Patent Publication Number: US-6211538-B1

Title: Electroluminescent device including a blue light emitting thick-film electroluminescent layer and a red light emitting thin-film electroluminescent layer

Description:
FIELD OF THE INVENTION 
     The present invention relates to an electroluminnescent device and a method for manufacturing thereof; and, more particularly, to a color electroluminnescent device and a method for manufacturing thereof. 
     BACKGROUND OF THE INVENTION 
     In recent years, elctroluminescent (EL) devices in both a thin-film EL type and a thick-film type have been suggested to display a multi-color image. Both of the thin-film and thick-film EL devices, however, are burdened with major shortcomings. 
     To be more specific, the thin-film EL device, while capable of providing a red light of a commercially acceptable brightness level, is incapable of providing the same for a blue light of a commercially acceptable brightness level, whereas the thick-film EL device, while capable of providing a blue light of a commercially acceptable brightness level, is incapable of providing the same for a red light of a commercially acceptable brightness level. 
     In other words, neither the thin-film EL device nor the thick-film EL device could provide the blue light and red lights of a commercially acceptable brightness level concurrently to thereby prevent the EL devices from displaying a full-color image of a commercially acceptable brightness level. 
     SUMMARY OF THE INVENTION 
     It is, therefore, a primary object of the present invention to provide an electroluminescent (EL) device and a method for manufacturing thereof capable of providing a blue light and a red light having a commercially acceptable brightness level. 
     It is another object of the present invention to provide an electroluminescent (EL) device and a method for manufacturing thereof capable of displaying a full-color image by generating a blue light, a green light and a red light, having a commercially acceptable brightness level. 
     In accordance with the present invention, there is provided an EL device comprising: a substrate; a thick-film electroluminescent (EL) layered structure formed on either on top or bottom of the substrate, the thick-film EL layered structure including a blue light emitting thick-film EL layer; a thin-film EL layered structure formed on either on top of the substrate or on top of the thick-film EL layered structure, the thin-film EL layered structure including a red light emitting thin-film EL layer; and a green light emitting EL layer to be included either in the thick-film EL layered structure as a green light emitting thick-film EL layer or in the thin-film EL layered structure as a green light emitting thin-film EL layer. 
    
    
     BRIEF DESCRIPTION OF THE DRAWINGS 
     The above and other objects and features of the present invention will become apparent from the following description of preferred embodiments given with reference to the accompanying drawings, in which: 
     FIG. 1 represents a schematic cross sectional view of a full-color electroluminescent (EL) device in accordance with a first preferred embodiment of the present invention; 
     FIG. 2 presents a schematic cross sectional view of a full-color EL device in accordance with a second preferred embodiment of the present invention; 
     FIG. 3 illustrates a schematic cross sectional view of a full-color EL device in accordance with a third preferred embodiment of the present invention; 
     FIG. 4 depicts a schematic cross sectional view of a full-color EL device in accordance with a fourth preferred embodiment of the present invention; 
     FIGS. 5A to  5 F set forth schematic cross sectional views for illustrating a method for manufacturing the full-color EL device represented in FIG. 1; and 
     FIGS. 6A to  6 D offer schematic cross sectional views for illustrating a method for manufacturing the full-color EL device presented in FIG.  2 . 
    
    
     DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS 
     In accordance with a preferred embodiment of the present invention, an electroluminescent (EL) device includes a substrate; a thick-film EL layered structure formed on top of the substrate; and a thin-film EL layered structure formed on top of the thick-film EL layered structure. 
     In accordance with another preferred embodiment of the present invention, an EL device includes a substrate; a thick-film EL layered structure formed on bottom of the substrate; and a thin-film EL layered structure formed on top of the substrate. 
     In accordance with the present invention, the thick-film EL layered structure includes a blue light emitting thick-film EL layer; and the thin-film EL layered structure includes a red light emitting thin-film EL layer. 
     Further, in accordance with the present invention, a green light emitting EL layer is included either in the thick-film EL layered structure as a green light emitting thick-film EL layer or in the thin-film EL layered structure as a green light emitting thin-film EL layer. 
     Referring to FIGS. 1-4, there are shown schematic cross sectional views of full-color EL devices  100 ,  200 ,  300  and  400  having different structures in accordance with the preferred embodiment of the present invention. In FIGS. 1-4, arrows represent main paths of the light beams emitted from the corresponding EL layers, respectively. 
     FIGS. 5A to  5 F set forth schematic cross sectional views for illustrating a method for manufacturing the full-color EL device  100  shown in FIG.  1 . FIGS. 6A to  6 D offer schematic cross sectional views for illustrating a method for manufacturing the full-color EL device  200  represented in FIG.  2 . 
     FIG. 1 represents a schematic cross sectional view of the full-color EL device  100  in accordance with a first preferred embodiment of the present invention. Referring to FIG. 1, the full-color EL device  100  includes a substrate  101  made of a transparent insulating material, e.g., glass; a thick-film EL layered structure  130  formed on top of the substrate  101 , the thick-film EL layered structure  130  including a blue light emitting thick-film EL layer  104  to generate a blue light; and a thin-film EL layered structure  150  formed on top of the thick-film EL layered structure  130 , the thin-film EL layered structure  150  including a red light emitting thin-film EL layer  115  to generate a red light. 
     In detail, the thick-film EL layered structure  130  includes a first electrode film  102  formed on top of the substrate  101 ; a first insulation film  103  formed on top of the first electrode film  102  and partially on top of the substrate  101 ; the blue light emitting thick-film EL layer  104  formed on top of the first insulation film  103 ; a second electrode film  105  formed on top of the blue light emitting thick-film EL layer  104 ; and a second insulation film  106  formed on top of the second electrode film  105 , partially on top of the blue light emitting thick-film EL layer  104  and the first insulation film  103 . 
     As shown in FIG. 5A, the first electrode film  102  made of, e.g., silver (Ag), is formed by using, e.g., a screen printing method. The first insulation film  103  made of an insulating material, e.g., BaTiO 3 , is formed by using either, e.g., a spray coating method or a screen printing method. The blue light emitting thick-film EL layer  104 , e.g., made of ZnS:Cu, is formed by using a thick-film EL layer forming method, e.g., either a spray coating method or a screen printing method. 
     As shown in FIG. 5B, the second electrode film  105 , e.g., made of either Aluminum (Al) or Indium Tin Oxide In 2 O 3 :SnO 2  (ITO), is formed by using, e.g., a sputtering method; and the second insulation film  106  made of an insulating material, e.g., Y 2 O 3 , is formed by using either, e.g., a sputtering method or an electron-beam evaporation method. 
     It should be noted that the center points of the first electrode film  102 , the blue light emitting thick-film EL layer  104  and the second electrode film  105  are perpendicularly aligned. 
     The thin-film EL layered structure  150  includes a third electrode film  111  and a fourth electrode film  112 , the third and fourth electrode film  111  and  112  being separated from each other and formed on top of the second insulation film  106 ; a third insulation film  113  formed on tops of the third and fourth electrode film&#39;s  111  and  112  and partially on top of the second insulation film  106 ; the red light emitting thin-film EL layer  115  and a green light emitting thin-film EL layer  114 , the red light emitting thin-film EL layer  115  and the green light emitting thin-film EL layer  114  being separated from each other and formed on top of the third insulation film  113 ; a fourth insulation film  116  formed on tops of the green light emitting thin-film EL layer  114  and the red light emitting thin-film EL layer  115  and partially on top of the third insulation film  113 . 
     The thin-film EL layered structure  150  further includes a fifth electrode film  117  and a sixth electrode film  118 , the fifth and sixth electrode films  117  and  118  being separated from each other and formed on top of the fourth insulation film  116 . It should be noted that the center points of the fourth electrode film  112 , the green light emitting thin-film EL layer  114  and the fifth electrode film  117  are aligned perpendicularly; and the centers of the third electrode film  111 , the red light emitting thin-film EL layer  115  and the sixth electrode film  118  are also perpendicularly aligned. 
     The third electrode film  111  and the fourth electrode film  112  are made of, e.g., ITO and formed by using, e.g., a sputtering method. The third insulation film  113  made of insulating material, e.g., Y 2 O 3 , is subsequently formed by employing, e.g., a sputtering method. 
     Thereafter, as shown in FIG. 5C, the green light emitting thin-film EL layer  114 , e.g., made of ZnS:Tb, is formed on top of the third insulation film  113  by using a thin-film EL layer forming method, e.g., one of a sputtering method, an electron-beam evaporation method and an atomic layer epitaxy growth (ALE) method. As shown in FIG. 5D, the red light emitting thin-film EL layer  115 , e.g., made of CaS:Cu, is formed on top of the third insulation film  113  by using a thin-film EL layer forming method. 
     As shown in FIG. SE, the fourth insulation film  116 , e.g., made of Y 2 O 3 , is formed by using, e.g., a sputtering method. Then, as shown in FIG. SF, the fifth electrode film  117  and the sixth electrode film  118  are made of, e.g., ITO and formed by using, e.g. a sputtering method. 
     In general, the thin-film EL layered structure  150  further includes a protection layer  119  made of a material which is resistant to water, a chemical attack and a physical impact from outside, e.g., parylene or glass. The protection layer  119  is formed on tops of the fifth electrode film  117  and the sixth electrode film  118  and partially on top of the fourth insulation film  116 . 
     In accordance with a preferred embodiment of the present invention, the thickness of the substrate  101  ranges from about 0.8 mm to about 1.2 mm; the thickness of each of the first and second electrode films  102  and  105  ranges from about 0.8 μm to about 1.2 μm; the thickness of the blue light emitting thick-film EL layer  104  ranges from about 30 μm to about 40 μm; and the thickness of each of the first and second insulation films  103  and  106  ranges from about 5 μm to about 10 μm. 
     Further, the thickness of the third to sixth electrode films  111 ,  112 ,  117  and  118  range from about 0.3 μm to about 0.4 μm, respectively; the same for the thin-film EL layers  114  and  115  range from about 0.8 μm to about 1.0 μm, respectively; and the thickness of each of the third and fourth insulation films  113  and  116  ranges from about 0.2 μm to about 0.4 μm. 
     It should be also noted that the so-called conventional photolithography process including an etching technique is employed in forming the films or layers  111  to  118  included in the thin-film EL layered structure  150 . 
     FIG. 2 presents a schematic cross sectional view of the full-color EL device  200  in accordance with a second preferred embodiment of the present invention. 
     Referring to FIG. 2, the full-color EL device  200  includes a substrate  201 ; a thick-film EL layered structure  230  formed on top of the substrate  201 , the thick-film EL layered structure  230  including a blue light emitting thick-film EL layer  205  to generate a blue light and a green light emitting thick-film EL layer  206  to generate a green light; and a thin-film EL layered structure  250  formed on top of the thick-film EL layered structure  230 , the thin-film EL layered structure  250  including a red light emitting thin-film EL layer  213  to generate a red light. 
     In detail, the thick-film EL layered structure  230  includes an 11th electrode film  203  and a 12th electrode film  204 , the 11th and 12th electrode films  203  and  204  being separated from each other and formed on top of the substrate  201 ; the blue light emitting thick-film EL layer  205  formed on top of the 12th electrode film  204 ; a green light emitting thick-film EL layer  204  formed on top of the 11th electrode film  203 ; an 11th insulation film  207  formed partially on tops of the substrate  201 , the 11th and 12th electrode films  203  and  204  and on tops of the blue light emitting thick-film EL layer  205  and the green light emitting thick-film EL layer  206 . 
     The thick-film EL layered structure  230  further includes a 13th electrode film  208  and a 14th electrode film  209 , the 13th and 14th electrode films  208  and  209  being separated from each other and formed on top of the 11th insulation film  207 ; and a 12th insulation film  210  formed on tops of the 13th and 14th electrode films  208  and  209  and partially on top of the 11th insulation film  207 . 
     It should be noted that the center points of the 12th electrode film  204 , the blue light emitting thick-film EL layer  205  and the 13th electrode film  208  are perpendicularly aligned; and the center points of the 11th electrode film  203 , the green light emitting thick-film EL layer  206  and the 14th electrode film  209  are also perpendicularly aligned. 
     As depicted in FIG. 6A, each of the 11th electrode film  203 , e.g., made of silver (Ag) and the 12th electrode film  204 , e.g., made of Ag is formed on top of the substrate  201 , e.g., made of glass by using, e.g., a screen printing method. The blue light emitting thick-film EL layer  205 , e.g., made of ZnS:Cu is formed on top of the 12th electrode film  204  by using a thick-film EL layer forming method, e.g., a spray coating method or a screen printing method. 
     Thereafter, as represented in FIG. 6B, the green light emitting thick-film EL layer  206 , e.g., made of one of ZnS:Tb, ZnS:Cu and ZnS:Mn is formed by using the thick-film EL layer forming method. The 11th insulation film  207 , e.g., Y 2 O 3  is formed by using, e.g., a sputtering method. 
     Next, as shown in FIG. 6C, each of the 13th electrode film  208 , e.g., made of ITO and the 14th electrode film  209 , e.g., made of ITO is formed by using, e.g., an electron-beam evaporation method. The 12th insulation film  210 , e.g., made of Y 2 O 3  is formed by using, e.g., a sputtering method. 
     The thin-film EL layered structure  250  includes a 15th electrode film  211  formed on top of the 12th insulation film  210 ; and a 13th insulation film  212  formed on top of the 15th electrode film  211  and partially on top of the 12th insulation film  210 . 
     The thin-film EL layered structure  250  further includes the red light emitting thin-film EL layer  213  formed on top of the 13th insulation film  212 ; a 14th insulation film  214  formed on top of the red light emitting thin-film EL layer  213  and partially on top of the 13th insulation film  212 ; and a 16th electrode film  215  formed on top of the 14th insulation film  214 . 
     As set forth in FIG. 6D, the 15th electrode film  211 , e.g., made of ITO is formed by using, e.g., an electron-beam evaporation method. The red light emitting thin-film EL layer  213 , e.g., made of CaS:Eu is formed by using, e.g., an electron-beam evaporation method. 
     The 14th insulation film  214 , e.g., made of Y 2 O 3  is formed by using, e.g., an electron-beam evaporation method; and the 16th electrode film  215 , e.g., made of ITO, is formed by using, e.g., an electron-beam evaporation method. 
     It should be noted that the center points of the 15th electrode film  211 , the red light emitting thin-film EL layer  213  and the 16th electrode film  215  are aligned along an approximately same straight line. 
     In general, the thin-film EL layered structure  250  usually further includes a protection layer  216  made of, e.g., either parylene or glass, wherein the protection layer  216  is formed on top of the 16th electrode film  215  and partially on top of the 14th insulation film  214 . 
     It should be noted that if the green light emitting thick-film EL layer  206  is made of ZnS:Cu, the atomic percent concentration of Cu in the green light emitting thick-film EL layer  206  is set to be lower than that in the blue light emitting thick-film EL layer  205 . 
     In detail, in accordance with a preferred embodiment of the present invention, a blue light of a commercially acceptable brightness level from the blue light emitting thick-film EL layer  205  is obtained by applying an AC voltage with a frequency of about 1 KHz between the electrode films  204  and  208 . 
     In contrast, to obtain a green light of a commercially acceptable brightness level from the green light emitting thick-film EL layer  206 , an AC voltage with a frequency of about 400 Hz is applied between the electrode films  203  and  209  under the condition that the atomic percent concentration of Cu in the green light emitting thick-film EL layer  206  is lower than that in the blue light emitting thick-film EL layer  205 . 
     FIG. 3 illustrates a schematic cross sectional view of the full-color EL device  300  in accordance with a third preferred embodiment of the present invention. 
     Referring to FIG. 3, the full-color EL device  300  includes a substrate  310 , e.g., made of glass; a thick-film EL layered structure  330  formed on bottom of the substrate  310 , the thick-film EL layered structure  330  including a blue light emitting thick-film EL layer  312  to generate a blue light; a thin-film EL layered structure  350  formed on top of the substrate  310 , the thin-film EL layered structure  350  including a red light emitting thin-film EL layer  325  to generate a red light and a green light emitting thin-film EL layer  326  to generate a green light. 
     In detail, the thick-film EL layered structure  330  includes a 21st electrode film  311  formed on bottom of the substrate  310 ; the blue light emitting thick-film EL layer  312  formed on bottom of the 21st electrode film  311 ; a 21st insulation film  313  formed on bottom of the blue light emitting thick-film EL layer  312 , partially on bottoms of the 21st electrode film  311  and the substrate  310 ; and a 22nd electrode film  314  formed on bottom of the 21st insulation film  313 . 
     It should be noted that the center points of the 21st electrode film  311 , the blue light emitting thick-film EL layer  312  and the 22nd electrode film  314  are aligned perpendicularly. 
     In general, the thick-film EL layered structure  330  further includes a protection layer  315 , e.g., made of parylene, formed on bottom of the 22nd electrode film  314  and partially on bottom of the 21st insulation film  313 . 
     The thin-film EL layered structure  350  includes a 23rd electrode film  322  and a 24th electrode film  323 , the 23rd and 24th electrode film  322  and  323  being separated from each other and formed on top of the substrate  310 ; a 23rd insulation film  324  formed on tops of the 23rd and 24th electrode film&#39;s  322  and  323  and partially on top of the substrate  310 ; the red light emitting thin-film EL layer  325  and a green light emitting thin-film EL layer  326 , the red light emitting thin-film EL layer  325  and the green light emitting thin-film EL layer  326  being separated from each other and formed on top of the 23rd insulation film  324 ; a 24th insulation film  327  formed on tops of the red light emitting thin-film EL layer  325  and the green light emitting thin-film EL layer  326  and partially on top of the 23rd insulation film  324 . 
     The thin-film EL layered structure  350  further includes a 25th electrode film  328  and a 26th electrode film  329 , the 25th and 26th electrode films  328  and  329  being separated from each other and formed on top of the 24th insulation film  327 . 
     It should be noted that the center points of the 24th electrode film  323 , the green light emitting thin-film EL layer  326  and the 25th electrode film  328  are aligned perpendicularly; and the 23rd electrode film  322 , the red light emitting thin-film EL layer  325  and the 26th electrode film  329  are also perpendicularly aligned. 
     In general, the thin-film EL layered structure  350  usually further includes a protection layer  340 , e.g., made of parylene, wherein the protection layer  340  is formed on tops of the 25th electrode film  328  and the 26th electrode film  329  and partially on top of the 24th insulation film  327 . 
     FIG. 4 depicts a schematic cross sectional view of the full-color EL device  400  in accordance with a fourth preferred embodiment of the present invention. 
     Referring to FIG. 4, the full-color EL device  400  includes a substrate  410 , e.g., made of glass; a thick-film EL layered structure  430  including a blue light emitting thick-film EL layer  413  to generate a blue light and a green light emitting thick-film EL layer  414  to generate a green light, wherein the thick-film EL layered structure  430  is formed on bottom of the substrate  410 ; and a thin-film EL layered structure  450  formed on top of the substrate  410  including a red light emitting thin-film EL layer  424  to generate a red light. 
     In detail, the thick-film EL layered structure  430  includes a 31st electrode film  411  and a 32nd electrode film  412 , the 31st and 32nd electrode films  411  and  412  being separated from each other and formed on bottom of the substrate  410 ; the blue light emitting thick-film EL layer  413  formed on bottom of the 31st electrode film  411 ; and a green light emitting thick-film EL layer  414  formed on bottom of the 32nd electrode film  412 . 
     The thick-film EL layered structure  450  further includes a 31st insulation film  415  formed partially on bottoms of the 31st electrode film  411 , the 32nd electrode film  412  and the substrate  450  and on bottoms of the blue light emitting thick-film EL layer  413  and the green light emitting thick-film EL layer  414 ; and a 33rd electrode film  416  and a 34th electrode film  417 , the 33rd and 34th electrode films  417  being separated from each other and formed on bottom of the 31st insulation film  415 . 
     It should be noted that the center points of the 31st electrode film  411 , the blue light emitting thick-film EL layer  413  and the 34th electrode film  417  are aligned perpendicularly; and the center points of the 32nd electrode film  412 , the green light emitting thick-film EL layer  414  and the 33rd electrode film  416  are also aligned perpendicularly. 
     In general, the thick-film EL layered structure  430  further includes a protection layer  418 , e.g., made of parylene, formed on bottom of the 33rd and 34th electrode films  416  and  417  and partially on bottom of the 31st insulation film  415 . 
     The thin-film EL layered structure  450  includes a 35th electrode film  422  formed on top of the substrate  410 ; a 33rd insulation film  423  formed on top of the 35th electrode film  422  and partially on top of the substrate  410 ; the red light emitting thin-film EL layer  424  formed on top of the 33rd insulation film  423 ; a 34th insulation film  425  formed on top of the red light emitting thin-film EL layer  424  and partially on top of the 33rd insulation film  423 ; and a 36th electrode film  426  formed on top of the 34th insulation film  425 . 
     It should be noted that the center points of the 35th electrode film  422 , the red light emitting thin-film EL layer  424  and the 36th electrode film  426  are aligned perpendicularly. 
     In general, the thin-film EL layered structure  450  further includes a protection layer  427 , e.g., made of parylene, wherein the protection layer  427  is formed on top of the 36th electrode film  426  and partially on top of the 34th insulation film  425 . 
     It should be noted that the films or layers included in each of the thick-film EL layered structure&#39;s  230 ,  330  and  430  have almost equal thickness to the corresponding films or layers in the thick-film EL layered structure  130 , respectively; the films or layers included in each of the thin-film EL layered structure&#39;s  250 ,  350  and  450  have almost equal thickness to the corresponding films or layers in the thin-film EL layered structure  150 , respectively. 
     For the sake of simplicity, the description of the methods for manufacturing the thick-film EL layered structure  330  and the thin-film EL layered structure  350  are omitted since the methods therefor are similar to those of the thick-film EL layered structure  130  and the thin-film EL layered structure  150 , respectively. 
     The description of the methods for the manufacturing the thick-film EL layered structure  430  and the thin-film EL layered structure  450  are also omitted since the methods therefor are similar to those of the thick-film EL layered structure  130  and the thin-film EL layered structure  150 , respectively. 
     Further, as represented by arrows in FIGS. 1-4, it is preferable that three main paths of red, green and blue light beams from the corresponding EL layers in each of the EL devices  100 ,  200 ,  300  and  400  are not overlapped with each other to thereby enable each of the EL devices to emit a light of a commercially acceptable brightness level and be easily controlled by an electrode control circuit (not shown) therefor. 
     For example, as shown in FIG. 1, the blue light emitting thick-film EL layer  104  is located between the green light emitting thin-film EL layer  114  and the red light emitting thin-film EL layer  115 ; and as shown in FIG. 3, the blue light emitting thick-film EL layer  312  is located between the red light emitting thin-film EL layer  325  the green light emitting thin-film EL layer  326 . 
     The red light emitting thin-film EL layer  213  is located either left or right of all of the blue light emitting thick-film EL layer  205  and the green light emitting thick-film EL layer  206 ; and the red light emitting thin-film EL layer  424  is located either left or right of all of the green light emitting thick-film EL layer  414  and the blue light emitting thick-film EL layer  413 . 
     It should be noted that in accordance with another preferred embodiment of the present invention, the red light emitting thin-film EL layer  213  is located between the blue light emitting thick-film EL layer  205  and the green light emitting thick-film EL layer  206 ; and the red light emitting thin-film EL layer  424  is located between the green light emitting thick-film EL layer  414  and the blue light emitting thick-film EL layer  413 . 
     Even though the three main paths of red, green and blue light beams from the corresponding EL layers included in each of the EL devices  100 ,  200 ,  300  and  400  are directed upward, respectively, as shown in FIGS. 1-4, it should be noted that in accordance with other preferred embodiments, the three main paths can also be directed downward, respectively. 
     It should be also noted that each of the insulation films and electrode films included in each EL device of the present invention should be transparent in case that the corresponding light beam passes therethrough and be either opaque or transparent in case that the corresponding light beam does not pass therethrough. 
     As described above, in accordance with the present invention, there is provided an EL device including a red light emitting thin-film EL layer, a blue light emitting thick-film EL layer and a green light emitting EL layer either as a green light emitting thin-film EL layer or as a green light emitting thick-film EL layer, thereby allowing the inventive EL device to display a full-color image of a commercially acceptable brightness level. 
     While the present invention has been described with respect to certain preferred embodiments only, other modifications and variations may be made without departing from the spirit and scope of the present invention as set forth in the following claims.