Title: Protected organic electronic devices and methods for making the same
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.
Patent Number: 6,897,474 Issued on 05/24/2005 to Brown, et al.
| Inventors:
|
Brown; Julia J. (Yardley, PA);
Weaver; Michael Stuart (Princeton, NJ);
Lu; Min-Hao Michael (Lawrenceville, NJ)
|
| Assignee:
|
Universal Display Corporation (Ewing, NJ)
|
| Appl. No.:
|
407820 |
| Filed:
|
April 4, 2003 |
| Current U.S. Class: |
257/40 |
| Intern'l Class: |
H01L 035/24 |
| Field of Search: |
257/40
|
References Cited [Referenced By]
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| 5703436 | Dec., 1997 | Forrest et al.
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| 5707745 | Jan., 1998 | Forrest et al.
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| 5757126 | May., 1998 | Harvey, III et al.
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| 5920080 | Jul., 1999 | Jones.
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| 6146225 | Nov., 2000 | Sheats et al.
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| 6224948 | May., 2001 | Affinito.
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| 6268695 | Jul., 2001 | Affinito.
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| 2002/0125822 | Sep., 2002 | Graff et al.
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| 2003/0062830 | Apr., 2003 | Guenther et al.
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| 2004/0080938 | Apr., 2004 | Holman et al.
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| Foreign Patent Documents |
| 0405361 | Jan., 1991 | EP.
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| 1116987 | Jul., 2001 | EP.
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| 08236271 | Sep., 1996 | JP.
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| WO 0026973 | May., 2000 | WO.
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| WO 0036665 | Jun., 2000 | WO.
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| WO 0205361 | Jan., 2002 | WO.
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| WO 0306/5470 | Aug., 2003 | WO.
| |
Other References
Jeff Silvernail et al., Packaging OLED Displays using Dual Stage Pressure Sensitive
Adhesives, Jul. 12, 2002.
Jeff Silvernail et al., "Packaging OLED Displays using Dual Stage Pressure Sensitive
Adhesives, " Power Point presentation, Oct. 11, 2002.
"Vertical-Cavity Organic Light-Emitting Diode Display," IBM Technical Disclosure
Bulletin, vol. 40, No. 9, Sep. 1997, pp. 165-167.
Craig Adhesives and Coatings Company, UV Pressure Sensitive Adhesives, http://www.craigadhesivescom/UVLaminating.htm;
and Products, http://www.craigadhesives.com/products.htm.
Adhesives Research Inc., Standard Product Catalogue, http://www.adhesivesresearch.com/catalog/home/htm;
Specialty Industrial and Electronics Tapes, www.adhesivesresearch.com/catalog/indust/htm;
Industrial and Electronics Products, www.adhesivesresearch.com/catalog/indelec.htm;
Product Development Process www.adhesivesresearch.com/techcntr/atcprddv.htm; and
Materials Technologies, www.adhesivesrescarch.com/techcntr/atcrnatr.htm.
Hybrid Design For Organic Electroluminescent Devices, IBM Technical Disclosure
Bulletin, Sep. 1, 2997, vol. 40, Issue 9, p. 115-116.
M.H. Lu et al., "High -efficiency top-emitting organic light-emitting devices,"
Applied Physics Letters, vol. 81, No. 21, Nov. 18, 2002, pp. 3921-3923.
|
Primary Examiner: Nelms; David
Assistant Examiner: Le; Thao P.
Attorney, Agent or Firm: Mayer Fortkort & Williams, PC, Bonham, Esq.; David B.
Parent Case Text
STATEMENT OF RELATED APPLICATION
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."
Claims
1. A top emitting OLED structure comprising:
a substrate layer;
an OLED region disposed over the substrate layer, said OLED region comprising
a bottom electrode comprising a reflective layer, a light-emitting region over
said bottom electrode, and a transparent top electrode over said light-emitting
region;
an optional intervening layer disposed over said transparent top electrode;
an adhesive layer disposed over said substrate layer, said OLED region, and said
optional intervening layer, wherein the refractive index of the adhesive layer
material is lower than the refractive index of the material that is adjacent to
and below said adhesive layer; and
a transparent layer disposed over the adhesive layer;
wherein an OLED microcavity is formed between (a) the top of said reflective
layer and (b) the bottom of said adhesive layer.
2. The top emitting OLED structure of claim 1, wherein said bottom electrode
is an anode and said top electrode is a cathode.
3. The top emitting OLED structure of claim 2, wherein said anode comprises a
reflective metal layer and a transparent conductive metal oxide layer disposed
over said reflective metal layer.
4. The top emitting OLED structure of claim 2, wherein said cathode comprises
a transparent metal layer and a transparent conductive metal oxide layer disposed
over said transparent metal layer.
5. The top emitting OLED structure of claim 1 wherein said adhesive layer is
a glue.
6. The top emitting OLED structure of claim 1, wherein said adhesive layer is
a pressure sensitive adhesive layer.
7. The top emitting OLED structure of claim 6, wherein said adhesive layer is
a low-temperature-curable adhesive layer.
8. The top emitting OLED structure of claim 6, wherein said adhesive layer is
a radiation-curable adhesive layer.
9. The top emitting OLED structure of claim 6, wherein said adhesive layer is
an ultraviolet-radiation-curable adhesive layer.
10. The top emitting OLED structure of claim 1, wherein said adhesive layer displays
low out-gassing of harmful species.
11. The top emitting OLED structure of claim 6, wherein said adhesive layer comprises
a first portion disposed over said OLED region and a second portion that is not
disposed over said OLED region, and wherein said first portion has a lower refractive
index than said second portion.
12. The top emitting OLED structure of claim 11, wherein said second portion
has a higher crosslink density than said first portion.
13. The top emitting OLED structure of claim 1, wherein said optional intervening
layer is present.
14. The top emitting OLED structure of claim 13, wherein said optional intervening
layer comprises a material selected from a silicon oxide, a silicon nitride, a
silicon oxynitride, a metal oxide, an organic compound, and an organometallic compound.
15. The top emitting OLED structure of claim 1, wherein said OLED structure is
a flexible OLED structure.
16. The top emitting OLED structure of claim 1, wherein said substrate layer
is selected from a metal layer, a semiconductor layer, a glass layer, a ceramic
layer, a polymer layer, and a composite material layer.
17. The top emitting OLED structure of claim 1, wherein said barrier layer is
a glass layer.
18. The top emitting OLED structure of claim 1, wherein the optical thickness
of said microcavity is less than 5000 Angstroms.
19. The top emitting OLED structure of claim 1, wherein said barrier layer is
a composite material layer that comprises (a) a polymer substrate sub-layer and
(b) at least two alternating pairs of high-density sub-layers and planarizing sub-layers,
which high-density sub-layers may be the same or different from each other and
which planarizing sub-layers may be the same or different from each other.
20. The top emitting OLED structure of claim 1, wherein the optical thickness
of said microcavity is less than 3000 Angstroms.
21. The top emitting OLED structure of claim 1, wherein the refractive index
of the adhesive layer material is lower by at least 0.3 units than the refractive
index of the material that is adjacent to and below the adhesive layer.
22. The top emitting OLED structure of claim 1, wherein the refractive index
of the adhesive layer material is lower by at least 0.5 units than the refractive
index of the material that is adjacent to and below the adhesive layer.
Description
FIELD OF THE INVENTION
The present invention relates to organic electronic devices that are protected
from environmental elements such as moisture and oxygen.
BACKGROUND OF THE INVENTION
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.
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.
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.
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.
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.
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.
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".
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.
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.
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
The above and other challenges of the prior art are addressed by the present invention.
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.
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.
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.
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.
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.
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.
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.
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.
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.
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.
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.
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.
The method can be, for example, a roll-to-roll processing method, allowing for
continuous device production.
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.
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.
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.
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.
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.
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.
The adhesive layer can be, for example, a pressure sensitive adhesive layer such
as that discussed above, or a glue.
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.
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.
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.
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.
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.
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.
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.
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.
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
FIGS. 1A and 1B are schematic representations (cross-sectional views) of known
OLED structures.
FIG. 2A is a schematic cross-sectional view of an OLED structure in accordance
with one embodiment of the present invention.
FIG. 2B is a schematic plan view of the adhesive layer of FIG. 2A, in accordance
with an embodiment of the present invention.
FIG. 3 is a schematic cross-sectional view of an OLED structure in accordance
with another embodiment of the present invention.
FIG. 4 is a schematic cross-sectional view of an OLED structure in accordance
with yet another embodiment of the present invention.
FIG. 5 is a schematic cross-sectional view of an OLED structure in accordance
with still another embodiment of the present invention.
FIG. 6 is a schematic cross-sectional view of an OLED structure in accordance
with another embodiment of the present invention.
FIG. 7 is a schematic illustration of an OLED structure lamination process,
in accordance with an embodiment of the present invention.
FIG. 8 is a schematic illustration of an OLED structure lamination process,
in accordance with another embodiment of the present invention.
FIG. 9 is a schematic cross-sectional view of an OLED structure in accordance
with another embodiment of the present invention.
FIG. 10 is a schematic illustration of an OLED structure lamination process,
in accordance with another embodiment of the present invention.
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
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.
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).
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.
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.
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.
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.
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.
Ceramics also offer low permeability, and they provide transparency as well
in some cases.
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.
Composite materials are also among those materials preferred for use in
connection with the substrate layer 110 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.
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.
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.
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.
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.
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.
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.
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.
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.
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 (18 Nov. 2002).
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.
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.
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.
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.
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.
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.
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.
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.
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.
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.
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.
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.
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.
In some embodiments of the present invention, a getter material is provided within
the adhesive layer.
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.
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.
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.
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.
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
3N
4), silicon oxynitrides, aluminum oxides (typically Al
2O
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.
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.
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.
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.
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.
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.
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
