U.S. patent application number 11/859581 was filed with the patent office on 2008-01-10 for transparent conductive articles and methods of making same.
This patent application is currently assigned to 3M Innovative Properties Company. Invention is credited to Clark I. Bright.
Application Number | 20080008893 11/859581 |
Document ID | / |
Family ID | 26804119 |
Filed Date | 2008-01-10 |
United States Patent
Application |
20080008893 |
Kind Code |
A1 |
Bright; Clark I. |
January 10, 2008 |
TRANSPARENT CONDUCTIVE ARTICLES AND METHODS OF MAKING SAME
Abstract
A lightweight, flexible, plastic substrate used to construct
displays, including flat panel displays, to package materials and
for electro luminescence lamps is coated with at least one layer,
such that the substrate has desired barrier and electrode
characteristics. The display medium of the flat panel display is
protected from oxygen and moisture in order to avoid degradation
with the coating. The layer with barrier and electrode
characteristics has both a low enough resistance to function as an
electrode for the display, and low oxygen and moisture
permeability. For lower permeability and/or higher conductivity,
multiple alternating layers of barrier materials and conductive
materials are applied. The barrier material includes at least one
of a thin metallic film, an organic polymer, a thin transparent
dielectric, a thin transparent metal nitride, and a thin
transparent conductive oxide. The conductive material includes at
least one of a thin transparent conductive oxide, a thin
transparent metallic film, and a thin transparent metal nitride.
Preferably there is a Polymer Multi Layer (PML) processed base coat
deposited over the substrate. The base coat produces substrate
smoothing, and more importantly, in combination with another layer,
the base coat improves vapor barrier properties. In the preferred
embodiment, a PML processed top coat barrier layer is deposited
before the coating contacts a surface, such as a roller. The PML
processed top coat also excludes moisture (water vapor) and
atmospheric gases that chemically degrade the device
performance.
Inventors: |
Bright; Clark I.; (Tucson,
AZ) |
Correspondence
Address: |
3M INNOVATIVE PROPERTIES COMPANY
PO BOX 33427
ST. PAUL
MN
55133-3427
US
|
Assignee: |
3M Innovative Properties
Company
|
Family ID: |
26804119 |
Appl. No.: |
11/859581 |
Filed: |
September 21, 2007 |
Related U.S. Patent Documents
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Application
Number |
Filing Date |
Patent Number |
|
|
10317623 |
Dec 12, 2002 |
7276291 |
|
|
11859581 |
Sep 21, 2007 |
|
|
|
09939008 |
Aug 24, 2001 |
7186465 |
|
|
10317623 |
Dec 12, 2002 |
|
|
|
09419870 |
Oct 18, 1999 |
|
|
|
09939008 |
Aug 24, 2001 |
|
|
|
60106871 |
Nov 2, 1998 |
|
|
|
Current U.S.
Class: |
428/458 ;
427/454 |
Current CPC
Class: |
Y02P 70/50 20151101;
G02F 1/133345 20130101; H01L 2251/5338 20130101; G02F 1/133305
20130101; Y10T 428/31681 20150401; C23C 16/545 20130101; Y10T
428/31794 20150401; Y10T 428/31692 20150401; C23C 16/0272 20130101;
Y02E 10/549 20130101; H01L 51/5215 20130101; Y10T 428/31678
20150401; H01L 51/5256 20130101; Y10T 428/31667 20150401; Y10T
428/31935 20150401; H01L 51/0097 20130101; Y02P 70/521 20151101;
Y10T 428/12576 20150115; H01L 51/5206 20130101 |
Class at
Publication: |
428/458 ;
427/454 |
International
Class: |
B32B 15/08 20060101
B32B015/08; B05D 1/08 20060101 B05D001/08 |
Claims
1. An article comprising a flexible plastic substrate coated with
multiple layers of transparent conductive metal nitride separated
by one or more layers of polymer, the article being sufficiently
flexible to be processable in a web coater.
2. An article comprising a flexible plastic substrate coated with
multiple layers of transparent conductive metal separated by one or
more layers of polymer.
3. An article comprising a flexible substrate, at least one layer
of polymer and an optically enhanced transparent conductive three
layer configuration comprising adjacent layers of: a) conductive
oxide, metal, and conductive oxide; b) conductive oxide, metal
nitride, and conductive oxide; c) metal nitride, metal, and metal
nitride; or d) conductive oxide, metal, and metal oxide.
4. An article according to claim 3 wherein the conductive layers
are electrically connected in parallel.
5. An article according to claim 3 comprising a conductive oxide
layer of one or more of cadmium oxide, tin oxide, indium oxide,
zinc oxide, gallium-containing oxide, and magnesium oxide, which
oxides may be doped or undoped.
6. An article according to claim 3 comprising a metal nitride layer
of one or more nitride of a Group III or IV element of the Periodic
Table.
7. A process for fabricating an article comprising: a) providing a
flexible plastic substrate, which optionally has a hard coat; and
b) depositing over the substrate multiple layers of transparent
conductive oxide that are separated by one or more layers of
in-situ polymerized organic monomer.
8. A process according to claim 7 further comprising applying a
polymeric base coat to smooth the substrate prior to deposition of
transparent conductive oxide.
9. A process according to claim 7 further comprising heating the
substrate during or after deposition of transparent conductive
oxide.
10. A process according to claim 7 further comprising depositing
transparent conductive oxide in a hydrogen-containing plasma.
11. A process according to claim 7 wherein the multiple layers are
deposited in a single vacuum chamber.
12. A process according to claim 7 further comprising electrically
connecting the transparent conductive oxide layers in parallel.
13. A process according to claim 7 comprising contacting the
transparent conductive oxide layers with a roller without causing
cracking or crazing of the conductive oxide layers sufficient to
reduce conductivity.
14. A process for fabricating an article comprising: a) providing a
flexible plastic substrate; and b) depositing over the substrate a
layer of in-situ polymerized organic monomer and an optically
enhanced transparent conductive three layer configuration
comprising layers of conductive oxide, metal nitride or dielectric;
metal or metal nitride; and conductive oxide, metal nitride or
dielectric.
15. A process according to claim 14 further comprising electrically
connecting the conductive layers in parallel.
16. An article according to claim 3 wherein tile transparent
conductive three layer configuration comprises adjacent layers of
conductive oxide, conductive metal nitride, and conductive
oxide.
17. An article according to claim 3 wherein the transparent
conductive three layer configuration comprises adjacent layers of
silicon nitride, metal, and another metal nitride.
18. An article according to claim 3 comprising: a) a first
transparent conductive three layer configuration and b) a layer of
transparent conductive oxide or a second transparent conductive
three layer configuration separated by one or more layers of
polymer.
19. An article according to claim 1 wherein the article is
roll-to-roll processable.
Description
CROSS-REFERENCE TO RELATED APPLICATIONS
[0001] This application claims the benefit of U.S. patent
application Ser. No. 10/317623, which is a Continuation of U.S.
patent application Ser. No. 09/939008, filed Aug. 24, 2001, which
is a Divisional Application of U.S. application Ser. No. 09/419870,
filed Oct. 18, 1999, now abandoned, which claims the benefit of
U.S. Provisional Application No. 60/106871, filed Nov. 2, 1998, all
of which are incorporated by reference, including the original
specification, first substitute specification, second substitute
specification, and all attached Appendices of U.S. application Ser.
No. 09/419870.
FIELD OF THE INVENTION
[0002] This invention relates to composite substrates for flat
panel displays (FPD), packaging materials and light sources
(electro luminescence lamps) comprising a plastic substrate having
thin film barrier and conductive layers,in particular, multiple
thin alternating layers of metallic film, transparent conductive
oxide (TCO), metal nitride, and organic polymers deposited over the
plastic substrate.
BACKGROUND OF THE INVENTION
[0003] The use of portable electronic devices incorporating flat
panel displays is prevalent and increasing rapidly. Because of the
portable nature of these devices, it is desired to minimize both
the size and weight and maximize durability. The display portion of
the device is generally larger and denser as compared to the rest
of the device, and is manufactured on glass substrates.
Accordingly, a smaller, lighter and more durable portable
electronic device is most effectively achieved with a smaller,
lighter and shatterproof electronic device display.
[0004] Despite being lightweight, plastic has not been considered a
viable substrate material to be used for the manufacture of flat
panel displays for multiple reasons. Most importantly, flat panel
displays fabricated with plastic substrates tend to fail
prematurely due to degradation of display medium (display matrix)
and/or metallic electrodes. In particular, the metallic electrodes
and the display medium which is often positioned between the
electrodes, become degraded when atmospheric oxygen and water vapor
permeate the substrate and chemically degrade the active portion of
the display matrix which is generally comprised of liquid crystals
and/or light emitting devices. In addition, common optical quality
plastic substrates, e.g. polyethylene terephthalate (PET), have
limited thermal properties. In particular, there is a limited
temperature range that allows useful optical quality (e.g. clarity,
transparency, and uniform index of refraction) to be maintained,
while maintaining the substrate's mechanical strength and
properties.
SUMMARY OF THE INVENTION
[0005] The present invention is directed to the fabrication of flat
panel displays on lightweight, flexible, plastic substrates.
Because plastic substrates for FPDs are flexible, smaller and
lighter than glass substrates, the electronic device with the
plastic FPD is more portable, space-efficient and lightweight. In
addition, electroluminescent and organic light emitting devices
fabricated on flexible polymeric substrates in a coating process
have lower manufacturing costs than those with glass substrates,
and improved ruggedness.
[0006] A display medium of the flat panel display is sandwiched
between two electrode layers. At least one of the electrodes is
transparent for viewing of the display. The display medium is
protected from oxidative or moisture degradation. In the present
invention, at least one layer, having both barrier characteristics
and the ability to function as an electrode, is deposited over the
substrate. In particular, the layer has both low oxygen and water
vapor permeability, and a low enough resistivity to function as an
electrode for the display. For lower permeability and/or higher
conductivity, multiple alternating layers of barrier materials and
conductive materials are applied. In an alternative embodiment, the
conductive layers (e.g. transparent conductive oxide layers) are in
direct electrical contact. The barrier material includes at least
one of an organic polymer, a transparent dielectric, a transparent
metal nitride and/or a transparent conductive oxide. The conductive
material includes at least one of a thin transparent conductive
oxide, a thin transparent metallic film and/or a metal nitride.
[0007] Using a smoothing base coat layer over the plastic substrate
imparts good optical quality throughout the substrate layers and
provides a pristine surface for nucleation of the deposited barrier
or conductive layer, e.g. TCO. The pristine surface smooths over
any surface roughness of the plastic substrate, thereby adding to
the FPD lifetime and optical quality. Additionally, a hardcoat
layer is applied over the substrate in lieu of or in addition to
the smoothing basecoat layer.
[0008] The smoothing basecoat and hardcoat layers may be applied by
one of many well known non-vacuum liquid coating processes, e.g.
preferably by Gravure, or fabricated through a polymer multilayer
(PML) coating process. Related desirable coating processes are
disclosed in U.S. Pat. Nos. 5,547,508, 5,395,644, 5,260,095, U.S.
patent application Ser. No. 08/939,594, filed Sep. 29, 1997,
entitled "Plasma enhanced chemical deposition with low vapor
pressure compounds" herein incorporated by reference, Thin Film
Processes II, chapters 11-2, 4, 5, and IV-1, edited by John L.
Vossen and Wermer Kern, Academic Press, 1991, ISBN 0-12-728251-3,
and Deposition Technologies for Films and Coatings, Developments
and Applications, Rointan F. Bunshah et al, Chapters 5, 6, 8 and 9,
Noyes Publications, 1982, ISBN 0-8155-0906-5.
[0009] The terms PML and PML process as used in this application
are generic and mean any form of a PML process, including Plasma
PML processes (PPML processes) and liquid PML processes (LML
processes). The basic vacuum evaporation PML process is used to
deposit organic monomers over the plastic substrate. The organic
monomer is then polymerized in-situ by electron beam, a plasma
process, or UV radiation.
[0010] The PML process is compatible with physical vapor deposition
processes for layers such as TCO layers. Both processes are carried
out in combined sequences within a properly designed single vacuum
chamber. However, often multiple vacuum chambers are used, for
example, if a substrate is hardcoated previously.
[0011] The PML deposited organic polymer layer is used to produce
substrate surface smoothing and improve barrier coatings in the
multilayer structure. The benefit of a smooth substrate surface is
that there is a clean surface for adhesion, nucleation, and growth
of a deposited barrier or conductive layer, e.g. a TCO.
Additionally, a PML deposited organic polymer layer provides
protection of an underlying barrier layer in order to minimize
holes or other defects in the layer so that there is low
permeability.
[0012] Neither a single layer barrier coating with a metal oxide
layer such as thin film dielectric coatings of alumina or silica or
other certain metal oxides, nor a plastic flat panel display with a
thick metallic film layer having an optical density of greater than
2.0 renders low enough permeability for the processing and
manufacture of plastic flat panel displays with acceptable
lifetimes. Even where a single thick layer or multiple thin layers
of dielectrics, metals or the combination thereof are used, the
improvement in performance is minimal. In order to provide barrier
properties sufficient for optical quality plastic flat panel
displays, a transparent dielectric barrier, such as SiO.sub.2-x or
Al.sub.2O.sub.3-y, is deposited over a plastic substrate. When
dielectric layers are combined with PML deposited organic polymer
layers, outstanding barrier properties are achieved on flexible
plastic substrates. Alternatively to the dielectric layer, a
barrier coating of ITO (called "indium tin oxide", which is
actually "Tin doped indium oxide," a mixture of indium oxide and
tin oxide) or another TCO barrier is deposited over the substrate.
In yet another alternative embodiment, both TCO barrier layers and
PML processed organic polymer layers are deposited over the plastic
substrate. Moreover, in yet another alternative, both TCO barrier
layers with PML processed organic polymer layers and the
transparent dielectric barrier layers are deposited over the
plastic or polymeric substrate. Multilayer structures of such
organic and inorganic layers deposited over a plastic substrate
exhibit significantly improved barrier properties as compared to
inorganic, organic, or metallic layers alone.
[0013] In an embodiment, a PML processed top coat polymer layer is
applied before the previously deposited layer contacts a surface,
such as a roller, thereby protecting the previously deposited
layer. The PML processed top coat greatly enhances the exclusion of
moisture (water vapor) and atmospheric gases that chemically
degrade the display medium and decrease the device performance,
even though the polymer topcoat is not, itself, a good barrier
material.
[0014] Metal oxide dielectric barriers have previously been
deposited by evaporation, sputtering, and chemical vapor deposition
processes onto glass substrates. However, for achieving metal oxide
thin films with bulk material-like properties on glass substrates,
a high temperature deposition method is used, which would melt the
plastic substrate, thereby negatively impacting the mechanical
properties of the plastic substrate. In the present invention, the
PML family of processes used for depositing an organic dielectric
does not require such high temperatures and therefore does not
significantly alter the mechanical properties of the plastic
substrate. However, organic polymer layers alone do not provide
substantial barrier properties, particularly against water
vapor.
[0015] When TCOs are deposited at low temperatures to accommodate
the thermal and mechanical limits of the substrate, for example, by
magnetron sputtering, electron-beam evaporation or plasma enhanced
chemical vapor deposition (PECVD), the subsequent TCO coatings have
less than bulk conductivity, i.e. low overall levels of
conductivity. TCO films with a larger thickness deposited through
these methods achieve acceptable conductive levels for portable
electronic devices. However, these thick films of TCO are subject
to cracking, crazing and, in some instances, delamination from the
substrate, especially when they are processed by a heat treatment
step or a coating process involving mechanical rollers (e.g. web
coating). Accordingly, the TCO coating is deposited in a series of
thin, separated layers, yet still maintains high conductive levels.
Multiple thin layers of TCO avoid the problems associated with
thicker layers, and advantageously are electrically connected in
parallel to provide adequate electrical performance
characteristics.
[0016] The thin layers of TCO are preferably deposited in
combination with layers from the PML process, which leads to
improved optical, electrical and mechanical performance. In
particular, the polymer layers separate the TCO layers. Superior
surface properties (low surface roughness, and high optical
quality), barrier properties (low vapor permeability) and
mechanical properties result when TCO coatings are deposited by
magnetron sputtering on a plastic substrate in combination with the
PML process.
[0017] Preferably, moderate annealing temperature conditions, with
respect to substrate limits, are used for TCO (including ITO, "tin
doped indium oxide") deposition because high temperature conditions
result in melting of the plastic, and low temperature conditions
yields ITO layers with undesirable high resistivity. (The
resistivity of ITO is a function of the oxygen and tin content, as
well as the deposition conditions, such as temperature). A low
resistivity for the ITO layers is desired. The resistivity of ITO
decreases with a thicker TCO layer. But as discussed previously,
thick TCO layers are prone to cracking or crazing. Multiple thin
layers of TCO, as described in the present invention, will not
crack and will yield a lower resistivity. Moreover, the surface
resistivity of a thin film of TCO in multiple layers is low for a
given total film thickness, due to its improved microstructure.
[0018] In a first embodiment of the present invention, a polymer
smoothing coating is deposited over the substrate. The smoothing
coating is applied by a PML process or liquid coating. A TCO, metal
nitride, or metal layer is then deposited over the smoothing layer.
Additionally, multiple alternating layers of a protective polymer
layer and an additional TCO, metal nitride, or metal layer is
deposited. Preferably, the alternating layers are of the same
material, e.g. TCO/polymer/TCO, etc.
[0019] In a second embodiment, multiple alternating layers of
polymer layers and metal oxide or metal nitride are deposited over
the substrate or a polymer smoothing coating layer. A TCO layer is
then deposited over the top of multiple alternating layers. These
multiple alternating layers together with the TCO have adequate
barrier and conductivity characteristics.
[0020] In a third embodiment, a substrate is coated with a TCO
layer, a metal coating, and another TCO layer. This three layer
configuration is called "optically enhanced metal," or an induced
transmission filter and has similar characteristics as and is
substitutable for a single TCO layer. With the optically enhanced
metal good conductivity, optical transmission and barrier
properties are achieved. A similar structure using metal nitrides
substituted for the metal coating or the TCO layer, or one or more
metal oxide layers substituted for one or more TCO layers,
functions equivalently to the optically enhanced metal. For
example, a further embodiment is comprised of a TCO layer, a
conductive metal nitride layer and another TCO layer.
Alternatively, the structure is a silicon nitride layer, a metal
layer and another metal nitride layer.
[0021] In a fourth embodiment, a substrate is alternatively coated
with an inorganic layer (such as TCO, metal nitride, or dielectric
metal oxides), and polymer layers to provide both barrier and
conductive properties.
BRIEF DESCRIPTION OF THE DRAWINGS
[0022] The aspects of the present invention described above in
summary and below in more detail as well as various advantageous
aspects will become appreciated as the same becomes better
understood with reference to the specification, claims and drawings
wherein:
[0023] FIG. 1 is a cross-sectional view of a composite substrate
for a flat panel display (FPD) of the present invention;
[0024] FIG. 2 is a cross-sectional view of another embodiment of
conductive barrier layer 3 of FIG. 1;
[0025] FIG. 3 is a cross-sectional view of another embodiment of
conductive barrier layer 3 of FIG. 1;
[0026] FIG. 4 is a cross-sectional view of another embodiment of
conductive barrier layer 3;
[0027] FIG. 5 is a cross-sectional view of another embodiment of
conductive barrier layer 3 of FIG. 1;
[0028] FIG. 6 is a cross-sectional view of an embodiment of a
conductive barrier layer;
[0029] FIG. 7 is a cross-sectional view of an embodiment of
conductive barrier layers of FIG. 1;
[0030] FIG. 8 is a cross-sectional view of an embodiment of
conductive barrier layers of FIG. 1;
[0031] FIG. 9 is a cross-sectional view of an embodiment of
conductive barrier layers of FIG. 1;
[0032] FIG. 10 is a cross-sectional view of an embodiment of
conductive barrier layers of FIG. 1;
[0033] FIG. 11 is a cross-sectional view of an embodiment of
conductive barrier layers of FIG. 1;
[0034] FIG. 12 is a cross-sectional view of an embodiment of
conductive barrier layers;
[0035] FIG. 13 is a schematic illustration of a coating apparatus
for forming the conductive barrier layer of FIG. 1;
[0036] FIG. 14a is a schematic illustration of a laminating process
for the FPD of FIG. 1;
[0037] FIG. 14b is a cross-sectional view of the FPD before
undergoing a bonding process;
[0038] FIG. 14c is a cross-sectional view of the FPD after
undergoing a bonding process;
[0039] FIG. 15 is a chart showing water vapor permeability of an
ITO film deposited on a polyethylene terephthalate (PET) substrate
versus ITO film sheet resistance;
[0040] FIG. 16 is a chart showing water vapor permeability of ITO
film deposited on a PET substrate versus ITO film thickness;
[0041] FIG. 17 is a chart showing oxygen permeability of ITO film
deposited on a PET substrate versus ITO film thickness;
[0042] FIG. 18 is a chart showing oxygen permeability of ITO film
deposited on a PET substrate versus ITO film sheet resistance;
[0043] FIG. 19 is a chart showing transmittance and reflectance
spectra (for an ITO layer over a silver film layer over an ITO
layer over a PET substrate at a sheet resistance of 14 Ohms/Square)
versus wavelength;
[0044] FIG. 20 is a chart showing transmittance and reflectance
spectra (for an ITO layer over a PET substrate at a sheet
resistance of 29 Ohms/Square) versus wavelength;
[0045] FIG. 21 is a chart showing transmittance and reflectance
spectra (for an ITO layer over a PET substrate at a sheet
resistance of 57 Ohms/Square) versus wavelength;
[0046] FIG. 22 is a chart showing transmittance and reflectance
spectra (for an ITO layer over a PET substrate at a sheet
resistance of 65 Ohms/Square) versus wavelength;
[0047] FIG. 23 is a chart showing transmittance and reflectance
spectra (for an ITO layer over a PET substrate at a sheet
resistance of 347 Ohms/Square) versus wavelength;
[0048] FIG. 24 is a chart showing oxygen permeability of an ITO
film deposited on a flexible plastic substrate versus
thickness;
[0049] FIG. 25 is a chart showing water vapor permeability of an
ITO film deposited on a flexible plastic substrate versus
thickness;
[0050] FIG. 26 is a chart showing transmittance and reflectance
spectra (for semi-reactively sputtered ITO on a PET substrate;
polymer/ITO=25 nm) versus wavelength;
[0051] FIG. 27 is a chart showing transmittance and reflectance
spectra (for semi-reactively sputtered ITO on a PET substrate;
polymer/ITO=153 nm) versus wavelength;
[0052] FIG. 28 is a chart showing transmittance and reflectance
spectra (for semi-reactively sputtered ITO on a PET substrate;
polymer/ITO=134 nm) versus wavelength;
[0053] FIG. 29 is a chart showing transmittance and reflectance
spectra (for semi-reactively sputtered ITO/polymer on a PET
substrate; two ITO layers=50 nm total) versus wavelength; and
[0054] FIG. 30 is a chart showing transmittance and reflectance
spectra (for semi-reactively sputtered ITO/polymer on a PET
substrate; two ITO layers=299 nm total) versus wavelength.
DETAILED DESCRIPTION OF THE INVENTION
[0055] A flat panel display (FPD) 1, of the present invention as
shown in FIG. 1, employs at least one lightweight, plastic
substrate 38 for fabricating FPDs. In one embodiment, the plastic
is flexible. In another embodiment, the substrate used in the flat
panel display is glass. In an alternative embodiment, there are two
plastic substrates used to construct the FPD. In between two
substrates of the flat panel display are at least two electrodes.
At least one of the electrodes is transparent for viewing of the
display. A display medium 2 for the flat panel display is usually
positioned between the two electrodes. The display medium, as well
as some electrode material, are protected from oxidative
degradation and reaction with or incorporation of moisture.
[0056] The displays are fabricated using plastic substrates such as
various polyolefins, e.g. polypropylene (PP), various polyesters,
e.g. polyethylene terephthalate (PET), polymethylmethacrylate
(PMMA) and other polymers such as polyethylene napthalate (PEN),
polyethersulphone (PES), polyestercarbonate (PC), polyetherimide
(PEI), polyarylate (PAR), polyimide (PI), and polymers with trade
names ARTON.RTM. (Japanese Synthetic Rubber Co., Tokyo, Japan) and
AVATREL.TM. (B.F. Goodrich, Brecksville, Ohio). See Appendix A for
deposition temperature capabilities of the particular plastic
substrate.
[0057] In the present invention, at least one layer, a conductive
barrier layer 3 has both barrier characteristics (to protect the
display medium and/or the metal electrode from oxidative
degradation and reaction with or incorporation of moisture) and the
ability to function as an electrode. The conductive barrier layer
is deposited over the substrate to form a composite substrate, as
shown in FIG. 6. In particular, layer 3 has both low oxygen and
moisture (water vapor) permeability, and a low enough resistivity
to function as an electrode for the display.
[0058] As shown in the general embodiments of FIGS. 2 through 5,
conductive barrier layer 3 comprises at least one sublayer 3.sup.1
deposited over the substrate, for instance a single ITO layer. In
an embodiment, at least one pair of sublayers, a dyad, of a polymer
layer 24 and a layer of TCO 22, metal 12, metal nitride 14 or metal
oxide 16, is deposited over the substrate. FIG. 2 illustrates the
sublayer having a dyad of metal 12 and metal oxide 16. FIG. 3
illustrates the sublayer having a dyad of metal nitride 14 and
metal oxide 16. FIG. 4 illustrates the sublayer having a dyad of
dielectric 17 and TCO 22. FIG. 5 illustrates the TCO layer 22
deposited over the dielectric layer 17 which is deposited over the
polymer layer 24. The sublayers 3.sup.1 deposited on either side of
the pairs illustrated in FIGS. 2-4 are, for example, a single ITO
layer, additional dyads of the same materials, and/or a polymer
coating. In an exemplary embodiment, multiple alternating sublayer
pairs, comprised of the same materials as the original sublayer
pair, are deposited over the substrate or over the previously
deposited sublayer. In another embodiment the multiple alternating
sublayer pairs deposited over the previously deposited sublayer
comprise different sublayer materials than the previously deposited
sublayer.
[0059] There are a myriad of possibilities for materials comprising
the sublayers of the conductive barrier layer. FIGS. 2-5 illustrate
generally only some of the more preferred embodiments of sublayer
3.sup.1 materials for conductive barrier layer 3, while FIGS. 7-12
illustrate particularly the more preferred embodiments for the
conductive barrier layer.
[0060] In one embodiment shown in FIG. 9, for example, a base
coating 20 is deposited over the substrate 38. The base coating is
a polymer smoothing coating applied by a PML process and/or an
organic hardcoat. The base coating can be deposited by a non-vacuum
liquid coating process (to render a hardcoated PET) or applied by a
PML process. When a hardcoat is deposited, the plastic substrate is
rendered abrasion resistant. A TCO layer 22 (or metal layer 12) is
then deposited over the base coat. In another embodiment, multiple
alternating layers of a protective polymer layer 24 and at least
one TCO layer 22 (or metal layer 12) are additionally deposited
(see FIG. 9). Preferably, the alternating layers additionally
deposited are of the same material, e.g. TCO/polymer/TCO, etc.
Alternatively, there is no base coat 20 for the embodiment of
alternating layers of polymer/TCO/polymer (not shown). In another
embodiment, also shown in FIG. 9, a metal conductor or reflector 12
overlays the top polymer layer 24.
[0061] In the embodiment shown in FIG. 7, a substrate is coated
with a TCO layer, a metal coating, and another TCO layer. This
three layer configuration is called an "optically enhanced metal,"
or "induced transmission filter" and has characteristics similar to
a single TCO layer, and is also substitutable for a single TCO
layer. With the optically enhanced metal, good conductivity,
transmission and barrier properties are achieved. In a preferred
embodiment, deposited on the three layers is polymer layer 24 (see
FIG. 8). The polymer layer 24 may be alternating with the optically
enhanced metal (not shown). Alternatively, base coat 20 is
deposited over the substrate as shown in FIG. 7. Additionally or
alternatively, another dyad (a metal and TCO pair) is deposited
over the top TCO layer and/or an additional polymer layer 24 (a
polymer overcoat) is deposited over the previously deposited dyad
(see FIG. 8). In another alternative, a thick metal layer 12 is
deposited over the polymer overcoat layer, as also shown in FIG. 8.
Alternatively, the metal nitride layer 14 is substituted for one or
more of the metal layers in the above described embodiments, for
example, see FIGS. 10 and 11.
[0062] In still another embodiment, the substrate is alternatively
coated with an inorganic layer (such as the TCO layer or the
dielectric metal oxide layer), and polymer layers to provide both
barrier and conductive properties.
[0063] FIG. 12 illustrates metal layer 12 sandwiched between two
metal nitride layers 14. Alternatively, additional dyads (metal and
metal nitride pair) are deposited over the metal nitride layer.
Further embodiments of this dyad pair are similar to the TCO/metal
dyad pair embodiments of FIGS. 7-8, i.e. the TCO layers of FIGS.
7-8 are replaced by one or more metal nitride layers.
[0064] In another alternative embodiment, the dielectric layer
replaces one or more TCO layers in the above described embodiments
(see generally FIGS. 4 and 5). As shown in FIG. 5, multiple
alternating layers of dielectric 17 and polymer layers 24 are
deposited over the substrate 38. The number of multiple alternating
layers (or dyads) vary, and is represented here by 3.sup.1,
sublayers of the conductive barrier layer 3. A TCO layer 22 (or
metal layer 12) is then deposited over the top of multiple
alternating layers. These multiple alternating layers together with
the TCO have adequate barrier and conductivity characteristics as
described in more detail below.
[0065] Each TCO layer 22 of the above embodiments is a single TCO
layer. Alternatively, the TCO layers in the Figures described above
represents the thickness of two TCO layers from adjacent layers of
"optically enhanced metal" of FIG. 8 or the metal nitride
alternative of FIG. 11.
[0066] Preferably, the metal layers that are in the alternating
dyad pairs or in between the TCO, metal nitride, or dielectric
layers, are thin. The metal layers that are adjacent the "display
medium," i.e. overlaying the dyad layers, or on the substrate, have
a greater thickness than the sandwiched metal layers.
[0067] Sublayer 3.sup.1 materials that provide transparent barrier
properties are thin transparent metal oxides 16, and/or thin
transparent metallic films 12, and/or thin metal nitrides 14, for
example silicon nitride, and aluminum nitride. The polymer layer 24
enhances barrier properties by reducing the number of holes and
defects in the films upon which or under which, they are deposited.
The metal oxide layer 16 comprises the dielectric layer 17 and/or
the transparent conductive oxide layer 22. Thicknesses for the
barrier layers are in the nanometer and angstrom range. Thicknesses
for the PML deposited layers are in the micron and submicron range.
For example, improved barrier coating occurs when a PML deposited
organic polymer layer (a base coat), and/or a metal oxide layer is
placed over the plastic substrate. See Table 2.
[0068] Sublayer 3.sup.1 materials that provide conductive
properties include the thin TCO layer 22, a thin transparent
metallic film layer 12 (such as aluminum, silver, copper, gold,
platinum, palladium, and alloys thereof, and the metal nitride
layer 14 (such as transition metal nitrides, for example, titanium
nitride, zirconium nitride, hafnium nitride, and nitrides of Group
IIIA and IVA elements of the Periodic Table, e.g. gallium nitride).
Thicknesses for the conductive layers are in the nanometer and
angstrom range. Preferably the conductive film (TCO) is formed by
multiple thin conductive layers (of TCO) separated by polymer
layers. The conductive (TCO) layers are deposited with electrical
contact to each other, so that a low resistivity is achieved.
Consequently, the conductive film (TCO) functions as both the
electrode and a barrier.
[0069] In the preferred embodiment, the PML processed base coat 20
is deposited over the substrate as shown in FIG. 9. The base coat
produces substrate smoothing, and more importantly, in combination
with other layers, the base coat has surprisingly effective vapor
barrier enhancement properties because of the smoothing and
protection characteristics. The sublayers are preferably deposited
in combination with the process illustrated in FIG. 13, as
described below.
[0070] Using the smoothing base coat layer over the plastic
substrate imparts good optical and barrier quality throughout the
substrate layers and provides a pristine surface for nucleation of
the deposited TCO electrode layer. The basecoat smooths over any
surface roughness of the plastic substrate, thereby adding to the
FPD lifetime and optical quality.
[0071] In an exemplary embodiment, one or more metal oxide layers
are replaced with the TCO layer. When TCO coatings, including ITO
("Tin doped indium oxide"), cadmium oxides (CdSn.sub.2O.sub.4,
CdGa.sub.2O.sub.4, CdIn.sub.2O.sub.4, CdSb.sub.2O.sub.6,
CdGeQ.sub.4, tin oxides (various alloys and dopants thereof),
indium oxides (In.sub.2O.sub.3: Ga, GaInO.sub.3 (Sn, Ge),
(GaIn).sub.2O.sub.3), zinc oxides (ZnO(Al), ZnO(Ga), ZnSnO.sub.3,
Zn.sub.2SnO.sub.4, Zn.sub.2In.sub.2O.sub.5,
Zn.sub.3In.sub.2O.sub.6), and/or magnesium oxides
(MgIn.sub.2O.sub.4, MgIn.sub.2O.sub.4--Zn.sub.2In.sub.2O.sub.5) are
deposited on the plastic substrate at a low temperature, they have
an amorphous microstructure. For characteristics of the above TCO
materials, see Table A. The amorphous structure and oxygen
deficiency of the TCO theoretically allows the TCO coating to
exhibit conductive properties and barrier properties similar to
transparent dielectric barrier layers, such as nonstoichiometric
types of silica or alumina. Also, because of the oxygen deficiency,
and amorphous structure, the barrier layers gather the oxygen and
keep the oxygen from passing through. Multiple thin layers of TCO
function as both a transparent electrode and a transparent barrier
layer. The benefit of using TCO alternating with metallic film
layers, besides the beneficial barrier properties, is that all the
layers of the structure are conductive, thus improving
conductivity.
[0072] In the preferred embodiment, a suitable apparatus for
coating the substrate with conductive and barrier layers is
illustrated schematically in FIG. 13. All of the coating equipment
is positioned in a vacuum chamber 36. A roll of polypropylene,
polyester or other suitable plastic sheet is mounted on a pay-out
reel 37. Plastic sheet 38 forming the substrate is wrapped around a
first rotatable drum 39, and fed to a take-up reel 41. A roller 42
is employed, as appropriate, for guiding the sheet material from
the payout reel to the drum and/or to the take-up reel.
[0073] A flash evaporator 43 is mounted in proximity to the drum at
a first coating station. The flash evaporator deposits a layer or
film of monomer, typically an acrylate, on the substrate sheet as
it travels around the drum. After being coated with a
TABLE-US-00001 TABLE A EMERGING TRANSPARENT CONDUCTING OXIDES FOR
ELECTRO-OPTICAL APPLICATIONS CHARACTERISTICS OF EMERGING TCO
MATERIALS Carrier Film Transmittance Resistivity Concentration
Mobility Thickness Material (%) (.times.10.sup.-4 .OMEGA.cm
(.times.10.sup.20 cm.sup.-3) (cm.sup.2/V.sup.-1s.sup.-1) (nm)
References MgIn.sub.2O.sub.4 85 20 1.8 15 Minami, T. et al., Thin
Solid Films 270, 1995 MgIn.sub.2O.sub.4--Zn.sub.2In.sub.2O.sub.5 82
10 3 2 400 Minami, T. et al. I CMC TF 1995 In.sub.2O.sub.3:Ga 85
5.8 5 20 400 Minami, T. et al. JVST A 15(3), 1997 GaInO.sub.3 90 29
4 10 1000 Phillips, J. et al. (Sn, Ge) Appl. Phys. Lett 65(1) 1994
(GaIn).sub.2O.sub.3 90 10 3 20 100 Minami, T. et al. JVST A 15(3),
1997 ZnO(Al) 90 1.4 9.9 45 150 Imaeda, K. et al. 43.sup.rd AVS
Symp. 1996 ZnO(Ga) 90 2.7 13 18 230 Imaeda, K. et al. 43.sup.rd AVS
Symp. 1996 ZnSnO.sub.3 80 45 1 20 310 Minami, T. et al. JVST A
13(3) 1995 Zn.sub.2SnO.sub.4 92 570 0.058 19.0 620 Wu, X. et al
JVST A 15(3), 1997 Zn.sub.2In.sub.2O.sub.5 95 2.9 6.0 30 400
Minami, T. et al. Thin Solid Films 290-291, 1996
Zn.sub.3In.sub.2O.sub.6 80 3.8 3.4 46 1400 Phillips, J. et al.
Appl. Phys. Lett. 67(15), 1995 ITO 91 1-2 10 37 140 Helz, B., OIC
Topical Meeting, 1998
monomer, the substrate sheet passes a radiation station where the
monomer is irradiated by a source 44 such as an electron gun or
source of ultraviolet (UV) radiation. The UV radiation or electron
bombardment of the film induces polymerization of the monomer.
[0074] The sheet then passes coating station 46 where a coating of
TCO is preferably applied by magnetron sputtering. The sheet then
passes another flash evaporator 47 where another layer of monomer
is deposited over the TCO layer. The sheet then passes radiation
station 48 and the monomer is polymerized. Depending on whether a
layer of monomer is above or below the TCO layer, either evaporator
43 or 47 is used. Clearly, if the TCO layer is to be sandwiched
between layers of polymer, both evaporators and their respective
radiation sources are used. In addition to magnetron sputtering,
the TCO layer is processed by one of thermal evaporation, chemical
vapor deposition, plasma enhanced chemical vapor deposition, and
electron beam evaporation. Chemical vapor deposition is a high
temperature process, and is therefore the least desirable for use
with plastic substrates but is acceptable for metal foil
substrates.
[0075] In an alternative embodiment, a LML smoothing or hardcoat
layer applicator 52 is mounted in proximity to the drum at a first
coating station. The liquid smoothing applicator deposits a layer
of monomer, e.g. acrylate, over the substrate. This layer of
monomer is cured by irradiation from an ultraviolet or electron
beam source 44 adjacent the drum (the positions of source 44 and
applicator 52 are interchanged). Additionally, the sheet then
passes coating station 46 where a coating of thin metal film, metal
oxide, and/or metal nitride is applied by one of vacuum sputtering,
vacuum metallizing, plasma assisted chemical vapor deposition, or
electron beam evaporation. For example, silicon oxides is deposited
by a plasma enhanced chemical vapor deposition process using a
metal organic precursor and an oxidizing or inert carrier gas
coating station 46 alternatively containing deposition sources.
[0076] The various layers described are deposited in several
processes, in addition to vacuum coating techniques. For instance,
the layers are deposited through nonvacuum (atmospheric) roll
coating. Alternatively or additionally, the layers are deposited by
an in line coating machine, whereby a conveyor belt runs the
substrate to be coated past multiple coating stations. In a further
alternative, the layers are deposited by an intermittent motion
machine, that is either in a vacuum process or a nonvacuum process.
In yet another alternative, the layers are coated using a multitude
of machines and/or processes. For instance, the plastic substrate
is first coated through atmospheric roll coating with a cured
polymer and subsequently coated by vacuum deposition, or liquid
coated, such as Gravure coating.
[0077] For multiple layers of organic polymer coatings deposited in
the PML process, take up reel 41, with the sheet wound thereon,
functions as the pay out reel 37, and the process is repeated as
desired by coating in both directions. For this alternative,
additional curing stations are mounted on the opposite side of
evaporators 43 or 47. The roll of sheet is removed from the vacuum
system for use.
[0078] FIG. 14a illustrates a laminating process for the FPD where
plastic substrates, hardcoating, and a display medium are bonded
together, for example, with an adhesive and pressure, temperature
or UV radiation. FIGS. 14b and 14c are cross-sectional schematic
views of the FPD before and after undergoing the bonding process,
respectively. The laminating process is one of the alternate
methods for bonding the layers to construct the FPD. Because the
layers of the present invention are thin, cracking, crazing, and
delamination are avoided using processing methods of this type.
FIGS. 14b and 14c illustrate schematically the flat panel display
with an exterior protective overcoat 4 and the display medium 2.
The display medium also may be liquid, or deposited over either
substrate, or over a carrier film.
[0079] Transparent dielectric layers with good barrier properties
and a high refractive index, such as metal oxides like titanium
oxide or aluminum oxide, or metal nitrides such as silicon nitride
or aluminum nitride, used in combination with thin, transparent
metallic film layers provide a transparent conductive barrier
coating. The metal oxide or metal nitride layers are deposited at
specific thicknesses to optimize the optical performance (e.g.
transmittance) of a particular display. Preferably, the thin
metallic film layer is sandwiched in between layers of metal oxide
or metal nitride. Multiple alternating layers of metal oxides or
metal nitrides, with their barrier properties, and the highly
conductive metallic film layers provide increased barrier
performance and conductivity for a particular display medium.
[0080] The optical and electrical performance of transparent
conductive oxide coatings are also improved by mildly heating the
coated substrate during deposition or by post-annealing the coated
substrate. As shown in the Experimental Results below, even though
the PET substrate was heated to a moderate temperature of only
65.degree. C., the resistivity of the ITO was still low enough to
effectively operate as an electrode, because of the multiple thin
layers of ITO.
[0081] In an alternative embodiment, the thin conductive metal
nitride layer is substituted for one or more thin metallic film
layers, for example, for the metal layers in the "optically
enhanced metal" (see FIG. 11). Metal oxide or TCO layers are
utilized with the metal nitride layer for enhancing both the
optical and electrical performance characteristics. Metal nitrides
have good gas barrier properties. However, to achieve very low
moisture (water vapor) and oxygen permeability, there is a minimum
thickness of barrier material, e.g. the metal nitride layer.
Because of the higher optical transparency silicon nitride thin
films, for example, are attractive candidates for flexible FPD as
barrier layers for atmospheric gases.
[0082] In another alternative embodiment, at least one of the
metallic film layers in, for example, the "optically enhanced
metal" is replaced with a polymer layer formed via the PML
processes.
Results of Conducted Experiments
[0083] The plastic substrate for a flat panel display has a very
low oxygen and water vapor permeability, a surface roughness much
less than the barrier film thickness, a high Tg (the glass
transition temperature) to allow a higher temperature and/or higher
energy ITO deposition process, and a high transparency with low
birefringence.
[0084] Defects in the coated layers limit the barrier properties.
For instance, rough substrates, particulates, and roller contact,
damage the coated layers. Rough substrates with thin film barriers
are smoothed and prevented from damage by roller contact, with an
organic basecoat and polymer top coat.
[0085] Multiple layers of TCO deposited on the substrate achieve
lower surface resistivity than a single thick layer of TCO because
the single layer cracks and/or crazes from stress. Further, the
multiple TCO layers act as electrodes connected in parallel. Using
a non-stoichiometric dielectric of a group including silicon
oxides, aluminum oxides, and silicon nitrides, allows for the
fabrication of efficient thin film barriers for flexible plastic
films.
[0086] Measured data for films made of sputtered ITO exhibited
exceptional barrier properties. The optical, electrical and barrier
properties were measured for ITO sputter-deposited directly onto a
PET substrate, and also measured with a PML acrylic basecoat over
the substrate before deposition of the ITO, in a roll-to-roll (web)
coating process. See FIGS. 15-18, and the descriptions of these
Figures below. The typical performance of a single ITO layer
deposited on a basecoated PET substrate is 85% T (Transmittance)
and 80 ohms/square. The ITO layer has a physical thickness of about
140 nm, for a one-half wave optical thickness, while the PET
substrate has a thickness of about 0.007''. For the single layer
ITO film, oxygen permeability ranged from 0.005 to 0.05 oxygen
cc/m.sup.2/day, while the water vapor permeability ranged from
0.005 to 0.05 g/m.sup.2/day.
[0087] FIG. 15 discloses a chart showing water vapor permeability
of (1) ITO film deposited over the PET substrate, and (2) a PET
substrate coated with "optically enhanced metal": an ITO film
layer, a silver layer, and another ITO film layer, versus ITO film
resistance. No smoothing base coat was applied to the substrate in
either case. The ITO layer was DC sputter deposited onto the PET
substrate. The deposited ITO film alone is reactively sputtered
from a metal target in a web coater. The solid lines shown connect
the midpoints of the range of permeability results at each measured
resistance for the ITO film sheet. The chart shows that for the ITO
film layer, the water vapor permeability dips to a minimal value of
approximately 0.006 g/m.sup.2 day at a resistance of about 60
ohms/square. The water vapor permeability reaches a maximum of
approximately 0.21 g/m.sup.2 day at a resistance of about 350
ohms/square. For the silver layer in between the ITO film layers,
the approximate water vapor permeability range was 0.04 to 0.075
g/m.sup.2 day for the sheet resistance at about 12 ohms/square.
[0088] FIG. 16 discloses a chart showing water vapor permeability
of an (1) ITO film deposited over the PET substrate, and (2) a PET
substrate coated with "optically enhanced metal," an ITO film
layer, a silver layer, and another ITO film layer, versus ITO film
sheet thickness. The parameters for the ITO layer alone is analyzed
in the same manner as above. The chart shows that for the ITO film
layer, the water vapor permeability dips to a minimal value of
approximately 0.006 g/m.sup.2 day at an ITO thickness of about 120
nm. The water vapor permeability reaches a maximum of approximately
0.21 g/m.sup.2 day at an ITO thickness of about 40 nm. For the
substrate with the sandwiched silver layer, the approximate water
vapor permeability range was 0.04 to 0.075 g/m.sup.2day for a total
ITO coating thickness of approximately 120 nm.
[0089] FIGS. 17 and 18 disclose charts showing oxygen permeability
of ITO film deposited on a PET substrate versus ITO film thickness
and versus sheet resistivity, respectively. FIG. 17 shows that the
permeability dips to a minimal value of approximately 0.017
g/m.sup.2 day at an ITO thickness of about 220 nm. The permeability
reaches a maximum of approximately 0.9 cc/m.sup.2 day at an ITO
thickness of about 40 nm.
[0090] As shown in Table 1, alternating barrier layers of PML
deposited organic polymers and dielectrics have permeation rates
below the limits of the instruments, which is 0.005 g/m.sup.2 day
for Permatran-W 3/31, which is an instrument that measures water
vapor transmission rates, and 0.005 cc/m.sup.2 day for Ox-Tran
2/20, which is an instrument that measures oxygen transmission
rates.
[0091] The transparent dielectric barrier layer or the single layer
of TCO deposited on the substrate has suitable barrier properties
for the plastic FPD. The preferable barrier properties vary by the
type of display technology: liquid crystal display (LCD), organic
light emitting display (OLED), or thin film electro luminescent
displays (TFELD). The acceptable value of vapor permeation with
plastic substrates for FPD depends on the sensitivity of the
specific display technology utilized. For example, the LCD is much
less sensitive to vapor permeation than the OLED or TFELD. For the
LCD, maximum oxygen permeability is in the range of about 0.01 to
0.1 cc/m.sup.2 day, while the maximum water vapor permeability is
in the range of about 0.01 to 0.1 g/m.sup.2 day. For both OLED and
TFELD, permeabilities of .ltoreq.0.001 cc/m.sup.2day for oxygen,
and .ltoreq.0.001 g/m.sup.2 day for moisture (water vapor) are
preferred.
[0092] A polymer OLED and a small molecule OLED describe the two
basic technologies for the layer that emits light in the OLED. For
polymer OLED's, the light emitting material is deposited by flow
coating, spin coating, gravure coating, meniscus coating, curtain
coating or any common liquid coating or printing techniques. The
small molecule OLED is normally thermally evaporated in a vacuum,
but may also be processed with nonvacuum coating methods. When the
ITO layer is deposited by nonvacuum processes such as by screen
printing, the process of the present invention is entirely
nonvacuum. Alternatively, the process of the present invention
takes place by both vacuum and nonvacuum methods. Preferably, the
process takes place entirely in a vacuum to avoid contamination by
particulates, moisture and oxygen. Superior barrier films and other
films result from the cleaner vacuum process.
[0093] As shown in FIGS. 15 and 16, and described above, for the
LCD as long as the ITO sheet resistance is below about 250
Ohms/square, and the ITO film thickness is between about 75 and 225
nm, the water vapor permeability is within desirable limits for the
LCD. As shown in FIG. 17, the oxygen permeability is within
desirable limits for the LCD as long as the ITO film thickness is
above about 85 nm and the sheet resistance is below about 150
Ohm/square. Because of the lower permeabilities preferred for the
emissive displays (e.g. OLED and thin film electro luminescent
displays), the barrier capability is enhanced by multilayer
dielectric or TCO barriers in combination with PML processed
polymer coatings (i.e. composite barrier layers of PML deposited
organic polymer layers, dielectric layers and/or TCO layers).
[0094] Table B illustrates water vapor and oxygen permeability
versus ITO thickness for semi-reactively sputtered ITO. The
measured results for semi-reactively and reactively sputtered ITO,
as well as the differences between a single ITO layer and two ITO
layers (with a polymer layer in between the two layers) made with a
semi-reactive process, are illustrated in FIGS. 24 and 25.
`Semi-reactively` sputtered refers to films, DC magnetron sputtered
from a ceramic target The differences between the two processes are
believed to be due to the specific process parameters, and not
inherent to the process type. As shown, for the same total
thickness deposited by the same reactive process, two ITO layers
have higher conductivity and lower permeability as compared to the
single ITO layer. Further, the two ITO layers have higher
electrical performance, because the single ITO layer cracks and/or
crazes.
[0095] The preferred thickness for the deposited layers is
different for conductivity properties than for barrier properties.
The thickness of the deposited film is related to the film's
conductive and barrier properties. The critical thickness for
barrier properties of these layers varies with the material and, to
a lesser extent, how the layer is deposited. For ITO, the critical
thickness is about 20 nanometers (or 200 angstroms), minimum. The
lower thickness limits for some of the metal oxides which are
typically used in packing applications is in about the 10 to 30
nanometer range. Generally, 5-10 nanometers is the minimum
thickness for adequate barrier properties. Enhanced conductive
properties result from film thicknesses in the range of about 20
nanometers to 300 nanometers. If the single layer film is thicker
than that range, then the film starts cracking, and hence, loses
conductivity and barrier properties. For maximizing single layer
optical transmission, it is well known that certain optical
thicknesses, e.g. one-half wave, of thin films are selected. The
typical physical thickness is in the range of about TABLE-US-00002
TABLE B TRANSPARENT BARRIER COATINGS BASED ON ITO FOR FLEXIBLE
PLASTIC DISPLAYS Experimental Results for ITO Barriers on PET
Semi-Reactively Sputtered Total ITO Surface H.sub.2O O.sub.2
Thickness Resistivity Rho Luminoust Permeance Permeance (nm)
(ohms/square) (.times.10.sup.-4 n-cm) (%) (cc/m.sup.2-day)
(g/m.sup.2-day) 123.3 38.3 4.685 84 0.038 0.827 172.4 29.9 5.145 82
0.073 1.19 299.2 17.2 5.15 .about.81 0.049 0.081 49.9 188.4 9.4
.about.81 0.036 0.156 218.5 31.8 6.94 .about.80 0.0621 0.038 117.05
57.48 6.64 .about.82 0.12 0.0246 74.3 348.5 25.6 .about.86 0.2375
0.8625
20 to 300 nanometers for ITO on a flexible 'substrate.
[0096] FIGS. 20-23 are charts showing transmittance and reflectance
spectra versus wavelength for an ITO layer deposited over a PET
substrate at a sheet resistance of 29 Ohms/Square, 57 Ohms/Square,
65 Ohms/Square, and 347 Ohms/Square, respectively. As shown,
generally, for a range of the sheet resistance, the percentage of
spectral transmittance and reflectance remains relatively constant.
For example, at about a wavelength of 500 nm, the transmittance
percentage is about 80% for resistance ranging from 29 ohms/square
to 347 ohms/square. DC sputter deposited ITO on a hardcoated PET
substrate exhibited a sheet resistivity of 46.9 Ohms/square, which
is a volume resistivity of approximately 5.times.10.sup.-4 Ohm-cm,
and a visible transmittance of about 84.7%. Generally, the
transmittance increases (and the reflectance decreases) as the
plasma wavelength increases. There is always a compromise between
high optical transmittance and high conductivity.
[0097] In contrast to FIGS. 20-23, in FIG. 19 the transmittance
decreases and the reflectance increases at the higher wavelengths.
FIG. 19 is a chart showing transmittance and reflectance spectra
versus wavelength for a more preferred embodiment of the present
invention. FIG. 19 shows the transmittance spectra for a PET
substrate coated with layers of an ITO, silver film, and another
ITO at a sheet resistance of 14 Ohms/Square.
[0098] FIGS. 26-30 illustrate the Transmittance and Reflectance of
semi-reactively sputtered ITO on a PET substrate for various
thicknesses versus wavelength. The transmittance and reflectance of
a substrate coated with a polymer layer and an ITO layer, a
substrate with an ITO layer, and a substrate with two ITO layers
(with a polymer layer in between the two ITO layers) are
illustrated. Generally, transmittance and conductivity are
inversely related. Improved optical performance is achieved by
controlling the thickness and index of the polymer layers.
[0099] For a transparent electrode, conductivity specifications
varies with display technology and addressing method. The surface
resistivity for LCD's is about 50-300 Ohms/square, and for OLED's
is about 10-100 Ohms/square. The corresponding visible
transmittance for LCD's is about 90%, and for OLED's is about
80-85%. The thickness of the conductor layer is compatible with the
vacuum web coating processing for the flexible plastic
substrate.
[0100] Table 1 shows the test results for oxygen and water vapor
transmission rates of various samples of a PET substrate coated
with a single ITO layer with different Ohms/square coatings and a
substrate coated with an ITO layer, a metal layer, and another ITO
layer. The test conditions were as follows: the temperature was at
23.degree. C./73.4.degree. F. On each side of the barrier for the
oxygen transmission rate tests, the relative humidity was 0%. On
one side of the barrier for the water vapor transmission rate
tests, the relative humidity was 100%, but the other side of the
barrier had a relative humidity of 0%.
[0101] The first eight samples of Table 1 are of a plastic
substrate coated with a single ITO film layer, each with different
nominal ITO thickness and sheet resistances. For example, the
`25-1` is the first sample with a sheet resistance of 25
Ohm/square; whereas `25-2` is the second sample from the same lot.
The last two samples are of a substrate coated with an ITO layer, a
metal coating, and another ITO layer, with a nominal sheet
resistance of 10 Ohm/square. This 3 layer configuration is the
"optically enhanced metal," or "induced transmission filter," and
has similar characteristics to a single TCO layer. With the
optically enhanced metal, good conductivity, transmission and
barrier properties are achieved. Preferably the ITO layers, which
antireflect the metal, each have a thickness of about 30-60
nanometers. In several instances, the samples were tested two
times. For example, the second column for the 25 and 60 Ohms/square
samples reflects the results of the second test.
[0102] Although the present invention has been described and is
illustrated with respect to various embodiments thereof, it is to
be understood that it is not to be so limited, because changes and
modifications may be made therein which are within the full
intended scope of this invention as hereinafter claimed. In
particular, the structure disclosed in the present invention for
flat panel displays is schematic for LCD and other display
technologies, such as polymer organic light emitting diode (POLED),
small molecule organic light emitting diode (OLED) displays, and
thin film electroluminescent. TABLE-US-00003 TABLE 1 Water Vapor
Transmission Oxygen Transmission Rate Sample Rate (g/m.sup.2 day)
(cc/m.sup.2 day) 25-1 0.026 <0.005.sup.1 0.017 0.087 25-2 0.097
<0.005.sup.1 0.584 0.257 60-1 0.042 0.059 0.071 60-2 0.050 0.204
0.090 60-3 0.007 <0.005.sup.2 60-4 <0.005.sup.1 0.014 300-1
0.243 0.861 300-2 0.232 0.864 M-10-1 0.076 0.035 M-10-2 0.041 0.024
.sup.1The actual water vapor transmission rate was at least as low
as the lower limit of the instrument, Permatran-W 3/31, 0.005
g/m.sup.2 day. .sup.2The actual oxygen transmission rate was at
least as low as the lower limit of the instrument, Ox-Tran 2/20,
0.005 cc/m.sup.2 day.
[0103] Table 2 compares permeation rates for different coatings,
including multiple dyad (an acrylate/oxide pair) layers on the
polyethylene terephthalate (PET) substrate, and coatings on
oriented polypropylene (OPP) substrates. As shown, a single dyad on
a substrate has high oxygen and moisture permeation resistance. In
some instances, two oxygen transmission rate tests were conducted,
and the results were shown in a second column. Footnote.sup.1
denotes the typical permeation rate for the PET substrate.
TABLE-US-00004 TABLE 2 Water Vapor Transmission Rate Oxygen
Transmission Rate Sample (g/m.sup.2 day) (cc/m.sup.2 day) 2 mil PET
30.5, 272.sup.1 per micron 5.3, 1550.sup.1 per film thickness
micron film thickness Food packaging - target 1.55 1.5 values
(PET/oxide) 2 mil PET/single dyad <0.0078 0.03 (23.degree. C.) 2
mil PET/seven dyads <0.0078 <0.016 (23.degree. C.) 7 mil
PET/hardcoat 7.6 -- (23.degree. C.) 7 mil PET/hardcoat/ <0.0078,
90% 0.2682, 0.6061, single dyad (38.degree. C.) Relative Humidity
100% RH 100% RH (RH), 100% O.sub.2 7 mil PET/hardcoat/ <0.0078,
90% RH, 0.0098, 0.0128, single dyad/ITO (38.degree. C.) 100%
O.sub.2 100% RH 100% RH PET/oxide 0.7-1.5 0.15-0.9 PET/Al 0.6 0.17
OPP, copolymer, 1 mil 1800 1.3 OPP/oxide 17-546 0.08-0.4 OPP/Al 20
0.11
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