Patent Publication Number: US-2007114928-A1

Title: Planar light source and method for fabricating the same

Description:
BACKGROUND OF THE INVENTION  
      1. Field of Invention  
      The present invention relates to a planar light source and the fabricating method thereof. More particularly, the present invention relates to a planar light source with a simple structure and the fabricating method thereof with simplified process.  
      2. Description of Related Art  
      The planar light source is widely used in the backlight of LCD display panels and even other fields because it has excellent light-emitting efficiency and evenness, and is capable of providing the light source for a large area. The planar light source is a kind of plasma light-emitting device, wherein, electrons emitted from the cathode will move between the cathode and the anode and collide with the inert gas in the discharge space so that the gas will be ionized and excited to form plasma. After that, the excited atoms in the plasma will degenerate into ground state with emitting Ultra-Violet, and the emitted ultra violet will further excite the phosphor in the planar light source to produce the visible light.  
       FIG. 1  is a diagram of a conventional planar light source.  FIG. 1 A  is a partial cross-sectional view of the planar light source in  FIG. 1 . Referring to both  FIGS. 1 and 1 A, the conventional planar light source  100  includes an upper substrate  110 , a lower substrate  120 , a phosphor layer  130   a , another phosphor layer  130   b , a reflective layer  140 , a dielectric layer  150 , electrode modules  160 , a plurality of spacers  170 , and a discharge gas (not shown) located in the discharge spaces  180 . Wherein, the electrode modules  160  include anodes  160   a  and cathodes  160   b . When the electrons (not shown) emitted from the cathodes  160   b  move towards the anodes  160   a , the electrons will collide with the discharge gas in the discharge spaces  180  to turn the discharge gas into plasma. Next, the phosphor layers  130   a  and  130   b  will be excited by the ultra violet emitted from the plasma to give off visible light.  
      Referring to  FIGS. 1 and 1 A again, to maintain the discharge spaces  180 , a plurality of spacers  170  are disposed to support the upper substrate  110  and the lower substrate  120 . However, the disposition of the spacers  170  will occupy some space between the upper substrate  110  and the lower substrate  120 , therefore the discharge spaces  180  will be reduced accordingly. As a result, the coating area of the phosphor layers  130   a  and  130   b  located in the discharge spaces  180  will also be reduced. Moreover, frit glue will be used when the spacers  170  are disposed to paste the spacers  170  on the lower substrate  120 .  
       FIG. 1B  is a partial enlarged view of area A in  FIG. 1A . Referring to  FIG. 1B , the frit glue  190  is used for pasting the spacers  170  on the lower substrate  120 . However, the frit glue  190  will react with the reflective layer  140  and the lower substrate  120  so that the part of the reflective layer  140  and the lower substrate  120  in contact with the frit glue  190  will be eroded. Accordingly, a crack  195  will occur in the part of the reflective layer  140  and the lower substrate  120 . This will not only affect the fastening effect of the spacers  170  to the lower substrate  120 , but also damage the reflective layer  140  and the lower substrate  120 . Certainly, the same problem will happen to the upper substrate  110  connected to the spacers  170 .  
      Moreover, the fabricating process of the conventional planar light source is very complicated.  FIG. 2  is the fabricating flowchart of a lower substrate of the planar light source in  FIG. 1 . Referring to both  FIGS. 1 and 2 , first, the lower substrate  120  is provide, as shown in step  210 . Then, the reflective layer  140  is fabricated on the lower substrate  120 , as shown in step  220 . Next, a plurality of electrode modules  160  are fabricated on the reflective layer  140 , as shown in step  230 . After that, the dielectric layer  150  is formed to cover the electrode modules  160 , as shown in step  240 . Next, the phosphor layer  130   b  is formed on the dielectric layer  150 , as shown in step  250 .  
      Note that in step  240 , the required pattern and thickness of the dielectric layer  140  located on the lower substrate  120  are acquired through multiple printing processes. Since the printing process is time-consuming, the production capacity of the lower substrate  120  is decreased. Moreover, the printing process may result in uneven thickness of the pattern film due to printing shift; accordingly the light-emitting performance of different areas may be very different.  
      In particular, the step of disposing the spacers  170  must be performed to maintain the discharge spaces  180  when the upper substrate  110  and the lower substrate  120  are bound together. Since a plurality of spacers  170  are pasted respectively on the lower substrate  120  by the frit glue  190 , the process of disposing the spacers  170  will be time-consuming and complicated, thus the production capacity of the planar light source  100  cannot be improved.  
     SUMMARY OF THE INVENTION  
      Accordingly, the present invention is directed to provide a planar light source which can increase the coating area of the phosphor layer and prevent cracks in the substrate.  
      According to another aspect of the present invention, a fabricating method for a planar light source is provided, which has simple process and can increase the yield of the planar light source.  
      To accomplish the aforementioned and other objectives, the present invention provides a planar light source including a first substrate, a plurality of electrode modules, a second substrate, a plurality of dielectric spacers, a first phosphor layer, and a discharge gas. The electrode modules are disposed on the first substrate. The second substrate is disposed above the first substrate. The dielectric spacers cover the electrode modules and are connected between the first substrate and the second substrate, and the dielectric spacers divide the space between the first substrate and the second substrate into a plurality of discharge spaces. The first phosphor layer is disposed in the discharge spaces. The discharge gas is disposed in the discharge spaces.  
      In an embodiment of the present invention, the width of the part of each of the dielectric spacers in contact with the first substrate is greater than the width of the part in contact with the second substrate, and the cross section of each dielectric spacer is, for example, a trapezoid.  
      In an embodiment of the present invention, the thicknesses of the dielectric spacers are between about 100 μm and 5,000 μm.  
      In an embodiment of the present invention, the planar light source further includes a second phosphor layer covering the surface of the second substrate.  
      In an embodiment of the present invention, each of the dielectric spacers includes a top section and a body section, and the planar light source further includes a third phosphor layer disposed on the second substrate, and located between the top sections and in the discharge spaces.  
      In an embodiment of the present invention, the planar light source further includes a reflective layer disposed between the first substrate and the electrode modules.  
      In an embodiment of the present invention, the material of the electrode modules is selected from the group including silver, copper, and combinations thereof.  
      In an embodiment of the present invention, the discharge gas is selected from the group including xenon gas, neon gas, argon gas, and combinations thereof.  
      To accomplish the aforementioned and other objectives, the present invention further provides a fabricating method for the planar light source. First, the first substrate is provided whereon a plurality of electrode modules have been formed. Then, the dielectric material layer covering the electrode modules and having a thickness is formed on the first substrate. Next, the dielectric material layer is patterned to form a plurality of dielectric spacers. Next, the second substrate is provided and the space between the first substrate and the second substrate is divided into a plurality of discharge spaces by the dielectric spacers. After that, the first phosphor layer is formed in the discharge spaces. Then, the first substrate and the second substrate are bound together, and meanwhile, the discharge spaces are filled with the discharge gas, wherein the dielectric spacers are connected between the first substrate and the second substrate.  
      In an embodiment of the present invention, the method of forming the dielectric material layer on the first substrate includes a coating process.  
      In an embodiment of the present invention, a sinter process is further performed to the dielectric material layer after the dielectric material layer has been formed on the first substrate.  
      In an embodiment of the present invention, the thickness of the dielectric material layer is between about 100 μm and 5,000 μm.  
      In an embodiment of the present invention, the method of patterning the dielectric material layer includes the following steps: first, a photoresist film is adhered to the dielectric material layer; after that, a lithography process is performed to the photoresist film to form a patterned photoresist film; next, an etching process is performed to the dielectric material layer by using the patterned photoresist film as the etching mask to form dielectric spacers.  
      In an embodiment of the present invention, the method of forming the first phosphor layer in the discharge spaces includes a coating process.  
      In an embodiment of the present invention, the fabricating method for the planar light source further includes forming the second phosphor layer on the surface of the second substrate.  
      In an embodiment of the present invention, the fabricating method for the planar light source further includes forming a reflective layer on the first substrate before the electrode modules are formed.  
      Since in the present invention, dielectric spacers are used to replace the conventional spacers, the space occupied by the conventional spacers can be reduced and the discharge space of the planar light source in the present invention can be increased. Accordingly, the coating area of the phosphor layer in the discharge spaces can be increased. Moreover, the dielectric spacers are formed through a photolithography process. Because of without using frit glue, cracks can be prevented in the substrate. Furthermore, because the dielectric spacers are formed in a film deposition process combined with a photolithography process, the fabricating process of the planar light source in the present invention is simpler compared to the conventional process of fabricating the dielectric layer by multiple printing processes. Accordingly, the yield of planar light source can be increased.  
      In order to make the aforementioned and other objects, features and advantages of the present invention comprehensible, a preferred embodiment accompanied with figures is described in detail below.  
      It is to be understood that both the foregoing general description and the following detailed description are exemplary, and are intended to provide further explanation of the invention as claimed. 
    
    
     BRIEF DESCRIPTION OF THE DRAWINGS  
      The accompanying drawings are included to provide a further understanding of the invention, and are incorporated in and constitute a part of this specification. The drawings illustrate embodiments of the invention and, together with the description, serve to explain the principles of the invention.  
       FIG. 1  is a diagram of a conventional planar light source.  
       FIG. 1A  is a partial cross-sectional view of the planar light source in  FIG. 1 .  
       FIG. 1B  is a partial enlarged view of area A in  FIG. 1A .  
       FIG. 2  is a fabricating flowchart of a lower substrate of the planar light source in  FIG. 1 .  
       FIG. 3  is a diagram of a planar light source according to an embodiment of the present invention.  
       FIG. 4  is a diagram of another planar light source according to an embodiment of the present invention.  
       FIGS. 5A  to  5 G are cross-sectional diagrams illustrating a fabricating method for a planar light source according to an embodiment of the present invention. 
    
    
     DESCRIPTION OF EMBODIMENTS  
       FIG. 3  is a diagram of a planar light source according to an embodiment of the present invention. Referring to  FIG. 3 , the planar light source  300  includes a first substrate  310 , a plurality of electrode modules  320 , a second substrate  330 , a plurality of dielectric spacers  340 , a phosphor layer  350 , and a discharge gas  360 . The electrode modules  320  are disposed on the first substrate  310 . The second substrate  330  is disposed above the first substrate  310 . The dielectric spacers  340  cover the electrode modules  320  and are connected between the first substrate  310  and the second substrate  330 , and the space between the first substrate  310  and the second substrate  330  is divided into a plurality of discharge spaces  370  by the dielectric spacers  340 . The phosphor layer  350  is disposed in the discharge spaces  370 . The discharge gas  360  is disposed in the discharge spaces  370 .  
      Referring to  FIG. 3  again, in an embodiment, the first substrate  310  is, for example, a glass substrate. The electrode modules  320  include anodes  320   a  and cathodes  320   b , wherein the electrode modules  320  are arranged on the first substrate  310  in the sequence of anode  320   a , cathode  320   b , anode  320   a , and cathode  320   b . However, the electrode modules  320  may also be arranged on the first substrate  310  in the sequence of anode  320   a , cathode  320   b , cathode  320   b , and anode  320   a  (not shown). In addition, the material of the electrode modules  320  is selected from the group including silver, copper, and combinations thereof.  
      The second substrate  330  is, for example, a glass substrate. The planar light source  300  further includes another phosphor layer  390  covering the surface of the second substrate  330 . Thus, the ultra violet emitted by the plasma in the discharge spaces  370  can further excite another phosphor layer  390  to give off the visible light in addition to exciting the phosphor layer  350  to give off the visible light, so that the brightness of the planar light source  300  is increased. In an embodiment, the planar light source  300  may also have a reflective layer  380  disposed between the first substrate  310  and the electrode modules  320 . The reflective layer  380  is fabricated with a material of high reflectivity and is used for reflecting visible light to further improve the efficiency of visible light utilization. The discharge gas  360  is inert gas filling up the discharge spaces  370 . In an embodiment, the discharge gas  360  is selected from the group including xenon gas, neon gas, argon gas, and combinations thereof.  
      Note that in the present invention, the dielectric spacers  340  are disposed to replace the conventional spacers  170 . In an embodiment, the width WI of the part of each dielectric spacer  340  in contact with the first substrate  310  is greater than the width W 2  of the part in contact with the second substrate  330 , and the cross section of each dielectric spacer  340  is, for example, a trapezoid, as shown in  FIG. 3 . Accordingly, the dielectric spacers are more supportive and so can better maintain the discharge spaces  370  between the first substrate  310  and the second substrate  330 . Moreover, the thicknesses of the dielectric spacers  340  are between, for example, about 100 μm and 5,000 μm. In other words, the thicknesses of the dielectric spacers  340  correspond to the thicknesses of the conventional spacers  170 . Therefore, the conventional spacers  170  are omitted in the present invention, and the discharge spaces  370  between the first substrate  310  and the second substrate  330  are maintained by the dielectric spacers  340 .  
       FIG. 4  is a diagram of another planar light source according to an embodiment of the present invention. Referring to  FIG. 4 , the composition of the planar light source  302  is similar to the composition of the planar light source  300  shown in  FIG. 3 , wherein same reference numerals refer to the same elements. Note that in the present embodiment, each dielectric spacer  340  includes a top section  342  and a body section  344 , and the planar light source  302  further includes a phosphor layer  392  disposed on the second substrate  330  and located between the top sections  342  and in the discharge spaces  370 . To be specific, in the planar light source  302 , the top sections  342  of the dielectric spacers  340  are disposed on the second substrate  330  and the body sections  344  of the dielectric spacers  340  are disposed on the first substrate  310 . Thus, the dielectric spacers  340  as shown in  FIG. 4  can support the first substrate  310  and the second substrate  330  better to maintain the discharge spaces  370 . In particular, the first substrate  310  and the second substrate  330  can be aligned effectively through the top sections  342  and the body sections  344 , so that the binding precision is improved. Moreover, the disposition of the phosphor layer  392  shown in  FIG. 4  may reduce the usage of the phosphor layer  392  and may further reduce the fabricating cost of the planar light source  302 .  
      In overview, the dielectric spacers  340  in the present invention act as the conventional spacers  170 . Since the conventional spacers  170  are not needed in the present invention, the discharge spaces  370  of the planar light source  300  and  302  in the present invention are larger compared to that of the conventional planar light source  100 . Accordingly, the coating area of the phosphor layer  350  is increased and further the brightness of the planar light sources  300  and  302  is increased too. Moreover, since the conventional spacers  170  are not needed in the present invention, and the dielectric spacers  340  are fabricated through a film deposition process and a photolithography process, frit glue is not needed. Accordingly, cracks can be prevented in the substrate. The fabricating method for a planar light source in the present invention will be described below.  
       FIGS. 5A  to  5 G are cross-sectional diagrams of a fabricating method for a planar light source according to an embodiment of the present invention. First, a first substrate  410  is provided whereon a plurality of electrode modules  420  have been formed, as shown in  FIG. 5A . In an embodiment, the electrode modules  420  have, for example, anodes  420   a  and cathodes  420   b , and the formation method of the electrode modules  420  is, for example, a printing process, or by forming an electrode material layer (not shown) on the surface of the first substrate  410 , then forming the electrode modules  420  through a photolithography process. This method is known to those skilled in the art so will not be explained again. In addition, in an embodiment, a reflective layer  430  may be formed on the first substrate  410  before the electrode modules  420  are formed. The formation method of the reflective layer  430  is, for example, a printing or coating process.  
      Next, a dielectric material layer  440  covering the electrode modules  420  and having a thickness d is formed on the first substrate  410 , as shown in  FIG. 5B . In an embodiment, the method of forming the dielectric material layer  440  on the first substrate  410  includes a coating process, and the thickness of the formed dielectric material layer  440  is between about 100 μm and 5,000 μm. In addition, a sinter process  450  is further performed to the dielectric material layer  440  to solidify the dielectric material layer  440  after the dielectric material layer  440  has been formed on the first substrate  410 .  
      Again, the dielectric material layer  440  is patterned to form a plurality of dielectric spacers  470 . In an embodiment, the method of patterning the dielectric material layer  440  is, for example, through the steps shown in  FIG. 5C  to  5 E. First, as shown in  FIG. 5C , a photoresist film  460  is adhered to the dielectric material layer  440 . After that, as shown in  FIG. 5D , a lithography process is performed to the photoresist film  460  to form a patterned photoresist film  460   a . Next, an etching process is performed to the dielectric material layer  440  by using the patterned photoresist film  460   a  as the etching mask to form a plurality of dielectric spacers  470  as shown in  FIG. 5E . Note that since the thickness of the dielectric material layer  440  corresponds to the thickness of the conventional spacers  170 , the dielectric spacers  470  formed by the photolithography process have the effect as spacers.  
      In the present invention, the dielectric spacers  470  are formed by using the dielectric material layer  440 . Compared to the conventional planar light source  100 , where both the dielectric layer  140  and the spacers  170  are disposed, the process of the present invention is simpler. And the dielectric spacers  470  are fabricated through a film deposition process combined with a photolithography process; therefore, uneven thickness of the pattern film incurred by printing shift in the conventional technology, which may further result in different light-emitting performance at different areas, may be avoided.  
      Next, a second substrate  480  is provided, wherein the space between the first substrate  410  and the second substrate  480  is divided into a plurality of discharge spaces  500  by the dielectric spacers  470 , as shown in  FIG. 5F . In an embodiment, a phosphor layer  490   a  is further formed on the surface of the second substrate  480 ; the phosphor layer  490   a  is, for example, fully covering the second substrate  480  as shown in  FIG. 5F , or is formed correspondingly in the discharge spaces  500 , as shown in  FIG. 4 . Moreover, a dielectric layer (not shown) may be further formed on the second substrate  480 , which may be bound with the dielectric spacers  470  correspondingly to form the structure of the dielectric spacers  340  as shown in  FIG. 4 . Accordingly, the binding precision of the first substrate  410  and the second substrate  480  can be enhanced.  
      After that, a phosphor layer  490   b  is formed in the discharge spaces  500 , as shown in  FIG. 5F . In an embodiment, the method of forming the phosphor layer  490   b  in the discharge spaces  500  includes a coating process.  
      Next, the first substrate  410  and the second substrate  480  are bound together, and meanwhile, the discharge spaces  500  are filled with the discharge gas  510 , wherein the dielectric spacers  470  are connected between the first substrate  410  and the second substrate  480 , as shown in  FIG. 5G . Accordingly, the discharge spaces  500  between the first substrate  410  and the second substrate  480  can be maintained by the dielectric spacers  470 .  
      In overview, the planar light source and the fabricating method thereof in the present invention have at least the following advantages:  
      (1) The space occupied by the conventional spacers can be reduced by replacing the conventional spacers with dielectric spacers. Accordingly, the discharge spaces can be increased, and further the coating area of the phosphor layer in the discharge spaces can be increased.  
      (2) Cracks in the substrate can be prevented since frit glue is not used in the present invention.  
      (3) Since the dielectric spacers are fabricated through a film deposition process combined with a photolithography process, compared to the conventional process, where the dielectric layer is fabricated and a plurality of spacers are disposed through multiple printing process, the fabricating process for the planar light source in the present invention is simpler. Accordingly, the yield of the planar light source is increased.  
      It will be apparent to those skilled in the art that various modifications and variations can be made to the structure of the present invention without departing from the scope or spirit of the invention. In view of the foregoing, it is intended that the present invention cover modifications and variations of this invention provided they fall within the scope of the following claims and their equivalents.