Abstract:
The invention provides an illumination device, method for fabricating the same, and system for displaying images utilizing the same. The illumination device includes a substrate, a first electrode, an illumination layer, and a second electrode. The substrate has a plurality of illumination regions. The first electrode overlies the substrate and has a first bump disposed in a first illumination region of the plurality of the illumination regions. The illumination layer overlies the first electrode. The second electrode overlies the illumination layer.

Description:
CROSS REFERENCE TO RELATED APPLICATIONS 
       [0001]    This Application claims priority of Taiwan Patent Application No. 098104611, filed on Feb. 13, 2009, the entirety of which is incorporated by reference herein. 
       BACKGROUND OF THE INVENTION 
       [0002]    1. Field of the Invention 
         [0003]    The invention relates to illumination devices of systems for displaying images. 
         [0004]    2. Description of the Related Art 
         [0005]    Colorimetric purity provided by an organic light emitting diode (OLED) is important for full color flat panel displays employing OLEDs. The OLED may utilize microcavity effect, wherein emitted light of specific wavelengths are enhanced by the constructive interference thereof, and emitted light of other specific wavelengths are weakened by the destructive interference thereof, such that the full width at half maximum (FWHM) of the emitted light is narrowed. Specifically, a transflective electrode is formed in a light-emitting part of an illumination device and a reflective electrode is formed in an opposite side to the transflective electrode to induce interference of photons from an illumination layer of the illumination device between the transflective and reflective electrodes. The intensity of light with specific colors in emitted light from the OLED can be enhanced by controlling the microcavities. Thus, light with better colorimetric purity can be obtained by obtainment of trichromatic light utilizing a light filtration material, resulting in lower light loss due to light filtration, decreasing energy (electrical power) consumption. 
         [0006]    U.S. Pat. No. 7,129,634 and SID 04 DIGEST (pages 1017-1019) disclose OLEDs utilized in display devices where transparent microcavity spacer layers and transparent electrodes with different thicknesses are respectively disposed in pixel areas of different colors. However, because the transparent microcavity spacer layer and transparent electrode in one single pixel area respectively have constant thicknesses, multiple deposition and etching steps are required for different thicknesses, complicating the fabrication process and increasing costs. 
         [0007]    Thus, a novel illumination device, method for fabricating the same, and system for displaying images utilizing the same are required to solve the described problems. 
       BRIEF SUMMARY OF THE INVENTION 
       [0008]    An embodiment of the present invention provides an illumination device. The illumination device includes a substrate, a first electrode, an illumination layer, and a second electrode. The substrate comprises a plurality of illumination regions. The first electrode overlies the substrate and comprises a first bump disposed in a first illumination region of the plurality of the illumination regions. The illumination layer overlies the first electrode. The second electrode is deposited on the illumination layer. 
         [0009]    An embodiment of the present invention provides a system for displaying images, which includes a display panel and an input unit. The display panel comprises the forward illumination device. The input unit is coupled to the display panel and provides an input signal to the display panel for displaying images. 
         [0010]    An embodiment of the present invention provides a method for fabricating an illumination device. First, a substrate comprising a plurality of illumination regions having a first illumination region and a second illumination region is provided. Then, an electrode base layer of a first electrode is formed on the substrate in each of the plurality of illumination regions. Next, a first island-like transparent layer of the first electrode is formed in the first illumination region on the substrate. Further, an illumination layer is deposited on the first electrode. Finally, a second electrode is formed on the illumination layer. 
         [0011]    Further scope of the applicability of the invention will become apparent from the detailed descriptions given hereinafter. It should be understood however, that the detailed descriptions and specific examples, while indicating preferred embodiments of the invention, are given by way of illustration only, as various changes and modifications within the spirit and scope of the invention will become apparent to those skilled in the Art from the detailed descriptions. 
         [0012]    A detailed description is given in the following embodiments with reference to the accompanying drawings. 
     
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS 
         [0013]    The invention can be more fully understood by reading the subsequent detailed description and examples with references made to the accompanying drawings, wherein: 
           [0014]      FIG. 1  shows an exemplary top view of an illumination device of a preferred embodiment of the invention; 
           [0015]      FIGS. 2A through 2C  show exemplary top views of the arrangements of bumps of a preferred embodiment of the invention; 
           [0016]      FIG. 3A  schematically shows a system for displaying images of a preferred embodiment of the invention; and 
           [0017]      FIG. 3B  shows a schematic layout of a display panel of a preferred embodiment of the invention. 
       
    
    
     DETAILED DESCRIPTION OF THE INVENTION 
       [0018]    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. 
         [0019]    Next, the concepts and specific practice modes of the invention is described in detail by the embodiments and the attached drawings. In the drawings or description, similar elements are indicated by similar reference numerals and/or letters. Further, the element shape or thickness in the drawings can be expanded for simplification or convenience of indication. Moreover, elements which are not shown or described can be in every form known by those skilled in the art. 
         [0020]    Specific embodiments of the present invention for fabrication of an illumination device and a system for displaying images are described. It is noted that the concepts of the invention can be applied to any known or newly developed illumination devices and systems for displaying images. 
         [0021]    Referring to  FIG. 1 , an illumination device  10  comprises a device substrate  100  and structures formed thereon. A display panel  400  of a system for displaying images comprises the illumination device  10 , and may further comprises an opposite substrate  200  and structures formed thereon. 
         [0022]    The illumination device  10  comprises a device substrate  100 , an optically reflective layer  110 , a first electrode  120 , an illumination layer  140 , and a second electrode  150 . The illumination device  10  can be a top-emitting type illumination device. The optically reflective layer  110  is formed of a reflective material. The first electrode  120  may be formed of a transparent material such as indium tin oxide (ITO). The second electrode  150  can be formed of a transflective material. The device substrate  100  may be transparent or opaque. 
         [0023]    The device substrate  100  is predetermined to be divided into a plurality of illumination regions such as four illumination regions  100 R,  100 G,  100 B, and  100 W. Every illumination region is equipped with an optional switch  101 , which can be a thin film transistor, disposed on the device substrate  100 . If the illumination device  10  is not applied to display panels, the switches  101  may not be disposed on the device substrate  100 . 
         [0024]    In  FIG. 1 , a planarization layer  102  is optionally formed on the device substrate  100 . If the device substrate  100  comprises the switches  101 , openings can be formed in the planarization layer  102  to expose terminals of the switches  101 . 
         [0025]    The optically reflective layers  110  corresponding to partial illumination regions are formed above the device substrate  100 . For example, the planarization layer  102  is formed in each of the illumination regions  100 R,  100 G,  100 B, and  100 W, and the optically reflective layer  110  is formed overlying the planarization layer  102 . The optically reflective layer  110  can be formed of aluminum or other optically reflective materials. Then, a layer of the first electrodes  120  is formed on the device substrate  100 , wherein the first electrodes  120  in the illumination regions  100 R,  100 G,  100 B, and  100 W are disposed on the optically reflective layer  110 . In this embodiment, the first electrodes  120  in the illumination regions  100 R and  100 W comprise bumps  120   b  and  120   a.  In other embodiments, the first electrode  120  in at least one of the illumination regions may comprise a bump or bumps of any types and any quantities, controlling the microcavities in every illumination region and adjusting light spectrums emitted from every illumination region. 
         [0026]    In  FIG. 1 , the aspect profiles of the bumps  120   b  and  120   a  are determined by the stacking structure of the first electrodes  120  comprising an electrode base layer  121  and island-like transparent layers  123  and  122 . The electrode base layer  121  is disposed in every illumination region, and preferably formed of the same material as that of the island-like transparent layers  122  and  123 , decreasing the quantities of heterogeneous interfaces along the optical paths. The first electrode  120  in the illumination region  100 R comprises the electrode base layer  121  covering the island-like transparent layers  123 . The first electrode  120  in the illumination region  100 W comprises the electrode base layer  121  covering the island-like transparent layers  122 . The first electrodes  120 , disposed in the illumination regions  100 G and  100 B without any bumps, comprise the electrode base layer  121 , but do not have any island-like transparent layers. Further, stacking sequences between the electrode base layer  121  and the island-like transparent layers  122 ,  123  of the bumps  120   a  and  120   b  can be reversed. 
         [0027]    In  FIG. 1 , the bump  120   a  and the island-like transparent layer  122  are respectively different from the bump  120   b  and the island-like transparent layer  123  in quantity, cross-sectional shape, and thickness. In other embodiments, the arrangements of the bump(s) and the island-like transparent layer(s) of the first electrode  120  in one of the illumination region is respectively different from that of the first electrode  120  in any other illumination region in quantity, cross-sectional shape, thickness, arranged patterns, aspect profiles, or combinations thereof. 
         [0028]    Referring to  FIGS. 2A through 2C , the constitution of bumps  125  are similar with or equivalent to those of the bumps  120   a  and  120   b  shown in  FIG. 1 . The interval between the bumps  125  in an illumination region  100 E 1  in  FIG. 2A  is different from that between the bumps  125  in an illumination region  100 E 2  in  FIG. 2B , and thus, the bumps  125  in the illumination regions  100 E 1  and  100 E 2  are arranged in different patterns. While the bumps  125  in the illumination regions  100 E 1  and  100 E 3  in  FIGS. 2A and 2C  are arranged in the same pattern, the positions of the bumps  125  in the illumination region  100 E 1  relative to the boundaries of the illumination region  100 E 1  are different from those of the bumps  125  in the illumination region  100 E 3  relative to the boundaries of the illumination region  100 E 3 . Thus, the aspect profile of the illumination region  100 E 1  and the bumps  125  therein is different from that of the illumination region  100 E 3  and the bumps  125  therein. The types of different arrangements of bumps  125  in the different illumination aforementioned regions can be applied to the bumps in every illumination region shown in  FIG. 1 . 
         [0029]    The island-like transparent layers  122  and  123  can be formed by subsequent processes according to the required thicknesses of the bumps  120   a  and  120   b.  An overall transparent electrode layer (not shown) is formed overlying the optically reflective layer  110 , followed by formation of a resist layer (not shown) overlying the transparent electrode layer. Then, a typical lithography step can be performed by utilization of a mask comprising a pattern of the island-like transparent layers  122  and  123 , followed by etching the transparent electrode layer, thus completing the island-like transparent layers  122  and  123  of a transparent and electrically conductive material. In some embodiments, the island-like transparent layers  122  and  123  with different thicknesses can be formed by utilization of a mask comprising patterns with different optical transparency in the lithography step. Next, the electrode base layer  121  of a transparent and electrically conductive material is coated overlying an overall surface of a structure of the device substrate  100  where the island-like transparent layers  122  and  123  are formed, and covers the island-like transparent layers  122  and  123 , revealing the aspect profiles of the bumps  120   a  and  120   b  and completing the first electrodes  120 , optionally followed by lithography and etching steps, electrically isolating the first electrodes  120  in every illumination region. Thus, the microcavities of the illumination device can be controlled by operation of only one step of a combination of material deposition and patterning. At this time, the first electrodes  120  in every illumination region are electrically isolated from each other. Further, optional pixel definition layers  130  can be formed overlying the first electrode  120  among the illumination regions  100 R,  100 G,  100 B, and  100 W as required. The pixel definition layers  130  are formed of a transparent dielectric, assisting electric isolation between the first electrodes  120 . 
         [0030]    Then, an illumination layer  140  is formed overlying the first electrodes  120 . The illumination layer  140  can be an organic electroluminescence illumination layer comprising several stacking layers, which include a hole injection layer (HIL), a hole transport layer (HTL), a main illumination layer, an electron transport layer (ETL), an electron injection layer (EIL), and etc. arranged in a sequence from the interface between the first electrodes  120  and the illumination layer  140 , for example. When the pixel definition layers  130  are formed, the illumination layer  140  covers the pixel definition layers  130 . Next, a second electrode  150  is formed overlying the illumination layer  140 . The optically reflective layer  110 , the first electrodes  120 , the illumination layer  140 , and the second electrode  150  of this embodiment can be formed of any known materials and known fabrication methods, and thus detailed descriptions thereof are abbreviated. 
         [0031]    In this embodiment, an organic light emitting diode comprises the optically reflective layer  110 , the first electrodes  120 , the illumination layer  140 , and the second electrode  150 . In an embodiment of the present invention, the microcavity between the optically reflective layer  110  and the second electrode  150  are controlled by controlling arrangements of the bumps of the first electrodes  120 , providing more adjustable factors for achieving a required frequency of an emitting light more accurately in contrast to prior art. In the prior art, the microcavity only can be controlled by controlling the thickness of the microcavity spacer layer or the transparent electrode. Further, the bumps of the first electrodes  120  can be formed by an additional step of a combination of film deposition and patterning, decreasing the production cycle time and process cost. Moreover, the optical paths of light reflected by the optically reflective layer  110  pass through the bumps of the first electrodes  120 . Thus, the variances between lengths of the optical paths of light with different emitting angles from the illumination device viewed can be decreased by appropriate arrangement of the bumps, widening the viewing angle of a system for displaying images of an embodiment of the invention. 
         [0032]    In  FIG. 1 , an optional passivation layer  160  can be formed overlying the second electrode  150  as required. The passivation layer  160  can be formed of a transparent dielectric layer with chemical passivity. 
         [0033]    The display panel  400  further comprises an opposite substrate  200 . There is a space S between the parallel substrates  200  and  100 . Thus, light rays from the illumination regions  100 R,  100 G,  100 B, and  100 W of the device substrate  100  reach and respectively pass through the corresponding light transmissive regions  200 R,  200 G,  200 B, and  200 W of the opposite substrate  200 . A light shielding layer  210  can be disposed overlying an incident surface  200   a  receiving light from the illumination regions  100 R,  100 G,  100 B, and  100 W among the light transmissive regions  200 R,  200 G,  200 B, and  200 W. The light shielding layer  210  can be formed of metals, polymers, or other light shielding materials with low optical reflection. 
         [0034]    In this embodiment, light rays from the illumination regions  100 R,  100 G,  100 B, and  100 W are all white, and thus, it is necessary to dispose a layer of color filters in at least some of the light transmissive regions of the opposite substrate  200 . Regarding the sequentially arranged light transmissive regions  200 R,  200 G,  200 B, and  200 W, for example, a red light color filter layer  220 R, a green light color filter layer  200 G and a blue light color filter layer  200 B are respectively disposed in the light transmissive regions  200 R,  200 G, and  200 B, but no color filter layer is disposed in the light transmissive region  200 W. As a result, a red light pixel region is formed by a combination of the illumination region  100 R and the light transmissive region  200 R, a green light pixel region is formed by a combination of the illumination region  100 G and the light transmissive region  200 G, a blue light pixel region is formed by a combination of the illumination region  100 B and the light transmissive region  200 B, and a white light pixel region is formed by a combination of the illumination region  100 W and the light transmissive region  200 W. 
         [0035]    In other embodiments, the illumination layer  140  in the illumination regions  100 R,  100 G,  100 B, and  100 W can respectively emit red, green, blue, and white light rays, and thus, no color filter layer is required. 
         [0036]      FIGS. 3A and 3B  show a system for displaying images of another preferred embodiment of the invention. The system comprises a display panel  400  or an electronic device  600 . 
         [0037]    As shown in  FIG. 3A , the display panel  400  can be utilized for fabricating various electronic devices  600  comprising the display panel  400  and an input unit  500 . The input unit  500  is coupled to the display panel  400 , inputting signals, such as image signals, into the display panel  400  for displaying images. The electronic device  600  can be a cell phone, a digital camera, a personal digital assistant (PDA), a notebook computer, a desktop computer, a television, a car display, or a portable digital video disc (DVD) player. 
         [0038]      FIG. 3B  shows an exemplary layout of the display panel  400 . The display panel  400  comprises a display area  410 , a scanning driver area  420 , a data driver area  430 , and an optional circuit area  440 . The display area  410  comprises a plurality of the switches  101  shown in  FIG. 1 . The scanning driver area  420  and the data driver area  430  are disposed by sides of the display area  410 . The scanning driver area  420  applies electrical voltage to pixel electrodes in the display area  410 . The data driver area  430  applies electrical voltage to gate electrodes of the thin film transistors in the display area  410 . 
         [0039]    Next, the effects of embodiments of the invention are verified by utilization of the display panels of the subsequent Comparative Example, Experimental Example 1, and Experimental Example 2. The process conditions and materials of the display panels of the three examples follow the aforementioned descriptions for the display panel  400  shown in  FIG. 1 , and all of the specific conditions can be utilized in any embodiments of the invention but cannot limit the claim scope of this application. 
         [0040]    First, controlled factors of the display panels of the three examples are subsequently listed. 
         [0041]    The material of the device substrates  100  was glass with a thickness between 0.3 mm and 0.7 mm. The switches  101  were polycrystalline silicon type thin film transistors. The planarization layers  102  were organic polymers or inorganic oxides, and between 2 μm and 3 μm thick. The optically reflective layers  110  were aluminum alloys and between 500 Å and 3000 Å thick. The pixel definition layers  130  were organic polymers or inorganic oxides, and between 0.1 μm and 5 μm thick. The illumination layers  140  comprised hole injection layers, hole transport layers, main illumination layers, electron transport layers, and electron injection layers. The second electrodes  150  were indium tin oxide and between 500 Å and 3000 Å thick. The passivation layers  160  were silicon oxide, and between 0.1 μm and 10 μm thick. The opposite substrates  200  were glass and between 0.3 mm and 0.7 mm thick. The light shielding layers  210  were formed. The layers of color filters comprised red light color filter layers  220 R, green light color filter layers  200 G and blue light color filter layers  200 B. The values of the space S were between 1 μm and 10 μm. 
         [0042]    Next, variable factors and conditions of the display panels of the three examples are subsequently listed. 
         [0043]    (a) The Comparative Example: The first electrode  120  without bumps, that is, consisting of the electrode base layers  121  only, were made of indium tin oxide with thickness of 800 Å. The hole transport layer was formed of NPB (N,N′-diphenyl-N,N′-bis(1-naphthyl)-1,1′-biphenyl-4,4′-diamine) with thickness of 300 Å. 
         [0044]    (b) The Experimental Example 1: The first electrode  120  comprised an 800 Å thick electrode base layer  121  and a pair of island-like transparent layers  122 , both of which were 300 Å thick. The electrode base layer  121  and the island-like transparent layers  122  were both made of indium tin oxide. The hole transport layer was formed of NPB with thickness of 300 Å. 
         [0045]    (c) The Experimental Example 2: The conditions of the first electrode  120  was the same as those in the experiment example 1. The hole transport layer was formed of NPB with thickness of 1700 Å. 
         [0046]    Chromaticity coordinates (defined by CIE 1931 standard) of light from the display panels of the Comparative Example, the Experimental Example 1, and the Experimental Example 2 were measured and listed in the subsequent Table 1. 
         [0000]    
       
         
               
               
               
               
               
               
               
             
               
               
               
               
               
               
               
               
               
               
               
               
               
             
           
               
                   
                 TABLE 1 
               
             
             
               
                   
                   
               
               
                   
                 white 
                 white 
                 white 
                   
                   
                   
               
               
                   
                 light in 
                 light in 
                 light in 
               
               
                   
                 CIE, and 
                 CIE, and 
                 CIE, and 
               
               
                   
                 viewing 
                 viewing 
                 viewing 
                 red 
                 green 
                 blue 
               
               
                   
                 angle is 0 
                 angle is 45 
                 angle is 60 
                 light in 
                 light in 
                 light in 
               
               
                   
                 degree 
                 degrees 
                 degrees 
                 CIE 
                 CIE 
                 CIE 
               
             
          
           
               
                   
                 CIE x 
                 CIE y 
                 CIE x 
                 CIE y 
                 CIE x 
                 CIE y 
                 CIE x 
                 CIE y 
                 CIE x 
                 CIE y 
                 CIE x 
                 CIE y 
               
               
                   
               
               
                 Comparative 
                 0.25 
                 0.30 
                 0.35 
                 0.23 
                 0.41 
                 0.29 
                 0.66 
                 0.33 
                 0.14 
                 0.55 
                 0.12 
                 0.11 
               
               
                 Example 
               
               
                 Experimental 
                 0.32 
                 0.27 
                 0.35 
                 0.29 
                 0.36 
                 0.30 
                 0.66 
                 0.33 
                 0.27 
                 0.57 
                 0.13 
                 0.14 
               
               
                 Example 1 
               
               
                 Experimental 
                 0.33 
                 0.31 
                 0.31 
                 0.31 
                 0.30 
                 0.32 
                 0.66 
                 0.33 
                 0.27 
                 0.57 
                 0.13 
                 0.14 
               
               
                 Example 2 
               
               
                   
               
             
          
         
       
     
         [0047]    According to the results shown in Table 1, the colorimetric purity performances of white light, red light, green light, and blue light provided by the display panels of the Experimental Examples 1 and 2 having the first electrodes  120  comprising bumps, both performed better than those provided by the display panel of the Comparative Example having the first electrodes  120  without bumps. Further, regarding the performance of wider viewing angle, the chrominance differences of the white light provided by the display panels of the Experimental Examples 1 and 2 between viewing angles of 0 degree, 45 degrees, and 60 degrees were all less than 0.02, and the wider viewing angle performances provided by the display panels of the Experimental Examples 1 and 2 were both better than that of the display panel of the Comparative Example. 
         [0048]    While the invention has been described by way of example and in terms of preferred embodiment, it is to be understood that the invention is not limited thereto. 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.