U.S. patent application number 12/578095 was filed with the patent office on 2010-02-04 for method of forming structures using drop-on-demand printing.
This patent application is currently assigned to CANON KABUSHIKI KAISHA. Invention is credited to Nicholas Rowland Bingham, Alison Joan Lennon, Peter Kirkland Thomson.
Application Number | 20100024725 12/578095 |
Document ID | / |
Family ID | 37533349 |
Filed Date | 2010-02-04 |
United States Patent
Application |
20100024725 |
Kind Code |
A1 |
Lennon; Alison Joan ; et
al. |
February 4, 2010 |
METHOD OF FORMING STRUCTURES USING DROP-ON-DEMAND PRINTING
Abstract
A method and apparatus are described for forming a structure on
a substrate. The structure may be a circuit element. The method
uses a digital specification 910 for forming the structure,
including specifications for printing and curing. The structure is
printed (step 112) using a drop-on-demand printer 400, wherein the
printing dispenses at least one material on the substrate 420
according to the digital specification 910. The structure is cured
(step 130) by irradiating the dispensed material from one or more
electromagnetic radiation sources 520, 525 in the printer 400,
wherein curing parameters are specified by the digital
specification 910 to obtain a desired electrical property when the
structure is a circuit element. The curing specification may
specify the intensity of the irradiation and the location of
irradiation points in the print region.
Inventors: |
Lennon; Alison Joan;
(Balmain, AU) ; Thomson; Peter Kirkland; (Beaumont
Hills, AU) ; Bingham; Nicholas Rowland; (North Ryde,
AU) |
Correspondence
Address: |
WILLIAM J. SMITH
13698 OTUSSO DRIVE
PERRYSBURG
OH
43551
US
|
Assignee: |
CANON KABUSHIKI KAISHA
Tokyo
JP
|
Family ID: |
37533349 |
Appl. No.: |
12/578095 |
Filed: |
October 13, 2009 |
Related U.S. Patent Documents
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Application
Number |
Filing Date |
Patent Number |
|
|
11432626 |
May 12, 2006 |
|
|
|
12578095 |
|
|
|
|
Current U.S.
Class: |
118/697 ;
118/704 |
Current CPC
Class: |
B41J 11/002 20130101;
H05K 3/125 20130101; B41J 3/407 20130101; H05K 2203/107 20130101;
H05K 1/095 20130101; H05K 2201/0257 20130101; H05K 3/1283
20130101 |
Class at
Publication: |
118/697 ;
118/704 |
International
Class: |
B05C 5/00 20060101
B05C005/00 |
Foreign Application Data
Date |
Code |
Application Number |
May 19, 2005 |
AU |
2005202167 |
May 19, 2005 |
AU |
20050216703 |
Claims
1. An apparatus for forming a circuit element on a substrate, the
apparatus comprising: a computer arranged to select a digital
specification for forming the circuit element; a drop-on-demand
printer coupled to the computer and configured to print the circuit
element by depositing at least one material on the substrate
according to the digital specification; and at least one
electromagnetic radiation source coupled to the computer and
configured to cure the circuit element by irradiating the deposited
material with electromagnetic radiation according to curing
parameters specified by the digital specification to thereby obtain
a desired electrical property of the circuit element.
2. An apparatus according to claim 1, wherein the drop-on-demand
printer includes an ink-jet print head assembly, the ink-jet print
head assembly comprising: at least one cartridge for storing
material to be dispensed; a print head corresponding to each
cartridge for dispensing the material onto a substrate; and a
plurality of electromagnetic radiation sources each configured to
cure the dispensed material by irradiation of the dispensed
material.
3. An apparatus according to claim 2, wherein the ink-jet print
head assembly further comprises means for receiving signals that
control a firing of nozzles of print heads and to initiate
radiation pulses of the plurality of radiation sources.
4. An apparatus for forming a structure on a substrate, the
apparatus comprising: a computer arranged to select a digital
representation for the structure and to identify at least one
region in the digital representation; a drop-on-demand printer
coupled to the computer and configured to print the identified
region by depositing at least one material on the substrate
according to the digital representation; and at least one
electromagnetic radiation source coupled to the computer and
configured to cure the region according to the digital
representation by irradiating the deposited material with
electromagnetic radiation according to an intensity of the
irradiation and a location of irradiation points in the region
specified by the digital representation.
5. A system for forming a circuit element on a substrate, the
system comprising: a data storage containing one or more digital
specifications for circuit elements; a drop-on-demand printer in
communication with the data storage for forming a selected circuit
element, the printer comprising: one or more print heads for
dispensing material from one or more cartridges to thereby deposit
the material on the substrate using a drop-on-demand technique
according to a digital specification for the selected circuit
element; and one or more sources of electromagnetic radiation
arranged to cure the deposited material by irradiating the
deposited material with electromagnetic radiation according to
curing parameters specified by the digital representation to
thereby obtain a desired electrical property of the selected
circuit element.
6. A system according to claim 5, wherein the printer includes a
print head assembly that comprises the one or more print heads and
the one or more sources of electromagnetic radiation.
7. A system according to claim 5, wherein the printer includes a
positioning system to control a position of the substrate relative
to the one or more print heads and the one or more sources of
electromagnetic radiation.
8. A system for forming a structure on a substrate, the system
comprising: a data storage containing one or more digital
specifications for structures; a drop-on-demand printer in
communication with the data storage for forming a selected
structure, the printer comprising: one or more print heads for
dispensing material from one or more cartridges to thereby deposit
the material on the substrate using a drop-on-demand technique
according to a digital specification for the selected structure;
and one or more sources of electromagnetic radiation arranged to
cure the deposited material by irradiating the deposited material
with electromagnetic radiation according to an radiation intensity
and locations of irradiation points on the substrate specified by
the digital specification for the selected structure.
Description
CROSS-REFERENCE TO RELATED PATENT APPLICATIONS
[0001] This application is a divisional application of U.S. patent
application Ser. No. 11/432,626 filed 12 May 2006, which claims the
right of priority under 35 U.S.C. .sctn.119 based on Australian
Patent Application No. 2005202167, filed 19 May 2005, both of which
are incorporated by reference herein in their entirety as if fully
set forth herein.
COPYRIGHT NOTICE
[0002] This patent specification contains material that is subject
to copyright protection. The copyright owner has no objection to
the reproduction of this patent specification or related materials
from associated patent office files for the purposes of review, but
otherwise reserves all copyright whatsoever.
TECHNICAL FIELD OF THE INVENTION
[0003] The present invention relates to the formation of physical
structures using drop-on-demand printing. In particular, the
present invention relates to the formation of circuit elements
using drop-on-demand printing.
BACKGROUND
[0004] Conventional methods for forming structures such as
electronic circuits involve plating, lithography and etching steps.
These methods are well suited for high-volume production. However,
they involve many steps and much wasted material as exposed
photoresist is etched away. In another approach, three-dimensional
structures can be formed by depositing layer after layer of
material using drop-on demand printing methods. Electronic circuit
elements are an example of such structures, which can be formed by
printing a number of discrete layers on a substrate using materials
having specific electrical properties. For example, a transistor
can be formed by printing conducting, semiconducting and insulating
materials in a particular layered pattern.
[0005] Drop-on-demand printing is a known printing technique where
a droplet of ink is ejected by a thermal or piezoelectric inkjet
print head. The droplet is ejected onto a substrate where the
droplet dries and forms a dot of a pattern (e.g., a printed photo).
In contrast to etching procedures, there is no wasted material.
[0006] A three-dimensional structure can be formed by dispensing
layers of materials according to the patterns determined by a
three-dimensional digital representation. Crump in U.S. Pat. No.
5,121,329, issued on 9 Jun. 1992, describes a method of forming
three-dimensional structures using a dispensing head connected to a
CAD system. The dispensing head can dispense material at a
controlled rate onto a substrate in a predetermined pattern
dictated by the CAD system. Materials are heated above their
solidification temperatures and dispensed as fluids, which then
solidify after deposition and cooling. This method is limited to
materials that can be solidified in this way.
[0007] The formation of three-dimensional structures by selectively
irradiating liquid photo-curable polymers has also been described
in U.S. Pat. No. 4,575,330 (issued to Hull on 11 Mar. 1986), and
U.S. Pat. Nos. 4,752,498 and 4,801,477 (issued to Fudim on 21 Jun.
1988 and 31 Jan. 1989, respectively). This technique, which is
known as photosolidication, involves focussing ultraviolet (UV)
light in a predetermined pattern either over the surface of a layer
of liquid or within the volume of a liquid to cure (solidify)
polymer material. Although this method also enables the design of
objects using a CAD package, it is limited in the way different
materials can be incorporated in the object as the liquids mix
before curing.
[0008] U.S. Pat. Nos. 6,503,831 and 6,713,389 (issued to Speakman
on 7 Jan. 2003 and 30 Mar. 2004 respectively) describe
drop-on-demand printing of inks for electronic circuit elements.
Curing (or solidification) of printed material is achieved using
conventional drying and/or radiation-enhanced drying or curing. The
curing process can include radiation-induced cross-linking of
organic materials. In particular, Speakman describes a radiation
source close to the nozzle (on the print head) that can be used to
treat deposited material either before, during or after deposition.
One of the advantages of irradiating in-flight is to partially cure
the material before deposition and thus reduce dot sizes before
impact on the substrate. In general, the term "cure" with relation
to polymer materials is used to refer to solidification of the
deposited material.
[0009] Mogensen in U.S. Pat. No. 6,697,694 issued on 24 Feb. 2004
describes a similar method for printing flexible circuits by
printing layers of materials using techniques that include
drop-on-demand printing. In this patent, a method and apparatus is
described whereby materials are dispensed on a flexible substrate
in a predetermined pattern using a dispensing unit which can plot
patterns using motions in the x,y and z axes relative to the
substrate. Printed material is then cured by a separate curing
unit, which can also be moved relative to the substrate. Layers are
formed by successively printing and then curing each layer. The
described curing unit can either provide UV, infrared, or gamma
radiation. Alternatively, curing can be achieved using heating
methods.
[0010] US Patent Application No. 2004/0041892 (Yoneyama et al.)
describes a method of tuning the power of the curing irradiation
(used with polymer inks) depending on the humidity measured by a
sensor located close to the print head. The irradiation power is
controlled within the circuitry of the printer and is used simply
to maximise the polymerisation of the deposited ink.
[0011] Drop-on-demand printing has also been used to deposit
inorganic nanoparticle materials that can be cured to form
conductive elements. In these cases, the curing process results in
the nanoparticles sintering or fusing to form conductive elements
which have a lower resistance. In particular, curing of metal
nanoparticle films has been achieved by heating the printed inks to
temperatures of 150 to 200.degree. C. However, this heating step
limits substrates that can be used to those that can survive the
curing temperatures required. More recently, Chung et al. have
described a method of sintering metal nanoparticle films by
irradiating the films with an Argon ion laser (514 nm) in
"In-tandem deposition and sintering of printed gold nanoparticle
inks induced by continuous Gaussian laser irradiation" published in
Applied Physics A, volume 79, 1259-1261 in 2004. Like heat curing,
laser irradiation can cause coalescence of the individual
nanoparticles resulting in conductive gold films. Curing of
nanoparticle inks using white light irradiation (provided by flash
lamps used by cameras) has also been described in the PCT Patent
Publication No. WO 03/018645 (Reda et al.). These irradiation
methods of curing are advantageous because the curing step does not
necessarily damage the substrate thus allowing a wider range of
substrates to be used (e.g., flexible plastics).
SUMMARY
[0012] It is an object of the present invention to substantially
overcome, or at least ameliorate, one or more disadvantages of
existing arrangements.
[0013] The arrangements described herein relate to methods of
printing and curing nanoparticle films using a system in which an
operator can design and form a three-dimensional structure.
Irradiation parameters may be varied in a controlled way to form
structures having designed physical or electrical properties.
[0014] According to a first aspect of the invention there is
provided a method of forming a circuit element on a substrate, said
method comprising the steps of:
[0015] selecting a digital specification for forming the circuit
element;
[0016] printing the circuit element using a drop-on-demand printer,
wherein said printing step dispenses at least one material on the
substrate according to the digital specification; and
[0017] curing the circuit element by irradiating the dispensed
material from one or more electromagnetic radiation sources in the
printer, wherein curing parameters of said curing step are
specified by the digital specification to obtain a desired
electrical property of the circuit element.
[0018] According to a second aspect of the invention there is
provided a method of forming a structure on a substrate, said
method comprising the steps of:
[0019] selecting a digital representation for the structure;
[0020] identifying at least one region in the digital
representation;
[0021] printing the identified region using a drop-on-demand
printer, wherein at least one material is dispensed on the
substrate according to said digital representation; and
[0022] curing the region according to the digital representation by
irradiating the dispensed material from one or more electromagnetic
radiation sources, wherein the digital representation specifies the
intensity of the irradiation and the location of irradiation points
in the region.
[0023] According to a further aspect of the invention there is
provided an apparatus for forming a circuit element on a substrate,
said apparatus comprising:
[0024] means for selecting a digital specification for forming the
circuit element;
[0025] means for printing the circuit element using a
drop-on-demand technique, wherein at least one material is
dispensed on the substrate according to the digital specification;
and
[0026] means for curing the circuit element by irradiating the
dispensed material from one or more electromagnetic radiation
sources, wherein curing parameters are specified by the digital
specification to obtain a desired electrical property of the
circuit element.
[0027] According to a further aspect of the invention there is
provided an apparatus for of forming a structure on a substrate,
said apparatus comprising:
[0028] means for selecting a digital representation for the
structure;
[0029] means for identifying at least one region in the digital
representation;
[0030] means for printing the identified region using a
drop-on-demand technique, wherein at least one material is
dispensed on the substrate according to said digital
representation; and
[0031] means for curing the region according to the digital
representation by irradiating the dispensed material from one or
more electromagnetic radiation sources, wherein the digital
representation specifies the intensity of the irradiation and the
location of irradiation points in the region.
[0032] According to a further aspect of the invention there is
provided a system for forming a circuit element on a substrate
comprising:
[0033] data storage containing one or more digital specifications
for circuit elements;
[0034] a printer in communication with said data storage for
forming a selected circuit element, said printer comprising: [0035]
one or more cartridges for depositing material from said one or
more cartridges onto the substrate using a drop-on-demand
technique, wherein the depositing is performed according to the
digital specification for the selected circuit element; and [0036]
one or more sources of electromagnetic radiation for curing the
deposited material by irradiating the dispensed material, wherein
curing parameters are specified by the digital representation to
obtain a desired electrical property of the circuit element.
[0037] According to a further aspect of the invention there is
provided a system for forming a structure on a substrate
comprising:
[0038] data storage containing one or more digital specifications
for structures;
[0039] a printer in communication with said data storage for
forming a selected structure, said printer comprising: [0040] one
or more cartridges for depositing material from said one or more
cartridges onto the substrate using a drop-on-demand technique,
wherein the depositing is performed according to the digital
specification for the selected structure; and [0041] one or more
sources of electromagnetic radiation for curing the deposited
material, wherein the digital specification for the selected
structure specifies radiation intensity and locations of
irradiation points on the substrate.
[0042] According to a further aspect of the invention there is
provided a computer program product comprising machine-readable
program code recorded on a machine-readable recording medium, for
controlling the operation of a data processing machine on which the
program code executes to perform a method of forming a circuit
element on a substrate, said method comprising the steps of:
[0043] selecting a digital specification for forming the circuit
element;
[0044] instructing the operation of a drop-on-demand printer to
print the circuit element, wherein the printer dispenses at least
one material on the substrate according to the digital
specification; and
[0045] instructing the operation of one or more irradiation sources
in the printer to cure the circuit element by irradiating the
dispensed material, wherein curing parameters are specified by the
digital specification to obtain a desired electrical property of
the circuit element.
[0046] According to a further aspect of the invention there is
provided a computer program product comprising machine-readable
program code recorded on a machine-readable recording medium, for
controlling the operation of a data processing machine on which the
program code executes to perform a method of forming a structure on
a substrate, said method comprising the steps of:
[0047] selecting a digital representation for the structure;
[0048] identifying at least one region in the digital
representation;
[0049] instructing the operation of a drop-on-demand printer to
print the identified region, wherein at least one material is
dispensed on the substrate according to said digital
representation; and
[0050] instructing the operation of one or more electromagnetic
radiation sources to cure the region according to the digital
representation by irradiating the dispensed material, wherein the
digital representation specifies the intensity of the irradiation
and the location of irradiation points in the region.
[0051] According to a further aspect of the invention there is
provided a computer program comprising machine-readable program
code for controlling the operation of a data processing apparatus
on which the program code executes to perform a method of forming a
circuit element on a substrate, said method comprising the steps
of:
[0052] selecting a digital representation for the circuit
element;
[0053] identifying at least one region in the digital
representation;
[0054] instructing the operation of a drop-on-demand printer to
print the identified region, wherein the printer dispenses at least
one material on the substrate according to the digital
representation; and
[0055] instructing the operation of one or more irradiation sources
in the printer to cure the region by irradiating the dispensed
material, wherein curing parameters are specified by the digital
representation to obtain a desired electrical property of the
circuit element.
[0056] According to a further aspect of the invention there is
provided a computer program comprising machine-readable program
code for controlling the operation of a data processing apparatus
on which the program code executes to perform a method of forming a
structure on a substrate, said method comprising the steps of:
[0057] selecting a digital representation for the structure;
[0058] identifying at least one region in the digital
representation;
[0059] instructing the operation of a drop-on-demand printer to
print the identified region, wherein at least one material is
dispensed on the substrate according to said digital
representation; and
[0060] instructing the operation of one or more electromagnetic
radiation sources to cure the region according to the digital
representation by irradiating the dispensed material, wherein the
digital representation specifies the intensity of the irradiation
and the location of irradiation points in the region.
[0061] Other aspects of the present invention are also
disclosed.
BRIEF DESCRIPTION OF THE DRAWINGS
[0062] One or more embodiments of the invention are described below
with reference to the drawings, in which:
[0063] FIG. 1 is a flowchart showing a method of forming a
structure, such as a conductive element;
[0064] FIG. 2 is a flowchart showing a method of depositing the
material required for an object of the structure formed using the
method of FIG. 1;
[0065] FIG. 3 is a flowchart showing a method of curing an object
of the structure formed with the method of FIG. 1;
[0066] FIG. 4A shows a printing system that may be used to perform
the method of FIG. 1;
[0067] FIG. 4B is a schematic block diagram of the control system
of the printing system of FIG. 4A;
[0068] FIG. 5 is a schematic diagram of the print head assembly
used by the printing system of FIG. 4A;
[0069] FIG. 6 is a schematic diagram showing the nozzle arrangement
of an individual print head in the print head assembly of FIG.
5;
[0070] FIG. 7 is a graph showing the relationship between linker
length of agents, used to cap gold (Au) nanoparticles, and
resulting film resistance (before curing);
[0071] FIG. 8 is a graph showing the relationship between the
number of flashes, by a Xenon flash gun, and the resulting film
resistance (after curing);
[0072] FIG. 9 is a schematic diagram depicting the digital
representation of a structure to be formed by the method of FIG.
1;
[0073] FIG. 10 is a schematic diagram of a computer on which steps
of the described methods may be performed;
[0074] FIGS. 11A-11C show an example of the formation of a circuit
element according to the present disclosure; and
[0075] FIG. 12 is a flowchart of one method that may be used to
form the circuit element of FIGS. 11A-11C.
DETAILED DESCRIPTION INCLUDING BEST MODE
Overview
[0076] In the following description, reference is made to the
accompanying drawings which form part hereof. The drawings
illustrate specific arrangements in which the invention may be
practiced. It is understood that other arrangements may also be
utilized and structural changes could be made without departing
from the scope of the present invention.
[0077] The described arrangements provide a programmable method for
forming physical structures, and in particular circuit elements,
using a drop-on-demand printing device. Materials for a structure
are deposited on a substrate and then cured in a programmed way to
obtain structures having the desired physical and electrical
properties. The formed structures can be three-dimensional
structures, such as plastic mouldings, or electrical circuits and
their components.
[0078] The term "drop-on-demand" printing includes but is not
limited to the use of a digitally defined pressure pulse to force a
fluid meniscus out of a nozzle and on to a substrate surface. The
pressure pulse can be thermally, piezoelectrically, magnetically or
otherwise generated. The most common methods employed for drop-on
demand printing are thermal and piezoelectric inkjets.
[0079] In conventional imaging, images to be printed are typically
represented using any of the known pixel-based image formats such
as TIFF, JPEG, PNG, etc. The colour of individual pixels in a
colour image representation is typically represented as a sequence
of intensity values in a particular colour space. For example, in
the RGB colour space each pixel is represented by a red (R), green
(G) and blue (B) intensity value. The collection of intensity
values for a particular colour/parameter of a colour space in the
image representation is often referred to as a channel. When image
representations are printed, the pixels of the colour image format
are converted to dots of different colour ink on a page. Most
commercial inkjet printers contain a number of ink cartridges
(e.g., Cyan, Magenta, Yellow and blacK). During printing, each
pixel of the image is mapped to an arrangement of dots, which are
dispensed from the ink cartridges and deposited onto the substrate
to resemble the desired colour of the pixel. So, for example, to
print a red pixel, dots of magenta and yellow ink are deposited to
achieve the required shade of red.
[0080] In conventional imaging (e.g., photo printing), the
materials being deposited are pigment-based or dye-based inks.
These inks interact with the substrate to form, on drying, an image
as defined by the programmed image representation. In some cases,
each pixel in the image may correspond to one dot of ink on the
page. However, for most inkjet printers which employ small droplet
sizes such as 2 pL or less, software and/or firmware is used to
convert a pattern of pixels into a corresponding pattern of dots.
In many cases, a pixel in an image will correspond to more than one
drop of deposited ink on a page.
[0081] In an analogous way, materials which are used to form
structures having specific structural or electrical properties, can
also be deposited on a substrate using a drop-on-demand printing
device according to a programmed representation of the desired
structure to be formed. In many cases, the structures to be formed
are three-dimensional. They can be formed by depositing a number of
layers of one or more materials on a substrate. Typically, this
process requires a curing procedure to be effected between layers
to dry or cure the printed material to form a solid and not
over-wet the substrate. Liquid polymeric materials can be deposited
and then cured to form a solid material by initiating a
polymerisation reaction by irradiating the deposited material using
ultraviolet electromagnetic radiation. The formation of solid
structures by curing using electromagnetic irradiation of liquid
polymer materials is described in, for example, published US Patent
Application No. 20040041892, filed 25 Aug. 2003 and will not be
described further here.
[0082] Deposited materials can include polymer-based materials or
metal nanoparticle materials. These materials can be provided in
cartridges containing either liquid or solid material. In the
latter case, the solid material is melted as required to form a
liquid which can be ejected by a drop-on-demand printing
system.
[0083] In one arrangement, aqueous solutions of metal (gold) Au
nanoparticles are prepared according the methods disclosed in the
PCT Publication No. WO 03/018645, which is incorporated herein by
cross-reference. These solutions can be deposited on a substrate
and irradiated (cured) using an electromagnetic radiation source
such as a Xenon photo flash to form conductive films that have
substantially lower resistance than the non-irradiated deposited
material. This process is disclosed in the PCT Publication No. WO
03/018645. The electromagnetic source interacts with the deposited
material to effect a change in electrical properties of the
material.
[0084] In the arrangement described herein, one or more
electromagnetic sources can be used to irradiate deposited material
for the purposes of controlling the final resistance of the cured
material. These irradiation sources can include but are not limited
to Xenon photo flash units (e.g., Canon Model 550 EX), UV light
sources, laser or laser diodes light sources and/or laser diode
arrays.
[0085] The resistance of the irradiated films can be controlled by
specifying parameters of the irradiation such as radiation source,
intensity, duration, spatial resolution, and delay between material
deposition and irradiation. These parameters are preferably
controlled for the substructures within a structure. In other
words, the electrical properties of the printed (ie. deposited and
cured) materials can be tuned by specifying the irradiation
parameters for individual parts of the structure to be formed. For
example, if the structure to be formed is a field effect transistor
then different irradiation properties can be defined for each of
the substructures comprising source and drain electrodes, the
insulating layer and the semiconducting element of the field effect
transistor. In alternative arrangements the irradiation parameters
for structures are controlled at a point or pixel level.
[0086] The word "curing" is often used synonymously to refer, on
the one hand to polymerisation of polymers and, on the other hand,
to the sintering or annealing of metal nanoparticles. However, the
physical processes involved are very different. Curing of polymers
involves initiating reactions, which form bonds between monomer
components or cross-linking different organic ink constituents.
Annealing or sintering of metal nanoparticles refers to a process
whereby the individual nanoparticles are brought closer or fuse to
facilitate better electron flow through the deposited material. The
currently described arrangement relies on the latter process,
whereby the irradiation parameters are used to control the
electrical properties of the deposited material. The word "curing"
is used in this description in the broad sense of effecting changes
in physical (including chemical and electrical) properties of
materials.
[0087] However, with appropriate amendments, the described
arrangements may also be used with irradiation sources for the
purpose of control of polymerisation or solidification. In these
alternative arrangements, the ability to program the irradiation
parameters for a structure may be used to control the final
physical properties of the formed structure. In addition, it is
possible to have a printing system for curing plastic moulding
containing conductive elements. This system may contain a UV
irradiation source for the polymer material used for the plastic
moulding and a further laser or Xenon photo flash irradiation
source to control the resistance of the conductive elements that
are contained within the plastic moulding.
[0088] Previously disclosed curing methods for liquid polymers have
not allowed programmed control over the parameters of the
irradiation (e.g., radiation source, intensity, duration, density
of irradiation exposure points, and delay between printing and
curing). Using the described arrangements, it is possible to
specify specific irradiation properties for individual objects (or
substructures) of the structure to be formed and thus control the
physical properties of the structure being formed. For example, the
curing intensity can be varied to ensure more complete curing of
particular parts (e.g., surfaces) of a three-dimensional structure.
In another example, different curing intensities can be easily
programmed for different materials. This means a new material,
which requires a higher or lower curing intensity, can be easily
added to the system without any hardware or firmware changes.
[0089] The arrangement described with reference to the drawings
provides a system for forming conductive circuit elements that have
programmable final resistances, using a thermal inkjet device. The
final resistance of a conductive element depends both on the
material used and the irradiation parameters used in the cure step
of the formation process. These parameters can be designed and
stored within a CAD-based digital representation of the structure
to be formed. This digital representation is used by a thermal
inkjet printing device to form the designed structure with the
desired electrical properties.
[0090] The structures formed using the described methods may be
used in or comprise radio-frequency identification tags, batteries,
fuel cells, photovoltaic devices, driving electronics for flexible
displays and microsensors.
Printing System
[0091] A printing system 400 shown in FIGS. 4A and 4B may be used
to perform the described methods. FIG. 4A depicts the printing
system 400 in rear view. A print head assembly 450 is mounted at
the centre of a fixed track 430 over a substrate 420. The substrate
420 is supported on a flat substrate carrier 425 and the substrate
carrier 425 is controlled to move in the x, y and z-axis by a
motion precision system 494 (in FIG. 4B) contained in the device
base 410. The motion precision system 494 uses stepper motors to
control the position of the substrate carrier 425 with respect to
the device base 410 and the fixed print head assembly 450. In one
arrangement, the motion precision system 494 used by the printing
system 400 has a resolution of 0.0106 mm/step in each of the x, y
and z axes.
[0092] The substrate 420 can be any suitable receiving surface for
the deposited material. Suitable substrates include but are not
limited to flexible substrates such as polyester or polyvinyl
alcohol films and coated papers commonly used for inkjet photo
printing (e.g., Canon Photo Paper Pro.TM. and fumed silica coated
papers produced by Mitsubishi Paper Mills Limited). The substrate
420 is constrained to the substrate carrier 425 by suction.
Alternatively, the substrate 420 can be fixed to the substrate
carrier 425 by adhesive mounts or acrylic backing films. A set of
intersecting perpendicular metal guides 435 are provided on the
substrate carrier 420 to enable the substrate 420 to be correctly
aligned on the substrate carrier 425.
[0093] The print device housing 460 has two units fixed to opposite
sides of the device base 410. The print device housing 460
physically supports the fixed track 430 on which the print head
assembly 450 is mounted. The housing 460 also contains a print head
assembly controller 496 (in FIG. 4B) which sends electrical signals
to the print head assembly 450 via connections housed in the fixed
track 430. These signals control the individual nozzles that are to
fire (i.e., dispense material) and initiate irradiation pulses from
radiation sources fixed to the print head assembly 450. In the
described arrangement the print head assembly 450 does not move
along the fixed track 430. Instead, the motion precision system 494
moves the substrate carrier 425 to be positioned at the correct
(x,y,z) location under the print head assembly 450.
[0094] On the rear of the device base 410 is located the power
source connection 470 and a Universal Serial Bus (USB) port
connection 480. Preferably, the driving software located on a
computer 491 can communicate with a device controller 492 directly
using the USB connection 480. In alternative arrangements, the
driving software located on a computer 491 may communicate with the
device controller 492 via a parallel port or an Ethernet network
connection. The device controller 492 is located in the device base
410. The device controller 492 communicates directly with the print
head assembly controller 496 and the motion precision system 494.
In turn, the print head assembly controller 496 communicates with
the print head assembly 450, and the motion precision system 494
communicates with the substrate carrier 425. The front panel of the
housing 460 (not shown in FIG. 4) contains a switch for turning the
device on and off.
[0095] The computer 491 in which the driving software operates may
be specially constructed for the required purposes, or may comprise
a general purpose computer or other device selectively activated or
reconfigured by a computer program stored in the computer. The
algorithms and displays presented herein are not inherently related
to any particular computer or other apparatus. The structure of a
conventional general purpose computer is illustrated in FIG.
10.
[0096] The computer program running on the computer 491 may be
stored on any computer readable medium, including storage devices
such as magnetic or optical disks, memory chips, or other storage
devices suitable for interfacing with a general purpose computer.
The computer readable medium may also include a hard-wired medium
such as exemplified in the Internet system, or wireless medium such
as exemplified in the GSM mobile telephone system.
[0097] The computer system 491 may be formed by a computer module
1001, input devices such as a keyboard 1002 and mouse 1003, output
devices including a printer 1015, a display device 1014 and
loudspeakers 1017. A Modulator-Demodulator (Modem) transceiver
device 1016 is used by the computer module 1001 for communicating
to and from a communications network 1020, for example connectable
via a telephone line 1021 or other functional medium. The modem
1016 can be used to obtain access to the Internet, and other
network systems, such as a Local Area Network (LAN) or a Wide Area
Network (WAN), and may be incorporated into the computer module
1001 in some implementations.
[0098] The computer module 1001 typically includes at least one
processor unit 1005, and a memory unit 1006, for example formed
from semiconductor random access memory (RAM) and read only memory
(ROM). The module 1001 also includes an number of input/output
(I/O) interfaces including an audio-video interface 1007 that
couples to the video display 1014 and loudspeakers 1017, an I/O
interface 1013 for the keyboard 1002 and mouse 1003 and optionally
a joystick (not illustrated), and an interface 1008 for the modem
1016 and printer 1015. In some implementations, the modem 1016 may
be incorporated within the computer module 1001, for example within
the interface 1008. A storage device 1009 is provided and typically
includes a hard disk drive 1010 and a floppy disk drive 1011. A
magnetic tape drive (not illustrated) may also be used. A CD-ROM
drive 1012 is typically provided as a non-volatile source of data.
The components 1005 to 1013 of the computer module 1001, typically
communicate via an interconnected bus 1004 and in a manner which
results in a conventional mode of operation of the computer system
491 known to those in the relevant art. Examples of computers on
which the described arrangements can be practised include IBM-PCs
and compatibles, Sun Sparcstations or alike computer systems
evolved therefrom.
[0099] Typically, the application program is resident on the hard
disk drive 1010 and read and controlled in its execution by the
processor 1005. Intermediate storage of the program and any data
fetched from the network 1020 may be accomplished using the
semiconductor memory 1006, possibly in concert with the hard disk
drive 1010. Still further, the software can also be loaded into the
computer system 491 from other computer readable media. The term
"computer readable medium" as used herein refers to any storage or
transmission medium that participates in providing instructions
and/or data to the computer system 491 for execution and/or
processing.
[0100] FIG. 5 shows an example 500 of the print head assembly 450.
The exemplary print head assembly 500 contains eight ink/material
cartridges 501, 502, 503, 504, 505, 506, 507 and 508. These
cartridges can be used to store materials that have different
electrical properties (e.g., highly conductive, moderately
conductive, insulating, semiconducting, etc.). Other arrangements
may use a different number of material cartridges. Below each
cartridge 501-508 is a corresponding print head 530 mounted on a
print head surface 510. The print head assembly 500 receives
electrical signals from the print head assembly controller 496
(contained within the device housing 460) that result in the
ejection of droplets (e.g., 550) from specified nozzles of a
specified one of the print heads 530. The distance between the
print head surface 510 and the surface of the substrate 420 is
controlled to be 1.5 mm. This distance is selected to ensure
optimal accuracy of drop placement onto the substrate 420.
[0101] The print head 530 associated with each cartridge 501-508 is
desirably a thermal inkjet print head 600 used by the Canon i9950
inkjet printer and shown in more detail in FIG. 6. Each print head
600 contains 768 thermal inkjet nozzles (such as nozzles 625). The
nozzles 625 are arranged in two lines 610 and 620, each line
containing 384 nozzles. The lines 610 and 620 are separated by
central resin coated area 605. The spacing 630 between individual
nozzles is 1/600 inch (approximately 0.0423 mm). If each nozzle 625
in the line 610 ejects a single drop of material, then 600 droplets
per inch can be evenly deposited in a line. The two lines of
nozzles 610, 620 are offset by a distance 640, equivalent to half a
nozzle. The offset 640 enables a resolvable pitch of 1/1200 inch.
Clearly, other print head configurations can also be used.
[0102] The printing system 400 enables material to be deposited
using drop densities of 600.times.600 drops per inch,
1200.times.1200 drops per inch, and 2400.times.2400 drops per inch.
The pitch of 2400 drops per inch is achieved using a combination of
the motion precision system 494 and the inherent pitch of the print
head 600 as shown by offset distance 640 in FIG. 6. For all the
above drop densities the placement of drops in the x-axis is
controlled by the motion precision system 494.
[0103] The print head assembly 450 shown in FIG. 5 also supports
one or more irradiation sources adjacent to the material cartridges
501-508. In the described arrangement, two irradiation sources are
provided: a Xenon photo flash unit 525 (as used in the Canon Model
550 EX); and a CrystaLaser.TM. 200 mW ultra-compact diode pumped
solid-state (DPSS) green laser (532 nm) 520 available from
Crystalaser of Reno, Nev., USA. The Xenon flash unit 525 acts as a
broadband source of radiation and the laser 520 as a narrowband
source.
[0104] The irradiation sources 520, 525 are positioned to lie 6 mm
from the surface of the substrate 420. These irradiation sources
525, 520 have different effective irradiation areas and can be used
for large area and small area curing, respectively. So, for
example, the Xenon flash unit 525 will effectively cure a
relatively large circular area (0.5 cm.sup.2). This means that the
distance between irradiation points can be as large as 2 mm.
[0105] The DPSS laser irradiation source 520 is used as a small
area irradiation curing source. The laser source 520 has a beam
diameter (1/e.sup.2) of 0.36 mm and a beam divergence of 2 mrad
resulting in an effective circular cure area of 0.11 mm.sup.2. This
irradiation source 520 enables curing of finer features. For
example, the distance between laser curing irradiation points can
be as small as 180 .mu.m. The density or spacing of irradiation
exposure points (herein after referred to as exposure density) to
use for a laser curing source depends on the laser beam diameter,
beam divergence and whether any modulation of the beam shape is
used. Irradiation sources such as lasers can also be used to
irradiate continuously as the substrate 420 is moved by the motion
precision system 494.
[0106] In the described arrangement, no special optics (e.g.,
reflectors or lens) are used to control the divergence of the laser
beam. However, in alternative arrangements, reflectors and/or lens
may be used to modulate the beam shape and consequently control the
effective resolution of an irradiation source. Furthermore,
radiation can be delivered to the substrate using optical fibres.
For example, UV radiation from a quartz halogen lamp contained in
the device housing 460 could be supplied to the substrate 420 via
an optical fibre.
[0107] Arrays of light emitting diodes (LEDs), as sourced from
companies like TheLEDlight.com of Carson City, Nev., USA, can also
be used for low exposure density curing (i.e., large area curing).
Similarly, other compact laser sources could also be used for high
exposure density curing. Laser wavelengths in the 500 to 540 nm
wavelength have been found to be suitable for the curing of the
nanoparticle inks used by the described arrangement. Other laser
wavelengths may be used for different nano-ink preparations.
[0108] In an alternative arrangement, a number of individual
identical irradiation sources are mounted in an array, separate
from the print head, and moved to lie over a raster line of the
structure to be cured. The individual cure intensities are loaded
into local memories associated with the irradiation sources and
then the array is initiated to flash together. The array is then
moved to lie over the next raster line in the structure to be
cured. This arrangement may be used when large structures need to
be formed quickly. However, when fine control is required over the
delay between printing and curing and the structures to be cured
are relatively small, the speed advantage of line curing over point
curing may not be as significant.
Formation of Structures using Nanoparticle Materials
[0109] Preferably, the conductive elements are formed by depositing
and curing aqueous solutions containing metal Au nanoparticles
which have been prepared as described in the PCT Publication No. WO
03/018645. Preferably the aqueous inks have a surface tension of
.about.32-34 mN/m and a viscosity of .about.10-15 mPas. These
solution properties ensure that the drops are ejected in a reliable
manner by the print system 400 with a well-defined drop volume of 2
pL. Clearly, other suitable metal nanoparticle solutions (e.g.,
using silver (Ag) nanoparticles or nanoparticles containing both Au
and Ag) may also be used.
[0110] In many cases, a conductive element requires many layers of
material (conductive ink) to be deposited on the substrate. For
example, in order to form a conductive element that can act as an
antenna, many layers of conductive ink must be deposited in order
to achieve the necessary skin depth required to induce a current
using a radiofrequency signal. In addition, circuit elements, such
as transistors, consist of several layers of materials. For a
transistor (such as printed by Plastic Logic of Cambridge, UK), the
semiconductor and conductive source and drain contacts must be laid
down in a first layer. Then a layer of insulator must be deposited.
In order for this layer to be isolating (i.e., allow no leakage of
current) many layers of insulating material may need to be
deposited. Finally, a conductive gate electrode must be deposited
over the insulator. This means that the structure to be printed
involves the deposition of many layers of one or more types of
materials. Each of the layers, and indeed components of each layer,
may require a different irradiation process to be performed.
Digital Representation
[0111] The structures to be formed may be represented or specified
digitally as a collection of layered objects, or substructures as
shown in FIG. 9. In addition to location and size, each object is
associated with print and cure specifications. The digital
representation, incorporating the print and cure specifications
describes the objects and circuit element formed thereby, and may
be formed by the computer system of FIG. 10 and transmitted to and
received by a printer such as the printer 400.
[0112] The print specification for an object includes a sequence of
one or more printing steps that are to be performed for the object.
Each printing step identifies the cartridge 501-508, and therefore
material, to be used to print the object. The printing step also
specifies the drop density (i.e., drops per inch) to be used in the
printing.
[0113] The cure specification for an object includes a sequence of
zero or more curing steps to be performed for the object. Each
curing step identifies an irradiation source 520, 525 to be used to
cure the object, together with the irradiation intensity to be
used, the duration of the irradiation, the density of irradiation
exposure points, and the delay between printing and curing the
object.
[0114] A number of curing steps may be required to obtain a desired
curing result. For example, a repeated curing step may result in a
conductive track having a lower resistance than would be possible
with a single curing step. Clearly, other printing and curing
parameters could also be specified.
[0115] CAD software packages, such as TurboCAD.TM. (from Avanquest,
UK) or AutoCAD.TM. (from AutoDesk), may be used to design and
specify the objects of a structure and to organise the objects into
layers. This information may be stored in standard CAD DXF files as
shown by 910 in FIG. 9. Clearly, other data formats may also be
used to store information for the layers and objects of the
structure to form.
[0116] Each layer contains one or more vector objects, and each
object has a number of properties including the position of the
object in x-y-z coordinate space and the processing position of the
object within the layer. For example, in FIG. 9 the DXF file 910
contains a number of layers. The first layer 925 contains a number
of objects such as object 930.
[0117] In the preferred arrangement, collections of print
specifications 915 and cure specifications 920 are stored
separately from the DXF files. This means that print and cure
specifications can be used by more than one DXF file. For example,
the print and cure specifications to form a resistor having a
specified resistance may be designed, stored and re-used for
another circuit structure.
[0118] Each print and cure specification contains a number of
steps. For example, cure specification 950 consists of steps 955
and 960. An object 930 in a layer in the DXF file 910 contains a
reference 940 to the print specification 945 to use when printing
and a reference 935 to the cure specification 950 to use when
curing.
[0119] When a structure is selected to be formed, the objects for
the structure are processed in layer order as indicated in FIG. 9.
In other words, the first layer of objects is processed, followed
by the second layer and so on. Within each layer, objects are
processed in order of their assigned processing position. When each
object is processed, the stored print and cure specifications,
which are referenced by the DXF files, are used to control the
printing and curing of the object. The specifications can be
fetched when required or pre-fetched and cached for the structure
or a set of structures which are to be formed.
[0120] In an alternative arrangement, each object is associated
with a list of print, cure and delay steps. Details of these steps
are stored in a specification file substantially similar to 915 and
920 in FIG. 9. Processing of each object in this arrangement
involves retrieving and processing each of the steps in their order
in the list. In this arrangement it is possible to carefully
control the delay between each step.
[0121] In a further arrangement, the structure to be formed is
represented as a collection of `print` and `cure` objects. At the
time of designing the structure, each object is classified as
either a `print` or `cure` object. Each `print` object can have
references to one or more associated `cure` objects. In this
arrangement, the structure is formed by processing the `print`
objects layer by layer. When each `print` object is identified for
processing, the associated `cure` objects are then fetched in
readiness for processing. In this arrangement, sequences of
printing and curing operations can be represented by a sequence of
individual `print` and `cure` objects which may print and cure,
respectively, different parts of a substructure in the
structure.
[0122] In a further arrangement, the structure to be formed is
represented as a sequence of two-dimensional print and cure images.
The colour channels of these print images are used to denote the
materials to be printed. For example, the red colour channel of an
image represented in the RGB colour space may be used to denote the
material in the first cartridge of the printer. The colour channels
of the cure images are used to denote the different irradiation
sources that are available in the printing system. The structure is
formed by processing the print and cure images to form layers of
the structure. The images are processed in strict sequence (i.e., a
first image is completely processed before the next image in the
sequence is processed).
[0123] Alternatively, bands of a print image can be printed
according to a print image and then cured according to the
corresponding area in a following cure image in the image sequence.
In this way, layers of material can be deposited and cured to form
a three-dimensional structure.
Structure Forming Process
[0124] FIGS. 1 to 3 illustrate a method of forming a structure,
such as a conductive element. The methods are operated in a
software module located in computer 491.
[0125] In step 105 of method 100, a digital representation of the
structure to be formed is selected. Preferably, this digital
representation is a CAD-based representation as previously
described, which references stored print and cure specifications
which are to be used for the individual objects in the structure.
The digital representation and the print and cure specifications
may be retrieved from memory or from a storage device such as a
hard disk. Instead of being retrieved, the digital representation
and/or print and cure specifications may be created for one-off
fabrication.
[0126] In step 110, a first object of the structure is identified
for processing. Preferably, the objects of a structure are
identified in layer order. Within a layer, objects are assigned a
priority that determines the order in which they are processed.
[0127] In step 112, the print specification associated with the
object is obtained. This specification can be fetched from a stored
collection of print and cure specifications. However, in one
arrangement all the required print and cure specifications required
for the structure being processed are loaded as part of a
pre-processing step and held in a memory cache of the software
application. In step 115, the object is printed using the printing
system 400 according to the print specification. This step involves
converting the vector shape representing the region to be printed
into the desired pattern of drops to be ejected by the print head
which deposits the required material. The actual pattern to be
generated depends on the drop density specified for each of the
print steps of the print specification (e.g., 2400.times.2400 drops
per inch). The method of printing the object corresponding to the
current object's print specification is described in more detail
below with reference to FIG. 2.
[0128] Next, in step 120 the method determines if there is an
associated cure specification for the current object. If a cure
specification exists (the YES option of step 120), then this cure
specification is processed in step 130, which is discussed in more
detail with reference to FIG. 3. If there is no cure specification
for the object (the NO option of step 120) then control passes to
step 140.
[0129] In step 140, the method 100 determines whether there are
further objects to process. If there are (the YES option of step
140) then the next object is fetched in step 160 and control
returns to step 112 to obtain the print specification for the new
object. If there are no further objects to process (the NO option
of step 140), then the structure is complete and the method 100
ends at step 190.
[0130] FIG. 2 shows the printing step 115 in more detail. In step
205, an initialising signal is sent to the motion precision system
494 via the device controller 492 to move the substrate 420 so that
the print head assembly 450 is located at the correct height over
the substrate 420. This height is specified by the z-offset given
for the object.
[0131] Then in step 207, the first print step of the print
specification is obtained. An object may have more than one print
step in a print specification. In the described arrangement, all
print steps for an object use the vector shape and the x, y, and z
initial coordinates specified for the object. Multiple print steps
can be used to print more than one layer of one or more materials
without curing. These additional layers are assumed to result in
minimal change in the distance between the print head assembly 450
and the substrate 420.
[0132] In step 210, the correct material/cartridge 501-508 is
identified using the material code stored with the print step and
in step 212 the drop density required to be used by the print step
is also identified. In step 215 the vector associated with the
object is converted into a raster drop pattern using the identified
required drop density. The drop density may vary for the different
print steps performed for an object. High drop densities and
printing more than one layer of an object before curing can be used
to deposit a larger amount of material before the curing process
commences for the object. For example, when depositing insulating
materials, it is important to create an isolating layer, so
typically a high drop density is used. The drop density used also
depends on how well the substrate can absorb the deposited
material. Depositing too much material before curing can result in
over-wetting of the substrate. The preferred method of constructing
the raster drop pattern for the vector objects uses the GNU libxmi
vector to raster conversion library available from the Free
Software Foundation, Inc of Boston, Mass., USA. Clearly, other
vector to raster algorithms could also be used.
[0133] In step 217, the raster drop pattern is sent with a
cartridge identifier and the initial (x,y) location for the region,
to the device controller 492 in the device base 410. The function
of the device controller 492 is to construct a set of nozzle firing
patterns at particular (x,y) locations that, summed together, will
form the drop pattern that the controller 492 has received for the
object. Controller 492 then controls a series of operations
involving moving the substrate 420 to lie under the print head
assembly 450 at the correct (x,y) location and then initiating the
print head assembly 450 to deposit the correct material according
to the provided nozzle firing pattern.
[0134] In step 220, the device controller 492 sends a signal to the
motion precision system 494 to position the substrate 420 at the
first of the constructed (x,y) locations under the fixed print head
assembly 450. Then in step 230, the controller 492 sends the
corresponding nozzle firing pattern and cartridge identifier to the
print head assembly controller 496. The print head assembly
controller 496 then sends the signals to the print head assembly
450, which results in material being deposited by the correct print
head 600 according to the nozzle firing pattern (step 240). The
signals result in current being applied to the heating elements of
individual nozzles (e.g., 625) of the print head 600 and droplets
of material being ejected onto the substrate 420.
[0135] As described previously, nozzles from both lines of nozzles
610 and 620 can be fired simultaneously. In other words,
effectively two lines of dots can be simultaneously ejected for
each substrate location. Higher drop densities in the y-axis than
1200 drops per inch can be achieved by using the motion precision
system 494 to accurately position the substrate 420 under the print
head assembly 450. Clearly, the device controller 492 may be
implemented to support other drop densities (print resolutions)
provided that the motion precision system 494 can support the
required resolution.
[0136] In the described arrangement, each print step is associated
with a single material code. This means that at any one time,
nozzles from only one print head 600 can be firing. Alternative
arrangements could allow material from more than one print head 600
to be deposited simultaneously therefore providing either: [0137]
(i) faster material deposition; or [0138] (ii) deposition of
additional materials required for curing (e.g., polymerisation
initiators, catalysts, cofactors).
[0139] In step 245, if the region represented by the raster drop
pattern received by the device controller 492 is complete, then
control passes to step 250. If the further deposition of material
is required in step 245 (the NO option of step 245), then control
returns to step 220 and the motion precision system 494 is
signalled to move the substrate to the next determined (x,y)
position and material deposition for the region continues. If all
the drops of the current region have been deposited (the YES option
of step 245) then control passes to step 250, where a test is
performed to see if there are further print steps for the current
object. If no further print steps exist (the NO option of step
250), the printing method 200 concludes at step 290. If there are
further print steps, control flow proceeds to step 260 to get the
next print step, following which the method 115 returns to step 210
to process the retrieved print step.
[0140] The preferred method by which the nozzle firing patterns are
generated by the device controller 492 (i.e. step 230) for a drop
pattern uses a lookup table to associate sequences of nozzle firing
patterns for each of the supported dot densities. So, for example,
to deposit a 600.times.600 drops per inch region, all the nozzles
of one line of nozzles can be fired and the motion precision system
494 can be used to move the substrate 1/600.sup.th inch to the left
and the nozzles from the same line of nozzles are fired at this new
location. The process is repeated until material has been deposited
over a region of the required width. The higher drop densities can
use patterns which utilise both lines of nozzles 610, 620. The
lookup table may incorporate nozzle firing patterns that minimise
the effect of systematic artefacts that may occur if one or more
nozzles is either not firing (e.g., clogged) or firing
unpredictably.
[0141] In the described arrangement, the device controller 492
constructs the sequence of nozzle firing patterns required to form
the raster drop pattern, which is received from the computer 491
via the USB port 480 of the printing system 400. In alternative
arrangements, the nozzle firing patterns could be constructed in
software in the computer 491 and then sent to the printing system
400 as a sequence of (x,y) locations and associated nozzle firing
patterns.
[0142] The method 130 of curing the object will now be described
with reference to FIG. 3. In the described arrangement, it is
assumed that the distance between the substrate 420 and the print
head assembly 450 (i.e., z position for the object) is correctly
set after the printing process 200. In step 305, the first cure
step of the cure specification is obtained. The radiation source
520, 525 to use for the current cure step is identified in step
310. Then using the associated exposure density, intensity,
duration and delay, an irradiation sequence is constructed for the
current cure step in step 315. This sequence contains instructions
to move the substrate 420 to a specified (x,y) location below the
print head assembly 450, initiate irradiation of the required
intensity and duration from the identified radiation source and
then move to the next irradiation point. The irradiation locations
are determined using the irradiation exposure density specified for
the cure step.
[0143] The exposure density used to cure the object is generally
independent of the drop density used to print the object. This is
because the exposure density is determined by the irradiation
source being used and the properties of that irradiation source.
For example, as mentioned previously, a Xenon flash unit 525
integrated into the print head assembly 450 as depicted in FIG. 5
can effect curing over a region of about 0.5 cm.sup.2. However, a
laser radiation source 520, as described previously, will cure a
much smaller area in a single pulse (.about.0.11 mm.sup.2).
[0144] The method 300 waits at step 320 until the required delay
between printing and curing has occurred. In the described
arrangement, this delay is measured from the time of the first
print step for the object. In alternative arrangements, the delay
could be implemented in a point-wise manner. For example, the time
delay is computed for each irradiation pulse. In this case the
delays are incorporated into the irradiation sequence and print
times must be recorded for each irradiation point for the object's
last print step. This variation means that the cure specification
for an object must be fetched and used to generate an irradiation
sequence template before the printing associated with the print
specification can commence. As printing proceeds the actual print
times can be used to instantiate the delays in the prepared
irradiation sequence template.
[0145] In step 325, the motion precision system 494 moves the
substrate 420 to the first (x,y) location required by the
irradiation sequence. The irradiation parameters for this location
are then sent to the print head assembly controller 496 in step
330. The print head assembly controller 496 then despatches the
required signals to the specified irradiation source 520, 525 on
the print head assembly 450. This results in the current location
being irradiated in step 340.
[0146] Step 345 checks whether there are more irradiation locations
in the irradiation sequence. If so, control returns to step 325
where the motion precision system 494 moves the substrate 420 to
lie under the next (x,y) location in the sequence. If all (x,y)
locations in the sequence have been processed (the NO option of
step 345) then control passes to step 350, where it is determined
whether there are any more cure steps for the current object. If
there are more cure steps (the YES option of step 350), then the
next cure step is obtained in step 360 and control returns to step
310. If there are no further cure steps then the method 300 ends in
step 390.
Resistance of Materials
[0147] The methods have been described with reference to forming
conductive elements, the final resistance values of which are
controlled by the selection of the desired material and the
specification of the appropriate curing parameters. Using the
preferred method of preparing metal nanoparticle inks (as described
in PCT Publication No. WO 03/018645), nanoparticle inks having
varying properties can be prepared. The prepared nanoparticles can
be capped with different inert, water-soluble, organo-sulfur
capping agents. For example, alkane thiols of different chain
length can be used as capping agents. The capping agents stabilize
the Au nanoparticles, preventing aggregation of the nanoparticles
during concentration and storage. The ink formation process
involves concentrating the capped Au nanoparticles, while removing
excess capping agent, inorganic salts and other impurities. The
removal of these impurities is important for the formation of
highly conductive nanoparticle films.
[0148] The type and length of linker molecule (capping agent)
controls the interparticle distance and therefore affects the final
resistances of printed films before curing. FIG. 7 shows a graph of
consistently measured resistance of films printed using alkane
thiols of different linker length. When the linker length of the
capping agent falls below .about.1 nm (as shown by portion 710 of
the graph), metallic conduction characteristics are observed.
Longer linker lengths make it difficult for electrons to tunnel
from one nanoparticle to another in the film and therefore result
in a higher film resistance. Therefore, different nanoparticle inks
can be used to form conductive elements and resistors of varying
resistance as a result of the different intrinsic properties of the
capped nanoparticles in the ink.
[0149] The final resistances are also affected by the type of
irradiation source used and parameters of the curing process. FIG.
8 shows how the sheet (film) resistance of printed nanoparticle
films varies with effective irradiation duration. The films were
formed by inkjet deposition of a 4% w/v capped Au nanoparticle
aqueous solution on paper with a fumed silica coating (as produced
by Mitsubishi Paper Mills Limited). Each printed film was exposed
to a different number of discrete 200 .mu.s flashes using a Xenon
photo flash unit (Canon model 550EX) using a power setting of 40
W/cm.sup.2. The sheet resistance was then measured for each film
and is plotted as a function of the number of flashes in FIG. 8.
The flash unit was placed a distance of 6 mm from the nanoparticle
film. This result demonstrates how the resistance of films can be
controlled by controlling the parameters of the curing process,
such as duration of the applied irradiation. It may be seen from
FIG. 8 that the film resistance decreases as the number of flashes
increases from 1 to 6 flashes. For more than 6 flashes, no further
decrease in resistance is seen.
[0150] The actual intensity and duration values to use for the
irradiation process depend on the type of nanoparticle material
used in the deposition or printing step, the effective radiation
area, the distance of the material from the irradiation source and
the granularity of the power control of the cure source. These
values must be calibrated beforehand by measuring the obtained
resistance value for each set of parameters. This calibration must
be performed for each substrate used as the substrate also affects
the final resistance of the printed structure. Preferably the
results of these calibrations are stored in lookup tables which can
be used when designing structures to be formed.
[0151] FIG. 11A shows a schematic representation of an electrical
circuit 1100 formed of a resistor R1 1108 and a resistor R2 1109 in
a classic "resistor-divider" configuration which incorporates three
connections or terminals 1102, 1104 and 1106. FIG. 11B shows a
print layout 1110 of the circuit 1100 which can be formed by the
depositing of Au nanoparticle materials onto a substrate according
to the principles of the present disclosure. Note that the print
layout 1110 is a single structure which is configured to have
multiple characteristics. Also, in order to form the resistors
1108, 1109 and connections 1102, 1104, 1106, a width W of the
layout may be uniform. This contrasts other fabrication
arrangements where structures or devices having differing
properties require different structural configurations. For example
in semiconductor manufacture, different resistor values may require
different doping levels or occupy different chip areas. In this
example, the different devices and characteristics are formed by
the dispensing and depositing of the material, in combination with
the curing process.
[0152] FIG. 11C illustrates the curing of the material deposited in
the layout 1110. Using the graph of FIG. 8, the connections and
terminals 1112, 1114 and 1116 are cured using 7 flashes of light,
to ensure a low film resistance of about 300 ohms for each. The
resistor R1 is formed by a portion 1118 cured using 3 flashes,
giving a film resistance of about 500 k ohms. The resistor R2 is
formed by a portion 1119 of the layout 1110 cured using 4 flashes,
giving a film resistance of about 40 k ohms. Note that the
resistance of the connections 1112, 1114 and 1116 is small compared
to the values of the resistors R1 and R2, and well within a 5%
tolerance commonly using in electronic circuit design. More
significantly, the series resistance of the connections 1112-1116
(about 900 ohms) is less than 0.2% of the series resistance (about
540 k ohms) of the resistors R1 and R2. As such the use of varying
the number of flashes to perform curing can afford predictably
accurate circuit formation. Importantly, once the various
sub-regions of the layout 1110 have been correspondingly cured, the
layout forms a single element or structure which has multiple
characteristics, in this case essentially a series connection of
five resistances (300+40 k+300+500 k+300 ohms).
[0153] FIG. 12 shows a flowchart 1200 of one approach that may be
used to form the resistor divider of FIG. 11C. Step 1202 acts as a
starting point and step 1204 operates to print the three
connections 1112, 1114 and 1116. The circuit the then cured in step
1206 with three flashes, giving the connections each a resistance
of 500 k ohms, according to FIG. 8. Step 8 then operates to print
the resistor R2 1119 between the connections 1114 and 1116. The
circuit, as a whole, is then cured in step 1210 with a single
flash. This causes the resistance of the connections to drop to
about 40 k ohms each, and the resistor R2 1119 to be about 1M ohm.
Step 1212 then operates to print the resistor R1 1118 between the
connections 1112 and 1116. Step 1214 the cures the entire circuit
using a further 3 flashes. This gives the resistor R1 1118 a
resistance of 500 k ohms and changes the resistance of the
connections 1112-1116 to about 300 ohms each (from a total of 7
flashes) and changes the resistance of resistor R2 to about 40 k
ohms (from a total of 4 flashes). The method ends at step 1216.
[0154] The method 1200 may be used where only the Xenon flash unit
525 is desired to operate, in view of its relatively large
irradiation area, as discussed above. The method 1200 as such has
three printing passes. Using a more focussed approach to
irradiation, for example using the laser 520, a single printing
pass may be used to form the circuit elements shown in FIG. 1C of
the circuit 1100.
[0155] The example of FIGS. 11 and 12 provides a simple circuit
element structure. Utilizing a range of nanoparticle materials
including resistive, semiconducting, insulating etc., as discussed
above, circuit elements may be formed each having multiple
characteristics. The characteristics may arise from the deposited
material, the mode of curing, or a combination of both. Further,
the structuring of individual circuit elements can provide for
complex circuits to be formed in 2 or 3 dimensions.
INDUSTRIAL APPLICABILITY
[0156] It is apparent from the above that the arrangements
described are applicable to the electronics and printing
industries.
[0157] The foregoing describes only some embodiments of the present
invention, and modifications and/or changes can be made thereto
without departing from the scope and spirit of the invention, the
embodiments being illustrative and not restrictive.
* * * * *