U.S. patent application number 10/530497 was filed with the patent office on 2006-07-13 for method for manufacturing a light emitting display.
Invention is credited to Antonius Johannes Maria Nellissen.
Application Number | 20060154550 10/530497 |
Document ID | / |
Family ID | 32103940 |
Filed Date | 2006-07-13 |
United States Patent
Application |
20060154550 |
Kind Code |
A1 |
Nellissen; Antonius Johannes
Maria |
July 13, 2006 |
Method for manufacturing a light emitting display
Abstract
The invention relates to a method for manufacturing a light
emitting display on a substrate comprising the steps of depositing
a first electrode layer on or over the substrate, forming a
plurality of light emitting layer segments on or over at least a
part of the first electrode layer, applying at least one protective
layer on or over at least one of the light emitting layer segments
and depositing a second electrode layer. By providing a protective
layer over the light emitting layer segments more freedom with
regard to processing conditions is obtained in depositing and/or
patterning of subsequent layers, since the susceptible light
emitting layer segments are protected by the protective layers.
Inventors: |
Nellissen; Antonius Johannes
Maria; (Eindhoven, NL) |
Correspondence
Address: |
PHILIPS INTELLECTUAL PROPERTY & STANDARDS
P.O. BOX 3001
BRIARCLIFF MANOR
NY
10510
US
|
Family ID: |
32103940 |
Appl. No.: |
10/530497 |
Filed: |
September 12, 2003 |
PCT Filed: |
September 12, 2003 |
PCT NO: |
PCT/IB03/03930 |
371 Date: |
October 31, 2005 |
Current U.S.
Class: |
445/24 ;
G9B/7.045; G9B/7.114; G9B/7.123; G9B/7.136 |
Current CPC
Class: |
G11B 7/08517 20130101;
G11B 7/1369 20130101; G11B 2007/0013 20130101; G11B 7/1356
20130101; G11B 7/14 20130101; G11B 7/1378 20130101 |
Class at
Publication: |
445/024 |
International
Class: |
H05B 33/14 20060101
H05B033/14 |
Foreign Application Data
Date |
Code |
Application Number |
Oct 16, 2002 |
EP |
02079280.0 |
Claims
1. Method for manufacturing a light emitting display on a substrate
comprising the steps of: depositing a first electrode layer on or
over said substrate; forming a plurality of light emitting layer
segments on or over at least a part of said first electrode layer;
applying at least one protective layer on or over at least one of
said light emitting layer segments; depositing a second electrode
layer.
2. Method according to claim 1, wherein said first electrode layer
is deposited on or over said substrate and comprises a material
transparent to the light to be emitted by said light emitting layer
segments in operation of the light emitting display.
3. Method according to claim 1, wherein said protective layer
comprises molybdenum or titanium.
4. Method according to claim 1, wherein said second electrode layer
is patterned by applying photolithography and subsequent etching in
correspondence to said light emitting layer segments.
5. Method according to claim 4, wherein said second electrode layer
is patterned such that it comprises recesses outside the areas
comprising said light emitting layer segments, beneath which
recesses said protective layer is substantially removed.
6. Method according to claim 5 wherein said patterned second
electrode layer and said recesses are covered by at least one
sealing film.
7. Method according to claim 1, wherein said second electrode layer
has a thickness larger than 0.5 .mu.m and preferably between 0.5
.mu.m and 3 .mu.m.
8. Light emitting display comprising: a substrate; a first
electrode layer deposited on or over said substrate; a plurality of
light emitting layer segments formed on or over said first
electrode layer; at least one protective layer applied on or over
at least some of said light emitting layer segments; a second
electrode layer.
9. Light emitting display according to claim 8, wherein said
protective layer comprises molybdenum or titanium.
10. Light emitting display according to claim 8, wherein said
second electrode layer has a thickness between 0.5 .mu.m and 3
.mu.m.
11. Light emitting display according to claim 8, wherein said
second electrode layer is patterned in correspondence with said
light emitting layer segments and said patterned second electrode
layer is covered by at least one sealing film.
12. Electric device comprising a light emitting display according
to one of the claims 8-11 and/or manufactured according one of the
claim 1-7.
Description
[0001] The invention relates to a method for manufacturing a light
emitting display on a substrate.
[0002] The invention further relates to a light emitting display
and to an electric device comprising such a display.
[0003] U.S. Pat. No. 5,962,970 discloses a method for manufacturing
an organic display panel wherein first display electrodes, organic
function layers including at least one organic electroluminescent
medium formed on exposed portions of the first display electrodes
and second display electrodes formed on the organic function layers
are deposited on a substrate. Electrically insulating ramparts
projecting from the substrate to a height up to 0.5 .mu.m are
employed for electrically disconnecting the adjacent second display
electrodes, which are deposited by evaporation of a metal.
[0004] However, this method for manufacturing a light emitting
display has several disadvantages relating to e.g. the use of the
electrically insulating ramparts. One of these disadvantages is the
limitation on the thickness for the second electrode as a result of
which the electrical resistance of this second electrode is high.
Moreover, the ramparts cause problems in sealing or encapsulating
the light emitting display from environmental influences resulting
in expensive sealing arrangements. Further the ramparts may be
unstable leading to requirements for careful handling of the
structures. Also processing flexibility for the light emitting
display has some limitations due to the susceptibility of the light
emitting layer segments of the display.
[0005] It is an object of the invention to provide an improved
method for manufacturing a light emitting display wherein at least
one of the above mentioned disadvantages is avoided or at least
reduced.
[0006] This object is achieved by providing a method for
manufacturing a light emitting display on a substrate comprising
the steps of: [0007] depositing a first electrode layer on or over
said substrate; [0008] forming a plurality of light emitting layer
segments on or over at least a part of said first electrode layer;
[0009] applying at least one protective layer on or over at least
one of said light emitting layer segments; [0010] depositing a
second electrode layer.
[0011] The invention further relates to a light emitting display
comprising: [0012] a substrate; [0013] a first electrode layer
deposited on or over said substrate; [0014] a plurality of light
emitting layer segments formed on or over said first electrode
layer; [0015] at least one protective layer applied on or over at
least some of said light emitting layer segments; [0016] a second
electrode layer.
[0017] By providing a protective layer over the light emitting
layer segments more freedom with regard to processing conditions is
obtained in depositing and/or patterning of subsequent layers,
since the susceptible light emitting layer segments are protected
by the protective layers. Processing using wet etching means can
e.g. be performed for structuring of layers applied after the
appliance of the protective layer. Preferably the light emitting
layer segments are entirely covered by the protective layer.
[0018] In a preferred embodiment of the invention the protective
layer comprises or consists of molybdenum or titanium. Molybdenum
or titanium layers or layers comprising these materials are
suitable to protect the light emitting layer segments for wet
etching means.
[0019] In a preferred embodiment of the invention the second
electrode layer is aluminium and/or is patterned by
photolithography and subsequent etching. Patterning of the second
electrode layer by such a process has become possible by the
application of the protective layer on the light emitting layer
segments, protecting the susceptible segment from e.g. wet etching
agents. Thus, the prior art electrically insulating ramparts do not
have to be applied for patterning the second electrode layer as a
result of which the thickness of this second electrode layer can be
significantly increased. A thick second electrode layer, larger
than 0.5 .mu.m, and preferably in the range of 0.5 to 3 .mu.m,
leads to a low electrical resistance and a short RC-time, which is
important for high switching frequencies. Moreover the shape of the
prior art ramparts provided problems with regard to obtaining an
appropriate sealing film for encapsulating the structure.
Photolithographic patterning of the second electrode layer provides
an appropriate starting point, e.g. a smooth surface, for further
encapsulation of the light emitting device.
[0020] In an embodiment of the invention the patterned second
electrode layer comprises recesses wherein the protective layer is
removed. A sealing film for encapsulation of the resulting
structure is preferably deposited on the patterned second electrode
layer and in the recesses. The sealing film can be made thin, e.g.
0.5 .mu.m, in contrast to the typically applied thick encapsulation
arrangements using e.g. individual metal caps for each structure or
light emitting device on the display with a thickness in the range
of 0.3 to 1 mm. The individual metal caps are typically glued to
the substrate and comprise a getter material. The approach
according to this embodiment enables encapsulation of substantially
all the structures of the display without using a getter material,
resulting in a considerable cost efficiency.
[0021] It should be appreciated that the previous embodiments, or
aspects thereof, may be combined.
[0022] The invention further relates to an electric device
comprising a light emitting display as described in the previous
paragraph. Such an electric device may relate to handheld devices
such as a mobile phone, a Personal Digital Assistant (PDA) or a
portable computer as well as to devices such as a Personal
Computer, a television set or a display on e.g. a dashboard of a
car.
[0023] WO 00/16938 discloses a method for manufacturing a colour
organic light emitting device structure, wherein a passivation
layer permitting lithographic patterning of colour changing media
using wet processing methods is employed. However, this passivation
layer is deposited over the second electrode layer of the OLED
drivers integrated in the substrate.
[0024] U.S. Pat. No. 5,998,926 discloses a method for manufacturing
an organic electroluminescent device wherein the cathode is formed
into a fine pattern by photolithography. However, the cathode layer
is deposited directly on the substrate and is patterned before the
organic electroluminescent layer is provided.
[0025] The invention will be further illustrated with reference to
the attached drawing, which shows a preferred embodiment according
to the invention.
[0026] FIGS. 1-4 schematically illustrate first to fourth
manufacturing steps for a light emitting display;
[0027] FIG. 5 schematically illustrates a top view at the fourth
manufacturing step according to FIG. 4.
[0028] FIG. 6 schematically illustrates a fifth manufacturing step
for a light emitting display;
[0029] FIG. 7 schematically illustrates an enlarged view of a light
emitting element during the fifth manufacturing step;
[0030] FIG. 8-13 schematically illustrate sixth to eleventh
manufacturing step for a light emitting display;
[0031] FIG. 14 schematically illustrates a light emitting
display.
[0032] In FIG. 1 a substrate 1 is provided for manufacturing the
light emitting display 14 (shown in FIG. 14). Preferably, the
substrate 1 is transparent with respect to the light to be emitted
by the light emitting layer segments 7R, 7B (shown in FIG. 6).
Suitable substrate materials include synthetic resin which may or
may not be flexible, quartz, ceramics and glass. The total
thickness of the substrate typically ranges from 100 to 700
.mu.m.
[0033] A first electrode layer 2, commonly referred to as the
anode, is deposited on or over the substrate 1, e.g. by vacuum
evaporation or sputtering. The first electrode layer can
subsequently be patterned by photolithography. Preferably the first
electrode layer 2 is transparent with respect to the light to be
emitted by the light emitting layer segments in operation of the
light emitting display 14. For example, a transparent
hole-injecting electrode material, such as Indium-Tin-Oxide (ITO),
is used. Conductive polymers such as a polyaniline (PANI) and a
poly-3,4-ethylenedioxythiophene (PEDOT) are also suitable
transparent hole-injecting electrode materials. Preferably, a PANI
layer has a thickness of 50 to 200 nm, and a PEDOT layer 100 to 300
nm.
[0034] In FIG. 2 a next manufacturing step is shown, wherein a low
resistive metal, such as a Molybdenum/Aluminium/Molybdenum (MAM)
layer 3 is deposited on or over the first electrode layer 2. The
MAM layer 3 is subsequently defined photolithographically, e.g. at
the positions where no light is to be generated. MAM layer 3 is
applied for contacting purposes and for decreasing the electrical
resistance to the first electrode layer 2. The total thickness of
MAM layer 3 typically ranges up to 0.5 .mu.m.
[0035] In FIG. 3 a next manufacturing step is shown, wherein an
insulating layer, such as novolack or acrylate, is spincoated over
the structure shown in FIG. 2 and is subsequently patterned by
means of photolithography. The insulating layer is e.g. baked at
220.degree. C. for 30 minutes. In patterning the insulating layer
delimiting means 4 define cavities or sites 5 between the
delimiting means 4 for the light emitting elements 7R and 7B to be
deposited further on. Moreover the delimiting means 4 assists in
the separation of the second electrode layer as will be described
in more detail below. The widths of the delimiting means 4 is
typically 20 .mu.m with a thickness of about 3 .mu.m. The
insulating layer or delimiting means 4 is of a hydrophilic nature,
i.e. it may exert an attractive force on liquid state
materials.
[0036] In FIG. 4 a next manufacturing step is shown wherein parts
6, repelling the fluid light emitting substance to be deposited
afterwards are applied on or over the delimiting means 4, bounding
the sites 5 of the light emitting elements. The repellent parts 6
may e.g. be strips of repellent material. These repellent parts 6
may be obtained in various ways. The repellent parts 6 are the
subject of a co-pending application of the applicant. The width of
the repellent part 6 may range from 5-15 .mu.m, e.g. 10 .mu.m.
[0037] FIG. 5 shows a top view of a part of the light emitting
display after the repellent parts 6 have been applied. In FIG. 5 it
is illustrated that the repellent parts 6 can be applied to bound
the cavities or sites 5 in a number of ways. FIG. 5 shows as
examples bounding by the repellent parts 6 along the entire
circumference of the sites 5 (left-hand column of cavities or sites
5) and a partial bounding by the repellent parts 6 (right-hand
column of cavities or sites 5). The way in which the repellent
parts 6 bound the sites 5 may be dependent on the process chosen
for deposition of the fluid light emitting substance or the
arrangement of colours for the various cavities or sites 5. If e.g.
the same colour is to be deposited in a column, repellent parts 6
that only partially bound the sites 5, according to the right-hand
column of FIG. 5, may be used, since flow of material between the
sites 5 in this column may not be harmful.
[0038] In FIG. 6 a next manufacturing step is shown, wherein the
fluid light emitting substance is deposited in the cavities or at
the sites 5 to obtain the light emitting elements or layer segments
7. It is noted that a light emitting element or layer segment 7 may
comprise several conductive polymer layers, such as a
polyethylenedioxythiophene (PEDOT) layer and a
polyphenylenevinylene (PPV). For a colour light emitting display
different materials may be used. In FIG. 6 light emitting element
or layer segment 7R refers to a red-light emitting material and
light emitting element or layer segment 7B refers to a blue light
emitting material. Conventionally a third material G emitting green
light is applied as well. The light emitting materials R, G and B
are preferably electroluminescent materials and are deposited by
inkjet-printing. The length of a light emitting element is e.g. 240
.mu.m.
[0039] FIG. 7 shows a detailed view of a cavity or site 5, wherein
the fluid red light emitting substance has been deposited and is
depicted in various stages of the drying process after deposition.
Due to evaporation of the solvents used, shrinkage, indicated by
the arrow, occurs leaving the red light emitting material behind in
the cavity or site 5. The light emitting material layer is
necessarily somewhat oversized with respect to the site 5 to avoid
shortcuts emanating if the light emitting display is operated, i.e.
a voltage is applied over the light emitting layer. The oversized
light emitting material is obtained, since the delimiting means 4
is of a hydrophilic nature.
[0040] However, the fluid light emitting substance of light
emitting element or layer segment 7R should not flow to an adjacent
light emitting element or layer segment 7B comprising a light
emitting of different colour. It is illustrated that this effect is
achieved by employing hydrophobic barriers as repellent parts
6.
[0041] In FIG. 8 a next manufacturing step is shown wherein
metallization is applied on or over the light emitting elements or
layer segments 7R and 7B. This metallization consists e.g. of a
barium layer 8' for reducing the barrier level for injecting
electrons, on top of which a second electrode layer 9, commonly
referred to as the cathode, is deposited. However, in the
manufacturing process applied here an additional molybdenum or
titanium layer 8'' is applied, acting as a diffusion barrier for
protecting the light emitting elements or layer segments 7R and 7B
for wet etching solutions. In FIG. 8 the barium layer 8' and the
titanium or molybdenum layer 8'' are shown as a single layer 8. The
thickness of the barium layer 8' is e.g. 5 nm, of the titanium or
molybdenum layer 8'' e.g. 100 nm and of the cathode layer 9 e.g. 2
.mu.m. Prior art cathode layers have a thickness of about 0.5 .mu.m
maximum. As a result of the thick cathode layer 9 in this
embodiment of the invention, the electrical resistance for applying
a voltage to the light emitting element 7 has significantly
decreased.
[0042] In FIG. 9 a next step of the manufacturing process is shown,
wherein the cathode layer 9, is patterned. Cathode layer 9 is made
of e.g. aluminium. Patterning of the cathode layer 9 is performed
by photolithography followed by wet etching recesses 10 in the
cathode layer 9. The wet etching process does not affect the light
emitting elements or layer segments 7R and 7B, since the titanium
layer or molybdenum layer 8'' acts as a diffusion barrier to the
wet etching means. For etching of aluminium a mixture of e.g.
acetic acid, phosphoric acid, and nitric acid may be used.
Typically, the parts of the patterned cathode layer 9 substantially
cover the light emitting layer segments 7R, 7B entirely. Patterning
can be performed such that the patterned parts of the cathode layer
9 are in correspondence with the light emitting layer segments 7R,
7B, i.e. that light can be emitted by these light emitting layer
segments 7R, 7B using the patterned parts of the cathode layer
9.
[0043] In FIG. 10 a next manufacturing process step is shown,
wherein the protective layer 8 is partially removed at the recesses
10 by plasma etching in a CF4/Ar environment.
[0044] In FIG. 11 a next manufacturing process step is shown,
wherein a SiN film 11 is deposited over the structure shown in FIG.
10. This film 11 hermetically seals the structure from liquid or
moisture that may affect the light emitting layers or elements 7R
and 7B, e.g. via the recesses 10. It is noted that the
manufacturing process steps shown in FIGS. 10 and 11 may be
performed in combination by using a cluster tool system with e.g.
an etching and a deposition tool module. In this case the structure
is not exposed to air between etching of the diffusion barrier and
hermetic sealing with SiN. The SiN layer 11 has a thickness of e.g.
0.5 .mu.m. As an alternative oxinitride SiN(x)O(y) may be used for
the sealing film 11. This small thickness of the film 11 is
sufficient for sealing, since the prior art electrical insulating
ramparts with their negatively shaped angles are no longer applied
as a result of the new way of cathode structuring with the
protective layer 8.
[0045] In FIG. 12 a next manufacturing process step is shown,
wherein a protection layer 12 is applied on or over the structure
shown in FIG. 11. This protection layer 12 is obtained e.g. by
spincoating a resist or by laminating a dry film resist and has a
thickness of e.g. 10 .mu.m. Recesses 13 can be obtained by
photolithography. The resist 12 is e.g. baked at 120.degree. C. for
30 minutes.
[0046] In FIG. 13 a final manufacturing process step is shown,
wherein the SiN film 11 is partially removed at the positions where
the cathode layer 9 is to be contacted by connecting leads for
operating the light emitting display. SiN film 11 may e.g. be
removed in a CF4 plasma.
[0047] In FIG. 14 a light emitting display 14, which may be a
polymer or small molecule light emitting diode device is depicted
as a part of an electric device 15. The light emitting display 14
is e.g. a colour display comprising display pixels 16 arranged in a
matrix of rows and columns comprising red, green and blue light
emitting layer segments 7R, 7G and 7B. These light emitting layer
segments may be light emitting diodes. It is noted that the light
emitting elements 7R, 7G and 7B may be arranged in several
configurations to form a display pixel 16, such as a rectangular or
a triangular configuration. The light emitting layer segments 7R
and 7B can be operated by applying signals to the first electrode
layer 2 and/or the second electrode layer 9 in an appropriate
manner.
[0048] For the purpose of teaching the invention, a preferred
embodiment of a method for manufacturing a light emitting display
has been described above. It will be apparent for the person
skilled in the art that other alternative and equivalent
embodiments of the invention can be conceived and reduced to
practice without departing from the true spirit of the invention,
the scope of the invention being only limited by the claims.
* * * * *