Abstract:
Organic light emitting material may be effectively passivated in organic light emitting device display manufacture by selectively applying an organic passivation material to the recently deposited organic light emitting material. By a selective deposition process, other areas of the display need not be immediately passivated. As a result, contact areas (and other areas which should not be passivated) may remain unpassivated during the manufacturing process. By using organic passivity materials, incompatibilities between the organic light material and the passivation material may be reduced. In many cases, it may be desirable to limit the temperatures that are applied during the curing process. In one embodiment, ultraviolet curing may be utilized.

Description:
BACKGROUND  
         [0001]    This invention relates generally to organic light emitting device displays.  
           [0002]    Organic light emitting devices use an organic or polymer material that emits light for displays in electronic devices. An organic material that is light emissive may be sandwiched between row and column electrodes. When a potential is applied to the light emitting material, it emits light of a particular wavelength. The emitted light passes through the column electrode which may be transparent in some embodiments. Organic light emitting devices offer the potential for relatively low cost displays made from organic light emitting material.  
           [0003]    One problem with organic light emitting materials is that they are relatively sensitive to moisture, oxygen and common solvents. Thus, even during the manufacturing process, the organic light emitting materials may be attacked by moisture and oxygen in the surrounding atmosphere and solvents used in the remaining portions of the manufacturing process.  
           [0004]    The conventional solution to this problem is to passivate the organic light emitting materials. However, passivating them quickly after they are deposited creates new problems. Particularly, if the organic light emitting material is immediately passivated after deposition, the passivation may obstruct the remainder of the manufacturing process. For example, the deposition of passivation material may obstruct contact pads as one example. Thus, additional process steps may be needed to remove passivation that was formed early in the process.  
           [0005]    Another problem is that the organic light emitting materials are not totally compatible with conventional passivation materials. Common passivation materials are inorganic materials such as silicon nitride, phosphosilicate glass and silicon carbide. Still another problem is that many of these common passivation materials require deposition temperatures that exceed the temperatures at which organic light emitting materials may be properly processed.  
           [0006]    Thus, there is a substantial need to promptly passivate organic light emitting materials after deposition. But doing so may create a range of problems. Thus, there is a need for a way to enable organic light emitting materials to be effectively passivated. 
       
    
    
     BRIEF DESCRIPTION OF THE DRAWINGS  
       [0007]    [0007]FIG. 1 is a cross-sectional view of an organic light emitting display in accordance with one embodiment of the present invention;  
         [0008]    [0008]FIG. 2 is a partial, enlarged cross-sectional view taken generally along the line  2 - 2  in FIG. 1;  
         [0009]    [0009]FIG. 3 is a schematic depiction of one embodiment of the present invention;  
         [0010]    [0010]FIG. 4 is a schematic depiction of another embodiment of the present invention;  
         [0011]    [0011]FIG. 5 is a schematic depiction of another embodiment of the present invention; and  
         [0012]    [0012]FIG. 6 is a depiction of the results of the process shown in FIG. 5 in accordance with one embodiment of the present invention. 
     
    
     DETAILED DESCRIPTION  
       [0013]    Referring to FIG. 1, an organic light emitting device (OLED) display  10  may, in one embodiment, include a two-part system. One part is the display panel  12 , which includes a display glass  13  and tri-pixels  15  deposited thereon. The tri-pixels  15  may include organic light emitting material that emits light of a wavelength corresponding to each of three colors of a tri-color color space. Also associated with the display panel  12  may be row and column electrodes.  
         [0014]    The second component includes a circuit board  18  that interacts both with the display panel  12  and with driver integrated circuits  20 . The driver integrated circuits  20  provide signals to control the operation of the tri-pixels  15 . These signals are distributed by the circuit board  18  to the appropriate tri-pixels  15 .  
         [0015]    The display panel  12 , the circuit board  18  and the integrated circuit devices  20  may all be coupled by surface mount technology in one embodiment. The surface mount technology may include the use of solder balls or bumps  14  that are reflowed to join the various components together.  
         [0016]    Referring to FIG. 2, the display panel  12  may include contact pads  28  that contact the solder balls or bumps  14 . The contact pads  28  may, in turn, make an electrical connection through a metallization  34  to a contact  32 . The contact  32 , in turn, may couple a pad  28  to a row electrode  25 .  
         [0017]    In FIG. 2, a set of three column electrodes  25  may be associated with each pixel P. One column electrode  25  may be utilized for each of the three colors of each pixel P in one embodiment.  
         [0018]    At the same time, the row electrodes  22  may be contacted by contacts  26  coupled by metallizations  30  to contact pads  28 . The contact pads  28  coupled to the metallizations  30  are also coupled to solder balls or bumps  14 . However, the metallizations  30  couple the contact pads  28  to the row electrodes  22   a  which may extend generally transversely to the column electrodes  25 . In each case, the contacts  28  may reside in a gap between adjacent column electrodes  25 .  
         [0019]    In some cases, the row electrodes  22  may be formed of metal such as aluminum while the column electrodes  25  may be formed of a transparent material such as indium tin oxide (ITO). Sandwiched between the column and row electrodes  25  and  22  is the organic light emitting material. Generally, an entire row of pixels is activated at a single time and then the particular columns are selectively activated to create light of the desired brightness and appropriate calibration values.  
         [0020]    Thus, it can be seen that the contacts  28  are in very close proximity to the pixels P. The pixels P include the organic light emitting material which advantageously may be promptly passivated. Because of the tendency of many organic light emitting materials to be attacked by moisture, oxygen or solvents, it may be desirable to passivate the organic light emitting material as soon as possible. However doing so early in the fabrication process may also result in the imposition of passivation materials in areas in which the passivation material may be detrimental. For example, if the structure shown in FIG. 2 were passivated, the contacts  28  would also be obscured and rendered ineffective by passivation. This would necessitate additional processes to remove the passivation from the contacts  28 .  
         [0021]    To overcome these and other problems, the passivation may be selectively applied. In other words, the passivation may be selectively applied to the areas coated by the OLED while excluding areas where passivation would be undesirable, such as the areas proximate to the contacts  28 . One selective, passivation deposition technique, shown in FIG. 3, involves an ink jet printer  44  to selectively apply passivation to areas  42  while leaving areas  40  over the display panel  20  uncovered. The ink jet printer  44  is capable of applying the passivation material through a nozzle  46  at a very high rate. In this way, passivation may be selectively applied.  
         [0022]    In accordance with another technique, a passivation sprayer  50  may be utilized to spray passivation  48  over the display panel  12 , as shown in FIG. 4. A mask  52  with openings  54  may be utilized to define the regions where passivation may be applied and where it should not be applied. For example, passivation may be applied, as indicated at  56 , and no passivation may provided at the areas  58 , in one example.  
         [0023]    In the spraying technique, an organic epoxy-based passivation material that has good moisture and solvent barrier may be applied by spraying through the mask  52 . The passivation is applied where needed leaving electrical contact areas uncoated. Advantageously, ultraviolet curable materials may be utilized. However, heat curable materials may also be utilized if excessive heat (which would damage the organic light emitting material) is not necessary.  
         [0024]    Turning next to FIG. 5, a screen printing technique may be utilized to passivate selectively. In this case, a screen  60  is applied over the display panel  20 . A squeegee  64  is passed across the surface of the screen  60  causing the material  68  to be pressed into the regions where the screen  60  is open and excluded from the regions where the screen  60  is not opened. Thus, the material  68  may be applied in the region  62  and excluded from the region  63 . The squeegee  64  may include a squeegee blade  66  in one embodiment. Thus, as shown in FIG. 6, the screen printed passivation  70  ends up in the region  62  and not in the region  60 .  
         [0025]    With screen printing processes, a range of passivation material viscosities may be utilized. Also, a screen printing process, with rapid ultraviolet curing at room temperature, makes for a very fast, low temperature, inline manufacturing process in one embodiment. The rapid processing time also limits the exposure of the organic light emitting material to air where moisture absorption can occur. The screen printing process is amenable to both liquid and paste passivation materials.  
         [0026]    Paste compositions, including both organic and inorganic materials, may be tailored to achieve desirable characteristics in the cured state, including higher resistance to moisture penetration, improved thermal conductivity, and thermal expansion better matched to the substrate.  
         [0027]    In general, by using organic materials, the incompatibilities between the organic light emitting material and the organic passivation material may be reduced. One particularly advantageous organic passivation material is the Norland UV Sealant  91  available from Norland Products, Inc., Cranbury, N.J., 08512. This material is a screenable paste adhesive that cures quickly at room temperature when exposed to ultraviolet light. It absorbs less than 0.14% of water in 24 hours at 50° C. Generally, a high intensity ultraviolet light source may be utilized to cure the material in 5 to 10 seconds using a 1,000 watt or 1,500 watt medium pressure mercury lamp at 4 to 6 inches. Of course, other materials may be utilized as well.  
         [0028]    While the present invention has been described with respect to a limited number of embodiments, those skilled in the art will appreciate numerous modifications and variations therefrom. It is intended that the appended claims cover all such modifications and variations as fall within the true spirit and scope of this present invention.