Abstract:
An OLED device includes a substrate, electrode layers and organic layers arranged on the substrate and at least one metal foil on top thereof. The first metal foil is electrically connected to one of the electrode layers. An enclosure of at least the organic layers is provided by the metal foil in conjunction with a sealant  113 . Thus, the metal foil plays a major role in forming an OLED package. In addition, the metal foil provides a low ohmic external connection, which for example can be used for applying a driving current to the OLED.

Description:
FIELD OF THE INVENTION 
   The present invention relates to an OLED (Organic Light Emitting Diode) device comprising a substrate, a first conducting layer overlying the substrate, a set of organic layers overlying the first conducting layer, and a second conducting layer overlying the set of organic layers. The layers are structured such that a plurality of pixels are formed thereby on the substrate. 
   BACKGROUND OF THE INVENTION 
   OLED devices require a moisture and oxygen free environment in order to protect the organic layers and ensure a long lifetime of the device. Consequently the OLEDs must be hermetically enclosed. A typical packaging method is disclosed in the patent application US 2004/0108811, where a cap is arranged above the OLEDs and is sealed against the substrate. Such a conventional package is cheap and easy to build, while causing the package to be relatively thick and rigid. Additionally such a conventional package suffers from mechanical problems. In particular large area packages that are exposed to low ambient pressure and temperature fluctuations are prone to failure. Additionally, the conventional package does not support electrical current transport towards the device. 
   SUMMARY OF THE INVENTION 
   An object of the present invention is to provide an OLED device packaging solution that alleviates the problems of prior art mentioned above. 
   Thus, in accordance with an aspect of the present invention the OLED device comprises a substrate, a first conducting layer overlying the substrate, a set of organic layers overlying the first conducting layer, a second conducting layer overlying the set of organic layers, and a first metal foil arranged on top of the second conducting layer. At least a portion of the first conducting layer constitutes a bottom electrode layer. At least a portion of the second conducting layer constitutes a top electrode layer. The first metal foil is electrically connected to one of said bottom and top electrode layers. An enclosure of at least the set of organic layers is provided by the first metal foil in conjunction with a sealant. 
   The metal foil has the double function of forming a flexible package together with the sealant and providing a good conductivity support for one of the electrode layers. 
   According to an embodiment of the OLED device, a second metal foil is arranged. The first and second metal foils are typically, but not necessarily, connected to different electrode layers for providing a good conductivity support for both electrode layers. 
   According to an embodiment of the OLED device, the contact portions open up for many different connection options for the second metal foil. 
   According to an embodiment of the OLED device, the device comprises three or more metal foils. This implies that at least two metal foils are connected to the same electrode layer. This is useful in many different applications. 
   For example, according to an embodiment of the OLED device, individual pixel or pixel group control is achievable. Examples of applications employing such control are white light devices where pixel groups of different colours are used; addressing of different pixel groups of icons; and tuning the colour temperature of the emitted light in accordance with customer desires. 
   Thus, in accordance with the invention the package comprises one or more metal foils, where all of them contribute more or less to the tightness of the package. 
   According to an embodiment of the OLED device, applications based on differently coloured pixels can be provided. 
   According to an embodiment of the OLED device, a very compact device is obtained, having a thickness close to that of OLED devices having a cap formed of a layer that is deposited on the top electrode layer, as disclosed in US 2002/0117663. The latter technique is however considerably more expensive and does not provide the function of a low resistivity connection for at least one electrode layer. 
   According to an embodiment of the OLED device as defined in claim  8 , an advantageous connection structure is obtained. 

   
     BRIEF DESCRIPTION OF THE DRAWINGS 
     The invention will now be described in more detail and with reference to the appended drawings in which: 
       FIGS. 1-4  in cross-sectional views schematically show different embodiments of the OLED device according to the present invention; 
       FIG. 5  in a cross-sectional view schematically shows the structure of an embodiment of the device in more detail; 
       FIG. 6  is an overall view of the embodiment in  FIG. 5 ; 
       FIG. 7  in a cross-sectional view schematically shows the structure of another embodiment of the device in more detail; and 
       FIG. 8  is an overall view of the embodiment in  FIG. 7 . 
   

   DESCRIPTION OF PREFERRED EMBODIMENTS 
   An OLED device according to a first embodiment of this invention, as shown in  FIG. 1 , comprises a substrate  103 , a first conducting layer, constituting a bottom electrode layer,  105  overlying the substrate  103 , a set of organic layers  107  overlying the bottom electrode layer  105 , and a second conducting layer, constituting a top electrode layer  109  overlying the set of organic layers  107 . In this embodiment the bottom electrode layer  105  is an anode and the top electrode layer  109  is a cathode. On top of the top electrode layer  109  a metal foil  111  is arranged. A sealant in the form of glue strings  113  is applied between the foil  111  and the top surface of the anode  105 . Thus a hermetic enclosure of the intermediate layers  107 ,  109  is obtained. The foil  111  is in direct contact with the cathode  109 , and provide for a low ohmic connection of driving circuitry to the cathode. It is to be noted that the resistivity of the metal foil, typically having a thickness of some tens of microns, is in the order of 0.001 ohm/square. In comparison, plated metal, typically having a thickness of about 5 micron, has a resistivity of about 0.01 ohm/square; Al thin film, typically having a thickness of 500 nm, has a resistivity of about 0.1 ohm/square; and ITO has a resistivity of about 15 ohm/square. Because the foil  111  is arranged on top of the top electrode layer, it is possible to have it cover substantially the whole area of the device. That is, the area of the foil  111  is approximately equal to the area of the substrate  103 . 
   The OLED device can have a plurality of pixels arranged on the substrate  103 , wherein each pixel comprises a portion of said bottom electrode layer, said organic layers and said top electrode layer.  FIG. 1  shows but a portion of the device constituting one pixel. In this embodiment, the sealant  113  can be provided such that a hermetic package is obtained for each individual pixel. 
   Since the device is emitting through the substrate  103 , the substrate preferably is made of glass and the anode  105  preferably is made of a commonly used transparent material, such as ITO (Indium Tin Oxide). The cathode  109  is made of any commonly used metal. The electrode and organic layers  105 ,  107 ,  109  generally are deposited by means of any commonly used technology. The foil preferably is made of Copper, while other low resistivity metals are also possible to use. 
   In  FIG. 2  a portion of an OLED device having a plurality of metal foils is shown. In this figure two pixels are shown. The structure shown is typical for a simple single colour device, such as a display having monochrome icon addressing. This embodiment comprises a substrate  203 , a bottom electrode layer  205 , applied as a blanket metallization, which thus is common for all pixels, a set of organic layers  207 , which set is also common for all pixels, and a top electrode layer  209 , which is divided into separate portions  209   a ,  209   b , one for each individual pixel, such as a first pixel  219  and a second pixel  221  respectively, shown in  FIG. 2 . The bottom electrode layer  205  is an anode, and the top electrode layer  209  is a cathode. 
   The device further comprises a first metal foil  211 , arranged on top of but separated from the top electrode layer  209 , a second metal foil  215 , on top of and separated from the first metal foil  211 , and a third metal foil  217 , on top of and separated from the second metal foil  215 . An insulating foil is arranged beneath each metal foil  211 ,  215 ,  217 , although not shown in the figure due to reasons of clarity. The insulating foils are preferably made of polyamide. However, there are many useful alternative materials, such as Teflon® based foils and liquid crystal polymers. First connection portions  212 , preferably strings of a conductive material, connect the first foil  211  with the anode  205 . Second connection portions  214  connect the second foil  215  with the cathodes, i.e. cathode portions, of a subgroup of the pixels including the cathode portion  209   a  of the first pixel  219 . Third connection portions  216  connect the third foil  217  with the cathodes of another subgroup of the pixels, including the cathode  209   b  of the second pixel  221 . With this structure it is possible to address individual pixel groups. 
   In  FIG. 3  a more complex structure is shown. The difference from the structure of  FIG. 2  is that the set of organic layers is divided into separate portions, one for each pixel, as well, such as a first pixel  319  and a second pixel  321 , respectively. Thus, an anode  305  overlay a substrate  303 , a set of organic layers  307  overlay the anode  305 , and is divided into organic layer pixel portions  307   a ,  307   b , a cathode  309  overlay the set of organic layers  307 , and is divided into cathode pixel portions  309   a ,  309   b  corresponding to the organic layer pixel portions  307   a ,  307   b  of the set of organic layers  307 , and first, second and third metal foils  311 ,  315 ,  317  are stacked on top of the cathode  309  with insulating foils in between. Connection portions are arranged in the same way as in the embodiment shown in  FIG. 2 . 
   With the embodiment of  FIG. 3 , it is possible to build a multi colour device, for example for the above-mentioned applications, such as a white light emitter. 
   In  FIG. 4  a further embodiment is shown. This embodiment corresponds to that of  FIG. 3  except for the anode layer that is divided into separate portions  405   a  and  405   b  one for each pixel the existence of a fourth metal foil and slightly differently connected foils. Thus, the device has a substrate  403 , an anode  405  on top of the substrate  403 , a pixilated set of organic layers  407  and cathode  409  on top of the anode  405 , and first, second, third and fourth metal foils  411 ,  415 ,  417  and  423  stacked thereon. The first foil  411  is connected via connection portions  412  to the cathodes of a first subgroup of pixels including the cathode  409   a  of a first pixel  419  as shown. The second foil  415  is connected by means of connection portions  414  to the cathodes of a second subgroup of pixels including the cathode  409   b  of a second pixel  421  as shown. The third foil  417  is connected via connection portions  416  to the anodes of the first subgroup of pixels, including the anode  405   a  of the first pixel  419 . The fourth foil  423  is connected via connection portions  418  to the anodes of the second subgroup of pixels including the anode  405   b  of the second pixel  421 . 
   With this structure it is possible to provide a multi colour device with segmented display features. 
   In  FIG. 5  a portion of 3-foil device having both anode and cathode connections at the top metal foil is shown in more detail. An ITO layer divided into portions  505   a - c  is deposited on the substrate  503 . Organic layers  507  divided into portions comprising first and second portions  507   a - b  are deposited on the ITO layer portions  505   a - c . A cathode layer  509  divided into portions comprise first and second cathode portions  509   a - b  deposited on the organic layer first and second portions  507   a - b . A first metal foil  511  is arranged above and distanced from the cathode layer  509 . A first insulating foil  513  is arranged on top of the first metal foil  511 . A second metal foil  515  is arranged on top of the first insulating foil  513 . A second insulating foil  517  is arranged on top of the second metal foil  515 . A third metal foil  519  is arranged on top of the second insulating foil  517 . 
   A first ITO portion  505   a  is connected to the cathode layer  509  via bridging portions  521  of the cathode layer extending past the organic layers  507  between the cathode layer  509  and the ITO layer, i.e. protruding downwards from the cathode layer  509 . The first metal foil  511  is connected to the first ITO portion  505   a  via a connection portion  523  consisting of a suitable ITO copper interconnect, for instance ACF (Anisotropic Conductive Film). Further, the first metal foil  511  is connected to a separate portion  520  of the third metal foil  519  by means of a via portion  522  through the second insulating foil  517 , a separate portion  524  of the second metal foil  515 , and a via portion  526  through the first insulating foil  513 . A major portion  534  of the second metal foil  515  is connected by means of a via portion  525  in the first insulating foil  513 , a separate portion  527  of the first metal foil  511 , and an ACF portion  529  to the second ITO portion  505   b , which act as an anode. A further connection, similar to the one just described, between the major portion  534  of the second metal foil  515  and another portion  505   c  of the anode is shown at  535 ,  537  and  539 . The third metal foil  519  is connected to the first ITO portion  505   c  by means of a via portion  531  through the second insulating foil  517 , a separate portion  533  of the second metal foil  515 , a via portion  535  through the first insulating foil  513 , a separate portion  537  of the first metal foil  511  and an ACF portion  539 . 
   Thus, in this embodiment the bottom conductive layer (ITO) is divided into at least two anode planes and one or more separate portions, which are used as intermediate contact elements between the first metal foil and the cathode. This solution for connecting the first metal foil to the cathode is advantageous in that only one type of interconnect technology is used throughout the OLED device, i.e. interconnect between ITO and Copper. By using ACF for this interconnect, a well known interconnect technology is applied. The use of an anisotropic interconnect also provide further ease of fabrication. If for instance anode and cathode connections are arranged in line, one line of interconnect foil can be used for both contacts. Other interconnection solutions are useful as well, although they may be less desirable. 
     FIG. 6  is an overall view of the just-described embodiment. Here it is shown that, in this embodiment, the sealant  604  is limited to edge portions of the substrate  603 . The stack of metal foils and insulating foils is shown schematically at  606 , and the ACF portions  605  are shown between the substrate  603  and the stack  606 . 
   In  FIG. 7  a portion of a 2-foil device having anode connections at the top metal foil and cathode connections to the bottom metal foil is shown in more detail. Since the principles for the connection portions are the same as already explained, only a brief explanation of this figure will be made. 
   The OLED device comprises a substrate  703 , a bottom electrode layer  705 , a set of organic layers  707 , a top electrode layer  709 , a first metal foil  711 , an insulating foil  713 , and a second top most metal foil  715 . 
   A portion  721  of the first metal foil  711  is connected to the cathode layer  709  via a connection portion  723  comprising an ACF portion, a separate portion of the bottom electrode layer  705 , and bridging portions past the organic layers  707 . The second metal foil  715  is connected via connection portions  717 ,  719 , in a similar way as the second foil of the 3-foil embodiment shown in  FIG. 5  to the bottom electrode layer  705 , and more particularly to the major portion thereof constituting the anode. 
   In  FIG. 8  the embodiment of  FIG. 7  is also shown, though in an overall view. The substrate is denoted  803  and the structure arranged on the substrate is denoted  805 . External connections  807 ,  809  are schematically illustrated, where an electrically positive connection  807  is attached to the top electrode layer and an electrically negative connection  809  is attached to the bottom electrode layer. 
   Above, embodiments of the OLED device according to the present invention have been described. These should be seen as merely non-limiting examples. As understood by those skilled in the art, many modifications and alternative embodiments are possible within the scope of the invention. 
   It is to be noted, that for the purposes of this application, and in particular with regard to the appended claims, the word “comprising” does not exclude other elements or steps, that the word “a” or “an”, does not exclude a plurality, which per se will be apparent to those skilled in the art. 
   Thus, in accordance with the present invention, there is provided an OLED structure having at least one metal foil on top of the electrode and organic layers arranged onto the substrate. The metal foil(s) is(are) used for a combination of providing low resistivity connections for external connectors to one of or, preferably, both the electrodes, and providing a package that is tight and flexible. The invention is particularly useful for driving large area OLEDs.