U.S. patent application number 10/459947 was filed with the patent office on 2003-11-06 for flexible organic electronic device with improved resistance to oxygen and moisture degradation.
Invention is credited to Carcia, Peter Francis, Scott, Robert.
Application Number | 20030207488 10/459947 |
Document ID | / |
Family ID | 26829449 |
Filed Date | 2003-11-06 |
United States Patent
Application |
20030207488 |
Kind Code |
A1 |
Carcia, Peter Francis ; et
al. |
November 6, 2003 |
Flexible organic electronic device with improved resistance to
oxygen and moisture degradation
Abstract
Flexible composite barrier structures are used to improve the
resistance, to oxygen and moisture degradation, of an organic
electronic device including at least one active layer comprising an
organic material.
Inventors: |
Carcia, Peter Francis;
(Wilmington, DE) ; Scott, Robert; (McLean,
DE) |
Correspondence
Address: |
E I DU PONT DE NEMOURS AND COMPANY
LEGAL PATENT RECORDS CENTER
BARLEY MILL PLAZA 25/1128
4417 LANCASTER PIKE
WILMINGTON
DE
19805
US
|
Family ID: |
26829449 |
Appl. No.: |
10/459947 |
Filed: |
June 12, 2003 |
Related U.S. Patent Documents
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Application
Number |
Filing Date |
Patent Number |
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10459947 |
Jun 12, 2003 |
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10374611 |
Feb 26, 2003 |
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10374611 |
Feb 26, 2003 |
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09551394 |
Apr 17, 2000 |
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60131416 |
Apr 28, 1999 |
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60137928 |
Jun 7, 1999 |
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Current U.S.
Class: |
438/82 ;
257/E25.008 |
Current CPC
Class: |
H01L 51/448 20130101;
Y10S 428/917 20130101; H01L 51/5256 20130101; H01L 51/42 20130101;
H01L 51/0001 20130101; H01L 2251/5338 20130101; H01L 51/0097
20130101; H01L 51/0504 20130101; Y02E 10/549 20130101; Y10T 428/259
20150115 |
Class at
Publication: |
438/82 |
International
Class: |
H01L 021/00 |
Claims
What is claimed is:
1. A flexible organic electronic device comprising in the order
listed: a) a first flexible composite barrier structure comprising
at least one layer of a first polymeric film and at least one layer
of a first barrier material, the first barrier structure having a
first inner surface; b) at least one first electrical contact
layer; c) at least one active layer comprising an organic active
material, said active layer having dimensions defined by a length
and a width; d) at least one second electrical contact layer; e) a
second flexible composite barrier structure comprising at least one
layer of a second polymeric film and at least one layer of a second
barrier material, the second barrier structure having a second
inner surface; wherein at least one of the first and second
composite barrier structures is light-transmitting; wherein the
first and second composite barrier structures are sealed together
to envelop the at least one active layer.
2. The device of claim 1 wherein a portion of the first electrical
contact layer and a portion of the second electrical contact layer
extend beyond the dimensions of the active layer, wherein the first
and second composite barrier structures are also sealed to the
extended portions of the first and second electrical contact
layers.
3. The device of claim 1 wherein the one second electrical contact
layer comprises a material having a lower work function than the
first electrical contact layer.
4. The device of claim 1 wherein the first electrical contact layer
is an anode and the second electrical contact layer is a
cathode.
5. The device of claim 1 wherein the first and second polymeric
films of the first and second composite barrier structures are
selected from polyolefins, polyesters, polyimides, polyamides,
polyacrylonitrile and polymethacrylonitrile; perfluorinated and
partially fluorinated polymers, polycarbonates, polyvinyl chloride,
polurethanes, polyacrylic resins, epoxy resins, and novolac
resins.
6. The device of claim 1 wherein the first and second barrier
materials are independently selected from metals, metal alloys,
inorganic oxides, inorganic nitrides, inorganic carbides, inorganic
fluorides, and combinations thereof.
7. The device of claim 1 wherein the first flexible composite
barrier structure and the first electrical contact layer are
light-transmitting.
8. The device of claim 7 wherein the first and second polymeric
films in the first composite barrier material are selected from
polyethylene terephthalate, polyethylene naphthalate, polyimide,
and combinations thereof.
9. The device of claim 1 wherein the barrier material is selected
from aluminum, nickel, chromium, copper, tin, stainless steel, and
alloys thereof.
10. The device of claim 1 wherein the a barrier material selected
from inorganic oxides, inorganic nitrides, inorganic fluorides,
inorganic carbides, and combinations thereof.
11. The device of claim 1 wherein the layer of first and second
barrier materials has a thickness in the range of 2-500 nm.
12. The device of claim 1 wherein the first flexible composite
barrier structure comprises two layers of polymeric film with a
layer of the first barrier material therebetween.
13. The device of claim 1 wherein the second flexible composite
barrier structure comprises two layers of polymeric film with a
layer of the second barrier material there between.
14. The device of claim 1 wherein the first flexible composite
barrier structure further comprises a layer of adhesive on the
first inner surface.
15. The device of claim 1 wherein the second flexible composite
barrier structure further comprises a layer of adhesive on the
second inner surface.
16. The device of claim 1 wherein at least one of the first inner
surface and the second inner surface contains an adhesive
component.
17. The device of claim 14 or claim 15 wherein the adhesive is
selected from polymer adhesive resins, amorphous polyesters,
copolyesters, polyester blends, nylon, polyurethanes, polyolefins,
vinyl alcohol, ethylene vinylacetate copolymer, copolymers of
ionomers and acids, and combinations thereof.
18. The device of claim 16 wherein the adhesive component is
selected from polymer adhesive resins, amorphous polyesters,
copolyesters, polyester blends, nylon, polyurethanes, polyolefins,
vinyl alcohol, ethylene vinylacetate copolymer, copolymers of
ionomers and acids, and combinations thereof.
19. The device of claim 1, wherein the active layer includes
electroluminescent material.
20. The device of claim 1, wherein the active layer includes a
conjugated polymer.
21. An electroluminescent display containing the device of claim
1.
22. A photodetector containing the device of claim 1.
23. A method for improving resistance to oxygen and moisture
degradation of a flexible organic electronic device comprising at
least one first electrical contact layer having a first electrical
contact layer outer surface and an opposite first electrical
contact layer inner surface, at least one active layer adjacent to
the first electrical contact layer inner surface, the active layer
comprising an organic active material, said active layer having a
set of dimensions, and at least one second electrical contact layer
having a second electrical contact layer outer surface and an
opposite second electrical contact layer inner surface, wherein the
second electrical contact layer inner surface is adjacent to the
active layer, the method comprising the steps of: placing a first
flexible composite barrier structure adjacent to the at least one
first electrical contact layer outer surface, the first flexible
composite barrier structure comprising at least one layer of a
first polymeric film and at least one layer of a first barrier
material, the first barrier structure having a first inner surface;
placing a second flexible composite barrier structure adjacent to
the at least one second electrical contact layer outer surface, the
second flexible composite barrier structure comprising at least one
layer of a second polymeric film and at least one layer of a second
barrier material, the second barrier structure having a second
inner surface; wherein at least one of the first and second
composite barrier structures is light-transmitting, sealing the
first inner surface and the second inner surface together outside
the dimensions of the active layer to envelop the active layer.
24. The method of claim 23 wherein a portion of the first
electrical contact layer and a portion of the second electrical
contact layer extend beyond the dimensions of the active layer,
wherein the first and second composite barrier structures are also
sealed to the extended portions of the first and second electrical
contact layers.
25. The method of claim 23 wherein the second electrical contact
layer comprises a material having a lower work function than the
first electrical contact layer.
26. The method of claim 23 wherein the first electrical contact
layer is a cathode and the second electrical contact layer is an
anode.
27. The method of claim 23 wherein the first and second polymeric
films of the first and second composite barrier structures are
selected from polyolefins, polyesters, polyimides, polyamides,
polyacrylonitrile and polymethacrylonitrile; perfluorinated and
partially fluorinated polymers, polycarbonates, polyvinyl chloride,
polurethanes, polyacrylic resins, epoxy resins, and novolac
resins.
28. The method of claim 23 wherein the first and second barrier
materials are selected from metals, metal alloys, inorganic oxides,
inorganic nitrides, inorganic carbides, inorganic fluorides, and
combinations thereof.
29. The method of claim 23 wherein the first flexible composite
barrier structure and the first electrical contact layer are
light-transmitting.
30. The method of claim 23 wherein the first and second polymeric
films in the first composite barrier material is selected from
polyethylene terephthalate, polyethylene naphthalate, polyimide,
and combinations thereof.
31. The method of claim 23 wherein the barrier material is selected
from aluminum, nickel, chromium, copper, tin, stainless steel, and
alloys thereof.
32. The method of claim 23 wherein the barrier material selected
from inorganic oxides, inorganic nitrides, inorganic fluorides,
inorganic carbides, and combinations thereof.
33. The method of claim 23 wherein the layer of first and second
barrier materials has a thickness in the range of 2-500 nm.
34. The method of claim 23 wherein the first flexible composite
barrier structure comprises two layers of polymeric film with a
layer of the first barrier material therebetween.
35. The method of claim 23 wherein the second flexible composite
barrier structure comprises two layer of polymeric film with a
layer of the first barrier material therebetween.
36. The method of claim 23 wherein the first flexible composite
barrier structure further comprises a layer of adhesive on the
first inner surface.
37. The method of claim 23 wherein the second flexible composite
barrier structure further comprises a layer of adhesive on the
second inner surface.
38. The method of claim 23 wherein at least one of the first inner
surface and the second inner surface contains an adhesive
component.
39. The method of claim 36 or 37 wherein the adhesive is selected
from polymer adhesive resins, amorphous polyesters, copolyesters,
polyester blends, nylon, polyurethanes, polyolefins, vinyl alcohol,
ethylene vinylacetate copolymer, copolymers of ionomers and acids,
and combinations thereof.
40. The method of claim 38 wherein the adhesive component is
selected from polymer adhesive resins, amorphous polyesters,
copolyesters, polyester blends, nylon, polyurethanes, polyolefins,
vinyl alcohol, ethylene vinylacetate copolymer, copolymers of
ionomers and acids, and combinations thereof.
41. The method of claim 23, wherein the active layer includes
electroluminescent material.
42. The method of claim 23, wherein the active layer includes a
conjugated polymer.
Description
BACKGROUND OF THE INVENTION
[0001] 1. Field of the Invention
[0002] This invention relates to organic electronic devices in
which the active layer is an organic material. More particularly,
it relates to electronic devices covered by flexible composite
barrier structures.
[0003] 2. Description of the Related Art
[0004] Organic electronic devices include devices that emit light
(such as light-emitting diodes that make up displays) or respond to
radiant energy (such as photodetectors). Displays may contain
active matrix addressing or passive matrix-addressing. In passive
matrix displays there is an array of electrode lines for addressing
individual pixels arranged in rows and columns; applying a voltage
between a particular row and column energizes the pixel with that
corresponding address. By analogy with active matrix liquid crystal
displays, the polymer electronic device (display) can be addressed
at individual pixels using a thin film transistor (TFT) device
which switches that pixel on and off. In such a configuration each
TFT is electrically connected by to "gate busline" and to "data
busline" that also need to be connected to the electrical driver
circuitry and thus sealed outside the active device area.
[0005] In all such devices, an organic active layer is sandwiched
between two electrical contact layers. At least one of the
electrical contact layers is light-transmitting so that light can
pass through the electrical contact layer. The organic active layer
may generate an electric signal in response to light through the at
least one light-transmitting electrical contact layer, or may emit
light through the light-transmitting electrical contact layer upon
application of electricity across the electrical contact layers. In
the latter case, the organic active layer contains an
electroluminescent material.
[0006] It is well known to use organic electroluminescent materials
as the active materials in light emitting diodes. Simple organic
molecules such as anthracene, thiadiazole derivatives, and coumarin
derivatives are known to show electro-luminescence. Semiconductive
conjugated polymers have also been used as electroluminescent
materials, as has been disclosed in, for example, Friend et al,
U.S. Pat. No. 5,247,190, Heeger et al., U.S. Pat. No. 5,408,109,
and Nakano et al., Published European Patent Application 443 861.
The organic materials can be tailored to provide emission at
various wavelengths. However, they frequently are degraded by
atmospheric gases, particularly oxygen and water vapor. This
sensitivity can severely limit the working lifetime of the device
if the materials are not properly sealed.
[0007] Typically, the device is fabricated on a glass substrate and
then hermetically sealed with epoxy to another sheet of glass. In
Nakamura et al, U.S. Pat. No. 5,427,858, an electroluminescent
device has a protection layer of a fluorine-containing polymer
which is optionally covered with a glass shield layer. In Tang,
U.S. Pat. No. 5,482,896, a material such as an epoxy or hot melt
adhesive is used to seal the edges of an electroluminescent device
between a rigid support and a thin (25-50 micron) glass substrate.
In Scozzafava et al., U.S. Pat. No. 5,073,446, an
electroluminescent device including a glass substrate has an outer
capping layer comprised of fused metal particles containing at
least 80% indium, in order to prevent oxidation of the second
electrical contact layer. However, having glass as a substrate
greatly increases the fragility of the device. Moreover, devices
having a glass substrates are not flexible at or below room
temperature and therefore cannot be conformed to curved
surfaces.
[0008] Therefore, there is a need to improve the chemical stability
of layers in organic electronic devices that are sensitive to
environmental elements. There is also a need to improve the
durability as well as the flexibility of such devices.
SUMMARY OF THE INVENTION
[0009] The present invention relates to a method for improving
resistance to oxygen and moisture degradation of a flexible organic
electronic device and to a flexible organic electronic device
having greatly improved resistance to environmental degradation,
particularly oxygen and moisture degradation, and improved
durability. The device includes an organic active layer sandwiched
between two electrical contact layers, the sandwich being sealed
between two flexible composite barrier structures. The flexible
composite barrier structures have oxygen and water vapor transport
rates of preferably less than 1.0 cc/m.sup.2/24 hr/atm.
[0010] In one embodiment of the invention, the device comprises in
the order listed:
[0011] (a) a first flexible composite barrier structure comprising
at least one layer of a first polymeric film and at least one layer
of a first barrier material;
[0012] (b) at least one first electrical contact layer;
[0013] (c) at least one active layer comprising an organic active
material, said active layer having dimensions defined by a length
and a width;
[0014] (d) at least one second electrical contact layer;
[0015] (e) a second flexible composite barrier structure comprising
at least one layer of a second polymeric film and at least one
layer of a second barrier material;
[0016] wherein at least one of the first and second composite
barrier structures is light-transmitting, and further wherein the
first and second composite barrier structures are sealed together,
to envelop the active layer.
[0017] In a second embodiment, the device includes a portion of the
first electrical contact layer and a portion of the second
electrical contact layer which extend beyond the dimensions of the
active layer, and the first and second composite barrier structures
are further sealed to the portion of the first electrical contact
layer and the portion of the second electrical contact layer that
extend beyond the dimensions of the active layer.
DESCRIPTION OF THE DRAWINGS
[0018] FIG. 1 is a schematic diagram of a top view of an organic
electronic device of the invention.
[0019] FIG. 2 is a schematic diagram of a cross-section at line 2-2
of the device of FIG. 1 before the device is sealed.
[0020] FIG. 3 is a schematic diagram of a top view at line 3-3 of
the device shown in FIG. 2.
[0021] FIG. 4 is a schematic diagram of a cross-section at line 2-2
of the device of FIG. 1 after it is sealed.
[0022] FIG. 5 is a plot of peel strength versus distance when
peeling apart a composite barrier structure of the invention sealed
to a pattern of electrodes on a polymeric support.
[0023] FIG. 6 is a schematic diagram of a composite barrier
structure being peeled from a support and an electrode
material.
[0024] FIG. 7(a) is a plot of light emission of a polymer light
emitting devices of the present invention at initial time and after
fifty days of ambient storage.
[0025] FIG. 7(b) is a plot of light emission of a polymer light
emitting devices without out the barrier structure of the present
invention, at initial time and after fifty days of ambient
storage.
DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS
[0026] The present invention relates to a device having at least,
in the order listed, a first flexible composite barrier structure;
a first electrical contact layer, a layer containing at least one
organic active material; a second electrical contact layer; and a
second flexible composite barrier structure.
[0027] It is understood that it is necessary to be able to connect
the electrical contact layers of the device to external circuitry
in order for the device to function.
[0028] In most cases this circuitry connection can be accomplished
by extending the electrical contact layers beyond the dimensions of
the active layer for the connection. The composite barrier
structures are then sealed together and to the extended portion of
the electrical contact layers, with the electrical contact layers
continuing beyond the seal. However, it is also possible to use
conductive pathways known as vias to connect the electrical contact
layers to external circuitry. The via openings can either be formed
in each layer as the device is assembled, or formed by drilling
through all the layers after the device is assembled. The openings
are then plated through using well-known techniques described in,
for example, Sinnadurai, Handbook of Microelectronic Packaging and
Interconnection Technologies (Electrochemical Publications Ltd.,
1985). If vias are used, the openings should be completely sealed
around the connecting wires to protect the active layer from
exposure to the external environment.
[0029] As used herein, the term "flexible" is intended to mean that
a planar sheet of the material is less rigid than glass having a
thickness of 1 millimeter at room temperature and preferably can be
bent at an angle of at least 10.degree. from the plane without
breaking. The term "light-transmitting" is intended to mean that
the material transmits at least 50% of light in the visible
spectrum (400-700 nm). The term "barrier" is intended to mean low
permeability to oxygen and water vapor.
[0030] The term "essentially X" is used to mean that the
composition of a particular material is mainly X, and may also
contain other ingredients that do not detrimentally affect the
functional properties of that material to a degree at which the
material can no longer perform its intended purpose.
[0031] When layer A is stated to be "adjacent to" a first surface
of layer B, it is meant that layer A is closer to a first surface
of layer B than it is to a second surface of layer B, such second
surface being disposed opposite of the first surface. As used
herein, the word "adjacent" does not necessarily mean that layer A
is immediately next to the first surface of layer B. Thus, it is
entirely possible that a layer C is disposed between layer A and
layer B, and it is still true that layer A is adjacent to the first
surface of layer B.
[0032] FIGS. 1-4 show one example of an organic electronic device
10 according to the invention. As best seen in FIGS. 2 and 4, the
device 10 includes a first flexible composite barrier structure 20,
a first electrical contact layer 30, an active layer 40, a second
electrical contact layer 50 and a second flexible composite barrier
structure 60. Depending upon the intended application, the device
10 can be connected directly to an electrical source 100, 120, as
best seen in FIGS. 1 and 3. Alternatively, device 10 may be
connected to at least one external circuit (not shown) and thereby
be a part of an overall electronic system (not shown).
[0033] As best seen in FIGS. 2 and 4, the first composite barrier
structure 20 has an inner surface 24 and is made up of two
polymeric layers 21A and 21B on either side of a layer of barrier
material 22. The patterned first electrical contact layer 30 is
placed adjacent to the inner surface 24 of the first composite
barrier structure 20. As best seen in FIGS. 1 and 3, the first
electrical contact layer pattern consists of lines across the width
44 of the active layer and extending beyond an edge 43A of the
active layer 40. The first electrical contact layer 30 extends
beyond the dimensions of the active layer 40 in areas 31. As best
seen in FIGS. 2 and 4, the patterned second electrical contact
layer 50 is adjacent to a second surface 48 of the active layer 40
opposite the surface 46 adjacent to the first electrical contact
layer 30, such that the active layer 40 is sandwiched between the
second electrical contact layer 50 and the first electrical contact
layer 30. As best seen in FIGS. 1, 2 and 4, the second electrical
contact layer pattern consists of lines across to the length 42 of
the active layer, and extending beyond another edge 45A, 44 of the
active layer 40. As best seen in FIGS. 1 and 2, the second
electrical contact layer extends beyond the dimensions of the
active layer in area 52. As best seen in FIGS. 2 and 4 the second
flexible composite barrier structure 60 is made up of two polymeric
layers 61A and 61B on either side of a layer of barrier material
62. On the inner surface 64 of the second barrier structure is an
adhesive layer 70
[0034] It is understood that the electrical contact layers 30, 50
may extend beyond any one or more of the active layer edges 43A,
43B, 45A, 45B, depending on the design of the device 10.
[0035] It is understood that FIGS. 1-4 have been drawn to represent
the relative order of the layers, exaggerating their separation,
and are not an accurate depiction of their relative dimensions.
[0036] As best seen in FIGS. 1, 2, and 4, the dimensions 65, 66 of
the second composite barrier structure 60 can be smaller than the
dimensions 26, 27 of the first composite barrier structure 20. In
the illustrated embodiment the dimensions 65, 66 of the second
composite structure 60 are greater than the dimensions 42, 44 of
the active layer 40 (not shown) in order to effectively seal the
active layer 40. In an embodiment (not shown) wherein at least one
of the electrical contact layers is also sensitive to environmental
degradation, the dimensions of the composite barrier structures
should be adjusted to also effectively seal the sensitive
electrical contact layer(s). It is thus understood that the
relative dimensions 65, 66 of the second composite barrier
structure 60 and the dimensions 26, 27 of the first composite
barrier structure 20 may vary so long as the composite barrier
structures 20, 60 can provide an effective seal for the device
10.
[0037] As best seen in FIG. 4, the first and second flexible
composite barrier structures 20 and 60 are sealed together by means
of adhesive layer 70 outside the dimensions of active layer 40, at
region 102. Although not explicitly shown in the drawings, the
first and second flexible composite barrier structures 20 and 60
are sealed at all edges such that the active layer 40 is completely
enveloped within the sealed edges. Preferably, the first and second
flexible composite barrier structure 20 and 60 are sealed in a way
that also envelopes all portions of the first and second electrical
contact layers 30, 50, except for area 31 of the first electrical
contact layer 30 and area 52 of the second electrical contact layer
50.
[0038] In the embodiment wherein device 10 is a light-emitting
diode, layer 30 can be a cathode (or an anode), layer 40 is a
light-emitting layer containing an electroluminescent material, and
layer 50 is the respective counterpart electrode, i.e.: an anode
(or a cathode), as the case may be.
[0039] 1. Flexible Composite Barrier Structures
[0040] The flexible composite barrier structures 20 and 60 are a
composite of at least one polymeric film layer and at least one
layer of barrier material. The two composite barrier structures can
be made of the same or different material. At least one of the two
composite layers should be light-transmitting, preferably
transmitting at least 80% in the visible region.
[0041] The polymeric film 21A, 21B, 61A, 61B useful in the
invention is dimensionally and physically stable under the
operating conditions of the device. Examples of suitable polymers
include materials containing essentially polyolefins, such as
polyethylene and polypropylene; polyesters such as polyethylene
terephthalate and polyethylene naphthalate; polyimides; polyamides;
polyacrylonitrile and polymethacrylonitrile; perfluorinated and
partially fluorinated polymers such as polytetrafluoroethylene and
copolymers of tetrafluoroethylene and 2,2-dimethyl-1,3-dioxole;
polystyrenes; polycarbonates; polyvinyl chloride; polurethanes;
polyacrylic resins, including homopolymers and copolymers of esters
of acrylic and/or methacrylic acid; epoxy resins; and novolac
resins. More than one layer of polymeric film can be used and
combinations of films with different compositions can be used. The
multiple layers can be joined together with appropriate adhesives
or by conventional layer producing processes such as known coating
and/or co-extrusion processes. The polymeric films generally have a
thickness in the range of about 0.5-10 mils (12.7-254 microns).
When more than one film layer is present, the individual
thicknesses can be much less.
[0042] It is understood that although the polymeric film 21A, 21B,
61A, 61B contains essentially the polymers described above, these
films may also include conventional additives. For example, many
commercially available polymeric films contain slip agents or matte
agents to prevent the layers of film from sticking together when
stored as a large roll. In some cases, the size of such additive
may cause irregularities and defects in the adjoining layer of
barrier material; such irregularities may detrimentally affect the
barrier properties of the composite barrier structure. Where the
additives detrimentally affect the composite barrier structure, a
polymeric film which is free of slip and matting agents, or in
which such agents are small or unobtrusive with respect to the
desired thickness of the layer of barrier material 22, 62 is
preferred. In some cases, slip coatings can be used.
[0043] In the composite structures 20, 60 of the invention, it is
preferred to have at least one layer of barrier material 22, 62
sandwiched between at least two layers of polymeric film 21A, 21B,
61A, 61B, as best seen in FIG. 4. Such a composite structure 20, 60
allows for very thin and flexible layers of barrier material which
are then protected by the outer layers of polymeric film from
damage. There may be more than one layer of barrier material (not
shown), each layer may be positioned between two polymeric layers.
The barrier layer can be applied to the first layer of polymeric
film by one of the processes described below. The second layer of
polymeric film can then be applied by lamination or coating,
casting or extrusion processes. The second polymeric film layer can
be of the same or different composition from the first. For
example, a polyester film 1-2 mils (25.4-50.8 microns) thick can be
coated with a 2-500 nm thick layer of silicon nitride (SiN.sub.x)
using plasma enhanced chemical vapor deposition. This layer can
then be overcoated with a solution of acrylic resin which is
allowed to dry, or an epoxy or novolac resin followed by curing.
Alternatively, the silicon nitride coated polyester film can be
laminated to a second layer of polyester film. The overall
thickness of the composite structure is generally in the range of
about 0.5-10 mils (12.3-254 microns), preferably 1-8 mils
(25.4-203.2 microns). Such overall thickness is affected by the
method used to apply or lay down the composite structure.
[0044] As best seen in FIGS. 2 and 4, an adhesive 70 is generally
applied to at least one surface of the composite structures 20, 60.
The composite barrier structures 20, 60 are sealed with the
adhesive by bringing the inner surfaces 24, 64 of the structures
20, 60 together. The adhesive 70 should be capable not only of
sealing the two composite structures together, but of sealing with
at least the portion of the electrical contact layers 31, 52
extending beyond the dimensions of the active layer 40. It is
understood that an adhesive layer (not shown) may be placed next to
the inner surface 24 of the first composite barrier structure 20 in
addition to, or instead of adhesive layer 70.
[0045] In another embodiment, an adhesive component can be
incorporated in at least one of the polymeric films 21A, 61B
adjacent to the active layer 40 instead of or in addition to the
separate adhesive layer 70. In such a case, a separate adhesive
layer 70 may not be necessary to seal the composite barrier
structures 20, 60 together.
[0046] Suitable adhesives, useful as a separate layer (such as
layer 70) and/or as a component of one of the polymeric film layers
21A, 61B include materials containing essentially polymer adhesive
resins, amorphous polyesters, copolyesters, polyester blends,
nylon, polyurethanes and polyolefins, including polyethylene,
polypropylene, polyethylene vinyl alcohol, ethylene vinylacetate
copolymer, copolymers of ionomers and acids. It is understood that,
where the adhesive layer is adjacent to a light-transmitting layer,
the adhesive layer should also be light-transmitting. Similarly, an
adhesive component to be incorporated into a light-transmitting
polymeric film layer should not detrimentally affect the
light-transmitting property of the polymeric film layer.
[0047] The barrier material useful in the barrier layers 22, 62 of
the invention can be a substance that, when formed as a continuous
film 1000 .ANG. in thickness, has an oxygen and water vapor
transport rate of less than 1.0 cc/m.sup.2/24 hr/atm, preferably
less than 0.2 cc/m.sup.2/24 hr/atm. Suitable barrier materials
include malleable and crack resistant materials that are capable of
flexing. Examples of such materials include those containing
essentially metals, such as aluminum, nickel, copper, tin and
stainless steel, as well as alloys. The barrier material can also
be any inorganic materials that are chemically stable to water and
oxygen, including inorganic oxides, nitrides, fluorides, and
carbides, such as those of silicon, aluminum, indium, titanium,
magnesium, hafnium, tantalum, and zirconium, and combinations
thereof.
[0048] Each of the barrier layers 22, 62 should be a continuous
layer that contains a minimal number of defects that increase the
material's oxygen and water vapor permeability characteristics so
that it can no long function as a barrier. Thus, for example,
defects such as pinholes or cracks would be undesirable. It is
understood that in addition to the size of defect, the area density
of defect (i.e., number of defects per unit area) also may affect
the functional characteristics of the barrier material. In order to
maintain flexibility, the layer of barrier material generally has a
thickness no greater than 1 micron, preferably no greater than 500
nm. In general, the barrier layer may have a thickness in the range
of 2-500 nm. However, with some flexible metal films, such as Al
foils it is possible to use barrier layers thicker than the
preferred ranges.
[0049] The barrier layers of the invention are composites
containing very thin layers of materials having very low
permeability.
[0050] The specific choice of polymeric film and barrier material
will depend on the processing conditions to which the composite
structure will be exposed and the light-transmission requirements.
When the composite structure 20 or 60 is used as a support with
additional layers built upon it, it may undergo various processing
conditions including vapor deposition processing and/or wet
chemical etching. In some cases the polymeric film will be the
outer layer of the composite structure which is exposed to further
processing. If they are subjected to chemical etching conditions,
materials such as polyesters, polyimides, and fluorinated polymers
are preferred polymeric materials. When the processing involves
vapor deposition steps, it is preferred that the polymeric film be
a polyimide with high a glass transition temperature (Tg) (e.g., Tg
of from 100.degree. C. to 350.degree. C.) or a polyester, more
preferably, polyethylene naphthalate. In some cases the barrier
material will be the outer layer of the composite structure that is
exposed to further processing. The barrier material should be
chosen to withstand these conditions. When the composite structure
20 or 60 is added as a last layer, it often will not undergo any
further processing. Therefore, the range of choices for the
composition of components in the composite barrier structure 20 or
60 placed as a last layer is much broader.
[0051] When the composite structure 20 or 60 is adjacent to a light
transmitting electrical contact layer, the composite barrier
structure should also be light-transmitting in order to transmit
light into the device or transmit light generated by the device.
Any light-transmitting layer of barrier material can be used in
this case, including glasses and inorganic oxides, nitrides,
fluorides, and carbides with band gaps greater than 2.5 eV.
Particularly preferred light transmitting barrier material are
glasses, such as materials essentially made of silicon nitrides
having formula (I) below; silicon oxides having formula (II) below;
aluminum oxides having formula (III) below; aluminum nitrides
having formula IV below:
SiN.sub.w, wherein w is between 0.8 and 1.2, inclusive Formula
(I)
SiO.sub.x, wherein w is between 1.5 and 2.0, inclusive Formula
(II)
AlO.sub.y, wherein y is between 1 and 1.5, inclusive Formula
(III)
AlN.sub.z, wherein z is between 0.8 and 1.2, inclusive Formula
(IV)
[0052] Also combinations of suitable materials can be used.
[0053] When the composite structure is adjacent to an opaque
electrical contact layer, there is no need for a light-transmitting
composite barrier structure.
[0054] To summarize, there are at least the following four types of
composite barrier structures that can be used depending on the
placement of the structure in the device: (i) the composite barrier
structure is used as a support upon which additional layers are
processed and is adjacent to a light-transmitting electrical
contact layer; (ii) the composite barrier structure is used as a
support upon which additional layers are processed and is adjacent
to an opaque electrical contact layer; (iii) the composite barrier
structure is the last layer applied and is adjacent to a
light-transmitting electrical contact layer; and (iv) the composite
barrier structure is the last layer applied and is adjacent to an
opaque electrical contact layer. The choice of materials used in
the component layers of the composite barrier structure is in part
dependent upon the type of composite structure.
[0055] The polymeric film layer 21A, 21B, 61A, 61B and the barrier
material 22, 62 can be combined together using any known
application technique that will produce the desired thicknesses and
uniformity, including coating processes such as spin coating and
spray coating, extrusion coating, casting, screen printing, and
vapor deposition processes. A preferred process is to apply the
barrier material 22, 62 to the polymeric film 21A or 21B, 61A or
61B, respectively, by a vapor deposition process. Such processes
include chemical vapor deposition and plasma enhanced chemical
vapor deposition, and physical deposition processes such as
evaporation, ion-plating and sputtering. Plasma enhanced chemical
vapor deposition is particularly preferred as it causes less
heating of the substrate (in this case, the polymeric film 21A,
21B, 61A, or 61B), and the coating flux is more uniform. It thereby
provides essentially defect-free layers.
[0056] 2. First Electrical Contact Layer
[0057] The first electrical contact layer 30, is applied to one
surface of the first flexible composite barrier structure. This
electrical contact layer can include any material capable of
injecting (or collecting) charge carriers into (or from, as the
case may be) the active layer 40.
[0058] Although not shown in the drawings, the first electrical
contact layer can be made of one single layer of material or can be
a composite of multiple layers of first electrical contact layer
material. Where the first electrical contact layer is an anode,
(i.e., an electrode that is particularly efficient for injecting or
collecting positive charge carriers) it can be, for example
materials containing a metal, mixed metal, alloy, metal oxide or
mixed-metal oxide, or it can be a conducting polymer. Suitable
metals include the Group IB metals, the metals in Groups IV, V, and
VI, and the Group VIII transition metals. If the first electrical
contact layer is to be light-transmitting, mixed-metal oxides of
Groups II, III and IV metals, such as indium-tin-oxide, or a
conducting polymer, such as polyaniline, can be used.
[0059] Although first electrical contact layer 30 is shown with
extended portions 31 to connect the device to external circuitry,
it is understood that devices (not shown) that incorporate other
means of circuitry connection (such as vias) would not require such
extended portions 31. It is further understood that the composition
of the first electrical contact layer 30 may vary across the
dimensions 26, 65 of the composite barrier layers 20, 60. For
example, where the first electrical contact layer 30 includes the
extended portions 31, parts of the extended portions that are
disposed outside of the sealed composite barrier layers 20, 60 may
be contain essentially a material (such as aluminum) that is more
resistant to environmental degradation or is a better conductor
than the first electrical contact layer composition that is
coextensive with the active layer 40. Thus, the first electrical
contact layer composition that is coextensive with the active layer
40 may be chosen to provide better electron band-gap matching. At
the same time the first electrical contact layer composition in the
extended portion 31 may be chosen to provide greater conductivity
and increased resistance to environmental degradation outside of
the sealed device. The varied composition can be provided by using
separate layers of first electrical contact layer material, or by
adjusting the alloyed composition within a first electrical contact
layer.
[0060] The first electrical contact layer 30 is usually applied by
a physical vapor deposition process. The term "physical vapor
deposition" refers to various deposition approaches carried out in
vacuo. Thus, for example, physical vapor deposition includes all
forms of sputtering, including ion beam sputtering, as well as all
forms of vapor deposition such as e-beam evaporation. A specific
form of physical vapor deposition useful in the present in
envention is a rf magentron sputtering.
[0061] In general, the first electrical contact layer will be
patterned. It is understood that the pattern may vary as desired.
The first electrical contact layer can be applied in a pattern by,
for example, positioning a patterned mask or photoresist on the
first flexible composite barrier structure prior to applying the
first electrical contact layer material. Alternatively, the first
electrical contact layer can be applied as an overall layer and
subsequently patterned using, for example, a photoresist and wet
chemical etching. The first electrical contact layer typically has
a thickness in the range of 50-500 nm. First electrical contact
layer materials and processes for patterning that are well known in
the art can be used.
[0062] 3. Organic Active Layer
[0063] Depending upon the application of the device 10, the active
layer 40 can be a light-emitting layer that is activated by an
applied voltage (such as in a light-emitting diode), a layer of
material that responds to radiant energy and generates a signal
with or without an applied bias voltage (such as in a
photodetector). Examples of photodetectors include photoconductive
cells, photoresistors, photoswitches, phototransistors, and
phototubes, and photovoltaic cells, as these terms are describe in
Markus, John, Electronics and Nucleonics Dictionary, 470 and 476
(McGraw-Hill, Inc. 1966).
[0064] Where the active layer is light-emitting, the layer will
emit light when sufficient bias voltage is applied to the
electrical contact layers. The light-emitting active layer may
contain any organic electroluminescent or other organic
light-emitting materials. Such materials can be small molecule
materials such as those described in, for example, Tang, U.S. Pat.
No. 4,356,429, Van Slyke et al., U.S. Pat. No. 4,539,507, the
relevant portions of which are incorporated herein by reference.
Alternatively, such materials can be polymeric materials such as
those described in Friend et al. (U.S. Pat. No. 5,247,190), Heeger
et al. (U.S. Pat. No. 5,408,109), Nakano et al. (U.S. Pat. No.
5,317,169), the relevant portions of which are incorporated herein
by reference. Preferred electroluminescent materials are
semiconductive conjugated polymers. An example of such a polymer is
poly(p-phenylenevinylene) referred to as PPV. The light-emitting
materials may be dispersed in a matrix of another material, with
and without additives, but preferably form a layer alone. The
active organic layer generally has a thickness in the range of
50-500 nm.
[0065] Where the active layer 40 is incorporated in a
photodetector, the layer responds to radiant energy and produces a
signal either with or without a biased voltage. Materials that
respond to radiant energy and is capable of generating a signal
with a biased voltage (such as in the case of a photoconductive
cells, photoresistors, photoswitches, phototransistors, phototubes)
include, for example, many conjugated polymers and
electroluminescent materials. Materials that respond to radiant
energy and is capable of generating a signal without a biased
voltage (such as in the case of a photoconductive cell or a
photovoltaic cell) include materials that chemically react to light
and thereby generate a signal. Such light-sensitive chemically
reactive materials include for example, many conjugated polymers
and electro- and photo-luminescent materials. Specific examples
include, but are not limited to, MEH-PPV ("Optocoupler made from
semiconducting polymers", G. Yu, K. Pakbaz, and A. J. Heeger,
Journal of Electronic Materials, Vol. 23, pp 925-928 (1994); and
MEH-PPV Composites with CN-PPV ("Efficient Photodiodes from
Interpenetrating Polymer Networks", J. J. M. Halls et al.
(Cambridge group) Nature Vol. 376, pp. 498-500, 1995).
[0066] A layer 40 containing the active organic material can be
applied to the first electrical contact layer 30 from solutions by
any conventional means, including spin-coating, casting, and
printing. The active organic materials can be applied directly by
vapor deposition processes, depending upon the nature of the
materials. It is also possible to apply an active polymer precursor
and then convert to the polymer, typically by heating.
[0067] The active layer 40 is applied over the first electrical
contact layer 30, but does not typically cover the entire layer. As
best seen in FIG. 2, there is a portion 31 of the first electrical
contact layer that extends beyond the dimensions of the active
layer in order to permit the connection with drive and/or detection
circuitry in the finished device.
[0068] 4. Second Electrical Contact Layer
[0069] The second electrical contact layer 50 is applied to the
other side of the active layer 40. Although not shown in the
drawings, the second electrical contact layer can be made of one
single layer of material or can be a composite of multiple layers
of material.
[0070] The second electrical contact layer can be a material
containing essentially any metal or nonmetal capable of injecting
(or collecting) charge carriers into (or from, as the case may be)
the active layer 40. Generally, where the second electrical contact
is a cathode (i.e., an electrode that is particularly efficient for
injecting or collecting electrons or negative charge carriers) the
cathode can be any metal or nonmetal having a lower work function
than the first electrical contact layer (in this case, an anode).
Materials for the second electrical contact layer can be selected
from alkalil metals of Group I (e.g., Li, Cs), the Group IIA
(alkaline earth) metals, the Group II metals, including the rare
earths and lanthanide, and the actinides. Materials such as
aluminum, indium, calcium, barium, and magnesium, as well as
combinations, can be used.
[0071] Although second electrical contact layer 50 is shown with
extended portions 52 to connect the device to external circuitry,
it is understood that devices (not shown) that incorporate other
means of circuitry connection (such as vias) would not require such
extended portions 52. It is further understood that the composition
of the second electrical contact layer 50 may vary across the
dimensions 27, 66 of the composite barrier layers 20, 60. For
example, where the second electrical contact layer 50 includes the
extended portions 52, parts of the extended portions that are
disposed outside of the sealed composite barrier layers 20, 60 may
be contain essentially a material (such as Aluminum) that is more
resistant to environmental degradation and/or is a better conductor
than the second electrical contact layer composition that is
coextensive with the active layer 40. Thus, the second electrical
contact layer composition that is coextensive with the active layer
40 may be chosen to provide better electron band-gap matching. At
the same time the second electrical contact layer composition in
the extended portion 52 may be chosen to provide greater
conductivity and increased resistance to environment degradation
outside of the sealed device. The varied composition can be
provided by a separate layer of second electrical contact layer
material, or could be alloyed within one second electrical contact
layer.
[0072] The second electrical contact layer is usually applied by a
physical vapor deposition process. In general, the second
electrical contact layer will be patterned, as discussed above in
reference to the first electrical contact layer 30. Similar
processing techniques can be used to pattern the second electrical
contact layer. The second electrical contact layer typically has a
thickness in the range of 50-500 nm. Second electrical contact
layer materials and processes for patterning well known in the art
can be used.
[0073] A portion 52 of the second electrical contact layer will
extend beyond the dimensions of the light-emitting layer 40. As
with the first electrical contact layer 30, this extended portion
52 allows for the connection to drive and/or detection circuitry in
the finished device.
[0074] 5. Other Optional Layers
[0075] It is known to have other layers in organic electronic
devices. For example, there can be a layer (not shown) between the
first electrical contact layer 30 and the active layer 40 to
facilitate electrical charge transport and/or electron band-gap
matching of the layers 30, 40 or reduce chemical reactivity between
the active layer 40 and the first electrical contact layer 30.
Similarly, a layer (not shown) can be placed between the active
layer 40 and the second electrical contact layer 50 to facilitate
electrical charge transport and/or electron band-gap matching
between the layers 40, 50 or reduce chemical reactivity between the
active layer 40 and the second electrical contact layer 50. Layers
that are known in the art can be used. In addition, any of the
above-described layers can be made of multiple layers.
Alternatively, some of all of first electrical contact layer 30,
active layer 40, and second electrical contact layer 50, may be
surface treated to increase charge carrier transport efficiency.
Furthermore, additional barrier layers (not shown) can also be
placed between one of more sets of the layers 20, 30, 40, 50, 60 to
protect them from adverse processing conditions.
[0076] The choice of materials for each of the component layers
21A, 22, 22B, 30, 40, 50, 61A, 62, 61B is preferably determined by
balancing the goals of providing a device with high electrooptical
efficiency.
[0077] In many instances, organic electronic devices of the
invention can be fabricated by first applying a first electrical
contact layer and building up the device from there. It is
understood that it is also possible to build up the layers from the
second electrical contact layer.
[0078] The following examples illustrate certain features and
advantages of the present invention.
EXAMPLES
[0079] The following examples are illustrative of the invention,
but not limiting.
Example 1
[0080] A flexible composite barrier structure was formed with
polyester film and a thin film barrier of SiN.sub.x. The SiN.sub.x
was coated using a microwave electron cyclotron resonance (ECR)
plasma onto a 0.002 inch (50.8 micron) thick film of
polyethylene-terephthalate (PET), Mylar.RTM. 200D supplied by E. I.
du Pont de Nemours and Company, Inc. (Wilmington, Del.). Prior to
deposition, the chamber was evacuated to a pressure of
1.5.times.10.sup.-7 Torr with a turbo-molecular pump. During
deposition, 2 standard cubic centimeters (sccm) of SiH.sub.4, 98
sccm of Ar, and 20 sccm of N.sub.2 were admitted into the chamber.
The plasma was sustained using 150W of microwave power at 2.455
GHz, while the magnetic field was adjusted to about 900 Gauss,
corresponding to the resonance condition for electron motion in the
plasma. A one hour deposition produced a SiN.sub.x film about 840
.ANG. thick, as determined by atomic force microscopy (AFM).
Chemical depth profiling by X-ray photoelectron spectroscopy (XPS)
revealed that films were essentially SiN.sub.x (x.about.1.15) with
some oxygen (.about.10%) and presumably some hydrogen (not
measurable with XPS) incorporation. The oxygen transport rate (OTR)
at 50% relative humidity through the coated PET film was evaluated
with a commercial instrument (MOCON Oxtran 2/20 made by Mocon,
Minneapolis, Minn.) and determined to be 0.012 cc
(O.sub.2)/m.sup.2/day/atm. For reference an uncoated film of
Mylar.RTM. 200D has an OTR of about 24 cc
(O.sub.2)/m.sup.2/day/atm. Therefore the SiN.sub.x coating provides
a barrier improvement factor of 2000.times..
Example 2
[0081] A second flexible composite barrier structure was formed
with a 200 .ANG. thick film barrier of SiN.sub.x. The SiN.sub.x was
coated using a microwave ECR plasma onto 0.002 inch (50.8 micron)
thick Mylar.RTM. 200D PET film. The gas flow conditions during
deposition were 2 sccm of SiH.sub.4, 98 sccm of Ar, and 20 sccm of
N.sub.2 at a microwave power of 100 W. The deposition lasted 30
minutes. The OTR of the SiN.sub.x coated PET was subsequently
determined to be 0.12 cc (O.sub.2)/m.sup.2/day/atm.
Example 3
[0082] This example illustrates the OTR of a flexible composite
barrier structure having a laminate structure. Lamination of
SiN.sub.x coated PET protects the SiN.sub.x coating from mechanical
damage, which will compromise barrier properties. PET, 0.002 inch
(50.8 micron) thick with about 1000 A coating of SiN.sub.x,
produced by microwave plasma Chemical Vapor Deposition (CVD), was
laminated to uncoated PET, also 0.002 inch (50.8 micron) thick
using a commercial adhesive, 3M 8142, from 3M (St. Paul, Minn.).
The laminator had a single rubber roll and was operated at
48.degree. C. and 35 psi. The final structure of the laminated film
was PET/1000 .ANG./SiN.sub.x/adhesive/PET. The OTR of this
laminated structure was subsequently determined to be 0.00825 cc
(O.sub.2)/m.sup.2/day/atm.
Example 4
[0083] This example illustrates a flexible composite barrier
structure having two laminated SiN.sub.x layers. Two PET films,
each coated with about 1000 .ANG. of SiN.sub.x by microwave plasma
enhanced CVD, were laminated together with an adhesive, using the
conditions of Example 3, so that the SiN.sub.x films were to the
inside of the structure, and OTR was measured. That is, the
structure was PET/SiN.sub.x/adhesive/SiN.sub.x- /PET. Prior to
lamination, it was determined that the individual SiN.sub.x coated
PET films had an OTR of about 0.0075 cc (O.sub.2)/m.sup.2/day/atm.
The OTR of the laminate structure was less than 0.005 cc
(O.sub.2)/m.sup.2/day/atm, the lower measuring limit of the MOCON
instrument.
Example 5
[0084] This example illustrates the formation of a non-transparent
composite barrier structure using (a combination of vapor deposited
aluminum and layers of barrier polymers is utilized to provide
oxygen and moisture barrier) aluminum as the barrier material.
[0085] A first metallized film was prepared with polyvinylidene
chloride copolymer-polyester-aluminum-polyvinylidene chloride
copolymer. A roll of Mylar.RTM. LB biaxially oriented polyester
film was placed in a vacuum chamber where it was unwound and
exposed to evaporated aluminum which condensed on the film surface
to a thickness of 400 .ANG. (or an optical density (OD) of 2.8).
The metallized film was then solvent coated with a composition that
was essentially a copolymer of vinylidene chloride/vinyl
chloride/methylmethacrylate/acrylonitrile, over the both sides of
the film. The dry coating weight was 1.6 g/m.sup.2 on both of the
coated sides.
[0086] A second metallized film was prepared by coating Mylar.RTM.
LB film with a polyethyleneimine primer from a 1% solution in
water. The dried coating weight was 0.02 to 0.2 g/m.sup.2. The
primed polyester film was then topcoated with polyvinyl alcohol in
a second coater station. Dry polyvinyl alcohol was diluted to a 10%
solutions using 95-98.degree. C. water and steam sparging to make a
coating bath. After cooling, the coating was applied using a
reverse gravure coating technique. The dry coating weight was
0.4-1.0 g/m.sup.2. The product was then aluminum vacuum metallized
as described above on the polyvinyl alcohol side to a thickness of
400 .ANG. (or an OD of 2.8).
[0087] A third "plain" or nonmetallized polyester film was coated
on one side with a 17% solids tetrahydrofuran solution of a mixture
of essentially poly(terephthalic/azeleic acid/ethylene glycol),
copolymer. This was the heat sealable layer. The coating was
applied by reverse metering coating to a dry coating weight of 6
g/m.sup.2.
[0088] The first and second metallized films were laminated
together via a solvent based polyurethane adhesive such that the
polyvinylidene chloride layer (which was over the aluminum) of the
first film was adjacent to the aluminum layer of the second film.
The third polyester film was then laminated to the combination of
the first two films via a solvent based polyurethane adhesive such
that the plain polyester surface of the combined first two films
was adjacent to the plain polyester film surface of the third film.
The basic overall laminate structure was omitting the adhesive and
primer layers: polyvinylidine chloride
copolymer-polyester-aluminum-polyvinylidene chloride
copolymer-aluminum-polyvinyl alcohol-polyester-polyester-solvent
coated polyester heat sealable layer The OTR was measured to be
0.00062 cc/m.sup.2/24 hr/atm by an external laboratory.
Example 6
[0089] This example illustrates the bond strength of the
heat-sealed composite barrier structure.
[0090] The composite barrier structure of Example 5 was heat sealed
to the following second materials representing a second barrier
structure:
1 Ex. 6-A: 0.004 inch (50.8 micron) thick PET (400D) Ex. 6-B: 0.004
inch (50.8 micron) thick PET (400D) coated with an unpatterned,
electrically conducting ITO film 1500-2000 .ANG. in thickness Ex.
6-C 0.004 inch (50.8 micron) thick PET (400D) coated with patterned
ITO lines, 1500-2000 .ANG. in thickness (1 mm line width/0.75 mm
spaces).
[0091] The composite barrier structure and the second material were
positioned such that the heat sealable layer was adjacent to the
second material, and adjacent to the ITO layer of the second
material, when present. Two 4.times.4 inch (10.2.times.10.2 cm)
pieces were cut and laid together. These were heat sealed using a
Sentinel Brand Machine, Model #12A8-0 (manufactured by Packaging
Group Inc., Hyannis, Mass.) with adjustable temperature and timer
controls. A one-inch (2.54 cm) seal was attained at the temperature
and dwell times indicated below, applying a pressure of 30 psi.
[0092] To determine bond strength after the heat seal was
completed, the sealed structures were cut into strips one inch
(2.54 cm) wide. Depending on film thickness, Scotch Red Colored
Cellophane Tape (Type 650) was applied to the thinner of the sealed
substrates to prevent breakage at the seal line. The peel strength
was then determined on an Instron Universal Testing Instrument,
Model 1122 (available from Instron Corp.). A 5 pound full scale
load limit was used with the crosshead speed set to run at 2 inches
(5.1 cm) per minute. The peel strengths were reported as the
average of 4 samples.
[0093] The adhesion tests to patterned ITO were measured both
perpendicular (.perp.) and parallel (//) to the ITO lines. Bond
strengths were measured after sealing at either 120.degree. C. or
140.degree. C. for 0.5 or 1.0 second. The results are summarized in
Table 1 below.
2 TABLE 1 120.degree. C. 140.degree. C. Example 0.5 s 1.0 s 0.5 s
1.0 s 6-A 667 g/in. 766 g/in. 864 g/in. 881 g/in. 6-B 1276 g/in.
913 g/in. 515 g/in. 358 g/in. 6-C (P-.perp.) 554 g/in. 668 g/in.
624 g/in. -- 6-C (P-//) 659 g/in. 923 g/in. 916 g/in. 988 g/in.
[0094] These peel tests indicate that the polyester heat sealable
layer bonds equally well, and under some conditions more strongly,
to transparent, conducting ITO compared to bonding to PET
alone.
[0095] The adhesion of the composite barrier structure to both
electrode material and to the support is illustrated in FIGS. 5 and
6. As shown in FIG. 5, the peel strength is plotted versus distance
as Sample 6-C (P-.perp.) is peeled apart. The peel strength varies
with regular peaks and valleys corresponding to the different
materials (electrode material or polymeric support) that the
barrier structure is peeled from. As shown in FIG. 6, the composite
barrier structure 300 is peeled alternately from electrode material
200 and polymeric support 400. If the barrier structure 300 bonded
to only the support material 400 it would be expected that the plot
of peel strength would have a single continuous value, without
peaks and valleys.
Example 7
[0096] This example illustrates polymer light emitting diode (PLED)
device lifetime with a composite barrier structure having silicon
nitride barrier layers (Sample 7) as it compares with that of a
device without the silicon nitride barrier layer (Comparative
sample Y). Ten Sample 7 devices and ten Comparative Y devices were
prepared and tested.
[0097] The basic PLED device structure of both Sample 7 and
Comparative Sample Y included a glass substrate with a transparent
conducting anode layer of indium tin oxide over-coated with about
100 nm each of a polymer hole-injecting layer and a yellow
light-emitting polymer layer. This was then coated with a thin
layer (.about.20 nm) of a low work function metal and covered with
a one micron thick layer of aluminum.
[0098] Sample 7 devices were further fabricated as follows: A
single layer of 2 mil thick PET (polyethylene terephthalate) about
six inches square was coated consecutively on both sides with a
silicon nitride barrier layer about 80 nm thick. The silicon
nitride layers were deposited by microwave, plasma-enhanced
(electron cyclotron resonance (ECR)) chemical vapor deposition
(CVD). The conditions during deposition were 150 watts microwave
power, 2.7 sccm of silane (SiH4), about 100 sccm of Ar, and 20 sccm
of N2. The silicon nitride coated PET was then laminated to another
2 mil thick sheet of non-coated PET using a 2 mil thick, commercial
adhesive, as described in Example 3 above, to form the composite
barrier structure. Sections of the laminate composite barrier
structure, 35 mm.times.25 mm, were then cut and used to seal PLED
devices of about the same area, using a commercial, ultraviolet
curable epoxy. A good barrier can prevent device degradation caused
by atmospheric gases infiltrating the device.
[0099] Comparative Sample Y devices were further prepared as
follows: similar PLED devices were also epoxy sealed with a similar
PET laminate, but without barrier layers of silicon nitride.
[0100] The light emission of Sample 7 and Comparative Sample Y
devices was measured four (4) days after device fabrication
(storage at ambient conditions) and then measured again after
storing the devices in ambient conditions for fifty (50) days after
device fabrication.
[0101] FIG. 7(a) shows a plot of light emission of Sample 7
photodiodes initially (500) and then Sample 7 light emission after
fifty (50) days (502). There was essentially no change in the light
emission of these devices.
[0102] In contrast, the performance of Comparative Sample Y devices
is markedly different. FIG. 7(b) shows a plot of light emission of
Comparative Sample Y photodiodes initially (600) and then Sample Y
light emission after 50 days (602). The light emission was
significantly reduced after fifty (50) days of ambient storage.
* * * * *