U.S. patent application number 11/589348 was filed with the patent office on 2007-02-22 for processes for removing organic layers and organic electronic devices formed by the processes.
Invention is credited to Mark Jeffrey Sellars, Nugent Truong.
Application Number | 20070040493 11/589348 |
Document ID | / |
Family ID | 35238841 |
Filed Date | 2007-02-22 |
United States Patent
Application |
20070040493 |
Kind Code |
A1 |
Sellars; Mark Jeffrey ; et
al. |
February 22, 2007 |
Processes for removing organic layers and organic electronic
devices formed by the processes
Abstract
A process for protecting first electrodes, conductive leads and
the underlying substrate from the process of removing organic
layers during the fabrication of an organic electronic device.
After first electrodes and conductive leads are formed over a
substrate, a protective layer is selectively formed over the
structure, with the protective layer not being disposed over
selected portions of the first electrodes, the conductive leads and
the substrate. Organic layers are then formed over the structure,
and second electrodes are formed over the organic layers. Those
portions of the organic layers disposed over the selected portions
of the first electrodes, conductive leads and substrate are
removed, and the protective layer protects adjacent portions of the
first electrodes, conductive leads and substrate from the process
of removing the portions of the organic layers.
Inventors: |
Sellars; Mark Jeffrey;
(Buellton, CA) ; Truong; Nugent; (Ventura,
CA) |
Correspondence
Address: |
E I DU PONT DE NEMOURS AND COMPANY;LEGAL PATENT RECORDS CENTER
BARLEY MILL PLAZA 25/1128
4417 LANCASTER PIKE
WILMINGTON
DE
19805
US
|
Family ID: |
35238841 |
Appl. No.: |
11/589348 |
Filed: |
October 30, 2006 |
Related U.S. Patent Documents
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Application
Number |
Filing Date |
Patent Number |
|
|
10840981 |
May 7, 2004 |
7151342 |
|
|
11589348 |
Oct 30, 2006 |
|
|
|
Current U.S.
Class: |
313/504 ;
445/24 |
Current CPC
Class: |
H01L 51/0017 20130101;
Y02E 10/549 20130101; Y02P 70/521 20151101; H01L 51/56 20130101;
Y02P 70/50 20151101 |
Class at
Publication: |
313/504 ;
445/024 |
International
Class: |
H05B 33/00 20070101
H05B033/00; H05B 33/10 20070101 H05B033/10 |
Goverment Interests
STATEMENT AS TO FEDERALLY SPONSORED RESEARCH
[0002] This invention was made with Government support under DARPA
grant number 4332. The Government may have certain rights in the
invention.
Claims
1. A process for forming an electronic device, comprising: forming
at least one first electrode over a substrate; forming at least one
conductive lead over the substrate, wherein the at least one
conductive lead is laterally spaced apart from the at least one
first electrode; forming a protective layer of material over
portions of the at least one first electrode and the at least one
conductive lead, wherein one or more selected portions of the at
least one first electrode and the at least one conductive lead are
left exposed by the protective layer; forming organic material over
the protective layer and the one or more selected portions; forming
at least one second electrode over the organic material; and
removing portions of the organic material to at least partially
expose the one or more selected portions.
2. The process of claim 1, wherein the one or more selected
portions include at least one portion of the at least one first
electrode and at least one portion of the at least one conductive
lead.
3. The process of claim 1, wherein the at least one first electrode
includes a pixel portion and an anode lead portion, wherein the
anode lead portion further comprises a wire bonding pad area.
4. The process of claim 3, wherein the one or more selected
portions includes the pixel portion, the wire bonding pad area, or
combinations thereof.
5. The process of claim 3, wherein the formation of the protective
layer includes: forming the protective layer over the at least one
first electrode and the at least one conductive lead; and
selectively removing portions of the protective layer over the one
or more selected portions.
6. The process of claim 5, wherein the selective removal of the
protective layer further includes selectively removing a portion of
the protective layer over the pixel portion of the at least one
first electrode.
7. The process of claim 5, wherein the selective removal of the
protective layer over the one or more selected portions includes:
forming a photoresist material over the one or more selected
portions before the formation of the protective layer; and
performing a photoresist material removal process, after the
formation of the protective layer, for removing the photoresist
material and portions of the protective layer disposed over the
photoresist material.
8. The process of claim 1, wherein the substrate is selected from a
plastic substrate, a ceramic substrate, a glass substrate, a metal
substrate, or combinations thereof.
9. The process of claim 1, wherein: the formation of the protective
layer further includes forming the protective layer over the
substrate, wherein a portion of the substrate is left exposed by
the protective layer; the formation of the organic material
includes forming the organic material over the substrate; and the
removal of portions of the organic material includes removing a
portion of the organic material to expose the portion of the
substrate.
10. The process of claim 1, wherein the removal of the portions of
the organic material is performed using laser ablation, plasma
etching, or combinations thereof.
11. The process of claim 1, further comprising: forming at least
one conductive bridge member that extends between and electrically
connects the at least one second electrode and the one or more
selected portions of the at least one conductive lead.
12. An organic electronic device made by the process of claim
1.
13. The device of claim 12, wherein the device is selected from a
light-emitting diode, a light-emitting diode display, a diode
laser, a photodetector, a photoconductive cell, a photoresistor, a
photoswitch, a phototransistor, a phototube, and IR detector, a
photovoltaic device, a solar cell, a transistor, or a diode.
Description
CROSS REFERENCE TO RELATED APPLICATIONS
[0001] This is a Division of Ser. No. 10/840,981, filed on May 7,
2004.
FIELD OF THE INVENTION
[0003] The invention relates generally to organic electronic
devices, and more particularly to processes for selectively
removing organic layers from portions of the device during
fabrication of an organic electronic device and organic electronic
devices formed by the processes.
BACKGROUND INFORMATION
[0004] For organic light emitting diode (OLED) devices, the laser
ablation process has been used to remove organic films from
unwanted areas of the device substrate. The first steps in the
fabrication of OLED devices are the growth and patterning of the
anode and leads films. The anode film is typically indium tin oxide
(ITO), and the leads may include a tri-layer sandwich including an
adhesion layer and a low-resistivity conducting layer. A typical
lead structure is Cr/Cu/Cr. After forming the patterned anode and
lead layers, the process involves patterning photoresist cathode
separation lines followed by the coating of two or more organic
layers, called the charge transport layer(s) and the
electroluminescent layer(s), over the entire substrate using a
liquid deposition technique. The substrate then goes into the laser
ablation system, where the laser beam is focused onto areas that
need to be cleared of the organic layers. These include the
cathode-to-leads electrical contact pads, bond pads, and the frame
(sometimes called rail) around the active area upon which glue is
dispensed for the encapsulating lid.
[0005] It has been found that the laser ablation process can crack
or otherwise damage the lead structure. Moreover, if a plastic
substrate is used, the laser ablation process also can damage the
moisture and oxygen barrier layer that is part of the substrate. It
has also been found that corrosion of the leads can occur in the
finished organic electronic device. Lastly, it can be difficult to
adequately remove the organic layers over the leads to provide good
electrical contact, as well as safely remove the organic layers
over the barrier layer at the rail so that the finished organic
electronic device can be properly sealed.
SUMMARY OF THE INVENTION
[0006] A process has been developed to safely remove organic layers
during fabrication of organic electronic devices. It has also been
discovered that this process protects conductive leads from
corrosion.
[0007] In one aspect of the present invention, an electronic device
comprises at least one first electrode disposed over a substrate,
at least one conductive lead disposed over the substrate and
laterally spaced apart from the at least one first electrode, a
protective layer of material selectively disposed over the at least
one first electrode and the at least one conductive lead, wherein
the protective layer is not disposed over one or more selected
portions of the at least one first electrode and the at least one
conductive lead, organic active material selectively disposed over
the protective layer, wherein the organic active material is not
disposed over at least part of the one or more selected portions,
and at least one second electrode disposed over the organic
material.
[0008] In another aspect of the present invention, a process for
forming an electronic device comprises forming at least one first
electrode over a substrate, forming at least one conductive lead
over the substrate, wherein the at least one conductive lead is
laterally spaced apart from the at least one first electrode,
forming a protective layer of material over portions of the at
least one first electrode and the at least one conductive lead,
wherein one or more selected portions of the at least one first
electrode and the at least one conductive lead are left exposed by
the protective layer, forming organic material over the protective
layer and the one or more selected portions, forming at least one
second electrode over the organic material, and removing portions
of the organic material to at least partially expose the one or
more selected portions.
[0009] Other features and advantages of the invention will be
apparent from the following detailed description, and from the
claims. The foregoing general description and the following
detailed description are exemplary and explanatory only and are not
restrictive of the invention, as defined in the appended
claims.
BRIEF DESCRIPTION OF THE DRAWINGS
[0010] The invention is illustrated by way of example and not
limitation in the accompanying figures.
[0011] FIG. 1 is a plan view of a portion of a structure of the
present invention, after forming anode strips and conductive leads
on a substrate.
[0012] FIG. 2 is a plan view of the structure of FIG. 1, after
forming a protective layer over selective portions thereof.
[0013] FIG. 3 is a plan view of the structure of FIG. 2, after
forming cathode separation strips thereon.
[0014] FIG. 4 is a cross-sectional view of the structure of FIG. 3
at sectioning lines 44.
[0015] FIG. 5 is a cross-sectional view of the structure of FIG. 4,
after forming a hole-transport layer and an organic active layer
thereon.
[0016] FIG. 6 is a top view of a shadow mask used for forming
cathode material on the structure.
[0017] FIG. 7 is a plan view of the structure of FIG. 5, after
forming the cathode material thereon.
[0018] FIG. 8 is a cross-sectional view of the structure of FIG. 7
at sectioning lines 8-8.
[0019] FIG. 9 is a plan view of the structure of FIG. 7, after
laser ablation is used to selectively remove portions of the
hole-transport and organic active layers.
[0020] FIG. 10 is a top view of a shadow mask used for forming
bridge material on the structure.
[0021] FIG. 11A is a plan view of the structure of FIG. 9, after
forming the bridge material thereon.
[0022] FIG. 11B is a cross-sectional view of the structure of FIG.
11A at sectioning lines 11B-11B.
[0023] FIG. 11C is a cross-sectional view of the structure of FIG.
11A at sectioning lines 11C-11C.
[0024] Skilled artisans appreciate that elements in the figures are
illustrated for simplicity and clarity and have not necessarily
been drawn to scale. For example, the dimensions of some of the
elements in the figures may be exaggerated relative to other
elements to help to improve understanding of embodiments of the
invention.
DETAILED DESCRIPTION
[0025] Reference is now made in detail to the exemplary
embodiment(s) of the invention, examples of which are illustrated
in the accompanying drawings. Wherever possible, the same reference
numbers will be used throughout the drawings to refer to the same
or like parts (elements).
[0026] A process has been developed to protect the leads and
barrier layer when portions of organic layer(s) are removed (e.g.
via laser ablation, plasma etching, or combinations thereof during
the fabrication of an organic electronic device. The process safely
removes the organic layer(s) over portions of the conductive leads
and wire bond pads for making an electrical connection, and over
portions of the barrier layer at the device rail (used for glue
dispensing for encapsulation) to reduce the likelihood that
contaminants will enter the device and significantly reduce its
operating lifetime.
[0027] The process results in an electronic device having at least
one first electrode disposed over a substrate, at least one
conductive lead disposed over the substrate and laterally spaced
apart from the at least one first electrode, a protective layer of
material selectively disposed over the at least one first electrode
and the at least one conductive lead, wherein the protective layer
is not disposed over one or more selected portions of the at least
one first electrode and the at least one conductive lead, an
organic active material selectively disposed over the protective
layer, wherein the organic active material is not disposed over at
least part of the one or more selected portions, and at least one
second electrode disposed over the organic material.
[0028] Before addressing details of embodiments described below,
some terms are defined or clarified. Unless otherwise defined, all
technical and scientific terms used herein have the same meaning as
commonly understood by one of ordinary skill in the art to which
this invention belongs. Although methods and materials similar or
equivalent to those described herein can be used in the practice or
testing of the present invention, suitable methods and materials
are described below. All publications, patent applications,
patents, and other references mentioned herein are incorporated by
reference in their entirety. In case of conflict, the present
specification, including definitions, will control. In addition,
the materials, methods, and examples are illustrative only and not
intended to be limiting.
[0029] As used herein, the terms "array," "peripheral circuitry"
and "remote circuitry" are intended to mean different areas or
components. For example, an array may include a number of pixels,
cells, or other electronic devices within an orderly arrangement
(usually designated by columns and rows) within a component. These
electronic devices may be controlled locally on the component by
peripheral circuitry, which may lie within the same component as
the array but outside the array itself. Remote circuitry typically
lies away from the peripheral circuitry and can send signals to or
receive signals from the array (typically via the peripheral
circuitry). The remote circuitry may also perform functions
unrelated to the array.
[0030] The term "active" when referring to a layer or material is
intended to mean a layer or material that exhibits
electro-radiative or electromagnetic properties. An active layer
material may emit radiation or exhibit a change in concentration of
electron-hole pairs when receiving radiation.
[0031] The term organic electronic devices includes, but is not
limited to, (1) devices that convert electrical energy into
radiation (e.g., a light-emitting diode, light emitting diode
display, or diode laser), (2) devices that detect signals through
electronics processes (e.g., photodetectors., photoconductive
cells, photoresistors, photoswitches, phototransistors, phototubes,
IR detectors), (3) devices that convert radiation into electrical
energy, (e.g., a photovoltaic device or solar cell), and (4)
devices that include one or more electronic components that include
one or more organic semi-conductor layers (e.g., a transistor or
diode).
[0032] Also as used herein, the terms "over" and "on" both
inclusively include "directly on" (no intermediate materials or
elements disposed therebetween) and "indirectly on" (intermediate
materials or elements disposed therebetween). For example, forming
an element "over a substrate" can include forming the element
directly on the substrate with no intermediate materials/elements
therebetween, as well as forming the element indirectly on the
substrate with one or more intermediate materials/elements
therebetween.
[0033] The term "electron withdrawing" is synonymous with "hole
injecting." Literally, holes represent a lack of electrons and are
typically formed by removing electrons, thereby creating an
illusion that positive charge carriers, called holes, are being
created or injected. The holes migrate by a shift of electrons, so
that an area with a lack of electrons is filled with electrons from
an adjacent layer, which give the appearance that the holes are
moving to that adjacent area. For simplicity, the terms holes, hole
injecting, hole transport, and their variants will be used.
[0034] The term "low work function material" is intended to mean a
material having a work function no greater than about 4.4 eV. The
term "high work function material" is intended to mean a material
having a work function of at least approximately 4.4 eV.
[0035] Group numbers corresponding to columns within the periodic
table of the elements use the "New Notation" convention as seen in
the CRC Handbook of Chemistry and Physics, 81.sup.st Edition
(2000).
[0036] To the extent not described herein, many details regarding
specific materials, processing acts, and circuits are conventional
and may be found in textbooks and other sources within the organic
light-emitting diode display, photo detector, and semiconductor
arts.
[0037] As used herein, the terms "comprises," "comprising,"
"includes," "including," "has," "having" or any other variation
thereof, are intended to cover a non-exclusive inclusion. For
example, a process, method, article, or apparatus that comprises a
list of elements is not necessarily limited to only those elements
but may include other elements not expressly listed or inherent to
such process, method, article, or apparatus. Further, unless
expressly stated to the contrary, "or" refers to an inclusive or
and not to an exclusive or. For example, a condition A or B is
satisfied by any one of the following: A is true (or present) and B
is false (or not present), A is false (or not present) and B is
true (or present), and both A and B are true (or present).
[0038] The term "layer" or "film" refers to a coating covering a
desired area. The area can be as large as an entire device or as
small as a specific functional area such as the actual visual
display, or as small as a single sub-pixel. Films can be formed by
any conventional deposition technique, including vapor deposition
and liquid deposition. Typical liquid deposition techniques
include, but are not limited to, continuous deposition techniques
such as spin coating, gravure coating, curtain coating, dip
coating, slot-die coating, spray coating, and continuous nozzle
coating; and discontinuous deposition techniques such as ink jet
printing, gravure printing, and screen printing. A "layer" of a
material shall include single or multiple layers of such
material.
[0039] The term "protective layer of material" shall mean one or
more layers of material(s) used to protect underlying materials or
structures from subsequent processing steps and/or from
contamination both during and after fabrication.
[0040] Attention is now directed to FIGS. 1-11C, which show the
processing steps for making a monochromatic passive matrix OLED
display according to one illustrative embodiment of the present
invention. Modifications that may be made for use with multi-color
or full-color passive matrix and active matrix OLED displays are
described later in this specification.
[0041] FIG. 1 includes a plan view of a portion of a substrate 10.
The substrate 10 can include nearly any type and number of
materials including conductive, semiconductive, or insulating
materials. If substrate 10 includes a conductive base material,
care may need to be exercised to ensure the proper electrical
isolation between parts of a component. The conductive base
material may be covered by an insulating layer having a sufficient
thickness to reduce the effects of parasitic capacitance between
overlying electrodes or conductors and the underlying conductive
base material. Skilled artisans are capable of determining an
appropriate thickness of an insulating layer to reduce the effects
of undesired capacitive coupling.
[0042] The substrate 10 may comprise a rigid material (e.g., glass,
alumina, or the like) or a flexible material comprising at least
one polymeric film. Examples of suitable polymers for the polymeric
film may be selected from one or more materials containing
essentially polyolefins (e.g., polyethylene, polypropylene, or the
like); polyesters (e.g., polyethylene terephthalate, polyethylene
naphthalate or the like); polyimides; polyamides;
polyacrylonitriles and polymethacrylonitriles; perfluorinated and
partially fluorinated polymers (e.g., polytetrafluoroethylene,
copolymers of tetrafluoroethylene and polystyrenes, and the like);
polycarbonates; polyvinyl chlorides; polyurethanes; polyacrylic
resins, including homopolymers and copolymers of esters of acrylic
or methacrylic acids; epoxy resins; Novolac resins; any combination
thereof; and the like. When multiple films are used, they can be
joined together with appropriate adhesives or by conventional layer
producing processes including known coating, co-extrusion, or other
similar processes. The polymeric films generally have a thickness
in the range of approximately 12-250 microns. When more than one
film layer is present, the individual thicknesses can be much
less.
[0043] Although the polymeric film(s) may contain essentially one
or more of the polymers described above, the film(s) may also
include one or more conventional additive(s). For example, many
commercially available polymeric films contain slip agents or matte
agents to prevent the layers of film from sticking together when
stored as a large roll.
[0044] If a polymeric substrate is used, a barrier layer may be
formed over its top surface to prevent contamination thereto. For
flexible substrates that include a plurality of polymeric films, at
least one layer of barrier material may be sandwiched between at
least two of the polymeric films. In one non-limiting example, a
polyester film approximately 25-50 microns thick can be coated with
an approximately 2-500 nm thick layer of silicon nitride
(SiN.sub.x) using plasma enhanced chemical vapor deposition or
physical vapor deposition (conventional Radio-Frequency (RF)
magnetron sputtering or inductively-coupled plasma physical vapor
deposition (ICP-PVD). The silicon nitride layer can then be
overcoated with a solution of acrylic resin that is allowed to dry,
or an epoxy or Novolac resin followed by curing. Alternatively, the
silicon nitride coated polyester film can be laminated to a second
layer of polyester film. The overall thickness of the composite
structure is generally in the range of approximately 12-250
microns, and more typically 25-200 microns. Such overall thickness
can be affected by the method used to apply or lay down the
composite structure.
[0045] After reading this specification, skilled artisans
appreciate that the selection of material(s) that can be used for
the substrate 10 is widely varied. Skilled artisans are capable of
selecting the appropriate material(s) based on their physical,
chemical, and electrical properties. For simplicity, the preferred
embodiment described below uses a flexible substrate generally
referred to as substrate 10, which includes one or more polymeric
layers covered by a barrier layer.
[0046] A first electrode layer is formed over the substrate 10, and
can include nearly any conductive material. In this illustrative
example of one embodiment, the electrode layer will eventually form
the anodes for the electronic devices that are being formed. The
first electrode layer can actually be plurality of conductive
layers. In an exemplary embodiment, the first electrode layer can
be indium tin oxide, with a thickness in a range of approximately
100-200 nm.
[0047] The first electrode layer is then patterned using any
conventional patterning technique (e.g. photolithography) to form
spaced apart anode strips 12 of the first electrode layer material,
as shown in FIG. 1. Alternately, the anode strips 12 may be formed
using a shadow mask, whereby the first electrode layer is initially
deposited in strips 12, and a separate patterning step is then
unnecessary. Anode strips 12 constitute first electrodes for the
organic electronic device.
[0048] In the embodiment shown in FIG. 1, each anode strip 12
terminates with an integrally formed anode lead portion 12a. The
anode lead portions 12a include bonding pad areas 12b to which
wires (i.e. from peripheral and/or remote circuitry) can be
connected. It should be noted that anode lead portions 12a can
alternatively be physically separated from the rest of anode strips
12, whereby separately formed conductive members (not shown) can
connect anode leads/strips 12a/12 together.
[0049] Note that FIG. 1 illustrates only a simplified portion of an
array of the electronic devices, without showing the peripheral and
remote circuitry areas of the substrate. Actual arrays typically
include many more pixels and are more elaborate, but a smaller and
simplified array portion is shown to better illustrate the
invention. The array may include a plurality of electronic devices
for a display (e.g., an electroluminescent display), a radiation
detector (e.g., a photo detector), a voltaic cell (e.g., a
photovoltaic cell), or the like.
[0050] Conductive leads 14 are formed to provide electrical
connections between the second electrode layer and peripheral and
remote circuitry. In this illustrative example of one embodiment,
the second electrode layer is a cathode layer. As shown in FIG. 1,
the conductive leads 14 are located near the sides of the array.
The anode strips 12 and conductive leads 14 are spaced apart from
one another. The conductive leads 14 may be formed using any
conventional technique and may comprise one or more layers of
chromium, aluminum, molybdenum, copper, alloys thereof, and
potentially other metals and alloys, as well as adhesion layer(s).
In one embodiment, the conductive leads 14 may comprise a plurality
of layers including Cr/Al/Cr, Cr/Cu/Cr, or Mo/Cu/Mo, however other
metals or combinations of layers may be used. The thickness of the
conductive leads 14 can be in a range of approximately 10-600 nm.
Note that the order in which the conductive leads 14 and anode
strips 12 are formed may be reversed in some embodiments.
[0051] As shown in FIG. 2, a protective layer 18 is next formed
over select areas of the anode strips 12, the conductive leads 14
and the exposed portions of substrate 10. This protective layer 18
serves to protect these select areas from later processing and from
outside contamination that can cause corrosion or degradation.
Protective layer 18 may, but not necessarily, be formed of
insulating material(s), since it may be formed directly on
conductive anode strips 12 and conductive leads 14. The protective
layer 18 may comprise single or multiple layers of metal oxide or
metal nitride insulating materials (e.g., silicon nitride, silicon
oxide, aluminum nitride, aluminum oxide, or combinations thereof),
as well as mixtures thereof.
[0052] The selected areas on which the protective layer 18 is
formed may include the anode strips 12 and the conductive leads 14,
but may not include wire bonding pad areas 12b and 14a at the
distal ends thereof (that will later serve as the electrical
connection to the peripheral/remote circuitry), and conductive lead
via areas 14b at the proximate ends of the conductive leads 14
adjacent the array (that will later serve as the electrical
connection to the second electrode members).
[0053] While the protective layer 18 can be formed using one of
several conventional techniques (e.g. deposition followed by
photolithographic etch, etc.), a lift-off stencil process is may be
used to avoid wet chemistry that can damage the existing structure.
This process is well known in the art, and begins by forming image
reversal photoresist only over those portions of the structure on
which the protective layer 18 is not to be formed, preferably with
a wedge-shaped cross-sectional profile (i.e. undercut). Then, the
protective material is formed over the structure, followed by a
photoresist strip process that removes the image reversal
photoresist along with the protective layer portions directly over
the photoresist.
[0054] For one embodiment of the present invention, a layer of
image reversal photoresist is formed over the structure shown in
FIG. 1 by a conventional deposition process. A photolithographic
exposure and dry etch process follows, which removes the
photoresist material except for portions over the wire bonding pad
areas 12b and 14a, the conductive lead via areas 14b, a rail
portion 10a of the substrate, and (for reasons described later) the
eventual pixel portions 16 of anode strips 12 (so that thin strips
of the protective layer 18 will remain in the finished device
between the pixel portions 16). Rail portion 10a is a (rectangular)
strip that encircles the anode strip pixel portions 16, but not the
wire bonding pad areas 12b and 14a (see FIG. 2).
[0055] The protective layer 18 is then formed over the structure
using a conventional deposition process (e.g. silicon nitride
formed via vacuum deposition with a thickness of about 1000 .ANG.).
A photoresist strip process is then used to remove the remaining
portions of the photoresist (and the portions of protective layer
18 over that photoresist), so that the protective layer 18 covers
the structure except the wire bonding pad areas 12b and 14a, the
cathode via areas 14b, the rail portion 10a of the substrate 10,
and the pixel portions 16 of anode strips 12, as shown in FIG. 2.
Other selected areas of the structure can also be chosen to be left
exposed by this protective layer formation process.
[0056] While the protective layer 18 could be removed from the
entire pixel area of the array structure, protective material is
left remaining between the pixel portions 16 in an exemplary
embodiment of the present invention for at least two reasons.
First, it can be difficult using a lift-off stencil process to
remove a solid block of material that is the size of the entire
array structure. Removing protective material just over each of the
pixel portions 16 is more reliable. Second, the protective material
left remaining between the pixel portions 16 can help reduce pixel
shrinkage, as explained later in this specification.
[0057] Cathode separation strips 22 are next formed by spin coating
an insulating material to a thickness of approximately 2-5 .mu.m
over the structure, and then patterning the insulating material to
form parallel, spaced apart strips 22 thereof extending across (and
orthogonally to) the anode strips 12, as illustrated in FIG. 3. The
cathode separation strips 22 extend beyond the anode strips 12, and
along both sides of each conductive lead 14. The cathode separation
strips 22 are separated by openings 24 in which portions of the
anode strips 12, substrate 10 and conductive leads 14 are left
exposed therein. It is in these openings 24 in which the cathodes
and conductive bridge members will later be formed. The peripheral
and remote circuitry areas of the substrate are not covered by the
cathode separation strips 22.
[0058] The cathode separation strips 22 may comprise a
photoimageable material including photoresist, polyimide, or the
like. In one embodiment, a Novolac positive photoimageable
photoresist with image reversal capability may be used. The cathode
separation strips 22 may have a wedge shaped cross section, and are
formed directly over the strips of protective layer 18 that are
disposed between the pixel portions 16, as shown in FIG. 4.
[0059] An optional hole-transport layer 32 and a layer of organic
active material 34 are next formed sequentially over the structure,
as shown in FIG. 5. Layers 32 and 34 may be formed by spin coating
appropriate materials as described below. One or both of the layers
may be cured after spin coating. The layers 32 and 34 overlie the
tops of the cathode separation strips 22 and along the bottoms of
openings 24 between the cathode separation strips 22. Although not
shown in FIG. 5, very thin portions of layers 32 and 34 may lie
along the sides of the cathode separation strips 22 at locations
above layer 34 within the openings 24. Note that the structures for
the cathode separation strips 22 are narrower near the substrate 10
and wider further from the substrate 10. In another embodiment, the
structures may have a more rounded cusp-like shape. The
significance of the structures is addressed later in this
specification.
[0060] The hole-transport layer 32 is an example of a charge
transport layer. The hole-transport layer 32 can be used to reduce
the amount of damage and potentially increase the lifetime and
reliability of the device compared to a device where the anode
strips 12 would directly contact a subsequently formed organic
active layer. In one specific embodiment, the hole-transport layer
32 can include an organic polymer, such as polyaniline (PANI),
poly(3,4-ethylenedioxythiophene) (PEDOT), and the like, or an
organic charge transfer compound, such as tetrathiafulvalene
tetracyanoquinodimethane (TTF-TCQN) and the like. Layer 32
typically has a thickness in a range of approximately 100-250
nm.
[0061] The hole-transport layer 32 typically is conductive to allow
electrons to be removed from the subsequently formed active region
and transferred to the conductive anode strips 12. Although the
conductive strips 12 and the optional hole-transport layer 32 are
both conductive, typically the conductivity of the anode strips 12
is significantly greater than that of the hole-transport layer
32.
[0062] Depending upon the application of the electronic device, the
organic active layer 34 can be a radiation-emitting layer that is
activated by a signal (such as in a light-emitting diode), or a
layer of material that responds to radiant energy and generates a
signal with or without an applied potential (such as in a
photodetector). Examples of electronic devices that may respond to
radiant energy include photoconductive cells, photoresistors,
photoswitches, phototransistors, phototubes, and photovoltaic
cells. After reading the specification, skilled artisans will
appreciate that other similar electronic devices may operate
outside the visible light spectrum, such as infrared, ultraviolet,
and the like.
[0063] When the organic active layer 34 is within a
radiation-emitting electronic device, the layer will emit radiation
when sufficient bias voltage is applied to the electrical contact
layers. The radiation-emitting organic active layer may contain
nearly any organic electroluminescent or other organic
radiation-emitting materials.
[0064] The organic active layer 34 can include any organic
electroluminescent (EL) material including, but not limited to,
fluorescent dyes, fluorescent and phosphorescent metal complexes,
conjugated polymers, and mixtures thereof. Examples of fluorescent
dyes include, but are not limited to, pyrene, perylene, rubrene,
derivatives thereof, and mixtures thereof. Examples of metal
complexes include, but are not limited to, metal chelated oxinoid
compounds, such as tris(8-hydroxyquinolato)aluminum (Alq.sub.3);
cyclometalated iridium and platinum electroluminescent compounds,
such as complexes of Iridium with phenylpyridine, phenylquinoline,
or phenylpyrimidine ligands as disclosed in Published PCT
Application WO 02/02714, and organometallic complexes described in,
for example, published applications US 2001/0019782, EP 1191612, WO
02/15645, and EP 1191614; and mixtures thereof. Electroluminescent
emissive layers comprising a charge carrying host material and a
metal complex have been described by Thompson et al., in U.S. Pat.
No. 6,303,238, and by Burrows and Thompson in published PCT
applications WO 00/70655 and WO 01/41512. Examples of conjugated
polymers include, but are not limited to poly(phenylenevinylenes),
polyfluorenes, poly(spirobifluorenes), polythiophenes,
poly(p-phenylenes), copolymers thereof, and mixtures thereof. The
organic active layer 34 in a radiation-emitting device generally
has a thickness in the range of approximately 40-100 nm.
[0065] When the organic active layer 34 is incorporated in a
radiation detector or current generator, the layer responds to
radiant energy and produces a signal or current either with or
without a biased voltage. Materials that respond to radiant energy
and are capable of generating a signal or current with a biased
voltage (such as in the case of photoconductive cells,
photoresistors, photoswitches, photodetectors, phototransistors,
and phototubes) include, for example, many conjugated polymers and
electroluminescent materials. Materials that respond to radiant
energy and are capable of generating a signal or current without a
biased voltage (such as in the case of a photoconductive cell or a
photovoltaic cell) include materials that react to radiation and
generate electron-hole pairs. The electrons or holes can be used in
generating a signal or current. Such radiation-sensitive charge
generating materials include for example, many conjugated polymers
and electroluminescent and photoluminescent materials. Specific
examples include, but are not limited to,
poly(2-methoxy,5-(2-ethyl-hexyloxy)-1,4-phenylene vinylene)
("MEH-PPV") and MEH-PPV composites with CN-PPV. The organic active
layer 34 in a radiation detector or current generator device
typically has a thickness in a range of approximately 50-500
nm.
[0066] Although not shown, an optional electron-transport layer may
be formed over the organic active layer 34. The electron-transport
layer is another example of a charge transport layer. The
electron-transport layer typically is conductive to allow electrons
to be injected from the subsequently formed cathode and transferred
to the organic active layer 34. Although the subsequently formed
cathode and the optional electron-transport layer are both
conductive, typically the conductivity of the cathode is
significantly greater than that of the electron-transport
layer.
[0067] In one specific embodiment, the electron-transport layer can
include metal-chelated oxinoid compounds (e.g., Alq.sub.3 or the
like); phenanthroline-based compounds (e.g.,
2,9-dimethyl-4,7-diphenyl-1,10-phenanthroline ("DDPA"),
4,7-diphenyl-1,10-phenanthroline ("DPA"), or the like); azole
compounds (e.g.,
2-(4-biphenyl)-5-(4-t-butylphenyl)-1,3,4-oxadiazole ("PBD" or the
like), 3-(4-biphenyl)-4-phenyl-5-(4-t-butylphenyl)-1,2,4-triazole
("TAZ" or the like); other similar compounds; or any one or more
combinations thereof. Alternatively, optional electron-transport
layer may be inorganic and comprise BaO, LiF, Li.sub.2O, or the
like. The electron-transport layer typically has a thickness in a
range of approximately 30-500 nm.
[0068] Next, the second electrode (cathode) layer may be formed on
the structure in the following manner. Portions of the structure
are masked, using a first shadow mask 40 having a central cathode
opening 42 surrounded by solid material 44, as shown in FIG. 6. The
first shadow mask 40 is placed over the structure leaving a center
portion of the array exposed via the cathode opening 42 and
covering the rest of the structure with the solid portion 44 of the
mask. Cathode material is then deposited on the exposed portion(s)
of the structure (through cathode opening 42) by vapor deposition
(e.g., evaporation, sputtering, or the like). Portions of the
deposited cathode material are formed overlying the cathode
separation strips 22 to form elongated conductive members 50, and
on those portions of organic material 34 in openings 24 to form
elongated cathode members 52, as shown in FIGS. 7 and 8. Due to the
directional nature of the physical vapor deposition and the shape
of the cathode separation strips 22, cathode members 52 are not
electrically connected to one another or to conductive members 50.
If the walls of the cathode separation strips 22 become closer to
vertical, an optional collimator may be used during deposition to
reduce the likelihood of an unintended electrical short between any
of the cathode members 52 and the conductive members 50.
[0069] In general, the cathode material is deposited as one or more
metal-containing layers of material having a low work function
(i.e. lower than that of anode strips 12). Materials for the
cathode material can be selected from Group 1 metals (e.g., Li, Cs,
or the like), the Group 2 (alkaline earth) metals, the rare earth
metals including the lanthanides and the actinides, and the like.
The cathode material is generally deposited with a thickness in a
range of approximately 300-500 nm. In one specific, non-limiting
embodiment, the cathode material is a barium layer of less than
approximately 10 nm followed by an aluminum layer of approximately
500 nm. Cathode members 52 constitute second electrodes for the
organic electronic device.
[0070] After the shadow mask 40 is removed, those selected portions
of organic active layer 34 and hole transport layer 32 overlying
the wire bonding pad areas 12b and 14a, the cathode via areas 14b,
and the substrate rail 10a are removed by, for example, laser
ablation, as illustrated in FIG. 9. The laser ablation process
includes focusing a laser beam on those selected portions of the
structure from which layers 32/34 are to be removed, where the
laser ablation parameters are set such that the laser beam ablates
away layers 32/34 without penetrating any portions of protective
layer 18. Thus, even if there is over-ablation (laser energy
applied to non-selected portions of the structure), only those
portions of the anode strips 12, conductive leads 14, and rail
portions 10a of the substrate 10 that were left exposed by the
formation of protective layer 18 are left exposed now. The areas of
the structure adjacent thereto are protected from the laser energy
by the protective layer 18.
[0071] Alternately, the selected portions of organic active layer
34 and hole transport layer 32 described above could be removed by
a plasma etch process instead of by laser ablation, where
protective layer 18 would serve to protect non-selected portions of
the structure from this etch process. An exemplary plasma etch
process is described in co-pending U.S. patent application Ser. No.
10/625,112 filed on Jul. 22, 2003, which is incorporated herein by
reference.
[0072] Conductive bridge material may be formed next using a second
shadow mask 60 as shown in FIG. 10. Second mask 60 is the same as
first mask 40, except that mask 60 has a central opening 62 formed
in the solid material 64 that is longer (in the direction parallel
to the cathode separator strips 22) than the cathode opening 42 of
first mask 40. When second shadow mask 60 is placed over the
structure, the added length of the central opening 62 leaves
exposed the central area of the array extending out to and
including conductive lead via areas 14b. The width of opening 62,
in the direction perpendicular to the cathode separator strips 22,
may be substantially the same or narrower than opening 42. The
solid material 64 is used to substantially prevent any bridge
material from being deposited over portions of the substrate 10
that could lead to electrical shorting.
[0073] After the second mask 60 is aligned to the substrate 10, the
conductive bridge material is deposited over the structure
portion(s) exposed by central opening 62 using physical vapor
deposition (e.g., evaporation, sputtering, or the like), resulting
in elongated conductive members 70 overlying conductive members 50
(over cathode separation strips 22), and conductive bridge members
72 that overlay cathode members 52 (in openings 24), as shown in
FIGS. 11A, 11B and 11C. Due to the directional nature of the
physical vapor deposition and the shape of the cathode separation
strips 22, conductive bridge members 72 are not electrically
connected to one another or to conductive members 70. If the walls
of the cathode separation strips 22 become closer to vertical, an
optional collimator may be used during deposition to reduce the
likelihood of an unintended electrical short between any of the
conductive bridge members 72 and the conductive members 70.
[0074] The conductive bridge material can be formed of any
appropriate conductive material, preferably a metal-containing
layer having a work function higher than that for the cathode
members 52. For example, conductive bridge members 72 may be made
of aluminum, copper, gold, and the like, with a thickness in the
range of approximately 100-300 nm.
[0075] As shown in FIGS. 11A-11C, the conductive bridge members 72
lie between the cathode separation strips 22, while conductive
members 70 overlie the cathode separation strips 22. Each
conductive bridge member 72 is formed over one of the cathode
members 52, and extends out and over the end of one of the
conductive leads 14, making electrical contact therewith at the
exposed conductive lead via area 14b. Therefore, conductive bridge
members 72 form conductive bridges that electrically connect and
contact the cathode members 52 and conductive leads 14. Wires or
other conductive members are eventually formed in a conventional
manner to electrically connect bonding pad areas 12b and 14a to the
periphery/remote circuitry.
[0076] Other circuitry not illustrated in FIGS. 1-11C may be formed
using any number of the previously described or additional layers.
Although not shown, additional insulating layer(s) and interconnect
level(s) may be formed to allow for circuitry in peripheral areas
(not shown) that may lie outside the array. Such circuitry may
include row or column decoders, strobes (e.g., row array strobe,
column array strobe, or the like), sense amplifiers, or the
like.
[0077] An encapsulating layer (not shown) can be formed over the
array (and possibly over the peripheral and remote circuitry) to
form a substantially completed electrical component, such as an
electronic display, a radiation detector, a voltaic cell, and the
like. The encapsulating layer may be attached at the rail portion
10b such that no organic layers lie between it and the substrate
10, thereby sealing the array portion of the device. Preferably,
only end portions of the conductive leads 14 and anode leads 12a
extend from the encapsulating layer so that electrical connections
can be made with wire bonding pad areas 12b and 14a. Radiation may
be transmitted through the encapsulating layer. If so, the
encapsulating layer should be transparent to the radiation.
[0078] In another set of embodiments, a full-color active matrix
display may be formed. An insulating layer of organic well
structures may be sequentially formed after forming the anode
strips 12 and conductive leads 14. Also, portions of the organic
layer 34 may selectively receive organic dye(s) using a precision
deposition technique to allow the different colors within a pixel
to be realized. For active matrix arrays, the cathode separation
strips 22 would not be formed, as a common cathode may be. If an
active matrix OLED display is being formed, thin-film circuits may
be present with substrate 10. Such thin-film circuits are
conventional.
[0079] In one embodiment, a multi-colored or full-color passive
matrix display may be formed. Six subpixels of two interleaved
pixels may be formed with a structure similar to that shown in
FIGS. 1-11C except additional layer previously described. For
example, referring to FIG. 1, the first and fourth anode strips 12
may correspond to blue subpixels in different pixels, the second
and fifth anode strips 12 may correspond to green subpixels in
those different pixels, and the third and sixth anode strips 12 may
correspond to red subpixels in those different pixels.
[0080] In still other embodiments, the anode and cathode can be
reversed. A high work function material can be formed corresponding
to the members 52. Another conductive material may be formed and
correspond to the conductive members 70 and 72 seen in FIGS.
11A-11C.
[0081] Each pixel is defined by the area in which a first electrode
(anode strip 12) and a second electrode (cathode member 52)
vertically overlap (intersect). During operation of a display,
appropriate potentials are placed on the anode strips 12 and the
cathode members 52 (via conductive leads 14) to cause radiation to
be emitted from the organic active layer 34 therebetween. More
specifically, when light is to be emitted, a potential difference
typically between 5 and 12 volts is applied between the appropriate
anode strip(s) 12 and cathode member(s) 52. Holes are injected into
the organic active layer 34 by the conductive anode strips 12 via
hole-transport layer 32, and electrons are injected into the
organic active layer 34 by the cathode members 52. When
electron-hole pairs combine within the organic active layer 34,
light or other radiation is emitted from the electronic device. In
a display, rows and columns can be given signals to activate the
appropriate pixels (electronic devices) to render a display to a
viewer in a human-understandable form.
[0082] During operation of a radiation detector, such as a
photodetector, sense amplifiers may be coupled to the conductive
members of the array along the rows or columns. A potential may be
maintained between the cathode members 52 and the anode strips 12
to allow better current flow to and from the electronic device to
peripheral circuitry, however, such potential difference may not be
sufficient to allow for the flow of current through the electronic
device. In one non-limiting example, a potential difference in a
range of approximately 0.5 to 1.5 V may be maintained across the
organic active layer 34 during the operation of a detector. A
relatively small amount of current may flow through the organic
active layer 34. When radiated by light or another radiation
source, sufficient energy may be received by the organic active
layer 34 to significantly increase the number of electrons and
holes within the organic active layer 34 and substantially increase
the flow of current through the electronic device.
[0083] The sense amplifiers may be used to determine the current,
and other peripheral (within the same component) or remote (not
within the same component) circuitry can be used to interpret the
information from the amount of current increase. This information
may be in a digital or analog form. Such information may be used to
create derivative information, such as imaging maps or other visual
information. If the detector is designed to be sensitive to
infrared radiation, an array of radiation detectors can be used to
map temperature differences across the surface of the detector or
temperature differences between objects spaced apart from the
detectors. Alternatively, such a detector can be used to detect the
presence of a flame (light or infrared radiation) for a fire alarm,
to determine ultraviolet radiation intensity from sunlight passing
through relatively thin stratus clouds, and the like.
[0084] In a voltaic cell, such as a photovoltaic cell, light or
other radiation can be converted to energy that can flow without an
external energy source. Whether using external power sources and
the specific potentials used depends on the particular application
of the electronic device. Skilled artisans are capable of designing
the electronic devices, peripheral circuitry, and potentially
remote circuitry, to best suit their particular needs.
[0085] Embodiments described above have benefits compared to
conventional techniques. Protective layer 18 protects anode strips
12, conductive leads 14 and any barrier layer on substrate 10 from
the laser ablation process, which can crack or otherwise damage
such strips, leads and layers. Protective layer 18 also protects
the anode strips 12 and conductive leads 14 from corrosion,
providing better device yield and manufacturability without
compromising device performance. Cracking of leads as seen with
over-ablation during laser ablation should be substantially
eliminated. Organic layers at the periphery of the device can allow
for a diffusion path in the film plane for moisture to ingress
under the encapsulating lid from the environment, thereby exposing
the pixels to moisture, which can destroy the device in a matter of
minutes. With the present invention, all of the organic material is
safely removed from the rail portion of the substrate by laser
ablation, because any barrier layer portions adjacent the rail
portion are protected from the laser energy by protective layer
18.
[0086] Unlike a conventional method, conductive leads 14 are
fabricated before the cathode members 52. In one embodiment
described herein, the surfaces of the conductive lead via areas 14b
may be cleaned before the conductive bridge members 72 are formed.
Reduced contact resistance may be achieved resulting in better
device performance.
[0087] Embodiments described herein may improve device lifetime and
electrical characteristics due to the elimination of organic
material between the anode strips 12. Specifically, with the
present invention, most if not all of the space between the anode
strips 12 is filled with the protective layer 18, instead of
organic materials, which can act as reservoirs of moisture that
release over time to cause pixel shrinkage. The storage life of a
device is reduced by moisture attacking the pixel edges where they
contact the anode strips. By avoiding the formation of organic
materials between the anode strips 12, this source of potential
pixel shrinkage can be avoided. The elimination of polymer material
between anode strips 12 can also reduce cross-talk between pixels,
which can be a problem with spin-on organic electronic devices.
[0088] It is to be understood that the present invention is not
limited to the embodiment(s) described above and illustrated
herein, but encompasses any and all variations falling within the
scope of the appended claims. For example, materials, processes and
numerical examples described above are exemplary only, and should
not be deemed to limit the claims in any way. A single layer of
material could be formed as more than one layer of like or similar
materials, and vice versa. Any benefits, advantages, solutions to
problems, and any element(s) that may cause any benefit, advantage,
or solution to occur or become more pronounced disclosed above are
not to be construed as a critical, required, or essential feature
or element of any or all the claims.
* * * * *