U.S. patent application number 10/346931 was filed with the patent office on 2003-07-10 for selective deposition of emissive layer in electroluminescent displays.
Invention is credited to Swanson, Leland S..
Application Number | 20030129299 10/346931 |
Document ID | / |
Family ID | 24871001 |
Filed Date | 2003-07-10 |
United States Patent
Application |
20030129299 |
Kind Code |
A1 |
Swanson, Leland S. |
July 10, 2003 |
Selective deposition of emissive layer in electroluminescent
displays
Abstract
A method for forming an emissive layer for an electroluminescent
display is provided that includes positioning a substrate (40) in
spaced relation to a port (88) of a microeffusion cell (86). The
method then provides for transporting the substrate (40) across the
port (88) at a substantially constant rate. The method then
provides for effusing an emissive material from the port (88) and
adhering at least a portion of the emissive material effused from
the port (88) to a defined region of the substrate (40) to form an
emissive strip (46) having a substantially constant width on the
substrate (40).
Inventors: |
Swanson, Leland S.;
(McKinney, TX) |
Correspondence
Address: |
TEXAS INSTRUMENTS INCORPORATED
P O BOX 655474, M/S 3999
DALLAS
TX
75265
|
Family ID: |
24871001 |
Appl. No.: |
10/346931 |
Filed: |
January 17, 2003 |
Related U.S. Patent Documents
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Application
Number |
Filing Date |
Patent Number |
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10346931 |
Jan 17, 2003 |
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09714672 |
Nov 16, 2000 |
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6537607 |
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Current U.S.
Class: |
427/66 |
Current CPC
Class: |
H01L 51/001 20130101;
H01L 51/0004 20130101; C23C 14/243 20130101; H01L 51/56 20130101;
H01L 27/3211 20130101; C23C 14/04 20130101; C23C 14/568
20130101 |
Class at
Publication: |
427/66 |
International
Class: |
B05D 005/12 |
Claims
What is claimed is:
1. A method for forming an emissive layer for an electroluminescent
display, comprising: positioning a substrate in spaced relation to
a port of a microeffusion cell; transporting the substrate across
the port at a substantially constant rate; effusing an emissive
material from the port; and adhering at least a portion of the
emissive material effused from the port to a defined region of the
substrate to form an emissive strip having a substantially constant
width on the substrate.
2. The method of claim 1, further comprising vacuuming effused
emissive material molecules that do not adhere to the
substrate.
3. The method of claim 1, wherein the substrate is an optically
transparent substrate.
4. The method of claim 1, further comprising providing a pressure
controlled vacuum environment including the microeffusion cell.
5. The method of claim 1, wherein effusing an emissive material
from the port effuses an emissive strip between 0.5 mm and 1 mm
wide.
6. The method of claim 1, wherein the substrate is transported
across the microeffusion cell at a distance of less than 0.5
millimeters.
7. A method for forming a pixel of an electroluminescent display,
comprising: providing a substrate including a first series of
substantially parallel and spaced apart contacts; forming a first
transport layer outwardly of the first series of contacts;
selectively depositing a plurality of emissive strips outwardly of
the first transport layer, the emissive strips comprising a
repeating pattern of disparate emissive strips; forming a second
transport layer outwardly of the plurality of emissive strips; and
forming a second series of substantially parallel and spaced apart
contacts outwardly from the second transport layer and over the
plurality of emissive strips, the second series of contacts
substantially perpendicular to the first series of contacts.
8. The method of claim 7, wherein: the first transport layer is a
hole transport layer; the second transport layer is an electron
transport layer; the first series of contacts is formed from a high
work function metal; and the second series of contacts is formed
from a low work function.
9. The method of claim 7, wherein the first series of contacts is
formed from indium-tin-oxide.
10. The method of claim 7, wherein the first series of contacts is
formed from an optically transparent metal oxide.
11. The method of claim 7, wherein the plurality of emissive strips
are separated by 0.1 mm or less.
12. The method of claim 7, wherein the plurality of emissive strips
are deposited in a repeating pattern of red, green, and blue
emissive strips.
13. A product produced by the method of claim 7.
14. A method for forming an electroluminescent display, comprising:
providing a plurality of effusion cells, each effusion cell having
a plurality of ports, the ports of each effusion cell offset from
the ports of the other effusion cells; providing an optically
transparent substrate having a first plurality of contacts formed
from a first metal and a first transport layer formed outwardly of
the first contacts; transporting the substrate across the plurality
of effusion cells; continuously effusing an emissive material from
the ports in each effusion cell to form a plurality of emissive
strips; forming a second transport layer over the effused emissive
material; and forming a second plurality of contacts, each second
contact orthogonal to the first plurality of contacts and over one
of the emissive strips.
15. The method of claim 14, wherein each emissive strip is
separated from an adjacent emissive strip by less than 0.1
millimeter.
16. The method of claim 14, wherein each second contact corresponds
to one of the plurality of emissive strips.
17. A flat panel display formed by the method of claim 14.
18. A microeffusion cell, comprising: a cell wall forming a
cylinder including a plurality of ports operable to effuse material
from within the cylinder; a heater element surrounding the cell
wall and operable to heat the material within the cylinder; a
material distribution system within the cylinder operable to evenly
distribute the material through the cylinder; at least one vacuum
tube associated with each port and operable to remove effused
material molecules that do not adhere to a substrate.
Description
BACKGROUND OF THE INVENTION
[0001] Flat screen displays are provided by light blocking,
reflecting technologies, and light emitting technologies. One type
of light blocking flat screen display is a liquid crystal display
(LCD). LCDs are based on blocking light from a separate light
source behind an LCD panel. One type of light emitting flat screen
display is based on light emitting diodes (LEDs). Since light
emitting displays generate light, a separate light source is not
used.
[0002] Light emitting displays include cathode ray tube (CRT),
plasma discharge, thin film electroluminescent, and light emitting
diode (LED) based architectures. The LED's can be either discrete
inorganic (i.e., III-V or II-VI compound semiconductor devices) or
thin film organic diodes. Thin films of organic compounds offer the
potential to realize optoelectronic devices with properties
unattainable with conventional semiconductor materials. Organic
electroluminescent devices are of considerable interest in various
display applications because of their high efficiency and variation
in colors. Using multilayer structures, emitting layers, transport
and luminescent materials, including polymers, and efficient
injection contacts, these organic-based devices can be operated
with a DC voltage as low as a few volts and provide luminous
efficiencies greater than 1 lm/W over a wide spectral range, making
possible the fabrication of a full-color display panel.
[0003] Organic light emitting material recombines a hole and an
electron thereby creating a photon of energy in the form of visible
light. Since color displays require a combination of colors, the
organic materials used in light emitting displays need to be
organized and patterned to provide a color element for each pixel.
Conventional patterning techniques such as photoresist techniques
are not applicable to patterning organic materials since the
solvent used in photoresist techniques cannot distinguish between
the resist material and the organic material.
[0004] One method of patterning organic materials is the use of a
shadow mask. The use of shadow masks includes building vertical
columns and depositing the organic material on a substrate from an
angle. Since the material is deposited at an angle, each vertical
column creates a shadow area behind the column that does not
receive the deposited material. Although this method has been used
for integrated circuit fabrication, the use of this method for
large flat screen light emitting displays is impractical since the
vertical columns would lose stability as height increases. In flat
screen displays, the larger the display, the larger the pixel.
Since multiple colors are necessary to create a color display,
multiple shadow masks and several fabrication steps are needed.
Using multiple shadow masks slows down the processing time and
increases the cost of the devices.
SUMMARY OF THE INVENTION
[0005] In accordance with the present invention, an improved method
for selective deposition of an emissive layer in electroluminescent
displays is provided that substantially eliminates or reduces
disadvantages and problems associated with conventional fabrication
techniques.
[0006] According to an embodiment of the present invention, there
is provided a method for forming an emissive layer for an
electroluminescent display that includes positioning a substrate in
spaced relation to a port of a microeffusion cell and transporting
the substrate across the port at a substantially constant rate. The
method then provides for effusing an emissive material from the
port and adhering at least a portion of the emissive material
effused from the port to a defined region of the substrate to form
an emissive strip having a substantially constant width on the
substrate.
[0007] The present invention provides various technical advantages
over conventional fabrication techniques for light emitting
displays. One technical advantage is that the present invention
provides a continuous process for fabricating flat panel displays.
In particular, emissive and other layers are continuously formed.
Another technical advantage is that by using selective deposition
for the emissive layer, any patterning steps are eliminated. This
leads to reduced fabrication time and fewer fabrication processing
steps. Another technical advantage is that manufacturing costs are
reduced as compared to using fabrication techniques such as shadow
masking. Other technical advantages may be readily apparent to one
skilled in the art from the following figures, description, and
claims.
BRIEF DESCRIPTION OF THE DRAWINGS
[0008] For a more complete understanding of the present invention
and the advantages thereof, reference is now made to the following
description taken in conjunction with the accompanying drawings,
wherein like reference numbers represent like parts, in which:
[0009] FIG. 1 illustrates a flat screen display architecture in
accordance with one embodiment of the present invention;
[0010] FIG. 2 illustrates a cross-section through a color element
of the flat screen display architecture of FIG. 1 in accordance
with one embodiment of the present invention;
[0011] FIG. 3 illustrates an apparatus for selective deposition of
an emissive layer for use in an electroluminescent display;
[0012] FIG. 4 illustrates a cross-section of a microeffusion cell
as used in the apparatus of FIG. 3.
[0013] FIG. 5 illustrates vacuum tubes for minimizing cross
contamination between emissive layer strips deposited by the
apparatus of FIG. 3; and
[0014] FIG. 6 is a flow diagram of a method for forming flat panel
electroluminescent displays in accordance with one embodiment of
the present invention.
DETAILED DESCRIPTION OF THE DRAWINGS
[0015] Referring to FIG. 1, a flat panel display is generally
indicated at 10. The flat panel display 10 includes a display grid
12, driver circuits 16 and address circuits 20 for driving the
display grid 12, and display logic 17 for operating the driver
circuits 16 and address circuits 20.
[0016] The display grid 12 includes a plurality of column contacts
14 extending substantially perpendicularly to a plurality of row
contacts 18. An intersection 21 is formed where a column contact 14
intersects a row contact 18. As described in more detail below,
each intersection 21 includes an emissive layer disposed between
the column contact 14 and the row contact 18. Each intersection 21
area together with the corresponding emissive layer forms a color
element 22 that emits light in response to activation of the
intersection 21 by the driver circuits 16 and the address circuits
20.
[0017] Color elements 22 emit light in one of a plurality of
colors. In one embodiment, the plurality of colors includes red,
green, and blue to form an RGB (red-green-blue) display. These
colors alternate such that a group of color elements 22 forms a
pixel 24. In one embodiment, each pixel 24 includes a red color
element 22 to emit light in the red spectrum, a green color element
22 to emit light in the green spectrum, and a blue color element 22
to emit light in the blue spectrum. However, any combination of
color elements 22 may be used. For example, in order to increase
brightness of a particular color element 22, a pixel 24 may have
more than one of the particular color element 22 depending on the
relative brightness of each color element 22. For a particular
display format, a larger panel size translates into a larger pixel
size. However, to improve resolution, smaller pixels may be used.
In one embodiment, each color element 22 in pixel 24 is between 0.5
mm and 1 mm wide. However, the present invention may be used to
fabricate color element sizes in excess of 1 mm wide and less than
0.5 mm.
[0018] Display logic 17 receives and decodes video signals. Driver
circuit 16 activates column contacts 14 based on instructions
received from display logic 17. For display of television and other
video signals, address circuit 20 activates one row contact 18, or
one group of row contacts 18 constituting a pixel 24, at a time.
Address circuit 20 sequentially activates each row in the flat
panel display 10. When a particular column contact 14 and row
contact 18 are activated, a potential is induced across the
intersection of the two contacts and this creates an electrical
current at the intersection. This current causes the emissive layer
within color element 22 at each intersection to emit photons of
light followed by a decay period. Since the photons of light are
emitted by the emissive layer within the color element 22, one of
the contacts, either column contact 14 or row contact 18, should be
optically transparent. In one embodiment, the optically transparent
contact is formed from indium-tin-oxide (ITO). However, any
suitable optically transparent electrically conductive metal oxide
may be used such as zinc oxide.
[0019] Referring to FIG. 2, a cross-section of a color element 22
is illustrated. The flat panel display 10 is supported by an
optically transparent substrate 40. Optically transparent substrate
40 may be any suitable substrate that is transparent in the visible
spectrum including glass and plastic. Each color element 22
includes a hole injector layer 42, a hole transport layer 44, an
emissive layer 46, an electron transport layer 48, and an electron
injector layer 50. A hole injector layer 42 releases holes
(positive charge carriers) in response to an electrical potential
across an intersection 21 between a column contact 14 and a row
contact 18. Positive charge carriers are regions of molecules that
are missing an electron. Hole transport layer 44 transports holes
to the adjacent layer and inhibits the transfer of electrons.
Electron injector layer 50 releases an electron in response to an
electrical potential across an intersection 21 between a column
contact 14 and a row contact 18. Electron transfer layer 48
transports electrons to the adjacent layer and inhibits the
transfer of holes. Emissive layer 46 emits photons of light in a
specified portion of the visible spectrum in response to holes
combining with electrons.
[0020] Column contacts 14 are disposed on substrate 40. In one
embodiment, column contact 14 comprises a hole injector layer 42
formed from an optically transparent metal oxide such as ITO. In
addition, hole injector layer 42 should be formed from a high work
function metal. A high work function metal typically has a work
function greater than or equal to 4.0 eV. Column contacts 14 are
formed from hole injector layer 42 and function as an anode for
color element 22. The material used to form hole injector layer 42
may be characterized by its ability to release holes in response to
an electrical potential.
[0021] A hole transport layer 44 is disposed on hole injector layer
42. The hole transport layer 44 typically comprises an aromatic
diamine but may be any suitable hole transport material. Aromatic
diamines are characterized by their ability to transport holes, but
not electrons, from one side of an aromatic diamine layer to an
opposite side of the aromatic diamine layer. In addition, aromatic
diamines produce films that are optically smooth and amorphous. An
example of this type of aromatic diamine is triphenyldiamine.
[0022] Emissive layer 46 is disposed on hole transport layer 44.
Emissive layer 46 is formed from a material that can emit a photon
of light in a specified portion of the visible spectrum in response
to activation of a column contact 14 and a row contact 18. In one
embodiment, emissive layer 46 may be formed from a luminescent film
belonging to the class of flourescent metal chelate complexes. An
example of a flourescent metal chelate complex would be
tris(8-hydroxyquinoline)aluminum (ALQ3).
[0023] An electron transport layer 48 is disposed on emissive layer
46. The material used to form electron transport layer 48 may be
characterized by its ability to transport electrons, but not holes,
from one side of a material layer to an opposite side of the
material layer. Electron transport layer 48 may be formed from
oxadiazole derivatives.
[0024] A row contact 18 is disposed on electron transport layer 48.
In one embodiment, row contact 18 is an electron injector layer 50
formed from a magnesium and silver alloy with a ratio of 10 to 1. A
low work function metal should be used. A low work function metal
typically has a work function less than 4.0 eV. However, any
suitable metal may be used. Row contacts 18 are formed from
electron injector layer 50 and function as a cathode for color
element 22.
[0025] In operation, the presence of an electrical current causes
hole injector layer 42 (high work function anode) to inject a hole
that is transported through hole transport layer 44 into emissive
layer 46 where it stops and awaits an electron from electron
injector layer 50. Electron injector layer 50 (low work function
cathode) injects an electron that is transported through electron
transport layer 48 into emissive layer 46. The injected hole and
injected electron meet in a molecule in emissive layer 46 where
they recombine to form a luminescent excited state. The luminescent
excited state releases a photon of light with a quantum efficiency
that is determined by the types of molecules used in the various
layers and the device architecture.
[0026] FIG. 3 illustrates an apparatus for depositing the emissive
layer 46 in accordance with one embodiment of the present
invention. In this embodiment, the emissive layer 46 comprises
discrete red, green, and blue strips to form color display pixels
24. It should be understood that other disparate strips can be
formed in accordance with the present invention.
[0027] Referring to FIG. 3, a bottom view of an apparatus for
selectively depositing emissive layer 46 is generally indicated at
80. The apparatus 80 includes a pressure controlled vacuum
environment 82, a conveyer 84, one or more microeffusion cells 86,
and material source 90 coupled to each microeffusion cell 86.
[0028] Pressure controlled vacuum environment 82 houses conveyer 84
and microeffusion cells 86 and provides for continuous insertion
and removal of the substrate 40 for selective deposition of the
emissive layer 46. As described in further detail below, the vacuum
in pressure controlled vacuum environment 82 facilitates the
selective deposition of the emissive layer 46.
[0029] The conveyor 84 conveys substrate 40 over the one or more
microeffusion cells 86. Microeffusion cells 86 selectively deposit
materials from the coupled source 90 on to the substrate 40 as it
is conveyed across the microeffusion cells. This results in strips
of material being deposited on substrate 40. Although apparatus 80
is used to deposit emissive layer 46, it may be used to deposit any
appropriate materials.
[0030] In one embodiment, three microeffusion cells 86 are used
corresponding to the red, green, and blue color elements 22 of a
pixel 24. Each microeffusion cell 86 is coupled to an appropriate
material source 90 to provide an emissive layer strip for a color
element 22 forming a pixel 24. Each microeffusion cell includes a
plurality of ports 88 through which material is effused onto
substrate 40. The ports 88 in microeffusion cells 86 are offset
from each other to form an appropriate sequence of emissive layer
strips 46. In one embodiment, the sequence of emissive layer strips
46 includes red, followed by green, followed by blue, and repeating
thereafter. The plurality of ports 88 allow all of the color
elements for the electroluminescent display to be continuously
formed in one pass of substrate 40 over the plurality of
microeffusion cells 86.
[0031] Microeffusion cells 86 create thin strips on substrate 40 by
substrate 40 being close to ports 88. These thin strips may be
between 0.5 mm and 1 mm wide. The distance between substrate 40 and
ports 88 may be varied to control deposition of the emissive layer
strips 46. In one embodiment, substrate 40 is conveyed across ports
88 at a distance of approximately 0.2 mm. The distance between
substrate 40 and ports 88 may be varied to alter the width of each
emissive layer strip 46.
[0032] The material in material source 90 may be in the form of a
solid, liquid, or gas. In one embodiment, the material in material
source 90 used to form emissive layer strips 46 is a solid in
powder form. In this embodiment, ports 88 point up to prevent the
powder from being prematurely removed from microeffusion cell 86 by
the force of gravity. Therefore, substrate 40 is attached to the
bottom surface of conveyor 84 such that ports 88 of microeffusion
cells 86 deposit material up through ports 88 onto substrate
40.
[0033] In operation, as substrate 12 is conveyed across the
plurality of microeffusion cells 86, emissive layer strips 46 are
deposited through the plurality of ports 88. The rate of conveyor
84 is initially determined by the effusion rate of vaporized
emissive material from the plurality of microeffusion cells 86 and
by the desired thickness of emissive layer 46. The conveyor rate
may be generally limited by the slowest effusion rate among the
plurality of microeffusion cells 86. Finally, the distance from
substrate 40 to port 88 is initially chosen to provide a certain
width of each emissive layer strip 46. The distance between
substrate 40 and ports 88 may be changed to control the width of
each emissive layer strip 46. In one embodiment, the substrate 40
is less than 0.2 mm from port 88. However, any suitable distance
may be used based on variables such as desired width of emissive
layer strips 46 or desired thickness of emissive layer strips
46.
[0034] The powder material in material source 90 is deposited on
substrate 40 with a sublimation process. When a solid is
sublimated, it is converted directly from the solid state into a
gaseous state. In one embodiment, this conversion is done through
the application of heat in microeffusion cell 86 to the emissive
material. Microeffusion cells 86 are heated to a temperature where
the emissive material is converted into a vapor that is expelled
through ports 88 onto substrate 40. In addition, a pressure
differential between the interior of microeffusion cell 86 and the
pressure controlled vacuum environment 82 causes the vapor to be
pulled from microeffusion cell 86. More specifically, pressure
controlled vacuum environment 82 is a controlled environment
including a carrier gas at a pressure level of 10.sup.-5 to
10.sup.-6 torr. The carrier gas assists in the selective deposition
of the vaporized emissive material through ports 88. In one
embodiment, the carrier gas is argon. The pressure inside
microeffusion cell 86 is greater than the pressure in pressure
controlled vacuum environment 82. Therefore the vaporized emissive
material in microeffusion cell 86 naturally moves towards the area
of low pressure outside port 88.
[0035] In order to facilitate adherence of the vaporized emissive
material to substrate 40, substrate 40 may be heated to a specified
temperature. The temperature is selected so as to maximize the
adherence of the vaporized stream of the emissive material
molecules to the substrate 40. The molecules of vaporized emissive
material that do not adhere to substrate 40 are vacuumed through
vacuum tubes on either side of each port 88 to prevent cross
contamination between adjacent emissive layer strips 46. The vacuum
tubes will be discussed in more detail with relation to FIGS. 4 and
5.
[0036] Various variables may be altered to controlled the selective
deposition process. Initially, the temperature of substrate 40 is
chosen to obtain the best adhesion of the effused material.
However, the temperature of substrate 40 may be altered to change
the amount of the fused material that adheres to substrate 40. The
temperature of each microeffusion cell 86 is chosen to provide a
particular pressure level within the microeffusion cell 86 and to
control the speed at which emissive material is effused from port
88. The microeffusion cell 86 temperature may be altered to change
the effusion characteristics of the microeffusion cell 86.
[0037] Another variable in the selective deposition process is the
size of each port 88. Altering the size of port 88 will alter the
effusion rate and other effusion characteristics of the
microeffusion cell 86. The pressured differential between the
interior of each microeffusion cell 86 and pressure controlled
vacuum environment 82 is initially chosen to provide an optimal
effusion rate for the particular emissive material being effused
from the microeffusion cell 86. Altering the pressure differential
may result in altering the effusion rate and other characteristics
of the selective deposition process. The pressure differential may
be altered by changing the vacuum level of pressure controlled
vacuum environment 82 or altering the temperature of microeffusion
cell 86.
[0038] FIGS. 4 and 5 provide additional details of a microeffusion
cell 86. Referring to FIG. 4, a cross-section of a microeffusion
cell 86 is generally indicated at 100. Microeffusion cell 86
includes a cell wall 102 surrounded by a heater element 104. Since
microeffusion cell 86 generally disperses solid emissive material
in the form of powder through a sublimation process, an apparatus
to evenly distribute the emissive material through microeffusion
cell 86 may be used. In one embodiment, a worm gear 106 is used in
the interior of microeffusion cell 86 to move solid emissive
material in the form of powder through the microeffusion cell 86.
Although the present invention is described using a worm gear 106,
other methods of distributing the solid emissive material through
microeffusion cell 86 may be used including a plunger system, an
air pressure system, an air vacuum system, or any other suitable
means of distributing a solid material in the form of powder
through microeffusion cell 86.
[0039] As previously described, the pressure differential between
the interior of microeffusion cell 86 and the area outside port 88
determines the effusion rate of microeffusion cell 86. Therefore,
the pressure gradient controls the selective deposition of emissive
layer strips 46. If the pressure inside microeffusion cell 86 is
greater than the pressure outside port 88, vaporized emissive
material is effused through port 88 onto substrate 12. If the
pressure inside microeffusion cell 86 is less than the pressure
outside port 88, essentially no emissive material is effused
through port 88. The pressure inside microeffusion cell is a
function of the temperature of the emissive material, the size of
port 88, and the pressure outside port 88. In addition, the
temperature of the emissive material is a function of the heat
applied by heater element 104, the molecule size of the emissive
material, and the strength of the bonds in the emissive
material.
[0040] A vacuum tube 108 exists on either side of port 88 to
capture vaporized emissive material that does not adhere to
substrate 12. Since substrate 12 is moved across port 88, the
vacuum tubes are preferably placed on the sides of port 88 relative
to the emissive layer strip 46 being selectively deposited by port
88. Details regarding the placement of vacuum tubes 108 are
illustrated in FIG. 5.
[0041] FIG. 6 is a flow diagram illustrating a method for
fabricating the flat panel display 10 in accordance with one
embodiment of the present invention. In this embodiment, the flat
panel display 10 is formed by a continuous process using strips of
materials deposited by microeffusion cells 46. Accordingly large,
flat panel displays can be fabricated quickly with minimal expense
and processing steps.
[0042] Referring to FIG. 6, a method for forming an
electroluminescent display commences at step 120 where column
contacts 14 are formed. Column contacts 14 are formed by depositing
a hole injector layer 42 onto an optically transparent substrate
40. Hole injector layer 42 is patterned and etched to form column
contacts 14 orthogonal to a long side of substrate 40. This step
prepares substrate 40 for selective deposition of emissive layer
strips 46 by apparatus 80. Substrate 40 may be a continuous sheet
of material or may be sized according to a size of the desired
electroluminescent display. In either case, the length of substrate
40 is generally greater than its width. Substrate 40 may be further
characterized as having parallel sides to form a generally
rectangular shape. Substrate 40 may be rigid or flexible.
[0043] Hole injector layer 42 is deposited using conventional
deposition techniques such as vapor deposition or chemical vapor
deposition. After depositing hole injector layer 42, hole injector
layer 42 is patterned and etched using conventional techniques to
form column contacts 14. Hole injector layer 42 may be on the order
of 1000 angstroms in thickness. Since this method is used to form a
light emitting display, hole injector layer 42 is preferably formed
from an optically transparent metal such as indium-tin-oxide.
However, any suitable metal may be used. In one embodiment, hole
injector layer 42 is formed from a high work function metal.
[0044] The method proceeds to step 122 where hole transport layer
44 is blanket deposited outwardly from hole injector layer 42. Hole
transport layer 44 may be formed from any suitable material that
allows holes to move from the bottom of hole transport layer 44 to
the top of hole transport layer 44. As previously described, the
material comprising hole transport layer 44 should also inhibit the
passing of free electrons. In one embodiment, hole transport layer
44 is formed from an aromatic diamine such as NPB. Hole transport
layer 44 may also be formed from an organic material. Hole
transport layer 44 may be on the order of 1000 angstroms in
thickness. Although hole transport layer 44 is described as being
blanket deposited over hole injector layer 46, hole transport layer
44 may be patterned such that hole transport layer 44 exists only
over hole injector layer 42.
[0045] The method proceeds to step 124 where emissive layer 46 is
selectively deposited in strips outwardly from hole transport layer
44 by apparatus 80. Substrate 40 is inserted into apparatus 80
where microeffusion cells 86 selectively deposit emissive layer
strips 46. Emissive layer strips 46 are deposited orthogonal to the
column contacts 14 of hole injector layer 46. Selective deposition
of emissive layer strips 46 allows a strip of material to be
continuously deposited along the length of substrate 40 in a
specified area without a separate patterning step and without
contamination of adjacent emissive layer strips 46. Adjacent
emissive layer strips 46 may be separated by a small area
containing no emissive material. In one embodiment, this small area
is on the order of 0.1 mm or less. Emissive layer strips may be on
the order of 500 angstroms in thickness. As previously described,
emissive layer strips 46 may be formed from any suitable material
that emits a photon of light in a particular portion of the visible
spectrum in response to the recombination of a hole and an
electron. In one embodiment, emissive layer strips 46 emit photons
of light in either the red, green, or blue portion of the visible
spectrum in order to form pixels 24 for a flat panel color display.
Emissive layer strips 46 alternate in color in order to form pixels
24.
[0046] The method proceeds to step 126 where electron transport
layer 48 is blanket deposited outwardly from emissive layer strips
46. As previously described, electron transport layer 48 may be
formed from any suitable material that allows free electrons to
pass from the top side of electron transport layer 48 to the bottom
side of electron transport layer 48 while inhibiting the passing of
holes through electron transport layer 48. In one embodiment,
electron transport layer 48 is formed from an oxadiazole
derivative. Electron transport layer 48 may be on the order of
1,000 angstroms in thickness. Although electron transport layer 48
is described as being blanket deposited over emissive layer strips
46, electron transport layer 48 may be patterned or selectively
deposited using apparatus 80 such that electron transport layer 48
only covers emissive layer strips 46.
[0047] The method proceeds to step 128 where row contacts 18 are
formed. Row contacts 18 are formed by depositing, patterning, and
etching an electron injector layer 50. The electron injector layer
50 is deposited, patterned and etched to form row contacts 18
outwardly from electron transport layer 48. Each row contact 18
exists immediately over an emissive layer strip 46. In another
embodiment, electron injector layer 50 is selectively deposited to
form row contacts 18 in a manner similar to the selective
deposition of emissive layer strips 46. As previously described,
electron injector layer 50 may be formed from any suitable low work
function metal including a magnesium and silver alloy. Electron
injector layer 50 may be on the order of 1,000 angstroms in
thickness. The metal comprising electron injector layer 50 need not
be transparent as is the metal comprising hole injector layer 46
since the photon of light emitted by emissive layer strips 46 is
visible through the optically transparent substrate 12.
[0048] Thus, it is apparent that there has been provided in
accordance with the present invention, a method for selective
deposition of an emissive layer in electroluminescent displays that
satisfies the advantage as set forth above such as elimination of a
separate patterning step. Although the present invention and its
advantages have been described In detail, it should be understood
that various changes, substitutions, and alterations may be readily
apparent to those skilled in the art and may be made without
departing from the spirit and the scope of the present invention as
defined by the following claims.
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