U.S. patent application number 13/596130 was filed with the patent office on 2013-12-19 for method for depositing and curing nanoparticle-based ink using spatial light modulator.
This patent application is currently assigned to INTRINSIQ MATERIALS, INC.. The applicant listed for this patent is Michael J. Carmody, Richard J. Dixon, Sujatha Ramanujan. Invention is credited to Michael J. Carmody, Richard J. Dixon, Sujatha Ramanujan.
Application Number | 20130337191 13/596130 |
Document ID | / |
Family ID | 49756161 |
Filed Date | 2013-12-19 |
United States Patent
Application |
20130337191 |
Kind Code |
A1 |
Ramanujan; Sujatha ; et
al. |
December 19, 2013 |
METHOD FOR DEPOSITING AND CURING NANOPARTICLE-BASED INK USING
SPATIAL LIGHT MODULATOR
Abstract
An apparatus for forming a pattern of a nanoparticle ink on a
substrate has a transport apparatus that is energizable to move the
substrate in a direction and a printing apparatus that deposits the
nanoparticle ink in a pattern on a surface of the moving substrate.
An illumination apparatus directs a patterned illumination to cure
the deposited ink pattern on the moving substrate, the illumination
apparatus having a light source that generates light directed
toward a uniformizer, a spatial light modulator energizable to form
a patterned illumination from the uniformized light, and an
illumination lens disposed to direct illumination from the spatial
light modulator onto the surface of the moving substrate.
Inventors: |
Ramanujan; Sujatha;
(Pittsford, NY) ; Carmody; Michael J.; (Webster,
NY) ; Dixon; Richard J.; (Swindon, GB) |
|
Applicant: |
Name |
City |
State |
Country |
Type |
Ramanujan; Sujatha
Carmody; Michael J.
Dixon; Richard J. |
Pittsford
Webster
Swindon |
NY
NY |
US
US
GB |
|
|
Assignee: |
INTRINSIQ MATERIALS, INC.
Rochester
NY
|
Family ID: |
49756161 |
Appl. No.: |
13/596130 |
Filed: |
August 28, 2012 |
Related U.S. Patent Documents
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Application
Number |
Filing Date |
Patent Number |
|
|
61661378 |
Jun 19, 2012 |
|
|
|
Current U.S.
Class: |
427/559 ;
118/641 |
Current CPC
Class: |
B41J 3/407 20130101;
H05K 2203/107 20130101; H05K 3/125 20130101; B41J 11/002 20130101;
H05K 2203/108 20130101; H05K 3/1283 20130101 |
Class at
Publication: |
427/559 ;
118/641 |
International
Class: |
B05D 3/02 20060101
B05D003/02; B05D 5/00 20060101 B05D005/00; B05C 5/00 20060101
B05C005/00 |
Claims
1. An apparatus for forming a pattern of a nanoparticle ink on a
substrate, the apparatus comprising: a transport apparatus that is
energizable to move the substrate in a direction; a printing
apparatus that deposits the nanoparticle ink in a pattern on a
surface of the moving substrate; and an illumination apparatus that
directs a patterned illumination to cure the deposited ink pattern
on the moving substrate, the illumination apparatus having: (i) a
light source that generates light directed toward a uniformizer;
(ii) a spatial light modulator energizable to form a patterned
illumination from the uniformized light; (iii) an illumination lens
disposed to direct illumination from the spatial light modulator
onto the surface of the moving substrate.
2. The apparatus of claim 1 further comprising a spatial filter in
a far field position for selecting particular orders of diffracted
light.
3. The apparatus of claim 1 wherein the spatial light modulator is
a digital micromirror array.
4. The apparatus of claim 1 wherein the spatial light modulator is
a liquid crystal device.
5. The apparatus of claim 1 wherein the spatial light modulator is
a phase modulator taken from the group consisting of a grating
light valve, a grating modulator array, and a grating
electromechanical system.
6. The apparatus of claim 1 wherein the light source comprises at
least one laser.
7. An apparatus for forming a pattern of a nanoparticle-based ink
on a substrate, the apparatus comprising: a printing apparatus that
is energizable to deposit the nanoparticle-based ink in a pattern
on a surface of the substrate; an illumination apparatus that
directs a patterned illumination to cure the deposited ink pattern
on the substrate, the illumination apparatus having: (i) a light
source that generates light directed toward a uniformizer; (ii) a
spatial light modulator energizable to form a patterned
illumination from the uniformized light; (iii) an illumination lens
disposed to direct illumination from the spatial light modulator
onto the surface of the moving substrate; and a transport apparatus
that is energizable to provide relative motion between the
substrate and the illumination apparatus.
8. The apparatus of claim 7 further comprising a spatial filter in
a far field position for selecting particular orders of diffracted
light.
9. The apparatus of claim 7 wherein the spatial light modulator is
a digital micromirror array.
10. The apparatus of claim 7 wherein the spatial light modulator is
a liquid crystal device.
11. The apparatus of claim 7 wherein the spatial light modulator is
a phase modulator taken from the group consisting of a grating
light valve, a grating modulator array, and a grating
electromechanical system.
12. The apparatus of claim 7 wherein the light source comprises at
least one laser.
13. The apparatus of claim 7 wherein the transport apparatus moves
the substrate past the illumination apparatus.
14. The apparatus of claim 7 wherein the light source emits
wavelengths that differ from each other by more than 25 nm.
15. A method for forming a pattern of a nanoparticle ink on a
substrate, the method comprising: energizing a transport apparatus
to move the substrate in a direction; depositing the nanoparticle
ink in a pattern on a surface of the moving substrate; and curing
the deposited ink pattern on the moving substrate by: (i)
generating light and directing the light toward a uniformizer; (ii)
energizing a spatial light modulator to form a patterned
illumination from the uniformized light; and (iii) directing the
patterned illumination from the spatial light modulator onto the
surface of the moving substrate.
16. The method of claim 15 wherein energizing the spatial light
modulator comprises energizing a phase modulator taken from the
group consisting of a grating light valve, a grating modulator
array, and a grating electromechanical system.
17. The method of claim 15 further comprising dithering the
illumination from the spatial light modulator.
Description
CROSS-REFERENCE TO RELATED APPLICATIONS
[0001] This application claims the benefit of U.S. Provisional
Patent Application Ser. No. 61/661,378, filed on Jun. 19, 2012,
entitled "A METHOD FOR DEPOSITING AND SINTERING NANO PARTICLE BASED
INK" in the names of Sujatha Ramanuj an et al., the contents of
which are incorporated fully herein by reference.
FIELD OF THE INVENTION
[0002] This invention relates in general to an apparatus and method
for depositing electronic ink onto media, and sintering the ink by
means of a spatially and temporally modulating a light beam.
BACKGROUND
[0003] Fabrication of mass-produced electronic items typically
involves temperature- and atmosphere-sensitive processing.
Conventional material deposition systems for electronic
fabrication, including plasma-enhanced chemical vapor deposition
PECVD and other vacuum deposition processes, rely on high
temperatures and rigidly controlled ambient conditions.
Conventional processes are typically subtractive, applying a
conductive or other coating over a surface, treating the coating to
form a pattern, then removing unwanted material. The conventional
method for forming copper traces is one example of this process,
requiring multiple processing steps with the use of toxic chemicals
and the complications and cost of proper waste disposal.
[0004] Recent advances in printed electronics provide solutions
that reduce the cost, complexity, and energy requirements of
conventional deposition methods and expand the range of substrate
materials that can be used. For printed electronics, materials can
be deposited and cured at temperatures compatible with paper and
plastic substrates and can be handled in air. In particular,
advances with nanoparticle-based inks, such as silver, copper, and
other metal nanoparticle-based inks, for example, make it feasible
to print electronic circuit structures using standard additive
printing systems such as inkjet and screen printing systems.
Advantageously, nanoparticle-based inks have lower curing
temperatures than those typically needed for bulk curing where
larger particles of the same material are used.
[0005] Commercially available systems for curing nanoparticles
typically employ heat from convection ovens or Xenon flash
illumination energy. In such illumination systems, the Xenon lamps
emit pulsed light that is directed onto films of nanoparticles to
be cured. High light energy levels are required for nanoparticle
curing. Exemplary nanoparticle-based inks such as Intrinsiq
Material Ltd. CI-002, a copper nanoparticle based inkjet ink, or
CP-001, a copper nanoparticle-based screen print ink, can be
sintered through the use of photonic energy from Xenon lamp or
other illumination, provided that the illumination system delivers
adequate energy to volatilize coatings used in the ink formulations
and to sinter and cure the inks over large surface areas.
[0006] Conventional approaches for conditioning of the nanoparticle
material, however, suffer from a number of deficiencies. Xenon lamp
emission is characteristically distributed over a broad range of
wavelengths and often includes wavelengths that can cause unwanted
effects, even at non-peak energy levels. This inherent spectral
spread in Xenon lamp emission can have effects that result in
incomplete or uneven curing. One result can be limited penetration
of light energy into thicker films or premature sealing of top
surface layers, trapping unwanted organic species in the remaining
structure. This type of problem can occur when higher frequency
light, such as light energy from the tail of the spectral
distribution, inadvertently sinters the film and renders its top
layers opaque to other wavelengths of emitted Xenon light, delaying
or preventing curing of the lower layers. When this happens, the
binder or organic suspension in which nanoparticles are suspended
is only partially removed, causing uneven sintering, which can
limit the conductivity of the applied materials.
[0007] With Xenon light, the distribution of energy intensity is
non-symmetrical; the co-lateral dispersive energy that is produced
can reduce curing efficiency or may even cause overheating and
damage to the substrate. Further, pulsing of the Xenon lamp or
other light source tends to create high energy peaks that can
ablate films rather than melt and reflow films. As a result, the
cured product may not have the desired structure.
[0008] Conventional methods are also limited with respect to the
number of substrates that can be used. With materials having high
thermal conductivity, such as aluminum, silicon, and ceramics, the
applied energy intended for curing may dissipate too quickly. With
such materials, heat can be drawn away from the area of incident
light before sintering occurs. Furthermore, particular wavelengths
emitted from the Xenon lamps can damage some polymeric films and
other substrates, making them less suitable for curing.
[0009] Thus, it can be seen that there is a need for improved
methods for sintering and curing nanoparticulate inks and similar
materials.
SUMMARY OF THE INVENTION
[0010] It is an object of the present invention to advance the art
of sintering and curing nanoparticle-based inks. With this object
in mind, embodiments of the present invention provide an apparatus
for forming a pattern of a nanoparticle ink on a substrate, the
apparatus comprising: [0011] a transport apparatus that is
energizable to move the substrate in a direction; [0012] a printing
apparatus that deposits the nanoparticle ink in a pattern on a
surface of the moving substrate; and [0013] an illumination
apparatus that directs a patterned illumination to cure the
deposited ink pattern on the moving substrate, the illumination
apparatus having: [0014] (i) a light source that generates light
directed toward a uniformizer; [0015] (ii) a spatial light
modulator energizable to form a patterned illumination from the
uniformized light; [0016] (iii) an illumination lens disposed to
direct illumination from the spatial light modulator onto the
surface of the moving substrate.
[0017] From an alternate aspect, the present invention provides a
method for forming a pattern of a nanoparticle ink on a substrate,
the method comprising: [0018] energizing a transport apparatus to
move the substrate in a direction; [0019] depositing the
nanoparticle ink in a pattern on a surface of the moving substrate;
and [0020] curing the deposited ink pattern on the moving substrate
by: [0021] (i) generating light and directing the light toward a
uniformizer; [0022] (ii) energizing a spatial light modulator to
form a patterned illumination from the uniformized light; and
[0023] (iii) directing the patterned illumination from the spatial
light modulator onto the surface of the moving substrate.
[0024] Among advantages provided by embodiments of the present
invention is the ability to direct sintering or curing energy in a
pattern that corresponds to the pattern of the printed ink.
Wavelength selectivity is also improved over conventional curing
methods, enabling more efficient curing and facilitating deposition
and curing of multiple materials. Embodiments of the present
invention may use one or more exposure levels for sintering
nanoparticle materials.
[0025] These and other aspects, objects, features and advantages of
the present invention will be more clearly understood and
appreciated from a review of the following detailed description of
the preferred embodiments and appended claims, and by reference to
the accompanying drawings.
BRIEF DESCRIPTION OF THE DRAWINGS
[0026] FIG. 1A is a flow chart showing a sequence for printing and
curing nano-materials for electronic applications, according to an
embodiment of the present invention.
[0027] FIG. 1B is a schematic diagram showing a printing and curing
system for use with electronic ink.
[0028] FIG. 1C is a schematic diagram showing a printing and curing
system for use with electronic ink, wherein printing and
illumination apparatus move past a stationary substrate.
[0029] FIG. 2 is a schematic diagram that shows components of an
illumination apparatus for a printing and curing system using a
bank of laser diodes.
[0030] FIG. 3 is a schematic diagram showing a printing and curing
system using two illumination apparatus for use with
nanoparticle-based electronic ink.
[0031] FIG. 4 is a schematic diagram showing a printing and curing
system using two printing apparatus and two illumination apparatus
for use with electronic ink.
[0032] FIG. 5 is a schematic diagram showing an illumination
apparatus having a mechanical dithering component.
[0033] FIG. 6 is a schematic diagram showing an illumination
apparatus having an optical dithering component prior to the
illumination lens.
[0034] FIG. 7 is a schematic diagram showing an illumination
apparatus having an optical dithering component after the
illumination lens.
[0035] FIG. 8 is a schematic diagram that shows a printing and
curing system using a spatial light modulator.
[0036] FIG. 9 is a schematic diagram that shows spatial
distribution of zeroth, first, and second orders of diffracted
light from one type of spatial light modulator.
[0037] FIG. 10 is a schematic diagram showing use of a phase
modulation spatial light modulator in an illumination apparatus
according to an embodiment of the present invention.
DETAILED DESCRIPTION OF THE INVENTION
[0038] The following is a detailed description of the preferred
embodiments of the invention, reference being made to the drawings
in which the same reference numerals identify the same elements of
structure in each of the several figures. It is understood that the
elements not shown specifically or described may take various forms
well know to those skilled in the art.
[0039] Where they are used, the terms "first", "second", and so on,
do not necessarily denote any ordinal or priority relation, but may
be used for more clearly distinguishing one element or time
interval from another.
[0040] In the context of the present disclosure, the term "ink" is
a term of art that broadly applies to a material that is deposited
in a pattern on a substrate in a viscous, generally fluid form and
is sintered and otherwise cured after deposition by applying a
curing energy such as heat or light energy. Sintering is a curing
process by which curing energy effects a structural change in the
composition of particles in the ink. Curing may also have
additional aspects for ink conditioning, such as sealing or removal
of organic coatings or other materials provided in the ink
formulation but not wanted in the final, printed product. In the
context of the present invention, the term "curing" is used to
include sintering as well as other curing processes that employ the
applied light energy for conditioning the deposited ink.
[0041] The terms "nanoparticle-based material", "nanoparticle-based
ink", "nanoparticle material" or "nanoparticulate material" refer
to an ink or other applied viscous fluid that has an appreciable
amount of nanoparticulate content, such as more than about 5% by
weight or volume.
[0042] In the context of the present invention, the term
"substrate" refers to any of a range of materials upon which the
nanoparticle ink is deposited for curing. Exemplary substrates
include plastics, textiles, paper, sheet materials, and other
materials that provide a suitable surface for depositing a pattern
of nanoparticle-based ink.
[0043] As used herein, the term "energizable" relates to a device
or set of components that perform an indicated function upon
receiving power and, optionally, upon receiving an enabling
signal.
[0044] The background section outlines a number of problems with
conventional methods for sintering using Xenon light and other
broadband light energy. Embodiments of the present invention
address the problem of curing and sintering for nanoparticle-based
materials using a light source that provides light to a spatial
light modulator for forming a patterned illumination from the
light. According to embodiments of the present invention, the
spatial light modulator is energized and used so that the patterned
light energy extends across the width of a substrate, allowing
single-pass curing of high volumes of material. Alternate
embodiments enable curing in a swath that does not fully extend
across the width of the substrate.
[0045] There are a number of challenges that complicate the task of
using laser diodes for this purpose. One problem relates to the
speed at which laser diodes can be shuttled to deliver the
necessary energy. Other difficulties relate to limitations of the
laser devices themselves. For example, placing a bank of lasers in
close proximity to a printing surface can lead to optical feedback,
jitter and other destabilizing effects. Yet another challenge for a
laser based system relates to delivery of uniform, dense, and
addressable pixilation in illumination.
[0046] Laser thermal printing systems have been disclosed that use
a fiber coupled diode array for dye sublimation and transfer. U.S.
Pat. No. 5,619,245, entitled "MULTI-BEAM OPTICAL SYSTEM USING
LENSLET ARRAYS IN LASER MULTI-BEAM PRINTERS AND RECORDERS" to
Kessler et al., for example, describes a multi-beam laser printhead
using a monolithic array of independently modulated diode lasers.
Systems of this type deliver laser energy with acceptable beam
quality and energy characteristics for transfer of a colorant from
a donor to a recipient medium using ablation or other mechanisms.
Optical characteristics such as depth of focus are optimized for
colorant transfer with these printheads. Registration and alignment
of the printhead to the donor and recipient media are tightly
controlled in this type of donor transfer printing apparatus, with
tight constraints on substrate spacing and handling. Energy levels
that are locally generated for donor ablation are quite high,
suitable for depositing a high-resolution array of colorant dots,
but significantly exceeding those needed for curing of applied
nanoparticulate inks.
[0047] According to an aspect of the invention there is provided a
method of printing high resolution electronic features by
depositing a pattern of nanoparticle-based ink onto a substrate and
then curing the deposited pattern using fiber-coupled diode
laser-based curing.
[0048] The flow diagram of FIG. 1A shows a sequence of steps for a
printing and curing method 10 for nanoparticle-based inks according
to an embodiment of the present invention. This method includes:
pretreating the substrate in a washing or cleaning step 20,
depositing adhesion promoting material in an optional coating step
30, depositing a pattern of nanoparticle ink in a printing step 40;
illuminating the pattern of deposited ink to transform the ink by
sintering and other curing processes using a laser diode array in a
curing step 50; and removing the untransformed ink and residual
materials in a removal step 60. Removal step 60 also includes
evaporating and exhausting excess material from the applied and
cured ink or coating.
[0049] The schematic diagram of FIG. 1B shows a printing and curing
system 80. The printing and curing system 80 has a substrate 120 on
which material is printed, a transport apparatus 90 with devices
such as rollers 110 or other components for providing relative
movement between printing and curing components and substrate 120,
a mount for substrate 120 which may include a heat sink or
temperature control element 100 designed to maintain substrate 120
at a suitable temperature at specific points in the process, an
optional substrate cleaning apparatus 130, an optional coating
apparatus 140, a printing apparatus 150 that is energizable for
deposition of the nanoparticulate electronic material, such as
using inkjet or screen print mechanisms, creating a pattern of
printed elements 160 on the substrate 120 surface. An illumination
apparatus 170 has two or more energizable laser diodes 180, each
with its corresponding coupling optics 185 that direct light
through a corresponding light guide, shown as an optical fiber 200.
Light from fibers 200 goes through a coupling block 210 and to an
illumination lens 220 for directing a pattern of illumination that
corresponds to the pattern of printed elements 160 on substrate
120. A washing apparatus 240 can be energized to perform a cleaning
operation to remove uncured ink or other material. An exhaust
element 250 is provided to help remove by-products of the printing
and curing process.
[0050] Transport apparatus 90 more generally provides relative
motion for forming a pattern and can also operate wherein substrate
120 is stationary and one or more of energizable surface
conditioning, printing, and curing components, such as apparatus
130, 140, 150, 170, 240, and 250 are swept along the surface of
substrate 120 to perform pattern deposition and curing operations.
FIG. 1C is a schematic diagram showing an alternate embodiment with
a printing and curing system 88 for use with electronic ink,
wherein printing and illumination apparatus 150 and 170 and other
components are coupled together as part of a pattern forming
apparatus 94 that moves past a stationary substrate 120. Transport
apparatus 90 may include a leadscrew or may be belt-driven, for
example. A dashed box indicates pattern forming apparatus 94.
Transport apparatus 90 moves pattern forming apparatus 94 from
right to left across substrate 120 in the arrangement of FIG.
1C.
[0051] Washing or cleaning step 20 in the sequence of FIG. 1A
consists of cleaning the substrate with solvents, or alternately
with surface treatments such as using corona discharge energy or
treating with compressed gases or other methods. It is found that
the method of the present invention is particularly suitable for,
but not limited to, use with a number of substrates including PET
(polyethylene terephthalate), PI (Polyimide), PE (polyethylene), PP
(Polypropylene), PVA (poly-vinyl alcohol), SiN (silicon nitride),
ITO (indium tin oxide) and glass. In general, substrates need to be
sufficiently clean in order to fully accept and cure the printed
ink materials. Failure to clean the substrate, either in line, by
energizing substrate cleaning apparatus 130 as depicted in the
process of FIG. 1B, or prior to printing using some other method,
can lead to poor adhesion, degraded electrical performance,
material contamination, and breakage.
[0052] According to an embodiment of the present invention, the
substrate 120 material is transported by means of transportation
apparatus 90 (FIG. 1B) and moved through system 80 in a
roll-to-roll, flat, sheet-fed, drum-fed, continuous, or
stop-and-start sequence. Along the transportation system are placed
one or more tracking elements such as reflectors or sensors 230.
Tracking elements provide optical or electrical feedback as to the
alignment of the elements of the printing chain. For example,
reflections of a tracking element in the curing process can
determine curing accuracy and substrate position. Sensors 230 can
be placed under the substrate in the assembly or along edges of the
substrate, as long as the illuminating wavelength reaches the
sensor 230.
[0053] Temperature control element 100 (FIG. 1B) may be a simple
heat sink or may be an apparatus designed to heat and cool the
substrate to a desired temperature, integrated into transport
apparatus 90. Maintaining temperature becomes a concern, since
heated substrates can expand or shrink under different temperature
conditions, with the risk of deformation of substrate or
end-printed structures. Furthermore, as heat energy from the
illumination system 170 can cause spatial temperature variations,
spatially varying the temperature may be useful for certain
applications.
[0054] Optional coating step 30 in the FIG. 1A sequence prepares
the surface with adhesion promoting materials. Coatings, applied by
energizing coating apparatus 140 in FIG. 1B, can be uniformly
deposited, such as by aerosol application, roll coating, or other
methods. Alternately, coatings are deposited selectively by inkjet
deposition, or other selective printing mechanism, such as aerosol
jet. This step, while not required in all cases, can significantly
enhance the ability of material to adhere to substrate 120.
Selective deposition of adhesion promoting materials can further
assist in delineation between electrically active printed
electronic structures and passive sections of a printed region.
Auxiliary drying equipment, not shown in the FIG. 1B or 1C
embodiments, may also be provided to facilitate drying or
solidifying of an applied coating.
[0055] Continuing with the FIG. 1A sequence, the nanoparticle ink
is deposited onto the substrate in printing step 40. The ink is
deposited by energizing nanoparticle ink printing apparatus 150.
Nanoparticle ink printing apparatus 150 uses a suitable deposition
method such as ink-jet, offset-lithography, screen printing,
indirect or direct gravure, flexography, aerosol application, or
some other method. The binder and/or coating present in the
nanoparticle ink helps to provide an even distribution of the ink.
The deposited layer can be of variable thickness and, in practice,
is typically in the thickness range between about 0.05-50 .mu.m,
but would not be limited to this range.
[0056] As shown in the perspective view of FIG. 2, drivers 300,
under control of a control logic processor 310, provide the
energizing signals for the individual laser diode 180 in each
channel in illumination apparatus 170. A small number of laser
diodes 180 are shown in FIG. 2. In embodiments of the present
invention, numerous laser diodes 180 can be employed. Laser diodes
180 are provided with an optional heat sink 320. Each laser diode
has corresponding coupling optics 185. An optical fiber 200 or
other light guide then directs the generated laser light through
coupling block 210 and lens 220. The laser diode 180 in each
channel can be independently energized or de-energized as needed.
This allows illumination apparatus 170 to direct light in a
pattern, in conjunction with the operation and speed of transport
apparatus 90. Advantageously, the pattern of illumination that is
provided corresponds to the pattern of nanoparticle material that
is applied by nano ink printing apparatus 150.
[0057] The use of laser light allows for the selection of a light
wavelength that is well suited for the sintering of the
nanoparticles while eliminating or minimizing damage to the
coating. By using lasers, embodiments of the present invention
apply monochromatic light to the substrate at wavelengths most
favorable to sintering and other curing functions, without
contributions from other wavelengths, such as lower wavelength
light that can be heavily absorbed in the upper layers of deposited
material. As noted earlier, absorption of wavelengths in upper
layers nearest the surface can cause these upper layers to be
inadvertently sealed, trapping binder and other materials that must
be removed from beneath the surface. Advantageously, laser
illumination provides sufficient energy for the removal of
component materials in the precursor nanomaterial. This includes
materials useful for improving ink application but not wanted in
the final product, such as organic binders and particle coatings.
With laser light, the spectral content and intensity can be
specified and controlled so that the laser delivers the proper
energy to the applied material, at the proper depth. In this way,
problems such as unwanted sealing of top layers can be avoided.
[0058] Thermal characteristics of the substrate can complicate the
task of sintering in a number of ways when conventional Xenon flash
energy is used. Substrates having relatively high thermal
conductivity, such as aluminum, silicon, and ceramic substrates,
for example, can conduct the needed heat away from the area of
incident light before sintering energy levels are reached.
Polymer-based substrates, such as ITO coated plastic substrates,
can be damaged due to the higher thermal conductivity of the ITO
coating. Embodiments of the present invention help to address
problems related to thermal response by using laser light that can
be focused onto a small area.
[0059] Coupling of the laser light to each channel 212 within a
coupling block 210, as shown in FIG. 2, is managed carefully, since
reflections from the fiber can cause inadvertent mode hopping and
other instabilities. Techniques for laser light routing and
coupling to prevent these problems are well known to those skilled
in the optical design arts. Optical fibers 200 extend to the
coupling block 210, which may consist of a series of V-grooves in
which the fibers are nested. Typical fibers include 50 um step core
index fibers with a Numerical Aperture (NA) of 0.2. Choice of
fibers takes into account that with lower Numerical Apertures, the
laser light will have a greater depth of focus. Subsequent
illumination lens 220 transmits the generated light. The spot
profile of the directed laser beam can be round or slightly or
highly elliptical, depending on the cross array imaging of the
printing lens. Laser diodes in the array have a first distance D1
between them, determined by factors such as size of components and
thermal considerations. Coupling block 210 and optical fibers 200
enable laser diode light channels to have a second distance D2
between them, wherein D2 is less than D1. Thus, features can be
written at high resolution. Optical fibers are step-index optical
fibers according to an embodiment of the present invention.
[0060] Commercially available solutions for driving the laser diode
include using a 12 bit DAC that provides a high speed amplifier
driving current to each channel or a constant current source
switching between the diode laser and a dummy load to ensure a fast
enough rise time, such as a <50 ns rise time. The driver can use
single pulses of light to deliver desired peak intensity as well as
to deliver total energy at a given level. Amplitude modulation may
be used. Additionally, due to the quick rise time, pulse width
modulation, or some combination of modulation techniques, can be
used to the deliver the desired energy.
[0061] The resolution of the printing structure can be further
determined by the relative energy profile of the illumination beam
at substrate 120 and the response of the applied ink material. By
way of reference, in a dye sublimation printing system, a 50 um
core fiber can produce a 2560 dpi (dots-per-inch) image, with a
spot size of 1 um. Similarly, in a material curing system, the
printed electronic element can be smaller than core beam size. This
effect can be used to interlace wavelengths and to obtain smaller
features.
[0062] Using fiber coupled lasers allows a number of advantages,
including a measure of thermal isolation. The local temperature of
the diode and drivers can be separated from the printing
environment. By mounting and spacing the laser diodes
appropriately, feedback and jitter can be minimized. Using modular
design techniques, laser assemblies can be readily replaced.
Embodiments of the present invention use one of several ways to
monitor diode operation. One technique is to maintain a feedback
loop within driver 300 for adjusting drive current to within
prescribed values. Alternately, feedback from the illumination
incident on the substrate surface is used.
[0063] According to an embodiment of the present invention, diode
laser arrays are formed of diodes having different emission
wavelengths, wherein the emission wavelengths of at least two of
the laser diodes in the array differ from each other by more than
25 nm. By spacing optical fibers 200 in the coupling block 210, the
subsequent illumination lens 220 accommodates accurate spot
placement for each wavelength. There can be some trade-off of spot
size verses proximity between the different wavelengths. The focal
spot size can also vary as a function of wavelength.
[0064] Advantageously, separate channels can be addressed
simultaneously or sequentially. With simultaneous addressing,
printing relies on the difference in required curing wavelengths
for different materials. For example, ink having high copper (Cu)
content tends to cure with applied energy in the near infrared,
whereas some inks high in silicon require shorter wavelengths.
[0065] When driving laser diodes, pulse width modulation (PWM) can
be used for controlling power levels and for temporally
interspersing the illumination wavelengths. This permits the use of
different wavelengths, both to cure different materials and to
provide curing energy at different depths. For example, a longer
wavelength can be useful for curing material at a greater depth.
Wavelengths that have been found to be suitable for curing include,
but are not limited to: 193 nm, 248 nm, 308 nm, 355 nm, 488 nm, 532
nm, 808 nm, 860 nm, 975 nm, 1064 nm, and CO.sub.2 laser
wavelengths.
Nanoparticle Ink Formulations
[0066] The printed electronic structures that can be formed by the
present method are made of a metal or semi-metal, such as
semiconductor material. Suitable metals for printing and curing in
a pattern include, but are not limited to, copper, gold, silver,
nickel, and other metals and alloys. Semi-metal materials including
silicon can also be used. Furthermore, silicon particles that have
been doped to provide semiconducting behavior (for example, doped
with phosphorous or arsenic) are also suitable. Therefore, the
present method can be used in production of both electronic
structures, such as connecting traces between devices, and
semiconducting devices themselves.
[0067] The nanoparticle ink used in embodiments of the present
invention comprises the metal or semi-metal with a binder or
coating (typically organic). The binder or coating in the ink helps
to prevent agglomeration and to maintain the surface area, which
confers many of the advantageous properties of nanoparticles. The
nanoparticles used in the ink formulation can be between 0.5-500
nm. Advantageously, therefore, the present invention can be
implemented for a wide range of nanoparticle inks including those
with larger particles which are often cheaper to produce. An
example of a suitable ink is the commercially available CI-002
formulation sold by Intrinsiq Materials, Rochester, N.Y. As noted
previously, inks need not be comprised solely of nanoparticles, but
may contain a mix with at least some percentage of nanoparticles,
as described previously, and larger particles.
[0068] The high surface area of the nanoparticles is advantageous,
so that the energy required to transform the nanoparticles in the
ink, such as by sintering or curing, is less than for bulk
materials. Therefore, as the laser illumination not only removes
the coating or binding materials in the ink formulation, it also
causes a transformation of the material. Upon receiving the
illumination energy, the individual metal/semi-metal nanoparticles
bond to form a metal/semi-metal structure, in the form of a
densified metal or semi-metal film (depending on the material of
the nanoparticle ink). As the laser illumination can be focused to
a small spot size, the metal structure that is formed is localized
to areas impacted by the laser. The high degree of accuracy with
which the laser can be directed results in the formation of the
high resolution printed structures.
[0069] Each deposited material or ink can have different curing
properties, responding differently to light of various wavelengths
and intensities. Where multiple materials are deposited, it may be
suitable to cure the different materials under the same conditions
or to vary wavelength and intensity levels appropriately. According
to an embodiment using a single illumination apparatus 170 as in
FIG. 1B, for example, each laser diode 180 has the same wavelength,
with variation in wavelength within the laser array to within no
more than about +/-1 nm of a nominal wavelength, but the intensity
of the directed illumination changes, depending on the spatial
position of apparatus 170 relative to the substrate 120 surface.
Individual laser diodes 180 can be energized at different power
levels over different portions of the applied pattern of printed
elements 160. Exposure duration can also be modified, such as by
varying the transport speed of transport apparatus 90 or using
pulse-width modulation, for example. According to an alternate
embodiment of the present invention, laser diode array 190 has
laser diodes 180 of different wavelengths, suitably positioned for
providing energy to the applied pattern of printed elements
160.
[0070] Referring again to the sequence of FIG. 1A, once the laser
diode array 190 has finished illuminating the substrate and the
desired image has been cured, the untransformed material is removed
in removal step 60. The ink that has been scanned by the laser beam
is transformed, typically by curing or sintering depending on the
strength of the laser and length of exposure. The properties of the
transformed, densified metallic structure differ from the
untransformed structure. It is possible to select washing
formulations and processes in removal step 60 to remove
untransformed, unbounded, or uncured materials from the substrate
surface while having little or no impact on cured regions. Such
washing formulations are well known in the art of
photolithography.
[0071] It is found that the present method is particularly suitable
for a number of substrates including PET, PI, PE, PP, PVA, PI, SiN,
ITO and glass. Therefore, the present application provides an
improved method for producing high resolution lines compared to
other systems. In particular, the direct transformation (curing,
sintering or otherwise) of the material by the laser allows for
higher resolution features, reduces or avoids the need for adding
further layers such as photoresist layers and requires fewer stages
to produce than do conventional methods. Printing and curing of
electronic materials and components can be performed at low volumes
as well as for large-scale, high volume production.
[0072] The schematic diagrams of FIGS. 3 and 4 show alternate
embodiments of the present invention for depositing more than a
single material. Processing using these systems repeats portions of
steps 40, 50, and 60 in the FIG. 1A sequence.
[0073] In an alternate embodiment of a printing and curing system
82 as shown in FIG. 3, multiple separate illumination diode arrays
190a and 190b are used to provide extra spatial coverage and/or
different illuminators, such as diodes of different wavelength. An
illumination apparatus 170a has a bank of multiple laser diodes
180a that are energizable to direct light through coupling optics
185a to optical fibers 200a, coupling block 210a, and an
illumination lens 220a. Similarly, an illumination apparatus 170b
has a bank of multiple laser diodes 180b that are energizable to
direct light through coupling optics 185b to optical fibers 200b,
coupling block 210b, and an illumination lens 220b. Using separate
illumination apparatus 170a and 170b allows each of the subsequent
illumination lenses 220a and 220b to be of simpler design, since
the respective wavelength spread for each lens can be minimized.
The arrangement of printing and curing system 82 is further
beneficial where particular printed areas of substrate 120 may need
additional illumination or where there is component failure in one
of illumination apparatus 170a or 170b.
[0074] Also shown in the embodiment of printing and curing system
82 in FIG. 3 are multiple washing apparatus 240 and exhaust
elements 250 for removing volatilized material. Optionally, one set
of washing and exhaust elements may suffice depending on factors
such as material characteristics and transport speed.
[0075] In an alternate embodiment, of a printing and curing system
84 as shown in FIG. 4, multiple printing apparatus 150a, 150b are
used, along with corresponding illumination diode arrays 190a,
190b. This arrangement allows additional spatial coverage for
depositing the same material, including deposition at different
feature sizes, or depositing and curing different nanoparticle ink
materials, such as materials with different viscosities, requiring
different preconditioning or curing, or having other different
characteristics. Printing apparatus 150a and 150b can be the same
type or different types of print systems. For example, the first
apparatus 150a may be an inkjet printer, and the second apparatus
150b a gravure printer. In the particular embodiment shown in FIG.
4, two washing apparatus 240 and a single exhaust element 250 are
shown; alternate embodiments with different numbers and
arrangements of these support systems can also be provided, as
described previously. The use of multiple illumination apparatus
170a and 170b provides the same advantages described with reference
to FIG. 3. In addition, further coatings may be applied between
printed layers of nanoparticle materials, such as an insulating
coating, for example.
[0076] According to an alternate embodiment of the present
invention, the illumination that is used for curing is spatially
dithered, or moved rapidly between nearby positions at a high rate
of speed. Dithering can be advantageous for increasing the area
coverage of laser light beams where there are a limited number of
light sources and for reducing excessive patterning or other
unwanted effects of the illumination system. Embodiments of FIGS.
5, 6, and 7 show various mechanisms that are energizable for
dithering and that can be used for one or more of illumination
apparatus 170, 170a, or 170b in the embodiments shown in FIGS. 1B,
3, and 4. The schematic view of FIG. 5 shows one type of mechanical
dithering apparatus 600 that has an actuator 610 with a coupling
620 to optical coupling block 210. According to an embodiment of
the present invention, actuator 610 is a piezoelectric actuator
that causes dithering by rapidly vibrating coupling block 210.
Alternately, actuator 610 can be coupled to other appropriate
elements in the optical system.
[0077] Spatial dithering can include the illumination lens 220
assembly or can be within the field of view of the lens assembly.
FIG. 6 depicts an optical dithering apparatus 700. To provide
dithering, a mirror element 720 is coupled to an energizable
actuator 710 to provide translation in either or both linear and
rotational directions, optically redirecting the illumination in
the optical path preceding the lens 220 assembly. This requires
that the dithered light falls within the field of the lens. In an
alternate embodiment shown in FIG. 7, the optical dithering
apparatus 700 is introduced in the optical path following
illumination lens 220. This design requires a sufficient depth of
focus and focal length.
[0078] In cases involving dithering, alignment tracking is useful
to help provide the illumination over the intended area. Sensors
230 and related components (FIGS. 1B, 3, 4) help to provide the
needed alignment tracking.
[0079] Embodiments of the present invention can provide a measure
of control over how the curing illumination is directed to surface
120, both for directing a pattern of light and for dithering. The
schematic diagram of FIG. 8 shows an alternate embodiment of a
printing and curing system 86 of the present invention having an
illumination apparatus 172 in which a spatial light modulator (SLM)
800 is used for directing laser light to the substrate surface 120.
Light from one or more laser diodes or other light source 820 is
conditioned by a uniformizer 810 and directed to SLM 800.
Uniformizer 810 can be, for example, any suitable type of light
homogenizer, such as a fly's-eye lens array, integrating rod, or
other light integrator. Light sources used as part of light source
820 can emit light of the same wavelength or light of different
wavelengths, that is, light of wavelengths that differ from each
other by more than 25 nm.
[0080] Spatial light modulator 800 pixelates the uniformized input
beam, breaking it into independent, spatially identified, modulated
portions. Each pixel is individually modulated temporally and with
respect to amplitude. The individual pixels are re-imaged at the
printing plane to sinter the deposited ink. With this arrangement,
the laser light can be pulsed or continuous; the SLM 800 provides
patterning and, optionally, dithering of the illumination light.
Advantages of SLM systems include a measure of control over light
output, response speed, and uniformity.
[0081] Spatial light modulation can be liquid crystal devices (LCD)
or micromechanical-based modulation devices, such as digital
micromirror DMD array, such as the Digital Light Processor (DLP)
from Texas Instruments, Inc., Dallas, Tex. With such devices, the
light intensity at each pixel is controlled by the modulator
output. Furthermore, with very fast modulation, the total light
intensity can be varied through pulse width modulation and pulse
frequency such that a cumulative energy target is approached.
[0082] Spatial light modulators can also be electro-optic
modulators whereby the spatial intensity is modulated by means of
electric field variations in an electro optic material. An example
of this type of device is the Electro-optic phase modulator from
Xerox Corp., Stamford, Conn. Other types of phase modulation are
provided by diffraction, using a GEMS (grating electromechanical
system), such as that described in U.S. Pat. No. 6,411,425 to
Kowarz et al. entitled "ELECTROMECHANICAL GRATING DISPLAY SYSTEM
WITH SPATIALLY SEPARATED LIGHT BEAMS"; a grating modulator array,
such as that described in U.S. Pat. No. 6,084,626 to Ramanujan et
al. entitled "GRATING MODULATOR ARRAY"; or a GLV (grating light
valve), such as that described in U.S. Pat. No. 5,481,579 entitled
"FLAT DIFFRACTION GRATING LIGHT VALVE" to Bloom et al. Additional
modulator types include semiconductor based SLMs.
[0083] The various types of SLM devices can directly modulate
intensity (amplitude) or can operate using frequency/phase
modulation. In the case of phase modulated light modulation, light
is selectively reflected or diffracted into a number of light beams
of discrete orders, forming a far-field pattern. This far-field
pattern can then be filtered to allow passage of select orders.
Those diffracted orders are then reimaged to the print surface,
with modulation achieved by temporally deflecting light into
specified orders.
[0084] Example far field patterns are shown in FIG. 9. In systems
that generate a far field pattern, a filter is used to select
different orders of light. Undeflected light, zeroth order light
824 is provided with the SLM in one state. Deflected light, shown
in FIG. 9 as first order light 828 and second order light 830, is
provided with the SLM in an alternate state. By selecting the
zeroth order light 824, thresholding applications wherein a minimal
light intensity is required can be enabled. By modulating light
into its various orders, the pixel profile and width can be altered
dynamically by means of addressing. For example, a spatial light
modulator whose pixel is defined by the field profile between
electrodes, can effectively provide wider pixels by maintaining a
wider field profile. Also, field profiles can readily be controlled
to provide sub-pixelization and varied subpixel intensities.
[0085] The simplified schematic of FIG. 10 shows components of
illumination apparatus 172 using phase modulation. A laser or laser
array 840 provides light through uniformizing optics 844 to spatial
light modulator 800. A far field 850 is formed between lenses 848
and 852, with a spatial filter 854 in far field position,
generating imaged pixels at an image plane 860.
[0086] Embodiments of the present invention advantageously allow
high resolution features to be produced in a single stage process.
In particular, the invention avoids the need for an extra layer,
such as a photoresist layer, and its subsequent processing.
Furthermore, unlike photoresist methods, the method of the present
invention does not require the use of etchants to remove the
unprotected, uncured structure. This is advantageous as it
simplifies the production process. In addition, embodiments of the
present invention allow a measure of accuracy with direct placement
of electronic traces and structures. It is known, for example, that
etchants used in conventional electronic patterning can result in
excessively sloped tracks or undercut, whereas the use of lasers to
directly cure/transform the material allows for well-defined edges
to be formed.
[0087] The invention has been described in detail with particular
reference to certain preferred embodiments thereof, but it will be
understood that variations and modifications can be effected within
the scope of the invention.
* * * * *