Patent Publication Number: US-7585198-B2

Title: Flat luminescent lamp and method for manufacturing the same

Description:
This application is a Divisional of U.S. patent application Ser. No. 09/894,903, filed Jun. 29, 2001 now U.S. Pat. No. 7,078,857 and claims the benefit of Korean Patent Application No. P 2000-83097 filed in Korea on Dec. 27, 2000, both of which are hereby incorporated by reference in their entirety. 
    
    
     BACKGROUND OF THE INVENTION 
     1. Field of the Invention 
     The present invention relates to a luminescent lamp, and more particularly, to a flat luminescent lamp and a method for manufacturing the same. 
     2. Discussion of the Related Art 
     Ultra thin flat panel display devices, especially liquid crystal display (LCD) devices, are widely used in monitors for notebook computers, spacecrafts, and aircrafts. 
     A passive luminescence LCD device usually includes a back light provided at the rear of a liquid crystal panel and used as a light source. The back light is inefficient because it increases the weight, power consumption, and thickness of the device. 
     The back light used as a light source of an LCD is formed in such a manner that a cylindrical fluorescent lamp is often used. There are two types of back light: a direct type and a light-guiding plate type. 
     In the direct type back light, a fluorescent lamp is mounted on a flat panel. To avoid having the shape of the fluorescent lamp displayed on a liquid crystal panel, it is necessary to maintain the distance between the fluorescent lamp and the liquid crystal panel and arrange a light-scattering means to achieve a uniform light distribution. As a result, it is difficult to form a LCD back light with a very thin size. 
     As the panel size gets larger, a light-emitting area of the back light increases. If the direct type back light has to cover a large area, the light-scattering means has to have a sufficient thickness to make the light-emitting area flat. This also makes it difficult to form a thin sized back light for LCD devices. 
     For the light-guiding plate type back light, a fluorescent lamp is mounted outside a flat panel so that light is dispersed in all sides using a light-guiding plate. In this case, since the fluorescent lamp is mounted at one side and light passes through the light-guiding plate, luminance becomes too low. Also, for uniform distribution of luminous intensity, advanced optical design and processing technologies are required. 
     Currently, to achieve high luminance, a direct type back light has been proposed in which a number of lamps are arranged below a display surface. Alternatively, a lamp with a bent shape is proposed. Recently, a flat luminescent back light with a flat surface facing a display surface of a panel is being researched and developed. This flat luminescent back light is disclosed in U.S. Pat. No. 6,034,470. 
     A related art flat luminescent lamp will be described with reference to the accompanying drawings. 
       FIG. 1  is a plane view illustrating a related art flat luminescent lamp, and  FIG. 2  is a sectional view taken along line I-I′ of  FIG. 1 . 
     As shown in  FIGS. 1 and 2 , the related art flat luminescent lamp includes a lower substrate  11 , an upper substrate  11   a , cathodes  13  formed on the lower substrate  11 , anodes  13   a  formed on the upper substrate  11   a , four frames  19   a ,  19   b ,  19   c , and  19   d  for sealing the lower and upper substrates  11   a  and  11  by a glass solder, and a plurality of support rods  21  formed between the lower and upper substrates  11  and  11   a.    
     The anodes  13   a  are formed in pairs at constant intervals. The cathodes  13  are formed on the corresponding lower substrate  11  between the anodes  13   a  The cathodes  13  and the anodes  13   a  are coated with a dielectric material, and an external voltage is applied to the cathodes  13  and the anodes  13   a  through a lead line. 
     A surface of the upper and lower substrates  11   a  and  11  facing a discharge space is coated with a fluorescent material. In the discharge space, a Xe gas induces discharge, forms plasma and emits ultraviolet rays (UV). The emitted UV comes into collision with the fluorescent material formed on the upper and lower substrates  11   a  and  11 . For this reason, the UV is excited to generate visible rays. 
     Additionally, a reflecting plate  14  is further provided on the lower substrate  11 . The reflecting plate  14  serves to prevent the visible rays generated in the discharge space from leaking out to the rear of the lower substrate  11 . The support rods  21  are made of a glass material so as not to interrupt emission of the visible rays. 
     Meanwhile, referring to  FIG. 2 , the cathodes  13  are formed on the lower substrate  11  of glass material, and a first dielectric material layer  12  is formed on the lower substrate  11  including the cathodes  13 . The reflecting plate  14  is formed on the first dielectric material layer  12  and a first phosphor layer  15  is formed on the reflecting plate  14 . The anodes  13   a  that induce discharge together with the cathodes  13  are formed on the upper substrate  11   a  of glass material. A second dielectric material layer  12   a  is formed on the upper substrate  11   a  including the anodes  13   a . A second phosphor layer  15   a  is formed on the second dielectric material layer  12   a . On the upper and lower substrates  11   a  and  11 , frames  19   a ,  19   b ,  19   c , and  19   d  are formed to seal the upper and lower substrates  11   a  and  11  by a glass solder. 
     The cathodes  13  and the anodes  13   a  are formed by a silk printing or vapor deposition process. 
     In the aforementioned related art flat luminescent lamp, if the voltage is applied to the cathodes  13  and the anodes  13   a  through the lead line, the Xe gas forms plasma in the discharge space between the cathodes  13  and the anodes  13   a  and emits UV. At this time, the UV comes into collision with the first and second phosphor layers  15  and  15   a  to generate visible rays. 
     However, the related art flat luminescent lamp has several problems. Since four frames and a number of the support rods are required to seal the lower and upper substrates, the number of parts for manufacturing the lamp increases and the process steps become complicated. This also leads to the increased weight and volume of the lamp. 
     SUMMARY OF THE INVENTION 
     Accordingly, the present invention is directed to a flat luminescent lamp and a method for manufacturing the same that substantially obviate one or more of the problems due to limitations and disadvantages of the related art. 
     An object of the present invention is to provide a flat luminescent lamp and a method for manufacturing the same, in which the number of parts is minimized to minimize the process steps, thereby reducing the manufacturing cost. 
     Additional features and advantages of the invention will be set forth in the description which follows, and in part will be apparent from the description, or may be learned by practice of the invention. The objectives and other advantages of the invention will be realized and attained by the structure particularly pointed out in the written description and claims hereof as well as the appended drawings. 
     To achieve these and other advantages and in accordance with the purpose of the present invention, as embodied and broadly described, a flat luminescent lamp according to the present invention includes first and second substrates attached to each other at a plurality of adhesive portions, a plurality of discharge spaces extended in a stripe shape in regions other than the adhesive portions, first and second electrodes arranged in the discharge spaces to be separated from each other, first and second phosphor layers formed in the discharge spaces including the first and second electrodes, and first and second frames sealing the first and second substrates. 
     To further achieve these and other advantages and in accordance with the purpose of the present invention, as embodied and broadly described, a method for manufacturing a flat luminescent lamp according to the present invention includes the steps of forming a plurality of stripe shaped grooves in first and second substrates, forming first and second electrodes on the first and second substrates in the grooves, forming a reflecting material layer on the first substrate in the grooves including the first electrode, forming first and second phosphor layers in the grooves including the reflecting material layer and the second electrode, attaching the first and second substrates to each other so that the grooves face each other, and sealing the first and second substrates after injecting a phosphor gas into the grooves. 
     In the preferred embodiment of the present invention, the grooves are respectively formed in the first and second substrates (lower and upper substrates), and the first and second substrates are attached to each other so that the grooves formed in the first substrate face the grooves formed in the second substrate. Before the first and second substrates are attached to each other, the first electrode which will be a cathode is formed in the groove of the first substrate and a first dielectric layer is formed in the grooves including the first electrode. A reflecting material layer is formed on the first dielectric layer and the first phosphor layer is formed on the reflecting material layer. 
     The second electrode which will be an anode is formed in the groove of the second substrate and a second dielectric layer is formed in the grooves including the second electrode. The second phosphor layer is formed on the second dielectric layer. 
     If the first and second substrates provided with the electrodes and the phosphor layers in the grooves are attached to each other to face each other, the grooves formed in the first substrate and the grooves formed in the second substrate form certain spaces that serve as discharge spaces. 
     It is to be understood that both the foregoing general description and the following detailed description are exemplary and explanatory and are intended to provide further explanation of the invention as claimed. 
    
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS 
       The accompanying drawings, which are included to provide a further understanding of the invention and are incorporated in and constitute a part of this specification, illustrate embodiments of the invention and together with the description serve to explain the principles of the invention. In the drawings: 
         FIG. 1  is a plane view illustrating a related art flat luminescent lamp; 
         FIG. 2  is a sectional view taken along line I-I′ of  FIG. 1 ; 
         FIG. 3  is a plane view illustrating a flat luminescent lamp according to the present invention; 
         FIG. 4  is a sectional view taken along line I-I′ of  FIG. 3 ; 
         FIG. 5  is a sectional view taken along line II-II′ of  FIG. 3 ; 
         FIG. 6  is a sectional view taken along line III-III′ of  FIG. 3 ; 
         FIGS. 7A to 7C  show discharge spaces according to a flat luminescent lamp of the present invention; and 
         FIGS. 8A to 8E  are sectional views illustrating process steps of manufacturing a flat luminescent lamp according to the present invention, in which  FIGS. 8A and 8E  are sectional views taken along line III-III′ of  FIG. 3  and  FIGS. 8B to 8D  are sectional views taken along line II-II′ of  FIG. 3 . 
     
    
    
     DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS 
     Reference will now be made in detail to the preferred embodiments of the present invention, examples of which are illustrated in the accompanying drawings. 
       FIG. 3  is a plane view illustrating a flat luminescent lamp according to the present invention,  FIG. 4  is a sectional view taken along line I-I′ of  FIG. 3 , and  FIG. 5  is a sectional view taken along line II-II′ of  FIG. 3 . 
     As shown in  FIGS. 3 to 5 , the flat luminescent lamp according to the present invention includes first and second substrates  31  and  31   a  attached to each other to face each other, each having a plurality of grooves on an attached surface. First and second electrodes  33  and  33   a  are arranged in the grooves to be separated from each other in the up and down direction. First and second phosphor layers  37  and  37   a  are formed in the grooves including the first and second electrodes  33  and  33   a . First and second frames  39  and  39   a  are used for sealing the first and second substrates  31  and  31   a.    
     The first and second substrates  31  and  31   a  are typically formed of a glass material. However, the first substrate  31  may be formed of a ceramic material. 
     The grooves have a stripe shape and are used as discharge spaces that emit white light by discharge between the first and second electrodes  33  and  33   a . Both ends of each groove are connected with both ends of a neighboring groove so that a light-emitting area is maximized. 
     The grooves are formed in vertical direction relative to the substrates while the first and second frames  39  and  39   a  are formed in horizontal direction relative to the substrates. 
     Areas marked by dotted lines in  FIG. 3  represent attached surfaces between the first and second substrates  31  and  31   a.    
     As shown in  FIG. 4 , a reflecting material layer  35  is further provided on the first substrate  31 . The reflecting material layer  35  serves to direct and concentrate the white light generated by discharge between the first and second electrodes  33  and  33   a  toward the second substrate  31   a  so that it does not leak out to the first substrate  31 . 
     A dielectric layer (not shown) may further be provided on an entire surface including the first and second electrodes  33  and  33   a  In such a case, the reflecting material layer  35  is formed on the dielectric layer. 
     The first electrode  33  is a cathode while the second electrode  33   a  is an anode. Preferably, the second electrode  33   a  is formed of a transparent conductive material such as indium tin oxide (ITO). The second electrodes  33   a  may also be formed of other transparent or non-transparent conductive material. If the second electrode  33   a  is formed of non-transparent material, a diffusion sheet is further provided on the second substrate  31   a  so that the white light is uniformly emitted along an entire region of the light-emitting surface. 
     Meanwhile, the discharge spaces are formed in a stripe shape, and both ends of each discharge space are connected with both ends of a neighboring discharge space. 
     The grooves which will be discharge spaces, as shown in  FIG. 6 , are formed in such a manner that both ends of each groove are connected with both ends of a neighboring groove to maximize a discharge space. 
     It is desirable that the grooves are formed in a shape that induces discharge. For example, if the grooves have a rectangular shape, the discharge efficiency at four corners may deteriorate. Accordingly, the grooves are preferably formed in a round shape as shown in  FIG. 7A  or a shape with a plurality of surfaces (e.g., a polygon shape) close to the round shape as shown in  FIG. 7B  so that the distance between a light-emitting central portion of the discharge space and the phosphor layer is uniformly maintained. 
     Furthermore, the first and second substrates  31  and  31   a  are attached to each other at a very small area so that brightness of light is maximized. 
     In  FIG. 3 , the second electrode  33   a  is formed of separate singular electrodes. However, as shown in  FIGS. 7A-7C , depending on electrode design, two electrodes in pairs may be formed or three electrodes or more in one group may be formed. 
     The operation of the aforementioned flat luminescent lamp according to the present invention is similar to the operation of the related art flat luminescent lamp. That is, if a voltage is applied to the first and second electrodes  33  and  33   a  after an external power source is respectively connected with them, Xe gas forms plasma and emits UV between the first and second electrodes  33  and  33   a . The UV comes into collision with the first and second phosphor layers  37  and  37   a  to generate white light. The white light is emitted to the second substrate  31   a  without being leaked out to the first substrate  31  by the reflecting material layer  35  formed in the first substrate  31 . 
     If the aforementioned flat luminescent lamp is used as a back light of an LCD device, an LCD panel is arranged at the rear of the second substrate  31   a.    
     A method for manufacturing the flat luminescent lamp according to the present invention will now be described with reference to  FIGS. 8A to 8E .  FIGS. 8A and 8E  are sectional views taken along line III-III′ of  FIG. 3 , and  FIGS. 8B to 8D  are sectional views taken along line II-II′ of  FIG. 3 . 
     As shown in  FIG. 8A , a plurality of grooves  32  are formed in the first and second substrates  31  and  31   a .  FIG. 8B  shows an enlarged inner portion of the grooves. Using silk printing, vapor deposition process, or photolithography process, the first electrode  33  (i.e., the cathode) is formed on the first substrate  31  while the second electrode  33   a  (i.e., the anode) is formed on the second substrate  31   a.    
     At this time, the grooves may be formed by molding or etching the first and second substrates  31  and  31   a  The second electrode  33   a  is formed of a transparent conductive material such as ITO so that the white light is emitted by passing through the transparent second electrode  33   a.    
     Additionally, the first and second electrodes  33  and  33   a  may be formed of a metal having low specific resistance, such as Ag, Cr, Pt, and Cu. 
     Afterwards, as shown in  FIG. 8C , the first dielectric layer  34  is formed on the first substrate  31  including the first electrode  33  while the second dielectric layer  34   a  is formed on the second substrate  31   a  including the second electrode  33   a.    
     Subsequently, as shown in  FIG. 8D , the reflecting material layer  35  of AlN, BaTiO 3 , SiN x , or SiO x  is formed on the first dielectric layer  34 . The reflecting material layer  35  is formed to direct and concentrate the white light generated by collision between the UV and the phosphor layers toward the second substrate  31   a  so that the white light does not leak out to the first substrate  31 . 
     The first and second phosphor layers  37  and  37   a  are formed on the reflecting material layer  35  and the second dielectric layer  34   a . The first and second substrate  31  and  31   a  are then attached to each other, as shown in  FIG. 8E . A phosphor gas, such as Xe gas, is injected between them through a gas injection hole (not shown), and the substrates  31  and  31   a  are sealed through first and second frames (not shown) using a solder means such as a glass solder. Thus, the process for manufacturing the flat luminescent lamp according to the present invention is completed. 
     The flat luminescent lamp according to the present invention can be used as a lighting device and can also be used as a separate light source at the rear or front of display devices such as monitors, notebook PCs, and TVs. 
     As described above, the flat luminescent lamp and the method for manufacturing the same according to the present invention have the following advantages. 
     Since only two frames are required and no separate support rod is formed between the first and second substrates, the number of parts required for making the lamp can be minimized, thereby saving the manufacturing cost. Furthermore, since no separate support rod is formed and the first and second substrates are directly attached to each other, it is possible to achieve strong support and improve durability of the product. Moreover, since the grooves are formed in the substrate and used as discharge spaces, the thickness and weight of the product can be minimized. 
     The foregoing embodiments are merely exemplary and are not to be construed as limiting the present invention. The present teachings can be readily applied to other types of apparatuses. The description of the present invention is intended to be illustrative, and not to limit the scope of the claims. Many alternatives, modifications, and variations will be apparent to those skilled in the art.