U.S. patent application number 10/216130 was filed with the patent office on 2003-01-16 for method of fabricating and structure of an active matrix light-emitting display device.
This patent application is currently assigned to SONY International (Europe) GmbH. Invention is credited to Lupo, Donald, Yasuda, Akio.
Application Number | 20030013220 10/216130 |
Document ID | / |
Family ID | 8232785 |
Filed Date | 2003-01-16 |
United States Patent
Application |
20030013220 |
Kind Code |
A1 |
Lupo, Donald ; et
al. |
January 16, 2003 |
Method of fabricating and structure of an active matrix
light-emitting display device
Abstract
The invention concerns active matrix light-emitting display
devices and a method of their fabrication wherein the problem of
chemically unstable cathode electrode layers is solved,
simultaneously offering a considerably higher aperture ratio and
brightness with rather low driving voltages. These advantages are
achieved by separate manufacture of a first substrate bearing TFT
elements of which the source and drain regions are at first covered
by a non-conductive passivation layer followed by a deposition of a
chemically stable cathode material layer and deposition of an
appropriately selected EL material layer. The anode side substrate
is independently prepared by at first depositing an anode layer
followed by application of an EL layer, then the two independently
manufactured layered substrates are alligned face-to-face and are
combined to a unified structure under application of heat and
pressure, the temperature being selected to have the glass
transition temperature of said EL layers in case of polymeric EL
material or to have the phase transition temperature for solid to
liquid crystalline state or isotropic state in case of crystalline
EL material.
Inventors: |
Lupo, Donald; (Frankfurt,
DE) ; Yasuda, Akio; (Stuttgart, DE) |
Correspondence
Address: |
FROMMER LAWRENCE & HAUG, LLP.
10TH FLOOR
745 FIFTH AVENUE
NEW YORK
NY
10151
US
|
Assignee: |
SONY International (Europe)
GmbH
|
Family ID: |
8232785 |
Appl. No.: |
10/216130 |
Filed: |
August 9, 2002 |
Related U.S. Patent Documents
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Application
Number |
Filing Date |
Patent Number |
|
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10216130 |
Aug 9, 2002 |
|
|
|
09415807 |
Oct 11, 1999 |
|
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6461885 |
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Current U.S.
Class: |
438/29 ; 438/149;
438/22; 438/99 |
Current CPC
Class: |
H01L 2251/5315 20130101;
H01L 27/3251 20130101; H01L 51/0024 20130101; H01L 27/3244
20130101; H01L 51/5221 20130101; H01L 51/56 20130101; H01L 51/5206
20130101 |
Class at
Publication: |
438/29 ; 438/22;
438/99; 438/149 |
International
Class: |
H01L 021/00; H01L
035/24 |
Foreign Application Data
Date |
Code |
Application Number |
Oct 13, 1998 |
EP |
98119323.82203 |
Claims
1. A method for fabricating an active matrix display device formed
of a plurality of pixels and comprising: at least one thin film
transistor element (TFT element) (2) is deposited on a first
substrate (1) for each pixel, at least the source region (S) and
the channel region (C) of said at least one TFT element (2) for
each pixel are covered by a non-conductive passivation layer (3)
such as to leave parts or all of the drain region (D) uncovered, a
cathode material layer structured into a plurality of pixel
electrode regions (5a, 5b, . . . ) is deposited so as to cover at
least a substantial part of each of said TFT elements, a first
active organic and/or polymeric electroluminescent material layer
(EL layer) (6) is applied to cover at least said pixel electrode
regions (5a, 5b, . . . ), a second substrate (8) is separately
prepared by depositing an anode layer (7a, 7b, . . . ) on one
surface of said second substrate and subsequently coating said
anode layer with a second active organic and/or polymeric EL
material layer (6'), said two substrates thus prepared and coated
are laminated together, said first and second EL material layers
(6, 6') being face-to-face and appropriately alligned, under
application of heat and/or pressure for a predetermined time, the
temperature being selected to have a glass transition temperature
of at least one of said EL layers (6, 6') in case of a polymeric EL
material or to have the phase transition temperature for solid to
liquid crystalline state or isotropic state in case of crystalline
EL material.
2. The method of claim 1, characterized in that a flattening layer
(4) is deposited before or after deposition of said cathod material
layer (5).
3. The method of claim 1 or 2, characterized in that after the
process of lamination the display device is encapsulated.
4. The method of claim 1 or 2 wherein said first substrate (1) is
non-transparent, characterized in that a stable metal which is
resistant to photolithographic processing is selected for said
cathode material layer (5).
5. The method of claim 4, characterized in that Al or an Al alloy
is selected as said stable metal.
6. The method of claim 1 or 2, characterized in that at least one
of said EL layers (6, 6') is prepared as a laminated composite
layer system of a plurality of EL materials.
7. The method of claim 1 or 2, characterized in that before
applying said EL material layer(s), said cathode material layer
(5a, 5b, . . . ) and/or said anode layer (7a, 7b, . . . ) is/are
modified by chemical treatment to adsorb functionalized
dipoles.
8. The method of claim 7, characterized in that for optimization of
charge carrier injection from said cathode and/or said anode
material layer(s), said chemical treatment is selected such that
the molecules attached to said cathode and/or said anode layer(s)
are of the same functional group for light emission and/or charge
transport as the active organic or polymeric EL material which is
adjacent to the such modified electrode layer(s).
9. The method of claim 1 or 2, characterized in that said
heat-supported lamination process of said two EL material coated
substrates is performed under a pressure of more than 10
g/cm.sup.2.
10. An active matrix display device formed of a plurality of pixels
and comprising: at least one thin film transistor (TFT) element
adhered on a first substrate (1) for each pixel; a structured
non-conductive passivation layer (3) covering the source (S) and
drain (D) regions of said TFT clement (2) and leaving at least part
of the drain region (D) uncovered; a low work function material
layer structured into pixel electrode areas (5a, 5b, . . . ) and
electrically contacting said uncovered part of said drain regions;
a second substrate (2) bearing an electrically conducting high work
function layer (7a, 7b, . . . ); and an active organic or polymeric
electroluminescent EL material layer (6, 6') placed between said
low work function pixel structured layer and said high work
function layer on said second substrate (8).
11. The display device of claim 10, characterized in that said low
work function material layer (5a, 5b, . . . ) and/or said high work
function layer (7a, 7b, . . . ) on said second substrate (8) are
modified by chemical treatment to comprise adsorbed functionalized
dipoles.
12. The display device according to claim 11, characterized in that
the functional groups used to attach the dipoles are carboxylic
acids, hydroxamine, thiols, phosphonates, sulfonates and/or
amines.
13. The display device according to claim 11, characterized in that
molecules attached to said modified electrodes comprise the same
functional group for light emission and/or charge transport as the
active organic or polymeric layer in the device adjacent to said
modified electrode.
14. The display device according to claim 11, characterized in that
molecules attached to said modified electrodes comprise structures
of the following formula R.sub.d--P--R.sub.a where P is a
.pi.-conjugated system such as 7where R.sub.d is an electron donor
group and R.sub.a is an electron acceptor group, wherein R.sub.d
may be chosen from the groups NR'R", OR' and SR' where R' and R"
represent independently of each other .dbd.H or
C.sub.nH(2.sub.n+1)R.sub.att with R.sub.att=attachement group
according to claim 12 or H and n=0-20, wherein R' and R" may be the
same or different, but one of R' and R" must be .noteq.H and
wherein R.sub.a may be chosen from the groups
R.sub.att--C.sub.nH.sub.oF.sub.p--SO.sub.2-- -NO.sub.2 and
COOR.sub.att, where o+p=2n+1 and n=0-20, under the condition that
one of R.sub.att.noteq.H.
15. The display device according to claim 14, characterized in that
the molecule attached to said modified electrode has the following
structural formula: 8
16. The display device according to claim 11, characterized in that
molecules attached to said modified electrodes comprise structures
of the following formula 9where R' and R" independently of each
other .dbd.H or C.sub.nH(.sub.2n+1)R.sub.att, wherein
R.sub.att=attachment group according to claim 12 or H, n=0-20 and
wherein R' and R" may be the same or different, under the condition
that one of R' and R" must be .noteq.H.
17. The display device according to claim 16, characterized in that
the molecule attached to said modified electrode has the following
structural formula: 10
Description
[0001] The invention relates to a method of fabricating and to the
set-up of an active matrix display device formed of a plurality of
pixels and comprising at least one thin film transistor element (in
the following TFT element) on a first substrate for each pixel, a
low work function material layer, in particular a structured
cathode layer forming or contacting a pixel electrode layer, an
active organic and/or polymeric electroluminescent material layer
(EL layer) covering at least said low work function conducting
layer, an electrically conducting high work function layer, in
particular an anode layer on said EL layer and structured into
elements desired for display as well as a second substrate covering
said layered arrangement.
[0002] Light emitting devices based on organic and polymeric
electroluminescent (EL) materials are known (see Lit. [1]). For
achieving a specific colour emission efficiency of such types of
light-emitting devices, WO 96/03015 A1 describes an advanced
fabrication process for a conjugated polymers based two part
integrally connected light-emitting device, in which each polymer
layer is separately pretreated, e.g. by a stretching process. The
advantages of a polymer based light-emitting devices, in particular
diodes, are high brightness with low power consumption and low
driving voltages. The device structure is a relatively simple
metal-polymer-transparent electrode sandwich wherein the material
of the transparent electrode may be indium tin oxide (ITO). It is
therefore realistic and principally known to combine light-emitting
polymer EL devices with active matrix driving like thin film
transistors (TFTs) as proposed for example in EP-0 845 770 A1 or
U.S. Pat. No. 5,747,928.
[0003] Typically, such devices require two electrodes of differing
work function, at least one of which is transparent: one high work
function anode (e.g. ITO, fluorine-dopen tin oxide, or gold) for
hole injection and a low work function cathode (e.g. Mg, Al, Li,
Ba, Ca) for electron injection into the organic or polymeric
material. Up to now the transparent electrode in efficient devices
is always the anode, which is in most cases applied to the
substrate before diode preparation. Sputtering of ITO onto a
finished device has been used, but the efficiency is poor and such
processes are expected to damage the active polymer or organic
layer. Frequently, but not necessarily, such devices comprise
separate layers for electron and hole injection transport as for
example proposed in the above mentioned WO-document, and
occasionally in addition they also sometimes comprise an additional
light-emitting layer sandwiched between the hole- and the
electron-transport layers (see Lit. [2]). Flexible devices on
polymeric substrates have also been reported wherein such
substrates are coated with a high work function electrode, usually
ITO and/or polyaniline (see Lit. [3]).
[0004] Active matrix liquid crystal displays (LCDs) driven by TFTs
are commercially widespread, for example in notebook computers. In
TFT/LCDs, an abbreviation of thin film transistor-addressed liquid
crystal displays, each pixel element (pixel) is controlled by a
thin film transistor. TFT/LCDs create a whole new world of
technology in consumer electronics and in computer and
communication systems. The market for TFT/LCDs is now growing much
faster than expected and has an impact on new application fields,
as well as conventional fields.
[0005] The structure of a single TFT in a matrix type arrangement
of hundreds of thousands of TFTs is a FET (field effect transistor)
and a pixel electrode. The pixel electrode is contacted to the
source (or drain) electrode of the FET, and thus the effective
window area (aperture ratio) is reduced by the size of the
transistor area. The aperture ratio governs the brightness of the
panel, thus the larger the aperture ratio becomes the brighter the
display panel is achieved.
[0006] The concept of TFT/LCDs is not new, but rather old. As early
as 1966 Weimer proposed the possibility of using TFTs as display
switches (see Lit. [4]). A more detailed concept was described in
1971 (Lit. [5]), where the use of diodes or triodes (transistors)
was discussed as switches for active matrix liquid crystal
displays. The use of storage capacitors implemented in parallel
with the liquid crystal cell capacitor was also mentioned.
[0007] Hydronated amorphous silicon (a-Si:H) was a late arrival in
TFT technologies. However, it had a great influence in achieving
practical TFT/LCDs. Since the first report by the Dundee group
(Lit. [6]), a-Si:H-TFT has been recognized as a suitable device for
TFT/LCDs. So far the combination of TFT and LCD technologies has
been greatly growing and the market is already rather large.
[0008] However, the principle problems of TFT/LCDs are
[0009] a large viewing angle dependence if the LCD due to the
application and use of twisted nematic (TN) type liquid
crystals,
[0010] considerable dependence of the switching speed on
temperature because the switching is greatly dependent on the
viscosity of the liquid crystal itself, and
[0011] the liquid crystal injection process, necessary for cell
filling takes several hours.
[0012] As mentioned above, the demand for portable uses of flat
panel displays is increasing leading to the request for thinner and
lighter flat panel displays. One approach to this goal are the
polysilicon-based TFT technologies which are also progressing,
especially with a proposal for integrating the required shift
register within the TFT panel, thus reducing the number of
connection lines of the TFT panel.
[0013] Recently a poly-Si-TFT-addressed polymeric EL display was
reported by Cambridge Display Technology. Also known are active
matrix driven displays based on polymeric EL materials, wherein the
active driving elements are thin film field effect transistors
(TFTs) of polysilicon or organic TFTs based on oligothiophene (Lit.
[5]). In these reports the TFTs are deposited onto the transparent
substrate before preparation of the EL devices.
[0014] Also known are techniques to modify the work function of
metallic and semiconductor surfaces by attachment of functionalized
dipolar layers, e.g. through chemisorption or electrochemical
attachment (see Lit. [6]). Such modification has been shown for
materials such as ITO, CdTe and CdS. An LED device comprising a
modified ITO electrode was recently reported (see Lit. [7]).
According to theoretical analysis, the change in the work function
is proportional to the dipole moment of the attached molecules and
their concentration, and is inversely proportional to their
dielectric constants.
[0015] Lamination is a well-known technique for combining desired
qualities of two or more different materials into a composite layer
system and involves joining of the layers under application of
pressure and/or heat (see Lit. [8]). Preparation of photovoltaic
cell based on polymers by laminating two parts together was
recently reported by Friend et al. (see Lit. [9]).
[0016] Cabrera et al. (see Lit. [10]) reported a class of
bifunctional materials for non-linear optics which comprised an
aromatic group, particularly a styryl group, functionalized at the
4 and 4' positions by trifluorosulfonate groups as an electron
acceptor at one end and electron donor groups such as ethers,
thioethers and amines on the other end. These materials exhibit
high dipole moments while showing a relatively small visible light
absorption. Due to the possibility of attaching further functional
groups, e.g. alkyl chains, to both donor and acceptor groups it was
possible to determine the direction of the dipole moment relative
to the second function group. No applications of these materials in
EL devices have been reported.
[0017] Bloor et al. (see Lit. [11]) have reported a class of
molecules derived from TCNQ which exhibit dipole moments of up to
25-30 Debyc. No applications of these materials to EL devices have
been reported.
[0018] In addition to the conceptional inconsistencies of
light-emitting devices briefly mentioned above, having regard to
the problems of which the invention offers a solution, the
following disadvantages, shortcomings or needs of the state of the
art have been discovered by the inventors.
[0019] a. The low work function cathode materials needed for high
efficiency devices are typically unstable against oxidation by
oxygen or water. Because of this, such devices and displays
comprising a matrix of such devices must be thoroughly encapsulated
to eliminate water and oxygen from the device. This is particularly
difficult when flexible devices on polymeric substrates are desired
(see e.g. U.S. Pat. No. 5,747,928), because a transparent, flexible
and thoroughly impervious barrier layer must be applied to the side
of the device comprising the transparent electrode, and thus far no
such materials with sufficient barrier properties have been
reported.
[0020] b. A further disadvantage of the use of oxidation sensitive
cathode materials is there incompatibility with standard
photolithographic processing, which will be necessary to achieve
high resolution multicolour displays at reasonable prices.
[0021] c. Under the current state of the art, it is necessary for
the achievement of high efficiency devices to prepare the devices
onto a transparent anode material deposited onto a substrate and to
evaporate the cathode onto the organic and/or polymeric layers.
This eliminates the possibility to modify the cathode work function
by chemical means and to use more stable materials.
[0022] d. Furthermore, according to the state of the art, in active
matrix displays comprising organic and/or polymeric EL devices it
is necessary to apply the (non-transparent) TFTs to the substrate
before preparation of the EL device. This is a problem because in
emissive displays, in which each pixel element consists of a
different device element like a TFT, it is difficult to obtain
uniformity over the screen, because of the deviation of the each
element's electrical properties. In order to circumvent a deviation
of the brightness over the screen, one should perform some
compensation by a built-in circuit in or for each pixel element. If
the additional circuits arc fabricated in the TFT pixel, it means a
reduction of the aperture ratio. With the conventional TFT concept,
the aperture ratio is reduced even more with an increase of the
resolution or number of the pixels on the panel.
[0023] With the above discussed observations and drawbacks in mind,
it is an object of the invention to teach a modified or new
manufacturing process and a new structure for active matrix display
devices offering high resolution displays with a good uniformity of
brightness over the screen and simultaneously showing a high
aperture ratio.
[0024] The invention concerns displays comprising devices which
contain organic or polymeric EL materials and its preparation and
application, wherein solution to the problems and the objects
described above can be achieved.
[0025] A method of fabricating an active display device according
the invention is defined in claim 1. Advantageous modifications and
embodiments of such a manufacturing method are the subject-matter
of dependent claims.
[0026] An active matrix display device and its specific structure
according to the invention is the subject-matter of claim 10 with
advantageous modifications and improved embodiments being defined
in further dependent claims.
[0027] As mentioned above, the combination of TFTs and LEPs
(light-emitting polymers) is promissing in terms of eliminating the
viewing dependence and temperature dependence of the response speed
in TFT/LCDs, which are crucial problems for displays available on
the market. However, the current state of the art leads to poor
aperture ratios for high resolution displays based on polymeric EL
material.
[0028] The invention as defined in at least one of the appended
claims solves the above problems by metal (pixel electrode)
fabrication on the TFT side of one of the substrates, such that at
least a major part of each TFT is burried under a pixel electrode
allowing for an active matrix addressing of the polymeric EL pixels
while maintaining a high aperture ratio even at high
resolution.
[0029] The fabrication method according to the invention and the
resulting product of an active matrix display device will be
described in further details by way of examples and embodiments and
with reference to the accompanying drawings of which
[0030] FIGS. 1A to 1K visualize sequences and intermediate results
of process steps for an active-matrix display device according to
the invention;
[0031] FIGS. 2A to 2K exemplify basically the same process steps as
FIG. 1 with an advantageous modification in FIG. 2A.sub.2;
[0032] FIGS. 3A to 3K show basically the same process steps and
intermediate production stages as FIGS. 2A to 2H with an
advantageous modification in FIG. 3D.sub.1; and
[0033] FIGS. 4A to 4K show process steps and intermediate
production stages corresponding to those of FIGS. 3A to 3K with a
further modification in FIG. 4G.sub.1.
[0034] A first sequence of process steps according to the invention
and one embodiment of the device prepared thereby are described
with reference to FIGS. 1A to 1K.
[0035] First, a matrix of TFTs 2, each comprising a source region
S, a drain D and a gap or channel region C, is prepared on a
substrate material 1, which may, but must not be transparent, and
may be, but is not limited to silicon wafers, transparent glass or
a transparent polymer material, e.g. PET, polysulfone,
cycloolefinic copolymers or polycarbonates or flexible composite
materials. The substrate may include reflective layers to reflect
light emitted in the direction of the substrate.
[0036] One or in the case of a multi-colour display more (e.g.
three or four) TFTs 2 can be assigned to each pixel of a display.
The actual fabrication procedure for the TFTs up to this point can
be almost the same as for conventional TFT substrates as used for
liquid crystal displays.
[0037] Next, a non-conductive passivation layer 3, which may
comprise inorganic (e.g. SiO.sub.2) and/or organic (e.g. a cured
photoresist) non-conductive materials, is applied in such a way as
to cover the source electrode or source region S and the gap or
channel region C but to leave at least some part of the drain
electrode or drain region D exposed. This layer 3 may be applied
using standard lithographic techniques but may also be applied
using other techniques such as shadow mask evaporation (see FIG.
1B).
[0038] Subsequently a matrix of cathodes 5, which can cover also
the area covered by the TFTs and which define the area of the
pixels in a display device according to the invention is applied,
for example by vacuum evaporation or sputtering. The cathode layer
5 (see FIG. 1C) may comprise but is not limited to Al, Mg, Ca, Ba,
Li, Ag, In or any alloys comprising two or more of these metals. In
a preferred embodiment of the invention a stable metal such as Al
or alloys thereof is used, which is resistant to photolithographic
processing. A cathode layer 5 may be structured into pixel elements
5a, 5b, . . . desired each for a display element by using
conventional processes, such as dry etching by oxygen or
tetrafluorocarbon etc., or by wet etching processes with e.g.
HNO.sub.3/CH.sub.3/COOH/H.sub.3PO.sub.4.
[0039] It may be and usually it is advantageous to apply an
additional flattening layer or partial layer 4 to the pixels in
such a way as to create a flat surface at the top of the cathode
layer 5 and the pixel electrodes 5a, 5b, . . . , respectively. This
may for example be done by evaporation of further cathode material
using for example a shadow mask or by spincoating of organic
materials out of a solution. Alternatively the flattening layer 4
may be applied using the same methods before deposition of the
cathode layer 5 (see FIGS. 1C and 1D).
[0040] After structuring the pixel areas (FIG. 1D) one or more
composite active organic and/or polymeric layer(s) is (are) applied
to the cathode material, i.e. on top of the pixel areas. The
composition of the layer(s) 6 may include any of the types of
materials known in the literature or referred to in the state of
the art. Coating may be done by spincoating, doctor blading,
transfer printing, curtain coating, slot-dye coating, or printing
techniques such as screen printing (see FIG. 1E).
[0041] On a second, preferably optically transparent substrate 8
(FIG. 1F), which may consist of but is not limited to any of the
materials described above for the first substrate 1, a transparent
high work function electrode, e.g. an anode 7 such as described in
the state of the art is deposited. If it is desired for certain
embodiments of the invention, the anode layer may be structured
into the elements 7a, 7b, . . . desired for a display using
standard methods such as lithography and etching. Structuring of
the anode is, however, optional and may not be necessary even for
high resolution displays. Subsequently one or more active organic
and/or polymeric layers 6' are applied to the structured anode
layer elements 7a, 7b. . . , respectively. The composition of such
polymeric layers may include any of the types of materials known in
the literature or referred to in the description of the state of
the art. Again, coating may be done by spin-coating, doctor
blading, transfer printing, curtain coating, slot-dye coating, or
other printing techniques such as screen printing.
[0042] The process for manufacturing said two layered structures
shown in FIG. 1E and FIG. 1H, respectively, is quite simple and
favourable for mass production.
[0043] Subsequently the two coated substrates 1 to 6 and 8 to 6'
are laminated-together by application of heat and/or pressure as
illustrated in FIG. 1K. As the polymers have glass transition
temperature or if it is a liquid crystalline polymer, it must have
phase transition temperature from solid to liquid crystalline state
or isotropic state, in which the viscosity of the polymer
decreases. Above these appropriately selected temperatures the
application of pressure can lead to good physical and electrical
contact between the two polymer layers 6 and 6'. Therefore, the
temperature of lamination should be higher than the glass
transition temperature of at least one of the organic and/or
polymeric layers. After or during the process of lamination the
device or display comprising such devices may be encapsulated if
this is necessary or desired.
[0044] In another modified process or embodiment of the invention
shown in FIG. 2A to FIG. 2K, a conventional TFT display substrate 1
such as used in the manufacture of liquid crystal displays is used
as a substrate. Such substrates contain a matrix of TFTs 2 and of
electrodes la usually made of ITO which define the pixel areas in
such LCDs (see e.g. EP 0 845 770 A1). To this substrate 1 already
provided with said TFTs 2 and said electrodes la is first applied
as above a non-conductive passivation layer 3 which covers the TFTs
2 but leaves part of the ITO electrodes 1a exposed. Subsequently a
matrix of cathodes, i.e. in large pixel areas 5a, 5b, . . . as
above is deposited, which cover also the area containing the TFTs 2
and which in each case define the active area of a pixel in a
device according to the invention.
[0045] According to this invention, each pixel area is defined by
the respective area 5a, 5b, . . . of the cathode. Thus the cathode
electrode is the respective pixel electrode. The source electrode
area S and the drain D of the TFT are covered by the non-conductive
passivation layer 3 while the drain electrode is in contact with
the respective cathode/pixel electrode 5a, 5b. By this arrangement
a high aperture ratio even at high resolution is achieved.
[0046] The further process steps depicted in FIGS. 2F to 2K are
essentially the same as those described above in connection with
FIGS. 1A to 1K. Again, if it is desired, an additional conductive
layer 4 for the purpose of flattening the layer structure may be
applied before or after deposition of the cathode layer 5 as
described above.
[0047] In preferred process modifications and embodiments of the
invention the pixel or cathode regions 5a, 5b, . . . and/or the
anode regions 7a, 7b, . . . my be modified chemically before
application of the organic and/or polymeric layer 6, 6' by
absorption of functionalized dipoles. The functional groups which
may be used to attach the dipoles may be, but are not limited
to:
[0048] Carboxylic acids
[0049] Hydroxamine
[0050] Thiols
[0051] Phosphonates
[0052] Sulfonates
[0053] Amine.
[0054] The molecules which are attached to the pixel regions 5a,
5b, . . . and/or the anode regions 7a, 7b, . . . in order to modify
them may comprise in one especially preferred embodiment of the
invention the same functional group for light emission and/or
charge transport as the active organic or polymeric layer in the
device which is adjacent to the thus modified electrode.
[0055] In another especially preferred embodiment of the invention
the attached molecules comprise structures of the following
formula
R.sub.d--P--R.sub.a
[0056] where P is a .pi.-conjugated system such as 1
[0057] where R.sub.d is an electron donor group and R.sub.a is an
electron acceptor group.
[0058] Rd may be chosen from the following groups
[0059] NRR'
[0060] NR'R"
[0061] OR'
[0062] SR'
[0063] where R, R' and R" are independently of each other equal H
or C.sub.nH(.sub.2n+1)R.sub.att.
[0064] R.sub.att=one of the above attachement groups or H,
[0065] n=0-20, preferred 0-10,
[0066] R' and R" may be the same or different, but one of R' and R"
must be .noteq.H.
[0067] R.sub.a may be chosen from the following groups:
1 R.sub.att -- C.sub.nH.sub.oF.sub.p -- SO.sub.2 -- NO.sub.2
COOR.sub.att where o + p = 2n + 1 n = 0-20, preferred 0-10.
Under the condition that one of R.sub.att .noteq.H.
[0068] In a particularly preferred embodiment of the invention the
attached molecules are of the form 2
[0069] where either R.sub.att or R.sub.att.sup.1 is an attachment
group.
[0070] In another particularly preferred embodiment of the
invention molecules of the following form are used for surface
modification: 3
[0071] where R' and R" independently of each other .dbd.H or
C.sub.nH(.sub.2n+1)R.sub.att,
[0072] R.sub.att=one of the above attachement groups or H,
[0073] n=0-20, preferred 0-10, and
[0074] R' and R" may be the same or different, but one of R' and R"
must be .noteq.H.
[0075] Subsequent to the modification of the cathode 5 and/or the
anode 7 the organic and/or polymeric material which is desired to
be proximate to the modified electrode is applied. As mentioned
above, this may be done by spincoating, doctor blading, transfer
printing, curtain coating, slot-dye coating, or other printing
techniques such as screen printing.
[0076] The main advantages of the invention over the state of the
art are the following:
[0077] The process of separate lamination allows for both
electrodes 5a, 5b, . . . and 7a, 7b, . . . to be chemically
modified for optimization of charge carrier injection which is not
possible when one electrode must be deposited directly on top of
the organic layer. In addition, the lamination of two polymer
coated films 6 and 8, respectively can lead to a convenient,
inexpensive production process which is compatible with a further
lamination step for encapsulation.
[0078] The modification of the electrodes 5a, 5b, . . . and 7a, 7b,
. . . , particularly the replacement of the usually unstable
cathode by a stable electrode material like Al or an Al alloy,
provides the possibility of manufacturing stable and efficient
display devices, in comparison to the state of the art, forcing one
to choose between stable cathode materials and high electron
injection efficiency. Therefore, it will be possible in the future
to prepare highly efficient organic light-emitting devices and
displays using materials which are less stringent in their
requirements for encapsulation and which are compatible with
standard lithographic techniques for preparing structures.
[0079] The process of a separate lamination furthermore allows for
the TFTs necessary for high resolution displays to be deposited
before the preparation of the light emitting element and on the
non-transparent side of the display device, thus enabling a display
with a higher aperture ratio than is possible with the state of the
art.
EXAMPLES
Example 1
[0080] A TFT panel of 513000 (1068.times.480) pixels and with a
diagonal size of 1.35 inches (3.43 cm) is selected and an Al
electrode (e.g. 5 in FIG. 1C) is vacuum evaporated at a thickness
of 50 nm. The panel is photo resist coated and processed by a usual
photolithographic process and dry etched with oxygen at a pressure
of 10.sup.-3 torr only at data and gate line areas. The etching
rate is 100 nm/min.
[0081] Subsequently (poly)octylfluorene of a molecular weight of
4000 dissolved in p-xylene at a concentration of ca. 20 mg/ml is
spin coated onto the thus prepared substrate. The spin coater
condition is 100 rpm for 4 seconds and then 3000 rpm for 30 seconds
to obtain a 70 nm thick film 6 on the Al electrode (cathode 5a, 5b,
. . . in FIG. 1D) of the TFT panel.
[0082] On a second substrate 8, which comprises 0.7 mm thick
Corning 7059 glass with a 50 nm ITO film 7, which may be structured
as needed using standard lithographic techniques (FIG. 1F), a 70 nm
layer 6' of poly(octylfluorene) is deposited as above, is set on a
previously applied polyfluorene film.
[0083] Then the TFT panel (FIG. 1E) is placed on a hot plate which
is set at 180.degree. C. and kept at this temperature for 3 min.
The second substrate (FIG. 1H) is applied to the first so that the
two polymer layers 6, 6' are in face-to face contact with each
other and heating is continued for another 3 min. Finally, a weight
of 1 kg is applied on the combined panel under maintenance of the
same temperature (see FIG. 1K).
[0084] The pressure at heat is maintained for 10 min. Subsequently
the whole device is cooled at a rate of 0.5.degree. C./min.
[0085] The glass edges of the laminated device are encapsulated
with epoxy resin to keep out water and oxygen.
[0086] With this process and the device structure mentioned above,
a TFT/LEP display with 513000 pixels and a diagonal size of 1.35"
(3.43 cm) is obtained which can have a brightness of 10 Cd/m.sup.2
and the driving voltages are below 15 V.
Example 2
[0087] A display device is prepared as in Example 1 with the
following modifications (see FIGS. 3A to 3K):
[0088] Between the etching of the Al electrode (cathode pixels 5a,
5b) and the deposition of layer 6 of poly(octylfluorene) the panel
is dipped into a breaker 10 (FIG. 3D.sub.1) containing a 5 mg/ml
solution in a mixture of acetonitrile and ethyl alcohol of the
following composition for 5 minutes: 4
[0089] Subsequently the panel is rinsed in ethanol and dried under
air at 50.degree. C. for 5 min before deposition of the polymer
layer 6. The rest of the preparation is as described in Example
1.
[0090] With the process of Example 2 and the structure described
above, a TFT-LEP display with 513000 pixels and a diagonal size of
1.35" (3.43 cm) is obtained with a brightness of about 50
Cd/m.sup.2 and with driving voltages below 15 V.
Example 3
[0091] A device is prepared as in Example 1 with the following
differences (see FIGS. 4A to 4K). Between the etching of the Al
electrode (e.g. cathode pixels 5a, 5b, . . . ;) and the deposition
of the layer 6 of poly(octylfluorene) the panel is dipped into a
breaker 10 containing a 5 mg/ml solution in a mixture of
acetonitrile and ethyl alcohol of the following chemical
composition for 5 min: 5
[0092] Subsequently the panel is rinsed in ethanol and dried under
air at 50.degree. C. for 5 min before deposition of the polymer
layer 6.
[0093] After preparation of the ITO electrodes (e.g. anodes 7a, 7b,
. . .) the second substrate is dipped into a breaker 11 containing
a 5 mg/ml solution in a mixture of acetonitrile and ethanol of the
following chemical composition for 5 min (FIG. 4D.sub.1): 6
[0094] Subsequently the panel is rinsed in ethanol and dried under
air at 50.degree. C. for 5 min before deposition of the polymer
layer 8. The rest of the preparation is as described in Example
1.
[0095] With the process and the arrangement described in this
Example a TFT/LEP display with 513000 pixels and a diagonal size of
1.35" (3,43 cm) is obtained having a brightness of 100 Cd/m.sup.2
and driving voltages below 12 V.
2 List of Reference Literature Lit. [1]: R. Friend, A. Holmes, D.
Bradley et al., Nature 347, 539 (1990) Lit. [2]: Riess, W. "Single-
and Heterolayer Polymeric Light Emitting Diodes Based on
Poly(p-phenylene vinylene) and Oxdiazole Polymers" Organic
electro-luminescent Materials and Devices, edited by Miyata, S. and
Nalwa, H. S., Gordon and Breach Science Publishers, Amsterdam, 1997
Lit. [3]: Heeger et al., Nature 357, 477 (1992) Lit. [4]: Weimer,
P. K. (1966) Field Effect Transistors, edited by J. T. Wallmark and
H. Johnson, New Jersey, Prentice Hall Lit. [5]: R. Friend et al.,
Science, in press; home page, Cambridge Display Technology Ltd;
www.cdt/bd.co.uk Lit. [6]: M. Bruening, E. Moons, D. Cahen. A.
Shanzer, J. Phys. Chem 99, 8368 (1995) Lit. [7]: F. Nucsch, L.
Si-Ahmed, B. Francois, L. Zuppiroli, Adv. Mater. 9, 222 (1997) Lit.
[8]: See, for example, S. A. Giddings, in Encyclopedia of Polymer
Science and Technology 2.sup.dn Ed., Vol. 8, 617 ff Lit. [9]: R.
Friend et al. Nature, in press Lit. [10]: Cabrera, A. Meyer, D.
Lupo et al. Nonlinear Optics 9, 161 (1995) Lit. [11]: D. Bloor et
al., J. American Chem. Soc. xx, xxx (xxxx)
* * * * *
References