FLANAGAN, Kevin, Warner (485 State Street, Albany, NY, 12203, US)
SCHAEPKENS, Marc (7 Guilder Place, Ballston Lake, NY, NY, US)
FLANAGAN, Kevin, Warner (485 State Street, Albany, NY, 12203, US)
| I Claim:
1. A method for making a composite article, said method comprising the steps
of:
providing a substrate having at least a substrate surface;
depositing a coating material on said substrate surface using plasma-enhanced
chemical-vapor deposition ("PECVD") wherein said coating material comprises an
organic material having a first refractive index and an inorganic material having a second
refractive index; and
varying the deposition rate of either the organic or inorganic material so as to
match the first and second refractive indices.
2. The method according to Claim 1 wherein said depositing is selected from
the group consisting of: radio-frequency plasma-enhanced chemical-vapor deposition,
expanding thermal-plasma chemical-vapor deposition, electron-cyclotron-resonance
plasma-enhanced chemical-vapor deposition, inductively-coupled plasma-enhanced
chemical- vapor deposition, and combinations thereof.
3. The method according to Claim 1 wherein said substrate comprises a
polymeric material selected from the group consisting of: polyethyleneterephthalate,
polyacrylates, polycarbonate, silicone, epoxy resins, silicone-functionalized epoxy resins,
polyester, polyimide, polyetherimide, polyethersulfone, polyethylenenapthalene,
polynorbonene, and poly(cyclic olefins).
4. The method according to Claim 1 wherein said coating material comprises
material selected from the group consisting of: organic, inorganic, ceramic materials, and
combinations thereof.
5. The method according to Claim 4 wherein said inorganic and ceramic
materials are selected from the group consisting of oxide, nitride, carbide, boride, and
combinations thereof of elements of Groups IIA, EEIA 5 IVA, VA, VIA, VIIA, EB, and IEB,
metals of Groups IIIB, EVB, and VB, and rare-earth metals.
6. The method according to Claim 58 further comprising effecting a
penetration of at least a portion of said coating material into said substrate to produce a
diffuse region between said substrate and said coating.
7. The method according to Claim 6 wherein said diffuse region is produced
by an energetic ion bombardment of a surface of said substrate to sputter a portion of a
material of said substrate, and depositing a mixed material comprising sputtered substrate
material and another material.
8. The method of Claim 1 wherein said substrate is flexible.
9. The method of Claim 1 wherein said substrate is substantially transparent.
10. The method of Claim 1 wherein said substrate comprises a metal.
11. The method of Claim 1 wherein said substrate comprises glass.
12. The method of Claim 1 wherein said coating has an oxygen permeability
rate of approximately 0.001 ml/m 2 -day or less.
13. The method of Claim 1 wherein said coating has a water vapor permeability
rate of approximately 0.000001 g/m 2 -day or less.
14. The method of Claim 1 wherein the PECVD deposition includes the use of
oxygen gas.
15. The method of Claim 14 wherein the oxygen flow rate is varied.
16. The method of Claim 15 wherein the inorganic material is substantially
silicon oxynitride.
17. The method of Claim 16 wherein the light transmittance of the coating
material is greater than 90 percent.
18. A method of making an assembly comprising a device, said method
comprising the steps of:
providing a substrate having a first substrate surface and a second substrate
surface;
depositing a coating material on one of said substrate surfaces using plasma-
enhanced chemical-vapor deposition ("PECVD") wherein said coating material comprises
an organic material having a first refractive index and an inorganic material having a
second refractive index;
matching the first and second refractive indices; and
disposing said device on said substrate.
19. The method of Claim 18 wherein the PECVD deposition includes the use of
oxygen gas.
20. The method of Claim 19 wherein the oxygen flow rate is varied.
21. The method of Claim 20 wherein the inorganic material is substantially
silicon oxynitride.
22. The method of Claim 21 wherein the light transmittance of the coating
material is greater than 90 percent.
23. The method of Claim 18 wherein said device is selected from the group
consisting of: liquid crystal displays, photovoltaic cells, integrated circuits, and
components of medical diagnostic systems.
24. The method of Claim 18 wherein said device is an organic
electroluminescent ("EL") member.
25. The method of Claim 24 wherein said EL member is an organic light
emitting diode.
26. The method of Claim 24 wherein said EL member comprises an organic EL
layer disposed between two electrodes.
27. The method of Claim 26 wherein said EL member further comprises a
reflective layer comprising material selected from the group consisting of: metals, metal
oxides, metal nitrides, metal carbides, metal oxynitrides, metal oxycarbides, and
combinations thereof.
28. The method of Claim 26 wherein said organic EL layer comprises a
material selected from the group consisting of poly(n-vinylcarbazole),
poly(alkylfluorene), poly(paraphenylene), polysilanes, derivatives thereof, mixtures
thereof, and copolymers thereof.
29. The method of Claim 26 wherein said organic EL layer comprises a
material selected from Hie group consisting of
l 5 2,3-tris{n-(4-diphenylaminophenyl) phenylamino} benzene, phenylanthracene,
tetraarylethene, coumarin, rubrene, tetraphenylbutadiene, anthracene, perylene, coronene,
aluminum-(picolymethylketone)-bis { 2,6-di(t-butyl)phenoxides } ,
scandium-(4-methoxy-picolymethylketone)-bis(acetylacetonate),
aluminum-acetylacetonate, gallium-acetylacetonate, and indium-acetylacetonate.
30. The method of Claim 26 further comprising a light-scattering layer, said
layer comprising scattering particles dispersed in a substantially transparent matrix and
being disposed on a surface of said substrate opposite to said organic EL member.
31. The method of Claim 30 further comprising particles of a photoluminescent
("PL") material mixed with scattering particles in said light-scattering layer, wherein said
PL material is selected from the group consisting of (Yi- X CE x ) 3 Al 5 O 12 ; (Y LX -
y GdχCe y ) 3 Al 5 O 12 ; (Y Lx Ce X ) 3 (Al Ly Ga x )O 12 ;
(Y 1 ^ y Gd x Ce 7 )(Al 5 - Z Ga 2 )O 12 ; (Gd Lx Ce x )Sc 2 Al 3 O 12 ; Ca 8 Mg(SiO 4 ) 4 Cl 2 :Eu 2+ , Mn 2+ ;
GdBO 3 :Ce 3+ ,Tb 3+ ; CeMgAl 11 Oi 9 ITb 3+ ; Y 2 SiO 5 :Ce 3+ ,Tb 3+ ; BaMg 2 Ali 6 O 27 :Eu 2+ ,Mn 2+ ;
Y 2 O 3 :Bi 3+ ,Eu 3+ ; Sr 2 P 2 O 7: Eu 2+ ,Mn 2+ ; SrMgP 2 O 7 :Eu 2+ ,Mn 2+ ; (Y,Gd)(V,B)O 4 :Eu 3+ ;
3.5MgO.0.5MgF 2 GeO 2 :Mn 4+ (magnesium fluorogemanate); BaMg 2 Ali 6 O 27 :Eu 2+ ;
Sr 5 (PO 4 ) 10 Cl 2 :Eu 2+ ; (Ca,Ba,Sr)(Al,Ga) 2 S 4 :Eu 2+ ; (Ba,Ca,Sr) 5 (PO 4 )io(Cl,F) 2 :Eu 2+ ,Mn 2+ ;
Lu 3 Al 5 O i 2 :Ce 3+ ; Tb 3 Al 5 O 12 :Ce 3+ ; and mixtures thereof; wherein 0 < x < l, 0 < y < l,
0 < z ≤ 5 and x+y < l.
32. The method of Claim 30 further comprising at least an organic PL material
dispersed in said scattering layer, said organic PL material being capable of absorbing at
least a portion of electromagnetic ("EM") radiation emitted by said organic EL material
and emitting EM radiation in a visible spectrum.
33. The method of Claim 26 wherein said organic EL member further
comprises at least an additional layer disposed between one of said electrodes and said
organic EL layer, said additional layer performing at least a function selected from the
group consisting of electron injection enhancement, electron transport enhancement, hole
injection enhancement, and hole transport enhancement.
34. The method of Claim 18 wherein said depositing is selected from the group
consisting of: radio-frequency plasma-enhanced chemical-vapor deposition, expanding
thermal-plasma chemical-vapor deposition, electron-cyclotron-resonance plasma-
enhanced chemical-vapor deposition, inductively-coupled plasma-enhanced chemical-
vapor deposition, and combinations thereof.
35. The method according to Claim 18 wherein said substrate comprises a
polymeric material selected from the group consisting of: polyethyleneterephthalate,
polyacrylates, polycarbonate, silicone, epoxy resins, silicone-functionalized epoxy resins,
polyester, polyimide, polyetherimide, polyethersulfone, polyethylenenapthalene,
polynorbonene, and poly(cyclic olefins).
36. The method according to Claim 18 wherein said coating material further
comprises material selected from the group consisting of: organic, inorganic, ceramic
materials, and combinations thereof.
37. The method according to Claim 36 wherein said inorganic and ceramic
materials are selected from the group consisting of oxide, nitride, carbide, boride, and
combinations thereof of elements of Groups IIA, IIIA, IVA, VA 5 VIA, VTIA, IB, and IIB,
metals of Groups HUB, IVB, and VB, and rare-earth metals.
38. The method according to Claim 18 further comprising effecting a
penetration of at least a portion of said coating material into said substrate to produce a
diffuse region between said substrate and said coating.
39. The method according to Claim 38 wherein said diffuse region is produced
by an energetic ion bombardment of a surface of said substrate to sputter a portion of a
material of said substrate, and depositing a mixed material comprising sputtered substrate
material and another material.
40. The method of Claim 18 wherein said substrate is flexible.
41. The method of Claim 18 wherein said substrate is substantially transparent.
42. The method of Claim 18 wherein said substrate comprises a metal.
43. The method of Claim 18 wherein said substrate comprises glass.
44. The method of Claim 18 wherein said coating has an oxygen permeability
rate of approximately 0.001 ml/m 2 -day or less.
45. The method of Claim 18 wherein said coating has a water vapor
permeability rate of approximately 0.000001 g/m 2 -day or less.
46. The method of Claim 18 wherein said coating and said substrate
encapsulate said device.
47. The method of Claim 18 wherein said coating encapsulates said substrate
and said device.
48. An apparatus comprising:
a substrate; and
a coating material on said substrate, said coating material comprising an organic
material having a first refractive index and an inorganic material having a second
refractive index wherein said first refractive index matches said second refractive index.
49. The apparatus of Claim 48 further comprising a device disposed on said
substrate.
50. The apparatus of Claim 48 wherein the inorganic material comprises silicon
oxynitride.
51. The apparatus of Claim 50 wherein the light transmittance of the coating
material is greater than 90 percent.
52. The apparatus of Claim 48 wherein said device is selected from the group
consisting of: liquid crystal displays, photovoltaic cells, integrated circuits, and
components of medical diagnostic systems.
53. The apparatus of Claim 48 wherein said device is an organic
electroluminescent ("EL") member.
54. The apparatus of Claim 53 wherein said EL member is an organic light
emitting diode.
55. The apparatus of Claim 53 wherein said EL member comprises an organic
EL layer disposed between two electrodes.
56. The apparatus of Claim 55 wherein said EL member further comprises a
reflective layer comprising material selected from the group consisting of: metals, metal
oxides, metal nitrides, metal carbides, metal oxynitrides, metal oxycarbides, and
combinations thereof.
57. The apparatus of Claim 55 further comprising a light-scattering layer, said
layer comprising scattering particles dispersed in a substantially transparent matrix and
being disposed on a surface of said substrate opposite to said organic EL member.
58. The apparatus of Claim 55 wherein said organic EL member further
comprises at least an additional layer disposed between one of said electrodes and said
organic EL layer, said additional layer performing at least a function selected from the
group consisting of electron injection enhancement, electron transport enhancement, hole
injection enhancement, and hole transport enhancement.
59. The apparatus according to Claim 48 wherein said substrate comprises a
polymeric material selected from the group consisting of: polyethyleneterephthalate,
polyacrylates, polycarbonate, silicone, epoxy resins, silicone-functionalized epoxy resins,
polyester, polyimide, polyetherimide, polyethersulfone, polyethylenenapthalene,
polynorbonene, and poly(cyclic olefins).
60. The apparatus according to Claim 48 wherein said coating material further
comprises material selected from the group consisting of: organic, inorganic, ceramic
materials, and combinations thereof.
61. The apparatus according to Claim 60 wherein said inorganic and ceramic
materials are selected from the group consisting of oxide, nitride, carbide, boride, and
combinations thereof of elements of Groups IIA, EIA, IVA, VA, VIA, VIIA, IB, and HB,
metals of Groups IIIB, IVB, and VB, and rare-earth metals.
62. The apparatus of Claim 48 wherein said substrate is flexible.
63. The apparatus of Claim 48 wherein said substrate is substantially
transparent.
64. The apparatus of Claim 48 wherein said substrate comprises a metal.
65. The apparatus of Claim 48 wherein said substrate comprises glass.
66. The apparatus of Claim 48 wherein said coating has an oxygen permeability
rate of approximately 0.001 ml/m 2 -day or less.
67. The apparatus of Claim 48 wherein said coating has a water vapor
permeability rate of approximately 0.000001 g/m 2 -day or less.
68. The apparatus of Claim 48 wherein said coating and said substrate
encapsulate said device.
69. The apparatus of Claim 48 wherein said coating encapsulates said substrate
and said device. |
DIFFUSION BARRIER COATINGS HAVING GRADED COMPOSITIONS
AND DEVICES INCORPORATING THE SAME
BACKGROUND OF THE INVENTION
[0001] The present invention relates generally to composite films having improved
resistance to diffusion of chemical species and to devices incorporating such composite
films. In particular, the present invention relates to light-emitting devices having at least
an organic electroluminescent material that incorporates such composite films and have
improved stability in the environment.
[0002] Electroluminescent ("EL") devices, which may be classified as either
organic or inorganic, are well known in graphic display and imaging art. EL devices have
been produced in different shapes for many applications. Inorganic EL devices, however,
typically suffer from a required high voltage and low brightness. On the other hand,
organic EL devices ("OELDs"), which have been developed more recently, offer the
benefits of lower activation voltage and higher brightness in addition to simple
manufacture, and, thus, the promise of more widespread applications.
[0003] An OELD is typically a thin film structure formed on a substrate such as
glass or transparent plastic. A light-emitting layer of an organic EL material and optional
adjacent semiconductor layers are sandwiched between a cathode and an anode. The
semiconductor layers may be either hole (positive-charge)-injecting or electron (negative
charge)-injecting layers and also comprise organic materials. The material for the light-
emitting layer may be selected from many organic EL materials. The light-emitting
organic layer may itself consist of multiple sublayers, each comprising a different organic
EL material. State-of-the-art organic EL materials can emit electromagnetic ("EM")
radiation having narrow ranges of wavelengths in the visible spectrum. Unless
specifically stated, the terms "EM radiation" and "light" are used interchangeably in this
disclosure to mean generally radiation having wavelengths in the range from ultraviolet
("UV") to mid-infrared ("mid-IR") or, in other words, wavelengths in the range from
about 300 nm to about 10 micrometer. To achieve white light, prior-art devices
incorporate closely arranged OELDs emitting blue, green, and red light. These colors are
mixed to produce white light.
[0004J Conventional OELDs are built on glass substrates because of a combination
of transparency and low permeability of glass to oxygen and water vapor. A high
permeability of these and other reactive species can lead to corrosion or other degradation
of the devices. However, glass substrates are not suitable for certain applications in
which flexibility is desired. In addition, manufacturing processes involving large glass
substrates are inherently slow and, therefore, result in high manufacturing cost. Flexible
plastic substrates have been used to build OELDs. However, these substrates are not
impervious to oxygen and water vapor, and, thus, are not suitable per se for the
manufacture of long-lasting OELDs. In order to improve the resistance of these
substrates to oxygen and water vapor, alternating layers of polymeric and ceramic
materials have been applied to a surface of a substrate. It has been suggested that in such
multilayer barriers, a polymeric layer acts to mask any defects in an adjacent ceramic
layer to reduce the diffusion rates of oxygen and/or water vapor through the channels
made possible by the defects in the ceramic layer. However, an interface between a
polymeric layer and a ceramic layer is generally weak due to the incompatibility of the
adjacent materials, and the layers, thus, are prone to be delaminated.
[0005] Therefore, there is a continued need to have robust films that have reduced
diffusion rates of environmentally reactive materials. It is also very desirable to provide
such films to produce flexible OELDs that are robust against degradation due to
environmental elements.
SUMMARY OF THE INVENTION
[0006] The present invention provides a substrate having at least a coating
disposed on a surface thereof, which coating is capable of reducing diffusion rates of
chemical species therethrough. The coating comprises a material the composition of
which varies across a thickness thereof. Such a coating will be termed interchangeably
hereinafter a "diffusion-barrier coating having graded composition," "graded-composition
diffusion-barrier coating," "graded-composition barrier coating," "diffusion-barrier
coating," or simply "graded-composition coating."
[0007] In one aspect of the present invention, the substrate comprises a polymeric
material.
[0008] In another aspect of the present invention, a region between the substrate
and the coating is diffuse such that there is a gradual change from the composition of the
bulk substrate to the composition portion of the coating adjacent to the substrate. In this
embodiment, a material of the coating adjacent to the substrate penetrates into the
substrate.
[0009] In still another aspect of the present invention, at least a substrate having a
diffusion-barrier coating having graded composition is included in an assembly
comprising a device sensitive to chemical species to protect such an assembly from attack
by these chemical species.
[0010] In still another aspect of the present invention, such a device is an OELD,
which comprises a pair of electrodes and an organic light-emitting layer sandwiched
therebetween.
[0011] hi yet another aspect of the present invention, an OELD is sandwiched
between two films, each having a diffusion-barrier coating having graded composition.
[0012] The present invention also provides a method for making a substrate coated
with a diffusion barrier coating having a graded composition. The method comprises the
steps of: (a) providing a substrate having a substrate surface; (b) depositing a coating
material having a first composition on the substrate surface; and (c) changing a
composition of the coating material substantially continuously such that the composition
of the coating varies from the first composition to a second composition across a
thickness of the coating.
[0013] In another aspect of the present invention, a method for making an assembly
comprising a device that is sensitive to chemical species comprises the steps of: (a)
providing at least a substrate coated with a diffusion barrier coating having a graded
composition; and (b) disposing the device on the substrate.
[0014] In another aspect of the present invention, such a device is an OELD, and
the method comprises the steps of: (a) providing at least a substrate coated with a
diffusion barrier coating having a graded composition; (b) forming a first electrode on the
substrate; (c) forming an organic light-emitting layer on the first electrode; and (d)
forming a second electrode on the organic light-emitting layer.
[0015] In still another aspect of the present invention, an OLED comprising a pair
of electrodes and an organic light-emitting layer disposed between the pair of electrodes
and a substrate coated with a diffusion barrier coating having a graded composition are
laminated to form a light source.
[0016] Other features and advantages of the present invention will be apparent
from a perusal of the following detailed description of the invention and the
accompanying drawings in which the same numerals refer to like elements.
BRIEF DESCRIPTION OF THE DRAWINGS
[0017] Figure 1 is a schematic diagram of a deposition apparatus using the
expanding thermal-plasma chemical-vapor deposition.
[0018] Figure 2 is a schematic diagram of the apparatus of Figure 1 used in a
continuous deposition.
[0019] Figure 3 is a schematic diagram of a deposition apparatus using the radio-
frequency plasma-enhanced chemical vapor deposition.
[0020] Figure 4 shows the elemental composition at various depths of a graded-
composition barrier coating of the present invention.
[0021] Figure 5 compares the oxygen transmission rates through an uncoated
substrate and one that is coated with a graded-composition barrier coating.
[0022] Figure 6 compares the water transmission rates through an uncoated
substrate and one that is coated with a graded-composition barrier coating.
[0023] Figure 7 shows the relative light transmission through a substrate having a
graded-composition barrier coating compared to that through an uncoated substrate.
[0024] Figure 8 shows schematically a device used with a substrate having a
graded-composition barrier coating.
[0025] Figure 9 shows schematically a construction of an OELD.
[0026] Figure 10 shows another embodiment of an OELD including a hole
injection enhancement layer.
[0027] Figure 11 shows another embodiment of an OELD including a hole
injection enhancement layer and a hole transport layer.
[0028] Figure 12 shows another embodiment of an OELD including an electron
injecting and transporting layer.
[0029] Figure 13 shows an OELD sealed between a substrate having a graded-
composition barrier coating and a reflective layer.
[0030] Figure 14 shows an OELD sealed between two substrates, each having a
graded-composition barrier coating.
[0031] Figure 15 shows a sealed OELD having a light conversion layer.
[0032] Figures 16(a) and 16(b) show coating composition and refractive index,
respectively, of an inorganic material at 550 run as a function of oxygen flow rate for a
graded UHB coating formed using a PECVD process.
[0033] Figure 17 shows the average optical transmittance in the visible light range
and the standard deviation of a graded UHB coating as functions of oxygen flow rate used
in a inorganic coating process using PECVD.
[0034] Figure 18 illustrates a comparison of an optical transmittance spectrum
before and after refractive index matching for a graded UHB coating.
DETAILED DESCRIPTION OF THE INVENTION
[0035] The present invention, in one aspect, provides a substrate having at least a
coating disposed on a surface thereof, which coating is capable of reducing diffusion rates
of chemical species through the substrate. The coating comprises a material, the
composition of which varies across a thickness thereof. Such a coated substrate finds
uses in providing protection to many devices or components; e.g., electronic devices, that
are susceptible to reactive chemical species normally encountered in the environment. In
another example, such a substrate or film having a diffusion-barrier coating having
graded composition can advantageously be used in packaging of materials, such as
foodstuff, that are easily spoiled by chemical or biological agents normally existing in the
environment.
[0036] Organic light-emitting material and/or cathode materials in OELDs are
susceptible to attack by reactive species existing in the environment, such as oxygen,
water vapor, hydrogen sulfide, SO x , NO x , solvents, etc. Films having a graded-
composition diffusion-barrier coating are particularly useful to extend the life of these
devices and render them more commercially viable. A barrier coating of the present
invention may be made by depositing reaction or recombination products of reacting
species onto a substrate or film. Varying the relative supply rates or changing the
identities of the reacting species results in a coating that has a graded composition across
its thickness. Thus, a coating of the present invention does not have distinct interfaces at
which the composition of the coating changes abruptly. Such abrupt changes in
composition tend to introduce weak spots in the coating structure where delamination can
easily occur. Substrate materials that benefit from having a graded-composition
diffusion-barrier coating are organic polymeric materials; such as
polyethyleneterephthalate ("PET"); polyacrylates; polycarbonate; silicone; epoxy resins,
silicone-functionalized epoxy resins; polyester such as Mylar (made by E.I. du Pont de
Nemours & Co.); polyimide such as Kapton H or Kapton E (made by du Pont), Apical
AV (made by Kanegafugi Chemical Industry Company), Upilex (made by UBE
Industries, Ltd.); polyethersulfones ("PES 5 " made by Sumitomo); polyetherimide such as
Ultem (made by General Electric Company); and polyethylenenaphthalene ("PEN").
[0037] Suitable coating compositions of regions across the thickness are organic,
inorganic, or ceramic materials. These materials are typically reaction or recombination
products of reacting plasma species and are deposited onto the substrate surface. Organic
coating materials typically comprises carbon, hydrogen, oxygen, and optionally other
minor elements, such as sulfur, nitrogen, silicon, etc., depending on the types of reactants.
Suitable reactants that result in organic compositions in the coating are straight or
branched alkanes, alkenes, alkynes, alcohols, aldehydes, ethers, alkylene oxides,
aromatics, etc., having up to 15 carbon atoms. Inorganic and ceramic coating materials
typically comprise oxide; nitride; carbide; boride; or combinations thereof of elements of
Groups DA, HIA 5 IVA, VA, VIA, VIIA, IB, and IIB; metals of Groups IIIB, IVB, and
VB; and rare-earth metals. For example, silicon carbide can de deposited onto a substrate
by recombination of plasmas generated from silane (SiH 4 ) and an organic material, such
as methane or xylene. Silicon oxycarbide can be deposited from plasmas generated from
silane, methane, and oxygen or silane and propylene oxide. Silicon oxycarbide also can
be deposited from plasmas generated from organosilicone precursors, such as
tetraethoxysilane (TEOS), hexamethyldisiloxane (HMDSO), hexamethyldisilazane
(HMDSN), or octamethylcyclotetrasiloxane (D4). Silicon nitride can be deposited from
plasmas generated from silane and ammonia. Aluminum oxycarbonitride can be
deposited from a plasma generated from a mixture of aluminum tartrate and ammonia.
Other combinations of reactants may be chosen to obtain a desired coating composition.
The choice of the particular reactants is within the skills of the artisans. A graded
composition of the coating is obtained by changing the compositions of the reactants fed
into the reactor chamber during the deposition of reaction products to form the coating.
[0038] Coating thickness is typically in the range from about 10 run to about 10000
nm, preferably from about 10 nm to about 1000 nm, and more preferably from about 10
nm to about 200 nm. It may be desired to choose a coating thickness that does not
impede the transmission of light through the substrate, such as a reduction in light
transmission being less than about 20 percent, preferably less than about 10 percent, and
more preferably less than about 5 percent. The coating may be formed by one of many
deposition techniques, such as plasma-enhanced chemical-vapor deposition ("PECVD"),
radio-frequency plasma-enhanced chemical-vapor deposition ("RFPECVD"), expanding
thermal-plasma chemical-vapor deposition ('εTPCVD"), sputtering including reactive
sputtering, electron-cyclotron-resonance plasma-enhanced chemical-vapor deposition
("ECRPECVD"), inductively coupled plasma-enhanced chemical-vapor deposition
("ICPECVD"), or combinations thereof.
[0039] Figure 1 schematically illustrates a reactor 10 and associated equipment for
the ETPCVD technique. At least one cathode 20; typically made of tungsten, is disposed
in a cathode housing 30. Anode plate 40 is disposed at one end of cathode housing 30.
Optionally, at least a cathode housing is electrically floating. A voltage applied between
cathode 20 and anode 40 generates an arc for plasma generation. A carrier gas, such as
argon, is fed through line 50 to the arc. A plasma is generated and exits a nozzle or
orifice 70 at the center of anode 40. A first reactant gas can be fed through line 60 into
the carrier gas line at a point between cathode 20 and anode 40. A second reactant gas is
fed through supply line 80 to a point downstream from orifice 70. Supply line 80 may
also terminate with a perforated ring disposed within expanding plasma beam 84 for
better mixing. Other reactant supply lines can be provided for different reactant species.
Radicals are generated from reactant gases, combined, carried to substrate 90, and
deposited thereon, which substrate is supported on substrate holder 100. Substrate holder
100 is disposed opposite and at a distance from nozzle 70 and is movable relative to
nozzle 70 by substrate-holder shaft 110. Reactor 10 is kept under vacuum via vacuum
connection 112. For example, when the coating on the substrate is desired to comprise
silicon nitride, the first reactant gas can be ammonia, and the second reactant gas can be
silane. The relative supply rates of first and second reactant gases are varied during
deposition to vary the composition of the deposited material as the coating is built up.
Although Figure 1 schematically shows a substrate as a single piece 90, a coating may be
deposited on a continuous substrate in similar equipment. For example, Figure 2 shows a
supply roll 120 of a thin polymeric substrate 115, which supply roll 120 is disposed on
one side of substrate holder 100, and a take-up roll 122 disposed on the other side of
substrate holder 100. As roll 120 continuously unwinds and roll 122 continuously winds,
uncoated substrate film 115 continuously receives the coating material as it passes over
substrate holder 100. In another embodiment of the invention, substrate film 115 passes
through an area opposite to many overlapping plasma beams, each being generated with
different or varying compositions to receive a coating, the composition of which varies
continuously through its thickness.
[0040] In the ETPCVD technique, the plasma is generated at a high pressure
compared to the regular PECVD technique. The plasma in arc channel 65 has a velocity
on the order of sound velocity. The plasma expands supersonically into reactor chamber
10 via nozzle 70 and moves supersonically toward substrate 90.
[0041] Figure 3 schematically shows reactor 200 and associated equipment for the
RFPECVD technique. Radio frequency ("RF") power is applied to cathode 210, which is
disposed in reactor 200, by RF generator and amplifier 204 and matching network 208,
which comprises a plurality of electrical and/or electronic components for generating
appropriate impedance or other electrical characteristics of the overall system to
maximize power transfer from RF generator and amplifier 204. Substrate 90 is disposed
on substrate holder 100 opposite to cathode 210 to receive plasma deposition. Substrate
holder may be grounded or electrically coupled to another RF generator and matching
network, if a different potential is desired. A reactant gas or a mixture of gases is fed into
a gas distributor 212 through a gas supply 214. Gas distributor 212 may have any shape
that promotes a substantially uniform distribution of gases. For example, it may be a ring
having perforations directed toward substrate holder 100. Alternatively, cathode 210 may
itself be hollow and porous and receives reactant gases. A plasma is generated and
maintained by the RF field and flows toward substrate 90. Precursor species in the
plasma are combined and deposited on substrate 90. The composition of the coating can
be varied while it is built up by varying the composition of the reactant gas mixture fed
into distributor 212. A continuous substrate such as a polymeric film may be coated with
a graded-composition coating by providing an unwinding supply roll and a take-up roll, as
described above. The substrate likewise can travel opposite to a plurality of deposition
stations, which supply varying gas compositions, to produce a continuous film having a
graded-composition coating.
[0042] ECRPECVD is another suitable deposition technique. This method
operates at low pressure, typically less than about 0.5 mm Hg 5 and typically without
electrodes. A discharge is generated by microwave. A magnetic field is used to create
the resonance condition of the electron gas, which results in a very high degree of
ionization due to electron acceleration at a distance away from the substrate. The low
pressure preserves a high number density of free radicals until the plasma reaches the
substrate and prevents normally undesirable severe bombardment thereof.
[0043] ICPECVD is another electrodeless deposition technique that can create
high-density plasma at low pressure. A plasma is generated by an electromagnetic field
generated by a concentric induction coil disposed outside one end of the deposition
chamber. The substrate is disposed in the deposition chamber at the opposite end.
Deposition can typically be carried out at pressure much less than 0.5 mm Hg.
[0044] In another embodiment of the present invention, the energy of the ions in a
plasma may be controlled such that they penetrate into a surface layer of the substrate to
create a diffuse transition region between the composition of the bulk substrate and the
composition of the coating. Such a transition prevents an abrupt change in the
composition and mitigates any chance for delamination of the coating.
[0045] A graded-composition coating having a thickness of about 500 nm was
formed on a polycarbonate substrate having a dimension of about 10 cm x 10 cm and a
thickness of about 0.2 mm using the RFPECVD technique and tested for water vapor and
oxygen transmission. Silane (maximum flow rate of about 500 standard cm 3 /minute,
ammonia (maximum flow rate of about 60 standard cmVminute), and propylene oxide
(maximum flow rate of about 500 standard cm 3 /minute) were used to produce the graded
coating comprising silicon, carbon, oxygen, and nitrogen. The rates of the reactant gases
were varied during deposition so that the composition of the coating varied continuously
across its thickness. The power fed to the RF electrode was about 100 W when plasma
was generated from propylene oxide, and about 200 W when a mixture of silane and
ammonia was fed into the reactor. The vacuum level in the reactor was about 0.2 mm Hg
and the average temperature was about 55°C. Figure 4 shows the elemental composition
of the coating, as measured by dynamic XPS, as a function of sputtering time to remove
portions of the thickness of the coating during the dynamic XPS testing, which is directly
related to the depth of the coating. Oxygen and water vapor transmission test results are
shown in Figures 5 and 6. The oxygen transmission rate through the coated plastic
substrate was reduced by over three orders of magnitude compared to the uncoated
substrate, and the water vapor transmission rate by over two orders of magnitude. Light
transmission at various wavelengths of the visible spectrum through the coated substrate
is shown in Figure 7. The reduction in light transmission in the blue to red region (about
430 nm to about 700 nm) was generally less than 7 percent.
[0046] A plastic substrate coated with a graded-composition coating, which is
formed by any method disclosed above can be advantageously used to produce flexible
light sources based on organic light-emitting materials. Other electronic devices that can
benefit from the protection afforded by a graded-composition coating are, for example,
displays include liquid crystal displays, photovoltaic devices, flexible integrated circuits,
or components of medical diagnostic systems. The term "flexible" means being capable
of being bent into a shape having a radius of curvature of less than about 100 cm. The
term "substantially transparent" means allowing a total transmission of at least about 50
percent, preferably at least about 80 percent, and more preferably at least 90 percent, of
light in the visible range (i.e., having wavelength in the range from about 400 nm to about
700 nm). It should be understood that the composition of a graded-composition barrier
coating does not necessarily vary monotonically from one surface to the other surface
thereof. A monotonically varying composition is only one case of graded-composition for
the barrier of the present invention.
[0047] Figure 8 is a schematic diagram of an embodiment of the present invention.
It should be understood that the figures accompanying this disclosure are not drawn to
scale. OELD or a light-emitting device 310 comprises an organic EL member 320
disposed on a substantially transparent substrate 340 having a graded-composition barrier
coating 350, as described above. The graded-composition barrier coating 350 may be
disposed or otherwise formed on either or both of the surfaces of the substrate 340
adjacent to the organic EL member 320. Preferably, the graded-composition barrier
coating 350 is disposed or formed on the surface of the substrate 340 adjacent to the
organic EL member 320 or it may completely cover the substrate 340. Although Figure 8
shows schematically a distinct interface between substrate 340 and coating 350, such a
coating may be formed such that there is no sharp interface therebetween, as described
above.
[0048] Substrate 340 may be a single piece or a structure comprising a plurality of
adjacent pieces of different materials and has an index of refraction (or refractive index)
in the range from about 1.05 to about 2.5, preferably from about 1.1 to about 1.6.
Preferably, substrate 340 is made of a substantially transparent polymeric material.
Examples of suitable polymeric materials are polyethylenterephathalate ("PET"),
polyacrylates, polycarbonate, silicone, epoxy resins, silicone-functionalized epoxy resins,
polyester, polyimide, polyetherimide, PES, PEN, polynorbonenes, or poly (cyclic olefins).
[0049] Light-emitting member 320 comprises at least one layer 330 of at least one
organic EL material sandwiched between two electrodes 322 and 338, as shown in Figure
9. As will be disclosed below, the light-emitting member may comprise one or more
additional layers between an electrode and the layer 330 of organic EL material. When a
voltage is supplied by a voltage source 326 and applied across electrodes 322 and 338,
light emits from the organic EL material. In a preferred embodiment, electrode 322 is a
cathode injecting negative charge carriers (electrons) into organic EL layer 330 and is
made of a material having a low work function; e.g., less than about 4 eV. Low- work
function materials suitable for use as a cathode are K, Li, Na, Mg, La, Ce, Ca, Sr, Ba, Al,
Ag, In, Sn, Zn, Zr, Sm, Eu, alloys thereof, or mixtures thereof. Preferred materials for the
manufacture of cathode layer 322 are Ag-Mg, Al-Li, In-Mg, and Al-Ca alloys. Layered
non-alloy structures are also possible, such as a thin layer of a metal such as Ca (thickness
from about 1 to about 10 run) or a non-metal such as LiF, covered by a thicker layer of
some other metal, such as aluminum or silver, hi this embodiment, electrode 338 is an
anode injecting positive charge carriers (or holes) into organic layer 330 and is made of a
material having a high work function; e.g., greater than about 4.5 eV, preferably from
about 5 eV to about 5.5 eV. Indium tin oxide ("ITO") is typically used for this purpose.
ITO is substantially transparent to light transmission and allows at least 80% light
transmitted therethrough. Therefore, light emitted from organic electroluminescent layer
330 can easily escape through the ITO anode layer without being seriously attenuated.
Other materials suitable for use as the anode layer are tin oxide, indium oxide, zinc oxide,
indium zinc oxide, cadmium tin oxide, and mixtures thereof. In addition, materials used
for the anode may be doped with aluminum of fluorine to improve charge injection
property. Electrode layers 322 and 338 may be deposited on the underlying element by
physical vapor deposition, chemical vapor deposition, ion beam-assisted deposition, or
sputtering. A thin, substantially transparent layer of a metal is also suitable.
[0050] Although the preferred order of the cathode and anode layers 322 and 338 is
disclosed above, the electrode layers may be reversed. Electrode layers 322 and 338 may
serve as the anode and cathode, respectively. Typically, the thickness of the cathode layer
in this case is about 200 nm.
[0051] Organic EL layer 330 serves as the transport medium for both holes and
electrons. In this layer these excited species combine and drop to a lower energy level,
concurrently emitting EM radiation in the visible range. Organic EL materials are chosen
to electroluminesce in the desired wavelength range. The thickness of the organic EL
layer 330 is preferably kept in the range of about 100 to about 300 nm. The organic EL
material may be a polymer, a copolymer, a mixture of polymers, or lower molecular-
weight organic molecules having unsaturated bonds. Such materials possess a
delocalized π-electron system, which gives the polymer chains or organic molecules the
ability to support positive and negative charge carriers with high mobility. Suitable EL
polymers are poly(N-vinylcarbazole) ("PVK", emitting violet-to-blue light in the
wavelengths of about 380-500 nm); poly(alkylfluorene) such as poly (9,9-
dihexylfluorene) (410-550 nm), poly(dioctylfluorene) (wavelength at peak EL emission of
436 nm), or poly{9,9-bis(3,6-dioxaheptyl)-fluorene-2,7-diyl} (400-550 nm);
poly(paraphenylene) derivatives such as poly(2-decyloxy-l,4-phenylene) (400-550 nm).
Mixtures of these polymers or copolymers based on one or more of these polymers and
others may be used to tune the color of emitted light.
[0052] Another class of suitable EL polymers is the polysilanes. Polysilanes are
linear silicon-backbone polymers substituted with a variety of alkyl and/or aryl side
groups. They are quasi one-dimensional materials with delocalized σ-conjugated
electrons along polymer backbone chains. Examples of polysilanes are poly(di-n-
butylsilane), poly(di-n-pentylsilane), poly(di-n-hexylsilane), poly(methylphenylsilane),
and poly{bis(p-butylphenyl)silane} which are disclosed in H. Suzuki et al., "Near-
Ultraviolet Electroluminescence From Polysilanes," 331 Thin Solid Films 64-70 (1998).
These polysilanes emit light having wavelengths in the range from about 320 nm to about
420 nm.
[0053] Organic materials having molecular weight less than about 5000 that are
made of a large number of aromatic units are also applicable. An example of such
materials is l,3,5-tris{n-(4-diphenylaminophenyl) phenylamino}benzene, which emits
light in the wavelength range of 380-500 nm. The organic EL layer also may be prepared
from lower molecular weight organic molecules, such as phenylanthracene,
tetraarylethene, coumarin, rubrene, tetraphenylbutadiene, anthracene, perylene, coronene,
or their derivatives. These materials generally emit light having maximum wavelength of
about 520 nm. Still other suitable materials are the low molecular-weight metal organic
complexes such as aluminum-, gallium-, and indium-acetylacetonate, which emit light in
the wavelength range of 415-457 nm, aluminum-(picolymethylketone)-bis{2,6-di(t-
butyl)phenoxide} or scandium-(4-memoxy-picolymiethylketone)-bis(acetylacetonate) ,
which emits in the range of 420-433 nm. For white light application, the preferred
organic EL materials are those emit light in the blue-green wavelengths.
[0054] More than one organic EL layer may be formed successively one on top of
another, each layer comprising a different organic EL material that emits in a different
wavelength range. Such a construction can facilitate a tuning of the color of the light
emitted from the overall light-emitting device 310.
[0055] Furthermore, one or more additional layers may be included in light-
emitting member 320 to increase the efficiency of the overall device 310. For example,
these additional layers can serve to improve the injection (electron or hole injection
enhancement layers) or transport (electron or hole transport layers) of charges into the
organic EL layer. The thickness of each of these layers is kept to below 500 nm,
preferably below 100 nm. Materials for these additional layers are typically low-to-
intermediate molecular weight (less than about 2000) organic molecules. They may be
applied during the manufacture of the device 310 by conventional methods such as spray
coating, dip coating, or physical or chemical vapor deposition. In one embodiment of the
present invention, as shown in Figure 10, a hole injection enhancement layer 336 is
formed between the anode layer 338 and the organic EL layer 330 to provide a higher
injected current at a given forward bias and/or a higher maximum current before the
failure of the device. Thus, the hole injection enhancement layer facilitates the injection
of holes from the anode. Suitable materials for the hole injection enhancement layer are
arylene-based compounds disclosed in U.S. Patent 5,998,803; such as 3, 4, 9, 10-
perylenetetra-carboxylic dianhydride or bis(l,2,5-thiadiazolo)-p-quinobis(l,3-dithiole).
[0056] In another embodiment of the present invention, as shown in Figure 11,
light-emitting member 320 further includes a hole transport layer 334 which is disposed
between the hole injection enhancement layer 336 and the organic EL layer 330. The
hole transport layer 334 has the functions of transporting holes and blocking the
transportation of electrons so that holes and electrons are optimally combined in the
organic EL layer 330. Materials suitable for the hole transport layer are triaryldiamine,
tetraphenyldiamine, aromatic tertiary amines, hydrazone derivatives, carbazole
derivatives, triazole derivatives, imidazole derivatives, oxadiazole derivatives having an
amino group, and polythiophenes as disclosed in U.S. Patent 6,023,371, which is
incorporated herein by reference.
[0057] In still another embodiment of the present invention, as shown
schematically in Figure 12, light-emitting member 320 includes an additional layer 324
which is disposed between the cathode layer 322 and the organic EL layer 330. Layer
324 has the combined function of injecting and transporting electrons to the organic EL
layer 330. Materials suitable for the electron injecting and transporting layer are metal
organic complexes such as tris(8-quinolinolato)aluminum, oxadiazole derivatives,
perylene derivatives, pyridine derivatives, pyrimidane derivatives, quinoline derivatives,
quinoxaline derivatives, diphenylquinone derivatives, and nitro-substituted fluorene
derivatives, as disclosed in U.S. Patent 6,023,371, which is incorporated herein by
reference.
[0058] A reflective metal layer 360 may be disposed on organic EL member 320 to
reflect any radiation emitted away from the substantially transparent substrate 340 and
direct such radiation toward the substrate 340 such that the total amount of radiation
emitted in this direction is increased. Reflective metal layer 360 also serves an additional
function of preventing diffusion of reactive environmental elements, such as oxygen and
water vapor, into the organic EL element 320. Such a diffusion otherwise can degrade
the long-term performance of the OELD. Suitable metals for the reflective layer 360 are
silver, aluminum, and alloys thereof. It may be advantageous to provide a thickness that
is sufficient to substantially prevent the diffusion of oxygen and water vapor, as long as
the thickness does not substantially reduce the flexibility of the entire device. In one
embodiment of the present invention, one or more additional layers of at least a different
material, such as a different metal or metal compound, may be formed on the reflective
layer to further reduce the rate of diffusion of oxygen and water vapor into the organic EL
member. In this case, the material for such additional layer or layers need not be a
reflective material. Compounds, such as metal oxides, nitrides, carbides, oxynitrides, or
oxycarbides, may be useful for this purpose.
[0059] In another embodiment of the present invention, as shown in Figure 13, a
bonding layer 358 of a substantially transparent organic polymeric material may be
disposed on the organic EL member 320 before the reflective metal layer 360 is deposited
thereon. Examples of materials suitable for forming the organic polymeric layer are
polyacrylates such as polymers or copolymers of acrylic acid, methacrylic acid, esters of
these acids, or acylonitrile; polyvinyl fluoride); poly(vinylidene chloride); polyvinyl
alcohol); copolymer of vinyl alcohol and glyoxal (also known as ethanedial or
oxaaldehyde); polyethyleneterephthalate, parylene (thermoplastic polymer based on p-
xylene), and polymers derived from cycloolefuis and their derivatives (such as
poly(arylcyclobutene) disclosed in U.S. Patents 4,540,763 and 5,185,391 which are
incorporated herein by reference). Preferably, the bonding layer material is an electrically
insulating and substantially transparent polymeric material. A suitable material is
polyacrylates.
[0060] In another embodiment of the present invention, as shown in Figure 14, a
second polymeric substrate 370 having a graded-composition barrier coating 372 is
disposed on organic EL member 320 opposite to substrate 340 to form a complete seal
around organic EL member 320. Graded-composition barrier coating 372 may be
disposed on either side of substrate 370. It may be preferred to dispose graded-
composition barrier coating 372 adjacent to organic EL member 320. Second polymeric
substrate 370 having graded-composition barrier coating 372 may also be disposed on
reflective metal layer 360 to provide even more protection to organic EL member 320.
Alternatively, graded-composition barrier 372 may be deposited directly on organic EL
member 320 instead of being disposed on a second polymeric substrate (such as 370). In
this case, the second substrate (such as 370) may be eliminated.
[0061] Alternatively, second substrate 370 having graded-composition barrier
coating 372 can be disposed between organic EL member 320 and reflector layer 360.
This configuration may be desirable when it can offer some manufacturing or cost
advantage, especially when the transparency of coated substrate 370 is also substantial.
[0062] In another embodiment of the present invention, the light-emitting device
310 further comprises a light-scattering material disposed in the path of light emitted
from the light-emitting device 310 to provide more uniform light therefrom. For
example, Figure 15 illustrates an embodiment comprising a layer 390 of scattering
material disposed on the substrate 340. The light-scattering material is provided by
choosing particles that range in size from about 10 ran to about 100 micrometers. A
preferred embodiment includes particles about 4 micrometers in size. For example, for a
device emitting white light, the particle size is preferably on the order of 50-65 nm.
Particles of the light-scattering material may be advantageously dispersed in a
substantially transparent polymeric film-forming material such as those disclosed above,
and the mixture is formed into a film which may be disposed on the substrate 340.
Suitable light-scattering materials are solids having refractive index higher than that of
the film forming material. Since typical film forming materials have refractive indices
between about 1.3 to about 1.6, the particulate scattering material should have a refractive
index higher than about 1.6 and should be optically transparent over the target wavelength
range. In addition, it is preferable that the light scattering material be non-toxic and
substantially resistant to degradation upon exposure to normal ambient environments. For
a device designed to provide visible illumination (wavelength in the range of about 400-
700 nm), examples of suitable light-scattering materials are ratile (TiO 2 ), hafnia (HfO 2 ),
zirconia (ZrO 2 ), zircon (ZrO 2 « SiO 2 ), gadolinium gallium garnet (Gd 3 Ga 5 Oi 2 ), barium
sulfate, yttria (Y 2 O 3 ), yttrium aluminum garnet ("YAG", Y 3 Al 5 O 12 ), calcite (CaCO 3 ),
sapphire (Al 2 O 3 ), diamond, magnesium oxide, germanium oxide. It is necessary to
prepare these compounds with a high degree of optical purity; i.e. impurities that absorb
light in the wavelength range of interest must be rigorously minimized. It is not necessary
that the compound be stoichiometrically pure, phase pure, and may contain appropriate
atomic substitutions; e.g., Gd, may be substituted for up to 60% of the yttrium in YAG.
Particles composed of high-refractive index glasses, such as may be obtained from Schott
Glass Technologies or Corning, Inc. may also be used, provided that they are impervious
to darkening from exposure to light emitted by the OELD and its phosphors. Scattering
of light may also be achieved with a plastic or glass film having a roughened or textured
surface (a "diffuser film"), the roughened features of which are typically on the order of a
fraction of the wavelength of the scattered light. In one embodiment of the present
invention, one surface of the substrate can be textured or roughened to promote light
scattering.
[0063] According to another aspect of the present invention, the light-scattering
particles in layer 390 can comprise a photoluminescent ("PL") material (or also herein
called a "phosphor"), which is capable of absorbing a portion of the EM radiation emitted
by the organic EL member having a first wavelength range and emitting EM radiation
having a second wavelength range. Thus, inclusion of such a PL material can provide a
tuning of color of light emitted from the OELD. The particle size and the interaction
between the surface of the particle and the polymeric medium determine how well
particles are dispersed in polymeric materials to form the film or layer 390. Many
micrometer-sized particles of oxide materials, such as zirconia, yttrium and rare-earth
garnets, and halophosphates, disperse well in standard silicone polymers, such as
poly(dimethylsiloxanes) by simple stirring. If necessary, other dispersant materials (such
as a surfactant or a polymeric material like poly(vinyl alcohol)) may be added such as are
used to suspend standard phosphors in solution. The phosphor particles may be prepared
from larger pieces of phosphor material by any grinding or pulverization method, such as
ball milling using zirconia-toughened balls or jet milling. They also may be prepared by
crystal growth from solution, and their size may be controlled by terminating the crystal
growth at an appropriate time. The preferred phosphor materials efficiently absorb EM
radiation emitted by the organic EL material and re-emit light in another spectral region.
Such a combination of the organic EL material and the phosphor allows for a flexibility in
tuning the color of light emitted by the light-emitting device 310. A particular phosphor
material or a mixture of phosphors may be chosen to emit a desired color or a range of
color to complement the color emitted by the organic EL material and that emitted by the
organic PL materials. An exemplary phosphor is the cerium-doped yttrium aluminum
oxide Y 3 AI 5 O 12 ) garnet ("YAG:Ce"). Other suitable phosphors are based on YAG doped
with more than one type of rare earth ions, such as
(Y 1 ^Gd x Ce 7 ) S Al 5 O 12 ("YAG:Gd,Ce"), (Yi. x Ce x ) 3 (Al μy Ga y )O 12 ("YAG:Ga,Ce"), (Yi*
y Gd x Ce y )(Al 5 . z Ga z )O 12 ("YAG:Gd,Ga,Ce"), and (Gd Lx Ce x )Sc 2 Al 3 O 12 ("GSAG") where 0
< x < l, 0 < y ≤ l, 0 < z < 5 and x + y ≤ 1. For example, the YAG:Gd,Ce phosphor shows
an absorption of light in the wavelength range from about 390 nm to about 530 nm (i.e.,
the blue-green spectral region) and an emission of light in the wavelength range from
about 490 nm to about 700 nm (i.e., the green-to-red spectral region). Related phosphors
include Lu 3 Al 5 O 12 and Tb 2 Al 5 O 12 , both doped with cerium. In addition, these cerium-
doped garnet phosphors may also be additionally doped with small amounts of Pr (such as
about 0.1-2 mole percent) to produce an additional enhancement of red emission. The
following are examples of phosphors that are efficiently excited by EM radiation emitted
in the wavelength region of 300 nm to about 500 nm by polysilanes and their derivatives.
[0064] Green-emitting phosphors: Ca g Mg(Si0 4 ) 4 Cl 2 :Eu 2+ ,Mn 2+ ;
GdBO 3 :Ce 3+ ,Tb 3+ ; CeMgAInO 19 : Tb 3+ ; Y 2 SiO 5 :Ce 3+ ,Tb 3+ ; and
BaMg 2 Al 16 O 2 :Eu 2+ 5 Mn 2+ .
[0065] Red-emitting phosphors: Y 2 O 3 :Bi 3+ ,Eu 3+ ; Sr 2 P 2 O 7 :Eu 2+ ,Mn 2+ ;
SrMgP 2 O 7 :Eu 2+ ,Mn 2+ ; (Y 5 Gd)(V 5 B)O 4 :Eu 3+ ; and 3.5MgO.0.5MgF 2 GeO 2 :Mn 4+
(magnesium fluorogeπnanate).
[0066] Blue-emitting phosphors:BaMg 2 Al 16 O 27 :Eu 2+ ; Sr 5 (PO 4 ) 10 Cl 2 :Eu 2+ ; and
(Ba,Ca 5 Sr) 5 (PO 4 )io(Cl,F) 2 :Eu 2+ 5 (Ca 5 Ba 5 Sr)(Al 5 Ga) 2 S 4 :Eu 2+ .
[0067] Yellow-emitting phosphors: (Ba,Ca 5 Sr) 5 (PO 4 ) 10 (Cl 5 F) 2 :Eu 2+ 5 Mn 2+ .
[0068] Still other ions may be incorporated into the phosphor to transfer energy
from the light emitted from the organic material to other activator ions in the phosphor
host lattice as a way to increase the energy utilization. For example, when Sb 3+ and Mn 2+
ions exist in the same phosphor lattice, Sb 3+ efficiently absorbs light in the blue region,
which is not absorbed very efficiently by Mn 2+ , and transfers the energy to Mn 2+ ion.
Thus, a larger total amount of light emitted by the organic EL material is absorbed by
both ions, resulting in higher quantum efficiency of the total device.
[0069] The photo luminescent material may also be an organic dye that can absorb
radiation emitted by the organic EL material and emit electromagnetic radiation in the
visible spectrum.
[0070] The phosphor particles are dispersed in a film-forming polymeric material,
such as polyacrylates, substantially transparent silicone or epoxy. A phosphor
composition of less than about 30, preferably less than about 10, percent by volume of the
mixture of polymeric material and phosphor is used. A solvent may be added into the
mixture to adjust the viscosity of the film-forming material to a desired level. The
mixture of the film-forming material and phosphor particles is formed into a layer by
spray coating, dip coating, printing, or casting on a substrate. Thereafter, the film is
removed from the substrate and disposed on the light-emitting member 320. The
thickness of film or layer 390 is preferably less than 1 mm, more preferably less than 500
μm. Preferably, the film-forming polymeric materials have refractive indices close to
those of the substrate 340 and the organic EL material; i.e., in the range from about 1.4 to
about 1.6.
[0071] According to one aspect of the present invention, particles of a scattering
material and a phosphor are dispersed in the same film or layer 390. In another
embodiment, scattering film 390 may be a diffuser film, which is a plastic film having a
roughened surface.
[0072] A method of making an OELD of the present invention is now described.
A cleaned flexible substrate, such as a plastic, is first provided. Then, a graded-
composition barrier coating is formed on at least a surface of the flexible substrate by a
one of many deposition techniques disclosed above.
[0073] A first electrically conducting material is deposited on the graded-
composition barrier coating to form a first electrode of the organic EL member 320.
Alternatively, the first electrode may be deposited on the surface of the substrate 340 that
has not been coated with graded-composition barrier coating. The first electrode may be
an anode or a cathode, and one or more appropriate materials are chosen among those
disclosed earlier for the electrodes. Preferably, the first electrode is an anode comprising
a transparent metal oxide, such as ITO. The first electrode material preferably sputter-
deposited on the substrate. Furthermore, the first electrode may be patterned to a desired
configuration by, for example, etching. At least one organic EL material is deposited on
the first electrode by physical or chemical vapor deposition, spin coating, dip coating,
spraying, printing, or casting, followed by polymerization, if necessary, or curing of the
material. The organic EL material may be diluted in a solvent to adjust its viscosity or
mixed with another polymeric material that serves as a film-forming vehicle. A second
electrically conducting material is deposited on the at least one organic EL material to
form a second electrode. Preferably, the second electrode is a cathode. The second
electrode may be deposited on the entire area of the organic EL material or patterned into
a desired shape or configuration. The thickness of the second electrode is kept to a
minimum, such as less than or equal to about 200 nm. The electrodes and the organic EL
material comprise the organic EL member 320.
[0074] A reflective metal is optionally deposited on the surface of the organic EL
member 320 opposite to substrate 340. The reflective metal may be deposited by, for
example, sputtering or physical vapor deposition. In one embodiment of the present
invention, a bonding layer of a substantially transparent material is deposited on the
organic EL member 320 before the layer of reflective metal is deposited thereon.
Preferably, the bonding layer comprises an electrically insulating and substantially
transparent polymeric material. The bonding layer may be deposited by one of the
methods disclosed above for deposition of an organic layer. The reflective metal layer is
formed so as to completely surround the organic EL member 320. Preferably, the
reflective metal layer together with the graded-composition barrier coating forms a
hermetic seal around the organic EL member 20. Furthermore, one or more additional
layers of other inorganic materials may be deposited on the reflective metal layer.
[0075] A mixture of particles of a scattering or PL material and a transparent
polymeric material is deposited on the surface of the substrate 340 opposite the organic
EL member. Alternatively the mixture may be cast into a tape by a tape
casting method, such as the doctor blade method. The tape is then cured and attached to
the substrate 340.
[0076] In another embodiment, subsets of layers necessary or desired for the
operation of an OELD of the present invention are formed in separate assemblies, and the
assemblies are laminated or attached together to produce a working device. For example,
a first substrate having a first graded-composition barrier coating, an assembly of an
organic EL member, and a second substrate having a second graded-composition barrier
coating are laminated together to provide a light source having improved resistance to
attack by chemical species in the environment.
[0077] In still another aspect of the present invention, large-area flexible displays
or lighting systems incorporate OELDs of the present invention.
[0078] In yet a further aspect of the present disclosure; a graded ultra-high barrier
("UHB") coating has been developed that comprises a graded single layer made up of
inorganic and organic materials. The UHB coating has been fabricated using plasma
enhanced chemical vapor deposition ("PECVD") techniques, and variations of PECVD.
One method uses a parallel plate capacitively coupled plasma reactor. In this barrier
structure, the organic materials effectively decouple defects growing in the thickness
direction in the inorganic materials, but, instead of having a sharp interface between
inorganic and organic materials, there are "transitional" zones where the coating
composition varies continuously from inorganic to organic and vice versa. These
transitional zones bridge the inorganic and organic materials and results in a single layer
structure with improved mechanical stability and stress relaxation relative to that of
multilayer barrier structures.
[0079] In a preferred embodiment, there are two base PECVD processes required
to fabricate the UHB coating - an inorganic and an organic process. The inorganic
process may utilize a combination of silane, ammonia, and oxygen gases to create a
material composition ranging between silicon nitride and silicon oxide. The organic
process may include a combination of Si-containing organic precursor and Ar gases to
create a Si-containing organic material. The inorganic and the organic processes may be
tailored such that the resulting materials have similar hardness (inorganic material: 10~15
GPa, organic material: <1 GPa) and elastic modulus (inorganic material: 50~100 GPa,
organic material: <10 GPa) to those of glass-like materials and thermoplastics,
respectively. Preferably, the graded UHB structure may be obtained by gradually mixing
the inorganic and the organic processes. At constant pressure and RF power, each mass
flow controller for each individual process gas may be programmed to achieve continuous
compositional changes, while the plasma remains on, in order to achieve a gradual change
in the coating composition from inorganic to organic materials and vice versa. For
example, if one wants to achieve a coating composition that comprises 90 % of inorganic
and 10 % of organic materials, the mass flow controllers for the inorganic and the organic
process gases are set at 90 % and 10 % with respect to their original values, respectively.
The thickness of the transitional zone is determined by the time to change the precursor
gas composition from the inorganic process to the organic process and vice versa.
Typically due to the non-linearity of the plasma process, mixing of precursors for two
different processes often results in unexpected coating compositions unless the process
conditions are carefully selected. In order to avoid such unexpected compositions, in one
embodiment the inorganic and the organic processes were developed at the same pressure
and RF power. In addition, the inorganic and the organic processes were engineered to
have comparable deposition rates.
[0080] Light transmittance and color neutrality are critical requirements for an
OELD substrate. One issue with the multilayer approach to a barrier layer is that the
separate organic and inorganic layers typically have different indices of refraction. This
leads to multiple reflections and usually additional loss of optical transmission through
the multilayer stack. One way around this is to engineer the thickness of the layers to
create an interference effect that improves light transmission. Unfortunately, the optimal
thicknesses for optical performance are usually not the optimal thicknesses for barrier
performance and so overall coating optimization involves an undesirable tradeoff.
[0081] The single graded layer UHB approach can circumvent this trade-off. In
particular, since PECVD (and variations of PECVD) may be utilized to deposit both
inorganic and organic materials, there is a large freedom to tailor film properties such as
refractive index through film composition. Thus it is possible to develop a process that
yields the same refractive index for both the organic and inorganic materials and hence
avoid multiple reflections. A preferred method for doing this is by modifying the
inorganic material such that its refractive index ("n") matched that of the organic material
(n~l .5). An alternative method is to modify the organic material to match the refractive
index of inorganic material.
[0082] Figure 16(a) shows the coating composition and Figure 16(b) the refractive
index of the inorganic material at 550 nm as a function of oxygen flow rate of the
PECVD process. In the non-limiting example shown in Figures 16(a) and 16(b), the
inorganic coatings were deposited on a silicon (Si) chip at various oxygen flow rates
while the total flow rate was maintained at a constant value. The coating composition
was obtained using X-ray Photoelectron Spectroscopy ("XPS") and the refractive index
was obtained using spectroscopic ellipsometry, as both are known in the art. One can see
that the atomic oxygen concentration increases rapidly with a small addition of oxygen in
the precursor gases, and simultaneously refractive index dramatically decreases from ~1.8
of silicon nitride to ~1.5 of silicon oxynitride. Then, atomic oxygen concentration
increases slowly and finally saturates with further increase in oxygen flow rate, and
refractive index decreases slowly to ~1.4 of silicon oxide.
[0083] In order to test the overall optical effect of these inorganic process
modifications, graded UHB coatings were deposited onto a polycarbonate film with
varying oxygen flow rates for the inorganic process and then the overall light
transmittance ("%T") through the coated films was collected using a UV-VIS
spectrometer, as is known in the art. The average %T and the standard deviation of %T
were calculated over the wavelength range of 400-700 nm to assess the optical
transparency and the amplitude of any interference effects, respectively. Figure 17 shows
these parameters as a function of oxygen flow rate. Note that the average %T is ~86 %
when the UHB coating includes silicon nitride as an inorganic material, but it increases to
above 90% as the oxygen flow rate in the inorganic process increases. One can also see
that the amplitude of interference is at a minimum when the oxygen flow fraction is ~0.2
- presumably where the refractive index of the inorganic material matches that of the
organic material. Figure 18 compares the complete %T spectra through two distinct
graded UHB coatings: (a) silicon nitride as the base inorganic material (oxygen flow
fraction of 0), and (b) silicon oxynitride as the base inorganic material (oxygen flow
fraction of 0.25). As can be seen in Figure 11 for this example, with the given silicon
oxynitride as the base inorganic material, the single layer graded barrier coating on the
polycarbonate substrate indeed has higher overall transmission and greatly minimized
interference fringes relative to that with silicon nitride as the base inorganic material.
This demonstrates that highly transparent and essentially color neutral barrier coatings
can be made with a single layer graded UHB.
[0084] While specific preferred embodiments of the present invention have been
disclosed in the foregoing, it will be appreciated by those skilled in the art that many
modifications, substitutions, or variations may be made thereto without departing from
the spirit and scope of the invention as defined in the appended claims.