U.S. patent application number 10/798712 was filed with the patent office on 2004-10-07 for method for forming an arrangement of barrier layers on a polymeric substrate.
Invention is credited to Gieres, Guenter, Henseler, Debora, Heuser, Karsten, Paetzold, Ralph, Wittmann, Georg.
Application Number | 20040197489 10/798712 |
Document ID | / |
Family ID | 32864949 |
Filed Date | 2004-10-07 |
United States Patent
Application |
20040197489 |
Kind Code |
A1 |
Heuser, Karsten ; et
al. |
October 7, 2004 |
Method for forming an arrangement of barrier layers on a polymeric
substrate
Abstract
Forming an arrangement of two ceramic barrier layers (5, 10) on
a polymeric substrate (1) includes the steps of applying a first
ceramic barrier layer (5) on the substrate (1). The surface (5A) of
the first barrier layer (5) is modified to introduce new nucleation
sites on the surface of the first layer. A second ceramic barrier
layer (10) is formed on the first barrier layer (5) using the new
nucleation sites. The second ceramic barrier layer is deposited
with independent nucleation sites such that a barrier stack of
enhanced quality is formed.
Inventors: |
Heuser, Karsten; (Erlangen,
DE) ; Wittmann, Georg; (Herzogenaurach, DE) ;
Gieres, Guenter; (Kleinsendelbach, DE) ; Paetzold,
Ralph; (Roth, DE) ; Henseler, Debora;
(Erlangen, DE) |
Correspondence
Address: |
FISH & RICHARDSON P.C.
3300 DAIN RAUSCHER PLAZA
MINNEAPOLIS
MN
55402
US
|
Family ID: |
32864949 |
Appl. No.: |
10/798712 |
Filed: |
March 10, 2004 |
Current U.S.
Class: |
427/535 ;
427/255.7 |
Current CPC
Class: |
B32B 27/00 20130101;
C23C 16/44 20130101; C23C 14/22 20130101; C23C 16/56 20130101 |
Class at
Publication: |
427/535 ;
427/255.7 |
International
Class: |
C23C 016/00 |
Foreign Application Data
Date |
Code |
Application Number |
Mar 10, 2003 |
EP |
03005270.8 |
Claims
What is claimed is:
1. A method for forming an arrangement of two barrier layers on a
substrate, comprising: forming a first ceramic barrier layer on a
substrate, wherein the first ceramic barrier layer has a first
surface and a second surface and the first surface is closer to the
substrate than the second surface; modifying at least a portion of
the second surface of the first ceramic barrier layer to introduce
first nucleation sites on the second surface; and forming a second
ceramic barrier layer on the first ceramic barrier layer, wherein
the second ceramic barrier layer is initiated at the first
nucleation sites.
2. The method of claim 1, wherein: modifying at least a portion of
the second surface of the first ceramic barrier layer includes
chemically modifying the second surface.
3. The method of claim 2, wherein: chemically modifying at least a
portion of the second surface of the first ceramic barrier layer
includes at least one modification techniques from the group
consisting of acid treatment, base treatment, exposure to water
vapor, plasma treatment and ozone treatment.
4. The method of claim 1, wherein: modifying at least a portion of
the second surface of the first ceramic barrier layer includes
mechanically modifying the second surface.
5. The method of claim 4, wherein: mechanically modifying at least
a portion of the second surface of the first ceramic barrier layer
includes at least one modification techniques from the group
consisting of ion milling, nano-grinding, melting the second
surface with a laser and tempering.
6. The method of claim 1, wherein: modifying at least a portion of
the second surface of the first ceramic barrier layer includes
forming a nucleation promoting material on the second surface.
7. The method of claim 1, wherein: forming a nucleation promoting
material on at least a portion of the second surface of the first
ceramic barrier layer includes forming at least one material from
the group consisting of a metal, a metal nitride and a metal
oxide.
8. The method of claim 7, wherein: forming the at least one
material includes applying a material with a critical nucleus of
one atom.
9. The method of claim 8, wherein: forming the at least one
material includes applying at least one material from the group
consisting of tantalum, chromium, tungsten, molybdenum, niobium,
tantalum nitride, titanium nitride, tantalum oxide and titanium
oxide.
10. The method of claim 7, wherein: applying the at least one
material includes applying a material with a critical nucleus of
one molecule.
11. The method of claim 10, wherein: forming at least one material
includes applying at least one of the materials from the group
consisting of tantalum, chromium, tungsten, molybdenum, niobium,
tantalum nitride, titanium nitride, tantalum oxide and titanium
oxide.
12. The method of claim 1, wherein: forming a first ceramic barrier
layer and a second ceramic barrier layer includes forming the first
and second ceramic barrier layers of at least one material from the
group consisting of a metal nitride, a metal oxide and a metal
oxynitride.
13. The method of claim 12, wherein: the metal is aluminum.
14. The method of claim 1, wherein: forming a first ceramic barrier
layer and a second ceramic barrier layer includes forming the first
and second ceramic barrier layers of at least one if possible
material from the group consisting of silicon nitride, silicon
oxide and silicon oxynitride.
15. The method of claim 1, wherein: forming a second ceramic
barrier layer includes depositing the second ceramic barrier layer
using chemical vapor deposition.
16. The method of claim 1, wherein: forming a second ceramic
barrier layer includes depositing the second ceramic barrier layer
using physical vapor deposition.
17. The method of claim 1, wherein: forming the first ceramic
barrier layer includes at least one technique selected from the
group consisting of laminating, printing, sputtering, spraying,
chemical vapor deposition and physical vapor deposition.
18. The method of claim 1, wherein: the substrate includes a
flexible transparent substrate.
19. The method of claim 1, wherein the second ceramic barrier layer
has a first surface and a second surface and the first surface of
the second ceramic barrier layer is closer than the second surface
to the first ceramic barrier layer, the method further comprising:
modifying at least a portion of the second surface to introduce
second nucleation sites on the second surface of the second ceramic
barrier layer; and forming a third ceramic barrier layer on the
second ceramic barrier layer, wherein the third ceramic barrier
layer is initiated at the second nucleation sites.
20. The method of claim 1, wherein: forming a first ceramic barrier
layer includes forming the layer to be between about 1 and about
250 nanometers thick.
21. The method of claim 1, wherein: forming a second ceramic
barrier layer includes forming the layer to be between about 1 and
about 250 nanometers thick.
22. The method of claim 1, wherein: forming a first ceramic barrier
layer includes forming the layer to be between about 10 and about
100 nanometers thick.
23. The method of claim 1, wherein: forming a second ceramic
barrier layer includes forming the layer to be between about 10 and
about 100 nanometers thick.
24. The method of claim 1, further comprising: forming an organic
electrical device on the second ceramic barrier layer.
25. The method of claim 1, further comprising: forming a first
electrically conductive layer on the second ceramic barrier layer;
forming a functional organic layer on the first electrically
conductive layer; and forming a second electrically conductive
layer on the functional organic layer.
26. The method of claim 25, further comprising: forming an
encapsulation over the second electrically conductive layer such
that the functional organic layer is sealed from the environment by
the encapsulation.
27. The method of claim 26, wherein forming an encapsulating
comprises: forming a third ceramic barrier layer over the second
electrically conductive layer, wherein the third ceramic barrier
layer has a first surface and a second surface and the first
surface is closer than the second surface to the second
electrically conductive layer; modifying the second surface of the
third ceramic barrier layer to introduce second nucleation sites on
the surface of the third ceramic barrier layer; and forming a
fourth ceramic barrier layer on the third ceramic barrier layer,
wherein the fourth ceramic barrier layer is initiated at the second
nucleation sites.
Description
CROSS-REFERENCE TO RELATED APPLICATIONS
[0001] This application claims priority to European Patent
Application No. 03005270.8, filed on Mar. 10, 2003, which is
incorporated by reference herein.
BACKGROUND
[0002] Many products, for example food, electronic devices and
pharmaceuticals, are very sensitive to moisture and oxidizing
agents. Many of these products rapidly degrade when exposed to
water, oxidizing agents or other gases or liquids. Polymeric
substrates, such as polymeric foils, are often used to package
these products. These foils frequently exhibit a permeability for
water vapor and for oxidizing agents in the range of more than 1
g/(m.sup.2*day). This high degree of permeability is unacceptable
for most of the products packaged in polymer foils.
[0003] One packaging application that uses polymeric substances is
the packaging of organic electroluminescent devices (OLEDs). An
OLED device includes a functional stack formed on a substrate. The
functional stack includes at least one organic functional layer
sandwiched between two conductive layers. The conductive layers
serve as electrodes (cathode and anode). When a voltage is applied
to the electrodes, charge carriers are injected through these
electrodes into the functional layers and upon recombination of the
charge carriers, visible radiation can be emitted
(electroluminescence). The functional stack of the OLED is very
sensitive to moisture and oxidizing agents, which can cause
oxidation of the metals of the electrodes or deterioration of the
organic functional layers. The next generation of organic
electroluminescent devices are likely to be arranged on flexible
substrates, such as polymeric substrates, and are under current
investigation. For a sufficient OLED lifetime, polymeric substrates
with a permeability for water or oxidizing agents below 10.sup.-6
g/(m.sup.2 day) are desirable.
[0004] Patent application WO 00/48749 A1 describes a method of
reinforcing polymeric foils with thin ceramic barrier layers in
order to block out gases or liquids more efficiently than when only
polymeric foils are used. Ceramic layers frequently have defects in
their microstructures that can serve as continuous paths for gases
and water vapor to pass through the ceramic barrier layers. These
defects lead to a decreased ability of the ceramic barrier layers
to serve as a barrier. In this context, all pathways through the
inorganic, ceramic barrier layers are called defects. Defects in
the context of this specification include pinholes, grain
boundaries, shadowing effects, and impurities, as well as other
imperfections in a material.
[0005] Patent publication WO 01/81649 A1 describes a method of
depositing several thin ceramic barrier layers on top of each other
on polymeric substrates to enhance the barrier abilities of the
polymeric substrates. This publication suggests decoupling defects
in successive ceramic barrier layers by changing the deposition
parameters and growth conditions for the deposition of the ceramic
barrier layers. According to the publication, this method should
lead to mismatched subsequent barrier layers that exhibit different
microstructures and therefore the paths for gases and water vapor
permeation are degraded, leading to enhanced barrier abilities.
Experiments carried out by the inventors indicate that ceramic
barrier stacks produced by this method exhibit enhanced barrier
abilities, but show no major improvements over applying a single
ceramic barrier layer when defects larger than grain boundaries,
e.g., pinholes or shadowing effects, are present.
SUMMARY
[0006] There is a need for polymeric substrates with improved
barrier abilities. The present invention can meet these needs by
forming an arrangement of barrier layers on a polymeric
substrate.
[0007] Methods for forming an arrangement of two ceramic barrier
layers on a polymeric substrate are described. In one
implementation, the method includes applying a first barrier layer
on a substrate. The surface of the first barrier layer is then
modified to introduce new nucleation sites on the surface of the
first layer. A second ceramic barrier layer is then formed on the
first barrier layer using the new nucleation sites.
[0008] Aspects of the techniques described herein may include none,
or one or more, of the following advantages. The new nucleation
sites on the first barrier layer can serve as a starting point for
the formation of the second ceramic barrier layer. Due to
thermodynamics, the second ceramic barrier layers can be formed on
the first barrier layers without continuing all the defects, such
as pinholes and grains, of the first layer throughout the barrier
layer. At least two thermodynamically decoupled layers may be grown
on top of each other with independent nucleation for each
layer.
[0009] Using methods described herein changes the grain boundaries
on the surface of the first ceramic barrier layer. Because the
grain boundaries can be reproduced in the second layer if no new
nucleation is introduced, then the defects may form a path for
water and oxidizing agents to travel through the ceramic barrier
layers. Introducing new nucleation sites can ensure that subsequent
layers can be formed on a ceramic barrier layer independent from
the morphology and the energetic conditions of the ceramic layer.
The nucleation can be sensitive to the kinetic energy and mobility
of the molecules on the surface of a layer on an atomic scale. An
arrangement of at least two ceramic barrier layers on a polymeric
substrate formed by the methods described herein may be less
permeable for gases and liquids than barrier stacks produced by
conventional methods.
BRIEF DESCRIPTION OF THE DRAWINGS
[0010] FIGS. 1A to 1C show one embodiment of the inventive method
in a cross-sectional view.
[0011] FIG. 2 shows a cross-section of an OLED device produced
according to one embodiment of the method of the invention.
DETAILED DESCRIPTION
[0012] A method for forming an arrangement of two ceramic barrier
layers on a polymeric substrate includes applying a first barrier
layer on the substrate. The surface of the first barrier layer is
then modified to introduce new nucleation sites on the surface of
the first layer. A second ceramic barrier layer is then formed on
the first barrier layer using the new nucleation sites.
[0013] The introduction of new nucleation sites on the surface of
the first layer can be performed by chemical surface modification,
mechanical surface modification or by the application of
nucleation-promoting material on the surface of the first layer.
The chemical surface modification can be performed by saturating
"dangling" unsaturated bonds on the surface of the first layer or
by changing the lattice parameters of the surface of the first
layer by, e.g., oxidation. Alternatively, or in addition, the
chemical surface modification can include acid treatment, base
treatment, water vapor treatment, plasma treatment or ozone
treatment. These modification methods can change the surface and
introduce new nucleation sites on the surface of the first layer
very efficiently.
[0014] Modifying the surface mechanically can include ion-milling,
nano-grinding, melting the surface with a laser-beam or tempering.
During ion-milling, the surface of a barrier layer can be treated
with ion beams, such as argon ion beams or oxygen ion beams, to
change the topology of the surface. During nano-grinding, the
surface of the barrier layer can be polished using abrasive
particles sized in the nanometer range. Tempering includes curing
barrier layer by applying temperatures higher than temperatures
applied during the formation of the barrier layer and to at least a
partial rearrangement of the crystal lattice of the surface of this
layer. Melting the surface with a laser-beam involves melting areas
of the first ceramic barrier layer to rearrange the crystal
lattice.
[0015] The surface of the a ceramic barrier layer can also be doped
with nucleation promoting materials. The materials can be selected
to have a small critical nucleus. The critical nucleus can include
a single atom or molecule. The critical nucleus denotes the minimum
number of atoms or molecules required to form a stable grain. The
nucleation promoting materials can be selected from a group of
metals, metal nitrides, metal oxides, silicon, silicon nitride and
silicon oxide. Specifically, nucleation promoting materials can be
selected from tantalum, chromium, tungsten, molybdenum, niobium,
titanium, tantalum nitride, titanium nitride, tantalum oxide and
titanium oxide. These materials are able to serve as nucleation
sites for the growth of the second ceramic barrier layer. The
nucleation promoting materials do not have to build up a continuous
layer on the surface of the ceramic barrier layer. The deposited
amount of nucleation promoting material on the surface of the first
layer can be below the mass needed to create a monomolecular layer,
i.e., the surface of the ceramic barrier layer need only be doped
with the nucleation promoting material.
[0016] In one implementation, a ceramic material that is selected
from one or more materials of a metal, metal oxides, metal
nitrides, metal oxynitrides, silicon, silicon oxides, silicon
nitrides and silicon oxynitrides is used to form ceramic barrier
layers. The metal for these metal nitrides, metal oxides or metal
oxynitrides can be aluminum. These ceramic materials are able to
serve as barrier layers that block out gases or liquids. Apart from
these materials, other ceramic materials including predominately
inorganic and non-metallic compounds or elements can be used. Each
ceramic barrier layer can be of the same material. Alternatively,
each ceramic barrier layer can include a different material than
the other ceramic barrier layers.
[0017] Forming subsequent ceramic barrier layers can include
deposition techniques, such as chemical vapor deposition (CVD) or
physical vapor deposition (PVD). These methods can be used to
deposit ceramic barrier layers of high quality on substrates.
[0018] The first barrier layer can be formed on a flexible,
transparent substrate, e.g., polyethyleneterepthalate (PET). In one
implementation, flexible, transparent substrates are used in
organo-optical devices, such as the abovementioned OLEDs, because
these substrates can be transparent to the light emitted by the
OLEDs.
[0019] In one implementation, a third ceramic barrier layer is
deposited on the surface of the second ceramic barrier layer by
repeating the steps of introducing nucleation sites and forming a
barrier layer using the new nucleation sites. In this
implementation, the surface of the second ceramic barrier layer is
also modified in order to introduce new nucleation sites. These new
nucleation sites can serve as starting points for the deposition of
the third ceramic barrier layer. An arrangement with three or more
ceramic barrier layers can be used for applications where an
extremely low permeation rate through the barrier layers for gases
and liquids is necessary.
[0020] In forming the first, second and subsequent barrier layers,
the barrier layers can have a thickness of about 1 to about 250 nm,
such as a thickness of about 10 to 100 nm. Such thin layers can be
used as barrier layers, for example, for transparent substrates on
flexible OLED devices, because the light emitted by the OLED can
pass through the thin barrier layers.
[0021] In one implementation, the arrangement of the ceramic
barrier layers on the polymeric substrate produced by the methods
described above can be used to build up organic electrical devices,
such as integrated plastic circuits or flexible organic light
sensors such as organic solar cells or photodetectors. Therefore it
is possible to form an organic functional layer after forming the
second barrier layer. In this implementation, the arrangement of
the substrate and the ceramic barrier layers can serve as a barrier
stack to protect the sensitive organic functional layer from
moisture or oxidizing agents.
[0022] In another implementation, subsequent steps of forming an
OLED are performed. A first electrically conductive layer can be
formed on the second barrier layer, and a functional organic layer
can be formed on the first electrically conductive layer. A second
electrically conductive layer can be formed on the functional
organic layer. The conductive layers, which, for example, can
comprise indium-tin oxide (ITO), can easily be patterned, e.g., to
form stripes. The first electrically conductive layer can be
patterned into a plurality of parallel electrode stripes, whereas
the second electrically conductive layer can also be formed into a
plurality of parallel electrode stripes running perpendicular to
the electrode stripes of the first conductive layer. The crossing
points between the electrode stripes of the first and of the second
conductive layers can form pixels of the OLED device.
[0023] Furthermore, it is possible to form an encapsulation over an
OLED device that is built up on a barrier arrangement.
Encapsulation can include forming a fourth ceramic barrier layer
over the second electrically conductive layer of the OLED device.
The surface of the fourth barrier layer is subsequently modified to
introduce new nucleation sites on the surface. Afterwards, a fifth
ceramic barrier layer is formed on the fourth ceramic barrier
layer. A similar encapsulation method can be use with other
electrical devices
[0024] FIG. 1A shows a first ceramic barrier layer 5 formed on a
substrate 1. The arrows 2 denote the formation of the first ceramic
barrier layer 5.
[0025] FIG. 1B is a cross-sectional view of the substrate 1 with
one barrier 5 layer having a modified surface 5A. The surface 5A of
the first ceramic barrier layer 5 is modified by chemical or
mechanical modification or by introduction of nucleation promoting
material to introduce new nucleation sites. The arrows 3 denote the
direction of the surface modification.
[0026] FIG. 1C shows an arrangement of the substrate 1, the first
ceramic barrier layer 5 and the second ceramic barrier layer 10
after depositing the second barrier layer 10. The second ceramic
barrier layer 10 is deposited on the modified surface 5A of the
first ceramic barrier layer 5. The new nucleation sites of the
surface 5A cause the first barrier layer to have a different
morphology in the areas of the first ceramic barrier layer 5 that
are located below the surface 5A as the corresponding portions of
the surface. The second layer 10 can be grown on the first ceramic
barrier layer with independent nucleation and different grain
boundaries.
[0027] FIG. 2 is a cross-sectional view of an OLED device formed by
methods described herein. The electrical functional stack of the
OLED device has at least one organic functional layer 20 inserted
between a first electrically conductive layer 15 and a second
electrically conductive layer 25. The electrical, functional stack
is formed on a barrier arrangement consisting of the polymeric
substrate 1, the first ceramic barrier layer 5 and the second
ceramic barrier layer 10, which is deposited on the modified
surface 5A of the first ceramic barrier layer using new nucleation
sites. An encapsulation 40 consisting of the third ceramic barrier
layer 30 and the fourth ceramic barrier layer 35 is formed on top
of the electrical, functional stack of the OLED device, sealing the
electrical, functional stack of the device from the environment.
The surface 30A of the third ceramic barrier layer 30 includes the
nucleation sites for forming the fourth ceramic barrier layer 40.
Contact pads 50, 60, which are connected to the first 15 and the
second electrically conductive layer 25 are present to enable an
electrical connection to the OLED. Therefore, the methods described
above can provide an OLED device with enhanced lifetime and can be
formed with a tight encapsulation.
* * * * *