U.S. patent application number 15/814316 was filed with the patent office on 2018-03-15 for organic thin film ink compositions and methods.
This patent application is currently assigned to Kateeva, Inc.. The applicant listed for this patent is Kateeva, Inc.. Invention is credited to Michelle Chan, Jianglong Chen, Rajsapan Jain, Inna Tregub.
Application Number | 20180072903 15/814316 |
Document ID | / |
Family ID | 55163710 |
Filed Date | 2018-03-15 |
United States Patent
Application |
20180072903 |
Kind Code |
A1 |
Jain; Rajsapan ; et
al. |
March 15, 2018 |
Organic Thin Film Ink Compositions and Methods
Abstract
The present teachings relate to various embodiments of an ink
composition, which once printed and cured forms an organic thin
film on a substrate such as, but not limited by, an OLED device
substrate. Various embodiments of the ink can be printed using an
industrial inkjet printing system that can be housed in a gas
enclosure, which gas enclosure defines an interior that has a
controlled environment maintained as an inert and substantially
low-particle process environment. Patterned printing of an organic
thin film on a substrate, for example, but not limited by, an OLED
device substrate, in such a controlled environment can ensure a
high-volume, high yield process for a variety of OLED devices.
Inventors: |
Jain; Rajsapan; (Sunnyvale,
CA) ; Chan; Michelle; (San Francisco, CA) ;
Tregub; Inna; (San Jose, CA) ; Chen; Jianglong;
(San Jose, CA) |
|
Applicant: |
Name |
City |
State |
Country |
Type |
Kateeva, Inc. |
Newark |
CA |
US |
|
|
Assignee: |
Kateeva, Inc.
Newark
CA
|
Family ID: |
55163710 |
Appl. No.: |
15/814316 |
Filed: |
November 15, 2017 |
Related U.S. Patent Documents
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Application
Number |
Filing Date |
Patent Number |
|
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14806276 |
Jul 22, 2015 |
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15814316 |
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62084751 |
Nov 26, 2014 |
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62035600 |
Aug 11, 2014 |
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62029228 |
Jul 25, 2014 |
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Current U.S.
Class: |
1/1 |
Current CPC
Class: |
H01L 51/56 20130101;
H01L 51/5253 20130101; H01L 51/0007 20130101; C09D 133/14 20130101;
C09D 11/30 20130101; H01L 21/823431 20130101; H01L 51/0004
20130101; C09D 11/101 20130101 |
International
Class: |
C09D 11/30 20140101
C09D011/30; C09D 133/14 20060101 C09D133/14; H01L 51/52 20060101
H01L051/52; H01L 51/00 20060101 H01L051/00; C09D 11/101 20140101
C09D011/101; H01L 21/8234 20060101 H01L021/8234 |
Claims
1. An organic light emitting device comprising: an optoelectronic
device substrate; and an encapsulation layer over the
optoelectronic device substrate, the encapsulation layer comprising
a polymeric film comprising: 75-95 wt. % polymerized polyethylene
glycol dimethacrylate monomer, polymerized polyethylene glycol
diacrylate monomer, or a combination thereof; 4-10 wt. %
polymerized pentaerythritol tetraacrylate, polymerized
pentaerythritol tetramethacrylate, or a combination thereof; and
1-15 wt. % of a polymerized spreading modifier, the spreading
modifier having a viscosity in the range from about 14 to about 18
cps at 22.degree. C. and a surface tension in the range from about
35 to about 39 dynes/cm at 22.degree. C. in its unpolymerized
state.
2. The device of claim 1, wherein the optoelectronic device
substrate is an organic light emitting device substrate comprising:
an anode, a cathode, and a light emissive layer.
3. The device of claim 1, wherein the encapsulation layer further
comprises a layer of inorganic material adjacent to the polymeric
film.
4. The device of claim 3, wherein the inorganic material is a metal
oxide.
5. The device of claim 1, wherein the spreading modifier has a
viscosity in the range from about 14 to about 16 cps at 22.degree.
C. and a surface tension in the range from about 35 to about 38
dynes/cm at 22.degree. C. in its unpolymerized state.
6. The device of claim 1, wherein the polymerized spreading
modifier comprises a polymerized alkoxylated aliphatic diacrylate
monomer, a polymerized alkoxylated aliphatic dimethacrylate
monomer, or a combination thereof.
7. The device of claim 5, wherein the polymerized spreading
modifier comprises a polymerized alkoxylated aliphatic diacrylate
monomer, a polymerized alkoxylated aliphatic dimethacrylate
monomer, or a combination thereof.
8. The device of claim 1, wherein the polymeric film comprises
75-95 wt. % polymerized polyethylene glycol dimethacrylate monomer
having a number average molecular weight of about 330 g/mole, and
4-10 wt. % polymerized pentaerythritol tetraacrylate.
9. The device of claim 8, wherein the spreading modifier comprises
polymerized alkoxylated aliphatic diacrylate monomer.
10. The device of claim 1, wherein the polymeric film comprises
85-95 wt. % polymerized polyethylene glycol dimethacrylate monomer,
polymerized the polyethylene glycol diacrylate monomer, or the
combination thereof.
Description
RELATED APPLICATIONS
[0001] The present application is continuation application of U.S.
patent application Ser. No. 14/806,276, filed Jul. 22, 2015. U.S.
patent application Ser. No. 14/806,276 claims priority to: U.S.
provisional patent application No. 62/029,228, filed on Jul. 25,
2014; U.S. provisional patent application No. 62/035,600, filed on
Aug. 11, 2014; and U.S. provisional patent application No.
62/084,751, filed on Nov. 26, 2014, the entire contents of which
are incorporated herein by reference.
FIELD
[0002] The present teachings relate to various embodiments of an
ink composition, and a polymeric thin film formed on a substrate,
such as, but not limited by, an OLED device substrate. Various
embodiments of the ink can be printed using an industrial inkjet
printing system that can be housed in a gas enclosure, which gas
enclosure defines an interior that has a controlled environment
maintained as an inert and substantially low-particle process
environment.
OVERVIEW
[0003] Interest in the potential of organic light-emitting diode
(OLED) display technology has been driven by OLED display
technology attributes that include demonstration of display panels
that have highly saturated colors, are high-contrast, ultrathin,
fast-responding, and energy efficient. Additionally, a variety of
substrate materials, including flexible polymeric materials, can be
used in the fabrication of OLED display technology. Though the
demonstration of displays for small screen applications, primarily
for cell phones, has served to emphasize the potential of the
technology, challenges remain in scaling high volume manufacturing
across a range of substrate formats in high yield.
[0004] With respect to scaling of formats, a Gen 5.5 substrate has
dimensions of about 130 cm.times.150 cm and can yield about eight
26'' flat panel displays. In comparison, larger format substrates
can include using Gen 7.5 and Gen 8.5 mother glass substrate sizes.
A Gen 7.5 mother glass has dimensions of about 195 cm.times.225 cm,
and can be cut into eight 42'' or six 47'' flat panel displays per
substrate. The mother glass used in Gen 8.5 is approximately 220
cm.times.250 cm, and can be cut to six 55'' or eight 46'' flat
panel displays per substrate. One indication of the challenges that
remain in scaling of OLED display manufacturing to larger formats
is that the high-volume manufacture of OLED displays in high yield
on substrates larger than Gen 5.5 substrates has proven to be
substantially challenging.
[0005] In principle, an OLED device may be manufactured by the
printing of various organic thin films, as well as other materials,
on a substrate using an OLED printing system. Such organic
materials can be susceptible to damage by oxidation and other
chemical processes. As such, printing of various organic stack
layers in an inert environment is indicated. Additionally, the need
for a substantially particle-free environment is indicated in order
to realize a high-yield manufacturing process. In addition to the
printing of various layers of an OLED stack into a plurality of
discrete pixel locations, patterned area printing using an
industrial inkjet system can be done. For example, during
fabrication of an OLED device, inkjet printing of various
encapsulation layers can be done. Given the sensitivity of the
various organic materials of an OLED stack that can be damaged by
oxidation and other chemical processes, as well as defects due to
particulate matter in a printed thin layer of a material, the
patterned printing of an encapsulation layer in an inert,
substantially particle free environment is also indicated.
[0006] However, housing an OLED printing system in a fashion that
can be scaled for various substrate sizes and can be done in an
inert, substantially low-particle printing environment can present
a variety of engineering challenges. Manufacturing tools for high
throughput large-format substrate printing, for example, such as
printing of Gen 7.5 and Gen 8.5 substrates, require substantially
large facilities. Accordingly, maintaining a large facility under
an inert atmosphere, requiring gas purification to remove reactive
atmospheric species, such as water vapor and oxygen, as well as
organic solvent vapors, as well as maintaining a substantially
low-particle printing environment, has proven to be significantly
challenging.
[0007] As such, challenges remain in scaling high volume
manufacturing of OLED display technology across a range of
substrate formats in high yield. Accordingly, there exists a need
for various embodiments a gas enclosure system of the present
teachings that can house an OLED printing system, in an inert,
substantially low-particle environment, and can be readily scaled
to provide for fabrication of OLED panels on a variety of
substrates sizes and substrate materials. Additionally, various gas
enclosure systems of the present teachings can provide for ready
access to an OLED printing system from the exterior during
processing and ready access to the interior for maintenance with
minimal downtime.
BRIEF DESCRIPTION OF THE DRAWINGS
[0008] A better understanding of the features and advantages of the
present disclosure will be obtained by reference to the
accompanying drawings, which are intended to illustrate, not limit,
the present teachings.
[0009] FIG. 1 is a schematic section view of an optoelectronic
device, illustrating various aspects of a fabrication.
[0010] FIG. 2(A) and FIG. 2(B) are film profiles of a polymeric
thin film formed on a substrate, according to various embodiments
of compositions, systems and methods of the present teachings. FIG.
2(A) displays a film of 8 .mu.m thickness, which was printed
without incorporating edge compensation. FIG. 2(B) is a film of 16
.mu.m thickness, which was printed using edge compensation.
[0011] FIG. 3 is a flow diagram depicting a process for forming a
polymeric thin film on a substrate, according to various
embodiments of compositions, systems and methods of the present
teachings.
[0012] FIG. 4 is a front perspective view of view of a printing
system tool in accordance with various embodiments of the present
teachings.
[0013] FIG. 5 is a schematic depiction of a UV curing module that
can be used in manufacturing a light emitting device.
[0014] FIG. 6 depicts an expanded iso perspective view of a
printing system in accordance with various embodiments of the
present teachings.
[0015] FIG. 7 is an iso perspective view of a printing system in
accordance with various embodiments of the present teachings.
[0016] FIG. 8 is a schematic view of various embodiments of gas
enclosure assembly and related system components the present
teachings.
[0017] FIG. 9(A) is a graph of the drop volume as a function of
jetting frequency at 22.degree. C. and 25.degree. C. for a
spreading modifier.
[0018] FIG. 9(B) is a graph of the drop velocity as a function of
jetting frequency at 22.degree. C. and 25.degree. C. for a
spreading modifier.
[0019] FIG. 9(C) is a graph of the drop trajectory as a function of
jetting frequency at 22.degree. C. and 25.degree. C. for a
spreading modifier.
[0020] FIG. 10(A) is a graph of the drop volume variation as a
function of jetting frequency at 22.degree. C. and 25.degree. C.
for a spreading modifier.
[0021] FIG. 10(B) is a graph of the drop velocity variation as a
function of jetting frequency at 22.degree. C. and 25.degree. C.
for a spreading modifier.
[0022] FIG. 11(A) is a graph of the ink drop velocity as a function
of jetting frequency at 25.degree. C. for an ink composition.
[0023] FIG. 11(B) is a graph of the ink drop volume as a function
of jetting frequency at 25.degree. C. for an ink composition.
[0024] FIG. 11(C) is a graph of the ink drop trajectory as a
function of jetting frequency at 25.degree. C. for an ink
composition.
[0025] FIG. 12 is a graph of the volume change of the printed ink
compositions that occurs upon curing as a function of
photoinitiator concentration.
[0026] FIG. 13 is a graph showing the correlation between weight
loss and photoinitiator concentration for a film cured at
120.degree. C., as measured by thermogravimetric analysis.
DETAILED DESCRIPTION OF THE DISCLOSURE
[0027] The present teachings relate to various embodiments of a ink
composition, which once printed and cured forms a polymeric thin
film on a substrate, such as, but not limited by, an OLED device
substrate. Various embodiments of the ink can be printed using an
industrial inkjet printing system that can be housed in a gas
enclosure, which gas enclosure defines an interior that has a
controlled environment maintained as an inert and substantially
low-particle process environment. Patterned printing of an organic
thin film on a substrate, for example, but not limited by, an OLED
device substrate, in such a controlled environment can ensure a
high-volume, high yield process for a variety of OLED devices.
[0028] It is contemplated that a wide variety of ink formulations
can be printed within the inert, substantially low-particle
environment of various embodiments of a gas enclosure system of the
present teachings. During the manufacture of an OLED display, an
OLED pixel can be formed to include an OLED film stack, which can
emit light of a specific peak wavelength when a voltage is applied.
An OLED film stack structure between an anode and a cathode can
include a hole injection layer (HIL), a hole transport layer (HTL),
an emissive layer (EL), an electron transport layer (ETL) and an
electron injection layer (EIL). In some embodiments of an OLED film
stack structure, an electron transport layer (ETL) can be combined
with an electron injection layer (EIL) to form an ETL/EIL layer.
According to the present teachings, various ink formulations for an
EL for various color pixel EL films of an OLED film stack can be
printed using inkjet printing. Additionally, for example, but not
limited by, the HIL, HTL, EML, and ETL/EIL layers can have ink
formulations that can be printed using inkjet printing.
[0029] As will be discussed in more detail subsequently herein, it
is further contemplated that an organic encapsulation layer can be
printed on an OLED panel using inkjet printing. An encapsulation
ink can comprise a polymer or polymer component, for example, but
not limited by, various polyethylene glycol monomer materials, an
acrylate, such as a mono- or multidentate acrylate, a methacrylate,
such as a mono- or multidentate methacrylate, or other material, as
well as copolymers and mixtures thereof, which can be cured using
thermal processing (e.g. bake), UV exposure, and combinations
thereof. As used herein polymer and copolymer can include any form
of a polymer component that can be formulated into an ink and cured
on a substrate to form an organic encapsulation layer. Such
polymeric components can include polymers and copolymers, as well
as precursors thereof, for example, but not limited by, monomers,
oligomers, and resins. According to the present teachings, inkjet
printing can provide several advantages. First, a range of vacuum
processing operations can be eliminated because such inkjet-based
fabrication can be performed at atmospheric pressure. Additionally,
during an inkjet printing process, an organic encapsulation layer
can be localized to cover portions of an OLED substrate over and
proximal to an active region, to effectively encapsulate an active
region, including lateral edges of the active region. The targeted
patterning using inkjet printing results in eliminating material
waste, as well as eliminating additional processing typically
required to achieve patterning of an organic layer.
[0030] Organic Thin Film Ink Compositions and Methods
[0031] Various embodiments of an organic thin layer ink composition
of the present teachings can be printed, for example, but not
limited by, on an optoelectronic device, such as a wide number of
OLED devices, to form an organic encapsulation layer. According to
various embodiments of compositions and methods, once cured, the
resulting polymeric thin film can provide a fluid barrier, as well
as providing planarization of a previously fabricated inorganic
encapsulation layer, and additionally providing flexibility desired
from an organic encapsulation layer. The fluid barriers can prevent
or reduce the permeation of, for example, water and/or oxygen into
the OLED devices.
[0032] As depicted in the schematic section view of FIG. 1, for
optoelectronic device 50, a substrate 52 can be provided. Various
embodiments of a substrate can include one or more of a thin
silica-based glass, as well as any of a number of flexible
polymeric materials. For example, substrate 52 can be transparent,
such as for use in a bottom-emitting optoelectronic device
configuration. One or more layers associated with an OLED stack,
such as various organic or other material can be deposited, inkjet
printed, or otherwise formed upon the substrate to provide an
active region 54, such as to provide electroluminescent region.
Note that active region 54 in FIG. 1 is illustrated schematically
as a single block, but can in detail further include a region
having complex topology or structure with multiple discrete devices
and film layers. In an example, 50 can include an OLED device, such
as comprising an emissive layer, or other layers, coupled to an
anode electrode and a cathode electrode. The phrase "active" need
not imply any requirement of amplification of electrical energy or
transistor activity, and can refer generally to a region wherein
optoelectrical activity (e.g., light emission) can occur.
Accordingly, active region 54 can be included as a portion of an
active matrix OLED or a passive matrix OLED device.
[0033] Respective layers included in an OLED device, such as in the
active region 54, can be on the order of tens or hundreds of
nanometers (nm) thick, or less. Additional organic layers that are
not active in the optoelectronic action of the OLED device can be
included, and such layers can be on the order of microns thick, or
less. An anode electrode or a cathode electrode can be coupled to
or can include electrode portion 56 that is laterally offset along
the substrate 52 from the active region 54. As will be discussed in
more detail herein, the active region 54 of the device 50 can
include materials that degrade in the presence of prolonged
exposure to various reactive species gaseous species, such as, but
not limited by, water, oxygen, as well as various solvent vapors
from device processing. Such degradation can impact stability and
reliability.
[0034] As depicted in FIG. 1, an inorganic layer 60A can be
provided for device 50, such as deposited or otherwise formed on
active region 54. For example, the inorganic layer can be blanket
coated (e.g., deposited) over an entirety, or substantially an
entirety of a surface of the substrate 52, including active region
54. Examples of inorganic materials useful for fabricating
inorganic layer 60A can include various oxides, such as one or more
of Al.sub.2O.sub.3, TiO.sub.2, HfO.sub.2, SiO.sub.xN.sub.y or one
or more other materials. Organic layer 62A can be printed, using
for example, inkjet printing. For example, as previous generally
discussed herein organic layer 62A can be printed using an organic
thin layer ink that can include various polymer materials can are
curable using one or more of a thermal (e.g., bake) or ultraviolet
exposure technique, and once cured can form polymeric thin film,
such as organic layer 62A. Organic layer 62A can serve as one or
more of a planarization layer to planarize and mechanically protect
the active region 54, or as a portion of an encapsulation stack
that collectively serves to suppress or inhibit moisture or gas
permeation into the active region 54. FIG. 1 illustrates generally
a multi-layer configuration of encapsulation material layers having
inorganic layer 60A such as including an oxide, and the organic
layer 62A, such as including a polymer that can be used to inhibit
or suppress exposure of the active region 54 to reactive gases,
such as, but not limited by, moisture or atmospheric gases. As
depicted in FIG. 1, the multi-layer configuration can be repeated
to include second inorganic layer 60B and second organic layer 62B.
Various additional embodiments of encapsulation layers can be
created to provide the mechanical and sealing properties desired
for an optoelectronic device. For example, the order of the
fabrication of the layers could be reversed, so that an organic
encapsulation layer is first fabricated, followed by the
fabrication of an inorganic layer. Additionally, more or less
numbers of layers can be provided. For example, a structure having
inorganic layers 60A and 60B as shown, and a single organic
encapsulation layer 62A can be fabricated.
[0035] For various embodiments of an organic thin layer ink of the
present teachings, can be composed of four starting materials.
According to the present teachings, various compositions of an
organic thin layer ink can include a polyethylene glycol
dimethacrylate and/or a polyethylene glycol diacrylate having a
number average molecular weight in the range from about 230 gm/mole
to about 440 gm/mole. For example, the organic thin layer ink can
include polyethylene glycol 200 dimethacrylate and/or polyethylene
glycol 200 diacrylate, having a number average molecular weight of
about 330 gm/mole and having the generalized structure as shown
below:
##STR00001##
where n is on average 4 and R is independently selected from H and
methyl groups.
[0036] For various embodiments of an organic thin layer ink of the
present teachings, polyethylene glycol 200 dimethacrylate can be
the primary component of an ink formulation and can be between
about 75-95 wt. % of various embodiments of organic thin layer ink
compositions.
[0037] In addition to polyethylene glycol 200 dimethacrylate,
pentaerythritol tetraacrylate or pentaerythritol tetramethacrylate
can be used as a primary cross-linking agent. The term `primary` is
used here to indicate that other components of the ink compositions
also participate in crosslinking, although that is not their main
functional purpose. For various embodiments of an organic thin
layer ink, can be between about 4-10 wt. % of an ink formulation. A
generalized structure for pentaerythritol tetraacrylate or
pentaerythritol tetramethacrylate is shown below.
##STR00002##
where R is independently selected from H and methyl groups.
[0038] According to the present teachings, a spreading modifier can
be used to tune the spreading characteristics of various
embodiments of the organic thin layer ink compositions. The
spreading modifier is a liquid having a lower surface tension than
the polyethylene glycol dimethacrylate of the ink composition at
the printing temperatures. By way of illustration, various
embodiments of the ink compositions comprise a spreading modifier
having a viscosity in the range from about 14 to about 18 cps at
22.degree. C. and a surface tension in the range from about 35 to
39 dynes/cm at 22.degree. C. This includes embodiments of the ink
compositions that comprise a spreading modifier having a viscosity
in the range from about 14 to about 16 cps at 22.degree. C. and a
surface tension in the range from about 35 to 38 dynes/cm at
22.degree. C. Methods for measuring viscosities and surface
tensions are well known and include the use of commercially
available rheometers (e.g., a DV-I Prime Brookfield rheometer) and
tensiometers (e.g., a SITA bubble pressure tensiometer). In some
embodiments of the ink compositions, the spreading modifier
comprises a multifunctional, such as difunctional, acrylate monomer
or oligomer or methacrylate monomer or oligomer. Acrylate and
methacrylate based spreading modifiers may be advantageous because
they are generally compatible with the polyethylene glycol
dimethacrylate and acrylate or methacrylate based multifunctional
crosslinking agents of the ink compositions. As such, their use
will not cause the precipitation of the other acrylate or
methacrylate based components from solution. In addition, acrylate
and methacrylate based spreading modifiers can participate in the
crosslinking of the polyethylene glycol dimethacrylate. That is,
the spreading modifier(s) can be incorporated into the polymer
through similar chemistry, so as not to remain as contaminants
after UV curing. Various embodiments of organic thin layer ink
compositions comprise the spreading modifiers in amounts of up to
about 15 wt. %. This includes embodiments of the organic thin layer
ink compositions that comprise the spreading modifiers in amounts
in the range from about 1 to about 15 wt. %.
[0039] In some embodiments of the ink compositions, the spreading
modifier comprises an alkoxylated aliphatic diacrylate. The formula
for an alkoxylated aliphatic diacrylate can be represented as
follows:
##STR00003##
where n can be between 3 to 12.
[0040] As various embodiments of organic thin layer ink
compositions can utilize various alkoxylated aliphatic diacrylate
materials for adjusting the spreading properties of an ink
formulation on a substrate, various embodiments of organic thin
layer ink compositions of the present teachings can have up to
about 15 wt. % of an alkoxylated aliphatic diacrylate component in
a formulation. Various alkoxylated aliphatic diacrylate materials
can be provided by Sartomer Corporation. For example, examples of
candidate Sartomer products can include Sartomer product number
SR-238B, which is 1,6 hexanediol diacrylate with a surface tension
of about 35 at 22.degree. C., as well as Sartomer product number
SR-9209A, which is described as a proprietary alkoxylated aliphatic
diacrylate and has a surface tension of about 35 dynes/cm at
22.degree. C. and a viscosity of about 15 cps at 22.degree. C. For
various embodiments of organic thin layer ink compositions, the
aliphatic portion of an alkoxylated aliphatic diacrylate component
can be between 3 to 12 repeating methylene units. For various
embodiments of organic thin layer ink compositions, the aliphatic
portion of an alkoxylated aliphatic diacrylate component can be
between 4 to 6 repeating methylene units.
[0041] In addition to various alkoxylated aliphatic diacrylate
components, various embodiments of organic thin layer ink
compositions can use alkoxylated aliphatic dimethacrylate
components to adjust the spreading characteristics of various
formulations. Various embodiments of organic thin layer ink
compositions of the present teachings can have up to about 15 wt. %
of an alkoxylated aliphatic dimethacrylate component in a
formulation. For various embodiments of organic thin layer ink
compositions, the aliphatic portion of an alkoxylated aliphatic
dimethacrylate component can be between 3 to 12 repeating methylene
units. For various embodiments of organic thin layer ink
compositions, the aliphatic portion of an alkoxylated aliphatic
dimethacrylate component can be between 4 to 6 repeating methylene
units. The formula for an alkoxylated aliphatic dimethacrylate can
be represented as follows:
##STR00004##
where n can be between 3 to 12.
[0042] Regarding initiation of the polymerization process, various
embodiments of organic thin layer ink compositions of the present
teachings can utilize numerous types of photoinitiators for
initiating the polymerization process. In various embodiments the
photoinitiators are present in amounts in the range from about 0.1
to about 8 wt. %. This includes embodiments in which the
photoinitiators are present in amounts in the range from about 1 to
about 5 wt. %. However, amounts outside of these ranges can also be
used. The photoinitiator may be a Type I or a Type II
photoinitiator. Type I photoinitiators undergo radiation-induced
cleavage to generate two free radicals, one of which is reactive
and initiates polymerization. Type II photoinitiators undergo a
radiation-induced conversion into an excited triplet state. The
molecules in the excited triplet state then react with molecules in
the ground state to produce polymerization initiating radicals.
[0043] The specific photoinitiator used for a given ink composition
is desirably selected such that they are activated at wavelengths
that are not damaging to the OLED materials. For this reason,
various embodiments of the ink compositions include photointiators
that have a primary absorbance with a peak in the range from about
368 to about 380 nm. The light source used to activate the
photoinitiators and induce the curing of the ink compositions is
desirably selected such that the absorbance range of the
photoinitiator matches or overlaps with the output of the light
source, whereby absorption of the light creates free radicals that
initiate polymerization. Suitable light sources may include mercury
arc lamps and UV light emitting diodes.
[0044] An acylphosphine oxide photoinitiator can be used, though it
is to be understood that a wide variety of photoinitiators can be
used. For example, but not limited by, photoinitiators from the
.alpha.-hydroxyketone, phenylglyoxylate, and .alpha.-aminoketone
classes of photoinitiators can also be considered. For initiating a
free-radical based polymerization, various classes of
photoinitiators can have an absorption profile of between about 200
nm to about 400 nm. For various embodiments of the compositions and
methods disclosed herein, 2,4,6-trimethylbenzoyl-diphenylphosphine
oxide (TPO) and 2,4,6-trimethylbenzoyl-diphenyl phosphinate have
desirable properties. For various embodiments of the compositions
and methods of the present teaching, an acylphosphine oxide
photoinitiator can be about 0.1-5 wt. % of a formulation. Examples
of acylphosphine photoinitiators include Irgacure.RTM. TPO
initiators for UV curing sold under the tradenames Irgacure.RTM.
TPO, a type I hemolytic initiator which; with absorption @ 380 nm;
Irgacure.RTM. TPO-L, a type I photoinitiator that absorbs at 380
nm; and Irgacure.RTM. 819 with absorption at 370 nm. By way of
illustration, a light source emitting at a nominal wavelength in
the range from 350 nm to 395 nm at a radiant energy density of up
to 1.5 J/cm.sup.2 could be used to cure an ink composition
comprising a TPO photoinitiator. Using the appropriate energy
sources, high levels of curing can be achieved. For example, some
embodiments of the cured films have a degree of curing of 90% or
greater, as measured by Fourier Transform Infrared (FTIR)
spectroscopy.
[0045] The appropriate amount of photoinitiator to include in a
given ink composition will depend on the nature of the selected
photoinitiator, crosslinking agent and, if present, spreading
modifier. However, the amount of photoinitiator is desirably
selected to minimize the volume change that takes place from the
time the ink composition is printed to the time the ink composition
is cured into a solid film. For example, for some embodiments of
the ink compositions, the volume difference between the layer of
printed ink composition and the solid organic polymeric thin film
formed via curing the ink composition is no greater than 1%.
Minimizing the volume change that occurs during curing improves the
uniformity of the cured film.
[0046] The present inventors have developed an accurate test for
measuring the volume change of ink compositions that takes place
during the curing. This test allows for the precise determination
of the appropriate amount of photoinitiator to be included in a
given ink composition formulation in order to minimize the volume
change that results from curing. In the test, a known volume of an
ink composition is carefully dispensed into the bottom of a
container with a known volume marking (for example, a volumetric
flask). The ink composition in the container is then exposed to a
radiation source that induces crosslinking and cures the ink
composition into a solid film. A volume of deionized (DI) water
corresponding to the volume indicated by the volume marking on the
container is then dispensed into the container with the cured film.
The portion of the DI water above the volume marking is then
extracted from the container and weighed to determine the volume of
the cured film. By way of illustration, the test can be carried out
in a laboratory as follows. Place a 5 mL glass volumetric flask
into a glove box, along with a UV-curable ink composition, and a
hand-held ultraviolet (UV) lamp. Using an Eppendorf pipette and an
appropriate tip, carefully dispense 500 .mu.L of the ink
composition into the volumetric flask without touching the tip to
the side walls, such that all of the ink composition is dispensed
into the bottom of flask. Place the volumetric flask over the UV
lamp and turn on the lamp to an appropriate wavelength setting
(e.g., 365 nm) for a time sufficient to fully cure the ink
composition (e.g., about 180 seconds). Note: the operator should be
wearing UV protective glasses. After the ink composition has cured
into a solid film, turn off the lamp and place a stopper on flask.
Take the stoppered flask with the cured film out of the glove box.
Place the flask on a weighing balance, without the glass stopper,
and measure its tare weight. Using a Pasteur pipette, carefully
dispense (avoiding the side walls) precisely 5 grams of DI water
into the volumetric flask. Then remove the flask from the balance,
place an empty dry vial on the balance and measure its tare weight.
Using a fresh dry Pasteur pipette carefully extract the portion of
DI water from volumetric flask that is above the 5 mL mark. At the
endpoint of the extraction, the low point of the meniscus of the
water must be aligned with the 5 mL mark, as determined by visual
inspection. Transfer the full amount of the extracted DI water into
the empty vial and measure its weight (w1). The percent volume
change (e.g., volume reduction) resulting from the curing of the
dispensed ink composition can be calculated using the following
equation:
Volume change %=100-((w1 grams/0.5 grams).times.100).
[0047] Using this test method, it has been discovered that even
small changes in the amount of photoinitiator in the ink
compositions can have a substantial affect on volume change that
takes place during curing and that this test can be used to
formulate ink compositions that undergo volume changes during
curing of no greater than 1%. Various embodiments of the ink
composition undergo volume changes during curing of no greater than
0.5%.
[0048] By way of illustration, the test method was used to
formulate an ink composition comprising polyethylene glycol 200
dimethacrylate, pentaerythritol tetraacrylate (PET), SR-9209A and
2,4,6-trimethylbenzoyl-diphenylphosphine oxide (TPO) as a
photoinitiator. Five ink compositions were formulated.
Each composition contained 4 wt. % SR-9209A and 7 wt. % PET. The
amount of TPO was adjusted as shown in Table 1 and the balance was
polyethylene glycol 200 dimethacrylate. In each test 0.5 ml of the
ink composition was initially dispensed into the flask. Except
where otherwise indicated, the cure time was 180 seconds.
TABLE-US-00001 TABLE 1 Volume Changes as a Result of Curing. Weight
of Post Curing Volume Ink TPO Extracted DI Change from Liquid
Composition (wt. %) Water (g) Ink to Solid Cured Film 1 0.5 0.4471
-11.58% 2 3 0.4891 -2.18% 3 3.5 0.4928 -1.44% 4 4 0.4977 -0.46% 5
4.5 0.5059 1.18%* 6 ~7.5 0.5214 4.28%** *Cure time = 300 seconds
**Cure time = 420 seconds
As shown in this table and graphically in FIG. 12, a quantity of 4
wt. % TPO provided the lowest volume change. The volume increases
for samples 5 and 6 were the result of film swelling. The weight
loss of the cured films was also measured via thermogravimetric
analysis for the ink compositions having different TPO
concentrations. The results, which are presented in Table 2 and
graphically in FIG. 13, show that a concentration of 4 wt. % TPO
also resulted in the lowest weight loss.
TABLE-US-00002 TABLE 2 TGA Analysis of Cured Films with Different %
of Photoinitiator. Post Curing Weight Loss from Ink TPO Liquid Ink
to Solid Cured Film at Composition (wt. %) 120.degree. C. (wt. %) 1
0.5 1.9 2 3 0.8 4 4 0.5 5 4.5 1.2
[0049] Generally, for ink compositions useful for inkjet printing
applications, the surface tension, viscosity and wetting properties
of the ink compositions should be tailored to allow the
compositions to be dispensed through an inkjet printing nozzle
without drying onto or clogging the nozzle at the temperature used
for printing (e.g., room temperature; .about.22.degree. C.). Once
formulated, various embodiments of organic thin layer ink
compositions can have a viscosity of between about 10 and about 25
(including, for example, between about 17 and about 21) centipoise
at 22.degree. C. and a surface tension of between about 32 and
about 45 (including, for example, between about 38 and about 41)
dynes/cm at 22.degree. C. As jetting temperatures can be between
about 22.degree. C. to about 40.degree. C., over such a temperature
range, various embodiments of organic thin layer ink formulations
can have a viscosity of between about 7-25 (including, for example,
between about 9 and about 19) centipoise and a surface tension of
between about 30 and about 45 dynes/cm in the temperature range of
the printhead.
[0050] Given that the initiation of polymerization can be induced
by light, inks can be prepared to prevent exposure to light. With
respect to preparation of organic thin layer ink compositions of
the present teachings, in order to ensure the stability of various
compositions, the compositions can be prepared in a dark or very
dimly lit room. For example, for the preparation of 30 grams of an
embodiments of an organic thin film ink formulation, in a fashion
that protects the direct exposure to light, the lid of a clean 40
mL amber vial (for example, Flacons, VWR trace clean) can be
removed and then can be placed on a balance; and tared. First, a
desired amount of a photoinitiator can be weighed into the vial.
For example, 1.2 gram of 2,4,6-trimethylbenzoyl-diphenylphosphine
oxide can be weighed into the vial for a target 4 wt. % of a 30
gram formulation. Next, 1.2 grams of SR-9209A can be weighed into
the vial for a target of 4 wt. %. After the addition of the
alkoxylated aliphatic diacrylate component, 25.5 grams of
polyethylene glycol 200 dimethacrylate can be weighed into the
vial, representing 85% of the 30 gram formulation. The final 7% of
the composition can be provided by weighing 2.1 grams of
pentaerythritol tetraacrylate into the vial. Regarding mixing to
provide uniform concentration of components, carefully insert a
Teflon.RTM. coated magnetic stir bar into the vial and secure the
cap of vial. Stir the solution for 30 minutes at temperatures in
the range from room temperature to 50.degree. C. and 600-1000 rpm.
Thereafter, filter the ink solution through 0.2 or 0.45 .mu.m PTFE
syringe filter or vacuum or pressure filtration methods, and
sonicate the filtered solution for 30 minutes at ambient
temperature. The ink composition is ready for use and should be
stored away from light in an inert environment, for example, in a
glove box. Various embodiments of an organic thin film ink
preparation as described can have a viscosity of between about 17
and about 19 centipoise at 22.degree. C. and a surface tension of
between about 37 and about 41 dynes/cm at 22.degree. C.
[0051] Once the ink compositions are prepared, they can be
dehydrated by mixing in the presence of molecular sieve beads for a
period of a day or more and then stored under a dry, inert
atmosphere, such as a compressed dry air or nitrogen atmosphere.
The ink composition should be stored in amber light or in the dark
in order to avoid or minimize premature polymerization. For
example, the ink composition can be stored in an amber vial.)
Drying and storage in a dry, inert atmosphere can keep the water
content of the ink compositions below about 300 ppm (including, for
example, below about 200 ppm), which is desirable for ink jet
printing, until the compositions are ready for use. Using the ink
composition prepared as described above, a dehydration process was
carried out and evaluated as follows. First a 2 gram aliquot of the
ink composition (prior to drying) was removed and its H.sub.2O
content was determined to be about 1200 ppm using Karl Fischer
coulometric titration. To the remainder of the ink composition was
added 3 Angstrom molecular sieve beads (10% w/w). The composition
was then placed on a roller to provide gentle agitation for 5 days,
after which the ink composition was transferred into the glove box
(H.sub.2O<10 ppm) and aliquoted into 20 amber vials (2 mL each),
followed by capping the vials, to provide a nitrogen headspace in
the vials. The remainder of the ink composition was removed from
the glove box and aliquoted, under ambient environment, into 20
amber vials (2 mL each), followed by capping the vials. The glove
box aliquoted vials were removed from the glove box (under an
N.sub.2 headspace) and, along with the vials aliquoted outside the
glove box (under ambient headspace), stowed under a fume hood.
Thereafter, one vial (each) was opened from the N.sub.2 headspace
group and the ambient headspace group and the water contents of the
ink compositions were measured, using Karl Fischer coulometric
titration, from day 0 through 4 (daily) and then on a
weekly/biweekly basis up to day 51. The data showed that the ink
compositions maintained under a nitrogen atmosphere (headspace) had
a water content of only 120 ppm after 51 days, while the ink
compositions maintained under an ambient atmosphere had a water
content that was three times as high (361.2 ppm) on day 51. The
same procedure can be used to produce the same results with a
compressed dry air headspace.
[0052] The ink compositions, particularly those stored under a dry,
inert atmosphere at room temperature (22.degree. C.), can be stable
for long periods of time, as determined by the lack of
precipitation or separation under visual inspection and the
stabilities in their room temperature viscosities and surface
tensions. Some embodiments of ink compositions experience a surface
tension change of 2% or less (for example, 1% or less) and a
viscosity change of 6% or less over a period of at least 160 days
at room temperature under a compressed dry air or under a nitrogen
atmosphere in the dark. For example, the viscosity (measured with a
Brookfield viscometer) of the ink composition prepared, dehydrated
and stored under compressed dry air or under a nitrogen atmosphere
in the dark, as described above, increased from 17.8 cP to only
18.7 cP over a period of 160 days at room temperature. At least a
portion of this minor increase may be attributed to the limits of
reproducibility of the instrument. The surface tension (measured
via dynamic SITA) of the ink composition changed from 39.9
dyne/cm.sup.2 to 39.7 dyne/cm.sup.2--a statistically insignificant
amount--over the same period.
[0053] An embodiment of an ink prepared as described above was
formulated and printed using a printing system as described in U.S.
Pat. No. 8,714,719, which is incorporated herein in its entirety.
The films were cured in an inert nitrogen environment using UV
radiation. The cured films displayed high transparency, as well as
being of uniform thickness. By way of illustration, some
embodiments of cured films made with the present ink compositions
have a film thickness variation of 5% or lower. Film thickness
uniformity can be measured using a profilometer tool, such as a
Veeco Dektak Profilometer tool. To carry out a thickness
measurement, a scratch can be made on the film using, for example,
a sharp needle on a substrate. Then the substrate can be placed on
the tool to measure the height of the scratch well, which
represents the thickness of the film printed on the substrate. FIG.
2A displays a film of 8 .mu.m thickness, which was printed without
incorporating edge compensation, and shows uniformity except at the
film edges, as expected. FIG. 2B is a film of 16 .mu.m thickness,
which was printed using edge compensation, and shows uniformity, as
expected. Further by way of illustration, some embodiments of the
cured films made with the present ink compositions have a
transmission of 90% or greater at wavelengths of 550 nm and above.
This includes cured films having a transmission of 99% or greater,
and 99.5% or greater, at wavelengths of 550 nm and above.
[0054] The suitability of an ink composition for inkjet printing
applications can be measured by its maximum stable jetting
frequency through a nozzle of an inkjet printhead. An ink
composition that displays stable jetting has constant, or
substantially constant, drop velocities, drop volumes and drop
trajectories over a range of jetting frequencies. Beyond the ink
composition's stable jetting frequency range, however, its drop
velocity, drop volume and/or drop trajectory become erratic with
increasing jetting frequency. In order to provide an ink
composition with a stable jetting frequency, it is desirable to
formulate the ink compositions from components that themselves have
good jetting properties. Thus, in some embodiments of the ink
compositions the spreading modifier is selected such that it is
characterized by a high jetting stability. Various embodiments of
the present ink compositions comprise spreading modifiers with
maximum stable jetting frequencies of at least 23 kHz at 22.degree.
C. This includes embodiments of the ink compositions that comprise
spreading modifiers having maximum stable jetting frequencies of at
least 24 kHz at 22.degree. C. and further includes embodiments of
the ink compositions that comprise spreading modifiers having
maximum stable jetting frequencies of at least 25 kHz at 22.degree.
C.
[0055] Stable jetting through an inkjet nozzle is illustrated in
FIGS. 9(A), 9(B) and 9(C), which show the effect of increased
jetting frequency on drop volume, drop velocity and drop trajectory
(angle), respectively, for the spreading modifier SR-9209A that
displays stable jetting up to a jetting frequency of about 24 kHz
at 22.degree. C. and up to about 26 kHz at 25.degree. C. The
frequency responses shown in FIGS. 9(A) through 9(C) were measured
by loading the SR-9209A into a printhead that is coupled with a
drop measuring instrument. A waveform for firing is developed and
the pulse times and voltages are adjusted and optimized to
establish a stable jetting range. For example, ink jet tests can be
conducted to assess the print performance of a spreading modifier
by examining the effects of changing the frequency on drop volume,
drop velocity and drop trajectory at 22.degree. C. and 25.degree.
C. Examples of results from this type of frequency response test,
after optimizing the pulse times and voltages, are illustrated in
the graphs of FIG. 9(A) through 9(C), which show the frequency
response of drop volume, velocity and trajectory respectively, for
the SR-9209A. The tests were run using a Dimatix.TM. SX3 printhead
and a JetXpert shadowgraphy setup by ImageXpert.RTM. as a drop
measuring instrument.
[0056] The jetting frequency response of a given composition, such
as a spreading modifier, may display some undulating variation in
drop volume and drop velocity as the jetting frequency increases,
but prior to the onset of the erratic jetting frequency response
that characterizes unstable jetting. It is desirable for a
composition to minimize the extent of these drop volume and
velocity variations in order to provide uniform and reproducible
deposition even at the higher frequency end of the composition's
stable jetting frequency range. Various embodiments of the present
ink compositions comprise spreading modifiers that undergo drop
volume variations of no more than about 15% up to their maximum
stable jetting frequency at 22.degree. C. This includes ink
compositions that comprise spreading modifiers that undergo drop
volume variations of no more than about 12% up to their maximum
stable jetting frequency at 22.degree. C. and further includes ink
compositions that comprise spreading modifiers that undergo drop
volume variations of no more than about 10% up to their maximum
stable jetting frequency at 22.degree. C. Various embodiments of
the present ink compositions comprise spreading modifiers that
undergo drop velocity variations of no more than about 15% up to
their maximum stable jetting frequency at 22.degree. C. This
includes ink compositions that comprise spreading modifiers that
undergo drop velocity variations of no more than about 12% up to
their maximum stable jetting frequency at 22.degree. C. and further
includes ink compositions that comprise spreading modifiers that
undergo drop velocity variations of no more than about 10% up to
their maximum stable jetting frequency at 22.degree. C.
[0057] Drop volume and velocity variations as a function of jetting
frequency at 22.degree. C. and 25.degree. C. are illustrated in
FIGS. 10(A) and 10(B), which show the drop volume and drop velocity
variations, respectively, for the SR-9209A of FIGS. 9(A)-9(C). The
SR-9209A has a drop volume variation of no greater than about 10%
and a drop velocity variation of no greater than about 12% up to
the maximum stable jetting frequency at 25.degree. C.
[0058] The formulated ink compositions comprising the spreading
modifiers are also capable of stable jetting at high frequencies at
room temperature and even higher jetting temperatures, including
jetting temperatures of up to about 50.degree. C. By way of
illustration, an ink composition containing 4 wt. % SR-9209A, 7 wt.
% PET, 4 wt. % TPO and 85 wt. % polyethylene glycol 200
dimethacrylate was jetted using the procedure described above for
jetting the spreading modifier SR-9209A. This procedure used a
printhead and a drop measuring instrument similar to those used in
the above-described jetting frequency response tests for the
spreading modifier. The printer used in the testing had four rows
per printhead and 28 nozzles per row. The results for the drop
velocity, volume and trajectory are shown in FIGS. 11(A), 11(B) and
11(C), respectively. The traces in FIGS. 11(A)-11(C) show the mean
values for the 28 nozzles for each of the four printhead rows. As
illustrated in these figures, stable jetting was observed for the
ink composition at 25.degree. C. for jetting frequencies up to at
least 25 kHz. The tests were repeating for the ink composition at a
jetting temperature of 40.degree. C. and, again, stable jetting in
terms of drop velocity, volume and trajectory was observed for
jetting frequencies up to at least 25 kHz.
[0059] Systems and Methods for Organic Thin Film Formation on a
Substrate
[0060] As previously discussed herein, manufacture of various OLED
devices on a variety of substrates can be done in an inert,
substantially particle-free environment to ensure high-yield
manufacturing.
[0061] For clearer perspective regarding substrate sizes that can
be used in manufacturing of various OLED devises, generations of
mother glass substrate sizes have been undergoing evolution for
flat panel displays fabricated by other-than OLED printing since
about the early 1990's. The first generation of mother glass
substrates, designated as Gen 1, is approximately 30 cm.times.40
cm, and therefore could produce a 15'' panel. Around the
mid-1990's, the existing technology for producing flat panel
displays had evolved to a mother glass substrate size of Gen 3.5,
which has dimensions of about 60 cm.times.72 cm. In comparison, a
Gen 5.5 substrate has dimensions of about 130 cm.times.150 cm.
[0062] As generations have advanced, mother glass sizes for Gen 7.5
and Gen 8.5 are in production for other-than OLED printing
fabrication processes. A Gen 7.5 mother glass has dimensions of
about 195 cm.times.225 cm, and can be cut into eight 42'' or six
47'' flat panels per substrate. The mother glass used in Gen 8.5 is
approximately 220.times.250 cm, and can be cut to six 55'' or eight
46'' flat panels per substrate. The promise of OLED flat panel
display for qualities such as truer color, higher contrast,
thinness, flexibility, transparency, and energy efficiency have
been realized, at the same time that OLED manufacturing is
practically limited to G 3.5 and smaller. Currently, OLED printing
is believed to be the optimal manufacturing technology to break
this limitation and enable OLED panel manufacturing for not only
mother glass sizes of Gen 3.5 and smaller, but at the largest
mother glass sizes, such as Gen 5.5, Gen 7.5, and Gen 8.5. One of
the features of OLED panel display technology includes that a
variety of substrate materials can be used, for example, but not
limited by, a variety of glass substrate materials, as well as a
variety of polymeric substrate materials. In that regard, sizes
recited from the terminology arising from the use of glass-based
substrates can be applied to substrates of any material suitable
for use in OLED printing.
[0063] Table 2 below relates generation substrate designation to
sizes as often can be found in various sources relating to
generation substrates for various OLED devices. Table 3 below
summarizes aspect ratios and areas for some known generation-sized
substrates as currently available in various sources relating to
generation-sized substrates. It should be understood that variation
of aspect ratio and hence size may be seen from manufacturer to
manufacturer. Additionally, It should be the information provided
in Table 3 can be subject to change, given the evolution of the
industry. In that regard, updated conversion factors for a specific
generation-sized substrate, as well as area in square meters can be
obtained any of a variety of generation-sized substrates.
TABLE-US-00003 TABLE 2 Correlation between area and substrate size
Generation ID X (mm) Y (mm) Area (m.sup.2) Gen 3.0 550 650 0.36 Gen
3.5 610 720 0.44 Gen 3.5 620 750 0.47 Gen 4 680 880 0.60 Gen 4 730
920 0.67 Gen 5 1100 1250 1.38 Gen 5 1100 1300 1.43 Gen 5.5 1300
1500 1.95 Gen 6 1500 1850 2.78 Gen 7.5 1950 2250 4.39 Gen 8 2160
2400 5.18 Gen 8 2160 2460 5.31 Gen 8.5 2200 2500 5.50 Gen 9 2400
2800 6.72 Gen 10 2850 3050 8.69
[0064] Manufacturing tools that in principle can allow for the
printing of a variety of substrate sizes that includes large-format
substrate sizes, can require substantially large facilities for
housing such OLED manufacturing tools. Accordingly, maintaining an
entire large facility under an inert atmosphere presents
engineering challenges, such as continual purification of a large
volume of an inert gas. Various embodiments of a gas enclosure
system can have a circulation and filtration system internal a gas
enclosure assembly in conjunction with a gas purification system
external a gas enclosure that together can provide continuous
circulation of a substantially low-particulate inert gas having
substantially low levels of reactive species throughout a gas
enclosure system. According to the present teachings, an inert gas
may be any gas that does not adversely alter a product being
fabricated under a defined set of conditions. Some commonly used
non-limiting examples of an inert gas for the processing of various
embodiments of an OLED device can include nitrogen, any of the
noble gases, and any combination thereof. Systems and methods of
the present teachings can provide a large facility that is
essentially hermetically sealed to prevent contamination of various
reactive atmospheric gases, such as water vapor and oxygen, as well
as organic solvent vapors generated from various printing
processes. According to the present teachings, an OLED printing
facility would maintain levels for each species of various reactive
species, including various reactive atmospheric gases, such as
water vapor and oxygen, as well as organic solvent vapors at 100
ppm or lower, for example, at 10 ppm or lower, at 1.0 ppm or lower,
or at 0.1 ppm or lower.
[0065] The need for printing an OLED panel in a facility in which
the levels of each of a reactive species should be maintained at
targeted low levels can be illustrated in reviewing the information
summarized in Table 4. The data summarized on Table 4 resulted from
the testing of each of a test coupon comprising organic thin film
compositions for each of red, green, and blue, fabricated in a
large-pixel, spin-coated device format. Such test coupons are
substantially easier to fabricate and test for the purpose of rapid
evaluation of various formulations and processes. Though test
coupon testing should not be confused with lifetime testing of a
printed panel, it can be indicative of the impact of various
formulations and processes on lifetime. The results shown in the
table below represent variation in the process step in the
fabrication of test coupons in which only the spin-coating
environment varied for test coupons fabricated in a nitrogen
environment where reactive species were less than 1 ppm compared to
test coupons similarly fabricated but in air instead of a nitrogen
environment.
[0066] It is evident through the inspection of the data in Table 4,
shown below, for test coupons fabricated under different processing
environments, particularly in the case of red and blue, that
printing in an environment that effectively reduces exposure of
organic thin film compositions to reactive species may have a
substantial impact on the stability of various ELs, and hence on
lifetime. The lifetime specification is of particular significance
for OLED panel technology, as this correlates directly to display
product longevity; a product specification for all panel
technologies, which has been challenging for OLED panel technology
to meet. In order to provide panels meeting requisite lifetime
specifications, levels of each of a reactive species, such as water
vapor, oxygen, as well as organic solvent vapors, can be maintained
at 100 ppm or lower, for example, at 10 ppm or lower, at 1.0 ppm or
lower, or at 0.1 ppm or lower with various embodiments of a gas
enclosure system of the present teachings.
TABLE-US-00004 TABLE 3 Impact of inert gas processing on lifetime
for OLED panels Process V Cd/A CIE (x, y) T95 T80 T50 Color
Environment @ 10 mA/cm.sup.2 @ 1000 Cd/m.sup.2 Red Nitrogen 6 9
(0.61, 0.38) 200 1750 10400 Air 6 8 (0.60, 0.39) 30 700 5600 Green
Nitrogen 7 66 (0.32, 0.63) 250 3700 32000 Air 7 61 (0.32, 0.62) 250
2450 19700 Blue Nitrogen 4 5 (0.14, 0.10) 150 750 3200 Air 4 5
(0.14, 0.10) 15 250 1800
[0067] In addition to providing an inert environment, maintaining a
substantially low-particle environment for OLED printing is of
particular importance, as even very small particles can lead to a
visible defect on an OLED panel. Particle control in a gas
enclosure system can present significant challenges not presented
for processes that can be done, for example, in atmospheric
conditions under open air, high flow laminar flow filtration
hoods.
[0068] For example, of a manufacturing facility can require a
substantial length of various service bundles that can be
operatively connected from various systems and assemblies to
provide optical, electrical, mechanical, and fluidic connections
required to operate, for example, but not limited by, a printing
system. Such service bundles used in the operation of a printing
system and located proximal to a substrate positioned for printing
can be an ongoing source of particulate matter. Additionally,
components used in a printing system, such as fans or linear motion
systems that use friction bearing, can be particle generating
components. Various embodiments of a gas circulation and filtration
system of the present teachings can be used in conjunction with
particle control components to contain and exhaust particulate
matter. Additionally, by using a variety of intrinsically
low-particle generating pneumatically operated components, such as,
but not limited by, substrate floatation tables, air bearings, and
pneumatically operated robots, and the like, a low particle
environment for various embodiments of a gas enclosure system can
be maintained. Regarding maintaining a substantially low-particle
environment, various embodiments of a gas circulation and
filtration system can be designed to provide a low particle inert
gas environment for airborne particulates meeting the standards of
International Standards Organization Standard (ISO) 14644-1:1999,
"Cleanrooms and associated controlled environments--Part 1:
Classification of air cleanliness," as specified by Class 1 through
Class 5
[0069] As depicted in FIG. 3, process 100 for printing an organic
thin film ink on a substrate and then curing the ink can include
step 110 of transferring a substrate from a manufacturing tool in
which, for example, an inorganic encapsulation layer was fabricated
on an OLED substrate device using a vapor deposition process. As
will be discussed in more detail subsequently herein, a substrate
can be transferred from an inorganic encapsulation fabrication tool
to a printing module of a printing tool There can be many
advantages of inkjet printing for a variety of processes that can
utilize pattered area printing. First, a range of vacuum processing
operations can be eliminated because such inkjet-based fabrication
can be performed at atmospheric pressure. Additionally, during an
inkjet printing process, an organic encapsulation layer can be
localized to cover portions of an OLED substrate over and proximal
to an active region, to effectively encapsulate an active region,
including lateral edges of the active region. The targeted
patterning using inkjet printing results in eliminating material
waste, as well as eliminating additional processing typically
required to achieve patterning of an organic layer, which can
result in enhanced particle contamination. For example, masking is
a well-known technique used for patterned film deposition, however,
masking techniques can create substantial particle
contamination.
[0070] In step 120, using various embodiments of organic thin layer
inks according to the present teachings, a printing tool can be
used to print an organic thin film layer over a target print area.
In the art of processing, total average cycle time or TACT can be
an expression of a unit of time for a particular process cycle. For
various embodiments of systems and methods of the present
teachings, for a step of printing an organic thin film ink, TACT
can be between about 30 seconds to about 120 seconds. Subsequently,
as indicated by step 130, the substrate can be transferred from a
printing module of a printing tool to a curing module. With respect
to a step of curing, as indicated by step 140, according to various
embodiments of systems and methods of the present teachings, before
curing is initiated, a step of allowing the printed organic thin
film ink to reach a film layer of uniform thickness can be done. In
various embodiments, such a leveling step can be considered a
separate step. In various embodiments of systems and methods,
leveling can be done in a dedicated chamber, for example, in a
holding chamber, and then a substrate can be transferred to a
curing chamber. For various embodiments of the present teachings,
as will be discussed in more detail herein, a step of leveling can
be done in the same chamber as the step of curing. According to
various embodiments of systems and methods of the present
teachings, TACT for a step of leveling can be between about 170
seconds to about 210 seconds, while TACT for a curing step
according to some embodiments can be between about 15 seconds to 60
seconds, while for other embodiments can be between about 25
seconds to about 35 seconds. After curing step 140, a substrate can
be transferred from a UV curing module to another processing
chamber, such as an output loadlock chamber, as indicated by
process step 150 of process 100.
[0071] In order to accomplish process 100 of FIG. 3, various
embodiments of manufacturing tools of the present teachings that
can provide inert, substantially particle-free environments can be
used, for example, as shown in FIG. 4. FIG. 4 depicts a perspective
view of OLED printing tool 4000 according to various embodiments of
the present teachings, which can include first module 4400,
printing module 4500, and second module 4600. Various modules, such
as first module 4400 can have first transfer chamber 4410, which
can have a gate, such as gate 4412, for each side of first transfer
chamber 4410 to accommodate various chambers having a specified
function. As depicted in FIG. 4 first transfer chamber 4410 can
have a load lock gate (not shown) for integration of first load
lock chamber 4450 with first transfer chamber 4410, as well as a
buffer gate (not shown) for integration of first buffer chamber
4460 with first transfer chamber 4410. Gate 4412 of first transfer
chamber 4410 can be used for a chamber or unit that can be movable,
such as, but not limited by, a load lock chamber. Observation
windows, such as observation windows 4402 and 4404 of first
transfer chamber 4410, as well as observation window 4406 of first
buffer chamber 4460, can be provided for an end user to, for
example, monitor a process. Printing module 4500 can include gas
enclosure 4510, which can have first panel assembly 4520, printing
system enclosure assembly 4540, and second panel assembly 4560. Gas
enclosure 4510 can house various embodiments of a printing
system.
[0072] Various embodiments of a gas enclosure can be contoured
around a printing system base, upon which a substrate support
apparatus can be mounted. Further, a gas enclosure can be contoured
around a bridge structure used for the X-axis movement of a
carriage assembly. As a non-limiting example, various embodiments
of a contoured gas enclosure according to the present teachings can
have a gas enclosure volume of between about 6 m.sup.3 to about 95
m.sup.3 for housing various embodiments of a printing system
capable of printing substrate sizes from Gen 3.5 to Gen 10. By way
a further non-limiting example, various embodiments of a contoured
gas enclosure according to the present teachings can have a gas
enclosure volume of between about 15 m.sup.3 to about 30 m.sup.3
for housing various embodiments of a printing system capable of
printing, for example, Gen 5.5 to Gen 8.5 substrate sizes. Such
embodiments of a contoured gas enclosure can be between about 30%
to about 70% savings in volume in comparison to a non-contoured
enclosure having non-contoured dimensions for width, length and
height.
[0073] Second module 4600 of FIG. 4 can include second transfer
chamber 4610, which can have a gate, such as gate 4612, for each
side of second transfer chamber 4610 to accommodate various
chambers having a specified function. As depicted in FIG. 4 second
transfer chamber 4610 can have a load lock gate (not shown) for
integration of second load lock chamber 4650 with second transfer
chamber 4610, as well as a gate (not shown) for integration of
second chamber 4660 with second transfer chamber 4610. Gate 4612 of
second transfer chamber 4610 can be used for a chamber or unit that
can be movable, such as, but not limited by, a load lock chamber.
Observation windows, such as observation windows 4602 and 4604 of
second transfer chamber 4610, can be provided for an end user to,
for example, monitor a process. According to various embodiments of
systems and methods of the present teachings, chamber 4660 of FIG.
4 can be a UV curing module. For example, chamber 4660 of FIG. 4
can be a UV curing module as depicted in FIG. 5.
[0074] First load lock chamber 4450 and second load lock chamber
4650 can be affixably associated with first transfer chamber 4410
and second transfer chamber 4610, respectively or can be movable,
such as on wheels or on a track assembly, so that they can be
readily positioned for use proximal a chamber. According to the
present teachings, a load lock chamber can be mounted to a support
structure and can have at least two gates. For example first load
lock chamber 4450 can be supported by first support structure 4454
and can have first gate 4452, as well as a second gate (not shown)
that can allow fluid communication with first transfer module 4410.
Similarly, second load lock chamber 4650 can be supported by second
support structure 4654 and can have second gate 4652, as well as a
first gate (not shown) that can allow fluid communication with
second transfer module 4610.
[0075] FIG. 5 illustrates generally an example an ultraviolet (UV
curing) module that can be used in manufacturing a light emitting
device. The treatment system can be included as a portion of other
systems or techniques described herein. For example, as indicated
in FIG. 5, UV curing module 4660 could be chamber 4660 of OLED
printing tool 4000 of FIG. 4. The system can include various
regions, such as for use as a curing chamber, or for use as a
combination curing and holding chamber. For various embodiments of
a curing chamber, a source of ultraviolet emission can be used such
as to treat one or more layers deposited on a substrate being
fabricated. For example, ultraviolet emission can be used to
polymerize or otherwise treat an organic layer deposited on the
substrate, such as for use in one or more processes related to
manufacturing a flat panel display assembly, such as including an
OLED display assembly.
[0076] According to the present teachings, a UV curing module can
include one or more enclosed UV curing chambers such as first UV
curing chamber 4661A, second UV curing chamber 4661B, and "Nth" UV
curing chamber 4661N. For example, three regions can be included
and in another example, other numbers of regions can be included.
The regions can be oriented in a "stacked" configuration along a
vertical axis of the system, such as shown illustratively in FIG.
5. Other configurations can be used, such as a radial configuration
of chambers extending outward from a central chamber. For example,
transfer chamber 4610 of FIG. 5 can be second transfer chamber 4610
of FIG. 4.
[0077] In an illustrative example, such as after deposition of an
organic layer on a substrate, a leveling operation can be
performed. As was previously discussed herein, a duration of a
leveling operation can generally be greater than a duration of an
ultraviolet treatment operation. Accordingly, in one approach,
respective holding regions or "buffer cells" can be used, such as
in a stacked configuration with each region configured to house a
substrate. In this approach, the leveling operation can proceed
without restricting access or otherwise tying up a separate
ultraviolet treatment region. However, multiple ultraviolet sources
can be used, such including user lower-cost sources. In this
manner, a throughput impact of idling an ultraviolet source need
not preclude use of the same UV curing chamber (e.g., 4661A through
4661N) for both a holding operation (e.g., buffering or leveling),
as well as for an ultraviolet treatment operation, because multiple
regions can be configured to provide ultraviolet treatment. Such an
approach can also provide redundancy of the ultraviolet sources
such that processing can continue even if a particular ultraviolet
source fails or is undergoing maintenance.
[0078] For example, first radiation source 4662A (e.g., an
ultraviolet-emitting LED array) can provide ultraviolet emission,
depicted as multiple arrows in FIG. 5. A UV apparatus can include a
UV single source, a liner array, or a two dimensional array of UV
source. The type of source selected can have a specified range of
wavelengths to a first substrate 2050A. As depicted in FIG. 5, a
first set of radiation sources 4662A are depicted. Though the term
"UV" is used, it is to be understood that the source has a
wavelength of light associated with an energy required to initiate
a polymerization reaction. In that regard, as free-radical
initiation can occur via thermal decomposition as well as
photolysis, a source of radiation can include any source effective
in initiating a polymerization reaction through a variety of
mechanism. The electromagnetic radiation emission can be coupled to
an interior of the enclosed region of first UV chamber 4661A such
as through a window 4663 (e.g., a quartz window or an assembly such
as including a normalization filter, or other filters or coatings).
According to various embodiments of the present teachings, the
environment within UV curing chamber 4661A can be inert and can be
isolated from a housing containing the first set of radiation
sources 4662A. According to various systems and methods, in the
second enclosed region of UV chamber 4661B, for example, the second
substrate 2050B can be held for a specified duration, such as for
leveling or to await availability of other processes. During the
specified holding duration, a second set of radiation sources 4662B
can be disabled.
[0079] Regarding support of substrates, such as 2050A and 2050B of
FIG. 5, the present inventors have recognized, among other things,
that for some operations or material systems, such as in relation
to leveling a deposited organic layer, visible defects can be
induced in the display regions of a substrate when the substrate is
supported in a non-uniform manner. For example, pins, support
frames, retracted lift-pins, or vacuum apertures in contact with a
substrate can induce visible defects in a finished device.
[0080] Without being bound by theory, it is believed that such
defects primarily result from localized variations in thermal
conductivity that can create local gradients in the temperature of
a substrate during, for example, a leveling operation. In an
example, a specified temperature uniformity can be maintained in a
local region of the substrate, for example, such that deviation in
temperature adjacent to or within the local region is limited. For
example, a significant temperature variation across the substrate
can be tolerated but such variation can have a limited gradient
such that the temperature does not vary significantly over a small
distance along the substrate. In this manner, abrupt changes in
visible characteristics of the finished display can be avoided and
such gradual changes are less likely to be noticed or even
detectable.
[0081] In one approach, regions outside the emitting or display
region of the substrate can be used to support a substrate outside
of active device areas of a substrate. However, because large
portions of a substrate can include emitting regions or portions of
the actual display region, it can be impractical to support the
substrate only at the periphery of such regions because such
support induces unacceptable mechanical forces or stresses
elsewhere across a substrate, which may either distort or fracture
a substrate. Additionally, the present inventors have also
recognized that a correlation can exist between particle generation
and a number of instances or locations of contact between other
apparatuses and a substrate.
[0082] Accordingly, the present inventors have recognized that a
substrate, such as substrates 2050A and 2050B of FIG. 5 can be
supported by a chuck, for example chuck 4664 of first UV chamber
4661A, such as during an ultraviolet treatment operation, such as
at least in part using a pressurized gas "P" to provide a gas
cushion. According to various examples, a substrate can be
supported exclusively by a controlled arrangement of the
pressurized gas, "P such as to float the substrate 2050A. In
another example, substrate 2050A can be mechanically supported in
part, such as at a periphery, by one or more pins (e.g., a pin
4666) or a support frame, and a weight of substrate 2050A can be
supported in a central region of substrate 2050A by the pressurized
gas, "P." In another approach, substrate 2050A can be supported by
a pressurized gas "P" impinging on a first surface of substrate
2050A, and an opposing force can be provided such as by a
mechanical stop 4668 contacting an opposing face of substrate
2050A. Though first UV chamber 4661A is used for the purpose of
illustration, it is to be understood that these teachings apply to
all UV chambers shown in FIG. 5. Though pressure is shown for the
teachings of FIG. 5, as will be discussed in more detail in
reference to the floatation table of FIG. 6, a chuck using pressure
and vacuum can also be utilized. In such an example where the
substrate 2050A is supported exclusively by the gas cushion, a
combination of positive gas pressure and vacuum can be applied
through the arrangement of ports. Such a zone having both pressure
and vacuum control can effectively provide a fluidic spring between
floatation chuck 4664 and substrate 2050A.
[0083] Transfer module 4610 of FIG. 5 can be a transfer module as
described for second transfer module 4610 of FIG. 4. Regarding the
floatation of a substrate, elevating handler 4612, which can be
housed in transfer module 4610, can also utilized substrate
floatation during a transfer process. Elevating handler 4612 can
include a table 4614 (or a corresponding end effector) including
pressurized gas "P" to support a substrate at least in part using
the pressurized gas. A conveyor, or other apparatus can be used to
transport a substrate from, for example, a printing module, such as
printing module 4550 of FIG. 4 through gate 4616. Such conveyance
means can also include such a pressurized gas arrangement, such
that a substrate can be conveyed along a path as indicated by the
horizontal arrow shown directing substrate 2050N to UV curing
chamber 4661N.
[0084] In the illustrative example of FIG. 5, an enclosed transfer
module 4610 can house the elevating handler 4612 and table 4614. An
inert environment having specified gas purity and specified
particulate levels can be established within the enclosed transfer
module 4610 as discussed extensively in relation to other examples
herein. For example, one or more fan filter units (FFUs) such as a
fan filter unit 5202 can be coupled to transfer module 4610. Duct
5201 can provide a return flow of inert gas to be recirculated
using FFU 5202. A gas purification system 3130 can be coupled to
the enclosed transfer module 4610. While a vertical flow
orientation is illustrated in FIG. 5, other configurations can be
used, such as a lateral flow configuration. Each of the regions
4661A through 4661N can either share one or more gas purification
loops or can each be served by a respective gas purification loop.
Similarly, one or more FFUs can be located to provide a laminar
airflow parallel to a surface of substrate in each of the regions
4661A through 4661N. A temperature within the enclosed transfer
module 4610 or within other portions of the system can be
controlled as described extensively in other examples herein, such
as using a temperature controller 3140. As will be described in
more detail in the teachings regarding FIG. 8 herein, the
temperature controller 3140 can be coupled, for example through a
heat exchanger, to the FFU 5202 or one or more FFUs elsewhere.
[0085] The regions 4661A through 4661N can each include a valve or
gate, such as to isolate the inert environment of each enclose
region 4661A through 4661N from the transfer module 4610 or from
each other. Accordingly, such as during maintenance, a particular
region can have its inert environment isolated from the rest of the
enclosed regions using a valve or gate.
[0086] An OLED inkjet printing system, such as OLED printing system
2000 of FIG. 6, can be housed in a gas enclosure, such as gas
enclosure 4510 of printing module 4500 of FIG. 4. Various
embodiments of a printing system of FIG. 6, can be comprised of
several devices and apparatuses, which allow the reliable placement
of ink drops onto specific locations on a substrate. Printing
requires relative motion between the printhead assembly and the
substrate. This can be accomplished with a motion system, typically
a gantry or split axis XYZ system. Either the printhead assembly
can move over a stationary substrate (gantry style), or both the
printhead and substrate can move, in the case of a split axis
configuration. In another embodiment, a printhead assembly can be
substantially stationary; for example, in the X and Y axes, and the
substrate can move in the X and Y axes relative to the printheads,
with Z axis motion provided either by a substrate support apparatus
or by a Z-axis motion system associated with a printhead assembly.
As the printheads move relative to the substrate, droplets of ink
are ejected at the correct time to be deposited in the desired
location on a substrate. A substrate can be inserted and removed
from the printer using a substrate loading and unloading system.
Depending on the printer configuration, this can be accomplished
with a mechanical conveyor, a substrate floatation table with a
conveyance assembly, or a substrate transfer robot with end
effector. For various embodiments of systems and methods of the
present teachings, an Y-axis motion system can be based on an
air-bearing gripper system.
[0087] An OLED inkjet printing system, such as OLED printing system
2000 of FIG. 6, can be comprised of several devices and
apparatuses, which allow the reliable placement of ink drops onto
specific locations on a substrate. These devices and apparatuses
can include, but are not limited to, a printhead assembly, ink
delivery system, a motion system for providing relative motion
between a printhead assembly and a substrate, substrate support
apparatus, substrate loading and unloading system, and printhead
management system.
[0088] A printhead assembly can include at least one inkjet head,
with at least one orifice capable of ejecting droplets of ink at a
controlled rate, velocity, and size. The inkjet head is fed by an
ink supply system which provides ink to the inkjet head. As shown
in an expanded view of FIG. 6, OLED inkjet printing system 2000 can
have a substrate, such as substrate 2050, which can be supported by
a substrate support apparatus, such as a chuck, for example, but
not limited by, a vacuum chuck, a substrate floatation chuck having
pressure ports, and a substrate floatation chuck having vacuum and
pressure ports. In various embodiments of systems and methods of
the present teachings, a substrate support apparatus can be a
substrate floatation table. As will be discussed in more detail
subsequently herein, substrate floatation table 2200 of FIG. 6 can
be used for supporting substrate 2050, and in conjunction with a
Y-axis motion system, can be part of a substrate conveyance system
providing for the frictionless conveyance of substrate 2050. A
Y-axis motion system of the present teachings can include first
Y-axis track 2351 and second Y-axis track 2352, which can include a
gripper system (not shown) for holding a substrate. Y-axis motion
can be provided by either a linear air bearing or linear mechanical
system. Substrate floatation table 2200 of OLED inkjet printing
system 2000 shown in FIG. 6 can define the travel of substrate 2050
through gas enclosure assembly 1000 of FIG. 1A during a printing
process.
[0089] FIG. 6 illustrates generally an example of substrate
floatation table 2200 for a printing system 2000 that can include a
floating conveyance of a substrate, which can have a porous medium
to provide floatation. In the example of FIG. 6, a handler or other
conveyance can be used to position a substrate 2050 in first region
2201 of a substrate floatation table 2200, such as located on a
conveyor. The conveyer can position the substrate 2050 at a
specified location within the printing system such as using either
mechanical contact (e.g., using an array of pins, a tray, or a
support frame configuration), or using gas cushion to controllably
float the substrate 2050 (e.g., an "air bearing" table
configuration). A printing region 2202 of the substrate floatation
table 2200 can be used to controllably deposit one or more layers
on the substrate 2050 during fabrication. The printing region 2202
can also be coupled to an second region 2203 of the substrate
floatation table 2200. The conveyer can extend along the first
region 2201, the printing region 2202, and the second region 2203
of the substrate floatation table 2200, and the substrate 2050 can
be repositioned as desired for various deposition tasks, or during
a single deposition operation. The controlled environments nearby
the first region 2201, the printing region 2202, and the second
region 2203 can be commonly-shared. According to various
embodiments of printing system 2000 of FIG. 6, first region 2201
can be an input region, and second region 2203 can be an output
region. For various embodiments of printing system 2000 of FIG. 6,
first region 2201 can be both an input and an output region.
Further, function referred to in association with regions 2201,
2202, and 2203, such as input, printing, and output for
illustration only. Such regions can be used for other processing
steps, such as conveyance of a substrate, or support of a substrate
such as during one or more of holding, drying, or thermal treatment
of the substrate in one or more other modules.
[0090] According to the floatation schemes shown in FIG. 6, in an
example where the substrate 2050 is supported exclusively by the
gas cushion, a combination of positive gas pressure and vacuum can
be applied through the arrangement of ports or using a distributed
porous medium. Such a zone having both pressure and vacuum control
can effectively provide a fluidic spring between the conveyor and a
substrate. A combination of positive pressure and vacuum control
can provide a fluidic spring with bidirectional stiffness. The gap
that exists between the substrate (e.g., substrate 2050) and a
surface can be referred to as the "fly height," and such a height
can be controlled or otherwise established by controlling the
positive pressure and vacuum port states. In this manner, the
substrate Z-axis height can be carefully controlled in, for
example, the printing region 2202. In some embodiments, mechanical
retaining techniques, such as pins or a frame, can be used to
restrict lateral translation of the substrate while the substrate
is supported by the gas cushion. Such retaining techniques can
include using spring loaded structures, such as to reduce the
instantaneous forces incident the sides of the substrate while the
substrate is being retained; this can be beneficial as a high force
impact between a laterally translating substrate and a retaining
means can cause substrate chipping or even catastrophic
breakage.
[0091] Elsewhere, as illustrated generally in FIG. 6, such as where
the fly height need not be controlled precisely, pressure-only
floatation zones can be provided, such as along the conveyor in the
first or second regions 2201 or 2203, or elsewhere. A "transition"
floatation zone can be provided such as where a ratio of pressure
to vacuum nozzles increases or decreases gradually. In an
illustrative example, there can be an essentially uniform height
between a pressure-vacuum zone, a transition zone, and a pressure
only zone, so that within tolerances, the three zones can lie
essentially in one plane. A fly height of a substrate over
pressure-only zones elsewhere can be greater than the fly height of
a substrate over a pressure-vacuum zone, such as in order to allow
enough height so that a substrate will not collide with a
floatation table in the pressure-only zones. In an illustrative
example, an OLED panel substrate can have a fly height of between
about 150 micrometers (.mu.) to about 300.mu. above pressure-only
zones, and then between about 30.mu. to about 50.mu. above a
pressure-vacuum zone. In an illustrative example, one or more
portions of the substrate floatation table 2200 or other
fabrication apparatus can include an "air bearing" assembly
provided by NewWay.RTM. Air Bearings (Aston, Pa., United States of
America).
[0092] A porous medium can be used to establish a distributed
pressurized gas cushion for floating conveyance or support of the
substrate 2050 during one or more of printing, buffering, drying,
or thermal treatment. For example, a porous medium "plate" such as
coupled to or included as a portion of a conveyor can provide a
"distributed" pressure to support the substrate 2050 in a manner
similar to the use of individual gas ports. The use of a
distributed pressurized gas cushion without using large gas port
apertures can in some instances further improve uniformity and
reduce or minimize the formation of mura or other visible defects,
such as in those instances where the use of relatively large gas
ports to create a gas cushion leads to non-uniformity, in spite of
the use of a gas cushion.
[0093] A porous medium can be obtained such as from Nano TEM Co.,
Ltd. (Niigata, Japan), such as having physical dimensions specified
to occupy an entirety of the substrate 2050, or specified regions
of the substrate such as display regions or regions outside display
regions. Such a porous medium can include a pore size specified to
provide a desired pressurized gas flow over a specified area, while
reducing or eliminating mura or other visible defect formation.
[0094] Printing requires relative motion between the printhead
assembly and the substrate. This can be accomplished with a motion
system, typically a gantry or split axis XYZ system. Either the
printhead assembly can move over a stationary substrate (gantry
style), or both the printhead and substrate can move, in the case
of a split axis configuration. In another embodiment, a printhead
assembly can be substantially stationary; for example, in the X and
Y axes, and the substrate can move in the X and Y axes relative to
the printheads, with Z axis motion provided either by a substrate
support apparatus or by a Z-axis motion system associated with a
printhead assembly. As the printheads move relative to the
substrate, droplets of ink are ejected at the correct time to be
deposited in the desired location on a substrate. A substrate can
be inserted and removed from the printer using a substrate loading
and unloading system. Depending on the printer configuration, this
can be accomplished with a mechanical conveyor, a substrate
floatation table with a conveyance assembly, or a substrate
transfer robot with end effector.
[0095] With respect to FIG. 6, printing system base 2100, can
include first riser 2120 and second riser 2122, upon which bridge
2130 is mounted. For various embodiments of OLED printing system
2000, bridge 2130 can support first X-axis carriage assembly 2301
and second X-axis carriage assembly 2302, which can control the
movement of first printhead assembly 2501 and second printhead
assembly 2502, respectively across bridge 2130. First printhead
assembly 2501 can be housed in first printhead assembly enclosure
2503, while second printhead assembly 2502 can be housed in second
printhead assembly enclosure 2504. For various embodiments of
printing system 2000, first X-axis carriage assembly 2301 and
second X-axis carriage assembly 2302 can utilize a linear air
bearing motion system, which are intrinsically low-particle
generating. According to various embodiments of a printing system
of the present teachings, an X-axis carriage can have a Z-axis
moving plate mounted thereupon. In FIG. 6, first X-axis carriage
assembly 2301 is depicted with first Z-axis moving plate 2310,
while second X-axis carriage assembly 2302 is depicted with second
Z-axis moving plate 2312. Though FIG. 6 depicts two carriage
assemblies and two printhead assemblies, for various embodiments of
OLED inkjet printing system 2000, there can be a single carriage
assembly and a single printhead assembly. For example, either of
first printhead assembly 2501 and second printhead assembly 2502
can be mounted on an X,Z-axis carriage assembly, while a camera
system for inspecting features of substrate 2050 can be mounted on
a second X,Z-axis carriage assembly.
[0096] In FIG. 6, each printhead assembly, such as first printhead
assembly 2501 and second printhead assembly 2502 of FIG. 6, can
have a plurality of printheads mounted in at least one printhead
device, as depicted in partial view for first printhead assembly
2501, which depicts a plurality of printhead devices 2505, each
printhead device having one or more printheads; e.g. nozzle
printing, thermal jet or ink-jet type. A printhead device can
include, for example, but not limited by, fluidic and electronic
connections to at least one printhead; each printhead having a
plurality of nozzles or orifices capable of ejecting ink at a
controlled rate, velocity and size. For various embodiments of
printing system 2000 of the present teachings, one or more
printheads of one or more printhead devices 2505 can be configured
to deposit one or more patterned organic layers on the substrate
2050 in a "face up" configuration of the substrate 2050. Such
layers can include one or more of an electron injection or
transport layer, a hole injection or transport layer, a blocking
layer, or an emission layer, for example. Such materials can
provide one or more electrically functional layers. For various
embodiments of printing system 2000, a printhead assembly can
include between about 1 to about 60 printhead devices, where each
printhead device can have between about 1 to about 30 printheads in
each printhead device. A printhead, for example, an industrial
inkjet head, can have between about 16 to about 2048 nozzles, which
can expel a droplet volume of between about 0.1 pL to about 200
pL.
[0097] According to various embodiments of a gas enclosure systems
of the present teachings, given the sheer number of printhead
devices and printheads, first printhead management system 2701 and
second printhead management system 2702 can be housed in an
auxiliary enclosure, which can be isolated from a printing system
enclosure during a printing process for performing various
measurement and maintenance tasks with little or no interruption to
the printing process. First printhead management system 2701 can be
mounted upon first printhead management platform 2703, while second
printhead management system 2702 can be mounted upon first
printhead management platform 2704. As depicted in FIG. 6, first
printhead assembly 2501 can be positioned relative to first
printhead management system 2701 in order to perform various
measurement and maintenance procedures that can be provided by
first printhead management system apparatuses 2707, 2709 and 2711.
Additionally, second printhead assembly 2502 can be positioned
relative to second printhead management system 2702 in order to
perform various measurement and maintenance procedures that can be
provided by second printhead management system apparatuses 2708,
2710 and 2712. First printhead management system apparatuses 2707,
2709, and 2011 can be mounted on linear rail motion system 2705 for
positioning relative to first printhead assembly 2501. Second
printhead management system apparatuses 2708, 2710, and 2012 can be
mounted on linear rail motion system 2706 for positioning relative
to second printhead assembly 2502. Apparatuses 2707, 2709, and 2011
of first printhead assembly 2701 and apparatuses 2708, 2710 and
2712 of second printhead assembly 2702 can be any of a variety of
subsystems or modules for performing various printhead management
functions. For example apparatuses 2707, 2709, and 2011 of first
printhead assembly 2701 and apparatuses 2708, 2710 and 2712 of
second printhead assembly 2702 can be any of a drop measurement
module, a printhead replacement module, a purge basin module, and a
blotter module.
[0098] For OLED printing system 2000 of FIG. 6, various embodiments
of a printing system can include substrate floatation table 2200,
supported by substrate floatation table base 2220. Substrate
floatation table base 2220 can be mounted on printing system base
2100. Various embodiments of printing system 2000 of FIG. 6 can
have first isolator set 2110 (second isolator of first isolator set
on opposing side not shown) and second isolator set 2112 (second
isolator of second isolator set on opposing side not shown)
Substrate floatation table 2200 of OLED printing system can support
substrate 2050, as well as defining the travel over which substrate
2050 can be moved through gas enclosure assembly 1000 during the
printing of an OLED substrate. A Y-axis motion system of the
present teachings can include first Y-axis track 2351 and second
V-axis track 2352, which can include a gripper system (not shown)
for holding a substrate. Y-axis motion can be provided by either a
linear air bearing or linear mechanical system. In that regard, in
conjunction with a motion system; as depicted in FIG. 6, a Y-axis
motion system, substrate floatation table 2200 can provide
frictionless conveyance of substrate 2050 through a printing
system.
[0099] In reference to FIG. 7, printing system 2001 can have all of
the elements previously described for printing system 2000 of FIG.
6. For example, but not limited by, printing system 2001 of FIG. 7
can have service bundle housing exhaust system 2400 for containing
and exhausting particles generated from a service bundle. Service
bundle housing exhaust system 2400 of printing system 2001 can
include service bundle housing 2410, which can house a service
bundle. According to the present teachings, a service bundle can be
operatively connected to a printing system to provide various
optical, electrical, mechanical and fluidic connections required to
operate various devices and apparatuses in a gas enclosure system,
for example, but not limited by, various devices and apparatuses
associated with a printing system. Printing system 2001 of FIG. 7
can have substrate support apparatus 2250 for supporting substrate
2050, which can be positioned with precision in the Y-axis
direction using Y-axis positioning system 2355. Both substrate
support apparatus 2250 and Y-axis positioning system 2355 are
supported by printing system base 2101. Substrate support apparatus
2250 can be mounted on Y-axis motion assembly 2355 and can be moved
on rail system 2360 using, for example, but not limited by, a
linear bearing system; either utilizing mechanical bearings or air
bearings. For various embodiments of gas enclosure systems, an air
bearing motion system helps facilitation frictionless conveyance in
the Y-axis direction for a substrate placed on substrate support
apparatus 2250. Y-axis motion system 2355 can also optionally use
dual rail motion, once again, provided by a linear air bearing
motion system or a linear mechanical bearing motion system.
[0100] Regarding motion systems supporting various carriage
assemblies of the present teachings, such as printing system 2000
of FIG. 6 and printing system 2001 of FIG. 7 can have a first
X-axis carriage that can be used for mounting a printhead assembly
and a second carriage assembly that can be used to mount a variety
of various assemblies, such as a camera assembly. For example, in
FIG. 7, orienting system 2001 can have assembly 2300A that is
depicted having printhead assembly 2500 mounted thereupon and
second X-axis carriage assembly 2300B that is depicted having
camera assembly 2550 mounted thereupon. Substrate 2050, which is on
substrate support apparatus 2250, can be located in various
positions proximal to bridge 2130, for example, during a printing
process. Substrate support apparatus 2250 can be mounted on
printing system base 2101. In FIG. 7, printing system 2001 can have
first X-axis carriage assembly 2300A and second X-axis carriage
assembly 2300B mounted on bridge 2130. First X-axis carriage
assembly 2300A can also include first Z-axis moving plate 2310A for
the Z-axis positioning of printhead assembly 2500, while second
X-axis carriage assembly 2300B can have second Z-axis moving plate
2310B for the Z-axis positioning of camera assembly 2550. In that
regard, various embodiments of carriage assemblies 2300A and 2300B
can provide precision X,Z positioning with respect to a substrate
positioned on substrate support 2250 for printhead assembly 2500
and camera assembly 2550, respectively. For various embodiments of
printing system 2001, first X-axis carriage assembly 2300A and
second X-axis carriage assembly 2300B can utilize a linear air
bearing motion system, which is intrinsically low-particle
generating.
[0101] A camera assembly 2550 can include camera 2552, camera mount
assembly 2554 and lens assembly 2556. Camera assembly 2550 can be
mounted to motion system 2300B on Z-axis moving plate 2310B, via
camera mount assembly 2556. Camera 2552 can be any image sensor
device that converts an optical image into an electronic signal,
such as by way of non-limiting example, a charge-coupled device
(CCD), a complementary metal-oxide-semiconductor (CMOS) device or
N-type metal-oxide-semiconductor (NMOS) device. Various image
sensor devices can be configured as an array of sensors for an area
scan camera, or a single row of sensors, for a line scan camera.
Camera assembly 2550 can be connected to image processing system
that can include, for example, a computer for storing, processing,
and providing results. As previously discussed herein for printing
system 2001 of FIG. 7, Z-axis moving plate 2310B can controllably
adjust the Z-axis position of camera assembly 2550 relative to
substrate 2050. During various processes, such as for example,
printing and data collection, substrate 2050 can be controllably
positioned relative to the camera assembly 2550 using the X-axis
motion system 2300B and Y-axis motion system 2355.
[0102] Various camera assemblies can utilize cameras having
different capabilities. In various embodiments, camera assembly
2550 of FIG. 7 can be a high-speed, high-resolution camera. In
various embodiments of systems and methods of the present
teachings, a line scan camera having about 8192 pixels, with a
working height of about 190 mm, and capable of scanning at about 34
kHz can be used. In various embodiments of systems and methods of
the present teachings, more than one camera can be mounted on an
X-axis carriage assembly for various embodiments of a printing
system substrate camera assembly, where each camera can have
different specifications regarding field of view and resolution.
For example, one camera can be a line scan camera for in situ
particle inspection, while a second camera can be for regular
navigation of a substrate in a gas enclosure system. Such a camera
useful for regular navigation can be an area scan camera having a
field of view in the range of about 5.4 mm.times.4 mm with a
magnification of about 0.9.times. to about 10.6 mm.times.8 mm with
a magnification of about 0.45.times.. In still other embodiments,
one camera can be a line scan camera for in situ particle
inspection, while a second camera can be for precise navigation of
a substrate in a gas enclosure system, for example, for substrate
alignment. Such a camera can be useful for precise navigation can
be an area scan camera having a field of view of about 0.7
mm.times.0.5 mm with a magnification of about 7.2.times.. Various
embodiments of a printing system according to the present teachings
may have one or more cameras mounted to an X-axis carriage assembly
for the purpose of, for example, inspecting various thin film
layers that can be printed on an optoelectronic device, as
previously described for FIG. 1.
[0103] FIG. 8 is a schematic diagram showing a gas enclosure system
500. Various embodiments of a gas enclosure system 500 according to
the present teachings can comprise, for example gas enclosure 4510
of FIG. 4 for various modules and chambers as described for FIG. 5.
For illustrative purposes, FIG. 8 will refer to gas enclosure 4510
of FIG. 4 for housing a printing system, though it is to be
understood that these teachings apply to a broad number of
enclosures, modules and chambers of the present teachings.
[0104] Gas purification loop 3130 can be in fluid communication gas
enclosure 4510, and at least one thermal regulation system 3140.
Additionally, various embodiments of gas enclosure system 500 can
have pressurized inert gas recirculation system 3000, which can
supply inert gas for operating various devices, such as a substrate
floatation table for an OLED printing system. Various embodiments
of a pressurized inert gas recirculation system 3000 can utilize a
compressor, a blower and combinations of the two as sources for
various embodiments of pressurized inert gas recirculation system
3000, as will be discussed in more detail subsequently herein.
Additionally, gas enclosure system 500 can have a circulation and
filtration system internal to gas enclosure system 500 (not
shown).
[0105] As depicted in FIG. 8, for various embodiments of a gas
enclosure assembly according to the present teachings, the design
of a filtration system can separate the inert gas circulated
through gas purification loop 3130 from the inert gas that is
continuously filtered and circulated internally for various
embodiments of gas enclosure assembly 1101. Gas purification loop
3130 includes outlet line 3131 from gas enclosure 4510 of FIG. 4,
to a solvent removal component 3132 and then to gas purification
system 3134. Inert gas purified of solvent and other reactive gas
species, such as oxygen and water vapor, are then returned to gas
enclosure 4510 through inlet line 3133. Gas purification loop 3130
may also include appropriate conduits and connections, and sensors,
for example, oxygen, water vapor and solvent vapor sensors. A gas
circulating unit, such as a fan, blower or motor and the like, can
be separately provided or integrated, for example, in gas
purification system 3134, to circulate gas through gas purification
loop 3130. According to various embodiments of gas enclosure
assembly 1101, though solvent removal system 3132 and gas
purification system 3134 are shown as separate units in the
schematic shown in FIG. 8, solvent removal system 3132 and gas
purification system 3134 can be housed together as a single
purification unit.
[0106] Gas purification loop 3130 of FIG. 8 can have solvent
removal system 3132 placed upstream of gas purification system
3134, so that inert gas circulated from gas enclosure 4510 of FIG.
4 passes through solvent removal system 3132 via outlet line 3131.
According to various embodiments, solvent removal system 3132 may
be a solvent trapping system based on adsorbing solvent vapor from
an inert gas passing through solvent removal system 3132 of FIG. 8.
A bed or beds of a sorbent, for example, but not limited by, such
as activated charcoal, molecular sieves, and the like, may
effectively remove a wide variety of organic solvent vapors. For
various embodiments of a gas enclosure system cold trap technology
may be employed to remove solvent vapors in solvent removal system
3132. As previously discussed herein, for various embodiments of a
gas enclosure system according to the present teachings, sensors,
such as oxygen, water vapor and solvent vapor sensors, may be used
to monitor the effective removal of such species from inert gas
continuously circulating through a gas enclosure system, such as
gas enclosure system 500 of FIG. 8. Various embodiments of a
solvent removal system can indicate when sorbent, such as activated
carbon, molecular sieves, and the like, has reached capacity, so
that the bed or beds of sorbent can be regenerated or replaced.
Regeneration of a molecular sieve can involve heating the molecular
sieve, contacting the molecular sieve with a forming gas, a
combination thereof, and the like. Molecular sieves configured to
trap various species, including oxygen, water vapor, and solvents,
can be regenerated by heating and exposure to a forming gas that
comprises hydrogen, for example, a forming gas comprising about 96%
nitrogen and 4% hydrogen, with said percentages being by volume or
by weight. Physical regeneration of activated charcoal can be done
using a similar procedure of heating under an inert
environment.
[0107] Any suitable gas purification system can be used for gas
purification system 3134 of gas purification loop 3130 of FIG. 8.
Gas purification systems available, for example, from MBRAUN Inc.,
of Statham, N.H., or Innovative Technology of Amesbury, Mass., may
be useful for integration into various embodiments of a gas
enclosure assembly according to the present teachings. Gas
purification system 3134 can be used to purify one or more inert
gases in gas enclosure system 500, for example, to purify the
entire gas atmosphere within gas enclosure assembly 1101. As
previously discussed herein, in order to circulate gas through gas
purification loop 3130, gas purification system 3134 can have a gas
circulating unit, such as a fan, blower or motor, and the like. In
that regard, a gas purification system can be selected depending on
the volume of the enclosure, which can define a volumetric flow
rate for moving an inert gas through a gas purification system. For
various embodiments of gas enclosure system having a gas enclosure
assembly with a volume of up to about 4 m.sup.3; a gas purification
system that can move about 84 m.sup.3/h can be used. For various
embodiments of gas enclosure system having a gas enclosure assembly
with a volume of up to about 10 m.sup.3; a gas purification system
that can move about 155 m.sup.3/h can be used. For various
embodiments of a gas enclosure assembly having a volume of between
about 52-114 m.sup.3, more than one gas purification system may be
used.
[0108] Any suitable gas filters or purifying devices can be
included in the gas purification system 3134 of the present
teachings. In some embodiments, a gas purification system can
comprise two parallel purifying devices, such that one of the
devices can be taken off line for maintenance and the other device
can be used to continue system operation without interruption. In
some embodiments, for example, the gas purification system can
comprise one or more molecular sieves. In some embodiments, the gas
purification system can comprise at least a first molecular sieve,
and a second molecular sieve, such that, when one of the molecular
sieves becomes saturated with impurities, or otherwise is deemed
not to be operating efficiently enough, the system can switch to
the other molecular sieve while regenerating the saturated or
non-efficient molecular sieve. A control unit can be provided for
determining the operational efficiency of each molecular sieve, for
switching between operation of different molecular sieves, for
regenerating one or more molecular sieves, or for a combination
thereof. As previously discussed herein, molecular sieves may be
regenerated and reused.
[0109] Thermal regulation system 3140 of FIG. 8 can include at
least one chiller 3142, which can have fluid outlet line 3141 for
circulating a coolant into gas enclosure assembly 1101, and fluid
inlet line 3143 for returning the coolant to the chiller. An at
least one fluid chiller 3142 can be provided for cooling the gas
atmosphere within gas enclosure system 500. For various embodiments
of a gas enclosure system of the present teachings, fluid chiller
3142 delivers cooled fluid to heat exchangers within the enclosure,
where inert gas is passed over a filtration system internal the
enclosure. At least one fluid chiller can also be provided with gas
enclosure system 500 to cool heat evolving from an apparatus
enclosed within gas enclosure system 500. For example, but not
limited by, at least one fluid chiller can also be provided for gas
enclosure system 500 to cool heat evolving from an OLED printing
system. Thermal regulation system 3140 can comprise heat-exchange
or Peltier devices and can have various cooling capacities. For
example, for various embodiments of a gas enclosure system, a
chiller can provide a cooling capacity of from between about 2 kW
to about 20 kW. Various embodiments of a gas enclosure system can
have a plurality of fluid chillers that can chill one or more
fluids. In some embodiments, the fluid chillers can utilize a
number of fluids as coolant, for example, but not limited by,
water, anti-freeze, a refrigerant, and a combination thereof as a
heat exchange fluid. Appropriate leak-free, locking connections can
be used in connecting the associated conduits and system
components.
[0110] The present teachings are intended to be illustrative, and
not restrictive. The Abstract is provided to comply with 37 C.F.R.
.sctn. 1.72(b), to allow the reader to quickly ascertain the nature
of the technical disclosure. It is submitted with the understanding
that it will not be used to interpret or limit the scope or meaning
of the claims. Also, in the above Detailed Description, various
features may be grouped together to streamline the disclosure. This
should not be interpreted as intending that an unclaimed disclosed
feature is essential to any claim. Rather, inventive subject matter
may lie in less than all features of a particular disclosed
embodiment. Thus, the following claims are hereby incorporated into
the Detailed Description as examples or embodiments, with each
claim standing on its own as a separate embodiment, and it is
contemplated that such embodiments can be combined with each other
in various combinations or permutations. The scope of the invention
should be determined with reference to the appended claims, along
with the full scope of equivalents to which such claims are
entitled.
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