U.S. patent application number 09/924574 was filed with the patent office on 2002-02-21 for novel organic opto-electronic devices and method for making the same.
Invention is credited to Mueller, Peter, Riel, Heike E., Riess, Walter, Vestweber, Horst.
Application Number | 20020020924 09/924574 |
Document ID | / |
Family ID | 8232543 |
Filed Date | 2002-02-21 |
United States Patent
Application |
20020020924 |
Kind Code |
A1 |
Mueller, Peter ; et
al. |
February 21, 2002 |
Novel organic opto-electronic devices and method for making the
same
Abstract
The present invention pertains to new flip-chip organic
opto-electronic structures and methods for making the same. The new
organic opto-electronic device includes at least two separate
parts. Each part comprises an electrode and at least one of these
electrodes carries an organic stack. After completion of these
separate parts both are brought together to form the complete
opto-electronic device. It is a crucial aspect of the new flip-chip
approach that spacers are integrated on one or both sides of the
parts and that an interface formation process is employed.
Inventors: |
Mueller, Peter; (Zurich,
CH) ; Riel, Heike E.; (Rueschlikon, CH) ;
Riess, Walter; (Adliswil, CH) ; Vestweber, Horst;
(Winterscheid, DE) |
Correspondence
Address: |
Marian Underweiser
IBM Corporation
Post Office Box 231
Yorktown Heights
NY
10501
US
|
Family ID: |
8232543 |
Appl. No.: |
09/924574 |
Filed: |
August 8, 2001 |
Related U.S. Patent Documents
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Application
Number |
Filing Date |
Patent Number |
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09924574 |
Aug 8, 2001 |
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09368153 |
Aug 4, 1999 |
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6316786 |
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Current U.S.
Class: |
257/778 ;
257/E25.008; 257/E27.119; 438/108 |
Current CPC
Class: |
H01L 25/046 20130101;
H01L 27/32 20130101; H01L 2924/12044 20130101; H01L 2224/81141
20130101; H01L 51/0024 20130101; H01L 51/525 20130101; H01L 51/5012
20130101; H01L 51/0081 20130101; H01L 2924/00 20130101; H01L
2924/12044 20130101; H01L 27/3211 20130101; H01L 51/5203 20130101;
H01L 2251/558 20130101 |
Class at
Publication: |
257/778 ;
438/108 |
International
Class: |
H01L 021/44; H01L
023/48 |
Foreign Application Data
Date |
Code |
Application Number |
Aug 29, 1998 |
EP |
98116408.0 |
Claims
What is claimed is:
1. An organic opto-electronic device comprising: a first flip-chip
part with a first electrode of thickness D1 formed on a first
substrate; a second flip-chip part with a second electrode formed
on a second substrate and carrying an organic stack, the thickness
of the second electrode and the organic stack being D2; and
non-conductive spacers of thickness D, with D=k(D1+D2) and
0.5.ltoreq.k<1; wherein the first flip-chip part and the second
flip-chip part are flipped together such that the organic stack is
sandwiched between the first electrode and the second electrode, a
minimum distance D is kept between the two substrates by the
spacers, and a stabilized interface is formed between the first
flip-chip part and the second flip-chip part.
2. The organic opto-electronic device of claim 1, wherein the
parameter k is not less than 0.9 and not greater than 0.98.
3. The organic opto-electronic device of claim 1, wherein the first
and second substrates comprise different materials.
4. The organic opto-electronic device of claim 1, wherein the
spacers are integrated on one of the two substrates.
5. The organic opto-electronic device of claim 1, wherein part of
the spacers are integrated on the first substrate and corresponding
parts are integrated on the second substrate.
6. The organic opto-electronic device of claim 1, wherein the first
substrate is semitransparent or transparent.
7. The organic opto-electronic device of claim 1, wherein the
second substrate is semitransparent or transparent.
8. The organic opto-electronic device of claim 1, wherein the first
electrode comprises a metal.
9. The organic opto-electronic device of claim 8, wherein the metal
is a low-workfunction elemental metal or a low-workfunction
alloy.
10. The organic opto-electronic device of claim 8, wherein the
metal is a metal selected from a group consisting of Mg, Ca, Li,
Al, Mg/Ag, Al/Li, and any combination thereof.
11. The organic opto-electronic device of claim 1, wherein the
first electrode comprises more than one layer.
12. The organic opto-electronic device of claim 1, wherein the
organic stack comprises an electroluminescent layer in which light
is generated if a voltage is applied between the first electrode
and the second electrode.
13. The organic opto-electronic device of claim 12, wherein the
first electrode comprises a metal-compound electrode.
14. The organic opto-electronic device of claim 12, wherein the
first electrode comprises a non-degenerate, wide-bandgap
semiconductor.
15. The organic opto-electronic device of claim 12, wherein the
organic stack comprises from the second substrate up the second
electrode, a first charge transport layer, and the
electroluminsecent layer.
16. The organic opto-electronic device of claim 12, wherein the
organic stack further comprises a second charge transport layer on
the electroluminsecent layer.
17. The organic opto-electronic device of claim 12, wherein the
first electrode or the second electrode comprises ITO or high
workfunction metals.
18. The organic opto-electronic device of claim 1, wherein the
spacers comprises silicon nitride, or SiN.sub.x, or SiO.sub.x, or
SiO.sub.2, or Siliconoxynitride (SiON), or organic compounds, or
aluminiumoxide, or aluminiumnitride, or titaniumoxide.
19. The organic opto-electronic device of claim 1, wherein the
spacers are formed separately from the two substrates and placed
between these two substrates when flipping them together.
20. The organic opto-electronic device of claim 19, wherein a mesh
of thickness D serves as spacers.
21. The organic opto-electronic device of claim 1, wherein the
first substrate comprises active and/or passive devices.
22. The organic opto-electronic device of claim 1, comprising
several organic light emitting devices each having an organic stack
and a corresponding first electrode.
23. The organic opto-electronic device of claim 1, wherein the
stabilized interface is an interface within the organic stack which
is uniform, or homogeneous, or interlinked.
24. A display having an organic light emitting device and means for
driving the organic light emitting device, the organic light
emitting device comprising a first flip-chip part with a first
electrode of thickness D1 formed on a first substance, and a second
flip-chip part with a second electrode formed on a second substrate
and carrying an organic stack, the thickness of the second
electrode and the organic stack being D2 and the organic stack
including an electroluminescent layer (EL) in which light is
generated if a voltage is applied between the first electrode and
the second electrode, the organic light emitting device further
including non-conductive spacers of thickness D, with D=k(D1+D2)
and 0.5.ltoreq.k.ltoreq.1, the first flip-chip part and the second
flip-chip part being flipped together such that the organic stack
is sandwiched between the first electrode and the second electrode,
a minimum distance D being kept between the two substrates by the
spacers, a stabilized interface being formed between the first
flip-chip part and the second flip-chip part, and the driving means
comprising means for applying the voltage between the first
electrode and the second electrode.
25. A method for making an organic opto-electronic device
comprising a first flip-chip part with a first substrate and a
first electrode and a second flip-chip part with a second substrate
and a second electrode which carries an organic stack, the method
comprising the steps: forming the first electrode on the first
substrate, forming the second electrode on the second substrate,
forming the organic stack on the second electrode, forming spacers
of thickness D, with D=k(D1+D2) and 0.5 .ltoreq.k.ltoreq.1,
flipping the first substrate and the second substrate together such
that the organic stack is sandwiched between the first electrode
and the second electrode, and such that a minimum distance D is
kept between the two substrates by the spacers, and applying an
interface formation process to form a stabilized interface between
the first flip-chip part and the second flip-chip part.
26. The method of claim 25, wherein the parameter k is not less
than 0.9 and not greater than 0.98.
27. The method of claim 25, wherein the spacers are formed on one
of the two substrates.
28. The method of claim 25, wherein part of the spacers are formed
on the first substrate and corresponding parts are formed on the
second substrate.
29. The method of claim 25, wherein the spacers are formed by using
micro-mechanical techniques.
30. The method of claim 25, wherein the first substrate with first
electrode and/or the second substrate with second electrode and
organic stack are tested before carrying out the step of flipping
the first substrate and second substrate together.
31. The method of claim 25, wherein the first electrode is formed
on the first substrate using processes which are not compatible
with the organic materials used in the organic stack.
32. The method of claim 25, wherein the first electrode is formed
on the first substrate using high temperature processes.
33. The method of claim 25, wherein the interface formation process
is either a heat treatment or a UV treatment.
34. The method of claim 25, wherein the spacers form walls defining
individual pixels.
35. The method of claim 34, wherein the pixels are filled with
color emitting material by using an ink-jet technique.
Description
BACKGROUND OF THE INVENTION
[0001] 1. Field of the Invention
[0002] The present invention concerns new organic opto-electronic
devices, such as organic light emitting diodes (OLEDs), organic
displays, organic solar cells, photodiodes and the like. Also
addressed is a new method for making such devices.
[0003] 2. Discussion of the Related Art
[0004] Organic light emitting diodes (OLEDs) are an emerging
technology with potential applications as discrete light emitting
devices, or as the active elements of light emitting arrays, such
as flat-panel displays. OLEDs are devices in which a stack of
organic layers is sandwiched between two electrodes. At least one
of these electrodes must be transparent in order for light--which
is generated in the active region of the organic stack--to escape.
To achieve high efficiency and low voltage operation each of the
organic layers as well as the electrodes have to be optimized for
their individual function; charge carrier injection, charge carrier
transport, charge carrier recombination, and light extraction.
Despite the great progress achieved in recent years, full
optimization is difficult to obtain using conventional approaches,
as will be outlined below.
[0005] OLEDs emit light which is generated by injection
electroluminescence (EL). Organic EL at low efficiency was observed
many years ago in metal/organic/metal structures as, for example,
reported in Pope et al., Journal Chem. Phys., Vol. 38, 1963, pp.
2024, and in "Recombination Radiation in Anthracene Crystals",
Helfrich et al., Physical Review Letters, Vol. 14, No. 7, 1965, pp.
229-231. Recent developments have been spurred largely by two
reports of high efficiency organic EL. These are C. W. Tang et al.,
"Organic electroluminescent diodes", Applied Physics Letters, Vol.
51, No. 12, 1987, pp. 913-915, and by a group from Cambridge
University in Burroughes et al., Nature, Vol. 347, 1990, pp. 539.
Tang used vacuum deposition of molecular compounds to form OLEDs
with two organic layers. Burroughes spin coated a polymer,
poly(p-phenylenevinylene), to form a single-organic-layer OLED. The
advances described by Tang and in subsequent work by N. Greenham et
al., Nature, Vol. 365, 1993, pp. 628-630, were achieved mainly
through improvements in OLED design derived from the selection of
appropriate organic multilayers and electrode metals.
[0006] To date, virtually all OLED device structures have been
built on glass substrates coated with indium-tin oxide (ITO), which
serves as a transparent anode, i.e. light is emitted through the
anode and substrate. This kind of a device structure is usually
referred to as cathode-up structure. The cathode is typically a
low-workfunction elemental metal or low-workfunction alloy, e.g.
Ca, Al, Mg/Ag, or Al/Li. Such cathodes are opaque. These
low-workfunction elemental metals and alloys belong to the first
class of cathode materials considered for OLEDs. In order to enable
a variety of possible applications, OLED structures suitable for
opaque substrates (i.e. substrates other than the conventional
glass substrates) are highly desirable. For example, if OLEDs could
be fabricated on silicon, this would permit the use of an
integrated active-matrix drive scheme. In such a structure light
must be emitted through the uppermost layers of the device rather
than through the substrate. One possible solution would be to build
OLEDs by depositing the layers in the opposite order, which means a
structure would be obtained with the transparent ITO anode
deposited on top (referred to as anode-up structure). This has
proved difficult, presumably due to the harsh conditions under
which the ITO is deposited.
[0007] Alternatively, devices could be fabricated with the normal
sequence of layers provided that a transparent cathode could be
found. Gallium Nitride (GaN) has already been suggested as one
possible cathode material for these kind of alternative cathode-up
structures, as disclosed and described in an international patent
application WO98/07202 with title "Gallium Nitride Based Cathodes
for Organic Electroluminescent Devices and Displays". The
international publication date of this patent application is Feb.
19, 1998. The GaN is a non-degenerate, wide-bandgap semiconductor
(nd-WBS). As described in the international application, all
nd-WBSs have the advantage that their wide bandgap makes them
transparent. It has been shown that the wide bandgap also leads to
a favorable alignment of either the conduction band or valance band
with the lowest unoccupied molecular orbitals (LUMO) or highest
occupied molecular orbital (HOMO) of the organic material into
which charge is to be injected. These non-degenerate, wide-bandgap
semiconductors form a second class of cathode materials considered
for OLEDs.
[0008] It has been shown that improved performance can be achieved
when the electrode materials are chosen to match the respective
molecular orbitals of the organic material into which it is
supposed to inject carriers. By choosing the optimized electrode
materials the energy barriers to injection of carriers can be
reduced.
[0009] It has been shown in U.S. Pat. No. 5,340,619, with title
"Method of manufacturing a color filter array", that ink-jet
printing or other printing technologies can be used to coat a
substrate. First, the substrate is coated with a blue resin which
is baked (cured) before red and green colored polyimide dyes are
each added and cured respectively. After all the colors are added
and cured, laser ablation is used to reduce the thickness of the
coating to develop a color filter array.
[0010] With multilayer device architectures now well understood and
commonly used, the major performance limitation of OLEDs is the
lack of ideal contact electrodes, and in particular the lack of
transparent and conducting materials which can be deposited on
organic layers without causing damage having a detrimental effect
on the device performance and reliability.
[0011] One figure of merit for electrode materials is the position
of the energy levels (bands) relative to those of the organic
materials. In some applications it is also desirable for the
electrode material to be transparent, as mentioned above.
Furthermore, the electrode should be chemically inert and capable
of forming a dense uniform film to effectively encapsulate the
OLED. It is also desirable that the electrode and/or electrode
deposition does not lead to a strong quenching of EL.
[0012] Another important figure of merit for electrode materials is
the ease of handling and problem-free deposition on organic layers.
Futhermore, the electrode materials have to be compatible to the
organic materials underneath which is often difficult to
achieve.
[0013] The incompatibility problems inherent to most electrode
materials used so far can be extended and generalized. The most
severe limitations in the deposition of metals and
semiconductor-based electrodes onto organic layers are:
[0014] damage of the organic materials during the deposition which
often leads to irreversible changes within the organic layers and
at their interfaces;
[0015] damage of the organic materials due to heat treatments
required to obtain electrodes with good physical, mechanical and
electrical and electro-optical properties. High process
temperatures lead to thermal damage of the organic materials such
as crystallization, interdiffusion and intermixing of the
organics.
[0016] low manufacturing yield because the more processing steps
are performed, the lower the output of fully functional devices
gets.
[0017] reduced number of materials available, because not-only
electrical, but also chemical compatibility with the organic
materials is required. For example, up to now no polymers can be
deposited on top of evaporated organic layers, because of
dissolving problems.
[0018] So far, there is a costly and time-consuming search for
better suited materials which may serve as stable, possibly
transparent electrodes.
SUMMARY OF THE INVENTION
[0019] It is therefore an object of the present invention to
provide a new and improved approach which allows to overcome some
or all of the above-mentioned problems and disadvantages.
[0020] It is an object of the present invention to provide new and
improved organic opto-electronic devices such as organic light
emitting devices, arrays and displays as well as solar cells and
photodiodes.
[0021] It is another object of the present invention to provide a
method for the formation of new and improved organic
opto-electronic devices such as organic light emitting devices,
arrays and displays as well as solar cells and photodiodes.
[0022] The above objects have been accomplished by providing new
flip-chip organic opto-electronic structures and methods for making
the same. According to the present invention, the opto-electronic
device includes at least of two separate parts. Each part comprises
an electrode and at least one of these electrodes carries an
organic stack. After completion of these separate parts both are
brought together forming the complete opto-electronic device. The
interface between the two flip-chip parts can be stabilized by
applying a special interface formation procedure.
[0023] It is a crucial aspect of the new flip-chip approach that
spacers are integrated on one or both sides of the parts. These
spacers have to meet the following criteria to ensure proper
operation of an organic opto-electronic structure:
[0024] the size and shape of the spacers have to be such that
sufficient electrical contact is provided between the organic
layers on the different pieces or the organic layer and the
electrode on the different parts.
[0025] the spacers must prevent short circuits. This means that the
spacers consist either of non conducting materials or if they are
conducting they should be electrical isolated at least from one
electrode structure.
[0026] the spacers have to be rigid, to protect the organic layers
from damage. This is especially important for flexible device
structures.
[0027] the total thickness of the spacers have to be chosen in such
a way, that sufficient electrical contact between the organic
layers is provided and damage between the organic layers is
avoided.
[0028] The inventive flip-chip approach allows to split off the
device fabrication process and therefore separates the respective
incompatible process steps. Both fabrication processes can thus be
separately and independently optimized.
[0029] It is an advantage of the present flip-chip approach that
both the organic structure and the electrode structure can be
tested and inspected before putting them together.
[0030] The inventive approach capitalizes primarily on the
inventor's finding that a contact of sufficiently high quality can
be obtained between the electrode structure and the organic
structure if the spacers are designed appropriately. It furthermore
is based on the conclusion derived from experiments, that an
organic opto-electronic device in fact can be put together using
two separate and discrete parts, namely an organic structure and a
complementary electrode structure. It can even be more general, in
that a structure is put together from two separate parts which both
consist of an electrode structure and parts of the active layers.
The approach to fabricate an organic device in two separate parts
is unique because experts currently working on organic devices are
in particular concerned about the quality of the interfaces between
adjacent layers. Until now it seemed to be inconceivable--if not
even completely out of the question--to `take` an organic device
apart. Should the interface quality of a flip-chip device according
to the present invention not be acceptable, one might employ a
special heat treatment. Experiments showed that the quality of the
interface formation can be adjusted or tailored by applying such a
special heat treatment.
[0031] The inventive approach further capitalizes on the inventor's
finding that the interface between the two flip-chip parts can be
stabilized, or optimized, or tailored by applying a special
interface formation procedure.
[0032] The results of the experiments are very surprising in
particular if one considers them in the light of the existing
prejudice.
[0033] It is also important to consider, that the inventive
approach is completely foreign to conventional semiconductor
technology where an electrode or metalization always is formed
right on the semiconducting layers to ensure intimate contact.
[0034] Other advantages will become obvious form the detailed
description and the drawings.
[0035] In one embodiment of the present invention a first substrate
carries electrodes only, whereas the second substrate carries an
electrode together with the complete organic stack of one or more
organic opto-electronic devices.
[0036] In another embodiment, the first substrate carries
electrodes and part of the organic layers. The second substrate
also carries some of the organic layers and another electrode.
[0037] In yet another embodiment, the present flip-chip approach is
used to make an organic light emitting array, such as a display for
example.
[0038] Employing a flip-chip technology in accordance with the
present invention adds flexibility in the choice of electrode
designs.
[0039] Some further advantages of the inventive approach are:
[0040] electrodes can be deposited at conditions otherwise not
suited for OLED formation (e.g. high temperature, aggressive
chemical environment, ion damage (sputter damage), high energy
particle processes);
[0041] electrodes can be easily patterened;
[0042] separate testing and inspection of both `halfs` is possible.
This helps to increase the yield and thus reduces manufacturing
costs.
[0043] each `half` can be made of optimized materials and using
optimized processes without having to take care of incompatibility
issues.
[0044] If appropriately designed, the spacers also serve as studs
or posts which protect the sensitive parts from being mechanically
damaged during handling, as will be discussed in connection with
FIGS. 1A and 1B.
[0045] The present approach is well suited for the formation of
large area displays, for example, where the yield is one of the
major cost factors. The larger an active matrix display gets, the
more likely it is that one transistor fails. In such a case the
whole display is not suited for use and has to be discarded. The
present approach leads to a drastically increased yield which in
turn allows to make cheaper display.
[0046] The spacers can provide conductive connection between
circuitry on the two halves. This is especially important for large
area displays where the conductivity of the common electrode limits
the device performance.
[0047] Additional spacers can be employed that provide a conductive
connection between circuitry on the two `halfs`.
BRIEF DESCRIPTION OF THE DRAWINGS
[0048] The invention is described in detail below with reference to
the following schematic drawings:
[0049] FIG. 1A is a schematic cross section of a first substrate
carrying an electrode (referred to as electrode structure) and a
second substrate carrying an organic light emitting stack with a
common electrode (referred to as organic structure), according to
the present invention.
[0050] FIG. 1B is a schematic cross section of a flip-chip organic
light emitting structure, according to the present invention, after
the electrode structure and the organic structure have been flipped
together.
[0051] FIG. 2 is a schematic cross section of a flip-chip organic
light emitting array, according to the present invention.
[0052] FIG. 3A is a schematic bottom-view of a first substrate with
electrode structure and a spacer, according to the present
invention.
[0053] FIG. 3B is a schematic bottom-view of a first substrate with
an electrode (referred to as electrode structure) and another
spacer, according to the present invention.
[0054] FIG. 3C is a schematic cross section of a first substrate
and second substrate with female and male spacers, according to the
present invention.
[0055] FIG. 4 is a schematic cross section of a flip-chip organic
light emitting array, according to the present invention.
DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS
[0056] In order to fabricate an ideal organic opto-electronic
device (such as an OLED) based on optimized materials and
characterized by an enhanced device performance and stability, we
propose a novel fabrication process, herein referred to as
flip-chip process. In contrast to a commonly used device
fabrication process, where the individual layers (e.g. an anode,
organic stack, and a cathode) are deposited subsequently on a
substrate, the flip-chip process splits off the device fabrication
process onto different substrates and therefore separates the
crucial fabrication processes. As addressed in the introductory
portion, these processes often are the deposition process of the
electrodes and electrode modifications. In order to avoid damage of
the device structure during alignment and fabrication, and to
ensure appropriate operation of the device, spacers are integrated
on at least one substrate.
[0057] Turning now to FIGS. 1A and 1B, a first embodiment of the
present invention is described. This first embodiment comprises a
first substrate 11 carrying an electrode 12 and two spacer halves
13. The first substrate 11 together with the electrode 12 are
herein referred to as electrode structure. Corresponding spacer
halves 15 are formed on a second substrate 16. This second
substrate 16 also comprises an organic stack 14 (herein referred to
as organic structure) and a common electrode 17. Such an organic
stack at least comprises a light emitting layer where light is
generated if an appropriate voltage is applied across the
electrodes. The flip-chip organic light emitting device 10 is shown
in assembled form in FIG. 1B. The two substrates 11 and 16 are
flipped together such that an intimate contact is provided between
the electrode 12 and the organic stack 14. The spacer halves 13 and
15 set the distance (D) between the two substrates 11 and 16.
Furthermore, these spacers precisely define the forces (pressure
and stress) acting upon the electrode 12 and the organic stack
14.
[0058] The substrate 16 may be a glass substrate for example. Any
other transparent substrate can be chosen as well. The organic
stack 14 comprises a transparent electrode 17. Well suited as
transparent electrode 17 is ITO, which then acts as anode. The
thickness of the anode 17 is chosen to provide as high a
conductance as possible. Well suited is a thickness of 100 nm or
more. In the present embodiment the anode 17 is 100 nm thick. Right
on top of the anode 17 there is at least one organic layer in which
electroluminescence takes place if an appropriate voltage is
applied. Such an organic layer is usually referred to as organic
emission layer (EML).
[0059] A cathode 12 is formed on the substrate 11. In the present
embodiment silicon serves as substrate 11. As cathode material a
low work function metal or alloy, for example Mg/Ag, is used. The
thickness of the cathode 12 is chosen to provide a high
conductance. Well suited is a thickness of 100 nm or more. In the
present embodiment the Mg/Ag cathode 12 is 500 nm thick.
[0060] Exemplary details of the first embodiment are given in the
following table.
1 Layer No. Material Width present example substrate 16 glass 0.05
mm-5 mm 2 mm anode 17 ITO 10-2000 nm 100 nm EL 14 Alq3 10-2000 nm
80 nm cathode 12 Mg/Ag 10-1000 nm 500 nm substrate 11 silicon 0.1
mm-5 mm 1 mm
[0061] Please note that the first embodiment is a cathode-up
structure where light 18 is emitted through the anode 17 and
substrate 16 into the half-space below the device 10, as indicated
in FIG. 1B.
[0062] The spacers 13 and 15 comprise silicon nitride, SiN.sub.x,
SiO.sub.x, SiO.sub.2, Siliconoxynitride (SiON), organic compounds
such as polyimides, aluminiumoxide, aluminiumnitride, or
titaniumoxide, for example. The combined thickness (D) of the two
spacer halves has to be slightly less than the thickness D1 of the
organic stack 14 and anode 17 and the thickness D2 of the electrode
structure 12 together. As a rule of thumb, D has to be between 80%
and 100% of D1+D2. Preferably, the thickness D is between 90% and
98% of D1+D2. Please note that in the present embodiment the spacer
halves 15 are thicker than the organic stack 14 and anode 17. This
has the advantage that the stack 14 is protected from being
mechanically damaged while handling the substrate 16. The thickness
of the spacers depends on the morphological properties of the
organic stack 14 and electrode 12 and can be adapted to achieve the
best results. It is important that the spacers are non-conducting
to prevent shorts. If needed, special spacers can be added that
provide for a conductive connection between circuitry of the
organic structure and circuitry on the electrode structure. The
spacers can be large (wide and long) if space permits. In OLED
display applications, however, instead of large spacers smaller
spacers are preferred. Every pixel of a display might be protected
by a very small spacer. Thus, extremely robust, large area and high
resolution displays can be fabricated with the inventive flip-chip
approach.
[0063] For a proper function of a device according to the present
invention, the quality of interface between the two flip-chip
parts, is of crucial importance. It has been demonstrated by the
inventors that the interface between the two flip-chip parts can be
stabilized, optimized and tailored by applying a special interface
formation procedure. This procedure can consist of a simple heating
process, or an exposure to intense light, or an UV curing process,
or a combination of any of these methods. Common to all these
procedures is that they lead in combination with the present
spacers to a homogeneous and uniform interface formation. A further
advantage of the described interface formation process is, that it
can be applied to any type of organic/organic, organic/inorganic,
and inorganic/inorganic interfaces.
[0064] A few examples of the special interface formation procedure
are given in the following. In the case of polymeric systems the
application of UV light can lead to crosslinking between polymers
of the two parts of the flip-chip device. In the case of a heat
treatment (polymers, small molecule systems) the interface is
warmed up for some time. The actual heating time as well as the
temperature depends on parameters like the chemical structure of
the material supposed to form an interface, and the desired depth
of the interface formation process (e.g. is the interface formation
supposed to be limited the immediate neighborghood of the two
flip-chip parts, or is the interface formation supposed to extend
into the two flip-chip parts). The heating time can vary from much
less than a second up to several hours and more. The interface
formation temperature is also system dependent. In the case of
organic and/or amorphous materials it should not exceed the glass
transition temperature of the most sensitive layer of the flip-chip
structure for a long time. For stable glass forming systems,
however, it can even be higher.
[0065] The spacers, according to the present invention, allow for
the application of a pressure between the two flip-chip parts
without running the risk to damage the device. One might even apply
an external force to increase the pressure between the two
flip-chip parts. The pressure also has an impact on the interface
formation process.
[0066] The present interface formation process allows to form a
chemically, morphologically, mechanically and electrically stable
interface.
[0067] In order to improve the interface formation process, one
might apply one or several special layers on the respective
surfaces of the two flip-chip parts such that a reaction can take
place or can be initiated when combining the two halves.
[0068] Due to the fact that the spacers define the distance D
between the first and second substrates, also flexible substrates
can be employed. This allows to realize flexible organic light
emitting displays and solar cells where the operation of the
individual OLEDs or the individual cells of the solar cell are not
influenced when bending the whole device because the spacers
provide small independent cells inside the device. The geometry of
these cells remains almost unchanged when bending the inventive
device.
[0069] If silicon is used as first substrate, micro-mechanical
techniques can be employed to define the spacers. Examples of
complicated spacers are illustrated in FIGS. 3A-3C. A bottom-view
of a first substrate 31 is given in FIG. 3A. The substrate 31
carries an electrode 32 and a set of spacers 33 arranged around the
electrode 32. A bottom-view of a first substrate 41 is given in
FIG. 3B. This substrate also carries an electrode 42 and a spacer
43. The spacer 43 forms a rectangular wall around the electrode 42.
Instead of a rectangular wall, any kind of a wall like structure
may serve as spacer. Well suited for example are honeycomb
structures. If using micro-mechanical techniques there are almost
no bounds to the shape and/or arrangement of spacers.
[0070] A cross-sectional view of two spacer halves 53 and 55 is
shown in FIG. 3C. The upper spacer 53 is formed on the first
substrate 51 which also carries an electrode (not shown). This
upper spacer 53 is a so-called female spacer which has a bay to
receive the corresponding counterpart spacer 55 (male spacer). The
male spacer 55 is formed on the second substrate 56 on which the
organic stack and an electrode is situated (not shown). This kind
of an arrangement and equivalent kinds of spacer structures allow a
precise alignment of the first and second substrates 51 and 56 if
flipped together.
[0071] It is to be noted that the spacers can also be formed
separately. One might for example form a first electrode on a first
substrate and grow an organic stack on this electrode. Another
electrode may be formed on a second substrate. In addition, a
spacer mesh or web (e.g. a honeycomb structure) can be formed
separately. Then the spacer mesh or web is placed on one of the two
structures before they are joined together. Such a spacer mesh or
web can be made using micro-mechanical techniques or molding
techniques, for example.
[0072] In the simplest case the spacers consist of robust,
non-conducting materials like silicon nitride, SiN.sub.x,
SiO.sub.x, SiO.sub.2, Siliconoxynitride (SiON), organic compounds
such as polyimides, aluminiumoxide, aluminiumnitride, or
titaniumoxide, for example. These materials can easily be deposited
on the structures and patterned. The shape of the spacers depends
on the actual task, for example for display application the fill
factor is a crucial point. Thus the size of the spacers should not
exceed 20% of the actual active area. The shape of the spacers can
be adapted to the special application. For some applications a
self-aligning geometry consisting of a male and a female spacer
part is of advantage.
[0073] If necessary for adequate lateral conductivity, an
additional layer or stack of layers could be deposited on top of
the cathode 12 to improve the electron injection into the cathode.
Note that the electrode structure might either carry a simple
one-layer electrode, a compound metal electrode, or a multi-layer
electrode. Even certain organic layers might be part of the
electrode structure. The anode 17 might also be a simple one-layer
electrode, a compound metal electrode, or a multi-layer
electrode.
[0074] Usually, the organic stack comprises several layers. Please
note that the layered structure of the organic stack is not shown
in FIGS. 1A and 1B.
[0075] When referring to the `first substrate`, substrates are
meant that are suited to carry an electrode. Silicon is an example
for such a substrate. Silicon has the advantage that driving
circuitry can be integrated such that complex driving schemes can
be realized.
[0076] If light is to be emitted through the first substrate the
following two conditions have to be met. First, the electrode
carried by the first substrate has to be semitransparent or
transparent. Second, the substrate has to be semitransparent or
transparent, too.
[0077] When using the expression `second substrate`, any substrate
is meant which is suited to carry an electrode 17 and at least
organic layer suited for light emission (EML) 14. If light is to be
emitted through the substrate 16, this substrate 16 as well as the
electrode 17 have to be semitransparent or transparent.
[0078] It is to be noted that also both substrates might be
transparent.
[0079] When using the expression `electrode`, any kind of a
structure is referred to which is suited to inject carriers
(electrons or holes) into an organic stack. The electrode structure
may comprise some organic layers in addition to the mere electrode
material. E.g., a transport layer may be formed on a metal
electrode. The electrode structure may be optimized by plasma-,
UV-, or ozone-treatments, heat and surface modifications, polishing
and the like to achieve the best materials and the most stable
electrodes.
[0080] Another embodiment of the present invention is illustrated
in FIG. 2. The shown device 20 is an anode-up array. From the glass
substrate 26 up the array comprises a cathode 27 and an organic
stack 24. To be more precise, the substrate 26 carries (listed in
the order of deposition) ITO/TiN/ETL/EL/HTL. Please note that light
is emitted from the active region within the organic stack 24
through the metal-compound cathode and ITO (together referred to as
cathode 27) and substrate 26. Please note that in the present
embodiment the organic stack 24 comprises an electron transport
layer (ETL), an electroluminescent layer (EL), and a hole transport
layer (HTL). In the following, exemplary details of the second
embodiment are specified. In the present embodiment, the substrate
21 just carries the anode 22.
2 Layer No. Material Width present example substrate 26 glass 0.05
mm-5 mm 3 mm outer cathode 27 ITO 10-2000 nm 20 nm cathode 27 TiN
10-100 nm 40 nm ETL and EL 24 Alq3 10-1000 nm 80 nm HTL 24 NPB
5-500 nm 50 nm anode 22 Ni 10-2000 nm 50 nm substrate 21 silicon
0.1 mm-5 mm 1 mm
[0081] As mentioned, the silicon substrate 21 can be fabricated to
contain active Si devices, such as for example an active matrix,
drivers, memory and so forth. Such a silicon substrate 21 with
integrated circuits can be used to realize inexpensive small area
organic displays with high resolution and performance as well as
large area displays, for example.
[0082] The substrate 21 carries spacers 23 and the substrate 26
carries spacers 25 which together define the distance between the
upper flip-chip part and the lower flip-chip part when both parts
of the device 20 are put together. The interface between the first
(upper) flip-chip part 25 and the second (lower) flip-chip part is
stabilized by an appropriate interface formation process. In the
present example this interface is an interface between the Ni anode
22 and the NPB hole transport layer 24.
[0083] On top of Si integrated circuits, stable electrodes can be
formed. Well suited for example are ITO, Al, Cu, Au, Pt, Ni, and
Cr. These electrodes 22 (which are part of the electrode structure)
together with the opposite electrode 27 formed underneath the
organic stack 24 are used to drive the organic stack 24 by applying
a voltage. The cross-section of FIG. 2 shows five OLEDs arranged as
an array. These OLEDs may be any color including blue or white.
[0084] Note that the electrode layer 27 can be a continuous layer
such that several adjacent OLEDs share a common electrode. The
electrode layer can consist of a combination of various cathode
materials, for example containing ITO, TiN, low workfunction metals
and alloys--as shown in the present example.
[0085] The organic stacks of the present devices may comprise:
[0086] at least one organic emission layers (EML), and
[0087] hole transport layer(s) (HTLs); and/or
[0088] electron transport layer(s) HTLs); and/or
[0089] inorganic injection/barrier/confinement layers; and/or
[0090] buffer layers.
[0091] TiN and the other metals can be deposited by a variety of
techniques, including vacuum evaporation, E-beam evaporation,
reactive sputtering, glow discharges, and chemical vapor deposition
(CVD). The higher temperature CVD processes can be used because the
electrode structure is made separately from the sensitive organic
stack. CVD is not suited for the fabrication of conventional OLEDs.
Vacuum evaporation, E-beam evaporation, reactive sputtering, and
glow discharges process are well suited for the formation of
electrodes. No care has to be taken when forming the electrode
structure about thermal stability and low glass transition
temperatures of the organic materials, sputter damage and thermal
stress in the layers of the organic stack.
[0092] Yet another embodiment of the present invention is described
in connection with FIG. 4. As shown in this figure, the organic
opto-electronic device 60 (an organic R, G, B color display)
comprises two halves 61 and 62. In the present embodiment, the
upper half 61 carries male spacers 63 and the lower half 62 carries
female spacers 64. It is one purpose of these spacers (like in the
other embodiments) to define the distance between the two halves 61
and 62. It is another purpose of the spacers to form walls within
the plane of the two halves that define the pixel size and shape.
The reason why the spacers are designed to form walls is best
understood when describing the method of making such the organic
opto-electronic device 60.
[0093] As described in connection with the other embodiments, the
individual halves of the organic color display 60 are fabricated
separately, to allow optimization of the various processing steps.
As shown in FIG. 4, the lower half 62 comprises silicon 68 with
integrated circuitry (not shown) to drive the pixels. After the
formation of the spacers, the pixels are filled with suitable
materials 65-67 of different color (e.g. R, G, B). Due to the
spacers serving as walls any intermixing of the different materials
65-67 (for example polymers) is avoided. In the present example,
the pixels of the upper half 61 comprises polymers 69. To obtain a
complete R, G, B display, the two halves 61 and 62 have to be
aligned and put together. Optimum performance is achieved by a
special interface formation procedure. Well suited in the present
example is a heat treatment to facilitate the formation of a proper
interface between the color pixels 65-67 and the polymer 69. The
upper half 61 carries a common ITO electrode 70 whereas each pixel
on the lower half 62 has an individual electrode 71-73 which allows
to turn them on and off individually. These individual electrodes
71-73 are connected to the above-mentioned appropriate driving
circuitry. If an appropriate voltage is applied to the pixels, then
the pixel 65 emits red light, the pixel 66 emits green light, and
the pixel 67 emits blue light. As described before, the spacers can
provide conductive connections between circuitry on the two
halves.
[0094] This is especially important for large area displays where
the conductivity of the common electrode limits the device
performance.
[0095] An ink-jet technique can be used to fill the individual
pixels. An ink-jet device has a droplet generator with nozzle from
which ink droplets are emitted and directed to the respective pixel
on the lower half 62. The ink-jet device or the lower half 62 may
be transported at a relatively high speed so that one pixel after
the other is filled with the appropriate color. Also the polymer 69
on the other half 61 can be filled using an ink-jet device.
[0096] The present invention allows the use of up to now not yet
considered electrode materials. Well suited as electrode (cathode)
material are metal-compounds with low workfunction. Metal-compound
in the present context stands for any carbide, nitride, or boride
of the early transition metals (such as group 4 and 5 transition
metals) and lanthanides. One example of such a metal-compound is
titanium nitride (TiN). These metal-compounds make up a whole new
class of low-workfunction, semi-transparent, conducting materials
very well suited as cathode for organic devices. Metal-compounds
are described and claimed in a related patent application with
application Ser. No. PCT/IB97/01565, entitled "Compound-Metal
Contacts for Organic Devices and Method for Making the Same" filed
on Dec. 15, 1997, presently assigned to the assignee of the instant
application.
[0097] Also well suited as electrode material is GaN and other
non-degenerate, wide-bandgap semiconductors (nd-WBS). These nd-WBS
electrode materials are addressed in the international patent
application WO98/07202 with title "Gallium Nitride Based Cathodes
for Organic Electroluminescent Devices and Displays". The
international publication date of this patent application is Feb.
19, 1998. All nd-WBSs have the advantage that their wide bandgap
makes them transparent.
[0098] Since both `halves` of the organic light emitting devices
are formed separately, even polymers can now be used in connection
with evaporated small molecule systems, which was not conceivable
so far because of the incompatibility of these two systems (for
example polyaniline, polythiophene (derivatives) as hole injecting
materials and PPV and PPV derivatives as emitting materials).
[0099] In the following some examples of the different organic
materials which can be used are given.
[0100] Electron Transport/Emitting Materials:
[0101] Alq.sub.3, Gaq.sub.3, Inq.sub.3, Scq.sub.3, (q refers to
8-hydroxyquinolate or it's derivatives) and other
8-hydroxyquinoline metal complexes such as Znq.sub.2, Beq.sub.2,
Mgq.sub.2, ZnMq.sub.2, BeMq.sub.2, BAlq, and AlPrq.sub.3, for
example. These materials can be used as the ETL or emission
layer.
[0102] Other classes of electron transporting materials are
electron-deficient nitrogen-containing systems, for example
oxadiazoles like PBD (and many derivatives), and triazoles, for
example TAZ (1,2,4-triazole).
[0103] Finally, materials containing quinoline, quinoxaline,
cinnoline, phthalazine and quinaziline functionalities are well
known for their electron transport capabilities.
[0104] Other materials are didecyl sexithiophene (DPS6T),
bis-triisopropylsilyl sexithiophene (2D6T), azomethin-zinc
complexes, pyrazine (e.g. BNVP), styrylanthracene derivatives (e.g.
BSA-1, BSA-2), non-planar distyrylarylene derivatives, for example
DPVBi (see C. Hosokawa and T. Kusumoto, International Symposium on
Inorganic and Organic Electroluminescence 1994, Hamamatsu, 42),
cyano-substituted polymers such as cyano-PPV (PPV means
poly(p-phenylenevinylene)) and cyano-PPV derivatives.
[0105] These functional groups can also be incorporated in
polymers, starburst and spiro compounds. Further classes are
materials containing pyridine, pyrimidine, pyrazine and pyridazine
functionalities.
[0106] The following materials are particularly well suited as
[0107] Emission Layers and Dopants:
[0108] Anthracene, pyridine derivatives (e.g. ATP), Azomethin-zinc
complexes, pyrazine (e.g. BNVP), styrylanthracene derivatives (e.g.
BSA-1, BSA-2), Coronene, Coumarin, DCM compounds (DCM1, DCM2),
distyiyl arylene derivatives (DSA), alkyl-substituted
distyrylbenzene derivatives (DSB), benzimidazole derivatives (e.g.
NB1), naphthostyrylamine derivatives (e.g. NSD), oxadiazole
derivatives (e.g. OXD, OXD-1, OXD-7),
N,N,N,N-tetrakis(m-methylphenyl)-1,3-diaminobenzene (PDA), perylene
and perylene derivatives, phenyl-substituted cyclopentadiene
derivatives, 12-phthaloperinone sexithiophene (6T), polythiophenes,
quinacridones (QA) (see T. Wakimoto et al., International Symposium
on Inorganic and Organic Electroluminescence, 1994, Hamamatsu, 77),
and substituted quinacridones (MQA), rubrene, DCJT (see for
example: C. Tang, SID Conference San Diego; Proceedings, 1996,
181), conjugated and non-conjugated polymers, for example PPV and
PPV derivatives, dialkoxy and dialkyl PPV derivatives, for example
MEH-PPV (poly(2-methoxy)-5-(2'-ethylhexoxy)-1,4-phenylene-vin-
ylene), poly(2,4-bis(cholestanoxyl)-1,4-phenylene-vinylene)
(BCHA-PPV), and segmented PPVs (see for example: E. Staring in
International Symposium on Inorganic and Organic
Electroluminescence, 1994, Hamamatsu, 48, and T. Oshino et al. in
Sumitomo Chemicals, 1995 monthly report).
[0109] Hole Transport Layers and Hole Injection Layers:
[0110] The following materials are suited as hole injection layers
and hole transport layers. Materials containing aromatic amino
groups, like tetraphenyldiaminodiphenyl (TPD-1, TPD-2, or TAD) and
NPB (see C. Tang, SID Meeting San Diego, 1996, and C. Adachi et al.
Applied Physics Letters, Vol. 66, p. 2679, 1995), TPA, NIPC, TPM,
DEH (for the abbreviations see for example: P. Borsenberger and
D.S. Weiss, Organic Photoreceptors for Imaging Systems, Marcel
Dekker, 1993). These aromatic amino groups can also be incorporated
in polymers, starburst (for example: TCTA, m-MTDATA, see Y.
Kuwabara et al., Advanced Materials, 6, p. 677, 1994, Y. Shirota et
al., Applied Physics Letters, Vol. 65, p. 807, 1994) and spiro
compounds.
[0111] Further examples are: Copper(II) phthalocyanine (CuPc),
[0112]
(N,N'-diphenyl-N,N'-bis-(4-phenylphenyl)-1,1'-biphenyl-4,4'-diamine-
), distyryl arylene derivatives (DSA), naphthalene,
naphthostyrylamine derivatives (e.g. NSD), quinacridone (QA),
poly(3-methylthiophene) (P3MT) and its derivatives, perylene and
perylene derivatives, polythiophene (PT),
3,4,9,10-perylenetetracarboxylic dianhydride (PTCDA), PPV and some
PPV derivatives, for example MEH-PPV, poly(9-vinylcarbazole) (PVK),
discotic liquid crystal materials (HPT).
[0113] There are many other organic materials known as being good
light emitters, charge transport materials, and charge injection
materials, and many more will be discovered. These materials can be
used as well for making light emitting structures according to the
present invention. More information on organic materials can be
found in text books and other well known publications, such as the
book "Inorganic and Organic Electroluminescence", edited by R. H.
Mauch et al., Wissenschaft und Technik Verlag, Berlin, Germany,
1996, and the book "1996 SID International Symposium, Digest of
Technical Papers", first edition, Vol. XXVII, May 1996, published
by Society for Information Display, 1526 Brookhollow Dr., Suite 82,
Santa Ana, Calif., USA.
[0114] Additionally, blend (i.e. guest-host) systems containing
active groups in a polymeric binder are also possible. The concepts
employed in the design of organic materials for OLED applications
are to a large extent derived from the extensive existing
experience in organic photoreceptors. A brief overview of some
organic materials used in the fabrication of organic photoreceptors
is found in the above mentioned publication of P. Brosenberger and
D. S. Weiss, and in Teltech, Technology Dossier Service, Organic
Electroluminescence (1995), as well as in the primary
literature.
[0115] OLEDs have been demonstrated using polymeric, oligomeric and
small organic molecules. The devices formed from each type of
molecule are similar in function, although the deposition of the
layers varies widely. The present invention is equally valid in all
forms described above for organic light emitting devices based on
polymers, oligomers, or small molecules, as well as starburst and
spiro compounds.
[0116] Small molecule devices are routinely made by vacuum
evaporation.
[0117] Evaporation can be performed in a Bell jar type chamber with
independently controlled resistive and electron-beam heating of
sources. It can also be performed in a molecular beam deposition
system incorporating multiple effusion cells and sputter sources.
Oligomeric and polymeric organics can also be deposited by
evaporation of their monomeric components with later polymerization
via heating or plasma excitation at the substrate. It is therefore
possible to co-polymerize or create mixtures by co-evaporation.
[0118] In general, polymer containing devices (single layer,
multilayer, polymer blend systems, etc.) are made by dissolving the
polymer in a solvent and spreading it over the substrate either by
spin coating or the doctor blade technique. With our novel method
we are able to fabricate now well defined multilayer structures
(i.e. with at least two layers) even with materials which dissolve
only in the same solvent.
[0119] Additionally, hybrid devices containing both polymeric and
evaporated small organic molecules are possible. In this case, the
polymer film is generally deposited first, since evaporated small
molecule layers often cannot withstand much solvent processing.
According to the present invention, one is now much more flexible
as far as the sequence of deposition is concerned.
[0120] More interesting is the possibility of making a
polymer/inorganic transport layer on top of which monomeric layers
are evaporated, possibly also incorporating alloys. If the polymer
is handled in an inert atmosphere prior to introduction to vacuum,
sufficient cleanliness for device fabrication is maintained.
* * * * *