U.S. patent application number 09/911952 was filed with the patent office on 2002-02-07 for thermal transfer element and process for forming organic electroluminescent devices.
This patent application is currently assigned to 3M Innovative Properties Company. Invention is credited to Baude, Paul F., Florczak, Jeffrey M., Hsu, Yong, McCormick, Fred B., Wolk, Martin B..
Application Number | 20020015907 09/911952 |
Document ID | / |
Family ID | 26925371 |
Filed Date | 2002-02-07 |
United States Patent
Application |
20020015907 |
Kind Code |
A1 |
Wolk, Martin B. ; et
al. |
February 7, 2002 |
Thermal transfer element and process for forming organic
electroluminescent devices
Abstract
Disclosed are thermal transfer elements and processes for
patterning solvent-coated layers and solvent-susceptible layers
onto the same receptor substrate. These donor elements and methods
are particularly suited for making organic electroluminescent
devices and displays. The donor elements can include a substrate,
an optional light-to-heat conversion layer, and a single or
multicomponent transfer layer that can be imagewise transferred to
a receptor to form an organic electroluminescent device, portions
thereof, or components therefor. The methods offer advantages over
conventional patterning techniques such as photolithography, and
make it possible to fabricate new organic electroluminescent device
constructions.
Inventors: |
Wolk, Martin B.; (Woodbury,
MN) ; Baude, Paul F.; (Maplewood, MN) ;
Florczak, Jeffrey M.; (Maplewood, MN) ; McCormick,
Fred B.; (Maplewood, MN) ; Hsu, Yong;
(Woodbury, MN) |
Correspondence
Address: |
Attention: William D. Miller
3M Office of Intellectual Property Counsel
P.O. Box 33427
St. Paul
MN
55133-3427
US
|
Assignee: |
3M Innovative Properties
Company
|
Family ID: |
26925371 |
Appl. No.: |
09/911952 |
Filed: |
July 24, 2001 |
Related U.S. Patent Documents
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Application
Number |
Filing Date |
Patent Number |
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09911952 |
Jul 24, 2001 |
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09662078 |
Sep 14, 2000 |
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6291116 |
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09662078 |
Sep 14, 2000 |
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09473115 |
Dec 28, 1999 |
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6194119 |
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09473115 |
Dec 28, 1999 |
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09231723 |
Jan 15, 1999 |
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6114088 |
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Current U.S.
Class: |
430/200 ;
156/234; 427/592; 427/66; 430/271.1; 430/273.1; 430/311; 430/312;
430/319; 430/330; 430/964; 503/227 |
Current CPC
Class: |
B41M 5/265 20130101;
H01L 27/3246 20130101; H05K 3/046 20130101; H01L 51/5012 20130101;
H01L 51/0002 20130101; G02B 6/138 20130101; H01L 51/0013 20130101;
B41M 5/38207 20130101; H01L 51/56 20130101; B41M 5/38214 20130101;
H01L 27/3283 20130101; G02B 6/1221 20130101; B41M 5/42 20130101;
H01L 51/0039 20130101; Y10S 430/165 20130101; B41M 5/392 20130101;
B41M 5/395 20130101; H05B 33/10 20130101; B41M 3/006 20130101; H01L
51/0004 20130101 |
Class at
Publication: |
430/200 ;
430/271.1; 430/273.1; 430/311; 430/312; 430/319; 430/330; 430/964;
503/227; 156/234; 427/66; 427/592 |
International
Class: |
G03F 007/039; G03F
007/095; G03F 007/34; B44C 001/165 |
Claims
What is claimed is:
1. A method for making an organic electroluminescent device
comprising thermally transferring a light emitting polymer layer
and a small molecule layer from one or more thermal transfer donor
elements to a receptor so that the light emitting polymer layer and
the small molecule layer are disposed between an anode and a
cathode on the receptor.
2. A thermal transfer donor element for use in making organic
electroluminescent devices, comprising in the following order: a
substrate; a light-to-heat conversion layer; an interlayer; and a
thermal transfer layer including, in the following order, a release
layer, a cathode layer, a light emitting polymer layer, a small
molecule hole transport layer, and an anode layer.
3. A method for patterning a first material and a second material
on a receptor, which method comprises selectively thermal
transferring the first material proximate to the second material on
the receptor from a first donor element, the first material being
formed on the donor element by solution coating using a solvent,
the second material being incompatible with said solvent, wherein
at least one of the first and second materials comprises an organic
electroluminescent material, an organic conductor, or an organic
semiconductor.
4. The method of claim 1, wherein the first material comprises a
light emitting polymer.
5. The method of claim 1, wherein the second material comprises an
organic small molecule material.
6. The method of claim 1, further comprising selectively thermal
transferring the second material on the receptor from a second
donor element.
7. The method of claim 1, wherein the second material is
selectively thermal transferred along with the first material from
the first donor sheet to the receptor.
8. The method of claim 1, wherein the first material is transferred
next to the second material on the receptor.
9. The method of claim 1, wherein after transfer the second
material is disposed between the first material and the
receptor.
10. The method of claim 1, wherein the step of selectively thermal
transferring the first material from the first donor element
comprises selectively heating the first donor element using a
thermal print head.
11. The method of claim 1, wherein the first donor element
comprises a substrate and a light-to-heat conversion layer disposed
between the substrate and the first material, and wherein the step
of selectively thermal transferring the first material comprises
selectively exposing the first donor element to imaging
radiation.
12. A method for patterning materials comprising the steps of:
forming a donor element comprising a donor substrate and a
multicomponent thermal transfer layer, the thermal transfer layer
having at least a first layer comprising a solvent-coated material
and a second layer comprising a solvent-susceptible material, the
solvent-susceptible material being incompatible with the solvent
used to coat the solvent-coated material, wherein the first layer
is disposed between the second layer and the donor substrate;
placing the thermal transfer layer proximate a receptor; and
selectively thermally transferring the multicomponent transfer
layer from the donor element to the receptor, wherein at least one
of the solvent-coated material and the solvent-susceptible material
comprises an organic electroluminescent material, an organic
conductor, or an organic semiconductor.
13. The method of claim 12, wherein the first layer comprises a
light emitting polymer.
14. The method of claim 12, wherein the second layer comprises an
organic small molecule material.
15. The method of claim 12, wherein the thermal transfer layer
comprises a conductor layer, a light emitting polymer layer, and a
small molecule layer.
16. The method of claim 12, wherein the donor element comprises a
substrate, a light-to-heat conversion layer disposed between the
substrate and the thermal transfer layer, and an interlayer
disposed between the light-to-heat conversion layer and the thermal
transfer layer.
17. The method of claim 16, wherein the donor element further
comprises a release layer disposed between the interlayer and the
thermal transfer layer.
18. The method of claim 17, wherein the release layer comprises
copper phthalocyanine.
19. The method of claim 12, wherein the step of selectively
thermally transferring comprises selectively heating the donor
element using a thermal print head.
20. The method of claim 12, wherein the step of selectively
thermally transferring comprises selectively exposing the donor
element to imaging radiation, the donor element including a
radiation absorber for converting the imaging radiation into
heat.
21. A method for patterning materials comprising the steps of:
thermally transferring selected portions of a first transfer layer
from a first donor element to a receptor, the first transfer layer
containing a first material, the first material being
solution-coated from a solvent onto the first donor; and thermally
transferring selected portions of a second transfer layer from a
second donor element to the receptor, the second transfer layer
containing a second material, the second material being
incompatible with the solvent, wherein at least one of the first
and second materials comprises an organic electroluminescent
material, an organic conductor, or an organic semiconductor.
22. The method of claim 21, wherein the first transfer layer
comprises multiple layers.
23. The method of claim 21, wherein the second transfer layer
comprises multiple layers.
24. The method of claim 21, wherein the first material comprises a
light emitting polymer.
25. The method of claim 21, wherein the second material comprises a
light emitting organic small molecule.
26. A method for making a thermal transfer donor element, which
method comprises forming a donor element that has a donor substrate
and a transfer layer, the transfer layer being formed by (a)
solution coating a first material using a solvent, (b) drying the
first material to substantially remove the solvent, and (c)
depositing a second material such that the first material is
disposed between the donor substrate and the second material, the
second material being incompatible with the solvent used to coat
the first material.
27. The method of claim 26, wherein the first material comprises a
light emitting polymer.
28. The method of claim 26, wherein the second material comprises
an organic small molecule material.
29. An organic electroluminescent display comprising: a first
organic electroluminescent device disposed on a display substrate,
the first organic electroluminescent device having an emitter layer
that is a light emitting polymer; and a second organic
electroluminescent device disposed on the display substrate, the
second organic electroluminescent device having an emitter layer
that is an organic small molecule material.
30. An organic electroluminescent display comprising an organic
electroluminescent device disposed on a display substrate, the
organic electroluminescent, device comprising, in the following
order from the substrate, a first electrode, a small molecule
charge transport layer, a polymer emitter layer, and a second
electrode.
Description
[0001] This application is a continuation-in-part of U.S. patent
application Ser. No. 09/231,723, filed Jan. 15, 1999, which is
incorporated herein by reference.
[0002] The present invention relates to methods and materials for
making and patterning organic electroluminescent devices as well as
to organic electroluminescent devices so made and to displays
employing organic electroluminescent devices.
BACKGROUND
[0003] Many miniature electronic and optical devices are formed
using layers of different materials stacked on each other. These
layers are often patterned to produce the devices. Examples of such
devices include optical displays in which each pixel is formed in a
patterned array, optical waveguide structures for telecommunication
devices, and metal-insulator-metal stacks for semiconductor-based
devices.
[0004] A conventional method for making these devices includes
forming one or more layers on a receptor substrate and patterning
the layers simultaneously or sequentially to form the device. In
many cases, multiple deposition and patterning steps are required
to prepare the ultimate device structure. For example, the
preparation of optical displays may require the separate formation
of red, green, and blue pixels. Although some layers may be
commonly deposited for each of these types of pixels, at least some
layers must be separately formed and often separately patterned.
Patterning of the layers is often performed by photolithographic
techniques that include, for example, covering a layer with a
photoresist, patterning the photoresist using a mask, removing a
portion of the photoresist to expose the underlying layer according
to the pattern, and then etching the exposed layer.
[0005] In some applications, it may be difficult or impractical to
produce devices using conventional photolithographic patterning.
For example, the number of patterning steps may be too large for
practical manufacture of the device. In addition, wet processing
steps in conventional photolithographic patterning may adversely
affect integrity, interfacial characteristics, and/or electrical or
optical properties of the previously deposited layers. It is
conceivable that many potentially advantageous device
constructions, designs, layouts, and materials are impractical
because of the limitations of conventional photolithographic
patterning. There is a need for new methods of forming these
devices with a reduced number of processing steps, particularly wet
processing steps. In at least some instances, this may allow for
the construction of devices with more reliability and more
complexity.
SUMMARY OF THE INVENTION
[0006] The present invention provides new thermal transfer donor
elements and methods of patterning using thermal transfer donor
elements. The donors and methods of the present invention are
particularly suited to patterning solvent-coated materials on the
same substrate as solvent-susceptible materials. This can be
especially useful in constructing organic electroluminescent
displays and devices as well as components for organic
electroluminescent displays and devices.
[0007] In one aspect, the present invention provides a method for
making an organic electroluminescent device that includes the step
of thermally transferring a light emitting polymer layer and a
small molecule layer from one or more thermal transfer donor
elements to a receptor so that the light emitting polymer layer and
the small molecule layer are disposed between an anode and a
cathode on the receptor.
[0008] In another aspect, the present invention provides a thermal
transfer donor element for use in making organic electroluminescent
devices that includes, in the following order, a substrate, a
light-to-heat conversion layer, an interlayer, and a thermal
transfer layer that has, in the following order, a release layer, a
cathode layer, a light emitting polymer layer, a small molecule
hole transport layer, and an anode layer.
[0009] In another aspect, the present invention provides a method
for patterning a first material and a second material on a
receptor, which method includes selectively thermal transferring
the first material proximate to the second material on the receptor
from a first donor element, the first material being formed on the
donor element by solution coating using a solvent, the second
material being incompatible with the solvent used to coat the first
material, wherein at least one of the first and second materials is
an organic electroluminescent material, an organic conductor, or an
organic semiconductor.
[0010] In another aspect, the present invention provides a method
for patterning materials that includes forming a donor element that
has a substrate and a multicomponent thermal transfer layer, the
thermal transfer layer having at least a first layer that includes
a solvent-coated material and a second layer that includes a
solvent susceptible material, the solvent-susceptible material
being incompatible with the solvent used to coat the solvent-coated
material, wherein the first layer is disposed between the second
layer and the donor substrate. Next, the thermal transfer layer of
the donor is placed proximate a receptor and the multicomponent
transfer layer is selectively thermally transferred from the donor
element to the receptor. At least one of the solvent-coated
material and the solvent-susceptible material is an organic
electroluminescent material, an organic conductor, or an organic
semiconductor.
[0011] In still another aspect, the present invention provides a
method for patterning materials that includes the steps of
thermally transferring selected portions of a first transfer layer
from a first donor element to a receptor, the first transfer layer
containing a first material, the first material being
solution-coated from a solvent onto the first donor, and thermally
transferring selected portions of a second transfer layer from a
second donor element t6 the receptor, the second transfer layer
containing a second material, the second material being
incompatible with the solvent. At least one of the first and second
materials is an organic electroluminescent material, an organic
conductor, or an organic semiconductor.
[0012] In yet another aspect, the present invention provides a
method for making a thermal transfer donor element, which method
includes forming a donor element that has a donor substrate and a
transfer layer, the transfer layer being formed by (a) solution
coating a first material using a solvent, (b) drying the first
material to substantially remove the solvent, and (c) depositing a
second material such that the first material is disposed between
the donor substrate and the second material, the second material
being incompatible with the solvent used to coat the first
material.
[0013] In another aspect, the present invention provides an organic
electroluminescent display that includes a first organic
electroluminescent device disposed on a display substrate, the
first organic electroluminescent device having an emitter layer
that is a light emitting polymer, and a second organic
electroluminescent device disposed on the display substrate, the
second organic electroluminescent device having an emitter layer
that is an organic small molecule material.
[0014] In another aspect, the present invention provides an organic
electroluminescent display that includes an organic
electroluminescent device disposed on a display substrates the
organic electroluminescent device including, in the following order
from the substrate, a first electrode, a small molecule charge
transport layer, a polymer emitter layer, and a second
electrode.
[0015] The above summary of the present invention is not intended
to describe each disclosed embodiment or every implementation of
the present invention. The Figures and the detailed description
which follow more particularly exemplify these embodiments.
[0016] It should be understood that by specifying an order in the
present document (e.g., order of steps to be performed, order of
layers on a substrate, etc.), it is not meant to preclude
intermediates between the items specified, as long as the items
appear in the order as specified.
BRIEF DESCRIPTION OF THE DRAWINGS
[0017] The invention may be more completely understood in
consideration of the following detailed description of various
embodiments of the invention in connection with the accompanying
drawings, in which:
[0018] FIG. 1A is a schematic cross-section of one example of a
thermal transfer element according to the invention;
[0019] FIG. 1B is a schematic cross-section of a second example of
a thermal transfer element according to the invention;
[0020] FIG. 1C is a schematic cross-section of a third example of a
thermal transfer element according to the invention;
[0021] FIG. 1D is a schematic cross-section of a fourth example of
a thermal transfer element according to the invention;
[0022] FIG. 2A is a schematic cross-section of a first example of a
transfer layer, according to the invention, for use in any of the
thermal transfer elements of FIGS. 1A to 1D;
[0023] FIG. 2B is a schematic cross-section of a second example of
a transfer layer, according to the invention, for use in any of the
thermal transfer elements of FIGS. 1A to 1D;
[0024] FIG. 2C is a schematic cross-section of a third example of a
transfer layer, according to the invention, for use in any of the
thermal transfer elements of FIGS. 1A to 1D;
[0025] FIG. 2D is a schematic cross-section of a fourth example of
a transfer layer, according to the invention, for use in any of the
thermal transfer elements of FIGS. 1A to 1D;
[0026] FIG. 2E is a schematic cross-section of a fifth example of a
transfer layer, according to the invention, for use in any of the
thermal transfer elements of FIGS. 1A to 1D;
[0027] FIG. 3A is a schematic cross-section of an example of a
transfer layer, according to the invention, for use in forming an
organic electroluminescent device;
[0028] FIG. 3B is a schematic cross-section of a second example of
a transfer layer, according to the invention, for use in forming an
organic electroluminescent device;
[0029] FIGS. 4A to 4C are cross-sectional views illustrating steps
in one example of a process for forming a display device according
to the invention;
[0030] FIGS. 5A and 5B are cross-sectional views illustrating steps
in one example of a process for forming a display device according
to the invention; and
[0031] FIG. 6 is a partial top view of a display device made
according to a method of the present invention.
[0032] While the invention is amenable to various modifications and
alternative forms, specifics thereof have been shown by way of
example in the drawings and will be described in detail. It should
be understood, however, that the intention is not to limit the
invention to the particular embodiments described. On the contrary,
the intention is to cover all modifications, equivalents, and
alternatives falling within the spirit and scope of the
invention.
DETAILED DESCRIPTION
[0033] The present invention is applicable to the formation or
partial formation of devices and other objects using thermal
transfer processes and thermal transfer donor elements for forming
the devices or other objects. As a particular example, a thermal
transfer element can be formed for making, at least in part, an
organic electroluminescent (OEL) device or array of devices, and
components for use in OEL displays. This can be accomplished, for
example, by thermal transfer of a single or a multicomponent
transfer unit of a thermal transfer element. It will be recognized
that single layer and multilayer transfers can be used to form
other devices and objects. While the present invention is not so
limited, an appreciation of various aspects of the invention will
be gained through a discussion of the examples provided below.
[0034] Materials can be patterned onto substrates by selective
thermal transfer of the materials from one or more thermal transfer
elements. A thermal transfer element can be heated by application
of directed heat on a selected portion of the thermal transfer
element. Heat can be generated using a heating element (e.g., a
resistive heating element), converting radiation (e.g., a beam of
light) to heat, and/or applying an electrical current to a layer of
the thermal transfer element to generate heat. In many instances,
thermal transfer using light from, for example, a lamp or laser, is
advantageous because of the accuracy and precision that can often
be achieved. The size and shape of the transferred pattern (e.g., a
line, circle, square, or other shape) can be controlled by, for
example, selecting the size of the light beam, the exposure pattern
of the light beam, the duration of directed beam contact with the
thermal transfer element, and the materials of the thermal transfer
element.
[0035] A thermal transfer element can include a transfer layer that
can be used to form various elements and devices, or portions
thereof. Exemplary materials and transfer layers include those that
can be used to form elements, devices, and portions thereof that
are useful in electronic displays. While the examples used in the
present invention most often focus on OEL devices and displays,
transfer of materials from thermal transfer elements can also be
used to form, at least in part, electronic circuitry, resistors,
capacitors, diodes, rectifiers, electroluminescent lamps, memory
elements, field effect transistors, bipolar transistors,
unijunction transistors MOS transistors,
metal-insulator-semiconductor transistors, organic transistors,
charge coupled devices, insulator-metal-insulator stacks, organic
conductor-metal-organic conductor stacks, integrated circuits,
photodetectors, lasers, lenses, waveguides, gratings, holographic
elements, filters (e.g., add-drop filters, gain-flattening filters,
cut-off filters, and the like), mirrors, splitters, couplers,
combiners, modulators, sensors (e.g., evanescent sensors, phase
modulation sensors, interferometric sensors, and the like), optical
cavities, piezoelectric devices, ferroelectric devices, thin film
batteries, or combinations thereof; for example, the combination of
field effect transistors and organic electroluminescent lamps as an
active matrix array for an optical display. Other items may be
formed by transferring a multicomponent transfer unit and/or a
single layer.
[0036] Thermal transfer using light can often provide better
accuracy and quality control for very small devices, such as small
optical and electronic devices, including, for example, transistors
and other components of integrated circuits, as well as components
for use in a display, such as electroluminescent lamps and control
circuitry. Moreover, thermal transfer using light may, at least in
some instances, provide for better registration when forming
multiple devices over an area that is large compared to the device
size. As an example, components of a display, which has many
pixels, can be formed using this method.
[0037] In some instances, multiple thermal transfer elements may be
used to form a device or other object, or to form adjacent devices,
other objects, or portions thereof The multiple thermal transfer
elements may include thermal transfer elements with multicomponent
transfer units and thermal transfer elements that transfer a single
layer. For example, a device or other object may be formed using
one or more thermal transfer elements with multicomponent transfer
units and/or one or more thermal transfer elements that each can be
used to transfer a single layer or a multilayer unit.
[0038] Thermal transfer of one or more layers to form a device or
an array of devices can also be useful, for example, to reduce or
eliminate wet processing steps of processes such as
photolithographic patterning, which are used to form many
electronic and optical devices. Thermal transfer to pattern layers
from donor elements can also be useful to de-couple layer coating
steps from patterning steps, for example where such coupling can
limit the types of layered structures, or the types of adjacent
structures, that can be patterned. In conventional patterning
processes such as photolithography, ink-jet, screen printing, and
various mask-based techniques, layers are typically coated directly
onto the substrate on which patterning occurs. Patterning can take
place simultaneously with coating (as for ink-jet, screen printing,
and some mask-based processes) or subsequent to coating via etching
or another removal technique. A difficulty with such conventional
approaches is that solvents used to coat materials, and/or etching
processes used to pattern materials, can damage, dissolve,
penetrate, and/or render inoperable previously coated or patterned
layers or materials.
[0039] In the present invention, materials can be coated onto
thermal transfer donor elements to form the transfer layers of the
donor elements. The transfer layer materials can then be patterned
via selective thermal transfer from the donor to a receptor.
Coating onto a donor followed by patterning via selective transfer
represents a de-coupling of layer coating steps from patterning
steps. An advantage of de-coupling coating and patterning steps is
that materials can be patterned on top of or next to other
materials that would be difficult to pattern, if possible at all,
using conventional patterning processes. For example, in methods of
the present invention a solvent-coated layer can be patterned on
top of a solvent-susceptible material that would be dissolved,
attacked, penetrated, and/or rendered inoperable for its intended
purpose in the presence of the solvent had the solvent-coated layer
been coated directly on the solvent-susceptible material.
[0040] A transfer layer of a donor element can be made by
solvent-coating a first material on the donor, suitably drying the
coating, and then depositing a second layer that includes material
that may be susceptible to the solvent used to coat the first
material. Damage to the second layer can be minimized or eliminated
by evaporation, or otherwise removal, of much or most of the
solvent before coating of the second layer. Upon thermal transfer
of this multicomponent transfer layer from the donor element to a
receptor, the second layer becomes positioned between the receptor
and the solvent-coated first material. Thermal transfer of multiple
layer units results in a reverse ordering of the transferred layers
on the receptor relative to the ordering on the donor element.
Because of this, solvent-susceptible layers can be pattered
underneath solvent-coated layers. In addition, the layers need not
be transferred together as a multiple layer unit. The
solvent-susceptible material(s) can be patterned by any suitable
method, including thermal transfer from a donor, followed by
another thermal transfer step using another donor to transfer the
solvent-coated material(s).
[0041] The same holds for patterned thermal transfer of
solvent-coated materials next to, but not necessarily in contact
with, materials or layers on a receptor that may be incompatible
with the solvent. As will be discussed in more detail below, the
formation of OEL devices provides particularly suited examples.
[0042] With these general concepts of the present invention in
mind, exemplary donor elements, thermal transfer methods, and
devices made by thermal transfer methods will now be described.
[0043] One example of a suitable thermal transfer element 100 is
illustrated in FIG. 1A. The thermal transfer element 100 includes a
donor substrate 102, an optional primer layer 104, a light-to-heat
conversion (LTHC) layer 106, an optional interlayer 108, an
optional release layer 112, and a transfer layer 110. Directed
light from a light-emitting source, such as a laser or lamp, can be
used to illuminate the thermal transfer element 100 according to a
pattern. The LTHC layer 106 contains a radiation absorber that
converts light energy to heat energy. The conversion of the light
energy to heat energy results in the transfer of a portion of the
transfer layer 110 to a receptor (not shown).
[0044] Another example of a thermal transfer element 120 includes a
donor substrate 122, an LTHC layer 124, an interlayer 126, and a
transfer layer 128, as illustrated in FIG. 1B. Another suitable
thermal transfer element 140 includes a donor substrate 142, an
LTHC layer 144, and a transfer layer 146, as illustrated in FIG.
1C. Yet another example of a thermal transfer element 160 includes
a donor substrate 162 and a transfer layer 164, as illustrated in
FIG. 1D, with an optional radiation absorber disposed in the donor
substrate 162 and/or transfer layer 164 to convert light energy to
heat energy. Alternatively, the thermal transfer element 160 may be
used without a radiation absorber for thermal transfer of the
transfer layer 164 using a heating element, such as a resistive
heating element, that contacts the thermal transfer element to
selectively heat the thermal transfer element and transfer the
transfer layer according to a pattern. A thermal transfer element
160 without radiation absorber may optionally include a release
layer, an interlayer, and/or other layers (e.g., a coating to
prevent sticking of the resistive heating element) used in the
art.
[0045] For thermal transfer using radiation (e.g., light), a
variety of radiation-emitting sources can be used in the present
invention. For analog techniques (e.g., exposure through a mask),
high-powered light sources (e.g., xenon flash lamps and lasers) are
useful. For digital imaging techniques, infrared, visible, and
ultraviolet lasers are particularly useful. Suitable lasers
include, for example, high power (.gtoreq.100 mW) single mode laser
diodes, fiber-coupled laser diodes, and diode-pumped solid state
lasers (e.g., Nd:YAG and Nd:YLF). Laser exposure dwell times can be
in the range from, for example, about 0.1 to 100 microseconds and
laser fluences can be in the range from, for example, about 0.01 to
about 1 J/cm.sup.2.
[0046] When high spot placement accuracy is required (e.g. for high
information full color display applications) over large substrate
areas, a laser is particularly useful as the radiation source.
Laser sources are compatible with both large rigid substrates such
as 1 m.times.1 m.times.1.1 mm glass, and continuous or sheeted film
substrates, such as 100 .mu.m polyimide sheets.
[0047] Resistive thermal print heads or arrays may be used, for
example, with simplified donor film constructions lacking an LTHC
layer and radiation absorber. This may be particularly useful with
smaller substrate sizes (e.g., less than approximately 30 cm in any
dimension) or for larger patterns, such as those required for
alphanumeric segmented displays.
[0048] During imaging, the thermal transfer element is typically
brought into intimate contact with a receptor. In at least some
instances, pressure or vacuum are used to hold the thermal transfer
element in intimate contact with the receptor. A radiation source
is then used to heat the LTHC layer (and/or other layer(s)
containing radiation absorber) in an imagewise fashion (e.g.,
digitally or by analog exposure through a mask) to perform
imagewise transfer of the transfer layer from the thermal transfer
element to the receptor according to a pattern.
[0049] Alternatively, a heating element, such as a resistive
heating element, may be used to transfer the multicomponent
transfer unit. The thermal transfer element is selectively
contacted with the heating element to cause thermal transfer of a
portion of the transfer layer according to a pattern. In another
embodiment, the thermal transfer element may include a layer that
can convert an electrical current applied to the layer into
heat.
[0050] Typically, the transfer layer is transferred to the receptor
without transferring any of the other layers of the thermal
transfer element, such as the optional interlayer and the LTHC
layer. The presence of the optional interlayer may eliminate or
reduce the transfer of the LTHC layer to the receptor and/or reduce
distortion in the transferred portion of the transfer layer.
Preferably, under imaging conditions, the adhesion of the
interlayer to the LTHC layer is greater than the adhesion of the
interlayer to the transfer layer. In some instances, a reflective
or an absorptive interlayer can be used to attenuate the level of
imaging radiation transmitted through the interlayer and reduce any
damage to the transferred portion of the transfer layer that may
result from interaction of the transmitted radiation with the
transfer layer and/or the receptor. This is particularly beneficial
in reducing thermal damage which may occur when the receptor is
highly absorptive of the imaging radiation.
[0051] Large thermal transfer elements can be used, including
thermal transfer elements that have length and width dimensions of
a meter or more. In operation, a laser can be rastered or otherwise
moved across the large thermal transfer element, the laser being
selectively operated to illuminate portions of the thermal transfer
element according to a desired pattern. Alternatively, the laser
may be stationary and the thermal transfer element moved beneath
the laser.
[0052] Thermal transfer donor substrates can be polymer films. One
suitable type of polymer film is a polyester film, for example,
polyethylene terephthalate or polyethylene naphthalate films.
However, other films with sufficient optical properties (if light
is used for heating and transfer), including high transmission of
light at a particular wavelength, as well as sufficient mechanical
and thermal stability for the particular application, can be used.
The donor substrate, in at least some instances, is flat so that
uniform coatings can be formed thereon. The donor substrate is also
typically selected from materials that remain stable despite
heating of the LTHC layer. The typical thickness of the donor
substrate ranges from 0.025 to 0.15 mm, preferably 0.05 to 0.1 mm,
although thicker or thinner donor substrates may be used.
[0053] Typically, the materials used to form the donor substrate
and the LTHC layer are selected to improve adhesion between the
LTHC layer and the donor substrate. An optional priming layer can
be used to increase uniformity during the coating of subsequent
layers and also increase the interlayer bonding strength between
the LTHC layer and the donor substrate. One example of a suitable
substrate with primer layer is available from Teijin Ltd. (Product
No. HPE100, Osaka, Japan).
[0054] For radiation-induced thermal transfer a light-to-heat
conversion (LTHC) layer is typically incorporated within the
thermal transfer element to couple the energy of light radiated
from a light-emitting source into the thermal transfer element. The
LTHC layer preferably includes a radiation absorber that absorbs
incident radiation (e.g., las er light) and converts at least a
portion of the incident radiation into heat to enable transfer of
the transfer layer from the thermal transfer element to the
receptor. In some embodiments, there is no separate LTHC layer and,
instead, the radiation absorber is disposed in another layer of the
thermal transfer element, such as the donor substrate or the
transfer layer. In other embodiments, the thermal transfer element
includes an LTHC layer and also includes additional radiation
absorber(s) disposed in one or more of the other layers of the
thermal transfer element, such as, for example, the donor substrate
or the transfer layer. In yet other embodiments, the thermal
transfer element does not include an LTHC layer or radiation
absorber and the transfer layer is transferred using a heating
element that contacts the thermal transfer element.
[0055] Typically, the radiation absorber in the LTHC layer (or
other layers) absorbs light in the infrared, visible, and/or
ultraviolet regions of the electromagnetic spectrum. The radiation
absorber is typically highly absorptive of the selected imaging
radiation, providing an optical density at the wavelength of the
imaging radiation in the range of 0.2 to 3, and preferably from 0.5
to 2. Suitable radiation absorbing materials can include, for
example, dyes (e.g., visible dyes, ultraviolet dyes, infrared dyes,
fluorescent dyes, and radiation-polarizing dyes), pigments, metals,
metal compounds, metal films, and other suitable absorbing
materials. Examples of suitable radiation absorbers can include
carbon black, metal oxides, and metal sulfides. One example of a
suitable LTHC layer can include a pigment, such as carbon black,
and a binder, such as an organic polymer. Another suitable LTHC
layer can include metal or metal/metal oxide formed as a thin film,
for example, black aluminum (i.e., a partially oxidized aluminum
having a black visual appearance). Metallic and metal compound
films may be formed by techniques, such as, for example, sputtering
and evaporative deposition. Particulate coatings may be formed
using a binder and any suitable dry or wet coating techniques.
[0056] Radiation absorber material can be uniformly disposed
throughout the LTHC layer or can be non-homogeneously distributed.
For example, as described in co-assigned U.S. patent application
Ser. No. ______ (attorney docket number 54992USA9A, entitled
"Thermal Mass Transfer Donor Elements", the disclosure of which is
wholly incorporated into this document, non-homogeneous LTHC layers
can be used to control temperature profiles in donor elements. This
can give rise to thermal transfer elements that have higher
transfer sensitivities (e.g., better fidelity between the intended
transfer patterns and actual transfer patterns).
[0057] Dyes suitable for use as radiation absorbers in an LTHC
layer may be present in particulate form, dissolved in a binder
material, or at least partially dispersed in a binder material.
When dispersed particulate radiation absorbers are used, the
particle size can be, at least in some instances, about 10 .mu.m or
less, and may be about 1 .mu.m or less. Suitable dyes include those
dyes that absorb in the IR region of the spectrum. Examples of such
dyes may be found in Matsuoka, M., "Infrared Absorbing Matcrials",
Plenum Press, New York, 1990; Matsuoka, M., Absorption Spectra of
Dyes for Diode Lasers, Bunshin Publishing Co., Tokyo, 1990, U.S.
Pat. Nos. 4,722,583; 4,833,124; 4,912,083; 4,942,141; 4,948,776;
4,948,778; 4,950,639; 4,940,640; 4,952,552; 5,023,229; 5,024,990;
5,156,938; 5,286,604; 5,340,699; 5,351,617; 5,360,694; and
5,401,607; European Patent Nos. 321,923 and 568,993; and Beilo, K.
A. et al., J. Chem. Soc., Chem. Commun., 1993, 452-454 (1993), all
of which are herein incorporated by reference. IR absorbers
marketed by Glendale Protective Technologies, Inc., Lakeland, Fla.,
under the designation CYASORB IR-99, IR-126 and IR-165 may also be
used. A specific dye may be chosen based on factors such as,
solubility in, and compatibility with, a specific binder and/or
coating solvent, as well as the wavelength range of absorption.
[0058] Pigmentary materials may also be used in the LTHC layer as
radiation absorbers. Examples of suitable pigments include carbon
black and graphite, as well as phthalocyanines, nickel dithiolenes,
and other pigments described in U.S. Pat. Nos. 5,166,024 and
5,351,617, incorporated herein by reference. Additionally, black
azo pigments based on copper or chromium complexes of, for example,
pyrazolone yellow, dianisidine red, and nickel azo yellow can be
useful. Inorganic pigments can also be used, including, for
example, oxides and sulfides of metals such as aluminum, bismuth,
tin, indium, zinc, titanium, chromium, molybdenum, tungsten,
cobalt, iridium, nickel, palladium, platinum, copper, silver, gold,
zirconium, iron, lead, and tellurium. Metal borides, carbides,
nitrides, carbonitrides, bronze-structured oxides, and oxides
structurally related to the bronze family (e.g., WO.sub.2.9) may
also be used.
[0059] Metal radiation absorbers may be used, either in the form of
particles, as described for instance in U.S. Pat. No. 4,252,671,
incorporated herein by reference, or as films, as disclosed in U.S.
Pat. No. 5,256,506, incorporated herein by reference. Suitable
metals include, for example, aluminum, bismuth, tin, indium,
tellurium and zinc.
[0060] As indicated, a particulate radiation absorber may be
disposed in a binder. The weight percent of the radiation absorber
in the coating, excluding the solvent in the calculation of weight
percent, is generally from 1 wt. % to 30 wt. %, preferably from 3
wt. % to 20 wt. %, and most preferably from 5 wt. % to 15 wt. %,
depending on the particular radiation absorber(s) and binder(s)
used in the LTHC.
[0061] Suitable binders for use in the LTHC layer include
film-forming polymers, such as, for example, phenolic resins (e.g.,
novolak and resole resins), polyvinyl butyral resins, polyvinyl
acetates, polyvinyl acetals, polyvinylidene chlorides,
polyacrylates, cellulosic ethers and esters, nitrocelluloses, and
polycarbonates. Suitable binders may include monomers, oligomers,
or polymers that have been or can be polymerized or crosslinked. In
some embodiments, the binder is primarily formed using a coating of
crosslinkable monomers and/or oligomers with optional polymer. When
a polymer is used in the binder, the binder includes 1 to 50 wt. %,
preferably, 10 to 45 wt. %, polymer (excluding the solvent when
calculating wt. %).
[0062] Upon coating on the donor substrate, the monomers,
oligomers, and polymers may be crosslinked to form the LTHC. In
some instances, if crosslinking of the LTHC layer is too low, the
LTHC layer may be damaged by the heat and/or permit the transfer of
a portion of the LTHC layer to the receptor with the transfer
layer.
[0063] The inclusion of a thermoplastic resin (e.g., polymer) may
improve, in at least some instances, the performance (e.g.,
transfer properties and/or coatability) of the LTHC layer. It is
thought that a thermoplastic resin may improve the adhesion of the
LTHC layer to the donor substrate. In one embodiment, the binder
includes 25 to 50 wt. % (excluding the solvent when calculating
weight percent) thermoplastic resin, and, preferably, 30 to 45 wt.
% thermoplastic resin, although lower amounts of thermoplastic
resin may be used (e.g., 1 to 15 wt. %). The thermoplastic resin is
typically chosen to be compatible (i.e., form a one-phase
combination) with the other materials of the binder. A solubility
parameter can be used to indicate compatibility, Polymer Handbook,
J. Brandrup, ed., pp. VII 519-557 (1989), incorporated herein by
reference. In at least some embodiments, a thermoplastic resin that
has a solubility parameter in the range of 9 to 13
(cal/cm.sup.3).sup.1/2, preferably, 9.5 to 12
(cal/cm.sup.3).sup.1/2, is chosen for the binder. Examples of
suitable thermoplastic resins include polyacrylics, styrene-acrylic
polymers and resins, and polyvinyl butyral.
[0064] Conventional coating aids, such as surfactants and
dispersing agents, may be added to facilitate the coating process.
The LTHC layer may be coated onto the donor substrate using a
variety of coating methods known in the art. A polymeric or organic
LTHC layer is coated, in at least some instances, to a thickness of
0.05 .mu.m to 20 .mu.m, preferably, 0.5 .mu.m to 10 .mu.m, and,
most preferably, 1 .mu.m to 7 .mu.m. An inorganic LTHC layer is
coated, in at least some instances, to a thickness in the range of
0.001 to 10 .mu.m, and preferably, 0.002 to 1 .mu.m.
[0065] An optional interlayer may be disposed between the LTHC
layer and transfer layer in thermal transfer elements to minimize
damage and contamination of the transferred portion of the transfer
layer and may also reduce distortion in the transferred portion of
the transfer layer. The interlayer may also influence the adhesion
of the transfer layer to the rest of the thermal transfer element.
Typically, the interlayer has high thermal resistance. Preferably,
the interlayer does not distort or chemically decompose under the
imaging conditions, particularly to an extent that renders the
transferred image non-functional. The interlayer typically remains
in contact with the LTHC layer during the transfer process and is
not substantially transferred with the transfer layer.
[0066] Suitable interlayers include, for example, polymer films,
metal layers (e.g., vapor deposited metal layers), inorganic layers
(e.g., sol-gel deposited layers and vapor deposited layers of
inorganic oxides (e.g., silica, titania, and other metal oxides)),
and organic/inorganic composite layers. Organic materials suitable
as interlayer materials include both thermoset and thermoplastic
materials. Suitable thermoset materials include resins that may be
crosslinked by heat, radiation, or chemical treatment including,
but not limited to, crosslinked or crosslinkable polyacrylates,
polymethacrylaies, polyesters, epoxies, and polyurethanes. The
thermoset materials may be coated onto the LTHC layer as, for
example, thermoplastic precursors and subsequently crosslinked to
form a crosslinked interlayer.
[0067] Suitable thermoplastic materials include, for example,
polyacrylates, polymethacrylates, polystyrenes, polyurethanes,
polysulfones, polyesters, and polyimides. These thermoplastic
organic materials may be applied via conventional coating
techniques (for example, solvent coating, spray coating, or
extrusion coating). Typically, the glass transition temperature
(T.sub.g) of thermoplastic materials suitable for use in the
interlayer is 25.degree. C. or greater, preferably 50.degree. C. or
greater, more preferably 100.degree. C. or greater, and, most
preferably, 150.degree. C. or greater. The interlayer may be either
transmissive, absorbing, reflective, or some combination thereof,
at the imaging radiation wavelength.
[0068] Inorganic materials suitable as interlayer materials
include, for example, metals, metal oxides, metal sulfides, and
inorganic carbon coatings, including those materials that are
highly transmissive or reflective at the imaging light wavelength.
These materials may be applied to the light-to-heat-conversion
layer via conventional techniques (e.g., vacuum sputtering, vacuum
evaporation, or plasma jet deposition).
[0069] The interlayer may provide a number of benefits. The
interlayer may be a barrier against the transfer of material from
the light-to-heat conversion layer. It may also modulate the
temperature attained in the transfer layer so that thermally
unstable materials can be transferred. The presence of an
interlayer may also result in improved plastic memory in the
transferred material.
[0070] The interlayer may contain additives, including, for
example, photoinitiators, surfactants, pigments, plasticizers, and
coating aids. The thickness of the interlayer may depend on factors
such as, for example, the material of the interlayer, the material
of the LTHC layer, the material of the transfer layer, the
wavelength of the imaging radiation, and the duration of exposure
of the thermal transfer element to imaging radiation. For polymer
interlayers, the thickness of the interlayer typically is in the
range of 0.05 .mu.m to 10 .mu.m, preferably, from about 0.1 .mu.m
to 4 .mu.m, more preferably, 0.5 to 3 .mu.m, and, most preferably,
0.8 to 2 .mu.m. For inorganic interlayers (e.g., metal or metal
compound interlayers), the thickness of the interlayer typically is
in the range of 0.005 m to 10 .mu.m, preferably, from about 0.01
.mu.m to 3 .mu.m, and, more preferably, from about 0.02 to 1
.mu.m.
[0071] Thermal transfer elements can include an optional release
layer. The optional release layer typically facilitates release of
the transfer layer from the rest of the thermal transfer element
(e.g., the interlayer and/or the LTHC layer) upon heating of the
thermal transfer element, for example, by a light-emitting source
or a heating element. In at least some cases, the release layer
provides some adhesion of the transfer layer to the rest of the
thermal transfer element prior to exposure to heat. Suitable
release layers include, for example, conducting and non-conducting
thermoplastic polymers, conducting and non-conducting filled
polymers, and/or conducting and non-conducting dispersions.
Examples of suitable polymers include acrylic polymers,
polyanilines, polythiophenes, poly(phenylenevinylenes),
polyacetylenes, and other conductive organic materials, such as
those listed in Handbook of Conductive Molecules and Polymers,
Vols. 1-4, H. S. Nalwa, ed., John Wiley and Sons, Chichester
(1997), incorporated herein by reference. Examples of suitable
conductive dispersions include inks containing carbon black,
graphite, ultrafine particulate indium tin oxide, ultrafine
antimony tin oxide, and commercially available materials from
companies such as Nanophase Technologies Corporation (Burr Ridge,
Ill.) and Metech (Elverson, Pa.). Other suitable materials for the
release layer include sublimable insulating materials and
sublimable semiconducting materials (such as phthalocyanines),
including, for example, the materials described in U.S. Pat. No.
5,747,217, incorporated herein by reference.
[0072] The release layer may be part of the transfer layer or a
separate layer. All or a portion of the release layer may be
transferred with the transfer layer. Alternatively, most or
substantially all of the release layer can remain with the donor
substrate when the transfer layer is transferred. In some
instances, for example with a release layer that includes a
sublimable material, a portion of the release layer may be
dissipated during the transfer process.
[0073] The transfer layers of thermal transfer elements of the
present invention can include one or more layers for transfer to a
receptor. These one or more layers may be formed using organic,
inorganic, organometallic, and other materials. Although the
transfer layer is described and illustrated as having one or more
discrete layers, it will be appreciated that, at least in some
instances where more than one layer is used, there may be an
interfacial region that includes at least a portion of each layer.
This may occur, for example, if there is mixing of the layers or
diffusion of material between the layers before, during, or after
transfer of the transfer layer. In other instances, individual
layers may be completely or partially mixed before, during, or
after transfer of the transfer layer. In any case, these structures
will be referred to as including more than one independent layer,
particularly if different functions of the device are performed by
the different regions.
[0074] One advantage of using a multicomponent transfer unit,
particularly if the layers do not mix, is that the important
interfacial characteristics of the layers in the multicomponent
transfer unit can be produced when the thermal transfer unit is
prepared and, preferably, retained during transfer.
[0075] One example of a transfer layer includes a single or
multicomponent transfer unit that is used to form at least part of
a multilayer device, such as an OEL device, or another device used
in connection with OEL devices, on a receptor. In some cases, the
transfer layer may include all of the layers needed to form an
operative device. In other cases, the transfer layer may include
fewer than all the layers needed to form an operative device, the
other layers being formed via transfer from one or more other donor
elements or via some other suitable transfer or patterning method.
In still other instances, one or more layers of a device may be
provided on the receptor, the remaining layer or layers being
included in the transfer layer of one or more donor elements.
Alternatively, one or more additional layers of a device may be
transferred onto the receptor after the transfer layer has been
patterned. In some instances, the transfer layer is used to form
only a single layer of a device.
[0076] In one embodiment, an exemplary transfer layer includes a
multicomponent transfer unit that is capable of forming at least
two layers of a multilayer device. These two layers of the
multilayer device often correspond to two layers of the transfer
layer. In this example, one of the layers that is formed by
transfer of the multicomponent transfer unit can be an active layer
(i.e., a layer that acts as a conducting, semiconducting, electron
blocking, hole blocking, light producing (e.g., luminescing, light
emitting, fluorescing, or phosphorescing), electron producing, or
hole producing layer). A second layer that is formed by transfer of
the multicomponent transfer unit can be another active layer or an
operational layer (i.e., a layer that acts as an insulating,
conducting, semiconducting, electron blocking, hole blocking, light
producing, electron producing, hole producing, light absorbing,
reflecting, diffracting, phase retarding, scattering, dispersing,
or diffusing layer in the device). The second layer can also be a
non-operational layer (i.e., a layer that does not perform a
function in the operation of the device, but is provided, for
example, to facilitate transfer and/or adherence of the transfer
unit to the receptor substrate during patterning). The
multicomponent transfer unit may also be used to form additional
active layers, operational layers, and/or non-operational
layers.
[0077] The transfer layer may include an adhesive layer disposed on
an outer surface of the transfer layer to facilitate adhesion to
the receptor. The adhesive layer may be an operational layer, for
example, if the adhesive layer conducts electricity between the
receptor and the other layers of the transfer layer, or a
non-operational layer, for example, if the adhesive layer only
adheres the transfer layer to the receptor. The adhesive layer may
be formed using, for example, thermoplastic polymers, including
conducting and non-conducting polymers, conducting and
non-conducting filled polymers, and/or conducting and
non-conducting dispersions. Examples of suitable polymers include
acrylic polymers, polyanilines, polythiophenes,
poly(phenylenevinylenes), polyacetylenes, and other conductive
organic materials such as those listed in Handbook of Conductive
Molecules and Polymers, Vols. 1-4, H. S. Nalwa, ed., John Wiley and
Sons, Chichester (1997), incorporated herein by reference. Examples
of suitable conductive dispersions include inks containing carbon
black, graphite, carbon nanotubes, ultrafine particulate indium tin
oxide, ultrafine antimony tin oxide, and commercially available
materials from companies such as Nanophase Technologies Corporation
(Burr Ridge, Ill.) and Metech (Elverson, Pa.). Conductive adhesive
layers can also include vapor or vacuum deposited organic
conductors such as N,N'-bis(1-naphthyl)-N,N'-diphenylbenzidine
(also known as NPB).
[0078] The transfer layer may also include a release layer disposed
on the surface of the transfer layer that is in contact with the
rest of the thermal transfer element. As described above, this
release layer may partially or completely transfer with the
remainder of the transfer layer, or substantially all of the
release layer may remain with the thermal transfer element, or the
release layer may dissipate in whole or in part, upon transfer of
the transfer layer. Suitable release layers are described
above.
[0079] Although the transfer layer may be formed with discrete
layers, it will be understood that, in at least some embodiments,
the transfer layer may include layers that have multiple components
and/or multiple uses in the device. It will also be understood
that, at least in some embodiments, two or more discrete layers may
be melted together during transfer or otherwise mixed or combined.
In any case, these layers, although mixed or combined, will be
referred to as individual layers.
[0080] One example of a transfer layer 170, illustrated in FIG. 2A,
includes a conductive metal or metal compound layer 172 and a
conductive polymer layer 174. Transfer layer 170 may be arranged so
that either layer 172 or layer 174 is the outer layer of the donor
(i.e., layer for contacting receptor (not shown) upon transfer).
The conductive polymer layer 174 may also act, at least in part, as
an adhesive layer to facilitate transfer to the receptor or
elements or layers previously formed on the receptor when the
conductive polymer layer 174 is the outer layer.
[0081] A second example of a transfer layer 180, illustrated in
FIG. 2B, includes a release layer 182, followed by a conductive
metal or metal compound layer 184, and then a conductive or
non-conductive polymer layer 186 for contact with a receptor (not
shown). In other embodiments, the ordering of layers 184 and 186
can be reversed so that layer 184 is the outer layer.
[0082] A third example of a transfer layer 190, illustrated in FIG.
2C, includes a conductive inorganic layer 191 (for example, vapor
deposited indium tin oxide), a conductive or non-conductive polymer
layer 192, and an optional release layer (not shown). Either layer
191 or layer 192 can be the outer layer.
[0083] A fourth example of a transfer layer 195, illustrated in
FIG. 2D, consists of a multilayer metal stack 196 of alternating
metals 197, 198, such as gold-aluminum-gold, and a conductive or
non-conductive polymer layer 199 for contact with a receptor.
[0084] A fifth example of a transfer layer 175, illustrated in FIG.
2E, includes a solvent-coated layer 176 and an adjacent layer 177
that is susceptible to the solvent used to coat layer 176. Layer
177 can be formed on solvent-coated layer 176 after layer
solvent-coated 176 is coated onto the donor element, and preferably
dried to substantially remove the solvent. Transfer layer 175 can
include additional layers (not shown) disposed above layer 177,
below layer 176, or between layers 176 and 177, including release
and adhesion layers. When transfer layer 175 is transferred to a
receptor (not shown), layer 177 will be disposed between the
receptor and solvent-coated layer 176.
[0085] The transfer of a one or more single or multicomponent
transfer units to form at least a portion of an OEL (organic
electroluminescent) device provides a particularly illustrative,
non-limiting example of the formation of an active device using a
thermal transfer element. In at least some instances, an OEL device
includes a thin layer, or layers, of one or more suitable organic
materials sandwiched between a cathode and an anode. Electrons are
injected into the organic layer(s) from the cathode and holes are
injected into the organic layer(s) from the anode. As the injected
charges migrate towards the oppositely charged electrodes, they may
recombine to form electron-hole pairs which are typically referred
to as excitons. These excitons, or excited state species, may emit
energy in the form of light as they decay back to a ground state
(see, for example, T. Tsutsui, MRS Bulletin, 22, 39-45 (1997),
incorporated herein by reference).
[0086] Illustrative examples of OEL device constructions include
molecularly dispersed polymer devices where charge carrying and/or
emitting species are dispersed in a polymer matrix (see J. Kido
"Organic Electroluminescent devices Based on Polymeric Materials",
Trends in Polymer Science, 2, 350-355 (1994), incorporated herein
by reference), conjugated polymer devices where layers of polymers
such as polyphenylene vinylene act as the charge carrying and
emitting species (see J. J. M. Halls et al., Thin Solid Films, 276,
13-20 (1996), herein incorporated by reference), vapor deposited
small molecule heterostructure devices (see U.S. Pat. No. 5,061,569
and C. H. Clien et al., "Recent Developments in Molecular Organic
Electroluminescent Materials", Macromolecular Symposia, 125, 1-48
(1997), herein incorporated by reference), light emitting
electrochemical cells (see Q. Pei et al., J. Amer. Chem. Soc., 118,
3922-3929 (1996), herein incorporated by reference), and vertically
stacked organic light-emitting diodes capable of emitting light of
multiple wavelengths (see U.S. Pat. No. 5,707,745 and Z. Shen et
al., Science, 276, 2009-2011 (1997), herein incorporated by
reference).
[0087] As used herein, the term "small molecule" refers to a
non-polymeric organic, inorganic, or organometallic molecule, and
the term "organic small molecule" refers to a non-polymer organic
or organometallic molecule. In OEL devices, small molecule
materials can be used as emitter layers, as charge transport
layers, as dopants in emitter layers (e.g., to control the emitted
color) or charge transport layers, and the like.
[0088] One suitable example of a transfer layer 200 for forming an
OEL device is illustrated in FIG. 3A. The transfer layer 200
includes an anode 202, an optional hole transport layer 204, an
electron transport/emitter layer 206, and a cathode 208. A separate
electron transport layer (not shown) can be included between
emitter layer 206 and cathode 208. Also, a separate electron
blocking layer (not shown) can be included between the emitter
layer and the anode, and a separate hole blocking layer (not shown)
can be included between the emitter layer and the cathode.
Alternatively, either the cathode or anode can be provided
separately on a receptor (e.g., as a conductive coating on the
receptor, or as patterned conductive stripes or pads on the
receptor) and not in the transfer layer. This is illustrated in
FIG. 3B, for an anode-less transfer layer 200' using primed
reference numerals to indicate layers in common with the transfer
layer 200.
[0089] The transfer layer 200 may also include one or more layers,
such as a release layer 210 and/or an adhesive layer 212, to
facilitate the transfer of the transfer layer to the receptor.
Either of these two layers can be conductive polymers to facilitate
electrical contact with a conductive layer or structure on the
receptor or conductive layer(s) formed subsequently on the transfer
layer. It will be understood that the positions of the release
layer and adhesive layer could be switched with respect to the
other layers of the transfer layer so that the transfer layer 200
can be transferred with either the anode or the cathode disposed
proximate to the receptor surface.
[0090] For many applications, such as display applications, it is
preferred that at least one of the cathode and anode be transparent
to the light emitted by the electroluminescent device. This depends
on the orientation of the device (i.e, whether the anode or the
cathode is closer to the receptor substrate) as well as the
direction of light emission (i.e., through the receptor substrate
or away from the receptor substrate).
[0091] The anode 202 and cathode 208 are typically formed using
conducting materials such as metals, alloys, metallic compounds,
metal oxides, conductive ceramics, conductive dispersions, and
conductive polymers, including, for example, gold, platinum,
palladium, aluminum, titanium, titanium nitride, indium tin oxide
(ITO), fluorine tin oxide (FTO), and polyaniline. The anode 202 and
the cathode 208 can be single layers of conducting materials or
they can include multiple layers. For example, an anode or a
cathode may include a layer of aluminum and a layer of gold, a
layer of aluminum and a layer of lithium fluoride, or a metal layer
and a conductive organic layer. It may be particularly useful to
provide a two-layer cathode (or anode) consisting of a conductive
organic layer (e.g., 0.1 to 5 microns thick) and a thin metal or
metal compound layer (e.g., 100 to 1000 Angstroms). Such a bilayer
electrode construction may be more resistant moisture or oxygen
that can damage underlying moisture- or oxygen-sensitive layers in
a device (e.g., organic light emitting layers). Such damage can
occur when there are pinholes in the thin metal layer, which can be
covered and sealed by the conductive organic layer. Damage and/or
device failure can be caused by cracking or fracturing of the thin
metal layer. Addition of a conductive organic layer can make the
metal layer more resistant to fracture, or can act as a diffusion
barrier against corrosive substances and as a conductive bridge
when fracturing occurs.
[0092] The hole transport layer 204 facilitates the injection of
holes into the device and their migration towards the cathode 208.
The hole transport layer 204 can further act as a barrier for the
passage of electrons to the anode 202. The hole transport layer 204
can include, for example, a diamine derivative, such as
N,N'-bis(3-methylphenyl)-N,N'-diph- enylbenzidine (also known as
TPD) or other hole conductive materials such as NPB. In general,
the hold transport layer can include organic small molecule
materials, conductive polymers, a polymer matrix doped with an
organic small molecule, and other suitable organic or inorganic
conductive or semiconductive materials.
[0093] The electron transport/emitter layer 206 facilitates the
injection of electrons and their migration towards the anode 202.
The electron transport/emitter layer 206 can further act as a
barrier for the passage of holes to the cathode 208. The electron
transport/emitter layer 206 is often formed from a metal chelate
compound, such as, for example, tris(8-hydroxyquinoline) aluminum
(ALQ). Emitter layers (and/or electron transport layers) can also
include light emitting polymers such as poly(phenylenevinylene)s
(PPVs), poly-para-phenylens (PPPs), and polyfluorenes (PFs);
organic small molecule materials, of which ALQ is an example;
polymers doped with organic small molecules; and other suitable
materials.
[0094] The interface between the hole transport layer 204 and
electron transport/emitter layer 206 forms a barrier for the
passage of holes and electrons and thereby creates a hole/electron
recombination zone and provides an efficient organic
electroluminescent device. When the emitter material is ALQ, the
OEL device emits blue-green light. The emission of light of
different colors may be achieved by the use of different emitters
and dopants in the electron transport/emitter layer 206 (see C. H.
Chen et al., "Recent Developments in Molecular Organic
Electroluminescent Materials", Macromolecular Symposia, 125, 1-48
(1997), herein incorporated by reference).
[0095] Other OEL multilayer device constructions may be transferred
using different transfer layers. For example, the hole transporting
layer 204 in FIG. 3A could also be an emitter layer and/or the hole
transporting layer 204 and the electron transporting/emitter layer
206 could be combined into one layer. Furthermore, a separate
emitter layer could be interposed between layers 204 and 206 in
FIG. 3A.
[0096] Patterning OEL materials and layers to form OEL devices
provides a particularly suited example to illustrate some
difficulties with conventional patterning techniques and how these
difficulties can be overcome according to the present invention.
With conventional patterning techniques, there may be some
materials or layers that cannot be used due to susceptibility to
attack, penetration, or dissolution from exposure to solvents or
etchants used coat or pattern other layers on the display
substrate. Thus, there may be device and/or display constructions
that cannot be made by conventional techniques because a
solvent-coated layer would be coated on top of or next to a
solvent-susceptible layer, or because an etchant would be used to
pattern layers on top of or next to other layers that are
susceptible to the etchant. For example, in forming an OEL device
that includes an anode on a substrate, a small molecule hole
transport layer on the anode, a light emitting polymer emitter on
the hole transport layer, and a cathode on the emitter layer, the
solvent used to coat the light emitting polymer may damage the hole
transport layer under conventional processing techniques. The same
limitations may hold for conventional patterning of adjacent OEL
devices, one of which contains a light emitting polymer emitter
layer and the other of which contains an organic small molecule
emitter layer. These limitations can be overcome using thermal
patterning methods of the present invention. Overcoming these
limitations allows a wider range of possible device constructions
and materials alternatives, and these in turn may be used to
achieve OEL devices and displays that exhibit characteristics such
as brightness, lifetime, color purity, efficiency, etc., that might
not otherwise be achieved. Thus, the present invention provides new
OEL device and display constructions (as well as new patterning
methods and new thermal transfer donor elements).
[0097] Stacks of different types of OEL materials and/or organic
charge transport layers, as well as other device layers can be
formed via thermal transfer from one or more donor elements. For
example, a donor element can be made that has a transfer layer that
includes a solvent-coated layer (e.g., a light emitting polymer, a
conductive polymer, etc.) and a vapor-deposited or vacuum deposited
layer (e.g., organic small molecule emitter or charge transport
layer, etc.). The solvent-coated layer can be any suitable material
such as light emitting-polymers, whether doped or un-doped, other
solvent-coatable conductive, semiconductive, or insulative
materials that can act as light emitters, charge carriers (electron
or hole transport), charge insulators (electron or hole blocking),
color filters buffer layers, and the like. The vapor-deposited
layer can be any suitable material including organic small molecule
light emitters and/or charge carriers, other vapor deposited
conductive or semiconductive organic or inorganic materials,
insulative materials, and the like. An exemplary embodiment is one
where the vapor deposited layer is coated over the solvent-coated
layer as part of the transfer layer of a thermal transfer donor
element so that, when transferred to a receptor, the vapor
deposited layer is disposed between the solvent-coated material and
the receptor. This is especially useful when the vapor deposited
material is incompatible with the solvent of the solvent-coated
material. Alternatively, different and/or incompatible layers or
stacks of layers can be thermally transferred from separate donor
elements to form multicomponent devices or structures on a
receptor. For example, a solvent-coated material can be transferred
on top of or next to a previously patterned material that is
incompatible with the solvent.
[0098] In general, multicomponent transfer layers of thermal
transfer donor elements can be formed by coating individual layers
according to the following guidelines: vapor deposited organic
small molecules or inorganic films can be deposited on top of any
other layer type; solvent borne small molecules or polymers can be
deposited on metal films or any material insoluble in the coating
solvent; water borne small molecules or polymers can be deposited
on metal films or any material insoluble in the aqueous solvent.
These transfer layers can be patterned by selective thermal
transfer onto receptors, including receptors that have layers
previously patterned or deposited thereon by any suitable method.
Also, any layer type that can be thermally mass transferred from a
donor element can be transferred on top of or next to any other
thermally mass transferred layers.
[0099] As discussed, OEL devices can be formed by selective thermal
transfer from one or more donor elements. Multiple devices can also
be transferred onto a receptor to form, a pixilated display. As an
example, an optical display can be formed as illustrated in FIGS.
4A through 4C. For example, green OEL devices 302 can be
transferred onto the receptor substrate 300, as shown in FIG. 4A.
Subsequently, blue OEL devices 304 and then red OEL devices 306 may
be transferred, as shown in FIGS. 4B and 4C. Each of the green,
blue, and red OEL devices 302, 304, 306 are transferred separately
using green, blue, and red thermal transfer elements, respectively.
Alternatively, the red, green, and blue thermal transfer elements
could be transferred on top of one another to create a multi-color
stacked OLED device of the type disclosed in U.S. Pat. No.
5,707,745, herein incorporated by reference. Another method for
forming a full color device includes depositing columns of hole
transport layer material and then sequentially depositing red,
green, and blue electron transport layer/emitter multicomponent
transfer units either parallel or perpendicular to the hole
transport material. Yet another method for forming a full color
device includes depositing red, green, and blue color filters
(either conventional transmissive filters, fluorescent filters, or
phosphors) and then depositing multicomponent transfer units
corresponding to white light or blue light emitters.
[0100] Still another method for forming multi-color pixilated OEL
displays is to pattern red, green, and blue emitters (for example)
from three separate donors, and then, in a separate step, to
pattern all the cathodes (and, optionally, electron transport
layers) from a single donor element. In this way, each OEL device
is patterned by at least two thermal transfers, the first of which
patterns the emitter portion (and, optionally, an adhesive layer, a
buffer layer, anode, hole injection layer, hole transport layer,
electron blocking layer, and the like), and the second of which
patterns the cathode portion (and, optionally, an electron
injection layer, electron transport layer, hole blocking layer, and
the like). One advantage of splitting the device layers between two
or more donor elements (e.g., an emitter donor and a cathode donor)
is that the same donor elements can be used to pattern the emitter
portion of OEL devices for either passive matrix or active matrix
display constructions. Generally, active matrix displays include a
common cathode that is deposited over all the devices. For this
construction, thermal transfer of an emitter stack that includes a
cathode may not be necessary, and having a cathode-less transfer
stack may be desirable. For passive matrix displays, cathode-less
donors can be used to transfer each of the emitter portions (a
different donor for each color, if multi-color is desired),
followed by patterning of the cathodes for each device from the
same, separate donor element. Thus, various emitter donors can be
used for various display constructions, all while using the same,
or similar, type of cathode donor.
[0101] Another advantage of the present invention is that OEL
devices, for example, can be transferred and patterned according to
the described methods to form adjacent devices having different,
and otherwise incompatible, types of emitter materials. For
example, red-emitting organic small molecule devices (e.g., that
use an active vapor-deposited small molecule layer) can be
patterned on the same receptor as blue-emitting light emitting
polymer devices (e.g., that use an active solution-coated light
emitting polymer layer). This allows flexibility to choose
light-emitting materials (and other device layer materials) based
on functionality (e.g., brightness, efficiency, lifetime,
conductivity, physical properties after patterning (e.g.,
flexibility, etc.)) rather than on compatibility with the
particular coating and/or patterning techniques used for the other
materials in the same or adjacent devices. The ability to choose
different types of emitter materials for different color devices in
an OEL display can offer greater flexibility in choosing
complementary device characteristics. The ability to use different
types of emitters can also become important when the preferred
emitter material for one OEL device is incompatible with the
preferred emitter material for another OEL device.
[0102] Referring again to FIG. 4, this example also illustrates
other advantages of using thermal transfer elements to pattern
multiple different devices on a receptor. For example, the. number
of processing steps can be reduced as compared to conventional
photolithography methods because many of the layers of each OEL
device can be transferred simultaneously, rather than using
multiple etching and masking steps. In addition, multiple devices
and patterns can be created using the same imaging hardware. Only
the thermal transfer element needs to be changed for each of the
different devices 302, 304, 306.
[0103] The receptor substrate may be any item suitable for a
particular application including, but not limited to, transparent
films, display black matrices, passive and active portions of
electronic displays (e.g., electrodes, thin film transistors,
organic transistors, etc.), metals, semiconductors, glass, various
papers, and plastics. Non-limiting examples of receptor substrates
which can be used in the present invention include anodized
aluminum and other metals, plastic films (e.g., polyethylene
terephthalate, polypropylene), indium tin oxide coated plastic
films, glass, indium tin oxide coated glass, flexible circuitry,
circuit boards, silicon or other semiconductors, and a variety of
different types of paper (e.g., filled or unfilled, calendered, or
coated). For OEL displays, the type of receptor used often depends
on whether the display is a top emission display (devices
positioned between the viewer and the receptor substrate) or a
bottom emission display (receptor substrate positioned between the
viewer and the devices). For a top emission display, the receptor
need not be transparent. For a bottom emission display, a
transparent receptor substrate is typically desired.
[0104] Various layers (e.g., an adhesive layer) may be coated onto
the receptor substrate to facilitate transfer of the transfer layer
to the receptor substrate. Other layers may be coated on the
receptor substrate to form a portion of a multilayer device. For
example, an OEL or other electronic device may be formed using a
receptor substrate having a metal and/or conductive organic anode
or cathode formed on the receptor substrate prior to transfer of
the transfer layer from the thermal transfer element. The anode or
cathode may be formed, for example, by deposition of one or more
conductive layers on the receptor substrate and patterning of the
layer into one or more anodes or cathodes using any suitable
method, for example, photolithographic techniques or the thermal
transfer techniques taught herein.
[0105] A particularly useful receptor substrate for patterning
multilayer devices is one that has a common electrode or a pattern
of electrodes along with a pattern of insulating barriers on top of
the electrode(s). The insulating barriers can be provided in a
pattern that corresponds to the intended position of the edges of
the multilayer devices to help prevent electrical shorts between
the receptor electrode(s) and the opposing electrode transferred
along with or on top of a multilayer stack. This is especially
useful in passive matrix displays. Also, in active matrix display
constructions, the insulating barriers can help isolate the
transistors of the active matrix from the common electrode, which
is generally provided. This can help prevent leakage currents and
parasitic capacitance which can reduce device efficiencies.
[0106] For example, FIG. 5A shows a cross-section of a receptor 500
that includes a substrate 501, a common electrode 502 disposed
thereon, and a set of parallel insulating strips 504 disposed on
the electrode 502. FIG. 5A also shows a donor element 510 that has
a multicomponent transfer layer 505 that includes at least two
layers, an electrode layer 508 and an emitter layer 506. Transfer
layer 505 is to be transferred as parallel lines onto receptor 500
so that when an electric field is applied between receptor
electrode 501 and device electrode 508, emitter layer 506 can emit
light. As a practical matter (and in large part due to the thinness
of layers 506 and 508), portions of electrode layer 508 at the
edges of the transferred line may be likely to contact portions of
the receptor after transfer. If this happened, the emitter device
could be rendered inoperable due to one or more electrical shorts.
Thus, insulating barriers 504 can be patterned onto the receptor
(by thermal transfer or other suitable means) to cover areas where
the edges of the transfer layers will be positioned upon transfer.
Thus, as shown in FIG. 5B, if layer 508 overlaps layer 506 at the
edges of a transferred line, layer 508 will contact insulating
barrier 504, and the overall device will not short out due to
contact with the underlying electrode 502 at the edges. Insulating
barriers can be used for both passive matrix displays and active
matrix displays.
[0107] Another receptor substrate useful for patterning OEL devices
is one that includes electrode pads for connecting the device
cathodes to the electronic driver system. For example, FIG. 6 shows
a receptor 600 for a passive matrix display that includes anodes
612a, 612b, 612c, and so on patterned in parallel lines, and a
plurality of contact pads 602a, 602b, 602c, 602d, and so on, for
connection to device cathodes. Parallel lines can then be
transferred from one or more donor elements to produce multilayer
stacks 610a, 610b, 610c, 610d, and so on, to complete OEL devices.
Each OEL device is positioned where an anode line and a multilayer
stack line cross. At the cross portions, an emitter layer (an
optional electron and hole transport and emitter layers, as well as
other layers) is disposed between an anode and a cathode. Each line
610 terminates at one end adjacent an electrode pad 602. Conductor
material can then be deposited in and around areas 604a, 604b,
604c, 604d, and so on, to connect the cathodes to the electrode
pads, which in turn can be connected to the driver electronics.
Conductor material can be deposited in areas 604 using any suitable
technique include photolithography and mask-based vapor deposition.
Alternatively, conductor material such as an organic conductor can
be selectively transferred into areas 604 by thermal transfer from
a donor element. As described above, thermal transfer from a donor
element can be used to eliminate wet etching steps that may be
required for photolithographic or mask-based techniques. Thermally
transferred organic conductive layers can also be used to
encapsulate the ends of the multilayer stacks, protecting the light
emitting layers from corrosive agents. While FIG. 6 shows the
situation for a passive matrix display, the concept of thermally
transferring an organic conductor to connect a device to an
electrode pad is equally applicable to active matrix displays.
EXAMPLES
[0108] In the following Examples, all of the vacuum deposited
materials were thermally evaporated and deposited at room
temperature. The deposition rate and thickness of each vacuum
deposited layer was monitored with a quartz crystal microbalance
(Leybold Inficon Inc., East Syracuse, N.Y.). The background
pressure (chamber pressure prior to the deposition) was roughly
1.times.10.sup.-5 torr (1.3.times.10.sup.-3 Pa).
[0109] The laser transfer system included a CW Nd:YAG laser,
acousto-optic modulator, collimating and beam expanding optics, an
optical isolator, a linear galvonometer and an f-theta scan lens.
The Nd:YAG laser was operating in the TEM 00 mode, and produced a
total power of 7.5 Watts. Scanning was accomplished with a high
precision linear galvanometer (Cambridge Technology Inc.,
Cambridge, Mass.). The laser was focused to a Gaussian spot with a
measured diameter between 100 .mu.m and 140 .mu.m at the 1/e.sup.2
intensity level. The spot was held constant across the scan width
by utilizing an f-theta scan lens. The laser spot was scanned
across the image surface at a velocity of about 5 meters/second.
The f-theta scan lens held the scan velocity uniform to within
0.1%, and the spot size constant to within .+-.3 microns.
Example 1
Preparation of a Substrate/LTHC/Interlayer Element
[0110] A carbon black light-to-heat conversion layer was prepared
by coating the following LTHC Coating Solution, according to Table
1, onto a 0.1 mm PET substrate with a Yasui Seiki Lab Coater, Model
CAG-150 (Yasui Seiki Co., Bloomington, Ind.) using a microgravure
roll of 381 helical cells per lineal cm (150 helical cells per
lineal inch).
1TABLE 1 LTHC Coating Solution Parts by Component Weight Raven .TM.
760 Ultra carbon black pigment 3.39 (available from Columbian
Chemicals, Atlanta, GA) Butvar .TM. B-98 0.61 (polyvinylbutyral
resin, available from Monsanto, St. Louis, MO) Joncryl .TM. 67 1.81
(acrylic resin, available from S.C. Johnson & Son, Racine, WI)
Elvacite .TM. 2669 9.42 (acrylic resin, available from ICI
Acrylics, Wilmington, DE) Disperbyk .TM. 161 0.3 dispersing aid,
available from Byk Chemie, Wallingford, CT) FC-430 .TM. 0.012
(fluorochemical surfactant, available from 3M, St. Paul, MN)
Ebecryl .TM. 629 14.13 (epoxy novolac acrylate, available from UCB
Radcure, N. Augusta, SC) Irgacure .TM. 369 0.95 (photocuring agent,
available from Ciba Specialty Chemicals, Tarrytown, NY) Irgacure
.TM. 184 0.14 (photocuring agent, available from Ciba Specialty
Chemicals, Tarrytown, NY) propylene glycol methyl ether acetate
16.78 1-methoxy-2-propanol 9.8 methyl ethyl ketone 42.66
[0111] The coating was in-line dried at 40.degree. C. and UV-cured
at 6.1 n/min using a Fusion Systems Model 1600 (400 W/in) UV curing
system fitted with H-bulbs (Fusion UV Systems, Inc., Gaithersburg,
MD). The dried coating had a thickness of approximately 3
microns.
[0112] Onto the carbon black coating of the light-to-heat
conversion layer was rotogravure coated an Interlayer Coating
Solution, according to Table 2, using the Yasui Seiki Lab Coater,
Model CAG-150 (Yasui Seiki Co., Bloomington, Ind.). This coating
was in-line dried (40.degree. C.) and UV-cured at 6.1 m/min using a
Fusion Systems Model I600 (600 W/in) fitted with H-bulbs. The
thickness of the resulting interlayer coating was approximately 1.7
microns.
2TABLE 2 Interlayer Coating Solution Component Parts by Weight
Butvar .TM. B-98 0.98 Joncryl .TM. 67 2.95 Sartomer .TM. SR351 .TM.
15.75 (trimethylolpropane triacrylate, available from Sartomer,
Exton, PA) Irgacure .TM. 369 1.38 Irgacure .TM. 184 0.2
1-methoxy-2-propanol 31.5 methyl ethyl ketone 47.24
Example 2
Preparation or Another Substrate/LTHC/Interlayer Element
[0113] A carbon black light-to-heat conversion layer was prepared
by coating the following LTHC Coating Solution, according to Table
3, onto a 0.1 mm PET substrate with a Yasui Seiki Lab Coater, Model
CAG-150 (Yasui Seiki Co., Bloomington, Ind.) using a microgravure
roll of 228.6 helical cells per lineal cm (90 helical cells per
lineal inch).
3TABLE 3 LTHC Coating Solution Parts by Component Weight Raven .TM.
760 Ultra carbon black pigment 3.78 (available from Columbian
Chemicals, Atlanta, GA) Butvar .TM. B-98 0.67 (polyvinylbutyral
resin, available from Monsanto, St. Louis, MO) Joncryl .TM. 67 2.02
(acrylic resin, available from S.C. Johnson & Son, Racine, WI)
Disperbyk .TM. 161 0.34 (dispersing aid, available from Byk Chemie,
Wallingford, CT) FC-430 .TM. 0.01 (fluorochemical surfactant,
available from 3M, St. Paul, MN) SR 351 .TM. 22.74
(trimethylolpropane triacrylate, available from Sartomer, Exton,
PA) Duracure .TM. 1173 1.48 (2-hydroxy-2-methyl-1-ph-
enyl-1-propanone photoinitiator, available from Ciba, Hawthorne,
NY) 1-methoxy-2-propanol 27.59 methyl ethyl ketone 41.38
[0114] The coating was in-line dried at 40.degree. C. and UV-cured
at 6.1 m/min using a Fusion Systems Model I600 (400 W/in) UV curing
system fitted with H-bulbs. The dried coating had a thickness of
approximately 3 microns.
[0115] Onto the carbon black coating of the light-to-heat
conversion layer was 10 rotogravure coated an Interlayer Coating
Solution, according to Table 4, using the Yasui Seiki Lab Coater,
Model CAG-150 (Yasui Seiki Co., Bloomington, Ind.). This coating
was in-line dried (40.degree. C.) and UV-cured at 6.1 m/min using a
Fusion Systems Model 1600 (600 W/in) fitted with H-bulbs. The
thickness of the resulting interlayer coating was approximately 1.7
microns.
4TABLE 4 Interlayer Coating Solution Component Parts by Weight
Butvar .TM. B-98 0.99 Joncryl .TM. 67 2.97 SR 351 .TM. 15.84
Duracure .TM. 1173 0.99 1-methoxy-2-propanol 31.68 methyl ethyl
ketone 47.52
Example 3
Hole Transport Thermal Transfer Element
[0116] A hole transport thermal transfer element was formed using
the substrate/LTHC/interlayer element of Example 1. A hole
transport coating solution, formed by mixing the components of
Table 5, was coated onto the interlayer using a #6 Mayer bar. The
coating was dried for 10 min at 60.degree. C.
5TABLE 5 Hole Transport Coating Solution Parts by Component Weight
N,N'-bis(3-methylphenyl)-N,N'-diphenylbenzidine 2.5
polyvinylcarbazole 2.5 cyclohexanone 97.5 propylene glycol methyl
ether acetate (PGMEA) 97.5
Example 4
OEL Small Molecule Thermal Transfer Element
[0117] An OEL thermal transfer element with a multicomponent
transfer layer was pre pared by applying coatings to a
substrate/LTHC/interlayer element formed according to Example 1. A
200 .ANG. layer of copper phthalocyanine w as deposited on the
interlayer as a semiconducting release layer. Next, a 250 .ANG.
layer of aluminum was deposited as a cathode layer. A 10 .ANG.
layer of lithium fluoride was deposited on the aluminum. Next, a
300 .ANG. layer of tris(8-hydroxyquinolinato) aluminum (ALQ) was
deposited as an electron transport layer. Finally, a 200 .ANG.
layer of N,N'-bis(3-methylphenyl)-N,N'-diphenylbenzidine (TPD) was
deposited as a hole transport layer.
Example 5
Preparation of an OEL Small Molecule Device
[0118] A receptor substrate of glass covered with indium tin oxide
(ITO) (resistivity of 10 .OMEGA./square, Thin Film Devices Inc.,
Anaheim, Calif.) was used to form the anode of the OEL device.
First, the hole transport thermal transfer element of Example 3 was
imaged onto the receptor. This was followed by imaging of the OEL
small molecule thermal transfer element of Example 4 to complete
the OEL device.
[0119] In each transfer, the transfer layer side of the thermal
transfer element was held in intimate contact with the receptor in
a vacuum chuck. A laser was directed to be incident upon the
substrate side of the thermal transfer elements. The exposures were
performed so that the two transfer layers were transferred with
correct registration. This produced 120 .mu.m wide lines. The final
OEL device had layers in the following order (from top to
bottom):
[0120] Aluminum Cathode
[0121] Lithium Fluoride
[0122] ALQ Electron Transport Layer/Emitter
[0123] TPD Hole Transport Layer (from OEL thermal transfer
element)
[0124] TPD Hole Transport Layer (from hole transport thermal
transfer element)
[0125] ITO and Glass Receptor
[0126] Electrical contact was made at the ITO anode and the
aluminum cathode.
[0127] When a potential was applied, the OEL device produced
visually detectable light.
[0128] The injection current was monitored as a function of the
applied potential (voltage) which was continuously swept from 0
volts to 10-30 volts. At one point 70 .mu.A at 10 volts flowing
through a 42 mm.times.80 .mu.m device was measured. This
corresponds to a current density of about 2 mA/cm.sup.2. The
current density is well within the normal operating range of small
molecule devices fabricated directly onto a receptor substrate
using conventional techniques.
Example 6
Another OEL Small Molecule Thermal Transfer Element
[0129] An OEL thermal transfer element with a multicomponent
transfer layer was prepared by applying coatings to a
substrate/LTHC/interlayer element prqpared according to Example 1.
A primer solution, according to Table 6, was first coated using a
#3 Mayer bar. The coating was dried at about 60.degree. C. for
about 5 minutes.
6TABLE 6 Primer Solution Parts by Component Weight PVP K-90
(polyvinyl pyrrolidone, International 2 Specialty Products, Wayne,
NJ) PVA Gohsenol KL-03 (polyvinyl alcohol, Nippon 2 Gohsci, Osaka,
Japan) Elvacite 2776 (acrylic polymer, ICI Acrylics) 4 DMEA
(dimethylethanolamine, Aldrich) 0.8 2-butoxyethanol (Aldrich) 0.8
deionized water 150.4
[0130] A 200 .ANG. layer of copper phthalocyanine was deposited as
a semiconducting release layer on the primer layer. Next, a 250
.ANG. layer of aluminum was deposited as a cathode layer. A 10
.ANG. layer of lithium fluoride was deposited on the aluminum.
Next, a 300 .ANG. layer of ALQ was deposited as an electron
transport layer. Finally, a 200 .ANG. layer of TPD was deposited as
a hole transport layer.
Example 7
Transfer of a Partial OEL Small Molecule Transfer Layer to a
Flexible Substrate
[0131] The receptor substrate consisted of a piece of 4 mil (about
100 .mu.m) PET film (unprimed HPE100, Teijin Ltd., Osaka, Japan).
First, the hole transport thermal transfer element of Example 3 was
imaged onto the receptor. Then the OEL thermal transfer element of
Example 6 was imaged onto the hole transport layer.
[0132] In each transfer, the transfer layer side of the thermal
transfer element was held in intimate contact with the receptor in
a vacuum chuck. A laser was directed to be incident upon the
substrate side of the thermal transfer elements. The exposures were
performed so that the two layers with correct registration. This
produced 120 .mu.m wide lines. The final construction had layers in
the following order (from top to bottom):
[0133] Aluminum Cathode
[0134] Lithium Fluoride
[0135] ALQ Electron Transport Layer/Emitter
[0136] TPD Hole Transport Layer (from OEL Thermal Transfer
Element)
[0137] TPD Hole Transport Layer (from hole transport thermal
transfer element)
[0138] PET Receptor
Example 8
OEL Light Emitting Polymer Thermal Transfer Element
[0139] An OEL thermal transfer element with a multicomponent
transfer layer was prepared by applying coatings to a
substrate/LTHC/interlayer element formed according to Example 1. A
100 .ANG. layer of copper phthalocyanine was deposited on the
interlayer as a release layer. Next, a 450 .ANG. layer of aluminum
was deposited as a cathode layer. A light emitting polymer coating
solution was then prepared by adding 2% by weight of
poly(9,9-di-n-octylfluorene) (designated "PFC8" in these Examples)
in toluene and then diluting the solution with MEK until a 1% by
weight concentration of PFC8 was achieved. PFC8 is a blue emitting
polyfluorene material that has a chemical structure as shown below,
and that can be synthesized according to the methods disclosed in
U.S. Pat. No. 5,777,070, which is incorporated into this document.
1
[0140] The coating solution was hand coated onto the aluminum layer
using a #6 Mayer bar and dried to form a 1000 .ANG. layer of PFC8
as a blue light emitting layer. Finally, a 500 .ANG. layer of NPB
was deposited as a hole transport layer.
Example 9
Another OEL Light Emitting Polymer Thermal Transfer Element
[0141] An OEL thermal transfer element with a multicomponent
transfer layer was prepared by applying coatings to a
substrate/LTHC/interlayer element formed according to Example 1. A
100 .ANG. layer of copper phthalocyanine was deposited on the
interlayer as a release layer. Next, a 450 .ANG. layer of aluminum
was deposited as a cathode layer. A light emitting polymer coating
solution was then prepared by adding 2% by weight of a copolymer of
PFC8 and benzothiadiazole (copolymer designated "PFC8/BDTZ" in
these Examples) in toluene and then diluting the solution with MEK
until a 1% by weight concentration of PFC8/BTDZ copolymer was
achieved. PFC8/BDTZ is a green light emitting polyfluorene
copolymer. The coating solution was hand coated onto the aluminum
layer using a #6 Mayer bar and dried to form a 1000 .ANG. layer of
PFC8/BTDZ as a green light emitting layer. Finally, a 500 .ANG.
layer of NPB was deposited as a hole transport layer.
Example 10
[0142] Preparation of an OEL Light Emitting Polymer Device
[0143] A receptor substrate of glass covered with ITO (resistivity
of 10 .OMEGA./square, Thin Film Devices Inc., Anaheim, Calif.) was
used to form the anode of the OEL devices. The ITO covered glass
was then spin coated at 3000 r.p.m. with an aqueous solution of
2.5% by weight polypyrrole (sold under the trade designation
Baytron-P, Bayer Corp., Pittsburgh, Pa.). The polypyrrole coating
was then dried at 80.degree. C. for 5 minutes to form a buffer
layer on the receptor substrate.
[0144] A blue light emitting polymer device was formed when the
thermal transfer element of Example 8 was imaged onto the receptor.
The transfer layer side of the thermal transfer element of Example
8 was held in intimate contact with the receptor in a vacuum chuck.
A laser was directed to be incident upon the substrate side of the
thermal transfer element, using a dose of 0.6 J/cm.sup.2. This
produced 100 .mu.m wide lines. The final OEL device had layers in
the following order (from top to bottom):
[0145] Aluminum Cathode
[0146] PFC8 Blue Light Emitting Polymer Layer
[0147] NPB Hole Transport Layer
[0148] Polypyrrole Buffer Layer (coated directly onto the
receptor)
[0149] ITO and Glass Receptor
[0150] Electrical contact was made at the ITO anode and the
aluminum cathode. When a potential was applied, the OEL device
produced visually detectable blue light.
Example 11
Preparation of another OEL Light Emitting Polymer Device
[0151] A receptor substrate of glass covered with ITO (resistivity
of 10 .OMEGA./square, Thin Film Devices Inc., Anaheim, Calif.) was
used to form the anode of the OEL devices. The ITO covered glass
was then spin coated at 3000 r.p.m. with an aqueous solution of
2.5% by weight polypyrrole. The polypyrrole coating was 'then dried
at 80.degree. C. for 5 minutes to form a buffer layer on the
receptor substrate.
[0152] A green light emitting polymer device was formed when the
thermal transfer element of Example 9 was imaged onto the receptor.
The transfer layer side of the thermal transfer element of Example
9 was held in intimate contact with the receptor in a vacuum chuck.
A laser was directed to be incident upon the substrate side of the
thermal transfer element, using a dose of 0.6 J/cm.sup.2. This
produced 100 .mu.m wide lines. The final OEL device had layers in
the following order (from top to bottom):
[0153] Aluminum Cathode
[0154] PFC8/BTDZ Green Light Emitting Polymer Layer
[0155] NPB Hole Transport Layer
[0156] Polypyrrole Buffer Layer (coated directly onto the
receptor)
[0157] ITO and Glass Receptor
[0158] Electrical contact was made at the ITO anode and the
aluminum cathode. When a potential was applied, the OEL device
produced visually detectable blue light.
[0159] Examples 8-11 demonstrate that OEL devices that have
solvent-coated light emitting polymer layers disposed on top of
vacuum-deposited organic small molecule layers can be patterned
onto substrates. This was accomplished by forming donor elements
that had organic small molecule material vapor coated onto dried
solvent-coated light emitting polymer layers, and then selectively
transferring the. multicomponent transfer stack to a receptor
substrate.
Example 12
Cathode Layer Thermal Transfer Element
[0160] A cathode layer thermal transfer element was formed using
the substrate/LTHC/interlayer element of Example 1. A 100 .ANG.
layer of copper phthalocyanine was deposited on the interlayer as a
release layer. Next, a 450 .ANG. layer of aluminum was deposited as
a cathode layer. Finally, a 500 A layer of
3-(4-Biphenyl)-4-phenyl-5-(4-tert-butylphenyl)-- 1,2,4-triazole
(TAZ-01) was deposited on the aluminum layer as an organic small
molecule electron transport/adhesion promoting layer.
Example 13
Light Emitting Polymer Thermal Transfer Element
[0161] A light emitting polymer thermal transfer element with a
single component transfer layer was prepared. A light emitting
polymer coating solution was prepared by adding 2% by weight of
PFC8 in toluene and then diluting the solution with MEK until a 1%
by weight concentration of PFC8 was achieved. The coating solution
was hand coated onto to the interlayer of a
substrate/LTHC/interlayer element (formed according to Example 1)
using a #6 Mayer bar. The coating was dried to form a 1000 .ANG.
polyfluorene transfer layer.
Example 14
Another Light Emitting Polymer Thermal Transfer Element
[0162] A light emitting polymer thermal transfer element with a
single component transfer layer was prepared. A light emitting
polymer coating solution was prepared by adding 2% by weight of
PFC8/BTDZ in toluene and then diluting the solution with MEK until
a 1% by weight concentration of PFC8/BTDZ was achieved. The coating
solution was hand coated onto to the interlayer of a
substrate/LTHC/interlayer element (formed according to Example 1)
using a #6 Mayer bar. The coating was dried to form a 1000 A
polyfluorene transfer layer.
Example 15
Preparation of an OEL Light Emitting Polymer Device
[0163] A receptor substrate of glass covered with ITO (resistivity
of 10 .OMEGA./square, Thin Film Devices Inc., Anaheim, Calif.) was
used to form the anode of the OEL devices. The ITO covered glass
was then spin coated at 3000 r.p.m. with an aqueous solution of
2.5% by weight polypyrrole. The polypyrrole coating was then dried
at 80.degree. C. for 5 minutes to form a buffer layer on the
receptor substrate.
[0164] The thermal transfer element of Example 13 was imaged onto
the receptor to form 100 .mu.m wide lines of a blue light emitting
polymer material on the polypyrrole buffer layer. The transfer
layer side of the thermal transfer element of Example 13 was held
in intimate contact with the receptor in a vacuum chuck. A laser
was directed to be incident upon the substrate side of the thermal
transfer element, using a dose of 0.6 J/cm.sup.2. Next, the cathode
thermal transfer element of Example 12 was imaged onto the receptor
to form 100 .mu.m wide lines on top of and in registry with the
lines of light emitting polymer material previously transferred.
The transfer layer side of the thermal transfer element of Example
12 was held in intimate contact with the receptor in a vacuum
chuck. A laser was directed to be incident upon the substrate side
of the thermal transfer element, using a dose of 0.6
J/cm.sup.2.
[0165] The final OEL device had layers in the following order (from
top to bottom):
[0166] Aluminum Cathode
[0167] TAZ-01 Electron Transport Layer
[0168] PFC8 Blue Light Emitting Polymer Layer
[0169] Polypyrrole Buffer Layer (coated directly onto the
receptor)
[0170] ITO and Glass Receptor
[0171] Electrical contact was made at the ITO anode and the
aluminum cathode. When a potential was applied, the OEL device
produced visually detectable blue light.
Example 16
Preparation of another OEL Light Emitting Polymer Device
[0172] A receptor substrate of glass covered with ITO (resistivity
of 10 .OMEGA./square, Thin Film Devices Inc., Anaheim, Calif.) was
used to form the anode of the OEL devices. The ITO covered glass
was then spin coated at 3000 r.p.m. with an aqueous solution of
2.5% by weight polypyrrole. The polypyrrole coating was then dried
at 80.degree. C. for 5 minutes to form a buffer layer on the
receptor substrate.
[0173] The thermal transfer element of Example 14 was imaged onto
the receptor to form 100 .mu.m wide lines of a green light emitting
polymer material on the polypyrrole buffer layer. The transfer
layer side of the thermal transfer element of Example 14 was held
in intimate contact with the receptor in a vacuum chuck. A laser
was directed to be incident upon the substrate side of the thermal
transfer element, using a dose of 0.6 J/cm.sup.2. Next, the cathode
thermal transfer element of Example 12 was imaged onto the receptor
to form 100 .mu.m wide lines on top of and in registry with the
lines of light emitting polymer material previously transferred.
The transfer layer side of the thermal transfer element of Example
12 was held in intimate contact with the receptor in a vacuum
chuck. A laser was directed to be incident upon the substrate side
of the thermal transfer element, using a dose of 0.6
J/cm.sup.2.
[0174] The final OEL device had layers in the following order (from
top to bottom):
[0175] Aluminum Cathode
[0176] TAZ-01 Electron Transport Layer
[0177] PFC8/BTDZ Green Light Emitting Polymer Layer
[0178] Polypyrrole Buffer Layer (coated directly onto the
receptor)
[0179] ITO and Glass Receptor
[0180] Electrical contact was made at the ITO anode and the
aluminum cathode. When a potential was applied, the OEL device
produced visually detectable green light.
[0181] Examples 12-16 demonstrate that the same cathode donor
element can be used to pattern cathode layers on top of different
emitter layers, previously patterned, to form OEL devices.
Example 17
Preparation of Small Molecule and Light Emitting Polymer OEL
Devices on the Same Receptor Substrate
[0182] This Example demonstrates that functional OEL devices that
have light emitting polymer emitter layers and OEL devices that
have organic small molecule emitter layers can be patterned next to
each other on receptor substrates.
[0183] A thermal transfer element with a multicomponent transfer
layer having a green light small molecule emitter ("Green SM
Donor") was prepared by applying coatings to a
substrate/LTHC/interlayer element formed according to Example 1. A
100 .ANG. layer of copper phthalocyanine was deposited on the
interlayer as a release layer. Next, a 450 .ANG. layer of aluminum
was deposited as a cathode layer. A 10 .ANG. layer of lithium
fluoride was deposited on the aluminum. Next, a 500 .ANG. layer of
ALQ was deposited as an electron transport layer. Finally, a 500
.ANG. layer of NPB was deposited as a hole transport layer.
[0184] A thermal transfer element with a multicomponent transfer
layer having a red light small molecule emitter ("Red SM Donor")
was prepared by applying coatings to a substrate/LTHC/interlayer
element formed according to Example 1. A 100 .ANG. layer of copper
phthalocyanine was deposited on the interlayer as a release layer.
Next, a 450 .ANG. layer of aluminum was deposited as a cathode
layer. A 10 .ANG. layer of lithium fluoride was deposited on the
aluminum. Next, a 500 .ANG. layer of ALQ was deposited as an
electron transport layer. Next, a layer of platinum octa ethyl
porphyrin (PtOEP) was vapor deposited on the ALQ layer as a dopant.
The PtOEP dopant was deposited to achieve a 2 to 3% by weight
concentration of the dopant in the ALQ emitter layer. Finally, a
500 .ANG. layer of NPB was deposited as a hole transport layer.
[0185] A thermal transfer element was made according to Example 8
to produce a donor element having a blue light emitting polymer
emitter ("Blue LEP Donor"). A thermal transfer element was made
according to Example 9 to produce a donor element having a green
light emitting polymer emitter ("Green LEP Donor").
[0186] A receptor substrate of glass covered with ITO (resistivity
of 10 .OMEGA./square, Thin Film Devices Inc., Anaheim, Calif.) was
used to form the anode of the OEL devices. The ITO covered glass
was then spin coated at 3000 r.p.m. with an aqueous solution of
2.5% by weight polypyrrole. The polypyrrolc coating was then dried
at 80.degree. C. for 5 minutes to form a buffer layer on the
receptor substrate.
[0187] The Blue LEP Donor was imaged onto the receptor substrate to
form a series of parallel lines. Next, the Red SM Donor was imaged
onto the same receptor for form a series of parallel lines, each
line positioned between lines transferred from the Blue LEP Donor.
Electrical contact was made at the ITO anodes and aluminum
cathodes. Visibly detected blue light was emitted from the lines
patterned from the Blue LEP Donor and visibly detected red light
was emitted from the lihes patterned from the Red SM Donor.
[0188] The Green LEP Donor was then imaged onto another receptor
substrate to form a series of parallel lines. Next, the Green SM
Donor was imaged onto the same receptor for form a series of
parallel lines, each line positioned between lines transferred from
the Green LEP Donor. Electrical contact was made at the ITO anodes
and aluminum cathodes. Visibly detected green light was emitted
from the lines patterned from the Green LEP Donor and visibly
detected green light was emitted from the lines patterned from the
Green SM Donor.
Example 18
Preparation of Red, Green, and Blue OEL Devices on the Same
Receptor Substrate
[0189] This Example demonstrates that functional red, green, and
blue OEL devices can be patterned next to each other on the same
receptor substrate.
[0190] A thermal transfer element with a multicomponent transfer
layer having a blue light small molecule emitter ("Blue SM Donor")
was prepared by applying coatings to a substrate/LTHC/interlayer
element formed according to Example 1. A 100 .ANG. layer of copper
phthalocyanine was deposited on the interlayer as a release layer.
Next, a 450 .ANG. layer of aluminum was deposited as a cathode
layer. A 10 .ANG. layer of lithium fluoride was deposited on the
aluminum. Next, a 500 .ANG. layer of
Bis(2-methyl-8-quinolinolato)(para-phenyl-phenolato)aluminum (BAlq)
was deposited as an electron transport/emitter layer. The BAlq was
synthesized as described in U.S. Pat. No. 5,141,671, the disclosure
of which is incorporated into this document. Next, a layer of
perylene was vapor deposited on the BAlq layer as a dopant. The
perylene dopant was deposited to achieve a 2 to 3% by weight
concentration of the dopant in the BAlq emitter layer. Finally, a
500 .ANG. layer of NPB was deposited as a hole transport layer.
[0191] A receptor substrate of glass covered with ITO (resistivity
of 10 .OMEGA./square, Thin Film Devices Inc., Anaheim, Calif.) was
used to form the anode of the OEL devices. The ITO covered glass
was then spin coated at 3000 r.p.m. with an aqueous solution of
2.5% by weight polypyrrole. The polypyrrole coating was then dried
at 80.degree. C. for 5 minutes to form a buffer layer on the
receptor substrate.
[0192] The Red SM Donor of Example 17, the Green SM Donor of
Example 17, and the Blue SM Donor of this Example were successively
imaged onto the receptor substrate to form a series of parallel
lines. The lines were patterned so that a line transferred from one
donor was positioned between lines transferred from each of the
other two donors. Electrical contact was made at the ITO anodes and
aluminum cathodes. Visibly detected green light was emitted from
the lines patterned from the Green SM Donor, visibly detected red
light was emitted from the lines patterned from the Red SM Donor,
and visibly detected blue light was emitted from the lines
patterned from the Blue SM Donor.
[0193] The present invention should not be considered limited to
the particular examples described above, but rather should be
understood to cover all aspects of the invention as fairly set out
in the attached claims. Various modifications, equivalent
processes, as well as numerous structures to which the present
invention may be applicable will be readily apparent to those of
skill in the art to which the present invention is directed upon
review of the instant specification.
* * * * *