U.S. patent application number 13/890486 was filed with the patent office on 2013-12-19 for methods and apparatus for depositing material using a dynamic pressure.
This patent application is currently assigned to The Trustees of Princeton University. The applicant listed for this patent is The Trustees of Princeton University. Invention is credited to Stephen R. Forrest, Max Shtein.
Application Number | 20130337173 13/890486 |
Document ID | / |
Family ID | 43605576 |
Filed Date | 2013-12-19 |
United States Patent
Application |
20130337173 |
Kind Code |
A1 |
Forrest; Stephen R. ; et
al. |
December 19, 2013 |
Methods and Apparatus for Depositing Material Using a Dynamic
Pressure
Abstract
A method of depositing organic material is provided. A carrier
gas carrying organic material is ejected from a nozzle at a flow
velocity that is at least 10% of the thermal velocity of the
carrier gas, such that the organic material is deposited onto a
substrate. In some embodiments, the dynamic pressure in a region
between the nozzle and the substrate surrounding the carrier gas is
at least 1 Torr, and more preferably 10 Torr, during the ejection.
In some embodiments, a guard flow is provided around the carrier
gas.
Inventors: |
Forrest; Stephen R.; (Ann
Arbor, MI) ; Shtein; Max; (Princeton, NJ) |
|
Applicant: |
Name |
City |
State |
Country |
Type |
The Trustees of Princeton University; |
|
|
US |
|
|
Assignee: |
The Trustees of Princeton
University
Princeton
NJ
|
Family ID: |
43605576 |
Appl. No.: |
13/890486 |
Filed: |
May 9, 2013 |
Related U.S. Patent Documents
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Application
Number |
Filing Date |
Patent Number |
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12823323 |
Jun 25, 2010 |
8535759 |
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13890486 |
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12786982 |
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7722927 |
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12786982 |
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10422269 |
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7404862 |
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12175641 |
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10233470 |
Sep 4, 2002 |
7431968 |
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10422269 |
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10690704 |
Oct 23, 2003 |
7744957 |
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12823323 |
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60317215 |
Sep 4, 2001 |
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60316264 |
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60316968 |
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60332090 |
Nov 21, 2001 |
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Current U.S.
Class: |
427/255.6 |
Current CPC
Class: |
H01L 51/0003 20130101;
B05D 1/60 20130101; C23C 14/12 20130101; H01L 51/0081 20130101;
C23C 14/228 20130101 |
Class at
Publication: |
427/255.6 |
International
Class: |
B05D 1/00 20060101
B05D001/00 |
Goverment Interests
STATEMENT AS TO RIGHTS TO INVENTIONS MADE UNDER FEDERALLY SPONSORED
RESEARCH OR DEVELOPMENT
[0002] This invention was made with Government support under
Contract No. F49620-92-J-0424 awarded by the U.S. Air Force OSR
(Office of Scientific Research) and Contract No. DAAD 19-02-2-00198
awarded by the Army Research Lab. The government has certain rights
in this invention.
Claims
1. A method of depositing an organic material, comprising: ejecting
a carrier gas carrying an organic material from a nozzle at a flow
velocity that is at least 10% of the thermal velocity of the
carrier gas, to form a layer of organic material on a substrate,
the layer comprising a plurality of separate films; wherein a
dynamic pressure in a region between the nozzle and the substrate
surrounding the carrier gas is at least 1 Torr.
2. The method of claim 1, wherein the dynamic pressure is at least
10 Torr.
3. The method of claim 2, wherein the background atmosphere is at
least 5 Torr.
4. The method of claim 2, further comprising: providing a guard
flow surrounding the organic material ejected from the nozzle.
5. The method of claim 4, wherein the background atmosphere is
ambient atmosphere at about 760 Torr.
6. The method of claim 2, wherein the dynamic pressure of at least
10 Torr is affected by a guard flow ejected from the nozzle.
7. The method of claim 6, wherein the background pressure is the
base pressure of a vacuum chamber, and is less than about 0.1
Torr.
8. The method of claim 7, wherein the molecular weight of the
organic material is greater than the molecular weight of the
carrier gas.
9. The method of claim 6, wherein the guard flow comprises a first
gas, the carrier gas comprises a second gas, and the molecular
weight of the first gas is greater than the molecular weight of the
second gas.
10. The method of claim 1, wherein the dynamic pressure is at least
about 760 Torr.
11. The method of claim 1, wherein the dynamic pressure is not
greater than about 2 times the background pressure.
12. The method of claim 1, wherein the dynamic pressure is not
greater than about 10 times the background pressure.
13. The method of claim 1, wherein the plurality of separate films
comprises a plurality of pixels.
14. The method of claim 1, wherein at least one of the nozzle
diameter, the nozzle length, and the nozzle-to-substrate separation
is about equal to the gas mean free path length.
15. The method of claim 1, wherein the dynamic pressure is at least
0.5 Torr greater than the background pressure.
Description
CROSS-REFERENCES TO RELATED APPLICATIONS
[0001] This patent application is a continuation of U.S. patent
application Ser. No. 12/823,323, filed Jun. 25, 2010, which is a
continuation-in-part of U.S. application Ser. No. 12/786,982, filed
May 25, 2010 (now U.S. Pat. No. 7,897,210, issued Mar. 1, 2011),
which claims priority to U.S. patent application Ser. No.
12/175,641, filed Jul. 18, 2008 (now U.S. Pat. No. 7,722,927,
issued May 25, 2010), which is a divisional of U.S. application
Ser. No. 10/422,269, filed Apr. 23, 2003 (now U.S. Pat. No.
7,404,862, issued Jul. 29, 2008), which is a continuation-in-part
of U.S. application Ser. No. 10/233,470, filed Sep. 4, 2002 (now
U.S. Pat. No. 7,431,968, issued Oct. 7, 2008), which claims the
benefit under 35 U.S.C. .sctn.119(e) of U.S. Provisional
Applications Nos. 60/317,215, filed on Sep. 4, 2001, 60/316,264,
filed on Sep. 4, 2001, 60/316,968, filed on Sep. 5, 2001, and
60/332,090, filed on Nov. 21, 2001, and which is related to U.S.
application Ser. No. 10/233,482, filed on Sep. 4, 2002 (now U.S.
Pat. No. 6,716,656, issued Apr. 6, 2004). All of these
above-mentioned Applications are herein incorporated by reference
in their entireties. This patent application is also a
continuation-in-part of U.S. application Ser. No. 10/690,704, filed
Oct. 23, 2003 (now U.S. Pat. No. 7,744,957, issued Jun. 29, 2010),
which is incorporated by reference in its entirety.
RESEARCH AGREEMENTS
[0003] The claimed invention was made by, on behalf of, and/or in
connection with one or more of the following parties to a joint
university-corporation research agreement: Princeton University,
The University of Southern California, and Universal Display
Corporation. The agreement was in effect on and before the date the
claimed invention was made, and the claimed invention was made as a
result of activities undertaken within the scope of the
agreement.
BACKGROUND OF THE INVENTION
Field of the Invention
[0004] The present invention relates to a method and apparatus for
depositing material.
[0005] Molecular organic compounds are employed as active materials
in a variety of applications, including organic light emitting
diodes (OLEDs), organic phototransistors, organic photovoltaic
cells, organic photodetectors, and thin films. Many of the
materials used to make such devices are relatively inexpensive, so
organic opto-electronic devices have the potential for cost
advantages over inorganic devices. In addition, the inherent
properties of organic materials, such as their flexibility, may
make them well suited for particular applications such as
fabrication on a flexible substrate. For OLEDs, the organic
materials may have performance advantages over conventional
materials. For example, the wavelength at which an organic emissive
layer emits light may generally be readily tuned with appropriate
dopants.
[0006] Organic optoelectronic devices such as thin film transistors
(TFTs), light emitting diodes (LEDs) and photovoltaic (PV) cells,
have gained considerable attention of researchers during the past
decade. Organic semiconductors can be deposited on a variety of
substrates, which potentially simplifies and lowers fabrication
costs when compared to inorganic semiconductors. However, the
unique processing requirements of organic semiconductors can also
limit their application. For example, light emitting devices and PV
cells typically consist of thin (<100 nm) films of either
conjugated polymers or monomers, sandwiched between conducting
electrodes. For full-color displays and multi-transistor circuits,
the active organic layers themselves must also be laterally
patterned. However, the organic layers are typically too fragile to
withstand conventional semiconductor processing methods such as
photolithography, plasma processing, or reactive ion etching. Many
fabrication and patterning techniques have therefore been developed
to address these unique requirements, emphasizing primarily the
ease and low cost of processing. Recent successes in fabricating
OLEDs have driven the development of OLED displays (see S. R.
Forrest, Chem. Rev. 97, 1793 (1997)). OLEDs make use of thin
organic films that emit light when voltage is applied across the
device. OLEDs are becoming an increasingly popular technology for
applications such as flat panel displays, illumination, and
backlighting. OLED configurations include double heterostructure,
single heterostructure, and single layer, and a wide variety of
organic materials may be used to fabricate OLEDs. Several OLED
materials and configurations are described in U.S. Pat. No.
5,707,745, which is incorporated herein by reference in its
entirety.
[0007] Typically, these thin (-100 nm) film devices (including
OLEDs and photovoltaic cells) are grown by thermal evaporation in
high vacuum, permitting the high degree of purity and structural
control needed for reliable and efficient operation (see S. R.
Forrest, Chem. Rev. 97, 1793 (1997)). However, control of film
thickness uniformity and dopant concentrations over large areas
needed for manufactured products can be difficult when using vacuum
evaporation (see S. Wolf and R. N. Tauber, Silicon Processing for
the VLSI Era (Lattice, 1986)). In addition, a considerable fraction
of the evaporant coats the cold walls of the deposition chamber.
Over time, inefficient use of materials results in a thick coating
which can flake off, leading to particulate contamination of the
system and substrate. The potential throughput for vacuum
evaporated organic thin film devices is low, resulting in high
production costs. Low-pressure organic vapor phase deposition
(LP-OVPD) has been demonstrated recently as a superior alternative
technique to vacuum thermal evaporation (VTE), in that OVPD
improves control over dopant concentration of the deposited film,
and is adaptable to rapid, particle-free, uniform deposition of
organics on large-area substrates (see M. A. Baldo, M. Deutsch, P.
E. Burrows, H. Gossenberger, M. Gerstenberg, V. S. Ban, and S. R.
Forrest, Adv. Mater. 10, 1505 (1998)).
[0008] Organic vapor phase deposition (OVPD) is inherently
different from the widely used vacuum thermal evaporation (VTE), in
that it uses a carrier gas to transport organic vapors into a
deposition chamber, where the molecules diffuse across a boundary
layer and physisorb on the substrate. This method of film
deposition is most similar to hydride vapor phase epitaxy used in
the growth of III-V semiconductors (see G. B. Stringfellow,
Organometallic Vapor-Phase Epitaxy (Academic, London, 1989); G. H.
Olsen, in GaInAsP, edited by T. P. Pearsall (Wiley, New York,
1982)). In LP-OVPD, the organic compound is thermally evaporated
and then transported through a hot-walled gas carrier tube into a
deposition chamber by an inert carrier gas toward a cooled
substrate where condensation occurs. Flow patterns may be
engineered to achieve a substrate-selective, uniform distribution
of organic vapors, resulting in a very uniform coating thickness
and minimized materials waste.
[0009] Using atmospheric pressure OVPD, Burrows et al. (see P. E.
Burrows, S. R. Forrest, L. S. Sapochak, J. Schwartz, P. Fenter, T.
Buma, V. S. Ban, and J. L. Forrest, J. Cryst. Growth 156, 91
(1995)) first synthesized a nonlinear optical organic salt
4'-dimethylamino-N-methyl-4-stilbazolium tosylate. In a variation
on this method, Vaeth and Jensen (see K. M. Vaeth and K. Jensen,
Appl. Phys. Lett. 71, 2091 (1997)) used nitrogen to transport
vapors of an aromatic precursor, which was polymerized on the
substrate to yield films of poly (s-phenylene vinylene), a
light-emitting polymer. Recently, Baldo and co-workers (see M. A.
Baldo, V. G. Kozlov, P. E. Burrows, S. R. Forrest, V. S. Ban, B.
Koene, and M. E. Thompson, Appl. Phys. Lett. 71, 3033 (1997)) have
demonstrated what is believed to be the first LP-OVPD growth of a
heterostructure OLED consisting of N,N-di-(3-methylphenyl)-N,N
diphenyl-4,4-diaminobiphenyl and aluminum tris(8-hydroxyqumoline)
(Alq.sub.3), as well as an optically pumped organic laser
consisting of rhodamine 6G doped into Alq.sub.3. More recently,
Shtein et al. have determined the physical mechanisms controlling
the growth of amorphous organic thin films by the process of
LP-OVPD (see M. Shtein, H. F. Gossenberger, J. B. Benziger, and S.
R. Forrest, J. Appl. Phys. 89:2, 1470 (2001)).
[0010] Virtually all of the organic materials used in thin film
devices have sufficiently high vapor pressures to be evaporated at
temperatures below 400.degree. C. and then to be transported in the
vapor phase by a carrier gas such as argon or nitrogen. This allows
for positioning of evaporation sources outside of the reactor tube
(as in the case of metalorganic chemical vapor deposition (see S.
Wolf and R. N. Tauber, Silicon Processing for the VLSI Era
(Lattice, 1986); G. B. Stringfellow, Organometallic Vapor-Phase
Epitaxy (Academic, London, 1989))), spatially separating the
functions of evaporation and transport, thus leading to precise
control over the deposition process.
[0011] Though these examples demonstrate that OVPD has certain
advantages over VTE in the deposition of organic films, especially
over large substrate areas, the prior art has not addressed the
special problems that arise when depositing an array of organic
material.
[0012] As is the case for fabrication of arrays using VTE, to adapt
OVPD to OLED technology, a shadow mask delineating the shape of the
desired pixel grid is placed close to the substrate to define the
pattern of deposition on the substrate. Control of the shadow mask
patterning is a critical step, for example, in the fabrication of
full-color OLED-based displays (see U.S. Pat. No. 6,048,630,
Burrows, et al.). Ideally, the resultant pattern on a substrate is
identical to that cut into the shadow mask, with minimal lateral
dispersion and optimal thickness uniformity of the deposited
material. However, despite the overall advantages of OVPD in
depositing organic layers, the use of the shadow mask in OVPD has
certain disadvantages including: significant lateral dispersion
compared to VTE; material waste; potential for dust contamination
on the film from the mask; and difficulty in controlling the
mask-substrate separation for large area applications.
[0013] As used herein, the term "organic" includes polymeric
materials as well as small molecule organic materials that may be
used to fabricate organic opto-electronic devices. "Small molecule"
refers to any organic material that is not a polymer, and "small
molecules" may actually be quite large. Small molecules may include
repeat units in some circumstances. For example, using a long chain
alkyl group as a substituent does not remove a molecule from the
"small molecule" class. Small molecules may also be incorporated
into polymers, for example as a pendent group on a polymer backbone
or as a part of the backbone. Small molecules may also serve as the
core moiety of a dendrimer, which consists of a series of chemical
shells built on the core moiety. The core moiety of a dendrimer may
be an fluorescent or phosphorescent small molecule emitter. A
dendrimer may be a "small molecule," and it is believed that all
dendrimers currently used in the field of OLEDs are small
molecules.
[0014] Early methods of patterning organic materials involved the
deposition of organic materials through a mask. The organic
materials may be deposited through an "integrated" mask which is
attached to the substrate on which the device is being fabricated,
as disclosed in U.S. Pat. No. 6,596,443, issued on Jul. 22, 2003,
which is incorporated by reference in its entirety. Or, the organic
materials may be deposited through a shadow mask that is not
integrally connected to the substrate, as disclosed in U.S. Pat.
No. 6,214,631, issued on Apr. 10, 2001, which is incorporated by
reference in its entirety. However, the resolution that may be
achieved with such masks is limited due to a number of factors,
including the resolution to which a mask may be reliably
fabricated, the buildup of organic material on the mask, and the
diffusion of organic material in between the mask and the substrate
over which it is being deposited.
[0015] As used herein, "top" means furthest away from the
substrate, while "bottom" means closest to the substrate. For
example, for a device having two electrodes, the bottom electrode
is the electrode closest to the substrate, and is generally the
first electrode fabricated. The bottom electrode has two surfaces,
a bottom surface closest to the substrate, and a top surface
further away from the substrate. Where a first layer is described
as "disposed over" a second layer, the first layer is disposed
further away from substrate. There may be other layers between the
first and second layer, unless it is specified that the first layer
is "in physical contact with" the second layer. For example, a
cathode may be described as "disposed over" an anode, even though
there are various organic layers in between.
[0016] As used herein, "solution processible" means capable of
being dissolved, dispersed, or transported in and/or deposited from
a liquid medium, either in solution or suspension form.
[0017] "Ambient" as used herein refers to the default state of a
parameter, when no effort is made to control that parameter beyond
the normal efforts associated with a home or office building. For
example, ambient atmosphere is 1 atm (or thereabout depending on
elevation) having the general chemical composition of air, and
ambient temperature is room temperature, or approximately 25
degrees C. (or thereabout). "Background" pressure is the pressure
in a chamber (vacuum or otherwise), measured far from any effects
caused, for example, by an OVJP jet.
BRIEF SUMMARY OF THE INVENTION
[0018] The present invention may provide methods for the patterned
deposition of organic materials onto substrates without the need
for a shadow mask.
[0019] A method of depositing organic material is provided. A
carrier gas carrying an organic material is ejected from a nozzle
at a flow velocity that is at least 10% of the thermal velocity of
the carrier gas, such that the organic material is deposited onto a
substrate.
[0020] In some embodiments, the dynamic pressure in a region
between the nozzle and the substrate surrounding the carrier gas is
at least 1 Torr, and more preferably 10 Torr, during the ejection.
In some embodiments, a guard flow is provided around the carrier
gas. In some embodiments, the background pressure is at least about
10e-3 Torr, more preferably about 0.1 Torr, more preferably about 1
Torr, more preferably about 10 Torr, more preferably about 100
Torr, and most preferably about 760 Torr.
[0021] A device is also provided. The device includes a nozzle,
which further includes a nozzle tube having a first exhaust
aperture and a first gas inlet; and a jacket surrounding the nozzle
tube, the jacket having a second exhaust aperture and a second gas
inlet. The second exhaust aperture completely surrounds the first
tube aperture. A carrier gas source and an organic source vessel
may be connected to the first gas inlet. A guard flow gas source
may be connected to the second gas inlet. The device may include an
array of such nozzles.
BRIEF DESCRIPTION OF THE DRAWINGS
[0022] FIG. 1 shows an embodiment of an OVJP apparatus having
multiple source cells.
[0023] FIG. 2 shows an embodiment of an OVJP nozzle that can
produce a guard flow.
[0024] FIG. 3 shows a schematic of an OVJP nozzle illustrating
carrier gas and organic molecule trajectories.
[0025] FIG. 4 shows a plot of the qualitative dependence of the
normalized deposit width vs. downstream pressure, and a related
plot of the qualitative relationship between nozzle radius,
nozzle/substrate separation, and downstream pressure.
[0026] FIG. 5 shows calculated velocity and flow lines for
particles ejected from a nozzle.
[0027] FIG. 6 shows calculated thickness profiles for various
downstream pressures.
[0028] FIG. 7 shows calculated thickness profiles for various
nozzle--substrate separation distances.
[0029] FIG. 8 shows an image printed by OVJP.
[0030] FIG. 9 shows an optical micrograph of pentacene dots printed
by OVJP.
[0031] FIG. 10 shows an optical micrograph of Alq.sub.3 dots
printed by OVJP.
[0032] FIG. 11 shows thickness profiles for the dots of FIG. 7.
[0033] FIG. 12 shows a plot of the full width half maximum of the
thickness profiles of FIG. 9 v. the square root of nozzle-substrate
separation.
[0034] FIG. 13 shows a scanning electron micrograph of a pentacene
line deposited by OVJP.
[0035] FIG. 14 shows a plot of drain-source current v. drain-source
voltage for a TFT deposited by OVJP.
[0036] FIG. 15 shows a plot of drain-source current v. gate-source
bias for a TFT deposited by OVJP.
[0037] FIG. 16 shows an embodiment of an OVJP apparatus.
[0038] FIG. 17 shows an enlarged cross-sectional view of a source
cell shown in FIG. 6.
[0039] FIG. 18 shows an enlarged side view of a source cell shown
in FIG. 16.
[0040] FIG. 19 shows another embodiment of an OVJP apparatus.
[0041] FIG. 20 shows a further embodiment of an OVJP apparatus.
[0042] FIG. 21 shows a photograph of the deposited organic material
from Example 1 showing interference fringes due to the variation in
thickness of the deposited organic material.
[0043] FIG. 22 shows a photograph of the deposited organic material
from Example 2 showing interference fringes due to the variation in
thickness of the deposited organic material.
[0044] FIG. 23 shows the light intensity profile of the photograph
of the deposited organic material from Example 2, and the physical
shape of the deposited organic material from Example 2.
[0045] FIG. 24 shows the structure of an OLED fabricated in-part by
an embodiment of the device of the invention.
[0046] FIG. 25 shows a plot of the electroluminescent (EL)
intensity as a function of wavelength for the OLED fabricated in
Example 3.
DETAILED DESCRIPTION OF THE INVENTION
[0047] The present invention will be described with reference to
the following illustrative embodiments.
[0048] As described in U.S. application Ser. No. 10/233,470, filed
Sep. 4, 2002 (now U.S. Pat. No. 7,431,968), which is incorporated
herein by reference in its entirety, organic vapor jet deposition
(OVJD) is a technique that allows for direct patterning of organic
films on substrates. In general, OVJD also may be referred to
herein as organic vapor jet printing (OVJP). OVJD, or OVJP, uses an
inert carrier gas, such as nitrogen or argon, to transport the
organic vapors from their source(s) and eject them from one or more
nozzles, producing collimated jets of organic vapor and carrier
gas. Upon striking the substrate, the organic vapors are condensed
out of the jet, forming a patterned deposit, whose shape can be
controlled by engineering the nozzle shape and flow dynamics of the
organic vapor and carrier gas.
[0049] Organic vapor jet printing (OVJP) allows for the direct
patterning during growth of molecular organic semiconductor thin
films. A hot inert carrier gas picks up organic vapor and expands
through a microscopic nozzle, resulting in a highly collimated jet.
The jet impinges on a cold substrate, leading to the selective
physisorption of the organic molecules but not the carrier gas. The
non-equilibrium nature of OVJP allows for high resolution, nearly
100% efficient, direct printing of organic semiconductor patterns
and devices. The deposition rates may be very high, for example up
to and exceeding 1000 .ANG./s. We demonstrate pattern resolution
determined in part by the nozzle diameter and separation from the
substrate. For example, employing a 20 .mu.m diameter orifice, we
obtained patterns of .about.25 .mu.m in diameter (1000 dots per
inch). Further, we print an archetypal pentacene channel thin film
transistor at a film deposition rate of 700 .ANG./s, resulting in
hole mobility of 0.25 cm.sup.2/Vs and current on/off ratio of
710.sup.5, (comparable to performance achieved with vacuum
deposited devices). Using a scaling analysis the influence of
process conditions on the printing resolution and speed are
determined. Combinatorial printing experiments and direct
simulation Monte-Carlo models support the analysis. The printing of
molecular organic semiconductors by OVJP allows for the rapid
fabrication of both small- and large-scale electronic circuits. The
process can be carried out in a range of upstream-to-downstream
pressure gradients, depending on the nozzle size and number, while
the downstream pressure preferably ranges from 0.1 to 1000 Torr.
Due to the highly localized and directional characteristic of OVJP,
embodiments of the invention allow for the direct organic film
patterning is possible for substrates of virtually arbitrary size
and shape. In addition to organic electronic device application,
the method of OVJP provides access to new film growth regimes using
highly localized hyperthermal organic beams, with additional, new
degrees of control of film and crystal morphology.
[0050] In embodiments of organic vapor jet printing (OVJP), a hot
inert carrier gas picks up molecular organic vapor and expands
through a microscopic nozzle. The resulting collimated gas jet
impinges onto a cold substrate, leading to the selective, localized
deposition of the organic molecules, but not the carrier gas.
Because OVJP does not use liquid solvents, it allows for greater
latitude in the choice of substrate material and shape than other
processes such as ink-jet printing, thereby permitting a wider
variety of organic semiconductors and structures to be deposited.
The molecules used for organic devices are typically stable against
decomposition and pyrolysis up to 350-450.degree. C., while having
vapor pressures of up to several millibar, allowing high practical
deposition rates.
[0051] One unique aspect of OVJP is that the organic species can be
accelerated by the flow of a much lighter carrier gas to
hyperthermal velocities. This can lead to denser and more ordered
thin films, which potentially broadens the processing window for
ultra-rapid growth of high quality thin films for device
applications. This acceleration may also the instantaneous local
deposition rate of OVJP to exceed that of the alternative
broad-area deposition methods, resulting in a competitive advantage
in the rapid printing of large-scale electronics. A typical OLED
heterostructure is 2000 .ANG. thick. At 1000 .ANG./s and using a
linear array of nozzles, each having a diameter to match the pixel
width, a 1000 pixel wide display can be printed in .about.30
minutes. The growth rates in the experiments discussed herein are
already several orders of magnitude higher than the typical rates
reported for fabrication of molecular organic electronic devices,
but they can be increased further--for each 10.degree. C. increase
in the source temperature, the evaporation rate approximately
doubles. OVJP is preferably used to deposit small molecule organic
materials because they generally have sufficient vapor pressure at
reasonable temperatures to allow for a high deposition rate.
However, OVJP may have applications to other materials, such as
polymers.
[0052] Embodiments of OVJP generally involve a "jet" of gas ejected
from a nozzle, as distinct from other techniques, such as OVPD
(organic vapor phase deposition), where a carrier gas may be used,
but there is no "jet." A "jet" occurs when the flow velocity
through the nozzle is sufficiently large to result in a
significantly anisotropic velocity distribution relative to the
isotropic velocities of a stagnant gas with molecules bouncing
around. One way of defining when a jet occurs is when the flow
velocity of the carrier gas is at least 10% of the thermal velocity
of the carrier gas molecules.
[0053] More generally, embodiments of the invention allow for
patterned vapor phase deposition at pressures higher than
previously thought possible in a region between a nozzle and a
substrate. Specifically, this "region between a nozzle and a
substrate" is the region surrounding the jet of carrier gas as it
travels from the nozzle to the substrate, which may interact with
the jet. One way of controlling the pressure in this region is
through the background pressure, which is the pressure in the room,
vacuum chamber, or other area in which the deposition is
occurring--for example, by depositing in a vacuum chamber. Another
way of controlling this pressure is though the use of a guard flow,
as described herein and as illustrated in FIG. 2, for example. A
guard flow may be desirable even in a pressure controlled
environment such as a vacuum chamber, to mitigate the effect of any
impurities that may be present.
[0054] An embodiment of an OVJP apparatus is schematically
illustrated in FIG. 1. Device 100 includes a first organic source
cell 110, a second organic source cell 120, a dilution channel 130,
a mixing chamber 140, a nozzle 150, and heating elements 160.
Organic source cells 110 and 120 may contain organic materials for
deposition on a substrate 170. Each organic source cell may contain
a different organic material or combination of organic materials.
Carrier gas source(s) 105, schematically represented as arrows, may
provide a flow of carrier gas to organic source cells 110 and 120,
and dilution channel 130. Valves or other mechanisms may be used to
determine whether, and how much, carrier gas flows through each of
the organic source cells 110 and 120, and dilution channel 130.
When a carrier gas flows through an organic source cell, the
organic material contained therein may sublimate, and is
subsequently carried by the carrier gas. The organic material and
carrier gas then mixes in the mixing chamber with any other carrier
gas and/or organic materials that enters from either the dilution
channel or another organic source cell. Dilution channel 130 may be
used to achieve more precise control at lower organic material
concentrations than might be possible without a dilution channel.
The mixture of one or more organic materials and carrier gas is
then expelled through nozzle 150 towards substrate 170. Heating
elements 160 may be used to control the temperature of the carrier
gas and organic materials in device 100. By controlling the flow
velocity and other parameters as explained herein, the flow
mechanics of the expelled material may be controlled to form a
collimated jet 155. Substrate 170 is disposed over a substrate
holder 180, which may include a cooling channel 190. Any suitable
positioning mechanism may be used to control the relative positions
of substrate 170 and device 100. Cooling channel 190 may be
connected to a coolant source, and may be used to control the
temperature of substrate holder 180 and substrate 170. The organic
material is then deposited on substrate 170, and the carrier gas
flows away to the sides.
[0055] Device 100 may be made of any suitable material. Stainless
steel is preferred for its durability and heat conductivity.
Although only two organic source cells 110 and 120 are shown for
clarity, more or less organic source cells may be used. Preferably,
heating elements 160 may achieve a uniform heating of device 100.
Preferably, individually metered carrier gas streams flow through
each source cell to regulate the rate of delivery of the organic
vapor. Device 100 also allows for "make-up" and "pusher" gas flow
through dilution channel 130. A make-up gas flow may be used to
regulate the concentration of organic vapor in addition to the
source temperature. Pusher gas flow helps to avoid back-diffusion
of vapor. In the embodiment of FIG. 1, both make-up and pusher
functions may be achieved through dilution channel 130. The motion
of substrate 170 is preferably along all 3 axes and
computer-controlled.
[0056] Another embodiment of an OVJP apparatus is schematically
illustrated in FIG. 2. Nozzle 200 comprises a nozzle tube 210 and a
jacket 220. Nozzle tube 210 is defined by nozzle tube wall 217.
Jacket 220, which is disposed adjacent to nozzle 210, is defined by
nozzle tube wall 217 and jacket wall 227. Nozzle tube 210 has a
first gas inlet 212 and a first exhaust aperture 215. Jacket 220
has a second gas inlet 222 and a second exhaust aperture 225. A
carrier gas source 230 provides a flow of carrier gas carrying
organic material to first gas inlet 212. A guard flow source 240
provides a flow of guard flow gas to second gas inlet 222. The
carrier gas, carrying material to be deposited, flows out of first
exhaust aperture 215. The guard flow gas flows out of second
exhaust aperture 225. The gas sources of FIG. 2 are illustrated
generally, and may include any components associated with providing
a controlled gas flow to the nozzle, such as tubes, valves, gas
cylinders, temperature control apparati, and other components.
[0057] In heated embodiments, heat may be provided in a variety of
ways. The carrier gas source is preferably heated to a temperature
suitable to sublimate, in a source cell, the appropriate
concentration of molecule to be deposited. Other heat sources may
be desirable to prevent the molecule from depositing onto the
nozzle and elsewhere (other than the substrate, where deposition is
desired) as it progresses out of the source cell and beyond.
Preferably, the guard flow source provides heated guard flow gas,
which then heats nozzle tube wall 217. Other heated embodiments may
be achieved by using RF or other heating mechanisms to directly
heat parts of nozzle 200, such as nozzle tube wall 217 and/or
jacket wall 227.
[0058] An appropriate guard flow may confine the carrier gas and
the molecules being deposited, and prevent them from spreading.
Thus, a desirable sharper and higher resolution may be achieved.
Preferably, the guard flow comprises a relatively heavy gas as
compared to the carrier gas. Preferably, the guard flow gas is
heavier than the molecular weight of the carrier gas, which enables
the guard flow to more effectively contain the carrier gas.
[0059] Although the deposition can be carried out at atmospheric
conditions, the downstream pressure, P.sub.L., is reduced to 0.1-10
Torr in some embodiments to promote mass transport. To maintain the
edge sharpness for deposited patterns as small as 25 .mu.m the
nozzle-to-substrate separation, s, is kept on the order of the
molecular mean free path, .lamda., at the deposition pressure,
(e.g. 100 um>.lamda.>1 .mu.m for 0.1 Torr<P.sub.L, <10
Torr). Edge sharpness is preferred for some embodiments but not
necessary. When .lamda., is on the order of the apparatus dimension
(which can be taken as either s, the nozzle diameter, a, or nozzle
length, L), the flow is said to undergo a transition from the
continuum to the free molecular flow regimes. Typical OVJP
conditions result in such transition regime flow.
[0060] A description of the physical picture of transitional flow
may be derived from experiment and direct simulation Monte-Carlo
(DSMC) techniques. The present specification, in addition to
demonstrating OVJP of high-resolution organic thin film patterns
and devices, examines how process conditions affect the growth rate
and pattern resolution. A scaling model is developed and compared
to DSMC simulations and OVJP experiment.
[0061] A mass balance on the organic species in the source cell (7)
gives the expression for the vapor pressure of the organic species
exiting the source cell:
P org = P org sat k k + V . / RT cell ( 1 ) ##EQU00001##
where P.sub.org is the vapor pressure, P.sub.org.sup.sat is the
saturation (equilibrium) vapor pressure of the organic material,
{dot over (V)} is the carrier gas volumetric flow velocity, and k
is a constant describing the kinetics of the evaporation from the
organic surface inside the source cell. Equation (1) shows that the
carrier gas flow rate, as well as the source temperature, may
regulate the flux of organic vapor, which is a consideration for
regulating the concentration of dopants in the deposited films.
[0062] Downstream from the source cell, OVJP differs significantly
from vapor-phase deposition and ink jet printing. Unlike
vapor-phase deposition, OVJP is not diffusion limited near the
substrate, and, unlike ink jet printing, OVJP does not take place
in the liquid phase. The flow rate of gas through the nozzle, Q, is
the product of the pressure driving force and the nozzle
conductance:
Q=C(P.sub.H-P.sub.L) (2)
where the driving force is the difference in the upstream and
downstream pressures (P.sub.H and P.sub.L), and the conductance, C,
is expressed as:
C = [ 4 3 L 2 .pi. kT M a 3 ] ( 0.1472 a .lamda. + 1 + 3.50 a /
.lamda. 1 + 5.17 a / .lamda. ) ( 3 ) ##EQU00002##
where the quantity in the first brackets is calculated from the
kinetic theory, and then modified by an empirical factor for
different gas mixtures and conditions. Due to the large difference
in the molecular weights of the organic and carrier gas species
used in OVJP, Eq. (3) may be further corrected to reflect thermal
slip near the inner wall of the nozzle.
[0063] While the light carrier gas species are strongly scattered
radially by the substrate, the heavier organic species retain more
of their axial momentum (in proportion to the ratio of the organic
molecular masse to that of the carrier gas, m.sub.om.sub.c). This
mechanism is confirmed by DSMC results, as shown in FIGS. 4 and 5.
If the separation s is on the order of the 2 near the substrate,
the organic molecules suffer few collisions within the
nozzle-substrate gap. Assuming that the organic moieties attain the
bulk flow velocity inside the nozzle, their transport rate u.sub.z
in the z-direction is:
u.sub.z.apprxeq. =Q/.pi..alpha..sup.2 (5)
The average velocity with which the organic molecules are dispersed
radially outward from the nozzle may be expressed as:
u r .apprxeq. u _ a 2 s m c m o s .lamda. + v D ( 6 )
##EQU00003##
where .chi. is the radial distance traveled after emerging from the
nozzle, m.sub.c and m.sub.o are the carrier gas and organic
molecular weights, respectively, while V.sub.D, is the contribution
from pure diffusivity of the organic particle. This (isotropic)
diffusion contribution can be approximated by:
v D = 6 Dt t ( 7 ) ##EQU00004##
where D and t are the gas diffusivity of the organic species and
the time spent en route to the substrate, respectively.
[0064] Assuming fully developed flow inside the nozzle, a low
(<1% molar) concentration of the organic species, incompressible
flow and mass conservation of the carrier gas phase, it can be
shown that the organic molecules travel radially outward from their
original position in the nozzle by a distance .chi.:
.chi. a = m c m o s .lamda. + 1 3 c _ s .lamda. u _ a 2 ( 8 )
##EQU00005##
where, m.sub.c/m.sub.o is the organic-to-carrier gas molecular mass
ratio, c is the molecular mean thermal velocity, and is the mean
flow velocity inside the nozzle. The first term in Eq. (8)
quantifies the horizontal momentum transfer to the organic
molecules from collisions with the diverging carrier gas, while the
second term represents the scaling of the radial diffusion rate to
the ballistic transport rate normal to the substrate.
[0065] Although Eq. (8) does not predict the exact deposit shape,
it shows the relative influence of process conditions on the
deposited pattern resolution. In particular, given that .lamda.=kT/
{square root over (2.sigma.P.sub.L)}, where .sigma. is the
cross-section of the molecule, the dispersion has a minimum for
some value of P.sub.L, as shown in FIG. 3. The value of P.sub.L
corresponding to maximum resolution is in the range of 1-50 Torr
for typical OVJP conditions. Equation (8) also suggests that
pattern definition is enhanced through use of a lighter carrier gas
(e.g. He instead of N.sub.2). Practically, is fixed by the desired
deposition rate via the total flux of the organic molecules in the
nozzle. Thus, for a given nozzle radius a, the remaining adjustable
parameters are s and P.sub.L. The operating conditions for maximum
pattern resolution can thus be plotted on a process diagram (FIG.
4), where the operating line dictates values of s for any given
P.sub.L. For example, to maintain high pattern resolution even at
large separation, s, the downstream pressure, F.sub.L, may be
decreased. The region above the operating line represents
diffusion-limited printing, while the region below corresponds to
convection-limited operation. Finally, the local dynamic pressure
in the region between the nozzle and the substrate generally
exceeds P.sub.L and scales inversely with s. This places a lower
limit on the effective F.sub.L, as indicated by the "Dynamic
Pressure Line", such that the minimum in the pattern dispersion
curve with P.sub.L may not be observable under practical OVJP
conditions.
[0066] A common feature of a single nozzle expansion is that it
produces a flux profile domed in the center for virtually all
upstream and downstream conditions. Thus, to achieve a
flattened-top deposit, the nozzle can be rastered over an area.
Alternatively, a bundle of nozzles or a miniaturized "showerhead"
can be used to produce the same effect. Since the conductance of a
nozzle scales with .alpha..sup.3 (see Eq.4), the printing speed can
be maximized in the latter approach. Furthermore, in view of Eq.
(8), an annular guard flow of a relatively heavy gas (e.g. Ar or
SF.sub.6) may be used in conjunction with a main flow of a lighter
gas (e.g. H.sub.2 or He) to increase deposit sharpness. The annular
guard flow may be used in connection with other methods of
increasing sharpness, such as rastering and the showerhead
approach. With a guard flow, the organic species are maximally
accelerated and collimated by the main carrier gas flow, while the
radial diffusion of species is hindered by the guard flow made up
of a heavier inert gas.
[0067] FIG. 3 shows a schematic illustrated of a nozzle 300 having
a hollow cylindrical configuration, in the vicinity of a substrate
310. Carrier gas stream lines (solid black lines) and an expected
trajectory of an organic molecule (curved arrow) are qualitatively
illustrated. Several variables from Equations 1-8 are illustrated
as well. Although the carrier gas flow field rapidly diverges due
to the proximity of the substrate to the nozzle outlet, the
relatively heavy organic molecules acquire trajectories
substantially more collimated than the carrier gas. As discussed
herein, the interplay between diffusive and convective processes at
the nozzle orifice dictates the relationship between the pattern
shape, nozzle radius (a), nozzle-to-substrate separation (s), and
the pressure in the region downstream from the nozzle (P.sub.L).
The scaling is usually such that s, the pattern resolution, and the
molecular mean free path (A) at F.sub.L are of the same magnitude,
as indicated in FIG. 3. This implies that downstream from the
nozzle, transport is intermediate between continuum and molecular
flow. Experiment and direct simulation Monte-Carlo (DSMC)
techniques are the best ways to obtain an understanding of this
type of transport.
[0068] FIG. 4 shows a plot of the qualitative dependence of the
pattern dispersion, .chi./.alpha., on the downstream pressure,
P.sub.L, and a related plot of the relationship between nozzle
radius, nozzle/substrate separation, and downstream pressure. Plot
410 shows a plot of the qualitative dependence of the pattern
dispersion, .chi./.alpha., on the downstream pressure, P.sub.L. The
dispersion is minimized at a given value of P.sub.L, due to the
opposing balance of convective and diffusive transport rates. Plot
420 shows a plot of the relationship between nozzle radius,
nozzle/substrate separation, and downstream pressure, for the
region identified by a circle in plot 410. The conditions for the
highest pattern resolution (minimum dispersion) are plotted to give
the optimum operating line. Working above or below this line may
decrease pattern resolution. Increasing s and P.sub.L, results in
diffusion controlled transport, while decreasing s and P.sub.L
results in convection controlled transport. The actual "dynamic
pressure," i.e. the pressure between the nozzle and the substrate
surrounding the jet, may be higher than the ambient (or background)
pressure P.sub.L, due to the interaction between the jet and the
ambient pressure. Hence, the "dynamic pressure" line is lower and
sets the practical operating regime. The operating regime signified
by the shaded region under the dynamic pressure line is
inaccessible by some embodiments. Without being limited to any
theory as to how the invention works, it is believed that the jet
flow decelerates near the substrate, and a part of the kinetic
energy of the jet stream is converted into potential energy in the
form of a higher pressure in the region immediately surrounding the
jet stream.
[0069] While there is no simple qualitative relationship that
exactly determines the dynamic pressure as a function of various
relevant parameters such as the background pressure, the stream
velocity, etc., it is believed that the dynamic pressure will
generally not exceed 10 times the background pressure for the case
of a jet ejected from a nozzle without a guard flow, at velocities
reasonably contemplated for OVJP, and where the nozzle-substrate
separation is on the same order of magnitude as the nozzle radius.
In most cases, the dynamic pressure will not exceed twice the
ambient pressure. The simulation needed to determine the dynamic
pressure is well within the skill of one in the art based on the
disclosure herein.
[0070] Details of the flow calculated by DSMC are shown in FIG. 5.
Plot 510 shows a vertical velocity component of the flow field. The
corresponding trajectories of the carrier gas and the organic
molecules (in this case, tris-(8-hydroxyquinoline)-aluminum, or
Alq.sub.3) plotted in plot 520. The velocity map shows the
acceleration of the flow through the nozzle, reaching a velocity
.about.200 m/s at the nozzle exit, and the stagnation front
immediately above the substrate surface, where the dynamic pressure
generally exceeds the ambient pressure, P.sub.L, far away from the
nozzle region. Velocity is represented as shading on plot 510, with
the highest velocity in the nozzle, and the lowest furthest away
from the nozzle. The heavy organic molecular trajectories, however,
cross the carrier gas flow lines, resulting in a well-defined
deposit. Preferably, the molecular weight if the organic material
is greater than the molecular weight of the carrier gas to achieve
this divergence between the organic trajectories and the carrier
gas trajectories.
[0071] The deposit profiles obtained from DSMC for different
printing conditions are plotted in FIGS. 6 and 7, where the
broadening of the deposit due to increasing s and P.sub.L is
evident. The pattern width first varies slowly with P.sub.L, but
then increases rapidly, indicating that the conditions are near the
dispersion minimum, but that the dynamic pressure exceeds
P.sub.L.
[0072] It is believed that the profile of the deposited material is
favorably affected by a dynamic pressure of at least 1 Torr, and
more preferably be a dynamic pressure of at least 10 Torr.
[0073] In some embodiments, specific apparatus configurations may
be used to achieve specific deposition advantages or arrangements.
For example, an embodiment of the device can be used to pattern
both single-component and doped organic thin films on a substrate.
Furthermore, embodiments of the device of the invention can be used
for the rapid deposition of laterally patterned, doped films and
multi-layer structures.
[0074] In an embodiment of the device as depicted in FIG. 16, the
device includes a nozzle 1, and an apparatus 2, with one or more
source cells 4, integrally connected to the nozzle 11 via a mixing
chamber 3. In this embodiment, the integral connection between the
apparatus 2 and the one or more nozzles 1 refers to their close,
proximal relationship. Although the apparatus 2 and the one or more
nozzles 1 are not necessarily rigidly connected to each other nor
made from a single piece of material, they are situated close
enough together such that they can be moved together as a single
unit. The apparatus 2 also includes a carrier gas inlet channel 5
leading to each source cell 4, a carrier gas outlet channel 6
leading from each source cell 4 to the mixing chamber 3, and a
first valve 7 capable of controlling the flow of a carrier gas
through the one or more source cells 4. In addition, the apparatus
2 includes a dilution channel 10 located in the middle of the
apparatus 2 which can be used to allow carrier gas to pass through
to the mixing chamber 3 without passing through a source cell 4,
thereby diluting the concentrations of the organic vapors in the
mixing chamber 3. The dilution channel 1610 can also serve as a
pressure relief channel for the device. In addition, although the
dilution channel 1610 is located in the middle of the apparatus 2
in the embodiment of the device as depicted in FIG. 16, other
embodiments of the device can include the dilution channel 1610
located at other positions within the apparatus 2.
[0075] In a preferred embodiment of the invention, there are a
plurality of source cells 4 to enable the deposition of multiple
organic materials through a single mixing chamber 3 and nozzle 1.
The flow of carrier gas through the source cells 4 may be
separately controlled for each source cell 4, such that different
organic materials or different mixtures of organic materials may be
deposited at any given time. For example, as is known in the art of
manufacturing OLEDs, the emissive layer of an OLED may contain an
emissive organic molecule (a dopant) doped into a different organic
host material. Thus, this preferred embodiment of the invention
could include a source cell 4 containing an organic dopant
material, such as fac tris(2-phenylpyridine) iridium
(Ir(ppy).sub.3), and another source cell 4 containing an organic
host material, such as 4,4'-N,N'-dicarbazole-biphenyl (CBP),
wherein the flow of carrier gas through these source cells 4 is
controlled such that the desired amounts of CBP and Ir(ppy).sub.3
are transported into the mixing chamber 3. Thereafter, the
resulting organic layer deposited by such an embodiment of the
device comprises a CBP layer doped with Ir(ppy).sub.3.
[0076] In the embodiment shown in FIG. 16, the apparatus 2
comprises a single-piece structure in the form of a cylinder
containing one or more source cells 4 (only one of which is shown
in FIG. 16), with each source cell containing an organic material.
Each of the source cells 4, which are also in the form of
cylinders, are contained in a cylindrical source bore 8 in the
apparatus. Although both the apparatus 2 and the source cells 4
(along with the accompanying cylindrical source bores 8) are in the
form of a cylinder in FIG. 16, the apparatus and the source cells
may be in various other geometrical forms, including but not
limited to, a square block, a rectangular block, a hexagonal block,
and an octagonal block. Furthermore, both the apparatus and the
source cells may have tapered geometries, such that the inlet and
outlet ends of the apparatus and/or source cell would have
different radii or dimensions. In addition, although the embodiment
of the device shown in FIG. 16 includes a single source cell 4
contained in a cylindrical source bore 8, additional source cells 4
may be positioned in a linear arrangement in a single cylindrical
source bore 8.
[0077] In other embodiments of the device of the invention, the
apparatus is not in the form of a single-piece structure, but
instead comprises one or more separate structures, wherein each
structure contains one of the one or more source cells.
Furthermore, the separate structures could be rigidly attached to
each other to increase the strength of the apparatus as a whole.
The structure could be any type of physical form, such as a tube or
a hollow square block, capable of containing one or more source
cells. For example, the apparatus could comprise one or more tubes,
with each tube containing one of the one or more source cells.
[0078] In the embodiment shown in FIG. 16, the first valve 7
includes a plurality of source-cell valves, wherein each
source-cell valve is associated with each carrier gas inlet channel
5. That is, each source-cell valve corresponds to a source cell 4
such that the source-cell valve is capable of controlling the flow
of the carrier gas into each carrier gas inlet channel 5. By
carefully selecting the opening and closing of selected source-cell
valves, the device shown in FIG. 16 can be used for the selective
patterned deposition of organic vapors, for example, on a
substrate.
[0079] In the embodiment of the invention shown in FIG. 16, the
source cell 4 has a first cylindrical portion having a first
radius, while each of the cylindrical source bores 8 has a second
radius which is slightly larger than the first radius of the source
cell 4. As used herein, the phrase "slightly larger" means allowing
for the rotation of the source cells 4 within the cylindrical
source bore 8, but impeding the flow of carrier gas therethrough.
Also shown in FIG. 16 is a valve 7 including an aperture 9 in the
source cell 4 that aligns with the inlet channel 5 when the source
cell 4 is in a first position, and does not align with the inlet
channel 5 when the source cell 4 is in a second position. By this
arrangement, shown in FIG. 16 and described above, each source cell
4 can be turned to an "on" position by rotating the source cell 4
about its own longitudinal axis into the first position, wherein
the aperture 9 does align with the inlet channel 5. In this first
position, carrier gas can flow through the carrier gas inlet
channel 5, the source cell 4, the carrier gas outlet channel 6, the
mixing chamber 3 and the nozzle 1. In addition, each source cell 4
can be nearly hermetically sealed in an "off" position by rotating
the source cell 4 about its own longitudinal axis into the second
position, wherein the aperture 9 does not align with the inlet
channel 5, thereby not allowing for the flow of carrier gas through
the source cell 4.
[0080] Preferably, in the embodiment shown in FIG. 16, the source
cell 4 with a first cylindrical portion having a first radius, and
each of the cylindrical source bores 8 having a second radius which
is slightly larger than the first radius of the source cell 4, are
sized and fitted such that hot-valving occurs when using the
device. As used herein, the term "hot-valving" refers to the
opening and/or closing of a hot, gas-tight seal between a source
cell 4 and a cylindrical source bore 8. The hot (preferably in the
range of about 150.degree. to about 500.degree. C., more preferably
about 215.degree. C.), gas-tight seal is preferred to prevent the
undesired passage of carrier gas through the apparatus and out of
the nozzle, which could generally not he achieved with the use of
lubricants and/or elastomeric seals (such as elastomeric o-rings)
which are commonly used in liquid-based systems, such as ink-jet
printing methods and devices. In addition, known sealants and
lubricants for gas-based systems, such as teflon and graphite, can
be used in accordance with the invention.
[0081] FIG. 17 shows an enlarged version of the embodiment of the
source cell 4 shown in FIG. 16. The reference numbers in FIGS.
16-20 are consistent throughout and refer to the same device
components in each Figure. FIG. 17 shows a cross-sectional view of
the source cell 4, while FIG. 18 shows a side view of the source
cell 4. As seen in FIGS. 16 and 17, the source cell 4 is in the
form of a cylinder, which may be opened for the purpose of cleaning
and filling with the organic material 11. The source cell 4 has an
inlet aperture 9 and an outlet aperture 1612. As can be seen by the
arrow in FIG. 3, the flow of the carrier gas is directed through
the inlet channel 5, the inlet aperture 9, the organic material 11,
the outlet aperture 12, and the outlet channel 6, the path of which
provides for more efficient organic vapor pick-up by the carrier
gas.
[0082] The preferred temperatures and pressures to be employed in
the method and with the device of the present invention are the
same as those typically employed in organic vapor phase deposition.
That is, preferred operating pressures for the invention range from
0.01 to 10 Torr. In addition, preferred operating temperatures for
the invention range from about 150.degree. to about 500.degree. C.
This temperature range is preferred because at temperatures below
about 150.degree. C. the resulting vapor pressure of the organic
material is generally too low to evaporate the organic material and
transport it in the vapor phase, while at temperatures above about
500.degree. C. the decomposition of the organic material is a
possible result.
[0083] In some embodiments, the one or more source cells may be
heated to generate the desired vapor pressure of the organic
material within the one or more source cells. The heating of the
one or more source cells can be accomplished via a heating element
and/or an insulating material positioned in any way such that heat
reaches the one or more source cells. Such heating elements and
insulating materials are known in the art, and are within the scope
of the present invention. For example, a separate heating element
could be positioned around each individual source cell, or a single
heating element could be positioned around the entire apparatus
which includes the one or more source cells. Thus, in the
embodiment of the device shown in FIG. 16, although not shown, a
heating element could be placed around the source cell 4, or a
heating element could be placed around the apparatus 2.
[0084] In addition, in some embodiments, the temperature of each of
the one or more source cells may be controlled as follows. The
heating element can generate an axial temperature gradient along
the structure which it is surrounding or adjacent to. For example,
if the heating element is positioned around the apparatus, such as
the cylindrical apparatus 2 shown in FIG. 16, an axial temperature
gradient is generated along the cylinder, while the source cell 4
can be pulled out of or pushed into its cylindrical source bore 8
to a desired position corresponding to the desired temperature
value. In the embodiment of the device shown in FIG. 16, the range
of adjustability is controlled by the temperature gradient along
the apparatus 2, the distance between the inlet and outlet orifices
of the source cell 4, as well as the distance and stagger between
the carrier gas inlet channel 5 and the carrier gas outlet channel
6. In general, the rate of organic vapor delivery is controlled
jointly by the source cell temperature, the flow rate of the
carrier gas through the source cell 4, and the flow rate of the
carrier gas through the dilution channel 10.
[0085] Embodiments of the device of the present invention are
preferably comprised of a metallic material, including but not
limited to, aluminum, stainless steel, titanium, and other alloys.
Preferably, the components of the device of the present invention,
particularly the source cells and the apparatus in which the source
bores contain the source cells, are comprised of materials having a
similar coefficient of thermal expansion (i.e., within about 10% of
one another), and more preferably, are comprised of the same
material. By employing materials in the device with a similar
coefficient of thermal expansion, differential expansion upon
heating of the source cells and the apparatus in which the source
bores contain the source cells is largely avoided. Thus, upon
heating the device to the desired temperature, the device will not
encounter the potential problems of a source cell expanding in a
source bore and "locking-up" therein, or of a gap developing
between the source cell and the source cell allowing for the
undesired passage of carrier gas therethrough. In addition, the
device of the invention can be manufactured by methods known in the
art, including but not limited to, casting, forging or
machining.
[0086] In another embodiment of the invention, the one or more
nozzles of the device are comprised of a low-emissivity material.
Because the one or more nozzles of the device are preferably within
about 1 millimeter from the substrate, when a low-emissivity
material, such as a ceramic, is used as the material for the one or
more nozzles, it largely avoids the problem of possible evaporation
of previously deposited organic layers on the substrate because the
low-emissivity material may emit less heat than other materials,
thereby lessening the possibility of evaporating such organic
layers.
[0087] In some embodiments, for example as shown in FIG. 19, the
device can further include a selector 13 located next to the
apparatus 2 which is capable of controlling the flow of carrier gas
into each carrier gas inlet channel 5. In FIG. 19, the selector 13
is placed upstream of the apparatus 2, and the selector 13 can
rotate rapidly about its own longitudinal axis to selectively
direct the flow of the carrier gas into the inlet channels 5 and
the cylindrical source bores 8. By carefully selecting the rate at
which the selector 13 rotates, the device shown in FIG. 19 can be
used for the selective patterned deposition of organic vapors, for
example, on a substrate.
[0088] In some embodiments, for example as shown in FIG. 20, the
entire apparatus 2 is capable of rotating about its own
longitudinal axis. In this embodiment, the flow of carrier gas into
each carrier gas inlet channel 5 is controlled by the rotational
position of the apparatus 2. For example, in the embodiment shown
in FIG. 20, there are two stationary inlet tubes 14 placed upstream
of the apparatus 2, which can rotate rapidly about its own
longitudinal axis to selectively direct the flow of the carrier gas
from the stationary inlet tube 14 into the selected source cell 4.
By carefully selecting the rate at which the apparatus 2 rotates,
the device shown in FIG. 20 can be used for the selective patterned
deposition of organic vapors, for example, on a substrate.
[0089] As the device of the invention can include one or more
nozzles and one or more source cells, embodiments of the device can
include any combination of nozzle and source cell quantities. For
example, an embodiment of the device could include one nozzle and
three source cells, wherein the three source cells include a first
source cell containing a first organic material capable of emitting
a blue spectra of light, a second source cell containing a second
organic material capable of emitting a green spectra of light, and
a third source sell containing a third organic material capable of
emitting a red spectra of light. Another embodiment of the device
could include an array of nozzles with one or more source cells,
while still another embodiment of the invention could include an
array of devices, each with one nozzle and a plurality of source
cells. All such combinations of nozzle and source cell quantities
are within the scope of the device of the present invention.
[0090] In an embodiment of the method of the invention, a method of
depositing an organic material is provided. The organic material
may be deposited, for example, as an amorphous or crystalline film.
The method comprises moving a substrate relative to an apparatus
integrally connected to one or more nozzles. The apparatus
comprises: one or more source cells, each source cell containing an
organic material; a carrier gas inlet leading to each source cell;
a carrier gas outlet leading from each source cell to one or more
nozzles; and a first valve capable of controlling the flow of a
carrier gas through the one or more source cells. The method also
comprises controlling the composition of the organic material
and/or the rate of the organic material which is ejected by the one
or more nozzles while moving the substrate relative to the
apparatus, resulting in an organic material being deposited over
the substrate.
[0091] According to this embodiment of the method of the invention,
the moving of a substrate relative to an apparatus can be
accomplished in more than one way. For example, the substrate can
be stationary and the apparatus can be moved in a direction
parallel to the plane of the substrate. In addition, the apparatus
can be stationary and the substrate can be moved in a direction
parallel to the plane of the substrate.
[0092] Furthermore, any embodiment of the apparatus or device of
the invention can be used in accordance with the method of the
invention. For example, the embodiment of the device which includes
a selector located next to the apparatus which is capable of
controlling the flow of carrier gas into each earner gas inlet
channel may be used to control the composition of the organic
material and/or the rate of the organic material which is ejected
by the apparatus while moving the substrate relative to the
apparatus. In addition, the embodiment of the apparatus which is
capable of rotating about its own longitudinal axis may be used to
control the composition of the organic material and/or the rate of
the organic material which is ejected by the apparatus while moving
the substrate relative to the apparatus.
[0093] Embodiments of the method of the invention can be used to
facilitate the rapid deposition and patterning of organic materials
on substrates. For example, the phrase "rapid deposition" may refer
to the deposition of an entire display (about 3 million pixels) in
about 10 seconds. Such rapid deposition can be achieved, for
example, by an embodiment of the device of the invention comprising
a row of nozzles and a plurality of source cells, wherein the row
of nozzles could move across a substrate depositing a different
organic layer with each pass over the substrate. For example, after
five passes over the substrate, a five-layered OLED would result.
Alternatively, the same embodiment of the device could make just
one pass over the substrate and still produce a five-layered OLED,
whereby the source cells of the device would be switched over each
pixel site such that five different layers resulted at each pixel
site, provided the device had a sufficient switching time for the
source cells (preferably about 10 milliseconds).
[0094] Such rapid deposition can be achieved with the device of the
invention because of the compactness of the device as compared to
previous devices. By positioning the organic material to be
transported by the carrier gas very close to the substrate on which
it is to be deposited in accordance with the present invention,
there is less latency involved in depositing the organic layer as
compared to previous configurations with a longer distance between
the organic material to be transported and the substrate on which
it is to be deposited. This longer distance between the organic
material and the substrate which is present in previous
configurations needs to be cleared out or flushed of any previous
organic material being transported by a carrier gas before a second
organic material can be deposited via such a configuration.
However, the compactness of the device of the present invention
allows the device to be able to rapidly deposit different organic
materials with rapid switching between the different source cells
containing the different organic materials. Preferably, the source
cells containing the organic materials are no greater than about 10
cm from the one or more nozzles of the device, with the one or more
nozzles preferably being within about 1 millimeter from the
substrate.
[0095] Such rapid deposition and patterning includes both
single-component and doped organic thin films deposited on a
substrate. Applications of such patterned organic materials on a
substrate include, but are not limited to, electronic,
optoelectronic, and optical device fabrication. Furthermore, the
device and method of the present invention are readily adaptable to
both large-scale deposition processes, such as the fabrication of
wall-sized displays, as well as small-scale deposition processes,
such as portable organic vapor jet printers for use in research
laboratories and/or private homes.
[0096] The present invention will now be described in detail with
respect to showing how certain specific representative embodiments
thereof can be made, the materials, apparatus and process steps
being understood as examples that are intended to be illustrative
only. In particular, the invention is not intended to be limited to
the methods, materials, conditions, process parameters, apparatus
and the like specifically recited herein.
Experimental
[0097] Devices were fabricated using an organic vapor jet printer
having an appearance similar to device 100 of FIG. 1. The organic
vapor jet printer consisted of a stainless steel, 5-source chamber,
approximately 40 mm in diameter and 60 mm long, with heated walls.
The source cells were 5 mm.times.10 mm hollow stainless steel
cylinders. The source materials were pentacene and
tris(8-hydroxyquinoline)-aluminum (Alq.sub.3), widely employed in
organic TFT and LED work, respectively. Both materials were
pre-purified twice by vacuum train sublimation and then loaded into
their respective cells, sandwiched between two small quartz wool
plugs. Depending upon the particular experiment, one or more of the
five source cells may not have been used. Nitrogen was used as the
carrier gas. The vapor and nitrogen were forced through a
collimating nozzle and onto a cooled substrate, which was mounted
on a computer-controlled, motorized xyz-motion stage. The
background gas pressure in the deposition chamber was maintained
between 0.1 and 1000 Torr by means of a roughing pump and a
throttle valve. The deposited patterns were imaged with optical and
scanning electron microscopes. The substrates used for the TFT
deposition were highly conductive silicon wafers with a 210 nm
thick layer of dry thermal SiO.sub.2 as a gate dielectric. Prior to
deposition of pentacene, the substrates were cleaned and exposed in
vacuum to a saturated vapor of octadecyl-trichlorosilane (OTS) for
15 minutes at room temperature. The cleaning procedure consisted of
sonication of the SiO.sub.2-coated substrates in a soap solution,
de-ionized water, acetone, trichloroethylene (twice), acetone
(twice), and isopropanol (twice), followed by a 10-minute exposure
in a UV-ozone chamber. Gold source and drain contacts were
deposited by vacuum thermal evaporation after the printing of
pentacene. A Hewlett-Packard Model 4155 parameter analyzer was used
to obtain the current-voltage transfer characteristics of the TFTs,
which were tested inside of a metallic isolation box, in the dark,
at ambient conditions.
[0098] FIG. 8 illustrates an image printed by OVJP at several
different scales. Image 810 shows the image superimposed on a
penny. Image 820 is the image with a 1.5 mm scale line. Image 830
is the image with a 100 micron scale line. The image was generated
by OVJP of Alg.sub.a (flow channel diameter .alpha.=20 .mu.m, wall
thickness L=100 .mu.M, nozzle to substrate distance s=20.+-.10
.mu.m, a dwell-time of 2 seconds above each pixel location, a
movement time between pixels of less than 0.2 sec, upstream
pressure 430 Torr, downstream pressure 0.24 Torr, Alq.sub.3 source
cell temperature=270.degree. C., substrate temperature=15.degree.
C., deposition rate approximately .tau..sub.dep=1300 .ANG./s). It
is expected that the deposition rate could be increased to over
8000 .ANG./s by increasing the source temperature to 300.degree.
C., without damaging the organic materials. At this growth rate, an
array of 800 nozzles can print an SVGA resolution display
(600.times.800 OLED pixels) in under one minute. This speed is
comparable to the current state-of-the-art inkjet printers, which
also use print heads containing in excess of 500 nozzles. To obtain
pixels with flat-top profiles, the nozzle can be rastered or
dithered laterally during growth; alternatively, a manifold of
closely spaced nozzles can replace the dithered single nozzle.
[0099] FIG. 9 shows an optical micrograph of rows of pentacene dots
printed on Si with a 40 .mu.m.times.250 .mu.M (.alpha..times.L)
nozzle outlet positioned at a distance s=30 .mu.m from the
substrate. Interference fringes reflected off of the substrate and
deposit surfaces allow the deposition shape to be determined, using
known techniques. Each row of dots was deposited at a different
chamber pressure (P.sub.1=1.33, P.sub.2=0.9, P.sub.3=0.5,
P.sub.4=0.17 Torr), while the upstream pressure was maintained
constant at Phigh=240 Torr. This combinatorial deposition shows the
OVJP regime where pattern resolution can be enhanced by increasing
the chamber pressure. This result is somewhat counterintuitive,
because one might expect a higher chamber pressure to result in
more scattering off of gas molecules in the chamber (for example,
as would be expected in OVPD), and thus a decreased resolution at
higher chamber pressures. Instead, it has been discovered that a
higher chamber pressure may enhance resolution. Without being
limited to any theory as to how aspects of the invention work, it
is believed that, in the flow regime of OVJP, a higher chamber
pressure confines the gas jet.
[0100] Based on these results, it is expected that OVJP may be
practiced at higher background pressures than one might otherwise
believe. In fact, at higher pressures, there is a favorable effect
on the shape of the deposition. This favorable affect is visible at
a background pressure of 0.1 Torr, and becomes more pronounced at
higher pressures such as 1 Torr, 10 Torr and 100 Torr. As
demonstrated herein, devices may be fabricated at atmospheric
pressure (760 Torr), which may greatly reduce the need for
expensive capital equipment for fabricating devices. It is believed
that the favorable effect may manifest at background pressures as
low as 10e-3 Torr, but may not be noticeable and as apparent as
demonstrated herein. In addition, the higher pressures (0.1 Torr
and above) may be achieved with less sophisticated vacuum
apparatus, so there is a significant advantage from a cost
perspective to operating at a background pressure higher than
previously thought possible.
[0101] FIG. 10 shows an optical micrograph of
tris-(8-hydroxyquinoline)-aluminum (Alq.sub.3) dots printed onto Si
using a 20 .mu.m.times.100 .mu.m nozzle, at P.sub.high=240 Torr and
P.sub.low=0.24 Torr. The distance from the nozzle outlet to the
substrate s was varied (25, 53.4, 81.8, 110.2, 138.2, and
167).+-.10 microns, with S1=25 and S6=167 .mu.m. The dwell time at
each dot location was 60 seconds.
[0102] FIG. 11 shows thickness profiles calculated from the
interference fringe patterns of FIG. 10. For sufficiently thick
deposits, light-interference fringes allow the deposit profile to
be determined.
[0103] Equation (8) predicts that the pattern dispersion, .chi.,
should scale as s.sup.1/2. FIG. 12 shows that (FWHM).sup.2 scales
linearly with s, in agreement with Eq. (8). The full width-half
maximum (FWHM), as taken from the thickness profiles of FIG. 11
after normalization, was used as a measure of .chi..
[0104] FIG. 13 shows a scanning electron micrograph (SEM) of a
pentacene line printed on SiO.sub.2 with a local deposition rate
>300 .ANG./s and s=35.+-.15 .mu.m. Image 1310 is the pentacene
line with a 500 micron scale line, while images 1320 are the same
pentacene line at a higher magnification with a 1 micron scale
line. The image reveals that the pentacene grows in the shape of
slanted nano-pillars. The nano-pillars situated to the left and the
right of the jet center tilt in toward the nozzle, toward the
direction from which gas flows. This effect is not observed in
diffusion-limited growth, such as occurs in OVPD, but may be caused
by the self-shadowing of pentacene crystallites during the highly
directional "feed" of the crystals during the OVJP process. This
directionality is due to the anisotropic molecular velocity
distribution in the gaseous jet. A similar crystal growth mode has
been observed during glancing angle deposition of metals. Seeding
the organic molecules in a fast-flowing carrier stream also allows
near-to hyper-thermal velocities to be reached by the adsorbent
and, consequently, the tuning of incident kinetic energy. This
decouples the film crystallization dynamics from surface
temperature, leading to highly ordered films even for relatively
cold substrates. This effect has important implications for
improving the performance of devices, such as polycrystalline
channel TFTs.
[0105] To demonstrate the feasibility of the very high local
deposition rates for device application, OVJP was used to print
pentacene channel TFTs. The pentacene channel was printed in the
form of a 6 mm.times.6 mm uniformly filled square by rastering the
narrow jet over a 5 mm.times.5 mm substrate area. The TFT channels
were defined by the Au drain-source electrodes, which were
deposited in vacuum immediately following the printing of
pentacene. The printing employed a 350 .mu.m diameter nozzle, with
s=1000 .mu.m, T.sub.source=220.degree. C.,
T.sub.substrate=20.degree. C., Q.sub.source=5 sccm,
Q.sub.dilution=5 sccm, P.sub.high=20 Torr, and P.sub.low,=0.165
Torr, resulting in a local pentacene growth rate .about.700
.ANG./s.
[0106] The active pentacene channel had a gate width/length ratio
of 1000/45 (.+-.5) .mu.m, and consisted of a 5000 .ANG. thick
pentacene film with an average grain diameter of <200 nm. The
device drain-source current (I.sub.DS) versus voltage (V.sub.DS)
characteristic is plotted in FIG. 14, showing the drain-source
current saturation behavior similar to that previously observed for
vacuum and OVPD grown pentacene TFTs. The characteristic was
obtained from the drain-source current saturation regime at
V.sub.DS=-40V. The TFT exhibited some hysteresis in the I.sub.DS
vs-V.sub.GS behavior, with the threshold voltage shifting from +10
to +17 V in the forward and reverse V.sub.GS directions, as
indicated. The I.sub.DS vs. the gate bias (V.sub.GS) is plotted in
FIG. 15, revealing an I.sub.DS on/off ratio of 710.sup.5 and a
channel field-effect hole mobility of .mu..sub.eff=0.25.+-.0.05
cm.sup.2/Vs in the saturation regime. The hole mobility of a
vacuum-deposited control TFT deposited via thermal evaporation was
similar, but, due to thinner pentacene in the channel region, it
showed a smaller source-drain off current.
[0107] Organic vapor jet printing was also used to print pentacene
TFTs in nitrogen at atmospheric pressure; the TFTs exhibited=0.2
cm.sup.2/Vs. The hole mobility of a vacuum-deposited control TFT
was within the experimental error of the values obtained by OVJP at
P.sub.L 0.2 Torr. The cost of device and circuit fabrication can be
significantly reduced by the ability to directly print
small-molecular organic transistors at ambient conditions, such as
in a nitrogen glove box.
[0108] The deposition of a working device at atmospheric pressure
is particularly significant, because it demonstrates the
feasibility of using OVJP without expensive and cumbersome vacuum
equipment that requires time to pump down. For example, the ability
to deposit at atmospheric pressure may greatly facilitate the
deposition of organic materials in a large scale assembly line. It
may be desirable to deposit in a controlled atmosphere to avoid
impurities, such as in a glove box filled with an inert gas such as
nitrogen, but such a controlled atmosphere may be significantly
cheaper, easier and faster to provide as compared to a vacuum.
Another way to control impurities from an ambient atmosphere is to
use a guard flow, such as that produced by the device illustrated
in FIG. 2.
EXAMPLES
Example 1
[0109] In Example 1, an embodiment of the device of the invention
as seen in FIG. 16 was used to deposit an organic material on a
silicon substrate. That is, the device included a single source
cell 4 containing an organic material, aluminum
tris(8-hydroxyquinoline) (Alq.sub.3), and a single nozzle 1 with an
inner diameter of about 350 .mu.m. In this example, the distance
between the end of the nozzle 1 and the substrate was in the range
of about 0.5 to about 1.0 mm, the deposition pressure was about 270
mTorr, and the source cell temperature was about 222.degree. C.
[0110] FIG. 21 shows a photograph of the deposited Alq.sub.3 from
Example 1 (from an overhead view looking down on the deposited
Alq.sub.3) showing interference fringes due to the variation in
thickness of the deposited Alq.sub.3. The width of the deposited
Alq.sub.3 shown in FIG. 21 is approximately 500 .mu.m.
Example 2
[0111] In Example 2, an embodiment of the device of the invention
as seen in FIG. 16 was used to deposit an organic material on a
silicon substrate. That is, the device included a single source
cell 4 containing an organic material, Alq.sub.3, and a single
nozzle 1. However, in the embodiment of the device used in Example
2, the nozzle 1 had an inner diameter of approximately 50 .mu.m. In
this example, the distance between the end of the nozzle 1 and the
substrate was in the range of about 0.5 to about 1.0 mm, the
deposition pressure was about 270 mTorr, and the source cell
temperature was varied within the range of 209.degree. to
225.degree. C.
[0112] FIG. 22 shows a photograph of the deposited Alq.sub.3 from
Example 2 (from an overhead view looking down on the deposited
Alq.sub.3) showing interference fringes due to the variation in
thickness of the deposited Alq.sub.3. The width of the deposited
Alq.sub.3 shown in FIG. 22 is approximately 100 .mu.m.
[0113] The physical shape of the deposited Alq.sub.3 from Example 2
is shown in FIG. 23. Curve 81 represents the light intensity
profile of the photograph of the deposited Alq.sub.3 from Example 2
(which is shown in FIG. 22), graphed as arbitrary units of
intensity as a function of x (.mu.m), wherein x represents the
distance from the center (0) of the deposited Alq.sub.3. The light
intensity profile 81 was then translated into curve 82 which
represents the physical shape of the deposited Alq.sub.3 from
Example 2, plotted as thickness (rim) as a function of x (.mu.m).
As can be seen in FIG. 23, curve 82 approximates a bell-shaped
curve, wherein during deposition the center of the nozzle 1 is
located approximately over the center of the deposited organic
material, denoted on the x-axis of FIG. 23 by the numeral "0."
Thus, in order to flatten-out this bell-shaped curve and deposit an
organic material with a flatter profile, the nozzle could be
dithered over a desired distance during the deposition process
thereby producing a flatter deposited organic material than that
shown in FIG. 23. Furthermore, a device of the invention could
include more than one nozzle 1 arranged in a linear array with
proper spacing between the nozzles such that the hell-shaped
deposits from each nozzle 1 would overlap to the extent that the
profile of the resulting organic material deposited from the array
of nozzles would more closely approximate a plateau rather than a
bell-shaped curve.
Example 3
[0114] In Example 3, an embodiment of the device of the invention
as seen in FIG. 16 was used to deposit an organic material as part
of the fabrication of an OLED. The structure of the fabricated OLED
98 can be seen in FIG. 24.
[0115] The process used to fabricate the OLED 98 shown in FIG. 24
proceeded as follows. A substrate 91 was comprised of a 12.5
mm.times.12.5 mm.times.1 mm glass slide. The substrate 91 was
pre-coated with a layer 92 of indium tin oxide (ITO), which served
as the anode of the OLED 98 structure. A hole injection layer 93
was deposited onto the ITO-layer 92, wherein the hole injection
layer 93 comprised about 100 .ANG. of copper phthalocyanine (CuPc).
A hole transporting layer 94 was deposited onto the hole injection
layer 93, wherein the hole transporting layer 94 comprised about
450 .ANG. of 4,4'-bis[N-(1-napthyl)-N-phenyl-amino]biphenyl
(.alpha.-NPD).
[0116] Next, an embodiment of the device of the invention as seen
in FIG. 16 was used to deposit dots 95 of the organic material
Alq.sub.3, a green emitter, onto the hole transporting layer 94,
but only on one half of the hole transporting layer 94 as shown in
FIG. 24. The deposited dots 95 were each approximately 150 .ANG.
thick. The device used to deposit the dots 95 included a single
source cell 4 containing the Alg.sub.a, and a single nozzle 1
having a length of about 5 mm and an inner diameter of about 50
.mu.m. While depositing the dots 95, the distance between the end
of the nozzle 1 and the hole transporting layer 94 was about 200
.mu.m, the deposition pressure was about 275 mTorr, the source cell
temperature was about 220.degree. C., and the deposition rate was
about 1.25 .ANG./sec.
[0117] An electron transporting layer 96 was then deposited over
the dots 95, and over the portions of the hole transporting layer
94 which were not covered by the dots 95. The electron transporting
layer 96 comprised about 500 .ANG. of
2,9-dimethyl-4,7-diphenyl-1,10-phenanthroline (BCP). Next, cathodes
97 were deposited over the electron transporting layer 96, one over
the half of the OLED 98 containing the dots 95, and one over the
other half of the OLED 98. The cathodes 97 each comprised an about
7 .ANG.-thick layer of LiF, capped by an about 1500 .ANG.-thick
layer of Al. The depositions of all of the layers of the OLED 98 of
Example 3, except for the deposition of the dots 95 as discussed
above, were done via high vacuum (.about.10.sup.-6 Torr) thermal
evaporation.
[0118] FIG. 25 shows a depiction of the electroluminescent (EL)
intensity as a function of wavelength for the OLED 98 fabricated in
Example 3. The three different curves shown in FIG. 25 denote
different portions of the OLED 98; namely, curve 101 represents
that portion of the OLED 98 containing the dots 95, while curves
102 and 103 represent two different locations within that portion
of the OLED 98 not containing the dots 95. Thus, the only OLED
structural difference represented by these curves 101, 102 and 103
is that curve 101 includes Alq.sub.3 dots 95 deposited by an
embodiment of the device of the invention as described above. As
can be seen in FIG. 25, although all three curves 101, 102 and 103
display a peak EL intensity at about 445 nm, only curve 101 has an
additional peak intensity at about 520 nm. This additional peak at
about 520 nm shown in curve 101 can be attributed to the green
emission of the Alq.sub.3 dots 95 which were deposited by the
embodiment of the device of the invention as described above.
[0119] Although the present invention is described with respect to
particular examples and preferred embodiments, it is understood
that the present invention is not limited to these examples and
embodiments. The present invention as claimed therefore includes
variations from the particular examples and preferred embodiments
described herein, as will be apparent to one of skill in the
art.
* * * * *