Abstract:
An organic electronic device structure and a method of making the same. According to a first aspect of the invention, an organic electronic device structure is provided, which comprises: (a) a substrate layer; (b) an organic electronic region disposed over the substrate layer; (c) an adhesive layer disposed over the organic electronic device; and (d) a barrier layer disposed over the adhesive layer. According to a second aspect of the present invention, an organic electronic device structure is provided, which comprises: (a) a substrate layer; (b) an organic electronic region disposed over the substrate layer; (c) a barrier layer disposed over the organic electronic region; (d) an adhesive layer disposed over the substrate layer and over the barrier layer; and (e) an additional layer disposed over the adhesive layer. According to yet another aspect of the invention, a method for providing an organic electronic device structure of provided. The method comprises: (1) providing a first region comprising (a) a substrate layer and (b) an organic electronic region provided over the substrate layer; (2) providing a second region comprising at least one additional layer; and (3) adhering the first region to the second region using a pressure sensitive adhesive layer. In many preferred embodiments, the organic electronic device region is an OLED region.

Description:
STATEMENT OF RELATED APPLICATION  
       [0001]    This application is a continuation-in-part of U.S. application Ser. No. 10/122,969 filed Apr. 12, 2002 and entitled “PROTECTED ORGANIC ELECTRONIC DEVICES AND METHODS FOR MAKING THE SAME.” 
     
    
     
       FIELD OF THE INVENTION  
         [0002]    The present invention relates to organic electronic devices that are protected from environmental elements such as moisture and oxygen.  
         BACKGROUND OF THE INVENTION  
         [0003]    Organic electronic devices including circuits, for example, organic light emitting diodes, organic electrochromic displays, organic photovoltaic devices and organic thin film transistors, are known in the art and are becoming increasingly important from an economic standpoint.  
           [0004]    As a specific example, organic light emitting devices (“OLEDs”), including both polymer and small-molecule OLEDs, are potential candidates for a great variety of virtual- and direct-view type displays, such as lap-top computers, televisions, digital watches, telephones, pagers, cellular telephones, calculators and the like. Unlike inorganic semiconductor light emitting devices, organic light emitting devices are generally simple and are relatively easy and inexpensive to fabricate. Also, OLEDs readily lend themselves to applications requiring a wide variety of colors and to applications that concern large-area devices.  
           [0005]    In general, two-dimensional OLED arrays for imaging applications are known in the art and typically include an OLED region, which contains a plurality of pixels arranged in rows and columns. FIG. 1A is a simplified schematic representation (cross-sectional view) of an OLED structure of the prior art. The OLED structure shown includes an OLED region  15  which includes a single pixel comprising an electrode region such as anode region  12 , a light emitting region  14  over the anode region  12 , and another electrode region such as cathode region  16  over the a light emitting region  14 . The OLED region  15  is disposed on a substrate  10 .  
           [0006]    Traditionally, light from the light-emitting layer  14  is passed downward through the substrate  10 . In such a “bottom-emitting” configuration, the substrate  10  and anode  12  are formed of transparent materials. The cathode  16  and cover  20  (i.e., barrier), on the other hand, need not be transparent in this configuration.  
           [0007]    Other OLED architectures are also known in the art, including “top-emitting” OLEDs and transparent OLEDs (or “TOLEDs”). For top-emitting OLEDs, light from the light emitting layer  14  is transmitted upward through cover  20 . Hence, the substrate  10  can be formed of opaque material, if desired, while the cover  20  is transparent. In top-emitting configurations based on a design like that illustrated in FIG. 1A, a transparent material is used for the cathode  16 , while the anode  12  need not be transparent.  
           [0008]    For TOLEDs, in which light is emitted out of both the top and bottom of the device, the substrate  10 , anode  12 , cathode  16  and cover  20  are all transparent.  
           [0009]    Structures are also known in which the positions of the anode  12  and cathode  16  in FIG. 1A are reversed as illustrated in FIG. 1B. Such devices are sometimes referred to as “inverted OLEDs”.  
           [0010]    In forming an OLED, a layer of reactive metal is typically utilized as the cathode to ensure efficient electron injection and low operating voltages. However, reactive metals and their interface with the organic material are susceptible to oxygen and moisture, which can severely limit the lifetime of the devices. Moisture and oxygen are also known to produce other deleterious effects, for instance, reactions with the organic materials themselves. For example, moisture and oxygen are known in the art to increase “dark spots” and pixel shrinkage in connection with OLEDs.  
           [0011]    With the aid of a sealing region  25 , the cover  20  and the substrate  10  cooperate to restrict transmission of oxygen and water vapor from an outer environment to the active pixel  15 . Typically, the cover  20  is attached to the substrate  10  via sealing region  25  under a clean, dry, inert atmosphere.  
           [0012]    Sealing region  25  is commonly an epoxy resin adhesive. Epoxy resins, however, are typically not flexible, rendering these materials undesirable for use in connection with flexible OLEDs (or “FOLEDS”). In addition, because they are typically inflexible, because they are not pressure sensitive, and because they are typically applied in liquid form, epoxy resins are not readily adaptable for use in web-based manufacturing techniques. Moreover, epoxy resins frequently contain ingredients that are deleterious to OLEDs. Analogous difficulties are encountered in organic electronic devices other than OLEDs.  
         SUMMARY OF THE INVENTION  
         [0013]    The above and other challenges of the prior art are addressed by the present invention.  
           [0014]    According to a first aspect of the invention, an organic electronic device structure is provided, which comprises: (a) a substrate layer; (b) an organic electronic region disposed over the substrate layer; (c) a pressure sensitive adhesive layer disposed over the organic electronic device; and (d) a barrier layer disposed over the adhesive layer. In many preferred embodiments, the organic electronic device region is an OLED region.  
           [0015]    The adhesive layer can be disposed over all or a portion of the organic electronic region. For example, the adhesive layer can be, for example, in the form a continuous layer that is disposed over the entire organic electronic region or in the form of a ring that is disposed over only a portion of the organic electronic region.  
           [0016]    The adhesive layer may be, for example, a low-temperature-curable adhesive layer. In preferred embodiments, the adhesive layer is a radiation-curable adhesive layer, more preferably an ultraviolet-radiation-curable adhesive layer. The adhesive layer also preferably displays low out-gassing of harmful species, as defined hereinbelow.  
           [0017]    In many embodiments, the organic electronic device structure will include a getter material, which can be provided within the adhesive region, if desired, or elsewhere.  
           [0018]    Preferred substrate layers, and barrier layers, for use in the organic electronic device structures of this aspect of the present invention include metal layers, semiconductor layers, glass layers, ceramic layers, polymer layers and composite material layers. Where a composite material layer is selected, it preferably comprises (a) a polymer substrate sub-layer and (b) at least two alternating pairs of high-density sub-layers and planarizing sub-layers. The planarizing sub-layers may be the same or different from each other, as can the high-density sub-layers.  
           [0019]    In some instances, it is preferred to include a protective layer between the organic electronic region and the adhesive layer of the organic electronic device structure. The protective layer comprises, for example, a material selected from a silicon oxide, a silicon nitride, a silicon oxynitride, a metal oxide, an organic compound and an organometallic compound. As another example, the protective layer comprises one or more high-density sub-layers and one or more planarizing sub-layers.  
           [0020]    In other embodiments, one or more spacer structures are provided between the substrate layer and the adhesive layer to prevent the adhesive layer from physically damaging the OLED region.  
           [0021]    According to a second aspect of the present invention, an organic electronic device structure is provided, which comprises: (a) a substrate layer; (b) an organic electronic region disposed over the substrate layer; (c) a barrier layer disposed over the organic electronic region; (d) a pressure sensitive adhesive layer disposed over the substrate layer and over the barrier layer; and (e) an additional layer disposed over the adhesive layer. In many preferred embodiments, the organic electronic device region is an OLED region.  
           [0022]    The adhesive layer in accordance with this aspect of the invention can be disposed over all or a portion of the barrier layer. The adhesive layer can be, for example, in the form a continuous layer that is disposed over the entire barrier layer or in the form of a ring that is disposed over only a portion of the barrier layer. As above, the adhesive layer may be, for example, a low-temperature-curable adhesive layer. In some preferred embodiments, the adhesive layer is a radiation-curable adhesive layer, more preferably an ultraviolet-radiation-curable adhesive layer. The adhesive layer also preferably displays low out-gassing of harmful species, as defined hereinbelow.  
           [0023]    Also as above, preferred substrate layers for use in the organic electronic device structures of this aspect of the present invention include metal layers, semiconductor layers, glass layers, ceramic layers, polymer layers and composite material layers. Where a composite material layer is selected, it preferably comprises (a) a polymer substrate sub-layer and (b) at least two alternating pairs of high-density sub-layers and planarizing sub-layers. Preferred barrier layers are composite material layers that comprise at least two alternating pairs of high-density sub-layers and planarizing sub-layers. The above planarizing sub-layers may be the same or different from each other, as can the high-density sub-layers.  
           [0024]    The additional layer in accordance with this aspect of the invention can have, for example additional barrier properties, scratch resistant properties, antireflective properties and/or circular polarizing properties. The latter properties are particularly preferred where the organic electronic device structure is a transparent OLED device structure or a top-emitting OLED device structure.  
           [0025]    According to yet another aspect of the invention, a method for providing an organic electronic device structure is provided. The method comprises: (1) providing a first region comprising (a) a substrate layer and (b) an organic electronic region provided over the substrate layer; (2) providing a second region comprising at least one additional layer; and (3) adhering the first region to the second region using a pressure sensitive adhesive layer. In this aspect of the invention, the organic electronic region is provided over the substrate layer prior to contacting the first region with the adhesive layer. In many preferred embodiments, the organic electronic device structure is an OLED structure.  
           [0026]    The method can be, for example, a roll-to-roll processing method, allowing for continuous device production.  
           [0027]    In many preferred embodiments, the first region is adhered to the second region by a method comprising: (a) providing an adhesive-primed region comprising (i) the adhesive layer and (ii) one of the first and second regions; and (b) contacting the adhesive-primed region with the other of the first and second regions. In these embodiments, the adhesive layer can be transferred from a release liner to either the first or the second regions to form the adhesive primed region.  
           [0028]    In some embodiments, a barrier layer is provided with the first region, in which case the organic electronic region is positioned between the substrate layer and the barrier layer. The second region in these embodiments can comprise, for example, a layer having additional barrier properties, scratch resistant properties, antireflective properties, and/or circular polarizing properties. In other embodiments, a barrier layer is provided within the second region.  
           [0029]    During production, gas bubbles can become trapped (a) within the adhesive layer or (b) between the adhesive layer and either or both of the first and second regions. In either case, it is preferred to remove such bubbles, for example, by applying one or more of (a) heat, (b) pressure and (c) vacuum.  
           [0030]    Analogous to the above, the adhesive layer is preferably cured without the application of high temperatures. In some preferred embodiments, the adhesive layer is subjected to a radiation-curing step, more preferably, to an ultraviolet-radiation-curing step.  
           [0031]    According to another aspect of the present invention, a top emitting OLED structure is provided that comprises: (a) a substrate layer; (b) an OLED region disposed over the substrate layer, the OLED region further comprising a bottom electrode comprising a reflective layer, a light-emitting region over the bottom electrode, and a transparent top electrode over the light-emitting region; (c) an optional intervening layer disposed over the transparent top electrode; (d) an adhesive layer disposed over the substrate layer, the OLED region, and the optional intervening layer where present, wherein the refractive index of the material forming the adhesive layer is lower than the refractive index of the material that is adjacent to and below the adhesive layer; and (e) a transparent layer disposed over the adhesive layer. In this aspect, an optical microcavity is formed between (a) the top of the reflective layer of the bottom electrode and (b) the bottom of the adhesive layer. The optical thickness of the optical microcavity is typically less than 5000 Angstroms, and preferably less than 3000 Angstroms. Typically, the refractive index of the adhesive layer material is lower by 0.3 units than the refractive index of the material that is adjacent to and below the adhesive layer.  
           [0032]    In certain embodiments, the bottom electrode is an anode and the top electrode is a cathode. For example, the anode can comprise a reflective metal layer and a transparent conductive metal oxide layer disposed over the reflective metal layer, while the cathode can comprise a transparent metal layer and a transparent conductive metal oxide layer disposed over the transparent metal layer.  
           [0033]    The adhesive layer can be, for example, a pressure sensitive adhesive layer such as that discussed above, or a glue.  
           [0034]    In certain embodiments, the adhesive layer comprises a first portion that is disposed over the OLED region and a second portion that is not disposed over the OLED region, wherein the second portion has a higher refractive index than the first portion. For example, the second portion can be crosslinked to a higher density than the first portion.  
           [0035]    In embodiments where the optional intervening layer is present, the intervening layer can be, for example, a protective layer comprising a material selected from a silicon oxide, a silicon nitride, a silicon oxynitride, a metal oxide, an organic compound, and an organometallic compound.  
           [0036]    An advantage of the present invention is that organic electronic structures are provided, which are effective in protecting sensitive device components from oxygen, moisture and other harmful species in the surrounding atmosphere.  
           [0037]    Another advantage of the present invention is that organic electronic structures are provided, which afford protection from these harmful species, while at the same time being flexible and conformable to other surfaces, if desired.  
           [0038]    Another advantage of the present invention is that organic electronic structures are provided, which contain adhesive systems that are not deleterious to the protected device components.  
           [0039]    Still another advantage of the present invention is that organic electronic structures are provided, which are amenable to continuous processing techniques, such as web-based (e.g., roll-to-roll) manufacturing methods.  
           [0040]    Yet another advantage of the present invention is that organic electronic device structures are provided, in which an air gap between the top of the organic electronic region and the cover is eliminated, reducing the risk of physical damage to the organic electronic region upon flexing the structure.  
           [0041]    Yet another advantage of the present invention is that a top-emitting OLED structures are provided in which superior outcoupling of light from the OLED region is obtained.  
           [0042]    These and other aspects, embodiments and advantages of the present invention will become readily apparent to those of ordinary skill in the art upon review of the disclosure to follow. 
       
    
    
     BRIEF DESCRIPTION OF THE DRAWINGS  
       [0043]    [0043]FIGS. 1A and 1B are schematic representations (cross-sectional views) of known OLED structures.  
         [0044]    [0044]FIG. 2A is a schematic cross-sectional view of an OLED structure in accordance with one embodiment of the present invention.  
         [0045]    [0045]FIG. 2B is a schematic plan view of the adhesive layer of FIG. 2A, in accordance with an embodiment of the present invention.  
         [0046]    [0046]FIG. 3 is a schematic cross-sectional view of an OLED structure in accordance with another embodiment of the present invention.  
         [0047]    [0047]FIG. 4 is a schematic cross-sectional view of an OLED structure in accordance with yet another embodiment of the present invention.  
         [0048]    [0048]FIG. 5 is a schematic cross-sectional view of an OLED structure in accordance with still another embodiment of the present invention.  
         [0049]    [0049]FIG. 6 is a schematic cross-sectional view of an OLED structure in accordance with another embodiment of the present invention.  
         [0050]    [0050]FIG. 7 is a schematic illustration of an OLED structure lamination process, in accordance with an embodiment of the present invention.  
         [0051]    [0051]FIG. 8 is a schematic illustration of an OLED structure lamination process, in accordance with another embodiment of the present invention.  
         [0052]    [0052]FIG. 9 is a schematic cross-sectional view of an OLED structure in accordance with another embodiment of the present invention.  
         [0053]    [0053]FIG. 10 is a schematic illustration of an OLED structure lamination process, in accordance with another embodiment of the present invention. 
     
    
       [0054]    As is typically the case with such figures, the above are simplified schematic representations presented for purposes of illustration only, and the actual structures will differ in numerous respects including the relative scale of the components.  
       DETAILED DESCRIPTION OF THE INVENTION  
       [0055]    The present invention now will be described more fully hereinafter with reference to the accompanying drawings in which preferred embodiments of the invention are shown. This invention may, however, be embodied in different forms and should not be construed as limited to the embodiments set forth herein. For example, although the embodiments below are directed to OLED structures, the techniques and structures of the present invention are applicable to other organic electronic devices as well.  
         [0056]    As used herein, a “layer” of a given material includes a region of that material whose thickness is small compared to both its length and width. Examples of layers include sheets, foils, films, laminations, coatings, and so forth. As used herein, a layer need not be planar, but can be bent, folded or otherwise contoured, for example, to at least partially, or even completely, envelop another component. As used herein, a layer can also include multiple sub-layers. As used herein, a layer can constitute a single region of material (for example, a patterned layer can be provided in the form of a ring) or it can consist of a collection of discrete regions of material (for example, a patterned layer can be provided in the form of a collection of bands or dots).  
         [0057]    [0057]FIG. 2A is a simplified schematic representation (cross-sectional view) of an OLED structure  100  in accordance with an embodiment of the present invention. The OLED structure  100  includes an OLED region  116  situated on a substrate layer  110 . Over the OLED region  116  is a barrier layer  120 . An adhesive layer  130  is provided to attach the barrier layer  120  to the OLED region  116  and substrate layer  110 .  
         [0058]    The substrate layer  110  and barrier layer  120  are selected to, among other things, restrict transmission of oxygen and water from the outside environment to the OLED region  116 . Depending on the application, the substrate layer  110  and barrier layer  120  can be opaque or transparent. For traditional bottom-emitting OLED structures, the substrate layer  110  will be transparent, as least in part, while the barrier layer  120  can be opaque. For top-emitting OLED structures, the substrate layer  110  can be opaque, while the barrier layer  120  will be transparent, at least in part. For TOLED structures, both the substrate layer  110  and the barrier layer  120  will be transparent, at least in part. By “transparent” is meant that attenuation of radiation as it passes through the region of interest is low, with transmissivities typically greater than 50%, preferably greater than 80%, at the wavelength of interest.  
         [0059]    The materials selected for the substrate layer  110  and barrier layer  120  will depend upon the application at hand and include semiconductors, metals, ceramics, polymers and composite layers.  
         [0060]    Semiconductors such as silicon offer good barrier properties to water, oxygen and other harmful species and also provide a substrate layer upon which electronic circuitry can be built.  
         [0061]    Metals also offer excellent barrier properties. Preferred materials include aluminum, gold, nickel, nickel alloys and indium, as well as other metals known in the art. Metals can be provided in a number of configurations as a barrier layer or substrate layer for an OLED structure, such as in the form of metal cans and foils. Where flexibility is desired, metal foils are preferred. For instance, OLED structures are known in the art that are referred to a flexible OLEDs (or “FOLEDS”). As the name suggests, these structures are flexible in nature, utilizing flexible substrate layer  110  and barrier layer  120  materials.  
         [0062]    Ceramics also offer low permeability, and they provide transparency as well in some cases.  
         [0063]    Polymers are often preferred where optical transparency is desired and flexibility is desired. Preferred low permeability polymers include polyesters, polyethersulphones, polyimides and fluorocarbons, with such layers commonly being used in connection with composite barriers as discussed below.  
         [0064]    Composite materials are also among those materials preferred for use in connection with the substrate layer  1   10  and barrier layer  120 . Composite materials are advantageous, for example, in that they can provide transparency and flexibility, while also providing good resistance to transmission of chemical species such as water and oxygen. Composite materials are discussed further below in connection with FIGS. 5 and 6.  
         [0065]    The adhesive layer  130  of FIG. 2A preferably provides a barrier to adverse exterior environmental species, including water and oxygen, and provides good adhesion between adjacent regions. The adhesive layer  130  also preferably displays low out-gassing of harmful species. As used herein, “displays low out-gassing of harmful species” means that out-gassing is sufficiently minimized to prevent unacceptably low product quality during production. For example, with respect to OLEDs, this expression means that out-gassing is sufficiently low to prevent the formation of an unacceptably high dark spot levels and/or pixel shrinkage during production and through the intended lifetime of the display.  
         [0066]    In some embodiments, the adhesive layer  130  of the present invention is also preferably a pressure sensitive adhesive layer, at least before it is cured. As used herein, a “pressure sensitive” adhesive is one that adheres with as little as finger pressure, while requiring no activation for adhesion. Moreover, as discussed further below, in some embodiments of the invention, the pressure sensitive adhesive layers of the present invention are provided on a release layer, making them desirable for web-based manufacturing techniques.  
         [0067]    Preferred pressure sensitive adhesives for the adhesive layers  130  of the present invention include the following: ARclean™ and ARclad® low-out-gassing adhesives available from Adhesives Research, Inc., Glen Rock, Pa.; Ultra-Clean Laminating Adhesive 501FL and Optically Clear Laminating Adhesive 8141 both available from 3M Bonding Systems Division, St. Paul, Minn.; and 1034-series adhesives available from Craig Adhesives and Coatings Company, Newark, N.J. The thickness of the adhesive region typically ranges from 0.5 to 10 mils, more preferably 0.5 to 5 mils.  
         [0068]    The OLED region  116  can be of any design known in the art. For example, the OLED region  116  can comprise one or many pixels, which typically comprise an upper electrode layer  116   ue  and a lower electrode layer  116   le,  one of which electrodes is the anode and the other of which electrodes is the cathode, as well as a light-emitting layer (emission layer)  116   e  disposed between the anode and cathode.  
         [0069]    The light emitting layer  116   e  can be provided in connection with a number of configurations, including the following: (a) a three-layer configuration comprising a hole transporting sub-layer, an emission sub-layer and an electron transporting sub-layer (i.e., a double heterostructure configuration), (b) a two-layer configuration comprising a hole transporting sub-layer and a sub-layer that provides both emission and electron transporting functions (i.e., a single heterostructure configuration) and (c) a configuration comprising a single layer that provides hole transporting, electron transporting and emission functions (i.e., a single layer configuration). In each configuration, additional layers may also be present, for example, layers that enhance hole injection or electron injection, or layers that serve to block holes or electrons or excitons. Several structures for such devices are discussed, for example, in U.S. Pat. No. 5,707,745, the entire disclosure of which is hereby incorporated by reference. Other more complex OLED architecture is also practiced in the art.  
         [0070]    Depending on the application, the anode may be a transparent anode or an opaque anode (which can be a reflective in some cases). Opaque anode materials include metals such as gold, chromium, magnesium/silver or other materials known in the art, while transparent anode materials include metal oxides such as indium tin oxide (ITO), zinc tin oxide or other materials known in the art. Similarly, the cathode can be transparent or opaque depending on the application. Opaque cathode materials may include metals such as aluminum, aluminum/lithium, aluminum/lithium fluoride, or other materials is known in the art, while transparent cathode materials may include metal/metal oxide combinations such as Mg—Ag/ITO, Ca/ITO or other materials known in the art.  
         [0071]    Where it is desirable to create an optical microcavity, thus enhancing outcoupling from the upper surface of the device  110 , the refractive index of the adhesive layer  130  is typically less than that of the top region of the adjacent upper electrode  116   ue,  and preferably as close to 1 (the refractive index of a vacuum) as possible.  
         [0072]    For example, in one specific embodiment of the invention, the device  110  is a top-emitting device. The upper electrode  116   ue  is a transparent cathode, comprising, for example, a metal oxide layer, such as a layer of ITO, over a thin reactive metal layer, such as a layer of Ca or Mg—Ag alloy. The lower electrode is a reflective anode, comprising, for example, a layer of transparent conductive oxide, such as a layer of ITO, over a layer of reflective metal, such as a layer of Ag, Al, Ni, Cr, etc. By “reflective” is meant that the amount of radiation reflected from a surface is high, with, with reflectivities typically greater than 50%, preferably greater than 80%, at the wavelength of interest. The refractive index of ITO (in this example, the top region of the upper electrode  116   ue ) typically ranges from about 1.8 to about 2.0. Thus, for enhanced microcavity effects, the refractive index of the adjacent adhesive layer  130  is less than this amount, for example, less than 1.7, 1.6, 1.5, 1.4, 1.3 or 1.2 and, indeed, as close to 1 as possible.  
         [0073]    In this embodiment, an optical microcavity is established between (a) a lower interface, associated with the top surface of the reflective metal layer and (b) an upper interface, associated with the bottom surface of the adhesive layer. Microcavity effects at visible wavelengths are further enhanced by ensuring that the optical distance between these interfaces is less than 5000 Angstroms, more preferably less than 4000 Angstroms, or even 3000 Angstroms or less. The optical distance is the sum of the product of the refractive index and the layer thickness for each region between the interfaces. Further information can be found, for example, in M. -H. Lu et al., “High-efficiency top-emitting organic light-emitting devices,”  Applied Physics Letters,  18 (21), 3921-3923 (Nov. 18, 2002).  
         [0074]    As noted above, preferred materials for the adhesive layer  130  include pressure sensitive adhesives, which are more preferably UV-curable. UV curing typically increases the crosslinking density of a given material. Increased crosslinking, in turn, is typically accompanied by an increase in the barrier properties of the material as well as an increase in the refractive index of the material. Consequently, it is desirable to vary the level of crosslinking within the adhesive layer in certain embodiments.  
         [0075]    For example, FIG. 2B is a schematic plan view of the adhesive layer  130  of the OLED structure of FIG. 2A. The position of the OLED region  160  that lies beneath the adhesive layer  130  is illustrated with dashed lines to provide a frame of reference. As can be seen from FIGS. 2A and 2B, the adhesive layer  130  forms an interface with the surrounding atmosphere at the outer edges of the device. As indicated above, the diffusivity of harmful molecules, such as water and/or oxygen molecules within a given substance typically decreases with an increase in crosslink density. Accordingly, the portion  130   h  of the adhesive layer  130  that lies near the edge of the device (illustrated with darker gray shading) is more highly crosslinked than the portion  130   l  of the adhesive layer  130  that lies away from the edge and over the OLED region  160  (illustrated with lighter gray shading) in the embodiment shown. The entirety of the adhesive layer  130  is not highly crosslinked in this embodiment, however, because an increase in crosslinking is also typically accompanied by an increase in refractive index. Accordingly, the beneficial increase in barrier properties that is observed with higher crosslinking can be traded off against the detrimental effect that higher crosslinking has upon microcavity effects, leading in this particular instance to an adhesive layer  130  having portions of higher  130   h  and lower  130   l  crosslink density.  
         [0076]    An advantage of an OLED structure  100  like that of FIG. 2A is that it is effective in protecting sensitive device components from oxygen, moisture and other harmful species in the surrounding atmosphere. This structure is also advantageous in that it is possible to produce OLED structures that are flexible and conformable to other surfaces.  
         [0077]    Furthermore, with the OLED structure  100  shown, the barrier layer  120  is securely affixed to the underlying regions. This is believed to be due to the fact that a large interfacial area exists between the adhesive layer  130  and adjacent regions. Moreover, where a thin adhesive layer  130  is utilized (e.g., 0.5 to 5 mils), there is only a very small difference in the radii of curvature between the layers on opposite sides of the adhesive layer  130 , minimizing stresses that arise upon flexing the structure  100 .  
         [0078]    A device like that of FIG. 2A can be constructed in a number of ways. According to one embodiment, the adhesive layer  130  is provided between two regions: (a) the barrier layer  120  and (b) the substrate layer  110  with attached OLED region  116  (as with most OLED fabrication processes, device fabrication is typically done in an inert atmosphere, for example, within a nitrogen glovebox). Any bubbles within the adhesive layer  130  or between the adhesive layer  130  and the adjacent regions can then be removed, for instance, by heating the adhesive layer  130  to lower the viscosity of the same (e.g., by heating to 40 to 70° C.), by applying a vacuum (e.g., in connection with a vacuum oven) to the structure, by applying pressure (e.g., using rollers) to the structure, or by a combination of two or all three of these techniques. After bubble removal, the adhesive layer  130  is preferably cured, for example, by simply allowing a sufficient amount of time to pass in the case of self-curing adhesives, by exposure to ultraviolet light in the case of UV-curable adhesives, by exposure to heat in the case of heat-curable adhesives, and so forth. Where a layer like that of FIG. 2B is desired, more cure is applied to the outer portion  130   h  than the inner portion  130   l  of the adhesive layer  130 , for example, using masks.  
         [0079]    In some embodiments, a protective layer  126  is provided between the adhesive layer  130  and the OLED region  116  as illustrated in FIG. 3. Protective layers are beneficial, for example, where the adhesive layer  130  contains particulate materials that would otherwise harm the OLED region  116 . In this instance, the protective layer  126  should be sufficiently thick and/or tough, such that the particulate materials in the adhesive layer  130  do not puncture the protective layer  126  and damage the underlying OLED region  116 . Preferred materials for the protective layer  126  include organometallic materials such as copper phthalocyanine (CuPc), organic compounds such as 4,4′-bis[N-(1-napthyl)-N-phenyl-amino] biphenyl (NPD), silicon compounds such as silicon oxide, silicon nitride and silicon oxynitride, metal oxides such as aluminum oxide, indium-tin oxide and zinc indium tin oxide, some of which materials are used as high-density materials for the cooperative barrier sub-layer structures discussed below.  
         [0080]    Where microcavity effects are to be taken into consideration, for example, in the case of a top-emitting OLED, the refractive index differential between the protective layer  126  (also referred to herein as an optional intervening layer) and the adjacent adhesive layer is preferably maximized. Typically, this involves maximizing the refractive index of the protective layer and minimizing the refractive index of the adhesive layer. The upper interface defining the microcavity continues to be that associated with the bottom surface of the adhesive layer as above. However, in this embodiment, there is now an additional layer (i.e., the protective layer  126 ) that must be taken into account when evaluating the optical length of the microcavity.  
         [0081]    In other embodiments, the protective layer  126  is a composite layer. For example, the protective layer can consist of a high-density sub-layer (e.g., a thin oxide layer) deposited over the OLED, followed by a planarizing (e.g., polymer) sub-layer and another high-density (e.g., oxide) sub-layer.  
         [0082]    Another way of addressing the presence of particulate materials in the adhesive layer  130  is by providing spacer structures (not shown) to separate the adhesive layer  130  from critical elements within the OLED region  116 . For example, where the OLED region contains a plurality of active pixels arranged in rows and columns, such spacer structures can be provided between the active pixels. This is advantageous from an outcoupling standpoint, because the gas/air found at the upper interface has a refractive index of close to 1.  
         [0083]    Although the adhesive layers  130  illustrated in FIGS. 2 and 3 lie adjacent to essentially the entire surface of the barrier layer  120  (this configuration is referred to herein as a “face seal”), other configurations are possible. For example, as seen in FIG. 4, the adhesive layer  130  can be provided in the form of a layer that is patterned in the shape of a ring (referred to herein as a “perimeter seal”), which laterally surrounds the OLED region  116 . In this embodiment, the substrate layer  110 , barrier layer  120  and ring-shaped adhesive layer  130  cooperate to surround the OLED region  116 , protecting it from species in the outside environment. Because the adhesive layer  130  need not come into contact with all portions of the OLED region  116 , this embodiment is beneficial, for example, where the adhesive layer  130  contains particulate materials that could harm the OLED region  116 .  
         [0084]    A getter material  118  may also be provided with the OLED structures  110  of the present invention, as illustrated in FIG. 4. The getter material can be essentially any getter material that reacts readily with active gases (including water and oxygen), forming stable low-vapor-pressure chemical compounds so as to remove the active gases from the gas phase. The getter material  118  is provided to remove reactive gases such as water and oxygen in the event that they penetrate the sealed package, before these gases have the opportunity to cause damage to the OLED region  116 . Desiccants, which are a class of getter material that remove water, are useful for the practice of the present invention.  
         [0085]    Preferred getter materials include Group IIA metals and metal oxides, such as calcium metal (Ca), barium metal (Ba), calcium oxide (CaO) and barium oxide (BaO). Preferred products include HICAP2000, a calcium oxide paste obtainable from Cookson SPM (Alpha Metals). Metal getter layers can be applied, for example, to the substrate layer or barrier layer using a number of techniques including vacuum deposition techniques such as thermal evaporation, sputtering, and electron-beam techniques. Essentially any desired pattern can be formed, for example, by resorting to a mask such as a shadow mask during the deposition process. Patterned getter layers in paste form, such as the above-mentioned CaO paste, can be provided by a number of techniques including screen-printing and dispensation through a syringe.  
         [0086]    In some instances, the patterned getter material may have marginal flexibility for the application at hand, for example, when the material is used within a FOLED. One way to address this issue is to make the dimensions of the getter material small, for example, by providing the getter material in a patterned layer consisting of a number of narrow bands or dots.  
         [0087]    In some embodiments of the present invention, a getter material is provided within the adhesive layer.  
         [0088]    As noted above, composite materials are among those materials preferred for use in connection with the substrate layer  110  and/or barrier layer  120 . Referring now to FIG. 5, for example, an OLED structure  100  is illustrated, which is like that of that of FIG. 2A, except that the substrate layer  110  of FIG. 5 is shown as comprising a substrate sub-layer  115  and a series cooperative barrier sub-layers. The cooperative barrier sub-layers include both sub-layers of planarizing material  111   a - c  and sub-layers of high-density material  112   a - c.  These cooperative barrier sub-layers are preferably provided in an alternating configuration. Preferably, 1 to 10 pairs of these sub-layers, more preferably 3 to 7 pairs, are used. Thus, although three alternating pairs are illustrated in FIG. 3, other sub-layer arrangements are possible.  
         [0089]    The cooperative barrier sub-layers  111   a - c  and  112   a - c  are disposed adjacent the polymeric substrate sub-layer  115  in the embodiment shown in FIG. 5. As a result, during manufacture, the substrate sub-layer  115  can act as a foundation upon which the cooperative barrier sub-layers  111   a - c  and  112   a - c  can be laid.  
         [0090]    Where flexibility is desired, the substrate sub-layer  115  may comprise paper, fabric, metal foil, flexible glass (available, for example, from Schott Glass Technologies) and/or polymer layers. Flexibility is desirable, for example, in the manufacture of FOLEDs and renders the devices formable using web-based, roll-to-roll manufacturing techniques. More preferred flexible substrate sub-layer materials are those that comprise one or more polymer components, including polyesters, polycarbonates, polyethers, polyimides, polyolefins, and fluoropolymers that are capable of providing a strong adhesive bond with other materials. Such polymer components can be supplied, for example, in connection with homopolymers, copolymers and polymer blends. Examples of some preferred polymer components include, for example, polyethersulphones, polyarylates, polyestercarbonates, polyethylenenaphthalates, polyethyleneterephthalates, polyetherimides, polyacrylates, polyimides such as Kapton® polyimide film available from DuPont, fluoropolymers such as Aclar® fluoropolymer available from Honeywell, Appear® PNB (polynorbornene) available from BF Goodrich and Arton® available from BF Goodrich. The substrate sub-layer  115  in this instance typically ranges from 75 to 625 microns in thickness.  
         [0091]    By “planarizing material” is meant a material that forms a smooth planar surface upon application, rather than forming a surface that reflects irregular contours of the underlying surface. Preferred planarizing materials include polymers, such as fluorinated polymers, parylenes, cyclotenes and polyacrylates and combinations thereof. Sub-layers of such planarizing materials  111   a - 111   c  can be provided using techniques known in the art, for example, by dipping, spin coating, sputtering, evaporative coating, spraying, flash evaporation, chemical vapor deposition and so forth.  
         [0092]    By “high-density material” is meant a material with sufficiently close atomic spacing such that diffusion of contaminant and deleterious species, particularly water and oxygen, are hindered. Preferred high-density materials include inorganic materials such as metal oxides, metal nitrides, metal carbides and metal oxynitrides and combinations thereof. More preferred are silicon oxides (SiOx), including silicon monoxide (SiO) and silicon dioxide (SiO 2 ), silicon nitrides (typically Si 3 N 4 ), silicon oxynitrides, aluminum oxides (typically Al 2 O 3 ), indium-tin oxides (ITO) and zinc indium tin oxides and combinations thereof. Sub-layers of high-density material  112   a - 112   c  can be applied using techniques known in the art such as thermal evaporation, sputtering, PECVD methods and electron-beam techniques.  
         [0093]    Examples of composite barrier layers comprising sub-layers of both high-density material and planarizing material formed on a polymer substrate sub-layer are disclosed, for example, in U.S. Pat. No. 5,757,126, the entire disclosure of which is hereby incorporated by reference.  
         [0094]    It is noted that the substrate layer  110  as illustrated in FIG. 5 can be inverted such that the substrate sub-layer  115  is at the bottommost position, as is seen in FIG. 6. Moreover, if desired, the barrier layer  120  can include a composite barrier layer. For example, as seen in FIG. 6, a barrier layer  120  is provided which includes a substrate sub-layer  125 , planarizing materials  121   a - b  and high-density layers  122   a - b.    
         [0095]    As noted above, due to their flexibility, composite substrates  110  and composite barrier layers  120  are useful in connection with FOLED devices. Their flexibility also renders them useful for web-based, roll-to-roll processing.  
         [0096]    One example of a web-based scheme for attaching a barrier region  123  (containing a flexible barrier layer, for example) to an OLED containing region  114  (containing a substrate layer, an OLED region, and a protective layer, for example) is illustrated in FIG. 7. As seen in this figure, the flexible barrier region  123  and an adhesive containing layer  135  (which includes an adhesive layer and an adjacent release layer in this example) are fed through heated rollers  200   a  to soften the adhesive and prevent bubbles from becoming established between the barrier region  123  and the adhesive layer. After emerging from the rollers  200   a,  the release layer  132  is removed. The resulting adhesive barrier region  140  (which consists of barrier region  123  layer with adjacent adhesive layer in this embodiment) is then fed, along with the OLED containing region  114 , through heater rollers  200   b  to again facilitate bubble removal. After emerging from the rollers  200   b,  the resulting OLED structure  110  is exposed to ultraviolet light to cure the adhesive layer. If desired, masking may also be used to facilitate ultraviolet curing of regions of film to different degrees in order to realize structures such as that of FIG. 2B. The positions of the barrier region  123  and the OLED containing region  114  in FIG. 7 can be reversed, if desired.  
         [0097]    Another processing scheme is illustrate in FIG. 8. As seen in this figure, a flexible barrier region  123  (containing a flexible barrier layer, for example), an adhesive layer  130 , and an OLED containing region  114  (containing, for example, a substrate layer, an OLED region, and a protective layer) are simultaneously fed through heated rollers  200 . As above, the heated rollers soften the adhesive and prevent bubbles from persisting between the adhesive layer  130  and the adjacent layers  120 ,  114 . After emerging from the rollers  200 , the resulting OLED structure  110  is exposed to ultraviolet light to cure the adhesive layer.  
         [0098]    Numerous additional variations are possible in accordance with the present invention, an example of which is illustrated in FIG. 9. Like FIGS. 5 and 6, an OLED region  116  is disposed over a substrate layer  110  that includes a substrate sub-layer  115  and an alternating series of planarizing material sub-layers  111   a - c  and high-density material planarizing material  112   a - c.  Moreover, like FIG. 6, the OLED structure of FIG. 9 contains a barrier layer  120 , which includes planarizing material sub-layers  121   a - b  and high-density sub-layers  122   a - b.  However, the barrier layer  120  of FIG. 9 does not contain a substrate sub-layer  125 , because the planarizing material sub-layers  121   a - 121   b  and high-density sub-layers  122   a - 122   b  have been deposited directly over the OLED region  116 , eliminating the need for a separate substrate sub-layer. Finally, a top layer  150  is attached to the remainder of the structure via adhesive layer  130 . Top layer  150  can be provided with a number of desirable properties, including barrier properties, scratch resistance, antireflective properties, circular polarizing properties and so forth. Hence, in the embodiment illustrated in FIG. 9, the adhesive region  130  is disposed between one region containing a top layer  150  and another region containing substrate layer  110 , OLED region  116  and barrier layer  120 . This is in contrast with the embodiments of FIGS.  3 - 6 , in which the adhesive layer  130  adheres one region containing a substrate layer  110  and an OLED region  116  to another region containing a barrier layer  120 .  
         [0099]    One example of a web-based scheme for attaching a top layer  150  to an OLED containing region  214  (containing a substrate layer, an OLED region, and a barrier layer, for example) is illustrated in FIG. 10. As seen in this figure, the top layer  150  and an adhesive containing layer  135  (which includes an adhesive layer and an adjacent release layer in this example) are fed through heated rollers  200   a  to soften the adhesive and prevent bubbles from persisting between the top layer  150  and the adhesive layer. After emerging from the rollers  200   a,  the release layer  132  is removed. The resulting adhesive top region  240  (which consists of top layer  150  layer with adjacent adhesive layer in this embodiment) is then fed, along with the OLED containing region  214 , through heated rollers  200   b  to again facilitate bubble removal. After emerging from the rollers  200   b,  the resulting OLED structure  110  is exposed to ultraviolet light to cure the adhesive layer. The positions of the top layer  150  and the OLED containing region  214  in FIG. 10 can be reversed, if desired the fabrication of the OLED structure  110 . Moreover, a process analogous to the process of FIG. 8 can also be used to fabricate the OLED structure  110 .  
         [0100]    Although the present invention has been described with respect to several exemplary embodiments, there are many other variations of the above-described embodiments that will be apparent to those of ordinary skill in the art. It is understood that these variations are within the teachings of the present invention, and that the invention is to be limited only by the claims appended hereto.