U.S. patent application number 09/458488 was filed with the patent office on 2001-08-16 for organic light emitting devices.
Invention is credited to BURROWS, PAUL EDWARD, FORREST, STEPHEN ROSS, MCCARTY, DENNIS MATTHEW, SAPOCHAK, LINDA SUSAN, THOMPSON, MARK EDWARD.
Application Number | 20010014391 09/458488 |
Document ID | / |
Family ID | 23394434 |
Filed Date | 2001-08-16 |
United States Patent
Application |
20010014391 |
Kind Code |
A1 |
FORREST, STEPHEN ROSS ; et
al. |
August 16, 2001 |
ORGANIC LIGHT EMITTING DEVICES
Abstract
A multicolor organic light emitting device employs vertically
stacked layers of double heterostructure devices which are
fabricated from organic compounds. The vertical stacked structure
is formed on a glass base having a transparent coating of ITO or
similar metal to provide a substrate. Deposited on the substrate is
the vertical stacked arrangement of three double heterostructure
devices, each fabricated from a suitable organic material. Stacking
is implemented such that the double heterostructure with the
longest wavelength is on the top of the stack. This constitutes the
device emitting red light on the top with the device having the
shortest wavelength, namely, the device emitting blue light, on the
bottom of the stack. Located between the red and blue device
structures is the green device structure. The devices are
configured as stacked to provide a staircase profile whereby each
device is separated from the other by a thin transparent conductive
contact layer to enable light emanating from each of the devices to
pass through the semitransparent contacts and through the lower
device structures while further enabling each of the devices to
receive a selective bias.
Inventors: |
FORREST, STEPHEN ROSS;
(PRINCETON, NJ) ; THOMPSON, MARK EDWARD; (HAMILTON
SQUARE, NJ) ; BURROWS, PAUL EDWARD; (PRINCETON,
NJ) ; SAPOCHAK, LINDA SUSAN; (FLORHAM PARK, NJ)
; MCCARTY, DENNIS MATTHEW; (SOUTHAMPTON, NJ) |
Correspondence
Address: |
KENYON & KENYON
ONE BROADWAY
NEW YORK
NY
10004
US
|
Family ID: |
23394434 |
Appl. No.: |
09/458488 |
Filed: |
December 9, 1999 |
Related U.S. Patent Documents
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Application
Number |
Filing Date |
Patent Number |
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09458488 |
Dec 9, 1999 |
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08966485 |
Nov 7, 1997 |
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6030700 |
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08966485 |
Nov 7, 1997 |
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08354674 |
Dec 13, 1994 |
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5707745 |
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Current U.S.
Class: |
428/336 ;
257/443; 257/94; 257/96; 257/98; 427/77; 427/78; 428/433; 428/434;
428/457 |
Current CPC
Class: |
H01L 2924/12033
20130101; Y10T 428/26 20150115; H01L 51/0036 20130101; H01L 24/82
20130101; H01L 51/0038 20130101; H01L 2924/12042 20130101; H01L
51/0034 20130101; H01L 27/3209 20130101; H01L 27/156 20130101; H01L
51/0059 20130101; H01L 51/5036 20130101; H01L 51/5234 20130101;
H01L 51/0084 20130101; H01L 2924/12041 20130101; H01L 2924/00
20130101; H01L 2924/00 20130101; H01L 2924/00 20130101; H01L
2924/00 20130101; H01L 51/008 20130101; H01L 51/5012 20130101; H01L
2924/12042 20130101; H01L 2924/12044 20130101; Y10T 428/265
20150115; H01L 51/0077 20130101; H01L 51/5048 20130101; H01L
51/0042 20130101; H01L 2251/5323 20130101; H01L 51/005 20130101;
H01L 51/0051 20130101; H01L 51/0035 20130101; Y10T 428/31678
20150401; H01L 51/0081 20130101; H01L 2924/12044 20130101; H01L
2924/12033 20130101; C09K 11/06 20130101; H01L 2924/12041
20130101 |
Class at
Publication: |
428/336 ; 257/94;
257/98; 257/443; 257/96; 427/77; 427/78; 428/457; 428/433;
428/434 |
International
Class: |
B32B 015/06; H01L
033/00; H01L 031/00 |
Claims
What is claimed is:
1. A multicolor light emitting device (LED) structure, comprising:
a plurality of at least a first and a second light emitting organic
device (LED) stacked one upon the other, to form a layered
structure, with each LED separated one from the other by a
transparent conductive layer to enable each device to receive a
separate bias potential to operate to emit light through the
stack.
2. The multicolor light emitting device structure of claim 1,
wherein each of said LED's emits a different wavelength of light
and therefore a different color when biased.
3. The multicolor light emitting device structure of claim 1,
including at least first through third light emitting devices
stacked upon one another, respectively.
4. The multicolor light emitting diode structure of claim 3,
wherein said first device emits the color blue (B), said second
device emits the color green (G) and third device emits the color
red (R).
5. The multicolor light emitting device structure of claim 4,
wherein said devices are stacked in the following sequence along
the vertical axis starting from a bottom point and directed upward,
wherein the first device emits a blue color, and has the second
device for emitting a green color located on top of the upper
surface of said blue emitting device, with the third device for
emitting a red color located on top of the upper surface of said
green emitting device, whereby said blue emitting device of the
shortest wavelength is at the bottom with the red emitting device
of the longest wavelength on top when the structure is aligned
vertically.
6. The multicolor light emitting device structure of claim 1,
wherein each LED device is a transparent double heterostructure
(DH) device fabricated from organic materials.
7. The multicolor light emitting device structure of claim 1,
wherein each LED device is a transparent single heterostructure
device fabricated from organic materials.
8. The multicolor light emitting device structure of claim 6,
wherein said transparent conductive layer includes indium tin oxide
(ITO).
9. The multicolor light emitting device structure of claim 7,
wherein said transparent conductive layer includes indium tin oxide
(ITO).
10. The multicolor light emitting device structure of claim 3,
wherein said at least first, second, and third organic LED's are
stacked in successive order over a common substrate.
11. The multicolor light emitting device structure of claim 10,
wherein said substrate is at the bottom of said LED structure, and
a topmost layer of said third organic LED included consists of
indium tin oxide (ITO) material serving as a contact for an
underlying metal material layer.
12. The multicolor light emitting device structure of claim 6,
wherein said transparent conductive layer comprises a metallic
layer having a work function less than about four electron volts,
and an ITO layer on said metallic layer.
13. The multicolor light emitting device structure of claim 6,
wherein said organic material is selected from the group consisting
of trivalent metal quinolate complexes, trivalent metal bridged
quinolate complexes, Schiff base divalent metal complexes, tin (iv)
metal complexes, metal acetylacetonate complexes, metal bidentate
ligand complexes, bisphosphonates, divalent metal
maleonitriledithiolate complexes, molecular charge transfer
complexes, aromatic and heterocyclic polymers and rare earth mixed
chelates.
14. The multicolor light emitting device structure of claim 13
wherein the trivalent metal quinolate complexes have the following
formula. 1wherein R is selected from the group consisting of
hydrogen, substituted and unsubstituted alkyl, aryl and a
heterocyclic group, L represents a ligand selected from the group
consisting of picolylmethylketone; substituted and unsubstituted
salicylaldehyde; a group of the formula R(O)CO-- wherein R is as
defined above; halogen; a group of the formula RO-- wherein R is as
defined above; and quinolates and derivatives thereof.
15. The multicolor light emitting device structure of claim 13
wherein the metal bidentate ligand complexes have the following
formula: MDL.sup.4.sub.2 wherein M is selected from trivalent
metals of Groups 3-13 of the Periodic Table and the Lanthanides, D
is a bidentate ligand and L.sup.4 is selected from the group
consisting of acetylacetonate; compounds of the formula OR.sup.3R
wherein R.sup.3 is Si or C and R is selected from the group
consisting of hydrogen, substituted and unsubstituted alkyl, aryl,
a heterocyclic group; 3,5-di(t-bu) phenol; 2,6-di(t-bu) phenol;
2,6-di(t-bu) cresol and a compound of the formula 2
16. The multicolor light emitting device structure of claim 15
wherein D is selected from the group consisting of
2-picolylketones, 2-quinaldylketones and 2-(o-phenoxy)
pyridineketones.
17. The multicolor light emitting device structure of claim 13
wherein the Schiff base divalent metal complexes are selected from
those having the formula 3wherein M.sup.1 is a divalent metal
chosen from Groups 2-12 of the Periodic Table, R.sup.1 is; selected
from the group consisting of 4wherein X is selected from the group
consisting of hydrogen, alkyl, alkoxy each having 1 to 8 carbon
atoms, aryl, a heterocyclic group, phosphino, halogen and
amine.
18. The multicolor light emitting device structure of claim 13
wherein the aromatic and heterocyclic polymers are selected from
the group consisting of poly (para-phenylene vinylene), poly
(dialkoxyphenylene vinylene), poly (thiophene), poly (phenylene),
poly (phenylacetylene) and poly (N-vinylcarbazole).
19. The multicolor light emitting device structure of claim 13
wherein the rare earth mixed chelates comprise a Lanthanide bonded
to a bidentate aromatic or heterocyclic group.
20. The multicolor light emitting device structure of claim 19
wherein the bidentate aromatic or heterocyclic group is selected
from the group consisting of salicylaldehydes and derivatives
thereof, salicyclic acid, quinolates, Schiff base ligands,
acetylacetonates, phenanthroline, bipyridine, quinoline and
pyridine.
21. The multicolor light emitting device structure of claim 19
wherein the divalent metal maleonitriledithiolate complexes have
the formula 5wherein M.sup.3 is a metal having a +2 charge, Y.sup.1
is selected from the group consisting of cyano and substituted and
unsubstituted phenyl, and L.sup.5 is a group having no charge.
22. The multicolor light emitting device structure of claim 21
wherein L.sup.5 is a group of the formula P(OR).sub.3 or P(R).sub.3
wherein R is selected from the group consisting of hydrogen,
substituted and unsubstituted alkyl, aryl and a heterocyclic
group.
23. The multicolor light emitting device structure of claim 13
wherein the bisphosphonates have the formula
M.sup.2.sub.x(O.sub.3P-organic-PO.sub.3)- .sub.y wherein M.sup.2 is
a metal ion and organic represents an aromatic or heterocyclic
fluorescent compound bifunctionalized with phosphonate groups.
24. The multicolor light emitting device structure of claim 13
wherein the trivalent metal bridged quinolate complexes have the
formula 6wherein M is a trivalent metal ion and Z is selected from
SiR or P.dbd.O wherein R is selected from the group consisting of
hydrogen, substituted or unsubstituted alkyl, aryl, or a
heterocyclic group.
25. The multicolor light emitting device structure of claim 13
wherein the tin (iv) metal complexes have the formula
SnL.sup.1.sub.2L.sup.2.sub.2 wherein L.sup.1 is selected from the
group consisting of salicylaldehydes, salicyclic acid, and
quinolates and L.sup.2 is selected from the group consisting of
substituted and unsubstituted alkyl, aryl and a heterocyclic
group.
26. The multicolor light emitting device structure of claim 13
wherein the molecular charge transfer complexes comprise an
electron acceptor complexed with an electron donor.
27. The multicolor light emitting device structure of claim 1,
wherein said devices are stacked in an order dependent upon and in
accordance with their respective emission wavelength and absorption
characteristics.
28. The multicolor light emitting device of claim 2, wherein the
longest wavelength LED is on top of the stack in the vertical
direction followed by successively shorter wavelength LED's, with
the shortest wavelength LED on the bottom of the stack.
29. A multicolor light emitting device structure, comprising: a
transparent substrate layer having deposited on a surface a first
transparent conductive coating; a first light emitting device
deposited on said first transparent conductive coating; a second
transparent conductive coating deposited on the surface of said
first device not in contact with said first coating; a second light
emitting device deposited on the surface of said second coating; a
third transparent conductive coating deposited on the surface of
said second device not in contact with said second coating; a third
light emitting device deposited on the surface of said third
coating; and a further conductive coating deposited on the surface
of said third device not in contact with said third coating.
30. The multicolor light emitting device structure of claim 29,
wherein said first, second, third and fourth conductive coatings
are adapted to receive individual sources of biasing potential,
respectively.
31. The multicolor light emitting device structure of claim 29,
wherein said devices and conductive layers are deposited to form a
staircase profile, with said transparent substrate being of a
greater length than said first device, with said first device being
of a greater length than said second device, with said second
device of a greater length than said third device, wherein each
step is covered by said respective conductive coating adapted for
applying operating potentials to said device structures, and
wherein said first through third transparent conductive coatings
allow light emitted by any of said devices, respectively, to pass
through said transparent substrate layer.
32. The multicolor light emitting device structure of claim 29,
wherein said further conductive coating, includes a third metal
that reflects upward directed light back to said substrate.
33. The multicolor light emitting device structure of claim 32,
wherein said further conductive coating further includes a
relatively thin indium tin oxide (ITO) layer between said thick
metal and said surface of said third device not in contact with
said third coating, said ITO layer serving as a contact for an
underlying metal material layer of said third light emitting diode
device.
34. The multicolor light emitting device structure of claim 29,
wherein said transparent substrate is glass, said first conductive
coating is indium tin oxide (ITO), and each of said second, third
and further conductive coatings are comprised of an ITO layer
disposed on a low work function metal layer.
35. The multicolor light emitting device structure of claim 29,
wherein each of said devices are double heterostructures (DH), with
said first device operative when biased to emit blue light (B),
said second device operative when biased to emit green light (G),
said third device operative when biased to emit red light (R).
36. The multicolor light emitting device structure of claim 35,
wherein each DH structure is comprised of organic compounds.
37. The multicolor light emitting device structure of claim 29,
wherein each of said devices are single heterostructures (SH), with
said first device operative when biased to emit blue light (B),
said second device operative when biased to emit green light (G),
and said third device operative when biased to emit red light
(R).
38. The multicolor light emitting device structure of claim 29,
wherein each of said devices are polymer structures, with said
first device operative when biased to emit blue light (B), said
second device operative when biased to emit green light (G), and
said third device operative when biased to emit red light (R).
39. A multicolor display, comprising: a plurality of multicolor
light emitting device pixel structures arranged in rows and columns
to provide a display surface with each pixel structure consisting
of at least one multicolor light emitting device structure wherein
each device structure comprises first, second and third light
emitting devices (LED's) stacked one upon the other to form a
layered structure, with each LED separated by a transparent
conductive layer, and whereby said display can be biased via said
conductive layers to cause said multicolor light emitting devices
to emit light when biased.
40. The multicolor display of claim 39, wherein said first LED
emits blue light (B), said second LED emits green light (G) and
said third LED emits red light (R).
41. The multicolor display of claim 39, wherein each LED device is
a double heterostructure (DH) device capable of emitting light as a
function of an organic compound employed in said device.
42. The multicolor display of claim 39, wherein each of said LED
devices is a single heterostructure (SH) device capable of emitting
light as a function of an organic compound employed in said
device.
43. The multicolor display of claim 39, wherein each of said LED
devices is polymer structured device capable of emitting light as a
function of an organic compound employed in said device.
44. The display of claim 39, wherein said plurality of multicolor
device structures as arranged in rows and columns on a glass
substrate coated with a thin transparent layer of ITO and with each
of said first, second and third LED devices of each pixel stacked
on said substrate to form a separate pixel location.
45. A method of fabricating a multicolor light emitting device
(LED) structure comprising the steps of: forming a first
transparent conductive layer upon a transparent substrate;
depositing a first hole transporting layer upon said first
transparent conductive layer; depositing a first organic emission
layer upon said first hole transporting layer to provide a first
emission color; depositing a first electron transporting layer upon
said first emission layer; depositing a second transparent
conductive layer upon said first electron transporting layer, said
second transparent conductive layer adapted to receive a first bias
potential; depositing a second hole transporting layer upon said
second transparent conductive layer; depositing a second organic
emission layer upon said second hole transporting layer to provide
a second emission color; depositing a second electron transporting
layer upon said second emission layer; and depositing a third
transparent conductive layer upon said second electron transporting
layer, said third transparent conductive layer adapted to receive a
second bias potential.
46. The method of claim 45, further including the step of shadow
masking a region of said first transparent conductive layer prior
to depositing said first hole transporting layer to expose said
region of said first transparent conductive layer thereby enabling
said first bias potential to be applied between said second
transparent conductive layer and said region of said first
transparent conductive layer.
47. The method of claim 45, further including the step of etching
away a region of said first hole transporting layer to expose a
portion of said first transparent conductive layer thereby enabling
said first bias potential to be applied between said second
transparent conductive layer and said exposed portion of said first
transparent conductive layer.
48. A method of fabricating a hermetically packaged multicolor
light emitting device (LED), comprising the steps of: forming a
first transparent conductive layer upon a transparent substrate;
masking said first conductive layer for depositing an SiO.sub.2
layer thereupon in a concentric pattern; forming on a portion of
said first SiO.sub.2 layer at least one multicolor LED, each
including at least a first and a second organic light emitting
devices (LED's) stacked one upon the other to form a layered
structure upon said first SiO.sub.2 layer; depositing via shadow
masking a plurality of metal contacts or circuit paths each having
one end terminating near an outer edge of said first SiO.sub.2
layer, and each having another end terminating on an individual
biasing electrode of said at least one multicolor LED; depositing
via shadow masking a second SiO.sub.2 layer as a ring concentric
with said first SiO.sub.2 layer and over outer portions of said
plurality of metal contacts but leaving exposed said one ends
thereof; depositing a ring of low temperature melting solder over
and concentric with said second SiO.sub.2 ring; depositing on the
bottom of a cover glass a metal ring positioned to be coincident
with said ring of solder; installing said cover glass over said
substrate and at least one multicolor LED, with said ring of solder
abutting against said metal ring on said cover glass; placing said
assembly in an inert gas atmosphere; and heating said ring of
solder to melt the solder for both forming an air tight seal, and
entrapping said inert gas in an interior region between the bottom
of said cover glass and underlying substrate.
49. The method of claim 48, wherein said multicolor LED forming
step further includes forming a plurality of multicolor LED devices
on said first SiO.sub.2 layer.
50. The method of claim 48, wherein said inert gas includes dry
nitrogen.
51. The method of claim 48, wherein said first transparent layer
includes indium tin oxide (ITO).
52. The method of claim 51, further including the step of
depositing a metal contact proximate an edge of and upon said ITO
layer for serving as a cathode electrode.
53. The method of claim 49, further including the step of
depositing a metal contact proximate an edge and upon said first
transparent conductive layer for serving as a cathode
electrode.
54. The method of claim 53, wherein said first transparent
conductive layer includes indium tin oxide (ITO).
55. A multicolor, energizable, light emitting structure,
comprising: at least three layers of conductive material; a
transparent, energizable, light emitting device (LED) disposed
between adjacent ones of said layers of conductive material,
respectively, so that said LEDs are stacked on each other with one
of said layers of conductive material disposed between each two of
said LEDs and the other layers of conductive material are disposed
on the outside of said LEDs; said layers of conductive material
disposed between adjacent ones of said LEDs and one of said outside
layers being substantially transparent; and means on each of said
layers of conductive material for being connected to a bias for
selectively energizing each of said LEDs.
56. The structure of claim 55, wherein each of said LEDs emits a
different color.
57. The structure of claim 56, wherein said LEDs are stacked in a
vertical array.
58. The structure of claim 57, further including: a third LED in
said stack; the middle one of said LEDs being operative to emit
light of a predetermined wavelength; one of the other LEDs being
operative to emit light of a longer wavelength; and the lowest LED
being operative to emit light of a shorter wavelength.
59. The structure of claim 57, further including: a transparent
substrate; said stack of LEDs and layers of conductive material
being supported by said transparent substrate in an order that
corresponds to the length of the light wave that said LEDs emit;
and said LED emitting the shortest wavelength is closest to said
transparent substrate so that the light emitted from each of said
LEDs when it is energized is transmitted through the other LEDs and
through said transparent substrate.
60. The structure of claim 59, further including: a layer of
anti-reflecting material disposed between said LED emitting the
shortest wavelength and said transparent substrate so that the
light emitted from each of said LEDs when it is energized is not
reflected from said transparent substrate.
61. The structure of claim 59, further including: a layer of
reflective material adjacent said LED emitting the longest
wavelength for reflecting light emitted from said LED back through
said substrate.
62. The structure of claim 55, wherein said layer of conductive
material includes indium-tin-oxide (ITO) and a metal.
63. The structure of claim 62, wherein said metal has a work
function of less than four electron volts.
64. The structure of claim 55, further including: a transparent
substrate; said stack of LEDs and layers of conductive material
being supported by said transparent substrate in an order that
corresponds to the length of the light wave that said LEDs emit;
and said LED emitting the shortest wavelength is closest to said
transparent substrate so that the light emitted from each of said
LEDs when it is energized is transmitted through the other LED and
through said transparent substrate with substantially reduced
absorption.
65. The structure of claim 64, further including: a layer of
anti-reflecting material disposed between said LED emitting the
shortest wavelength and said transparent substrate so that the
light emitted from each of said LEDs when it is energized is not
reflected from said transparent substrate.
66. The structure of claim 64, wherein said layer of conductive
material includes indium-tin-oxide (ITO) and a metal.
67. The structure of claim 66, wherein said metal has a work
function of less than four electron volts.
68. The structure of claim 64, further including: a layer of
reflective material adjacent said LED emitting the longest
wavelength for reflecting light emitted from said LED back through
said substrate.
69. The structure of claim 55, wherein each of said LEDs is a
double heterostructure.
70. The structure of claim 55, wherein each of said LEDs is a
single heterostructure.
71. An energizable, light emitting structure, comprising: a
transparent substrate; a first layer of substantially transparent,
electrically conductive material supported on said substrate; a
transparent, energizable, light emitting device (LED) supported on
said first layer of substantially transparent, electrically
conductive material, said LED including an emission layer; a second
layer of electrically conductive material supported by said LED;
and said LED being operative to produce light and transmit it
through said transparent substrate when energized.
72. The structure of claim 71, wherein said first and second layers
comprise indium-tin-oxide.
73. The structure of claim 72, wherein said second layer further
comprises a layer of metal that has a work function that is less
than four electron volts.
74. The structure of claim 73, wherein said metal is from the group
consisting of magnesium, arsenic and magnesium/gold alloy.
75. The structure of claim 71, further including: said second layer
of electrically conductive material being substantially
transparent; a second transparent, energizable, light emitting
device (LED) supported on said second layer of electrically
conductive material, said second LED including an emission layer; a
third layer of electrically conductive material supported by said
second LED; and said second LED being operative to produce light
and transmit it through said first LED and through said transparent
substrate when energized.
76. The energizable light emitting structure of claim 71, wherein
said emission layer includes at least one material is selected from
the group consisting of trivalent metal quinolate complexes,
trivalent metal bridged quinolate complexes, Schiff base divalent
metal complexes, tin (iv) metal complexes, metal acetylacetonate
complexes, metal bidentate ligand complexes, bisphosphonates,
divalent metal maleonitriledithiolate complexes, molecular charge
transfer complexes, aromatic and heterocyclic polymers and rare
earth mixed chelates.
77. A multicolor, energizable, light emitting display comprising: a
plurality of energizable, light emitting structures; each of said
structures comprising a plurality of transparent, light emitting
devices (LED) that are stacked on each other; each of said LEDs in
each of said structures being operative to emit a different color
light when energized; and means for selectively energizing at least
one of said LEDs in each of said structures so that the color
produced by each of said light: emitting structures is determined
by which LED or LEDs in each light emitting structure is energized
so that light emitted from said structures creates an image having
a predetermined shape and color.
78. The display of claim 77, wherein said energizable, light
emitting structures are arranged in an array, said array including
at least two axes, and each of said light emitting structures is at
the intersection of at least two of said axes.
79. The display of claim 78, wherein said axes define a horizontal
axis and a vertical axis.
80. The display of claim 78, wherein said means for selectively
energizing at least one of said LEDs in each of said structures
includes: means for selecting the structures and the LEDs in those
structures -to be energized; and means for serially scanning each
of said axes so that said means for selectively energizing at least
one of said LEDs scans along said axes so that said selected ones
of said LEDS at the intersection of said axes are serially
energized to emit light so that said image and said colors are
created serially.
81. The display of claim 77, wherein said means for selectively
energizing at least one of said LEDs in each of said structures
includes: means for substantially serially energizing said LEDs
that are in said structures so that said image and said colors are
created serially by said structures.
82. The display of claim 77, wherein said for means for selectively
energizing said LEDs is operative to simultaneously energize
selected ones of said LEDs in selected ones of said structures so
that said image and said colors are created simultaneously by said
selected ones of said LEDs in said selected ones of said
structures.
83. The display of claim 77, wherein each of said structures
further includes: a transparent substrate; said LEDs each having a
bottom and a top and defining a stack of LEDs having a bottom and a
top, said stack being supported on said transparent substrate; a
first layer of substantially transparent, electrically conductive
material, said first layer being disposed between said bottom LED
and said transparent substrate; at least one second layer of
substantially transparent, electrically conductive material, said
second layers being disposed between adjacent ones of said LEDs; a
first layer of electrically conductive material, said first layer
being disposed adjacent the top of said top LED; and means on each
of said layers of electrically conductive material for being
connected to a bias for selectively energizing each of said
LEDs.
84. The display of claim 83, wherein each of said layers of
substantially transparent, electrically conductive material and
said layer of electrically conductive material includes a layer of
indium-tin-oxide.
85. The display of claim 83, wherein each of said layers of
substantially transparent, electrically conductive material, and
said layer of electrically conductive material, includes a layer of
metal and a layer of indium-tin-oxide.
86. The display of claim 85, wherein said metal has a work function
of less than about four electron volts.
87. The display of claim 83, further including: a layer of
reflective material disposed on the layer of electrically
conductive material adjacent the top of said top LED so that light
from said LEDs is reflected through said transparent substrate by
said layer of reflective material.
88. The display of claim 87, further including: said stack of LEDs
is supported by said transparent substrate in an order that
corresponds to the wavelength of the light that said LEDs emit; and
said LED emitting the shortest wavelength is closest to said
transparent substrate so that the light emitted from each of said
LEDs when it is energized is transmitted through the other LEDs and
through said transparent substrate.
89. The display of claim 88, further including a layer of
anti-reflecting material disposed between said LED emitting the
shortest wavelength and said transparent substrate so that the
light emitted from each of said LEDs when it is energized is not
reflected from said transparent substrate.
90. The display of claim 77, further including: a transparent
substrate; each of said LEDs having a top and a bottom; at least
two layers of substantially transparent, electrically conductive
material, one of said layers being disposed on said transparent
substrate; the bottom of one of said LEDs in each of said
structures being supported on said one layer of substantially
transparent, electrically conductive material; the others of said
layers of substantially transparent, electrically conductive
material being disposed between the remainder of said LEDs so that
said LEDs define a stack; a layer of electrically conductive
material supported on the top of said LED in said stack that is
furthest from said transparent substrate; and means on each of said
layers of substantially transparent, electrically conductive
material and on said layer electrically conductive material for
being connected to a bias for selectively energizing each of said
LEDs.
91. The display of claim 90, wherein each of said layers of
substantially transparent, electrically conductive material, and
said layer of electrically conductive material include a layer of
indium-tin-oxide.
92. The display of claim 90, wherein said layers of substantially
transparent, electrically conductive material and each of said
layers of electrically conductive material include a layer of metal
and a layer of indium-tin-oxide.
93. The display of claim 92, wherein said metal has a work function
of less than about four electron volts.
94. The display of claim 90, further including: a layer of
reflective material disposed on said layer of substantially
transparent, electrically conductive material adjacent the top of
said top LED so that light is reflected through said transparent
substrate by said layer of reflective material.
95. The structure of claim 94, wherein said stack of LEDs is
supported by said transparent substrate in an order that
corresponds to the wavelength of the light that said LEDs emit, and
said LED emitting the shortest wavelength is closest to said
transparent substrate so that the light emitted from each of said
LEDs when it is energized is transmitted through the other LEDs and
through said transparent substrate.
96. The structure of claim 95, further including: a layer of
anti-reflecting material disposed between said LED emitting the
shortest wavelength and said transparent substrate so that the
light emitted from each of said LEDs when it is energized is not
reflected from said transparent substrate.
97. The display of claim 77, wherein said plurality of LED's
include: three LEDs; each of said LEDs being a double
heterostructure (DH); said LED closest to said transparent
substrate being operative when energized to emit blue light; said
LED furthest from said transparent substrate being operative when
energized to emit red light; and said other LED being operative
when energized to emit green light.
98. The multicolor light emitting display of claim 97, wherein each
of said LEDs includes an emission layer containing an organic
material selected from the group consisting of trivalent metal
quinolate complexes, trivalent metal bridged quinolate complexes,
Schiff base divalent metal complexes, tin (iv) metal complexes,
metal acetylacetonate complexes, metal bidentate ligand complexes,
bisphosphonates, divalent metal maleonitriledithiolate complexes,
molecular charge transfer complexes, aromatic and heterocyclic
polymers and rare earth mixed chelates.
99. The display of claim 77, wherein said plurality of LED's
include: three LEDs; each of said LEDs being single
heterostructures (SH); said LED closest to said transparent
substrate being operative when energized to emit blue light; said
LED furthest from said transparent substrate being operative when
energized to emit red light; and said other LED being operative
when energized to emit green light.
100. The multicolor light emitting display of claim 99, wherein
each of said LEDs includes an emission layer containing an organic
material selected from the group consisting of trivalent metal
quiniolate complexes, trivalent metal bridged quinolate complexes,
Schiff base divalent metal complexes, tin (iv) metal complexes,
metal acetylacetonate complexes, metal bidentate ligand complexes,
bisphosphonates, divalent metal maleonitriledithiolate complexes,
molecular charge transfer complexes, aromatic and heterocyclic
polymers and rare earth mixed chelates.
101. A method of fabricating a multicolor, energizable light
emitting structure, comprising the steps of: providing a
transparent substrate; providing a first substantially transparent
electrically conductive layer on said transparent substrate;
providing a first transparent, light emitting diode (LED) on said
substrate, said first LED being operable when energized to emit a
light of a first predetermined wavelength; providing a second
substantially transparent, electrically conductive layer on said
first LED; providing a second transparent, light emitting diode
(LED) on said second substantially transparent, electrically
conductive layer, said second LED being operable when energized to
emit a light of a second predetermined wavelength, that is longer
than said first predetermined wavelength; and an electrically
conductive layer on said second (LED).
102. A method as in claim 101, wherein said steps of providing said
first and second LEDs comprises the steps of forming each of said
LEDs by; depositing a hole transporting layer on said first and
second substantially transparent, electrically conductive layers;
depositing an emission layer on each of said hole transporting
layers; and depositing an electron transporting layer on each of
said emission layers.
103. The method of claim 102, wherein each of said emission layers
includes a material selected from the group consisting of trivalent
metal quinolate complexes, trivalent metal bridged quinolate
complexes, Schiff base divalent metal complexes, tin (iv) metal
complexes, metal acetylacetonate complexes, metal bidentate ligand
complexes, bisphosphonates, divalent metal maleon~itriledithiolate
complexes, molecular charge transfer complexes, aromatic and
heterocyclic polymers and rare earth mixed chelates.
104. A method as in claim 103, wherein each of said substantially
transparent electrically conductive layers and said layer of
electrically conductive layer are comprised of
indium-tin-oxide.
105. A method as in claim 102, further including: the step of
providing a layer of substantially transparent metal between said
LEDs; and a layer of said substantially transparent electrically
conductive material on each of said layers of substantially
transparent metal.
106. A method as in claim 105, wherein said metal has a work
function of less than about four electron volts.
107. A method as in claim 105, wherein said metal is from the group
consisting of magnesium, arsenic and magnesium/gold alloy.
108. A method as in claim 101, wherein said layer of electrically
conductive material has a reflective surface for reflecting light
emitted from said LEDs through said transparent substrate.
109. A method as in claim 101, further including the step of:
providing an electrical contact on each of said layers of
substantially transparent, electrically conductive material, and on
said layer of electrically conductive material so that each of said
layers can be connected to a source of bias potential.
110. A transparent energizable, light emitting device (LED),
comprising: an emission layer, a hole transporting layer and an
electron transporting layer; said emission layer being disposed
between said hole transporting layer and said electron transporting
layer; a first layer of substantially transparent electrically
conductive material, and a second layer of electrically conductive
material, said first layer being on said hole transporting layer,
said second layer being on said electron transporting layer; and
said emission layer consists of material selected from the group
consisting of trivalent metal quinolate complexes, trivalent metal
bridged quinolate complexes, Schiff base divalent metal complexes,
tin (iv) metal complexes, metal acetylacetonate complexes, metal
bidentate ligand complexes, bisphosphonates, divalent metal
maleonitriledithiolate complexes, molecular charge transfer
complexes, aromatic and heterocyclic polymers and rare earth mixed
chelates.
111. The device of claim 110, wherein said emission layer is no
more than about 200 .ANG. thick; said hole transporting layer is no
more than about 1000 .ANG. thick; and said electron transporting
layer is no more than about 1000 .ANG. thick.
Description
FIELD OF THE INVENTION
[0001] This invention relates to multicolor organic light emitting
devices and more particularly to such devices for use in flat panel
electronic displays.
BACKGROUND OF THE INVENTION
[0002] The electronic display is an indispensable way in modern
society to deliver information and is utilized in television sets,
computer terminals and in a host of other applications. No other
medium offers its speed, versatility and interactivity. Known
display technologies include plasma displays, light emitting diodes
(LEDs), thin film electroluminescent displays, and so forth.
[0003] The primary non-emissive technology makes use of the electro
optic properties of a class of organic molecules known as liquid
crystals (LCs) or liquid crystal displays (LCDs). LCDs operate
fairly reliably but have relatively low contrast and resolution,
and require high power backlighting. Active matrix displays employ
an array of transistors, each capable of activating a single LC
pixel. There is no doubt that the technology concerning flat panel
displays is of a significant concern and progress is continuously
being made. See an article entitled "Flat Panel Displays",
Scientific American, March 1993, pgs. 90-97 by S. W. Depp and W. E.
Howard. In that article, it is indicated that by 1995 flat panel
displays alone are expected to form a market of between 4 and 5
billion dollars. Desirable factors for any display technology is
the ability to provide a high resolution full color display at good
light level and at competitive pricing.
[0004] Color displays operate with the three primary colors red
(R), green (G) and blue (B). There has been considerable progress
in demonstrating red, green and blue light emitting devices (LEDs)
using organic thin film materials. These thin film materials are
deposited under high vacuum conditions. Such techniques have been
developed in numerous places throughout the world and this
technology is being worked on in many research facilities.
[0005] Presently, the most favored high efficiency organic emissive
structure is referred to as the double heterostructure LED which is
shown in FIG. 1A and designated as prior art. This structure is
very similar to conventional, inorganic LED's using materials as
GaAs or InP.
[0006] In the device shown in FIG. 1A, a support layer of glass 10
is coated by a thin layer of Indium Tin Oxide (ITO) 11 which layers
10 and 11 form the substrate 8. Next, a thin (100-500 .ANG.)
organic, predominantly hole transporting layer (HTL) 12 is
deposited on the ITO layer 11. Deposited on the surface of HTL
layer 12 is a thin (typically, 50 .ANG.-100 .ANG.) emission layer
(EL) 13. If the layers are too thin there may be lack of continuity
in the film, and thicker films tend to have a high internal
resistance requiring higher power operation. Emissive layer (EL) 13
provides the recombination site for electrons injected from a
100-500 .ANG. thick electron transporting layer 14 (ETL) with holes
from the HTL layer 12. The ETL material is characterized by its
considerably higher electron than hole mobility. Examples of prior
art ETL, EL and HTL materials are disclosed in U.S. Pat. No.
5,294,870 entitled "Organic Electroluminescent MultiColor Image
Display Device", issued on Mar. 15, 1994 to Tang et al.
[0007] Often, the EL layer 13 is doped with a highly fluorescent
dye to tune color and increase the electroluminescent efficiency of
the LED. The device as shown in FIG. 1A is completed by depositing
metal contacts 15, 16 and top electrode 17. Contacts 15 and 16 are
typically fabricated from indium or Ti/Pt/Au. Electrode 17 is often
a dual layer structure consisting of an alloy such as Mg/Ag 17'
directly contacting the organic ETL layer 14, and a thick, high
work function metal layer 17" such as gold (Au) or silver (Ag) on
the Mg/Ag. The thick metal 17" is opaque. When proper bias voltage
is applied between top electrode 17 and contacts 15 and 16, light
emission occurs through the glass substrate 10. An LED device of
FIG. 1A typically has luminescent external quantum efficiencies of
from 0.05 percent to 4 percent depending on the color of emission
and its structure.
[0008] Another known organic emissive structure referred as a
single heterostructure is shown in FIG. 1B and designated as prior
art. The difference in this structure relative to that of FIG. 1A,
is that the EL layer 13 serves also as an ETL layer, eliminating
the ETL layer 14 of FIG. 1A. However, the device of FIG. 1B, for
efficient operation, must incorporate an EL layer 13 having good
electron transport capability, otherwise a separate ETL layer 14
must be included as shown for the device of FIG. 1A.
[0009] Presently, the highest efficiencies have been observed in
green LED's. Furthermore, drive voltages of 3 to 10 volts have been
achieved. These early and very promising demonstrations have used
amorphous or highly polycrystalline organic layers. These
structures undoubtedly limit the charge carrier mobility across the
film which, in turn, limits current and increases drive voltage.
Migration and growth of crystallites arising from the
polycrystalline state is a pronounced failure mode of such devices.
Electrode contact degradation is also a pronounced failure
mechanism.
[0010] Yet another known LED device is shown in FIG. 1C,
illustrating a typical cross sectional view of a single layer
(polymer) LED. As shown, the device includes a glass support layer
1, coated by a thin ITO layer 3, for forming the base substrate. A
thin organic layer 5 of spin-coated polymer, for example, is formed
over ITO layer 3, and provides all of the functions of the HTL,
ETL, and EL layers of the previously described devices. A metal
electrode layer 6 is formed over organic layer 5. The metal is
typically Mg, Ca, or other conventionally used metals.
[0011] An example of a multicolor electroluminescent image display
device employing organic compounds for light emitting pixels is
disclosed in Tang et al., U.S. Pat. No. 5,294,870. This patent
discloses a plurality of light emitting pixels which contain an
organic medium for emitting blue light in blue-emitting subpixel
regions. Fluorescent media are laterally spaced from the
blue-emitting subpixel region. The fluorescent media absorb light
emitted by the organic medium and emit red and green light in
different subpixel regions. The use of materials doped with
fluorescent dyes to emit green or red on absorption of blue light
from the blue subpixel region is less efficient than direct
formation via green or red LED'S. The reason is that the efficiency
will be the product of (quantum efficiency for EL)*(quantum
efficiency for fluorescence)*(1-transmittance). Thus a drawback of
this display is that different laterally spaced subpixel regions
are required for each color emitted.
SUMMARY OF THE INVENTION
[0012] It is an object of the present invention to provide a
multicolor organic light emitting device employing several types of
organic electroluminescent media, each for emitting a distinct
color.
[0013] It is a further object of this invention to provide such a
device in a high definition multicolor display in which the organic
media are arranged in a stacked configuration such that any color
can be emitted from a common region of the display.
[0014] It is another object of the present invention to provide a
three color organic light emitting device which is extremely
reliable and relatively inexpensive to produce.
[0015] It is a further object to provide such a device which is
implemented by the growth of organic materials similar to those
materials used in electroluminescent diodes, to obtain an organic
LED which is highly reliable, compact, efficient and requires low
drive voltages for utilization in RGB displays.
[0016] In one embodiment of the invention, a multicolor light
emitting device (LED) structure comprises at least a first and a
second organic LED stacked one upon the other, and preferably
three, to form a layered structure, with each LED separated one
from the other by a transparent conductive layer to enable each
device to receive a separate bias potential to emit light through
the stack.
BRIEF DESCRIPTION OF THE DRAWINGS
[0017] FIG. 1A is a cross sectional view of a typical organic
double heterostructure light emitting device (LED) according to the
prior art.
[0018] FIG. 1B is a cross sectional view of a typical organic
single heterostructure light emitting device (LED) according to the
prior art.
[0019] FIG. 1C is a cross sectional view of a known single layer
polymer LED structure according to the prior art.
[0020] FIGS. 2A, 2B, and 2C are cross sectional views of an
integrated three color pixel utilizing crystalline organic light
emitting devices (LED's), respectively, according to embodiments of
this invention, respectively.
[0021] FIGS. 3-11 show a variety of organic compounds which may be
used to comprise the active emission layers for generating the
various colors.
[0022] FIGS. 12(A-E) illustrate a shadow masking process for the
fabrication of the multicolor LED according to the invention.
[0023] FIGS. 13(A-F) illustrate a dry etching process for the
fabrication of the multicolor LED according to the invention.
[0024] FIG. 14A shows a multicolor LED of one embodiment of this
invention configured for facilitating packaging thereof.
[0025] FIG. 14B shows a cross sectional view of a hermetic package
for another embodiment of the invention.
[0026] FIG. 14C is cross sectional view taken along 14C-14C of FIG.
14B.
[0027] FIG. 15 is a block diagram showing an RGB display utilizing
LED devices according to this invention together with display drive
circuitry.
[0028] FIG. 16 shows an LED device of another embodiment of the
invention extending the number of stacked LED's to N, where N is an
integer number 1, 2, 3, . . . N.
DETAILED DESCRIPTION OF THE INVENTION
[0029] FIG. 1A has been described and is a prior art double
heterostructure organic light emitting device. The basic
construction of the device of FIG. 1A is used in this invention as
will be described.
[0030] Referring to FIG. 2A, there is shown a schematic cross
section of a highly compact, integrated RGB pixel structure which
is implemented by grown or vacuum deposited organic layers, in one
embodiment of the invention. Based on the ability to grow organic
materials on a large variety of materials (including metals and
ITO), one can construct a stack of LED double heterostructures;
(DH) designated as 20, 21 and 22, in one embodiment of the
invention. For illustrative purposes, LED 20 is considered in a
bottom portion of the stack, LED 21 in a middle portion of the
stack, and LED 22 in a top portion of the stack, in the example of
FIG. 2A. Also, the stack is shown to be vertically oriented in FIG.
2A, but the LED can be otherwise oriented. In other embodiments, a
stack of single heterostructure (SH) LED's (see FIG. 1B), or a
stack of polymer-based LED devices (see FIG. 1C), are viable
alternatives to the DH LED's, with the SH devices being equally
viable as DH devices for light emitters. Also, SH and DH devices
comprising a combination of vacuum deposited and polymeric
light-emitting materials are considered to be within the spirit and
scope of this invention.
[0031] Each device structure as device 20, consists of an HTL layer
20H vacuum-deposited or grown on or otherwise deposited onto the
surface of an ITO layer 35. A top ETL layer 20T sandwiches an EL
layer 20E between the former and HTL layer 20H, for example, shown
in the device construction of FIG. 2A. The ETL layer 20T and other
ETL layers to be described are composed of organic materials such
as M(8-hydroxyquinolate), (M=metal ion; n=2-4). Examples of other
suitable organic ETL materials can be found in U.S. Pat. No.
5,294,870 to Tang et al. Formed on top of ETL layer 20T is a thin,
semi-transparent low work function (preferably, <4 eV) metal
layer 26M having a thickness typically less than 50 .ANG.. suitable
candidates include Mg, Mg/Ag, and As. Deposited on the top of metal
layer 26M is another transparent, thin conductive ITO layer 26I.
(For convenience herein, the double layer structure of metallic
layer 26M and ITO layer 26I is referred to as ITO/metal layers 26.)
Each of the double heterostructure devices as 20, 21 and 22 have a
bottom HTL layer formed on a transparent conductive layer of ITO
26I or 35. Next an EL layer is deposited and then another layer of
ETL. Each of the HTL, ETL, ITO, metal and organic EL layers are
transparent because of their composition and minimal thickness.
Each HTL layer may be 50-1000 .ANG. thick; each EL layer may be
50-200 .ANG. thick; each ETL layer may be 50-1000 .ANG. thick; each
metal layer 26M may be 50-100 .ANG. thick; and each ITO layer 26I
and 35 may be 1000-4000 .ANG. thick. For optimum performance, each
of the layers should preferably be kept towards the lower ends of
the above ranges. Thus, each LED 20, 21 and 22 (excluding ITO/metal
layers) are preferably close to 200 .ANG. thick.
[0032] If SH LED devices are used for providing LED's 20, 21, 22,
rather than DH LED devices, the ETL and EL layers are provided by a
single layer, such as layer 13, as previously described for the SH
of FIG. 1B. This layer 13 is typically Al-quinolate. This is shown
in FIG. 2B, where the EL layers 20E, 21E, and 22E, respectively,
provide both the EL and ETL layer functions. However, an advantage
of the DH LED stack of FIG. 2A, relative to a SH LED stack of FIG.
2B, is that the DH LED stack permits thinner overall construction
with high efficiency.
[0033] In FIGS. 2A and 2B, even though the centers of each of the
LED's are offset from one another, the total beam of light from
each device is substantially coincident between LED's 20, 21 and
22. While the beams of light are coincident in the concentric
configuration, the emitting or non-emitting device closer to the
glass substrate will be transparent to the emitting device or
devices further away from the glass substrate. However, the diodes
20, 21 and 22 need not be offset from one another and may
alternatively be stacked concentrically upon each other, whereupon
the beam of light from each device is wholly coincident with the
others. A concentric configuration is shown in FIG. 12E which will
be described below in regard to device fabrication processes. Note
that there is no difference in function between the offset and
concentric configurations. Each device emits light through glass
substrate 37 in a substantially omnidirectional pattern. The
voltages across, the three LED's in the stack 29 are controlled to
provide a desired resultant emission color and brightness for the
particular pixel at any instant of time. Thus, each LED as 22, 21
and 20 can be energized simultaneously with beams as R, G and B,
respectively, for example, directed through and visible via the
transparent layers, as shown schematically in FIGS. 2A and 2B. Each
DH structure 20, 21 and 22 is capable upon application of a
suitable bias voltage of emitting a different color light. The
double heterostructure LED 20 emits blue light. The double
heterostructure LED 21 emits green light while the double
heterostructure (DH) LED 22 emits red light. Different combinations
or individual ones of LED's 20, 21 and 22 can be activated to
selectively obtain a desired color of light for the respective
pixel partly dependent upon the magnitude of current in each of the
LED's 20, 21 and 22.
[0034] In the example of FIGS. 2A and 2B, LED's 20, 21 and 22 are
forward biased by batteries 32, 31 and 30, respectively. Current
flows from the positive terminal of each battery 32, 31 and 30,
into the anode terminal 40, 41, 42, respectively, of its associated
LED 20, 21 and 22, respectively, through the layers of each
respective device, and from terminals 21, 21 and 43, serving as
cathode terminals to negative terminals of each battery 32, 31, and
30, respectively. As a result, light is emitted from each of the
LED's 20, 21 and 22. The LED devices 20, 21 and 22 are made
selectively energizable by including means (not shown) for
selectively switching batteries 32, 31 and 30, respectively, into
and out of connection to their respective LED.
[0035] In the embodiments of the invention, relative to FIGS. 2A
and 2B, the top ITO contact 26I for LED 22 is transparent, making
the three color device shown useful for headup display
applications. However, in another embodiment of the invention, the
top contact 26I is formed from a thick metal, such as either Mg/Ag,
In, Ag, or Au, for reflecting light emitted upward back through
substrate 13, for substantially increasing the efficiency of the
device. Also, overall device efficiency can be increased by forming
a multilayer dielectric thin film coating between glass substrate
37 and the ITO layer 35, to provide an anti-reflecting surface.
Three sets of anti-reflecting layers are required, one to form an
anti-reflection coating at each wavelength emitted from the various
layers.
[0036] In another embodiment, the device of FIG. 2A is constructed
in an opposite or inverted manner, for providing light emission out
of the top of stack rather than the bottom as the former. An
example of an inverted structure, with reference to FIG. 2C, is to
replace ITO layer 35 with a thick, reflective metal layer 38. Blue
LED 20 is then provided by interchanging HTL layer 20H and ETL
layer 20T, with EL layer 20E remaining sandwiched between the
latter two layers. Furthermore, the metal contact layer 26M is now
deposited on top of ITO layer 26I. The green LED 21 and red LED 22
portions of the stack are each constructed with inverted layers
(the HTL and EL layers of each are interchanged, followed by
inverting the metal and ITO layers) as described for the inverted
blue LED 20. Note that in the inverted structure, the blue device
20 must be on top and the red device 22 on the bottom. Also, the
polarities of batteries 30, 31, and 32 are reversed. As a result,
the current flow through devices 20, 21 and 22, respectively, is in
the opposite direction relative to the embodiment of FIG. 2A, when
forward biased for emitting light.
[0037] The device in the cross sectional view has a step-like or
staircase profile, in this example. The transparent contact areas
(ITO) 26I permit separate biasing of each pixel element in the
stack and furthermore the material can be used as an etch stop
during the processing steps. The separate biasing of each DH LED
structure 20, 21 and 22 allows for wavelength tuning of the pixel
output to any of various desired colors of the visible spectrum as
defined in the CIE (Commission Internationale de
l'Eclairage/International Commission of Illumination) chromaticity
standard. The blue emitting LED 20 is placed at the bottom of the
stack and it is the largest of the three devices. Blue is on the
bottom because it is transparent to red and green light. Finally,
the materials "partitioning" using the transparent ITO/metal layers
26 facilitates manufacture of this device as will be described. It
is the very unique aspects of the vacuum growth and fabrication
processes associated with organic compounds which makes the pixel
LED devices shown in FIGS. 2A, 2B, and 2C possible. The vertical
layering shown in FIGS. 2A, 2B, and 2C allows for the fabrication
of three color pixels with the smallest possible area, hence,
making these ideal for high definition displays.
[0038] As seen in FIGS. 2A, 2B, and 2C, each device DH structure
20, 21 and 22 can emit light designated by arrows B, G and R,
respectively, either simultaneously or separately. Note that the
emitted light is from substantially the entire transverse portion
of each LED 20, 21 and 22, whereby the R, G, and B arrows are not
representative of the width of the actual emitted light,
respectively. In this way, the addition or subtraction of colors as
R, G and B is integrated by the eye causing different colors and
hues to be perceived. This is well known in the field of color
vision and display colorimetry. In the offset configuration shown,
the red, green and blue beams of light are substantially
coincident. If the devices are made small enough, that is about 50
microns or less, any one of a variety of colors can be produced
from the stack. However, it will appear as one color originating
from a single pixel.
[0039] The organic materials used in the DH structures are grown
one on top of the other or are vertically stacked with the longest
wavelength device 22 indicative of red light on the top and the
shortest wavelength element 20 indicative of blue light on the
bottom. In this manner, one minimizes light absorption in the pixel
or in the devices. Each of the DH LED devices are separated by
ITO/metal layers 26 (specifically, semitransparent metal layers
26M, and indium tin oxide layers 26I). The ITO layers 26I can
further be treated by metal deposition to provide distinct contact
areas on the exposed ITO surfaces, such as contacts 40, 41, 42 and
43. These contacts 40, 41, 42 and 43 are fabricated from indium,
platinum, gold, silver or alloys such as Ti/Pt/Au, Cr/Au, or Mg/Ag,
for example. Techniques for deposition of contacts using
conventional metal deposition or vapor deposition are well known.
The contacts, such as 40, 41, 42 and 43, enable separate biasing of
each LED in the stack. The significant chemical differences between
the organic LED materials and the transparent electrodes 26I
permits the electrodes to act as etch stop layers. This allows for
the selective etching and exposure of each pixel element during
device processing.
[0040] Each LED 20, 21, 22 has its own source of bias potential, in
this example shown schematically as batteries 32, 31, and 30,
respectively, which enables each LED to emit light. It is
understood that suitable signals can be employed in lieu of the
batteries 30, 31, 32, respectively. As is known, the LED requires a
minimum threshold voltage to emit light (each DH LED) and hence
this activating voltage is shown schematically by the battery
symbol.
[0041] The EL layers 20E, 21E, 22E may be fabricated from organic
compounds selected according to their ability to produce all
primary colors and intermediates thereof. The organic compounds are
generally selected from trivalent metal quinolate complexes,
trivalent metal bridged quinolate complexes, Schiff base divalent
metal complexes, tin (iv) metal complexes, metal acetylacetonate
complexes, metal bidentate ligand complexes, bisphosphonates,
divalent metal maleonitriledithiolate complexes, molecular charge
transfer complexes, aromatic and heterocyclic polymers and rare
earth mixed chelates, as described hereinafter.
[0042] The trivalent metal quinolate complexes are represented by
the structural formula shown in FIG. 3, wherein M is a trivalent
metal ion selected from Groups 3-13 of the Periodic Table and the
Larnthanides. Al.sup.+3, Ga.sup.+3 and In.sup.+3 are the preferred
trivalent metal ions.
[0043] R of FIG. 3 includes hydrogen, substituted and unsubstituted
alkyl, aryl and heterocyclic groups. The alkyl group may be
straight or branched chain and preferably has from 1 to 8 carbon
atoms. Examples of suitable alkyl groups are methyl and ethyl. The
preferred aryl group is phenyl and examples of the heterocyclic
group for R include pyridyl, imidazole, furan and thiophene.
[0044] The alkyl, aryl and heterocyclic groups of R may be
substituted with at least one substituent selected from aryl,
halogen, cyano and alkoxy, preferably having from 1 to 8 carbon
atoms. The preferred halogen is chloro.
[0045] The group L of FIG. 3 represents a ligand including
picolylmethylketone, substituted and unsubstituted salicylaldehyde
(e.g. salicylaldehyde substituted with barbituric acid), a group of
the formula R(O)CO-- wherein R is as defined above, halogen, a
group of the formula RO-- wherein R is as defined above, and
quinolates (e.g. 8-hydroxyquinoline) and derivatives thereof (e.g.
barbituric acid substituted quinolates). Preferred complexes
covered by the formula shown in FIG. 3 are those where M is
Ga.sup.+3 and L is chloro. Such compounds generate a blue emission.
When M is Ga.sup.+3 and L is methyl carboxylate, complexes emitting
in the blue to blue/green region are produced. A yellow or red
emission is expected by using either a barbituric acid substituted
salicylaldehyde or a barbituric acid substituted 8-hydroxyquinoline
for the L group. Green emissions may be produced by using a
quinolate for the L group.
[0046] The trivalent metal bridged quinolate complexes which may be
employed in the present invention are shown in FIGS. 4A and 4B.
These complexes generate green emissions and exhibit superior
environmental stability compared to trisquinolates (complexes of
FIG. 3 where L is a quinolate) used in prior art devices. The
trivalent metal ion M used in these complexes is as defined above
with Al.sup.+3, Ga.sup.+3, or In.sup.+3 being preferred. The group
Z shown in FIG. 4A has the formula SiR wherein R is as defined
above. Z may also be a group of the formula P.dbd.O which forms a
phosphate.
[0047] The Schiff base divalent metal complexes include those shown
in FIGS. 5A and 5B wherein M.sup.1 is a divalent metal chosen from
Groups 2-12 of the Periodic Table, preferably Zn (See, Y. Hanada,
et al., "Blue Electroluminescence in Thin Films of Axomethin--Zinc
Complexes", Japanese Journal of Applied Physics Vol. 32, pp.
L511-L513 (1993). The group R.sup.1 is selected from the structural
formulas shown in FIGS. 5A and 5B. The R.sup.1 group is preferably
coordinated to the metal of the complex through the amine or
nitrogen of the pyridyl group. X is selected from hydrogen, alkyl,
alkoxy, each having from 1 to 8 carbon atoms, aryl, a heterocyclic
group, phosphino, halide and amine. The preferred aryl group is
phenyl and the preferred heterocyclic group is selected from
pyridyl, imidazole, furan and thiophene. The X groups affect the
solubility of the Schiff base divalent metal complexes in organic
solvents. The particular Schiff base divalent metal complex shown
in FIG. 5B emits at a wavelength of 520 nm.
[0048] The tin (iv) metal complexes employed in the present
invention in the EL layers generate green emissions. Included among
these complexes are those having the formula
SnL.sup.1.sub.2L.sup.2.sub.2 where L.sup.1 is selected from
salicylaldehydes, salicyclic acid or quinolates (e.g.
8-hydroxyquinoline). L.sup.2 includes all groups as previously
defined for R except hydrogen. For example, tin (iv) metal
complexes where L.sup.1 is a quinolate and L.sup.2 is phenyl have
an emission wavelength (.lambda..sub.em) of 504 nm, the wavelength
resulting from measurements of photoluminescence in the solid
state.
[0049] The tin (iv) metal complexes also include those having the
structural formula of FIG. 6 wherein Y is sulfur or NR.sup.2 where
R.sup.2 is selected from hydrogen and substituted or unsubstituted,
alkyl and aryl. The alkyl group may be straight or branched chain
and preferably has from 1 to 8 carbon atoms. The preferred aryl
group is phenyl. The substituents for the alkyl and aryl groups
include alkyl and alkoxy having from 1 to 8 carbon atoms, cyano and
halogen. L.sup.3 may be selected from alkyl, aryl, halide,
guinolates (e.g. 8-hydroxyquinoline), salicylaldehydes, salicylic
acid, and maleonitriledithiolate ("mnt"). When A is S and Y is CN
and L.sup.3 is "mnt" an emission between red and orange is
expected.
[0050] The M(acetylacetonate).sub.3 complexes shown in FIG. 7
generate a blue emission. The metal ion M is selected from
trivalent metals of Groups 3-13 of the Periodic Table and the
Lanthanides. The preferred metal ions are Al.sup.+3, Ga.sup.+3 and
In.sup.+3. The group R in FIG. 7 is the same as defined for R in
FIG. 3. For example, when R is methyl, and M is selected from
Al.sup.+3, Ga.sup.+3 and In.sup.+3, respectively, the wavelengths
resulting from the measurements of photoluminescence in the solid
state is 415.sub.nm, 445.sub.nm and 457 nm, respectively (See J.
Kido et al., "Organic Electroluminescent Devices using Lanthanide
Complexes", Journal of Alloys and Compounds, Vol. 92, pp. 30-33
(1993).
[0051] The metal bidentate complexes employed in the present
invention generally produce blue emissions.
[0052] Such complexes have the formula MDL.sup.4.sub.2 wherein M is
selected from trivalent metals of Groups 3-13 of the Periodic Table
and the Lanthanides. The preferred metal ions are Al.sup.+3,
Ga.sup.+3, In.sup.+3 and Sc.sup.+3. D is a bidentate ligand
examples of which are shown in FIG. 8A. More specifically, the
bidentate ligand D includes 2-picoiLylketones, 2-quinaldylketones
and 2-(o-phenoxy) pyridine ketones where the R groups in FIG. 8A
are as defined above.
[0053] The preferred groups for L.sup.4 include acetylacetonate;
compounds of the formula OR.sup.3R wherein R.sup.3 is selected from
Si, C and R is selected from the same groups as described above;
3,5-di(t-bu) phenol; 2,6-di(t-bu) phenol; 2,6-di(t-bu) cresol; and
H.sub.2Bpz.sub.2, the latter compounds being shown in FIGS. 8B-8E,
respectively.
[0054] By way of example, the wavelength (.lambda..sub.em)
resulting from measurement of photoluminescence in the solid state
of aluminum (picolymethylketone) bis [2,6-di(t-bu) phenoxide] is
420 nm. The cresol derivative of the above compound also measured
420 nm. Aluminum (picolylmethylketone) bis (OSiPh.sub.3) and
scandium (4-methoxy-picolylmethylketone) bis (acetylacetonate) each
measured 433 nm, while aluminum [2-(O-phenoxy)pyridine] bis
[2,6-di(t-bu) phenoxide] measured 450 nm.
[0055] Bisphosphonate compounds are another class of compounds
which may be used in accordance with the present invention for the
EL layers. The bisphosphonates are represented by the general
formula:
M.sup.2.sub.x(O.sub.3P-organic-PO.sub.3).sub.y
[0056] M.sup.2 is a metal ion. It is a tetravalent metal ion (e.g.
Zr.sup.+4, Ti.sup.+4 and Hf.sup.+4 when x and y both equal 1. When
x is 3 and y is 2, the metal ion M.sup.2 is in the divalent state
and includes, for example, Zn.sup.+2, Cu.sup.+2 and Cd.sup.+2. The
term "organic" as used in the above formula means any aromatic or
heterocyclic fluorescent compound that can be bifunctionalized with
phosphonate groups.
[0057] The preferred bisphosphonate compounds include phenylene
vinylene bisphonsphonates as for example those shown in FIGS. 9A
and 9B. Specifically, FIG. 9A shows .beta.-styrenyl stilbene
bisphosphonates and FIG. 9B shows 4,4'-biphenyl
di(vinylphosphonates) where R is as described previously and
R.sup.4 is selected from substituted and unsubstituted alkyl
groups, preferably having 1-8 carbon atoms, and aryl. The preferred
to alkyl groups are methyl and ethyl. The preferred aryl group is
phenyl. The preferred substitutuents for the alkyl and aryl groups
include at least one substituent selected from aryl, halogen,
cyano, alkoxy, preferably having from 1 to 8 carbon atoms.
[0058] The divalent metal maleonitriledithiolate ("mnt") complexes
have the structural formula shown in FIG. 10. The divalent metal
ion M.sup.3 includes all metal ions having a +2 charge, preferably
transition metal ions such as Pt.sup.+2, Zn.sup.+2 and Pd.sup.+2.
Y.sup.1 is selected from cyano and substituted or unsubstituted
phenyl. The preferred substituents for phenyl are selected from
alkyl, cyano, chloro and 1,2,2-tricyanovinyl.
[0059] L.sup.5 represents a group having no charge. Preferred
groups for L.sup.5 include P(OR).sub.3 and P(R).sub.3 where R is as
described above or L.sup.5 may be a chelating ligand such as, for
example, 2,2'-dipyridyl; phenanthroline; 1,5-cyclooctadiene; or
bis(diphenylphosphino)methane.
[0060] Illustrative examples of the emission wavelengths of various
combinations of these compounds are shown in Table 1, as derived
from C. E. Johnson et al., "Luminescent Iridium(I), Rhodium(I), and
Platinum(II) Dithiolate Complexes", Journal of the American
Chemical Society, Vol. 105, pg. 1795 (1983).
1TABLE 1 Complex Wavelength* [Platinum(1, 5-cyclooctadiene) (mnt)]
560 nm [Platinum(P(OEt).sub.3).sub.2(mnt)] 566 nm
[Platinum(P(OPh).sub.3)- .sub.2(mnt)] 605 nm
[Platinum(bis(diphenylphosphino) methane) (mnt)] 610 nm
[Platinum(PPh.sub.3).sub.2(mnt) 652 nm *wavelength resulting from
measurement of photoluminescence in the solid state.
[0061] Molecular charge transfer complexes employed in the present
invention for the EL layers are those including an electron
acceptor structure complexed with an electron donor structure.
FIGS. 11A-11E show a variety of suitable electron acceptors which
may form a charge transfer complex with one of the electron donor
structures shown in FIGS. 11F-11J. The group R as shown in FIGS.
11A and 11H is the same as described above.
[0062] Films of these charge transfer materials are prepared by
either evaporating donor and acceptor molecules from separate cells
onto the substrate, or by evaporating the pre-made charge transfer
complex directly. The emission wavelengths may range from red to
blue, depending upon which acceptor is coupled with which
donor.
[0063] Polymers of aromatic and heterocyclic compounds which are
fluorescent in the solid state may be employed in the present
invention for the EL Layers. Such polymers may be used to generate
a variety of different colored emissions. Table II provides
examples of suitable polymers and the color of their associated
emissions.
2 TABLE II POLYMER EMISSION COLOR poly(para-phenylenevinylene) blue
to green poly(dialkoxyphenylenevinylene) red/orange poly(thiophene)
red poly(phenylene) blue poly(phenylacetylene) yellow to red
poly(N-vinylcarbazole) blue
[0064] The rare earth mixed chelates for use in the present
invention include any lanthanide elements (e.g. La, Pr, Nd, Sm, Eu,
and Tb) bonded to a bidentate aromatic or heterocyclic ligand. The
bidentate ligand serves to transport carriers (e.g. electrons) but
does not absorb the emission energy. Thus, the bidentate ligands
serve to transfer energy to the metal. Examples of the ligand in
the rare earth mixed chelates include salicyladehydes and
derivatives thereof, salicyclic acid, quinolates, Schiff base
ligands, acetylacetonates, phenanthroline, bipyridine, quinoline
and pyridine.
[0065] The hole transporting layers 20H, 21H and 22H may be
comprised of a porphorinic compound. In addition, the hole
transporting layers; 20H, 21H and 22H may have at least one hole
transporting aromatic tertiary amine which is a compound containing
at least one trivalent nitrogen atom that is bonded only to carbon
atoms, at least one of which is a member of an aromatic ring. For
example, the aromatic tertiary amine can be an arylamine, such as a
monoarylamine, diarylamine, triarylamine, or a polymeric arylamine.
Other suitable aromatic tertiary amines, as well as all porphyrinic
compounds, are disclosed in Tang et al., U.S. Pat. No. 5,294,870,
the teachings of which are incorporated herein in their entirety by
reference, provided any of such teachings are not inconsistent with
any teaching herein.
[0066] The fabrication of a stacked organic LED tricolor pixel
according to the present invention may be accomplished by either of
two processes: a shadow masking process or a dry etching process.
Both processes to be described assume, for illustrative purposes, a
double heterostructure LED construction, i.e., utilizing only one
organic compound layer for each active emission layer, with light
emerging from the bottom glass substrate surface. It should be
understood that multiple heterojunction organic LED's having
multiple organic compound layers for each active emission layer,
and/or inverted structures (with light emerging from the top
surface of the stack) can also be fabricated by one skilled in the
art making slight modifications to the processes described.
[0067] The shadow masking process steps according to the present
invention are illustrated in FIGS. 12(A-E). A glass substrate 50 to
be coated with a layer of ITO 52 is first cleaned by immersing the
substrate 50 for about five minutes in boiling trichloroethylene or
a similar chlorinated hydrocarbon. This is followed by rinsing in
acetone for about five minutes and then in methyl alcohol for
approximately five minutes. The substrate 50 is then blown dry with
ultrahigh purity (UHP) nitrogen. All of the cleaning solvents used
are preferably "electronic grade". After the cleaning procedure,
the ITO layer 52 is formed on substrate 50 in a vacuum using
conventional sputtering or electron beam methods.
[0068] A blue emitting LED 55 (see FIG. 12B) is then fabricated on
the ITO layer 52 as follows. A shadow mask 73 is placed on
predetermined outer portions of the ITO layer 52. The shadow mask
73 and other masks used during the shadow masking process should be
introduced and removed between process steps without exposing the
device to moisture, oxygen and other contaminants which would
reduce the operational lifetime of the device. This may be
accomplished by changing masks in an environment flooded with
nitrogen or an inert gas, or by placing the masks remotely onto the
device surface in the vacuum environment by remote handling
techniques. Through the opening of mask 73, a 50-100 .ANG. thick
hole transporting layer (HTL) 54 and 50-200 .ANG. thick blue
emission layer (EL) 56 (shown in FIG. 12B) are sequentially
deposited without exposure to air, i.e., in a vacuum. An electron
transporting layer (ETL) 58 having a thickness preferably of
50-1000 .ANG. is then deposited on EL 56. ETL 58 is then topped
with a semitransparent metal layer 60M which may preferably consist
of a 10% Ag in 90% Mg layer, or other low work function metal or
metal alloy layer, for example. Layer 60M is very thin, preferably
less than 1000 .ANG.. Layers 54, 56, 58 and 60M may be deposited by
any one of a number of conventional directional deposition
techniques such as vapor phase deposition, ion beam deposition,
electron beam deposition, sputtering and laser ablation.
[0069] An ITO contact layer 60I of about 1000-4000 .ANG. thick is
then formed on the metal layer 60M by means of conventional
sputtering or electron beam methods. For convenience herein, the
sandwich layers 60M and 60I will be referred to and shown as a
single layer 60, which is substantially the same as the layer 26 of
FIG. 2. The low work function metal portion 60M of each layer 60
directly contacts the ETL layer beneath it, while the ITO layer 60I
contacts the HTL layer immediately above it. Note that the entire
device fabrication process is best accomplished by maintaining the
vacuum throughout without disturbing the vacuum between steps.
[0070] FIG. 12C shows a green emitting LED 65 which is fabricated
on top of layer 60 using substantially the same shadow masking and
deposition techniques as those used to fabricate blue emitting LED
55. LED 65 comprises HTL 62, green emission layer 64 and ETL 66. A
second thin (<100 .ANG. thick, thin enough to be
semi-transparent but not so thin to lose electrical continuity)
metal layer 60M is deposited on ETL layer 66, followed by another
1000-4000 .ANG. thick ITO layer 60I to form a second sandwich layer
60.
[0071] Shown in FIG. 12D is a red emitting LED 75 fabricated upon
layer 60 (upon 60I to be specific) using similar shadow masking and
metal deposition methods. Red emitting LED 75 consists of a HTL 70,
a red emitting EL 72 and ETL 74. A top sandwich layer 60 of layers
60I and 60M are then formed on LED 75. As described above for the
embodiment of FIG. 2, similarly, the top transparent ITO layer 60I
can in an alternative embodiment be replaced by an appropriate
metal electrode serving also to function as a mirror for reflecting
upwardly directed light back through the substrate 50, thereby
decreasing light losses out of the top of the device. Each ETL
layer 74, 66 and 58 has a thickness of 50-200 .ANG.; each HTL layer
54, 62 and 70 is 100-500 .ANG. thick; and each EL layer 56, 64 and
72 is 50-1000 .ANG. thick. For optimum brightness and efficiency,
each of the layers including the ITO/metal layers should be kept as
close as possible towards the lower end of the above ranges.
[0072] The formation of electrical contacts 51 and 59 on ITO layer
52, and electrical contacts 88, 89, 92, 94 and 96 on the ITO
portion 60I of ITO/metal layers 60 is then preferably accomplished
in one step. These electrical contacts may be indium, platinum,
gold, silver or combinations such as Ti/Pt/Au, Cr/Au or Mg/Ag. They
may be deposited by vapor deposition or other suitable metal
deposition techniques after masking off the rest of the device.
[0073] The final step in the shadow masking process is to overcoat
the entire device with an insulating layer 97 as shown in FIG. 12E,
with the exception of all the metal contacts 51, 59, 88, 89, 92, 94
and 96 which are masked. Insulating layer 97 is impervious to
moisture, oxygen and other contaminants thereby preventing
contamination of the LED's. Insulating layer 97 may be SiO.sub.2, a
silicon nitride such as Si.sub.2N.sub.3 or other insulator
deposited by electron-beam, sputtering, or pyrolitically enhanced
or plasma enhanced CVD. The deposition technique used should not
elevate the device temperature above 120.degree. C. inasmuch as
these high temperatures may degrade the LED characteristics.
[0074] The dry etching process for fabricating the LED stack
according to the invention is illustrated in FIGS. 13(A-F).
Referring to FIG. 13A, a glass substrate 102 is first cleaned in
the same manner as in the shadow-mask process described above. An
ITO layer 101 is then deposited on the glass substrate 102 in a
vacuum using conventional sputtering or electron beam methods. An
HTL 104, blue EL 105, ETL 106 and sandwich layer comprising metal
layer 107M and ITO layer 107I, all of generally the same
thicknesses as in the shadow-masking process, are then deposited
over the full surface of the ITO layer 101, using either
conventional vacuum deposition, or in the case of polymers spin or
spray coating techniques. ITO/metal sandwich layer 107 consists of
a less than 100 .ANG. thick, low work function metal layer 107M
deposited directly on the ETL layer 106, and a 1000-4000 .ANG.
thick ITO layer 107I on the metal layer 107M. On the entire top
surface of ITO layer 107I, a 1000 .ANG.-2000 .ANG. thick layer of
silicon nitride or silicon dioxide masking material 108 is
deposited using low temperature plasma CVD. A positive photoresist
layer 109 such as HPR 1400 J is then spun-on the silicon nitride
layer 108. As shown in FIG. 13B the outer portions 110 (see FIG.
13A) of the photoresist layer 109 are exposed and removed using
standard photolithographic processes. The exposed outer portions
110 correspond to the areas where the bottom ITO layer 101 is to be
exposed and electrically contacted. Referring to FIG. 13C, the
outer regions 111 (defined in FIG. 13B) of the silicon nitride
layer 108 corresponding to the removed photoresist areas, are
removed using a CF.sub.4:O.sub.2 plasma. Then, using an ion milling
technique or another plasma etch, the exposed outer portions of
ITO/metal layers 107I and 107M are removed. An O.sub.2 plasma is
then employed to sequentially remove the corresponding exposed
outer portion of the ETL layer 106, EL layer 105, and HTL layer
104, respectively, and also to remove the remaining photoresist
layer 109 shown in FIG. 13D. Finally, a CF.sub.4:O.sub.2 plasma is
again applied to remove the silicon nitride mask 108, with the
resulting blue LED configuration shown in FIG. 13D.
[0075] The same sequence of dry etching process steps is used to
fabricate a green LED 115 atop the blue LED, except that SiNx 150
is overlaid as shown, followed by a photoresist mask 113 as shown
in FIG. 13E to mask the outer portion of ITO layer 101. Then the
deposition of HTL layer 114, green EL layer 116, and so on is
performed (see FIG. 13F). The same photolithography and etching
techniques used for blue LED fabrication are then employed to
complete the formation of the green LED 115. The red LED 117 is
then formed atop the green LED using substantially the same dry
etching process. A passivation layer 119 similar to layer 97 of
FIG. 12E is then deposited over the LED stack with suitable
patterning to expose electrical contacts, as was described for the
shadow masking process. A photoresist mask is used to allow dry
etching of holes in passiuation layer 119. Next, metal 152 is
deposited in the holes. A final photoresist layer and excess metal
is removed by a "lift-off" process.
[0076] Following the LED stack fabrication, whether performed by a
shadow mask, dry-etching or other method, the stack must be
properly packaged to achieve acceptable device performance and
reliability. FIGS. 14(A-C) illustrate embodiments of the invention
for faciliting packaging, and for providing a hermetic package for
up to four of the multicolor LED devices of the invention, for
example. The same reference numerals used in FIGS. 14(A-B) indicate
the identical respective features as in FIG. 12E. The package may
also be used with the nearly identical structure of FIG. 13F.
Referring to FIG. 14A, after overcoating the entire device with an
insulating layer 97, such as SiNx for example, access holes 120,
122, and 124 are formed using known etching/photomasking techniques
to expose the topmost metal layers 60M', 60M", and 60M'", for the
blue, green, and red LED (organic light emitting diode) devices,
respectively, in this example. Thereafter, suitable metal circuit
paths 126, 128, and 130 (typically of gold material), are deposited
in a path from the exposed metal layers 60M', 60M", and 60M'",
respectively, to edge located indium solder bumps 132, 133, and
134, respectively, using conventional processing steps. Similarly,
an anode electrode termination is provided via the metal (Au, for
example) circuit path 135 formed to have an inner end contacting
ITO layer 52, and an outer end terminating at an edge located
indium solder bump 136, all provided via conventional processing.
The device is then overcoated with additional insulating material
such as SiNx to form an insulated covering with solder bumps 132,
133, 134, and 136 being exposed along one edge. In this manner, the
organic LED device can be readily packaged using conventional
techniques, or the packaging embodiment of the invention as
described immediately below.
[0077] A method for making four multicolor LED devices on a common
substrate 50 in a packaged configuration will now be described,
with reference to FIGS. 14A, 14B, and 14C, respectively, for
another embodiment of the invention. The starting material includes
a glass substrate 50 coated with an overlayer of indium tin oxide
(ITO) 152. The following steps are used to obtain the packaged
multicolor organic LED array:
[0078] 1. Mask ITO layer 52 to deposit an SiO.sub.2 layer 138 in a
concentric square band ring pattern, in this example (some other
pattern can be employed), on top of ITO layer 52 using conventional
techniques.
[0079] 2. Form four three-color LED stacks sharing common layers in
region 140 on the SiO.sub.2 layer 138 using methods as taught above
for obtaining, for example, either of the structures of FIGS. 12E
or 13F, and 14A.
[0080] 3. Deposit via shadow masking metal contacts 170 through
181; each terminating at exterior ends on Sio.sub.2 layer 138, for
providing external electrical connecting or bonding pads 170
through 181', respectively. Note that contacts 126, 128, and 130 in
FIG. 14A are the same as every successive three of contacts
170-181, respectively. Each group of three contacts, namely 170
through 172, 173 through 175, 176 through 178, and 179 through 181,
terminate at their interior or other ends to provide an electrical
connection with the metal layers 60M', 60M", 60M'", respectively,
of each of the four organic LED devices, respectively. Another
metal contact 182 is deposited via shadow masking on an edge of ITO
layer 52 common to all four of the LED devices, for providing a
common anode connection, in this example. Note that if through
appropriate masking and etching the four LED devices are made in
completely independent layers, four anode contacts, respectively,
will have to provided for the latter array that can be operated in
a multiplexed manner. The multicolor LED array being described in
this example is a non-multiplexed array.
[0081] 4. Deposit via shadow masking, for example, a second
SiO.sub.2 layer 184 in a continuous band or ring leaving exposed
bonding pads 170' through 181', using either sputtering, or plasma
enhanced CVD, or electron beam deposition, for example.
[0082] 5. Deposit Pb--Sn or other low temperature melting solder in
a continuous band or ring 186 on top of the second SiO.sub.2 layer
or band 184.
[0083] 6. Deposit on the bottom of a cover glass 188 a metal ring
190 to be coincident with the solder seal ring 186.
[0084] 7. Install cover glass 188 over the assembly, as shown in
FIG. 14B, with metal ring 190 abutting against the solder ring
186.
[0085] 8. Place the assembly in an inert gas atmosphere, such as
dry nitrogen, and apply heat to melt solder ring 186 to obtain an
air tight seal, with the inert gas trapped in interior region
192.
[0086] Referring to FIG. 15, there is shown a display 194 which is
an RGB organic LED display. The dots 195 are ellipsis. A complete
display as 194 comprises a plurality of pixels such as 196. The
pixels are arranged as a XY matrix to cover the entire surface area
of a glass sheet coated with ITO. Each pixel includes a stacked LED
structure as that shown in FIG. 2. Instead of having fixed bias
means as batteries 30, 31 and 32 (FIG. 2) each of the lines of
terminals designated in FIG. 2 as blue (B), green (G) and red (R)
are brought out and coupled to suitable horizontal and vertical
scan processors 197 and 198, respectively, all under control of a
display generator 199 which may be a TV unit. Accordingly, each
matrix of LED's has at least two axes (x,y), and each LED is at the
intersection of at least two of the axes. Also, the x-axis may
represent a horizontal axis, and the y-axis a vertical axis. It is
well known now to convert television signals such as the NTSC
signals into the color components R, G and B for color displays.
Monitors for computers which utilize red, green and blue for
primary colors are also well known. The drive and control of such
devices by vertical and horizontal scanning techniques are also
known. The entire array of pixel structures deposited over the
surface of the display is scanned employing typical XY scanning
techniques as using XY addressing. These techniques are used in
active matrix displays.
[0087] One can use pulse width modulation to selectively energize
the red, green and blue inputs of each of the DH LED pixels
according to desired signal content. In this manner, each of the
LED's in each line of the display are selectively accessed and
addressed and are biased by many means such as by pulse width
modulation signals or by staircase generated voltages to enable
these devices to emit single colors or multiple colors, so that
light emitted from said structures creates an image having a
predetermined shape and color. Also, one can serially scan each of
the xy axes, and serially energize selected ones of the LED's in
the matrix to emit light for producing an image with colors created
serially vertically. Selected ones of the LED's may be
simultaneously energized.
[0088] As indicated above, the vertical layering technique shown in
FIG. 2 allows the fabrication of the three color DH LED pixel
within extremely small areas. This allows one to provide high
definition displays such as displays that have 300 to 600 lines per
inch resolution or greater. Such high resolution would not be
obtainable using prior art techniques in which the organic emission
layers or fluorescent mediums generating the different colors are
laterally spaced from one another.
[0089] Based on modern standards one can provide a LED device as
shown in FIG. 2 with an effective area small enough to enable
hundreds of pixel diodes to be stacked vertically and horizontally
within the area of a square inch. Therefore, the fabrication
techniques enables one to achieve extremely high resolution with
high light intensity.
[0090] In FIG. 16, another embodiment of the invention is shown for
a multicolor LED device including the stacking of up to N
individual LED's, where N is an integer number 1,2,3 . . . N.
Depending upon the state of the technology at any future time, N
will have a practical limit. The stacked N levels of LED's can, for
example, be provided using either the shadow masking process steps
previously described for FIGS. 12(A-E), or the dry etching process
illustrated in FIGS. 13A through 13F. The base or bottom portion of
the stacked array of FIG. 16 is a glass substrate 102 as shown in
FIG. 13F, for example, with an ITO layer 101 formed over substrate
102. The immediately overlying first LED device, and following LED
devices in this example, each include in succession over ITO layer
101 an HTL layer 154, an EL layer 156, an ETL layer 158, a metal
layer 160, and an ITO layer 162. The No level LED device 164
further includes a topmost metal layer (see layer 152 of FIG. 13F)
formed over the uppermost ITO layer 162 thereof. A passivation
layer 119 is deposited over the stack, as in the color stack of
FIG. 13F. The material for each EL layer 156 of each LED device is
selected for providing a particular color for the associated LED.
As in the three color device, shorter wavelength (blue) devices
must lie lower in the stack than the longer wavelength (red)
devices to avoid optical absorption by the red emitting layers. The
color selected for each respective LED and the actual number of
stacked LED's are dependent upon the particular application, and
the desired colors and shading capability to be provided. Such
multi-color devices can also be used in optical communications
networks, where each different optical channel is transmitted using
a different wavelength emitted from a given device in the stack.
The inherently concentric nature of the emitted light allows for
coupling of several wavelengths into a single optical transmission
fiber. In practical such stacked arrays, access holes are formed
down to the ITO layer 162 of each device followed by the deposition
of appropriate metallization for facilitating packaging and
electrical connection to each of the LED devices in the stack, in a
manner similar to that described for the stacked multicolor LED
device of FIGS. 14A, 14B, and 14C, for example.
[0091] This device can be used to provide a low cost, high
resolution, high brightness full color, flat panel display of any
size. This widens the scope of this invention to displays as small
as a few millimeters to the size of a building. The images created
on the display could be text or illustrations in full color, in any
resolution depending on the size of the individual LED's.
[0092] Those with skill in the art may recognize various
modifications to the embodiments of the invention described and
illustrated herein. Such modifications are meant to be covered by
the spirit and scope of the appended claims. For example, a
multicolor stacked LED device, such as the above-described three
color device of FIG. 2, in another embodiment of the invention can
be provided by forming LED 20 from a polymer device as shown in
FIG. 1C, or from a deposited metal phosphonate film, rather than
having all three layers laid down in vacuo. The two remaining
stacked LED's would be formed by vapor deposition.
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