Patent Publication Number: US-7586262-B2

Title: Flat fluorescent lamp and liquid crystal display

Description:
BACKGROUND OF THE INVENTION 
   1. Field of Invention 
   The present invention relates to a light source module and a display apparatus. More particularly, the present invention relates to a flat fluorescent lamp (FFL) with high luminous efficiency and a liquid crystal display (LCD) using the same. 
   2. Description of Related Art 
   Along with the progress in modern video technology, LCDs have been greatly used in display screens of consumable electronic products such as mobile phones, notebooks, personal computers and personal digital assistants (PDAs). However, as the liquid crystal panel of an LCD itself cannot emit light, a backlight module disposed under the liquid crystal panel is required to provide the display light source desired by the liquid crystal panel. Recently, the backlight modules on the market are mainly FFLs, cold cathode fluorescent lamps (CCFLs) and light emitting diodes (LEDs), wherein the FFLs are widely used in LCDs due to the advantages of being low in cost, taking up a small space and so on. 
     FIG. 1  is a partial sectional view of a conventional FFL, and  FIG. 2  is a top view of the FFL. In order to make the figure clear, a part of the means in  FIG. 1  is not shown in  FIG. 2 . Referring to  FIG. 1  and  FIG. 2 , a conventional FFL  100  forms a plurality of discharge spaces  132  between an upper substrate  120  and a lower substrate  110  via spacers  130 , wherein a discharge gas  140  is filled into the discharge spaces  132 . Moreover, an electrode set  150  is disposed on the lower substrate  110  in each of the discharge spaces  132 . The electrode set  150  comprises a first strip electrode  152  and a second strip electrode  154  (the electrodes  152 ,  154  are either anode or cathode). A dielectric layer  160  lies on the electrode set  150  to protect the electrode set  150 . Moreover, a fluorescent material  170  is coated on the outer walls of the upper substrate  120  and the dielectric layer  160 . 
   When a driving voltage is applied to the electrode set  150 , an electric field is formed between the first strip electrode  152  and the second strip electrode  154 , for dissociating the discharge gas  140  into plasma. Then, the electrons in an excited state in each ion in the plasma may emit UV light when returning to a ground state, and when the UV light emitted by the plasma irradiates the fluorescent material  170 , the fluorescent material  170  is excited to emit light. 
   It should be noted that conventionally to enhance the effect of the electric field to the discharge gas  140 , a plurality of electrode branches  152   a  is generally formed on both sides of the first strip electrode  152 , so as to form a main triangular discharge area  156  with the opposite second strip electrode  154  via the point discharge of the electrode branches  152   a . However, in practice, the brightness of the discharge area  156  is usually quite different from that of other areas except the discharge area  156 , thus affecting the uniformity of the whole surface light source. According to the practical situation, when the brightness of the top ends of the electrode branches  152   a  reaches 10000 nit, the brightness of other areas only reaches 6000 nit, and when the brightness of the top ends of the electrode branches  152   a  reaches 7000 nit, the brightness of other areas only reaches 4000 nit. 
   SUMMARY OF THE INVENTION 
   Accordingly, an objective of the present invention is to provide an FFL which has a better luminous efficiency and may output a uniform surface light source. 
   Another objective of the present invention is to provide an LCD, which achieves a better display effect via the above-mentioned FFL. 
   In order to achieve the above or other objectives, the present invention provides an FFL, which comprises a first substrate, a plurality of electrode sets, a patterned dielectric layer, a plurality of dielectric branches, a second substrate, a plurality of spacers, a fluorescent material and a discharge gas. The electrode sets are disposed on the first substrate, and each electrode set at least comprises a first strip electrode and a second strip electrode parallel to each other, wherein the side edge of the first strip electrode has a plurality of electrode branches extending towards the second strip electrode. Moreover, the patterned dielectric layer and the dielectric branches are disposed on the first substrate, wherein the patterned dielectric layer covers the electrode sets, and the dielectric branches are disposed around the electrode branches. Further, the second substrate is disposed opposite to the first substrate, and the spacers connect the first substrate and the second substrate, so as to form a plurality of discharge spaces between the first substrate and the second substrate. Each of the discharge spaces has an electrode set, and the fluorescent material and the discharge gas are disposed in the discharge spaces. 
   In an embodiment of the present invention, the dielectric branches adjoin the patterned dielectric layer above the first strip electrodes or adjoin the patterned dielectric layer above the second strip electrodes. 
   In the embodiment of the present invention, the dielectric branches on both sides of each electrode branch are parallel to each other. 
   In the embodiment of the present invention, a plurality of discharge areas is formed between the electrode branches of each first strip electrode and the opposite second strip electrode, and the dielectric branches are disposed along the edges of the discharge areas. 
   In the embodiment of the present invention, a part of the fluorescent material is distributed on both side walls of each dielectric branch, wherein one side of each dielectric branch far away from the electrode branch acquires more fluorescent material than the other side close to the electrode branch. 
   In the embodiment of the present invention, the patterned dielectric layer above each second strip electrode has a plurality of recesses, wherein the recesses in each discharge space are opposite to the electrode branches, and each recess is disposed between two adjacent dielectric branches. Moreover, another part of the fluorescent material is distributed in the recesses, and between the patterned dielectric layer above each second strip electrode and the adjacent spacer. 
   In the embodiment of the present invention, the above-mentioned FFL further comprises a reflecting layer, which is disposed above the first substrate and under the electrode sets. 
   The present invention further provides an LCD mainly formed by the above-mentioned FFL and a liquid crystal panel, wherein the FFL is disposed beside the liquid crystal panel for providing the backlight source required by the liquid crystal panel. 
   In view of the above, in the present invention, a plurality of dielectric branches is formed around the electrode branches, for increasing the coating area of the fluorescent material and adjusting the distribution position of the fluorescent material, so as to enhance the brightness of the FFL and improve the uniformity of the output light. Thus, the LCD achieves a better display effect. 
   In order to make the aforementioned and other objectives, features and advantages of the present invention comprehensible, preferred embodiments accompanied with drawings are described in detail below. 

   
     BRIEF DESCRIPTION OF THE DRAWINGS 
       FIG. 1  is a partial sectional view of a conventional FFL. 
       FIG. 2  is a top view of the FFL in  FIG. 1 . 
       FIG. 3  is a partial sectional view of an FFL according to a preferred embodiment of the present invention. 
       FIG. 4A  is a top view of the FFL in  FIG. 3 . 
       FIG. 4B  is a schematic partial view of the structures of the dielectric layer and the electrode in  FIG. 3 . 
       FIG. 5A  is a top view of another FFL of the present invention. 
       FIG. 5B  is a schematic partial view of the structures of the dielectric layer and the electrode in  FIG. 5A . 
       FIG. 6  is a schematic partial view of the structures of the dielectric layer and the electrode according to another embodiment of the present invention. 
       FIGS. 7 and 8  are respectively sectional views of the dielectric layer and the electrode of  FIG. 6  at different positions. 
       FIG. 9  is a schematic view of the LCD of the present invention. 
   

   DESCRIPTION OF EMBODIMENTS 
   The present invention can be applied to various FFLs, for solving the problem of non-uniformity of the output light due to the point discharge of the electrode branches. Recently, in a common FFL, the arrangements of the electrode sets are different, for example, each discharge space only has a pair of first strip electrode and second strip electrode, or has a plurality of interlaced first strip electrodes and second strip electrodes. Moreover, the shape of the electrode branch is various, such as square, circular and triangle. One of the above arrangements and shapes are illustrated as an example in the following embodiments, but they are not intended to limit the application scope of the present invention. The existing FFLs all can adopt the design of the dielectric branches provided by the present invention to improve the uniformity of the output light, or to further enhance the luminous efficacy of the output light. 
     FIG. 3  is a partial sectional view of an FFL according to a preferred embodiment of the present invention. As shown in  FIG. 3 , an FFL  300  comprises a first substrate  310 , a second substrate  320 , a plurality of spacers  330 , a discharge gas  340 , a plurality of electrode sets  350 , a patterned dielectric layer  360  and a fluorescent material  370 . The first substrate  310  is disposed opposite to the second substrate  320 , and the spacers  330  are connected between the first substrate  310  and the second substrate  320 , so as to form a plurality of discharge spaces  332  between the first substrate  310  and the second substrate. 
   Referring to  FIG. 3 , the discharge gas  340 , for example, an inert gas such as xenon, neon or argon, is filled in the discharge space  332 . The electrode set  350  is disposed on the first substrate  310 , wherein each electrode set  350  comprises an interlaced first strip electrode  352  and second strip electrode  354 , for being an anode and a cathode respectively. Moreover, the patterned dielectric layer  360  covers the electrode set  350 , so as to protect the electrode set  350  from being directly bombarded by the plasma ion. Moreover, the fluorescent material  370  is, for example, coated on the outer walls of the second substrate  320  and the dielectric layer  360 . A reflecting layer  312 , for example, made of metal is further formed on the first substrate  310  and under the electrode set  350 , for increasing the luminous efficiency. When a driving voltage is applied to the electrode set  350 , an electric field can be generated between the first strip electrode  352  and the second strip electrode  354 , for dissociating the discharge gas  340  into plasma. After that, the electrons in an excited state in each ion in the plasma may emit UV light when returning to a ground state, and when the UV light emitted by the plasma irradiates the fluorescent material  370 , the fluorescent material  370  is excited to emit light. 
     FIG. 4A  is a top view of the FFL  300 , and  FIG. 4B  is a schematic partial view of the structures of the dielectric layer and the electrode according to the present embodiment. In order to make the figure clear, the second substrate  320 , discharge gas  340 , fluorescent material  370  and other means in  FIG. 3  are not shown in  FIG. 4A . Referring to  FIG. 4A  and  FIG. 4B , a plurality of electrode branches  352   a  extending towards the second strip electrodes  354  is formed on both sides of the first strip electrode  352 , and a plurality of discharge areas  356  is formed between the electrode branches  352   a  and the opposite second strip electrodes  354  due to the point discharge of the electrode branches  352   a.    
   In the present embodiment, in order to improve the brightness and the luminous efficiency of the FFL  300 , a dielectric branch  380  is disposed respectively on both sides of the electrode branch  352   a . The dielectric branch  380 , for example, adjoins the patterned dielectric layer  360  above the second strip electrode  354 , and the dielectric branches  380  on both sides of each electrode branch  352   a  are parallel to each other, wherein a preferred scope of the height of the dielectric branches  380  is smaller than or equal to the thickness of the patterned dielectric layer  360 . Moreover, the dielectric branch  380  is, for example, fabricated by lamination printing with screen mask. 
   As the dielectric branches  380  are disposed on the both sides of the electrode branch  352   a , the coating area of the fluorescent material  370  is increased (for example, the side wall of the dielectric branches  380 ). In the present invention, the coating manners of the fluorescent material  370  are various, for example, the fluorescent material  370  can be uniformly distributed on both side walls of each dielectric branch  380  for increasing the coating area of the whole fluorescent material  370 , thus enhancing the luminous efficiency. Moreover, as the discharge area  356  has a high discharge efficiency, one side of each dielectric branch  380  far away from the electrode branch  352   a  may acquire more fluorescent material  370  than the other side close to the electrode branch  352   a , so as to compensate the discharge efficiency, thereby improving the uniformity of the whole surface light source. 
   The following table is the relation after comparing the brightness of the FFL of the present invention and a conventional FFL in practical operation, wherein the dimension of the dielectric branch adopted by the present invention is 3500×500×140 μm, and the thickness of the fluorescent material is 70 μm. It is known from the following table that the overall brightness of the FFL of the present invention is apparently higher than that of the conventional art. 
   
     
       
         
             
             
             
             
           
             
                 
                 
             
             
                 
               Brightness of 
               Brightness of 
               Overall 
             
             
                 
               Discharge Area 
               Other Areas 
               Brightness 
             
             
                 
                 
             
           
          
             
                 
             
          
         
         
             
             
             
             
          
             
               Conventional 
               12470 nit 
                9105 nit 
               10596 nit 
             
             
               Structure 
             
             
               Structure of Present 
               15022 nit 
               10188 nit 
               12393 nit 
             
             
               Invention 
             
             
               Rate of 
               above 20.5% 
               above 11.9% 
               above 17% 
             
             
               Improvement 
             
             
                 
             
          
         
       
     
   
   In the above embodiment, the dielectric branch adjoins the patterned dielectric layer opposite to the electrode branch. Besides, in other embodiments of the present invention, the dielectric branch, for example, adjoins the patterned dielectric layer on the same side as the electrode branch (i.e. above the first strip electrode), or is disposed at any appropriate position around the electrode branch. Moreover, the dielectric branches on both sides of the electrode branch can not only be disposed in parallel, but also, for example, disposed along the edges of the discharge areas, for achieving a better luminous efficiency. 
     FIG. 5A  is a top view of another FFL of the present invention, and  FIG. 5B  is a schematic partial view of the structures of the dielectric layer and the electrode of the present embodiment. In order to make the figure clear, only a part of the means are shown in  FIGS. 5A and 5B , and the complete structure can be seen in  FIG. 3  with reference to the related descriptions. In the present embodiment, a dielectric branch  580  is disposed along a discharge area  556  between an electrode branch  552   a  and a second strip electrode  554 , wherein similarly, a preferred scope of the thickness of the dielectric branch  580  is smaller than that of a patterned dielectric layer  560 . Besides, the dielectric branch  580  can also be fabricated by lamination printing with screen mask. 
   As the dielectric branch  580  of the present embodiment is disposed along the edge of the discharge area  556 , the discharge area  556  can be used effectively, such that the fluorescent material (not shown) on the side wall of the dielectric branch  580  adjacent to the discharge area  556  can fully react, so as to enhance the brightness of the output light. Moreover, the present embodiment can also modify the coating amount of the fluorescent material on both side walls of the dielectric branch  580  for adjusting the luminous effect, which will not be described in detail herein. 
   In addition to the above embodiments, the present invention can further enhance the luminous efficiency of the FFL. Referring to the above embodiments, when a driving voltage is applied to the electrode set, the dissociated plasma is generated between the first strip electrode and the second strip electrode, so the main light-emitting area of the FFL is located between the first strip electrode and the second strip electrode. In other words, as it is not easy to form an electric field between the spacer and the adjacent strip electrode, a dark area is formed. In order to solve the above problem, in the present invention, the conventional structure of the patterned dielectric layer can be designed to increase the operating area of the electric field in the discharge space, so as to improve the brightness of the FFL. The embodiment for illustration is as follows. 
     FIG. 6  is a schematic partial view of the structures of the dielectric layer and the electrode according to another embodiment of the present invention, and  FIG. 7  and  FIG. 8  are respectively sectional views of the dielectric layer and the electrode at different positions. The present embodiment varies based on the structure of the FFL as shown in  FIGS. 4A and 4B , so  FIGS. 6˜8  adopt the same numerals as those of the  FIGS. 4A and 4B  to indicate the similar elements, and the descriptions of the related elements can refer to the above embodiments, which will not be described in detail herein. As shown in  FIG. 6 , in the structures of the dielectric layer and the electrode of the present invention, a plurality of dielectric branches  380  is fabricated on the side surface of the patterned dielectric layer  360  above the second strip electrode  354  (referring to  FIG. 4A ), and in addition, a plurality of recesses  362  is formed on the patterned dielectric layer  360 . The recesses  362  are, for example, opposite to the electrode branch  352   a  on the first strip electrode  352 , and disposed between two adjacent dielectric branches  380 . As the patterned dielectric layer  360  has the recesses  362  disposed thereon, in the present embodiment, as shown in  FIG. 7 , the fluorescent material  370  is coated in the recesses  362  to increase the coating area of the fluorescent material  370 , thereby enhancing the whole luminous efficiency of the FFL. 
   Moreover, when discharging occurs between the electrode branch  352   a  and the opposite second strip electrode  354 , the generated electric field may affect the non-emitting areas between the spacer  330  and the adjacent second strip electrode  354  via the recesses  362 . Therefore, the present embodiment may be as shown in  FIG. 8 , wherein the fluorescent material  370  is coated on the areas between the spacer  330  and the patterned dielectric layer above the adjacent second strip electrode  354 , or the fluorescent material  370  originally coated on the position may be affected by the dissociated plasma to emit light. In other words, the design of forming the recesses  362  on the patterned dielectric layer  360  of the present embodiment not only increases the coating area of the fluorescent material  370 , but also enables areas that do not emit light originally to emit light by being affected by the electric field. Therefore, the luminous efficiency of the FFL is further enhanced. 
   The present invention further provides an LCD which utilizes the above-mentioned FFL.  FIG. 9  is a schematic view of the LCD of the present invention, wherein an LCD  900  mainly comprises a liquid crystal panel  910  and an FFL  920 . In the present embodiment, the FFL  920  may be one of the various FFLs provided by the present invention, and the liquid crystal panel  910  is disposed above the FFL  920 , for using the surface light source provided by the FFL  920  as the display light source. 
   To sum up, in the FFL and LCD of the present invention, a plurality of dielectric branches is formed around the electrode branches, so as to increase the coating area of the fluorescent material to improve the luminous efficiency of the FFL, thereby enhancing the display brightness of the LCD. Moreover, in the present invention, the distribution position of the fluorescent material is adjusted by the dielectric branches for compensating the discharge efficiency in different areas, so as to improve the uniformity of the whole surface light source, and make the LCD achieve a better display effect. 
   Though the present invention has been disclosed above by the preferred embodiments, they are not intended to limit the present invention. Anybody skilled in the art can make some modifications and variations without departing from the spirit and scope of the present invention. Therefore, the protecting range of the present invention falls in the appended claims.