U.S. patent application number 10/846749 was filed with the patent office on 2007-11-29 for barrier films for plastic substrates fabricated by atomic layer deposition.
Invention is credited to Peter Francis Carcia, Robert Scott McLean.
Application Number | 20070275181 10/846749 |
Document ID | / |
Family ID | 33476779 |
Filed Date | 2007-11-29 |
United States Patent
Application |
20070275181 |
Kind Code |
A1 |
Carcia; Peter Francis ; et
al. |
November 29, 2007 |
Barrier films for plastic substrates fabricated by atomic layer
deposition
Abstract
Gas permeation barriers can be deposited on plastic or glass
substrates by atomic layer deposition (ALD). The use of the ALD
coatings can reduce permeation by many orders of magnitude at
thicknesses of tens of nanometers with low concentrations of
coating defects. These thin coatings preserve the flexibility and
transparency of the plastic substrate. Such articles are useful in
container, electrical and electronic applications.
Inventors: |
Carcia; Peter Francis;
(Wilmington, DE) ; McLean; Robert Scott;
(Wilmington, DE) |
Correspondence
Address: |
E I DU PONT DE NEMOURS AND COMPANY;LEGAL PATENT RECORDS CENTER
BARLEY MILL PLAZA 25/1128
4417 LANCASTER PIKE
WILMINGTON
DE
19805
US
|
Family ID: |
33476779 |
Appl. No.: |
10/846749 |
Filed: |
May 14, 2004 |
Related U.S. Patent Documents
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Application
Number |
Filing Date |
Patent Number |
|
|
60471020 |
May 16, 2003 |
|
|
|
Current U.S.
Class: |
427/582 |
Current CPC
Class: |
H01L 21/31616 20130101;
H01L 21/3141 20130101; H01L 2924/0002 20130101; H01L 23/564
20130101; C23C 16/45555 20130101; C23C 16/403 20130101; G02F
1/133345 20130101; H01L 51/5253 20130101; H01L 21/0228 20130101;
H01L 2924/0002 20130101; Y02E 10/549 20130101; H01L 2924/12044
20130101; H01L 2924/00 20130101; C23C 16/45525 20130101; H01L
21/02178 20130101; Y10T 428/26 20150115; H01L 51/0096 20130101 |
Class at
Publication: |
427/582 |
International
Class: |
C23C 16/48 20060101
C23C016/48 |
Claims
1. An article comprising: a) a substrate made of a material
selected from the group consisting of plastic and glass, and b) a
gas permeation barrier deposited on said substrate by atomic layer
deposition.
2. An article comprising: a) a substrate made of a material
selected from the group consisting of plastic and glass, b) an
adhesion layer coated, and c) a gas permeation barrier deposited an
said substrate by atomic layer deposition.
3. An article comprising: a) a substrate made of a material
selected from the group consisting of plastic and glass, b) an
organic semiconductor, and c) a gas permeation barrier deposited by
atomic layer deposition.
4. An article comprising: a) a substrate made of a material
selected from the group consisting of plastic and glass, b) a
liquid crystal polymer, and c) a gas permeation barrier deposited
by atomic layer deposition
5. The article of any one of claims 1, 2, 3 or 4 where the article
is an enclosed container.
6. The article of any one of claims 1, 2, 3 or 4 where the article
is an electrical or electronic device.
7. The article of any one of claims 1, 2, 3 or 4 where the article
is a light-emitting polymer device.
8. The article of any one of claims 1, 2, 3 or 4 where the article
is an organic light emitting diode.
9. The article of any one of claims 1, 2, 3 or 4 where the article
is a transistor.
10. The article of any one of claims 1, 2, 3 or 4 where the article
is a circuit comprising a light emitting polymer device.
11. The article of any one of claims 1, 2, 3 or 4 where the article
is a circuit comprising a transistor.
12. The article of any one of claims 1, 2, 3 or 4 wherein the
article is an organic photovoltaic cell.
13. The article of any one of claims 1, 2, 3 or 4 wherein the a gas
permeation barrier deposited by atomic layer deposition is
deposited on a top side and a bottom side of the polymer.
14. A second article comprising a plurality of layers, each layer
comprising one article, as described in any one of claims 1, 2, 3
or 4, wherein articles are in contact to each other.
15. The second article of claim 11 wherein the articles of any one
of claims 1, 2, 3 or 4 are in contact with each other by lamination
means.
16. The article of any one of claims 1, 2, 3 or 4 wherein the
article is a liquid crystal display.
Description
FIELD OF THE INVENTION
[0001] The present invention relates to an article comprising a
plastic or glass substrate and an atmospheric gas penetration
barrier fabricated by atomic layer deposition. The article may be a
component of an electrical or electronic device such as an organic
light emitting diode. The article may also be used as a container
for applications where gas permeation is important.
TECHNICAL BACKGROUND
[0002] Featherby and Dehaven (WO 2001067504) disclose a
hermetically coated device. Formation of such a device includes the
steps of providing an integrated semiconductor circuit die,
applying a first layer comprising an inorganic material which
envelopes the circuit die, and applying a second layer enveloping
the circuit die.
[0003] Aintila (WO 9715070 A2) discloses contact bump formation on
metallic contact pad areas on the surface of a substrate comprising
using atomic layer epitaxy to form an oxide layer on the substrate
which is opened at required points in the subsequent process
step.
[0004] Aftergut and Ackerman (U.S. Pat. No. 5,641,984) disclose a
hermetically packaged radiation imager including a moisture
barrier. A dielectric material layer is deposited in an atomic
layer expitaxy technique as part of the sealing structure.
[0005] Aftergut and Ackerman (U.S. Pat. No. 5,707,880) disclose a
hermetically packaged radiation imager including a moisture barrier
comprising a dielectric material layer deposited by atomic layer
expitaxy.
[0006] None of the references disclosed a permeation barrier
comprising a polymer or glass substrate.
SUMMARY OF THE INVENTION
[0007] This invention describes an article comprising: [0008] a) a
substrate made of a material selected from the group consisting of
plastic and glass, and [0009] b) a film deposited upon said
substrate by atomic layer deposition. [0010] The present invention
is further an article comprising: [0011] a) A substrate made of a
material selected from the group consisting of plastic and glass;
[0012] b) an adhesion layer coated; and [0013] c) a gas permeation
barrier deposited by atomic layer deposition. Another embodiment of
the present invention is an article comprising: [0014] a) a
substrate made of a material selected from the group consisting of
plastic and glass; [0015] b) an organic semiconductor, and [0016]
c) a gas permeation barrier deposited by atomic layer deposition. A
yet further embodiment of the present invention is an article
comprising: [0017] a) A substrate made of a material selected from
the group consisting of plastic and glass, [0018] b) A liquid
crystal polymer, and [0019] c) a gas permeation barrier deposited
by atomic layer deposition
[0020] The invention further describes an embodiment that is an
enclosed container.
[0021] Another embodiment of the present invention is an electrical
or electronic device.
[0022] Yet another embodiment of the present invention is a
light-emitting polymer device.
[0023] Yet another embodiment of the present invention is liquid
crystalline polymer device.
[0024] The invention further describes an organic light emitting
diode.
[0025] Another embodiment of the present invention is a
transistor.
[0026] Yet another embodiment of the present invention is a circuit
comprising a light emitting polymer device.
[0027] A still further article is an organic photovoltaic cell.
[0028] A second article taught herein comprises a plurality of
layers, each layer comprising one article, as described above,
wherein the articles are in contact with each other. In one
embodiment of this second article of the articles above are in
contact with each other by lamination means.
BRIEF DESCRIPTION OF THE DRAWINGS
[0029] FIG. 1 shows a light-emitting polymer device with a barrier
substrate and a barrier top coat.
[0030] FIG. 2 shows a light-emitting polymer device with a barrier
substrate and a barrier capping layer.
[0031] FIG. 3 shows an organic transistor with a barrier substrate
and a barrier capping layer.
[0032] FIG. 4 shows an organic transistor with a barrier substrate
and a barrier capping layer.
[0033] FIG. 5 shows the measured optical transmission through 0.002
inch thick polyethylene naphthalate (PEN) coated with 25 nm of
Al.sub.2O.sub.3 barrier film.
DETAILED DESCRIPTION
[0034] The permeation of O.sub.2 and H.sub.2O vapor through polymer
films is facile. To reduce permeability for packaging applications,
polymers are coated with a thin inorganic film. Al-coated polyester
is common. Optically transparent barriers, predominantly SiOx or
AlO.sub.y, made either by physical vapor deposition (PVD) or
chemical vapor deposition (CVD), are also used in packaging. The
latter films are commercially available and are known in the
industry as "glass-coated" barrier films. They provide an
improvement for atmospheric gas permeation of about 10.times.,
reducing transmission rates to about 1.0 cc O.sub.2/m.sup.2/day and
1.0 ml H.sub.2O/m.sup.2/day through polyester film (M. Izu, B.
Dotter, and S. R. Ovshinsky, J. Photopolymer Science and
Technology., vol. 8 1995 pp 195-204). While this modest improvement
is a reasonable compromise between performance and cost for many
high-volume packaging applications, this performance falls far
short of packaging requirements in electronics. Electronic
packaging usually requires at least an order of magnitude longer
desired lifetime than, for example, beverage containing. As an
example, flexible displays based on organic light emitting polymers
(OLEDs), fabricated on flexible polyester substrates need an
estimated barrier improvement of 10.sup.5-10.sup.6.times. for
exclusion of atmospheric gases since gases can seriously degrade
both the light-emitting polymer and the water-sensitive metal
cathode which can frequently be Ca or Ba.
[0035] Because of their inherent free volume fraction, the
intrinsic permeability of polymers is, in general, too high by a
factor 10.sup.4-10.sup.6 to achieve the level of protection needed
in electronic applications, such as flexible OLED displays. Only
inorganic materials, with essentially zero permeability, can
provide adequate barrier protection. Ideally, a defect-free,
continuous thin-film coating of an inorganic should be impermeable
to atmospheric gases. However, the practical reality is that thin
films have defects, such as pinholes, either from the coating
process or from substrate imperfections which compromise barrier
properties. Even grain boundaries in films can present a pathway
for facile permeation. For the best barrier properties, films
should be deposited in a clean environment on clean, defect-free
substrates. The film structure should be amorphous. The deposition
process should be non-directional, (i.e. CVD is preferred over PVD)
and the growth mechanism to achieve a featureless microstructure
would ideally be layer-by-layer to avoid columnar growth with
granular microstructure.
[0036] Atomic layer deposition (ALD) is a film growth method that
satisfies many of these criteria for low permeation. A description
of the atomic layer deposition process can be found in "Atomic
Layer Epitaxy," by Tuomo Suntola in Thin Solid Films, vol. 216
(1992) pp. 84-89. As its name implies, films grown by ALD form by a
layer by layer process. In general, a vapor of film precursor is
absorbed on a substrate in a vacuum chamber. The vapor is then
pumped from the chamber, leaving a thin layer of absorbed
precursor, usually essentially a monolayer, on the substrate. A
reactant is then introduced into the chamber under thermal
conditions, which promote reaction with the absorbed precursor to
form a layer of the desired material. The reaction products are
pumped from the chamber. Subsequent layers of material can be
formed by again exposing the substrate to the precursor vapor and
repeating the deposition process. ALD is in contrast to growth by
common CVD and PVD methods where growth is initiated and proceeds
at finite numbers of nucleation sites on the substrate surface. The
latter technique can lead to a columnar microstructures with
boundaries between columns along which gas permeation can be
facile. ALD can produce very thin films with extremely low gas
permeability, making such films attractive as barrier layers for
packaging sensitive electronic devices and components built on
plastic substrates.
[0037] This invention describes barrier layers formed by ALD on
plastic substrates and useful for preventing the passage of
atmospheric gases. The substrates of this invention include the
general class of polymeric materials, such as described by but not
limited to those in Polymer Materials, (Wiley, New York, 1989) by
Christopher Hall or Polymer Permeability, (Elsevier, London, 1985)
by J. Comyn. Common examples include polyethylene terephthalate
(PET) and polyethylene naphthalate (PEN), which are commercially
available as film base by the roll. The materials formed by ALD,
suitable for barriers, include oxides and nitrides of Groups IVB,
VB, VIB, IIIA, and IVA of the Periodic Table and combinations
thereof. Of particular interest in this group are SiO.sub.2,
Al.sub.2O.sub.3, and Si.sub.3N.sub.4. One advantage of the oxides
in this group is optical transparency which is attractive for
electronic displays and photovoltaic cells where visible light must
either exit or enter the device. The nitrides of Si and Al are also
transparent in the visible spectrum.
[0038] The precursors used in the ALD process to form these barrier
materials can be selected from precursors known to those skilled in
the art and tabulated in published references such as M. Leskela
and M. Ritala, "ALD precursor chemistry: Evolution and future
challenges," in Journal de Physique IV, vol. 9, pp 837-852 (1999)
and references therein.
[0039] The preferred range of substrate temperature for
synthesizing these barrier coatings by ALD is 50.degree.
C.-250.degree. C. Too high temperature (>250.degree. C.) is
incompatible with processing of temperature-sensitive plastic
substrates, either because of chemical degradation of the plastic
substrate or disruption of the ALD coating because of large
dimensional changes of the substrate.
[0040] The preferred thickness range for barrier films is 2 nm-100
nm. A more preferred range is 2-50 nm. Thinner layers will be more
tolerant to flexing without causing the film to crack. This is
extremely important for polymer substrates where flexibility is a
desired property. Film cracking will compromise barrier properties.
Thin barrier films also increase transparency in the cases of
electronic devices where input or output of light is important.
There may be a minimum thickness corresponding to continuous film
coverage, for which all of the imperfections of the substrate are
covered by the barrier film. For a nearly defect-free substrate,
the threshold thickness for good barrier properties was estimated
to be at least 2 nm, but may be as thick as 10 nm.
[0041] Some oxide and nitride barrier layers coated by ALD may
require a "starting" or "adhesion layer" to promote adhesion to the
plastic substrate or the article requiring protection. The
preferred thickness of the adhesion layer is in the range of 1
nm-100 nm. The choice of the materials for the adhesion layer will
be from the same group of barrier materials. Aluminum oxide and
silicon oxide are preferred for the adhesion layer, which may also
be deposited by ALD, although other methods such as chemical and
physical vapor deposition or other deposition methods known in the
art may also be suitable.
[0042] The basic building block of the barrier structure is either:
(A) a single barrier layer with or without an adhesion layer,
coated by ALD on a plastic or glass substrate, or (B) a barrier
layer with or without an adhesion layer, coated by ALD on each side
of a plastic substrate. This basic structure can then be combined
in any number of combinations by laminating this building block to
itself to form multiple, independent barrier layers. It is known in
the art of barrier coatings that multiple layers, physically
separate, can improve the overall barrier properties by much more
than a simple multiplicative factor, corresponding the number of
layers. This is demonstrated, for example, in J. Phys. Chem. B
1997, vol. 101, pp 2259-2266, "Activated rate theory treatment of
oxygen and water transport through silicon oxide/poly(ethylene
terephthalate) composite barrier structures," by Y. G. Tropsha and
N. G. Harvey. This follows because the path for diffusing gas
molecules is tortuous through multiple barrier layers that are
separated. The effective diffusion path is much larger than the sum
of the thickness of the individual layers.
[0043] Another barrier configuration involves directly coating the
electronic or electro-optical device, requiring protection. In this
regard, ALD is particularly attractive because it forms a highly
conformal coating. Therefore devices with complex topographies can
be fully coated and protected.
EXAMPLES
Example 1
[0044] FIG. 1 shows a schematic representation of a light-emitting
polymer device. For simplicity, the light emitting polymer device
is shown as the light-emitting polymer (LEP) sandwiched between two
electrodes. In practice, a hole-conducting and/or
electron-conducting layer can be inserted between the appropriate
electrode and the LEP layer to increase device efficiency. The
anode is a layer of indium-tin oxide and the cathode is a Ca/Al
layer composite. With a voltage applied between the electrodes,
holes injected at the anode and electrons injected at the cathode
combine to form excitons which decay radioactively, emitting light
from the LEP. The LEP is typically a photosensitive polymer such as
poly-phenylene vinylene (PPV) or its derivatives. The cathode is
frequently Ba or Ca and is extremely reactive with atmospheric
gases, especially water vapor. Because of the use of these
sensitive materials, the device packaging needs to exclude
atmospheric gases in order to achieve reasonable device lifetimes.
In FIG. 1, the package is comprised of a barrier-substrate which
can be plastic or glass on which the LEP device is deposited and
then a top coated barrier film. The substrate is comprised of a
polyester film, polyethylene naphthalate (PEN) which is 0.004 inch
thick. Each side of the PEN film is coated with a 50 nm thick film
of Al.sub.2O.sub.3, which is deposited by atomic layer deposition,
using trimethylaluminum as the precursor for aluminum and ozone
(O.sub.3) as the oxidant. The substrate temperature during
deposition is 150.degree. C. In the ALD process, the PEN substrate
is placed in a vacuum chamber equipped with a mechanical pump. The
chamber is evacuated. The trimethylaluminum precursor is admitted
to the chamber at a pressure of 500 millitorr for approximately 2
seconds. The chamber is then purged with argon for approximately 2
seconds. The oxidant, ozone, is then admitted to the chamber at
approximately 500 millitorr for approximately 2 seconds. Finally,
the oxidant is purged with argon for approximately 2 seconds. This
deposition process is repeated approximately 50 times to obtain a
coating approximately 100 nanometers in thickness. The
Al.sub.2O.sub.3 layer is optically transparent in the visible. The
coated substrate may be flexed without loss of the coating. One of
the Al.sub.2O.sub.3 barriers is coated with indium-tin oxide
transparent conductor by rf magnetron sputtering from a 10% (by
weight) Sn-doped indium oxide target. The ITO film thickness is 150
nm. The LEP is spin coated on the ITO electrode, after which a
cathode of 5 nm Ca with about 1 .mu.m of Al are thermally
evaporated from Ca and Al metal sources, respectively. This LEP
device is then coated with a 50 nm-thick, top barrier layer film of
Al.sub.2O.sub.3, deposited by atomic layer deposition, again using
trimethylaluminum as the precursor for aluminum and ozone (O.sub.3)
as the oxidant. The resulting structure is now impervious to
atmospheric gases.
Example 2
[0045] Another version of a packaging scheme is shown in FIG. 2.
The top-coated barrier is replaced by an identical substrate
barrier structure (Al.sub.2O.sub.3/PEN/Al.sub.2O.sub.3) without an
ITO electrode as described in the Example 1 above. This capping
barrier structure is sealed to the substrate barrier using a layer
of epoxy.
Example 3
[0046] FIG. 3 illustrates a protection strategy with ALD barrier
coatings for an organic transistor. The transistor shown is a
bottom gate structure with the organic semiconductor as the final
or top layer. Because most organic semiconductors are air sensitive
and prolonged exposure degrades their properties, protection
strategies are necessary. In FIG. 3 the package is comprised of a
barrier-substrate on which the transistor is deposited and then
sealed to an identical capping barrier structure. The substrate is
comprised of a polyester film, polyethylene naphthalate (PEN),
0.004 inch thick. Each side of the PEN film is coated with a 50 nm
thick film of Al.sub.2O.sub.3, which is deposited by atomic layer
deposition, using trimethylaluminum as the precursor for aluminum
and ozone (O.sub.3) as the oxidant. The substrate temperature
during deposition is 150.degree. C. In the ALD process, the PEN
substrate is placed in a vacuum chamber equipped with a mechanical
pump. The chamber is evacuated. The trimethylaluminum precursor is
admitted to the chamber at a pressure of 500 millitorr for
approximately 2 seconds. The chamber is then purged with argon for
approximately 2 seconds. The oxidant, ozone, is then admitted to
the chamber at approximately 500 millitorr for approximately 2
seconds. Finally, the oxidant is purged with argon for
approximately 2 seconds. This deposition process is repeated
approximately 50 times to obtain a coating approximately 100
nanometers in thickness. A gate electrode of 100 nm thick Pd metal
is ion-beam sputtered through a shadow mask on to the barrier film
of Al.sub.2O.sub.3. A gate dielectric of 250 nm Si.sub.3N.sub.4 is
then deposited by plasma-enhanced chemical vapor deposition, also
through a mask to allow contact to the metal gate. This is followed
by patterning of 100 nm-thick Pd source and drain electrodes, ion
beam sputtered on the gate dielectric. Finally the top organic
semiconductor, e.g. pentacene, is thermally evaporated through a
shadow mask that allows contact to source-drain electrodes. The
entire transistor is capped with an
Al.sub.2O.sub.3/PEN/Al.sub.2O.sub.3 barrier-structure, sealed to
substrate barrier with an epoxy sealant.
Example 4
[0047] In FIG. 4, the capping barrier of Example 3 can be replaced
by a single layer of 50 nm-thick Al.sub.2O.sub.3, deposited by
atomic layer deposition, using trimethylaluminum as the precursor
for aluminum and ozone (O.sub.3) as the oxidant. Both packaging
structures for the organic transistor device are impervious to
atmospheric gases. The plastic substrate with barrier coatings can
also be replaced by an impermeable glass substrate. The barrier
capping layer is comprised of an initial adhesion layer of silicon
nitride deposited by plasma-enhanced chemical vapor deposition at
room temperature, followed by a 50 nm-thick Al203 barrier,
deposited by atomic layer deposition, as described in Example
3.
Example 5
[0048] A substrate film of polyethylene terephthalate (PEN), 0.002
inches thick, was coated by atomic layer deposition at 120.degree.
C. with Al.sub.2O.sub.3 about 25 nm thick on one side of the PEN
substrate. Prior to evaluating its permeability properties the
coated PEN substrate was flexed at least once to a radius of at
least 1.5 inches to remove the coated Al.sub.2O.sub.3-coated PEN
substrate from the rigid silicon carrier wafer, to which it was
attached with Kapton.RTM. tape during ALD deposition. The oxygen
transport rate with 50% relative humidity was measured with a
commercial instrument (MOCON Ox-Tran 2/20) through the film with
Al.sub.2O.sub.3 deposited by ALD. After 80 hours of measurement
time, within the measurement sensitivity (0.005
cc-O.sub.2/m.sup.2/day), no oxygen transport (<0.005
cc/m.sup.2/day) through the barrier film was detected, in spite of
the severe prior flexing. For comparison, we measured oxygen
transport of about 10 cc-O.sub.2/m2/day through an uncoated PEN
substrate. FIG. 5 shows that the optical transmission for this
Al.sub.2O.sub.3-coated PEN barrier and uncoated PEN is the same
(>80% transmittance above 400 nm) verifying the transparency of
the thin Al.sub.2O.sub.3 barrier coating.
* * * * *