the third subpixel B of each display pixel unit  60  are arranged in a delta formation, and the arrangement centralizes a distribution of the subpixels. Therefore, light is mixed more effectively, whereby display quality is improved. Additionally, due to the arrangement of the first pixel unit  54 , the second pixel unit  56 , and the third pixel unit  58 , the limitations on the shadow mask mentioned above are overcome, and precision of the pixel structure is increased. Please refer to  FIG. 7 , which is a flow chart of the present invention method of fabricating the pixel structure for use in an electroluminescent panel. As shown in  FIG. 7 , the method comprises: 
     Step  70 : Providing a substrate; 
     Step  72 : Providing a first shadow mask having a plurality of first openings patterned in an array of similar T shapes; 
     Step  74 : Utilizing the first shadow mask to evaporate a plurality of first subpixel units corresponding to each first opening onto the substrate, where each first subpixel unit comprises three first subpixels arranged in a delta formation; 
     Step  76 : Providing a second shadow mask having a plurality of second openings patterned in an array of similar T shapes; 
     Step  78 : Utilizing the second shadow mask to evaporate a plurality of second subpixel units corresponding to each second opening onto the substrate, where each second subpixel unit comprises three second subpixels arranged in a delta formation, and no second subpixel unit overlaps any of the plurality of first subpixel units; 
     Step  80 : Providing a third shadow mask having a plurality of third openings patterned in an array of similar T shapes; and 
     Step  82 : Utilizing the third shadow mask to evaporate a plurality of third subpixel units corresponding to each third opening onto the substrate, where each third subpixel unit comprises three third subpixels arranged in a delta formation, and no third subpixel unit overlaps any of the plurality of first subpixel units or any of the plurality of second subpixel units; 
     By the aforementioned steps, the pixel structure can be formed on the substrate. The display pixel unit of the pixel structure comprises one first subpixel of each first subpixel unit, one second subpixel of one second subpixel unit adjacent to the first subpixel unit, and one third subpixel of one third subpixel unit adjacent to the first subpixel unit. Please refer to  FIGS. 8-10 , which are diagrams of the shadow mask used to fabricate the pixel structure shown in  FIG. 5  according to the present invention.  FIG. 8  is a schematic diagram of the first shadow mask,  FIG. 9  is a schematic diagram of the second shadow mask, and  FIG. 10  is a schematic diagram of the third shadow mask. As shown in  FIGS. 8-10 , the first shadow mask  90 R comprises a plurality of first openings  92 R patterned in an array of similar T shapes. Each first opening  92 R in a same row is oriented differently from an adjacent first opening in the same row. The second shadow mask  90 G comprises a plurality of second openings  92 G patterned in an array of similar T shapes. Each second opening  92 G in a same row oriented differently from an adjacent second opening in the same row. The third shadow mask  90 B comprises a plurality of third openings  92 B patterned in an array of similar T shapes. Each third opening  92 B in a same row oriented differently from an adjacent third opening in the same row. 
     Arrangements of openings in the first shadow mask  90 R, the second shadow mask  90 G, and the third shadow mask  90 B are similar, a difference being that the arrangement of openings in each shadow mask is offset from the arrangement of openings in each other shadow mask. The arrangement of openings in the shadow mask increases a distance between each opening, so that production of the shadow mask does not face the above mentioned process limitation arising due to the consideration of the structural strength of the shadow mask. As can be seen from  FIGS. 8-10 , for the first shadow mask  90 R, the second shadow mask  90 G, and the third shadow mask  90 B, the distance separating each of the plurality of first openings  92 R, the distance separating each of the plurality of second openings  92 G, and the distance separating each of the plurality of third openings  92 B are all far over the process limitation. By utilizing the first shadow mask  90 R, the second shadow mask  90 G, and the third shadow mask  90 B in order in the evaporation deposition process, the pixel structure shown in  FIG. 5  can be fabricated. In such a way, although the distance separating the first openings  92 R, the distance separating the second openings  92 G, and the distance separating the third openings  92 B are respectively bigger than the distances separating subpixels of the prior art, when the shadow masks are combined, the pixel structure has smaller distances between subpixels, which effectively increases resolution. 
     By utilizing the pixel structure design and the method according to the present invention, the resolution of electroluminescent panel can be increased effectively. It is worthy of note that the pixel structure of the present invention can be applied to all kinds of full color display panels, such as OLED display panels or polymer light emitting diode (PLED) display panels. Therefore, depending on different display panel types, each subpixel can comprise an organic light emitting diode or a polymer light emitting diode to effectively increase resolution while still following the spirit of the pixel structure design of the present invention. 
     In summary, to improve a thin-film transistor display panel fabrication process, the pixel structure of the present invention and method of making the same can overcome the evaporation deposition process limitation to increase the precision of subpixel fabrication, exceeding 200 ppi in practice. Therefore, the evaporation deposition process is removed as a bottleneck for increasing resolution. 
     Those skilled in the art will readily observe that numerous modifications and alterations of the device and method may be made while retaining the teachings of the invention. Accordingly, the above disclosure should be construed as limited only by the metes and bounds of the appended claims.