Abstract:
A method for making organic light-emitting diodes on a flexible substrate includes supplying a flexible substrate, forming a plurality of thin-film layers on the flexible substrate to produce an organic light-emitting diode, disposing the flexible substrate above a barrier base and disposing a barrier cover over the substrate and the barrier base, and sealing the barrier base to the barrier cover to encapsulate the substrate between the barrier cover and the barrier base.

Description:
FIELD OF THE INVENTION 
     This invention pertains to the field of organic light-emitting devices (OLEDS) and more specifically to manufacture of OLEDs on flexible substrates. 
     BACKGROUND OF THE INVENTION 
     Flexible substrates offer a number of advantages in making OLEDs, particularly in their ability to be fed through web handling equipment. A considerable effort has been devoted to making flexible substrates including metals, plastics, and glasses. However, each of these materials has so far failed to deliver the right combination of price/performance to meet commercial needs. Plastics fail to provide an adequate barrier to moisture and oxygen infiltration, leading to premature failure of the OLED device produced on the substrate. Metals and glasses provide adequate barrier properties but have their own limitations. For metals, the obvious problem is that the metal is not transparent and therefore requires a transparent barrier layer for the other surface. In addition, since metals are conductive, an insulating layer should be deposited on the metal so that the OLED can be fabricated on top of the barrier layer. This increases complexity and cost. A number of glass companies have demonstrated glasses thin enough to be rolled on cores of a foot or less and are therefore flexible enough for web-handling, as long as all the material limitations are obeyed. However, this glass is expensive to produce and handle, especially because of the very large weight of a roll of glass. When broken, these glasses produce extremely sharp shards, often compared to razor blades. 
     In spite of the advantages of a flexible substrate for manufacture, a flexible substrate often has inadequate durability or rigidity for the final application. 
     SUMMARY OF THE INVENTION 
     It is therefore an object of the present invention to provide a web-compatible substrate on which the OLEDs are formed. The substrate is subsequently encapsulated between two barrier layers providing the required protection against oxygen and water vapor. 
     This object is achieved by a method for making organic light-emitting diodes on a flexible substrate comprising: 
     a) supplying a flexible substrate; 
     b) forming a plurality of thin-film layers on the flexible substrate to produce an organic light-emitting diode; 
     c) disposing the flexible substrate above a barrier base and disposing a barrier cover over the substrate and the barrier base; and 
     d) sealing the barrier base to the barrier cover to encapsulate the substrate between the barrier cover and the barrier base. 
     It is a feature of the present invention that it makes use of the benefits of web production without the drawbacks of flexible barrier substrates. 
    
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS 
         FIG. 1  is a schematic diagram of a prior art for producing OLEDs on a flexible substrate; 
         FIG. 2  is a schematic diagram of an embodiment of the present invention; 
         FIG. 3  is a schematic diagram of another embodiment of the invention using cut sheets of barrier cover and barrier base material; 
         FIG. 4  is a detailed schematic diagram of sealing and cutting in the embodiment of  FIG. 2 ; 
         FIG. 5A  is a schematic diagram illustrating one embodiment for making electrical contacts between OLED electrodes and external power sources; and 
         FIG. 5B  is a second view of the devices shown in  5 A. 
     
    
    
     DETAILED DESCRIPTION OF THE INVENTION 
       FIG. 1  illustrates a prior art structure for producing OLEDs on a web system using a flexible substrate. In this schematic, a flexible substrate  1  is provided on a substrate supply roll  5  which typically contains a considerable length of the substrate  1 . As the substrate  1  unrolls and works its way through a coating machine  45 , it passes a series of coating sources  10 ,  15 , and  20  which deposit organic material layers  30 ,  35 , and  40 . The coating sources can be evaporative sources in the case of small molecule OLEDs, or they can be inkjet heads, curtain coaters, or gravure printers for polymeric OLEDs, or they can employ any suitable coating technology depending on the type of OLED. 
     After coating is complete, a barrier cover material is provided from a barrier cover supply roll  25 . The barrier cover  50  is mated to the substrate/thin-film sandwich and the barrier cover  50  is bonded to the substrate. As already noted,  FIG. 1  is highly schematic. In typical web coating systems, the web (the substrate in the present invention) would traverse many different rollers to change direction, provide tensioning, drive the web, and accumulate the web when downstream processing slows or stops. 
       FIG. 2  is a schematic of an embodiment of the present invention. As in the prior art, a flexible substrate  1  is provided on a substrate supply roll  5  which typically contains a considerable length of the substrate. As the substrate unrolls and works its way through the coating machine  45 , the substrate passes a series of coating sources  10 ,  15 , and  20  which deposit material layers  30 ,  35 , and  40 . The coating sources can be evaporative sources in the case of small molecule OLEDs, or they can be inkjet heads, curtain coaters, or gravure printers for polymeric OLEDs, or they can employ any suitable coating technology depending on the type of OLED. Although not shown, the coating sources can contain the facility to produce a pattern of the deposited material. Patterning can be accomplished via masking, material removal, or by direct patterned deposition in which the deposition head is capable of directing material for deposition in selected locations. 
     After thin organic films forming the OLED have been deposited on the substrate, the substrate is sandwiched between a barrier cover  50  supplied from a barrier cover supply roll  25  and a barrier base  55 . The barrier base  55  is supplied from a barrier base supply roll  60 . The flexible substrate  1  is positioned above the barrier base  55  and below the barrier cover  50 . Either one of the barrier base or barrier cover should be transparent in order to permit the light produced by the OLED to exit the device. Both the barrier cover  50  and the barrier base  55  should provide a barrier to water vapor and oxygen. By removing the requirement that the substrate should be a barrier for water or oxygen, the present invention provides added flexibility in choosing suitable materials for the substrate. By removing the requirement that an OLED be formed on the barrier cover  50  or the barrier base  55 , the present invention provides added flexibility in choosing suitable materials for the barrier cover or the barrier base. For example, a nontransparent metal foil can readily be used as either the barrier cover  50  or the barrier base  55 . Either the barrier base  55  or barrier cover  50 , or both, can be made from polymeric materials. Still further, the present invention permits a wider selection of materials for use in forming the substrate. 
       FIG. 3  is a schematic of a second embodiment of the invention. In this embodiment, the barrier base  55  is supplied from a barrier base stack  75  of individual discrete sheets of barrier base material. Similarly, the barrier cover  50  is supplied from a barrier cover stack  70  of individual discrete sheets of barrier base material. A cut sheet  65  of OLED material is cut from the continuous substrate  1  with cutter  80  after all coating steps are complete. The cut sheet  65  is sandwiched between the barrier base and the barrier cover, which are sealed to one another. This embodiment of the invention facilitates the use of a wider range of barrier cover and barrier base materials because they are no longer required to be capable of being rolled. Low cost ordinary window glass can be used as the transparent choice between barrier base  55  and barrier cover  50 . A simple metal foil can be adequate to serve as the other barrier layer in this case since the window glass can provide the rigidity needed for many applications of the OLEDs that will be produced using this method. These are only two of the many materials that are suitable when this process is employed. The ability to select from among a wide variety of substrates and barrier materials makes the invention particularly well suited to a wide variety of products. For example, OLED flat-panel light sources intended for general illumination will generally be very price-sensitive in nature and will therefore utilize the lowest-cost barrier materials. On the other hand, OLED flat-panel displays will require distortion free barriers on the viewing side, even at the expense of higher material costs. 
       FIG. 4  is a schematic of an embodiment of the invention for sealing in the structure produced by  FIG. 2 . The substrate  1  coated with material thin-films  30 ,  35  and  45  are produced as described in the explanation of  FIG. 2 . In this embodiment, coated substrate (the substrate with the thin-films) is fed between the barrier cover  50  and barrier base  55 . A sealing unit  85 , shown schematically in this diagram as a laser, seals the barrier cover to the barrier base through the coated substrate. The coated substrate is cut in the process of forming the seal. The package, now including the barrier cover, barrier base, and coated substrate, continues to advance until it reached the cutter  80  which cuts through the barrier cover and barrier base (and the coated substrate if not already cut by the sealing process). 
     Although not shown, it will be clear to one of ordinary skill in the art that the method of  FIG. 3  in which the coated substrate is cut before being placed between the barrier cover  50  and the barrier base  55  can be applied in the system of  FIG. 2  which uses rolls of barrier base  55  and barrier cover  50 , rather than discrete pieces as in the embodiment of  FIG. 3 . Likewise, the embodiment of  FIG. 4  in which a continuous coated substrate is fed between the barrier cover and barrier base and sealed while uncut can be applied to the embodiment of  FIG. 3  in which the barrier cover  50  and barrier base  55  are supplied in discrete sheets. 
     Although the substrate supply  5  is shown as a continuous roll, it will be clear that a supply of discrete sheet material can also be used in a similar manner. 
     Another embodiment of the present invention is shown in  FIG. 5 .  FIG. 5A  shows where an anode lead  100  and a cathode lead  105  are provided on one or both of the barrier cover  50  or barrier base  55 .  FIG. 5B  shows how electrical contact is made between the anode lead  100  and the anode  95  of the organic light-emitting diode, and between the cathode lead  105  and the cathode  90  of the organic lighting diode on the substrate. When the seal is made directly between barrier cover  50  and barrier base  55 , the organic light-emitting diode is encapsulated with the anode lead  100  and the cathode lead  105  extending beyond the seal such that electrical power can be applied to the light-emitting diode through these leads. No part of flexible substrate  1 , however, is exposed to the atmosphere. The anode lead  100  and the cathode lead  105  are provided as metallic conductive films that can made by conventional film deposition techniques such as evaporation, sputtering, silk screening, electroless plating, or other deposition techniques. 
     The electrical leads, in the form of wires, tapes, or ribbons, can be attached to the anode and cathode of the OLED light-emitting diode and extended through and beyond the seal between the barrier cover  50  and barrier base  55  so that electrical power can be applied to the OLED light-emitting diode via these electrical leads causing it to emit light. When the substrate with the organic light-emitting diode is encapsulated, the seal is made directly between barrier cover  50  and barrier base  55  with no part of flexible substrate  1  exposed to the atmosphere. 
     The invention has been described in detail with particular reference to certain preferred embodiments thereof, but it will be understood that variations and modifications can be effected within the spirit and scope of the invention. 
     PARTS LIST 
     
         
           1  flexible substrate 
           5  substrate supply roll 
           10  coating source 
           15  coating source 
           20  coating source 
           25  barrier cover supply roll 
           30  material thin-film 
           35  material thin-film 
           40  material thin-film 
           45  coating machine 
           50  barrier cover 
           55  barrier base 
           60  barrier base supply roll 
           65  cut sheet 
           70  barrier cover supply stack 
           75  barrier base supply stack 
           80  cutter 
           85  sealing unit 
           90  cathode 
           95  anode 
           100  anode lead 
           105  cathode lead