Abstract:
In a plasma display panel, data electrodes are formed parallel to each other on a first substrate, and a selection voltage is to be applied to them. A dielectric layer covers a surface of the first substrate to include the data electrodes. Linear partitions are formed at a predetermined interval on the first substrate to be parallel to the data electrodes. A second substrate opposes the first substrate. A closed space between the first and second substrates is filled with a gas. A pair of sustain discharge electrodes are formed on the second substrate to intersect the data electrodes, and a discharge voltage is to be applied across them. Intersections of the pair of sustain discharge electrodes and data electrodes form matrix-like discharge cells. Stepped partitions are formed at a predetermined interval on the first substrate in a direction intersecting the linear partitions, and have heights smaller than those of the linear partitions. Notched openings are formed in the linear partitions at intersections of the linear and stepped partitions. A method of manufacturing a plasma display panel is also disclosed.

Description:
BACKGROUND OF THE INVENTION  
         [0001]    The present invention relates to a color plasma display panel (color PDP) used as a flat panel display, the area of which can be increased easily, in a display output device for a personal computer or workstation, a wall-hung television, or the like and, more particularly, to the structure of a color PDP in which the brightness is improved and the power consumption is reduced, and a method of manufacturing the same.  
           [0002]    A surface discharge type PDP is known well as a conventional PDP. In a surface discharge type PDP, a gas fills a hermetic space between one glass substrate (to be referred to as the second substrate hereinafter) with an electrode pair group covered with a dielectric layer and forming a large number of pairs, and the other glass substrate (to be referred to as the first substrate hereinafter) opposing it. When a voltage is applied to the electrode pairs of the second substrate, electric discharge occurs. Ultraviolet light from this discharge irradiates phosphors, thus displaying visible light emission.  
           [0003]    [0003]FIGS. 9A to  9 C and FIGS. 10A and 10B show the first prior art. According to the first prior art, data electrodes  212  and a dielectric layer  213  are formed on a flat first substrate  211 . Then, striped partitions  230  and thereafter a phosphor layer  215  are formed on the resultant structure. Reference numeral  200  denotes a discharge cell;  251 , a second substrate;  252 , a pair of sustain discharge electrodes;  253 , a dielectric layer; and  254 , a protective film.  
           [0004]    According to the second prior art, a PDP with partitions disclosed in Japanese Patent Laid-Open No. 10-149771 is available. More specifically, as shown in FIGS. 11A and 11B, partitions  330  are formed in parallel crosses on a first substrate  311 , and a phosphor layer  315  is formed on the resultant structure. Other than this, a PDP is available in which the discharge cell has a hexagonal shape, and partitions are formed around the discharge cell. Reference numeral  300  denotes a discharge cell;  312 , a data electrode;  313 , a dielectric layer;  351 , a second substrate;  352 , a pair of sustain discharge electrodes;  353 , a dielectric layer; and  354 , a protective film.  
           [0005]    According to the third prior art, as shown in FIGS. 12A and 12B, projections  440  are formed on a first substrate  411  in a direction perpendicular to partitions  430  parallel to data electrodes  412 , and a phosphor layer  415  is formed to cover the projections  440 . Reference numeral  400  denotes a discharge cell;  413 , a dielectric layer;  451 , a second substrate;  452 , a pair of sustain discharge electrodes;  453 , a dielectric layer; and  454 , a protective film.  
           [0006]    According to the fourth prior art, a PDP with partitions as disclosed in Japanese Patent Laid-Open Nos. 11-213896 and 2000-123747 is available. More specifically, as shown in FIGS. 13A and 13B, partitions  520  are formed on a first substrate  511  perpendicularly to continuous linear partitions  530 , to be lower than the linear partitions  530 . Reference numeral  500  denotes a discharge cell;  512 , a data electrode;  513 , a dielectric layer;  551 , a second substrate;  552 , a pair of sustain discharge electrodes; and  554 , a protective film.  
           [0007]    The following phenomena are seen in the conventional PDPs described above.  
           [0008]    As in the first and third prior arts, striped partitions are used, and no barriers are formed in a direction perpendicular to them. Alternatively, if the barriers are low, vacuum evacuation of a discharge cell portion in a PDP fabricating process is performed easily, while divergence of the light along the partitions of light-emitting region causes display unclearness. In order to prevent this, if light-shielding portions are formed at the two ends of the discharge cell in a direction perpendicular to the striped partitions, the light emission brightness decreases undesirably.  
           [0009]    If hexagonal partitions or partitions arranged in parallel crosses as in the second prior art are used, vacuum evacuation becomes difficult, and a vacuum evacuation process takes time. In order to avoid this, if the second and first substrates are arranged at a predetermined gap, electric discharge adversely affects adjacent discharge cells so a non-display cell may be unpreferably turned on or the brightness and efficiency decrease.  
           [0010]    A structure in which the projections  440  are formed on the phosphor surface may be available, as in the third prior art. In this case, however, the light emission brightness and efficiency are improved only a little. With the structure of the fourth prior art, vacuum evacuation is not improved sufficiently.  
         SUMMARY OF THE INVENTION  
         [0011]    It is an object of the present invention to provide a color PDP in which a light emission brightness and efficiency of a color plasma display are improved to realize a good display quality and a decrease in power consumption, and a method of manufacturing the same with which such a color PDP can easily be manufactured.  
           [0012]    In order to achieve the above object, according to the present invention, there is provided a plasma display panel comprising a first substrate, a plurality of selection electrodes which are formed parallel to each other on the first substrate and to which a selection voltage is to be applied, a first dielectric layer covering a surface of the first substrate to include the selection electrodes, a plurality of first partitions formed at a predetermined interval on the first substrate to be parallel to the selection electrodes, a second substrate arranged to oppose the first substrate, a closed space between the first and second substrates being filled with a gas, a plurality of pairs of discharge electrodes which are formed on the second substrate to intersect the selection electrodes and between which a discharge voltage is to be applied, intersections of the pairs of discharge electrodes and the selection electrodes forming matrix-like discharge cells, a plurality of second partitions which are formed at a predetermined interval on the first substrate in a direction intersecting the first partitions and have heights smaller than those of the first partitions, and notched openings formed in the first partitions at intersections of the first and second partitions. 
       
    
    
     BRIEF DESCRIPTION OF THE DRAWINGS  
       [0013]    [0013]FIG. 1A is a plan view of a plasma display panel (PDP) shown in FIGS. 3A and 3B;  
         [0014]    [0014]FIGS. 1B and 1C are sectional views taken along the lines A-A′ and B-B′, respectively, of FIG. 1A;  
         [0015]    [0015]FIGS. 2A to  2 H are sectional views showing the steps in manufacturing the PDP substrate shown in FIGS. 1A to  1 C;  
         [0016]    [0016]FIG. 3A is a plan view showing a PDP according to the first embodiment of the present invention;  
         [0017]    [0017]FIG. 3B is a sectional view taken along the line A-A′ of FIG. 3A;  
         [0018]    [0018]FIG. 4 is a sectional view of a PDP substrate according to the second embodiment of the present invention;  
         [0019]    [0019]FIG. 5A is a plan view of a PDP according to the third embodiment of the present invention;  
         [0020]    [0020]FIG. 5B is a sectional view taken along the line A-A′ of FIG. 5A;  
         [0021]    [0021]FIG. 6A is a plan view of a PDP according to the fourth embodiment of the present invention;  
         [0022]    [0022]FIG. 6B is a sectional view taken along the line A-A′ of FIG. 6A;  
         [0023]    [0023]FIG. 7A is a plan view of a PDP according to the fifth embodiment of the present invention;  
         [0024]    [0024]FIG. 7B is a sectional view taken along the line A-A′ of FIG. 7A;  
         [0025]    [0025]FIG. 8A is a plan view of a PDP according to the sixth embodiment of the present invention;  
         [0026]    [0026]FIG. 8B is a sectional view taken along the line A-A′ of FIG. 5A;  
         [0027]    [0027]FIG. 9A is a plan view of the PDP shown in FIGS. 10A and 10B;  
         [0028]    [0028]FIGS. 9B and 9C are sectional views taken along the lines A-A′ and B-B′, respectively, of FIG. 9A;  
         [0029]    [0029]FIG. 10A is a plan view of a PDP according to the first prior art;  
         [0030]    [0030]FIG. 10B is a sectional view taken along the line A-A′ of FIG. 10A;  
         [0031]    [0031]FIG. 11A is a plan view of a PDP according to the second prior art;  
         [0032]    [0032]FIG. 11B is a sectional view taken along the line A-A′ of FIG. 11A;  
         [0033]    [0033]FIG. 12A is a plan view of a PDP according to the third prior art;  
         [0034]    [0034]FIG. 12B is a sectional view taken along the line A-A′ of FIG. 12A;  
         [0035]    [0035]FIG. 13A is a plan view of a PDP according to the fourth prior art; and  
         [0036]    [0036]FIG. 13B is a sectional view taken along the line A-A′ of FIG. 13A. 
     
    
     DESCRIPTION OF THE PREFERRED EMBODIMENTS  
       [0037]    The present invention will be described in detail with reference to the accompanying drawings.  
         [0038]    [0038]FIGS. 1A to  1 C show a PDP substrate according to the first embodiment of the present invention. As shown in FIG. 1B, data electrodes (address electrodes)  12  forming a slitted screen, and a dielectric layer  13  are formed on a first substrate (rear substrate)  11 . On the dielectric layer  13 , linear partitions are formed between the data electrodes  12 , and stepped partitions  20  are formed in a direction perpendicular to the data electrodes  12 . As shown in FIG. 1A, a region surrounded by the adjacent stepped partitions  20  and adjacent linear partitions  30  form a discharge cell  100 . The stepped partitions  20  are arranged to intersect the linear partitions  30 , and are lower than the linear partitions  30 . Those portions of the linear partitions  30  where the stepped partitions  20  and linear partitions  30  intersect have notched openings  301  formed to expose flat upper surfaces  202  of the stepped partitions  20 , as shown in FIG. 1C. The linear partitions  30  are formed such that they are discontinued at these intersections in the longitudinal direction by the stepped partitions  20  and notched openings  301 .  
         [0039]    In this embodiment, as shown in FIG. 1C, the notched openings  301  are formed to coincide with the upper surfaces  202  of the stepped partitions  20 . However, the present invention is not limited to this. For example, each notched opening  301  may be formed such that its one side surface is located at least above the corresponding upper surface  202  and that its other side surface is located above either the corresponding upper surface  202 , the slant surface of the corresponding trapezoidal stepped partition  20 , or a position away from the corresponding stepped partition  20 . Alternatively, each notched opening  301  may be formed such that its one side surface is located at least on the slant surface of the corresponding trapezoidal stepped partition  20  and that its other side surface is located above either the corresponding upper surface  202 , the slant of the corresponding trapezoidal stepped partition  20 , or a position away from the corresponding stepped partition  20 . Alternatively, each notched opening  301  may be formed large so it accommodates the corresponding stepped partition  20  entirely.  
         [0040]    A method of manufacturing the first substrate  11  with respective constituent elements on it will be described in more detail with reference to FIGS. 2A to  2 H.  
         [0041]    First, data electrodes  12 , formed of a metal thin film made of one element or an alloy of aluminum, chromium, copper, and silver or a multilayered film of these elements, a film made of fine metal particles, or a mixture of fine metal particles and low-melting glass, are selectively formed on a first substrate  11  made of a material such as glass. The surface of the first substrate  11  including the data electrodes  12  is covered with a dielectric layer  13  made of low-melting glass (FIG. 2A). After that, stepped partitions  20  are selectively formed by printing or the like to be perpendicular to the data electrodes  12  (FIG. 2B).  
         [0042]    A photosensitive resist material such as a dry film is formed on the dielectric layer  13  and stepped partitions  20  (FIG. 2C), and a patterned photosensitive resist material  502  is left on the stepped partitions  20  (FIG. 2D). The spaces between the stepped partitions  20  are filled with a linear partition material  30  so as to be flush with the substantially patterned photosensitive resist material  502  (FIG. 2E). A photosensitive resist material such as a dry film is formed on the linear partition material  30  and photosensitive resist material  502 , and a patterned photosensitive resist material  503  is left to correspond to the regions of the linear partitions including the notched openings (FIG. 2F). The photosensitive resist material  503  is cut by etching such as sandblasting (FIG. 2G). Finally, the photosensitive resist materials  502  and  503  are removed (FIG. 2H). After that, a phosphor layer  15  (FIG. 1B) is formed on the dielectric layer  13  between the stepped partitions  20 . Thus, the PDP substrate shown in FIGS. 1A to  1 C can easily be manufactured.  
         [0043]    The stepped partitions  20  are made of a material containing low-melting glass as the major component. If this material contains white pigment powder, it can realize a high light emission efficiency. The phosphor layer  15  may be formed on the upper surfaces of the stepped partitions  20 . Before forming the phosphor layer, a powder layer of a white pigment such as titania may be formed under the phosphor layer  15 , so a higher light emission efficiency can be obtained. When the stepped partitions  20  are formed by printing or the like, they may be calcined before forming the linear partitions  30 .  
         [0044]    In order to further simplify the manufacturing process, a stepped partition material may be formed on the entire surface, and the stepped partitions  20  may be formed by sandblasting or the like. More specifically, a patterned photosensitive material is formed on the stepped partition material first, and then spaces among the patterned photosensitive material are filled with a linear partition material. A striped photosensitive material with notched openings  302  for leaving the linear partitions  30  is patterned on the resultant structure by sandblasting or the like. Then, the stepped partition material and the linear partition material are cut and processed simultaneously by sandblasting or the like, and calcined, to form the stepped partitions  20  and linear partitions  30 . In this case, if the stepped partition material and the linear partition material are the same, the process is more simplified.  
         [0045]    [0045]FIGS. 3A and 3B show a PDP formed of a first substrate  11  and a second substrate (front substrate)  51  opposing the first substrate  11 .  
         [0046]    As shown in FIG. 3A, a pair of sustain discharge electrodes  52  forming a slitted screen are formed on the second substrate  51  in a direction perpendicular to data electrodes  12  of the first substrate  11 . More specifically, the data electrodes  12  of the first substrate  11  and the pair of sustain discharge electrodes  52  of the second substrate  51  are arranged to form a grid, and their intersections form matrix-like discharge cells  100 . When forming the discharge cell  100 , the pair of sustain discharge electrodes  52  formed on the second substrate  51  are arranged inside upper surfaces  202  of stepped partitions  20 . Each pair of sustain discharge electrodes  52  are made up of a pair of X electrode (common electrode) and a Y electrode (individual electrode) that form a slitted screen. The pair of sustain discharge electrodes  52  are covered with a dielectric layer  53  and a protective film  54  made of magnesium oxide (MgO) or the like. The second substrate  51  and first substrate  11  formed in the above manner are arranged to oppose each other at a predetermined gap, as shown in FIG. 3B. Vacuum evacuation is performed at a high temperature, and a rare gas or a nitrogen-mixed or single-component discharge gas is sealed in the discharge space between the first and second substrates  11  and  51 , thus fabricating the PDP (new panel  1 ) according to the present invention.  
         [0047]    In the PDP fabricated in the above manner, ultraviolet light generated by discharge can irradiate the phosphor more effectively without decreasing the exhaust conductance of the vacuum evacuation step indispensable in the panel fabricating process, i.e., without increasing the evacuation time.  
         [0048]    A PDP (new panel  1 ) according to the first embodiment and a conventional PDP were fabricated, and the effect of the present invention was verified.  
         [0049]    A PDP according to the fourth prior art described above was fabricated in the same manner as with the method of manufacturing the PDP of the first embodiment, to serve as a prior art panel  1  having partitions  520  with no notched openings. For comparison, a PDP with a structure of the first prior art was fabricated to serve as a prior art panel  2 . The new panel  1  and prior art panel  1  have better light emission efficiencies than that of the prior art panel  2 . More specifically, the height of stepped partitions  20  was changed, and the light emission efficiency was measured. The effect of improving the light emission efficiency was apparent when the height of the stepped partitions  20  was 0.3 times or more, and preferably 0.5 times or more the height of linear partitions  30 .  
         [0050]    The heating vacuum evacuation process of panel fabrication was performed by detecting a gas discharged from the panel with a quadrupole gas analyzer. With the new panel  1 , the main residual gas component such as hydrocarbon or water decreased, within a period of time equal to that with the prior panel  2 , or a period of time shorter than that, to such a level that it did not adversely affect the panel characteristics. With the prior panel  1 , however, the decrease in residual gas component was slower than with the prior art panel  2 . In particular, when the height of the stepped partitions  20  was 0.8 times or more the height of the linear partitions, the evacuation time increased remarkably.  
         [0051]    [0051]FIG. 4 shows a PDP according to the second embodiment of the present invention. In the second embodiment, data electrodes  112  and a dielectric layer  113  are sequentially formed to extend over the upper portions of stepped partitions  120  and, between the stepped partitions  120 , phosphor layers  115  are formed on the dielectric layer  113 . In the first embodiment, the data electrodes  12  are hidden under the stepped partitions  20 . In the second embodiment, since the data electrodes  112  are formed extend over the stepped partitions  120 , discharge that is selectively generated between the data electrodes  12  and one of the pair of sustain discharge electrodes, i.e., write discharge, can be caused easily.  
         [0052]    [0052]FIGS. 5A and 5B show a PDP according to the third embodiment of the present invention. In this embodiment, light-shielding portions  60  for shielding light emission from cells and suppressing reflection of external light are formed on a second substrate  51  to correspond to upper surfaces  202  of the stepped partitions. When the light-shielding portions  60  are formed on the second substrate, unnecessary light-emitting regions or external light reflecting regions can be reduced, so that a high contrast can be obtained. Therefore, the PDP according to this embodiment can improve the light emission efficiency and display quality.  
         [0053]    An experimental result proving that the PDP according to this embodiment achieved a high light emission efficiency will be described hereinafter.  
         [0054]    Let Wel be the width of a pair of sustain discharge electrodes  52  on the second substrate  51 , Wbs be the width of each light-shielding portion  60 , Wr be the width of the upper surface  202  of each stepped partition  20  on a first substrate  11 , and Wp be the gap between the upper surfaces  202  on the stepped partitions  20 , as shown in FIG. 5A. These values were changed, and the light emission characteristics were evaluated. Consequently, when Wel was 1 to 1/1.5 times Wp, the effect of improving the light emission efficiency was apparent. When Wbs was 0.8 to 1.2 times Wr, a decrease in light emission efficiency was small, and the effect of improving the contrast was apparent. When Wr fell within the range of 0.3 to 0.5 times the length (Wr+Wp) of the discharge cell  100 , the effect of improving the light emission efficiency and contrast was apparent.  
         [0055]    To verify the effect of this embodiment, almost black light-shielding portions  60  were formed on those portions of the second substrate which corresponded to the upper surfaces  202  of the stepped partitions  20  of the first substrate of the new panel  1 , thus fabricating a new panel  2 . When similar light-shielding layers were formed on the prior art panel  2  described above, although the reflectance of the panel surface decreased to improve the contrast, the light emission efficiency decreased. In contrast to this, in the new panel  2 , since the light-emitting region is almost inside the light-shielding portions  60 , a high contrast was realized without substantially adversely affected by the light-shielding portions  60  while minimizing a decrease in light emission efficiency.  
         [0056]    As shown in FIGS. 6A and 6B, trace electrodes  55  for decreasing the interconnection resistance of the pair of sustain discharge electrodes  52  could be formed to overlap the light-shielding portions  60 . Therefore, a high light emission efficiency was realized without being adversely affected by light shielding performed by the trace electrodes  55 . If connecting portions  65  for connecting the trace electrodes  55  and the pair of sustain discharge electrodes  52  are formed to overlap the linear partitions  30 , the influence of light shielding can be minimized.  
         [0057]    [0057]FIGS. 6A and 6B show a PDP according to the fourth embodiment of the present invention. In this embodiment, trace electrodes  55  for decreasing the wiring resistance of a pair of sustain discharge electrodes  52  are formed to overlap light-shielding portions  60 , and the interconnections and the pair of sustain discharge electrodes  52  are connected to each other. According to this embodiment, the resistances of the interconnections extending from the pair of sustain discharge electrodes  52  can be decreased by utilizing the light-shielding portions  60 , so the uniformity of the display quality of the entire PDP can be improved.  
         [0058]    [0058]FIGS. 7A and 7B show a PDP according to the fifth embodiment of the present invention. In this embodiment, an underlying dielectric layer  57  is formed under the discharge gap of a pair of sustain discharge electrodes  152 , so the opposing portions of the pair of sustain discharge electrodes  152  can be formed to project toward the discharge space of the discharge gap. Hence, that portion of a dielectric layer  53  which is on the electrodes formed on these projecting portions can be formed thinner than other portions thereof.  
         [0059]    According to this embodiment, the current density of surface discharge can be suppressed while maintaining a high field strength in the discharge space around the ends of the opposing electrodes. Consequently, a decrease in discharge/maintenance voltage and an increase in light emission efficiency can be realized simultaneously, thereby improving the display quality.  
         [0060]    [0060]FIGS. 8A and 8B show a PDP according to the sixth embodiment of the present invention. In this embodiment, a lower dielectric layer  59  is formed partly on a pair of sustain discharge electrodes  52 . A pair of upper sustain discharge electrodes  58  are formed on the lower dielectric layer  59  such that they are separated from the pair of sustain discharge electrodes  52  by the lower dielectric layer  59 . The thickness of the dielectric layer  59  differs between the respective electrodes and discharge space.  
         [0061]    The pair of sustain discharge electrodes  52  are connected to the pair of upper sustain discharge electrodes  58  through trace electrodes  155  formed to overlap light-shielding portions  60 . In this case as well, the trace electrodes  155  are formed at regions opposing linear partitions  30  on the second substrate, as well as on the light-shielding portions  60 , and are connected to the pair of upper sustain discharge electrodes  58  through these regions.  
         [0062]    Consequently, in this embodiment as well, the thickness of a dielectric layer  53  on the pair of upper sustain discharge electrodes  58  can be decreased to be smaller than other portions thereof, so this embodiment has the same effect as that of the fifth embodiment in this respect. Conventionally, it is difficult to uniformly control a small thickness of the dielectric layer  53  on the projecting electrodes in the whole PDP. In contrast to this, according to this embodiment, the thickness of the dielectric layer  53  on the pair of upper sustain discharge electrodes  58  can be controlled stably.  
         [0063]    In particular, in the fifth and sixth embodiments, regarding the conditions for the gas to fill the space between the first and second substrates, assume that the gas component for mainly generating ultraviolet light is Xe, Kr, Ar, or nitrogen, and that its partial pressure is 100 hPa or more. In this case, since discharge that generates ultraviolet light strongly can be realized within a narrower discharge region, the above conditions are effective in improving the light emission efficiency of the PDP.  
         [0064]    In the above embodiments, a structure in which the notched openings  301  are formed in the linear partitions  30  of the first substrate  11  is described. When the characteristics of the PDP are studied comprehensively, an arrangement in which the light emission efficiency is improved while sacrificing the characteristics of vacuum evacuation to a certain degree may also be possible. To realize this arrangement, the structure of the first substrate  11  should have the same arrangement as that shown in FIGS. 13A and 13B in which the linear partitions  30  have no notched openings and the linear partitions are formed to cross over the stepped partitions  20 . Also, the conditions for the gas to fill the space between the first and second substrates  11  and  51  is set such that the gas component for mainly generating ultraviolet light is Xe, Kr, Ar, or nitrogen, and that its partial pressure is 100 hPa or more. Also, when the second substrate  51  has the structure of the fifth or sixth embodiment, discharge that can generate ultraviolet light strongly can be realized even if the width of the pair of sustain discharge electrodes is decreased.  
         [0065]    With this arrangement, although vacuum evacuation leaves room for improvement to a certain degree, the light emission efficiency of the PDP can be improved, and satisfactory characteristics can be obtained as the comprehensive characteristics of the PDP.  
         [0066]    The embodiments of the present invention are described concerning a case wherein main discharge is caused by surface discharge electrodes. When the structure of the present invention is applied to a PDP in which pairs of sustain discharge electrodes are respectively formed on the first and second substrates to form a pair, the same effect as those of the embodiments of the present invention can be obtained. More specifically, in a so-called opposite type PDP with an arrangement in which an electrode arranged on a second substrate  51  and having a width corresponding to the width of the pair of sustain discharge electrodes  52  shown in FIGS. 3A and 3B, and data electrodes  12  of a first substrate  11  form a pair of discharge electrodes that cause main discharge for exciting the phosphor layer to emit light, the same effect as that of the surface discharge type PDP described above can be observed.  
         [0067]    As has been described above, with the PDP according to the present invention, a partition structure to be formed on the data electrode side substrate is formed of linear partitions and partitions intersecting them and having a height smaller than that of the linear partitions, and the linear partitions have notches at their intersections. With this structure, vacuum evacuation of the discharge cell in the PDP fabricating process is facilitated more than in the prior art, and a high brightness and high light emission efficiency can be obtained, so the display quality can be improved consequently.