U.S. patent application number 15/352051 was filed with the patent office on 2017-03-02 for high resolution projection micro-stereolithography system and method.
The applicant listed for this patent is Matthew Alonso, Nicholas Fang, George Farquar, Steven Gemberling, Howon Lee, Christopher M. Spadaccini, Todd Weisgraber, Jun Xu. Invention is credited to Matthew Alonso, Nicholas Fang, George Farquar, Steven Gemberling, Howon Lee, Christopher M. Spadaccini, Todd Weisgraber, Jun Xu.
Application Number | 20170057162 15/352051 |
Document ID | / |
Family ID | 54334681 |
Filed Date | 2017-03-02 |
United States Patent
Application |
20170057162 |
Kind Code |
A1 |
Spadaccini; Christopher M. ;
et al. |
March 2, 2017 |
High Resolution Projection Micro-Stereolithography System And
Method
Abstract
A high-resolution P.mu.SL system and method incorporating one or
more of the following features with a standard P.mu.SL system using
a SLM projected digital image to form components in a
stereolithographic bath: a far-field superlens for producing
sub-diffraction-limited features, multiple spatial light modulators
(SLM) to generate spatially-controlled three-dimensional
interference holograms with nanoscale features, and the integration
of microfluidic components into the resin bath of a P.mu.SL system
to fabricate microstructures of different materials.
Inventors: |
Spadaccini; Christopher M.;
(Oakland, CA) ; Weisgraber; Todd; (Brentwood,
CA) ; Farquar; George; (Livermore, CA) ;
Gemberling; Steven; (Livermore, CA) ; Fang;
Nicholas; (Champaign, IL) ; Alonso; Matthew;
(Freeport, IL) ; Xu; Jun; (Urbana, IL) ;
Lee; Howon; (Urbana, IL) |
|
Applicant: |
Name |
City |
State |
Country |
Type |
Spadaccini; Christopher M.
Weisgraber; Todd
Farquar; George
Gemberling; Steven
Fang; Nicholas
Alonso; Matthew
Xu; Jun
Lee; Howon |
Oakland
Brentwood
Livermore
Livermore
Champaign
Freeport
Urbana
Urbana |
CA
CA
CA
CA
IL
IL
IL
IL |
US
US
US
US
US
US
US
US |
|
|
Family ID: |
54334681 |
Appl. No.: |
15/352051 |
Filed: |
November 15, 2016 |
Related U.S. Patent Documents
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Application
Number |
Filing Date |
Patent Number |
|
|
13149773 |
May 31, 2011 |
9492969 |
|
|
15352051 |
|
|
|
|
61349627 |
May 28, 2010 |
|
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Current U.S.
Class: |
1/1 |
Current CPC
Class: |
B33Y 10/00 20141201;
G03H 1/0476 20130101; B29C 64/124 20170801; G02B 1/002 20130101;
G03H 2223/17 20130101; G03H 2001/0094 20130101; G02B 1/007
20130101; G02B 5/008 20130101; B29C 64/135 20170801; G03F 7/70408
20130101; G03H 1/2294 20130101; B33Y 30/00 20141201; G03H 2001/0482
20130101; G03H 1/0005 20130101; G03H 2225/60 20130101; G03F 7/70416
20130101; G02B 27/56 20130101 |
International
Class: |
B29C 67/00 20060101
B29C067/00; B33Y 30/00 20060101 B33Y030/00; G02B 5/00 20060101
G02B005/00; G03H 1/04 20060101 G03H001/04; G02B 27/56 20060101
G02B027/56; G02B 1/00 20060101 G02B001/00; B33Y 10/00 20060101
B33Y010/00; G03H 1/00 20060101 G03H001/00 |
Goverment Interests
FEDERALLY SPONSORED RESEARCH OR DEVELOPMENT
[0002] The United States Government has rights in this invention
pursuant to Contract No. DE-AC52-07NA27344 between the United
States Department of Energy and Lawrence Livermore National
Security, LLC for the operation of Lawrence Livermore National
Laboratory.
Claims
1. A holographic projection micro-stereolithography (P.mu.SL)
system, comprising: a bath containing a photosensitive resin; and
at least two light projection systems, each projection system
comprising a light source; and a spatial light modulator (SLM)
adapted to produce a digital image when illuminated by the light
source, wherein the at least two light projection systems are
arranged to holographically interfere said digital images in the
photosensitive resin to volumetrically cure select regions thereof
in a holographic interference pattern.
2. The holographic projection micro-stereolithography (P.mu.SL)
system of claim 1, wherein each light projection system further
comprises a reduction lens, and a far-field superlens (FSL)
contactedly interfacing the photosensitive resin, said FSL
including a dielectric layer and a metal grating layer, and wherein
the FSL is arranged to convert a far-field image produced by the
SLM and reduced by the reduction lens into a near-field image for
volumetrically curing the select regions of the photosensitive
resin.
3. A holographically-controlled volumetric curing method of
photosensitive resin, comprising: providing a bath containing a
photosensitive resin, and at least two light projection systems,
each light projection system comprising a light source and a
spatial light modulator (SLM) adapted to produce a corresponding
digital image when illuminated by the light source; activating the
light projection systems to produce the digital images; and
directing the digital images of the light projection systems to
holographically interfere in the photosensitive resin so as to
volumetrically cure select regions thereof in a holographic
interference pattern.
4. The method of claim 3, wherein each light projection system
further comprises a reduction lens, and a far-field superlens (FSL)
contactedly interfacing the photosensitive resin, said FSL
including a dielectric layer and a metal grating layer, and wherein
the FSL is arranged to convert a far-field image produced by the
SLM and reduced by the reduction lens into a near-field image for
volumetrically curing the select regions of the photosensitive
resin.
Description
CROSS-REFERENCES TO RELATED APPLICATIONS
[0001] This application is a divisional of prior application Ser.
No. 13/149,773, filed May 31, 2011, which claims the benefit of
U.S. Provisional Application No. 61/349,627, filed May 28, 2010,
all of which is incorporated by reference herein.
FIELD OF THE INVENTION
[0003] The present invention relates to projection
micro-stereolithography (P.mu.SL) systems and methods, and more
particularly to an improved high-resolution P.mu.SL system and
method having one or more of the following features; a far-field
superlens for producing sub-diffraction-limited features, multiple
spatial light modulators (SLM) to generate spatially-controlled
three-dimensional interference holograms with nanoscale features,
and the integration of microfluidic components into the resin bath
of a P.mu.SL system to fabricate microstructures of different
materials.
BACKGROUND OF THE INVENTION
[0004] Stereolithography (SL) is a known rapid prototyping
technology which enables the generation of scale models of
complicated three-dimensional parts in a fraction of the time and
at a fraction of the cost of traditional methods. Generally, SL
involves the use of electromagnetic radiation (e.g. a UV laser
beam) to cure a photosensitive liquid (e.g. liquid photosensitive
monomer or resin) which solidifies upon exposure to electromagnetic
radiation of a given wavelength. When a layer is fully solidified
upon exposure, the component stage drops down to allow a fresh
layer of photosensitive liquid to flow over the solid surface. In
this manner, a three-dimensional (3D) structure is fabricated from
the bottom up, a layer at a time. SL provides a useful tool for
visualizing components to assist in the iterative design process,
as well for the direct fabrication of functional parts and
microdevices.
[0005] Various stereolithographic methods are known for
three-dimensional fabrication of microsystems. A first basic
technique uses a scanning laser system to serially trace the shape
of the desired part in a line-by-line manner over the free surface
of a photosensitive resin bath. The laser is controlled by a CAD
system that functions as an electronic mask, and typically allows
for a transverse resolution of about 150 .mu.m. In addition, the
photopolymer can be loaded with ceramic, metal, or other particles
to generate components of different materials. After initial
stereolithographic fabrication, the parts can be sintered to remove
the polymer and densify the functional material of interest. This
usually shrinks the part by some controllable amount. An
improvement on the scanning laser technique is known as the "Two
Photon Absorption" method. This process uses two low power, pulsed
laser beams which intersect deep within the resin bath. At the
intersection point, the beams form a small volume which has
sufficient photon flux to polymerize only the local material in the
volume. While the beams can write a completely three-dimensional
pattern into the resin bath, this is typically a slow process
because it writes in a point-by-point fashion. Moreover, the types
of resins available for this technique are severely limited due to
the need that they be highly transparent to the laser beams, which
also effectively prevents the loading of ceramic or metal particles
in the resin bath.
[0006] Projection micro-stereolithography (P.mu.SL) is a third, low
cost, high throughput, micro-scale, stereolithography technique
which projects a two dimensional image onto a photosensitive resin
bath rather than a single spot, to fabricate complex
three-dimensional microstructures in a bottom-up, layer-by-layer
fashion. Originally, P.mu.SL was first accomplished by using a set
of photomasks to project the two-dimensional image. Although
effective, this method requires a large number of photomasks thus
limiting the practical number of layers possible. The use of a
dynamically reconfigurable mask, via a spatial light modulator
(SLM) in P.mu.SL systems dramatically reduced process time
resulting in structures with thousand of layers. This was
demonstrated in the form of a liquid crystal display (LCD) in the
paper "Ceramic Microcomponents by Microstereolithography" by
Bertsch et al (2004 IEEE). However, the LCD had some intrinsic
drawbacks including large pixel sizes and low switching speeds.
[0007] The use of a Digital Micromirror Device (DMD, a trademark of
Texas Instruments) as the SLM in a P.mu.SL system is described in
the paper "Projection Micro-Stereolithography Using Digital
Micro-Mirror Dynamic Mask" by C. Sun et al (2005 Elsevier). Similar
to conventional SL techniques, P.mu.SL with a SLM is capable of
fabricating complex three-dimensional microstructures in a
bottom-up, layer-by-layer fashion. A CAD model is first sliced into
a series of closely spaced horizontal planes. These two-dimensional
slices are digitized in the form of an electronic image and
transmitted to the SLM. A UV lamp or LED illuminates the SLM which
acts as a dynamically reconfigurable photomask and transmits the
image through a reduction lens into a bath of photosensitive resin.
The resin that is exposed to the UV light is cured and anchored to
a platform and z-axis motion stage. The stage is then lowered a
small increment and the next two-dimensional slice is projected
into the resin and cured on top of the previously exposed
structure. This layer-by-layer fabrication continues until the
three-dimensional part is complete.
[0008] It is also known that imaging and lithography using
conventional optical components is restricted by the diffraction
limit. Features resolution in these systems is
[0009] limited to one half of the wavelength of the incident light
because they can only transmit the propagating components emanating
from the source. It would be advantageous to provide an improved
P.mu.SL-based fabrication system and method capable of fabricating
three-dimensional structures having sub-diffraction limited
features, as well as other capabilities which enhance the
resolution, materials flexibility, and process performance of
standard P.mu.SL.
SUMMARY OF THE INVENTION
[0010] One aspect of the present invention includes a projection
micro-stereolithography (P.mu.L) system for producing
sub-diffraction-limited features, comprising: a light source; a
spatial light modulator (SLM) illuminated by the light source; a
reduction lens; a stereolithographic bath containing a
photosensitive resin; and a far-field superlens (FSL) contactedly
interfacing the photosensitive resin, said FSL including a
dielectric layer and a metal grating layer, wherein the FSL is
arranged to convert a far-field image produced by the SLM and
reduced by the reduction lens into a near-field image for curing
select regions of the photosensitive resin.
[0011] Another aspect of the present invention includes a
projection micro-stereolithography (P.mu.SL) system, comprising: a
light source; a spatial light modulator (SLM) illuminated by the
light source; a reduction lens; a stereolithographic bath
containing a photosensitive resin; and a microfluidic system
integrated with the stereolithographic bath, said microfluidic
system having at least one inlet port fluidically connected to
deliver at least one type of photosensitive resin from at least one
source, and at least one outlet port.
[0012] Another aspect of the present invention includes a
holographic projection micro-stereolithography (P.mu.SL) system,
comprising: a stereolithographic bath containing a photosensitive
resin; and at least two light projection systems, each projection
system comprising a light source; and a spatial light modulator
(SLM) illuminated by the light source for illuminating the
photosensitive resin with a digital image, so that the holographic
interference of all the digital images in the photosensitive resin
cures select regions of the photosensitive resin.
[0013] Another aspect of the present invention includes a
holographic projection micro-stereolithography (P.mu.SL) system,
comprising: a bath containing a photosensitive resin; and at least
two light projection systems, each projection system comprising a
light source; and a spatial light modulator (SLM) adapted to
produce a digital image when illuminated by the light source,
wherein the at least two light projection systems are arranged to
holographically interfere said digital images in the photosensitive
resin, to cure select regions thereof.
[0014] And another aspect of the present invention includes a
holographically-controlled volumetric curing method of
photosensitive resin, comprising: providing a bath containing a
photosensitive resin, and at least two light projection systems,
each light projection system comprising a light source and a
spatial light modulator (SLM) adapted to produce a corresponding
digital image when illuminated by the light source; activating the
light projection systems to produce the digital images; and
directing the digital images of the light projection systems to
holographically interfere in the photosensitive resin so as to
volumetrically cure select regions thereof in a holographic
interference pattern.
[0015] Generally, the present invention involves an improved
high-resolution P.mu.SL system and method capable of rapidly
fabricating complex three-dimensional meso- to micro-scale
structures and components with micro/nano-scale precision (i.e.
including sub-diffraction-limited features). Similar to
conventional P.mu.SL, the present invention utilizes a SLM (such as
for example a DMD or a Liquid Crystal on Silicon (LCoS)) as a
dynamically reconfigurable photomask to project a two-dimensional
image onto the tree surface of a photosensitive resin bath. The
resin is cured and lowered a small increment into the bath and a
new image is projected and cured on the top of the previously
developed structure, to build a three-dimensional part in a
layer-by-layer fashion, from the bottom up. Additionally, the
P.mu.SL system and method of the present invention also
incorporates one or more of the following functional features to
improve resolution, flexibility, and process performance of
standard P.mu.SL; an integrated far-field superlens (FSL) which
overcomes the diffraction limit of light (i.e. one-quarter
wavelength) to produce nanometer scale features (tens of nanometers
or less than one-quarter the UV light wavelength) on a wide range
of substrates; and multiple SLMs arranged to generate
spatially-controlled three-dimensional interference holograms with
nanoscale features in a photosensitive resin bath of the P.mu.SL to
fabricate three-dimensional structures with a single exposure; and
microfluidic components integrated with the photosensitive resin
bath in order to use laminar flow control to optimally deliver and
distribute multiple photosensitive resins and other materials, so
as to produce multi-material microstructures.
Far-Field Superlens (FSL)
[0016] The FSL used in the present invention is a thin-film
grating-type structure (e.g. thin-film silver grating) which
amplify evanescent waves (which decay exponentially in mediums with
positive permittivity and permeability and carry subwavelength
information) to produce features which exist below the diffraction
limit. In particular, as used in the present invention, the
thin-film grating-type structures of the FSL convert amplified
evanescent waves into a propagating field, and thus convert a
near-field effect into a far-field phenomenon. It is notable
therefore that the fabricated sub-wavelength features are not
simply a reduced or smaller version of the projected image from the
SLM. There is not a 1:1 pattern transfer. Because the SLM projected
image is passing through a grating, sub-wavelength features on the
other side of the grating are fundamentally different in geometry
to that which was projected. Therefore the SLM projected far-field
image is calculated to generate the desired sub-wavelength features
on the other side of the FSL grating.
[0017] The FLS takes the form of a thin layer of material with
either negative permittivity or permeability (resulting in a
negative index of refraction). Noble metals such as silver are good
candidate materials for the FLS due to the ability to generate
negative permittivity by the collective excitation of conduction
electrons. The thin metal grating layer is designed such that, the
surface plasmons match the evanescent waves being imaged so that
the FLS enhances the amplitude of the field. Features as small as 5
.mu.m for example have been demonstrated.
[0018] The FSL includes a metallic grating layer connected to a
dielectric layer. The dielectric layer is selected from a material
that is transparent to the wavelength of a given light source, and
has a dielectric permittivity that matches that of the metal layer
(which may also be a metal-based composite or multilayer). Example
types include glass, quartz, PMMA, PDMS, parylene, mineral oil,
other oils, GaAs, ITO, etc. The thickness of the dielectric layer
will be dependent on strength of evanescent wave, and in
particular, should be less than the projected distance of the
evanescent wave which is at most hundreds of nanometers. Dielectric
layer thickness may be chosen based on the metallic grating layer
thickness because different metal-wavelength combinations will have
stronger Plasmon resonances and thus stronger projected evanescent
wave fields. It is notable however, that this is typically within
some small band, and still have to be very thin.
[0019] For the metallic grating layer of the FSL, a grating pattern
is necessary for converting far-field images to near-field, though
it can be dynamical, i.e. it can be generated optically,
electrically or acoustically. It is appreciated that a non-grating
thin metal film will form a simple near-field superlens. The
periodicity of the grating pattern may be designed based on the
wavelength of the light source and desired feature resolution. For
example, a silver grating FSL for P.mu.SL integration has been
constructed having a periodicity of about 200 nm, a silver line
width of 100 nm and a thickness of 50 nm. The grating aspect ratio
(length/width) can be increased to produce a larger FSL and more
area over which to fabricate. The metal grating layer thickness may
be from tens of nanometers to hundreds of nanometers. Example types
of metals may include, for example, silver, which is suitable for
longer UV wavelengths (300-400 nm), or other metals such as for
example aluminum, copper, gold, conductive oxides (ITO, doped ZnO),
Na, K, Au--Ag alloy, Co--Au, Ni--Ag alloy, multi-layered graphenes,
etc.
[0020] It is appreciated that the metallic grating layer may also
be formed as a multilayer comprising several thin film layers of
other materials, such as for example the combination of
silver/MgO/silver composite (or silver, Al.sub.2O.sub.3, silver)
which could serve as a superlens for wavelength of 500 nm. Such
metal composite/multilayers may enable operation of the FSL at
other wavelengths or simply may provide an alternative to silver in
the UV range. The layers of the multilayer can consist of a seed or
adhesion layer such as germanium or MgO. This is intended to
provide smooth growth of metallic layer such as Ag or Au. There is
also a composite layer made of metal and dielectrics, such as
MgO/Ag/MgO/Ag . . . thin film stacks, or it can contain porous
anodized Al2O3 or TiO2 with electroplated metal, such as Ag, Au, or
conductive oxide fillers. The importance of the composite layer is
to provide a impedance matching element for resonant transfer of
evanescent waves. In addition, a layer is integrated to convert
evanescent waves to far field. This can be implemented such as
metallic grating or dynamic grating produced by photorefractive
effect or electro-optical effects.
[0021] It is appreciated also that the FSL could be
electro-optically tuned and potentially integrated with
UV-emitters. For example, a ZnO nanowire emitter may be integrated
with the FSL such that each of the emitters could be individually
actuated, with tightly confined light spot with virtually no
crosstalk. They may be used in combination with digital projection
from far field, for near field pattern generations.
Digital Holographic P.mu.SL
[0022] Digital holographic masks are also used in the present
invention, which allows a variety of porous structures and
materials to be established and aperiodic features to be
intentionally positioned. In particular digital dynamic masks are
used to project the computed hologram into liquid polymers for
fabrication of highly interconnected functionally graded density
materials with nanometer precision. While holographic
nanolithography is a known method of 3D volumetric nanofabrication
by interfering multiple coherent beams interfere in 3D space, the
simple interference method typically cannot create designed defects
and features of arbitrary shape. They are typically also limited by
the depth of penetration in the solid photoreactive materials.
[0023] The present invention utilizes multiple light projection
systems to project respective digital images to the fabrication
zone, so as to holographically interfere and thereby cure select
portions of the photosensitive resin, which is preferably chosen
for photo-sensitivity and transparency. While the resin bath may be
loaded with metal or ceramic powders, this will change the optical
properties. Methods such as atomic layer deposition and
electroplating may be used to infiltrate the polymer mold with
liquid phase chemical reactants at low temperature.
Integration of Microfluidic Systems for Multi-Material
Fabrication
[0024] Another feature of the present invention is the integration
of microfluidic components and sub-systems (in particular laminar
flow systems) with the P.mu.SL system to provide the capability of
fabricating structures (such as 3D structures) with multiple,
heterogeneous materials in the same component. By incorporating
microfluidic systems into the resin bath of a P.mu.SL system, the
present invention has the ability to fabricate microstructures of
different materials in one process. By slowly flowing layers of
photosensitive resin a single exposure and curing step in one
material can be completed. A new material (different resin or
loading of metal/ceramic particles) can follow in another fluid
layer. This material can then be exposed and cured resulting in a
multilayer material. If the fluid is allowed to settle in void
areas then multiple materials can be cured on the same image plane
and concentric structures of different materials (such as double
shelled targets) may be fabricated. Laminar flow microfluidic
systems in particular provide for more uniform delivery and
distribution of materials and to allow for multiple material
components to be sequentially exposed.
[0025] Various types of materials (various photosensitive liquids
or slurries with metal or ceramic nanoparticles) may be injected
into the fabrication area through a single, valved, microfluidic
channel and port allows for the ability to sequentially fabricate
with different materials. For example, one material can flow into
the fabrication zone and layers lithographically formed. This
material then is removed via another microfluidic port while a new
material flows into the fabrication zone. More features/layers may
then be produced. The multiple materials could be in the same
device layer or could form a layered structure. Furthermore,
micofluidic integration may be implemented with multiple injection
ports for various materials. These ports could be arranged around
the fabrication area in almost any desired geometry including
radially oriented or at different vertical positions. This would
allow for more precise injection of different materials to specific
locations in the fabrication zone. The injection could occur
simultaneously or could be staged in time depending on the part to
be fabricated. In general, this will allow for additional material
and geometric flexibility in final fabricated part.
[0026] The introduction of different types of materials in to the
bath vessel may be enhanced by enclosing the fabrication zone and
liquid with a membrane cover. The membrane can be made of PDMS or
any other relatively inert material; however it needs to have some
gas permeability and be optically transparent. The membrane
provides several advantages; 1) it dampens any disturbances on the
free surface of the liquid monomer bath (this increase fabrication
speeds) and 2) it creates a completely enclosed fluidic bath which
results in smooth fluid flow around fabricated features. The
membrane must be permeable so that there is a thin layer of gas
between the membrane and the liquid otherwise fabricated features
may stick to the membrane. The below figures show and schematic of
how the membrane can be integrated into the P.mu.SL system and some
multimaterial parts fabricated with this technique.
BRIEF DESCRIPTION OF THE DRAWINGS
[0027] The accompanying drawings, which are incorporated into and
form a part of the disclosure, are as follows.
[0028] FIG. 1 is a flow diagram schematically illustrating the
optical path taken in a first exemplary embodiment of the present
invention for producing sub-diffraction-limited features.
[0029] FIG. 2 shows a schematic view of a second exemplary
embodiment of the present invention incorporating a far-field
superlens in the optical path of the P.mu.SL to produce
sub-diffraction-limited features of 3D micro- and nano-structures
in a layer-by-layer stereo lithographic fabrication process.
[0030] FIGS. 3A-C show schematic views of three exemplary methods
of superlens-liquid interfacing.
[0031] FIG. 4 shows a schematic view of another exemplary
embodiment of the present invention showing multiple projection
systems producing a structure based on a digital hologram generated
by multiple SLMs arranged around a photosensitive resin bath for
patterning 3D nanostructures without periodicity.
[0032] FIG. 5 shows an isometric illustration of three dynamically
configurable masks corresponding to three interfering beams which
produce a hologram of a complex 3D structure in a photosensitive
resin bath to fabricate the 3D structure in a single
snapshot/exposure.
[0033] FIG. 6 shows a schematic view of an exemplary microfluidic
system of the present invention for injecting multiple types of
photosensitive resins into a hath vessel of a P.mu.SL system.
[0034] FIG. 7 is a top view of an exemplary bath vessel of a
P.mu.SL having three injection ports and three outlet ports of an
integrated microfluidic system.
[0035] FIG. 8 is a schematic view of another exemplary embodiment
of the system of the present invention incorporating multiple SLMS
for 3D holographic stereolithography and a microfluidic system for
using multiple materials.
DETAILED DESCRIPTION
[0036] Turning now to the drawings, FIG. 1 shows a flow diagram
generally illustrating the primary components and the optical path
of a first exemplary embodiment of a P.mu.SL system 10 of the
present invention to produce three-dimensional structures (e.g.
meso- or micro-scale) with sub-diffraction-limited features. As
shown in FIG. 1, the system 10 generally includes a light source
11, such as for example a UV LED array, which produces
electromagnetic radiation (hereinafter "light") of a given
wavelength, (e.g. 350 nm for UV). The system also includes a SLM 12
which functions as a dynamically configurable mask to produce a
two-dimensional pattern/image from the light. The two dimensional
image produced from the SLM 12 is then reduced by a reduction lens
13, and projected onto an FSL 14 which is positioned adjacent a
photosensitive resin bath 14. The reduced two dimensional image
from the SLM (i.e. far field image), is converted by the FSL 14
into a different two-dimensional image (i.e. near-field image)
having sub-diffraction-limited features, i.e. features which exist
below the diffraction limit. The near-field image then selectively
cures local regions within the resin bath 14.
[0037] It is appreciated that the photosensitive resin bath
contains a liquid, such as a liquid photosensitive monomer or
resin, which is formed into a component when illuminated with the
projected beam. In particular, the liquid converts to solid upon
exposure to output of the superlens. Example material types include
hexandiol diacrylate (HDDA), polyethylene glycol diacrylate
(PEGDA), tBA-PEGDMA (a shape memory polymer), POSS-diacrylate, and
there could also be nanoparticles in the liquid such as gold,
copper, or ceramics. The photosensitive resin may also be loaded
with ceramic, metal, or other particles to generate components of
different materials. In this case, after initial stereolithographic
fabrication, the parts can be sintered to remove the polymer and
density the functional material of interest. This usually shrinks
the part by some controllable amount. It is also notable that by
varying the intensity of the UV light, various porosity/density
structures can be generated resulting in graded density materials.
This could be combined with the superlens or holographic projection
to generate graded density structures with <100 nm features.
[0038] FIG. 2 shows a second exemplary embodiment of the PuML
system of the present invention having a light source 26 (shown as
a UV source) which illuminates a SLM 28 via a beam splitter 27, and
a reduction lens 25 which projects the image onto a FSL 30. The SLM
is shown connected to a computer 29 which dynamically controls the
SLM to produce various digital masks, such as masks i, j, and k. It
is appreciated that the two-dimensional image formed by the SLM are
not the actual part or features, rather they are the far-field
image calculations corresponding to the desired near-field images
to be produced by the FSL 30 which are then used to selectively
cure portions of the photosensitive resin, as previously described
in the Summary. As shown in FIG. 2, the FSL is positioned to
contactedly interface directly with the photosensitive resin at a
liquid surface 22. The resin is shown contained in a
stereolithographic bath vessel 21, which is open at the top. A
z-axis stage 23 and 24 is also provided for lowering the part (such
as 31) as each layer is fabricated. The z-axis stage 23, 24 is also
shown connected to the computer 29 so as to be controlled by the
computer as each level is completed.
[0039] FIGS. 3A-C show three different embodiments by which the FSL
may interface with the photosensitive liquid resin. Although the
FSL is characterized as "far-field", this is only referring to one
side of the lens. When a SLM-produced two-dimensional image is
projected onto the FSL from the far-field, the FSL then generates
near-field sub-wavelength features in the liquid monomer resin
bath. Also, in order to have the required surface plasmons for the
lens to work, the thin film of silver must have an interface with a
dielectric material. It is appreciated that the FSL itself must be
maintained in close proximity to the photosensitive liquid.
However, it may not be desirable to use the liquid resin/monomer as
the dielectric material since the fabricated features may simply
stick to the FSL. FIG. 3A in particular shows an FSL 42 having a
dielectric layer 43 and a metal grating layer 44 interfaced with
the photosensitive resin 40 at a liquid surface 41. In particular,
the metal grating layer 44 is shown without an intermediate
dielectric material separating it from the resin, and instead
directly contacts the photosensitive resin. And incoming light
(e.g. the projected image) is shown at 45. FIG. 3B shows a second
embodiment of the FSL 46 also having a dielectric layer 49 like
FIG. 3A, but now also having an intermediate solid dielectric layer
48 which is formed (e.g. coated) over the metallic grating layer
47. The coating may be a very thin layer, e.g. <100 nm to
provide the metal dielectric interface. Example material types may
include PMMA, PDMS, glass, etc. And in FIG. 3C, another embodiment
is shown having a dielectric layer 51, and where another liquid 52
(such as an oil) is used as the dielectric interlayer. As shown in
the figure, a thin layer of the liquid dielectric 52 will remain in
contact with the FSL 50 due to surface tension effect. Similar to
the solid dielectric, the liquid dielectric interlayer provides the
metal dielectric interface. In this case, the liquid 52 fills voids
in the grading via surface tension effects and can provide a very
thin layer, it also prevents cored components from sticking to the
FSL. Example material types may include mineral oil, and other
oils. The FSL may be held in placed on top of the liquid surface by
conventional mounting hardware known in the art or, for example, on
a motion stage to ensure good positioning. Furthermore, the FSL may
be placed to cover the free liquid surface (in whole or in
part).
[0040] FIG. 4 shows a second exemplary embodiment of the system 80
of the present invention, with multiple electromagnetic radiation
projection systems 81-83 together stereolithographically producing
a three-dimensional structure 85 based on a digital hologram
generated by the multiple projection systems. The structures may be
aperiodic structures, designed features, or even fully 3D
holograms. In particular, the projection systems 81-83 each have
integrated SLMs (not shown) to produce digital masks, and are
arranged around a photosensitive resin hath vessel 83 to produce a
3D holographic interference pattern in liquid resin for patterning
3D nanostructures without periodicity. The vessel 83 is shown as
with optically transparent walls so that projections systems 82 and
83 may illuminate from the sides. The projection system 81
illuminates from the top through the open top side of the vessel 83
where the liquid level 84 is shown. A stage 86 (such as a z-axis
stage) may also be provided where the holographically produced
structure may be positioned.
[0041] Similarly, FIG. 5 shows an isometric illustration of three
dynamically configurable masks 91-93 corresponding to three
interfering beams which produce a hologram of a complex 3D
structure 90 in a photosensitive resin bath to fabricate the 3D
[0042] structure in a single snapshot/exposure. The three masks are
shown orthogonally oriented, such as on xyz-axes. However, as shown
in FIG. 8, multiple projection systems need not be orthogonal to
each other. It is appreciated that each of the projections systems
may also incorporate a FSL to produce sub-diffraction limited
features when holographically interfered with the near-field images
from the other projection systems. The holographic lithography
interferes light beams from multiple digital masks rather than
lasers, and can provide individual pixel control. With this
control, the interference pattern between the two or more beams can
be changed in 3D space resulting in locally controlled features and
aperiodic structures. In addition, true 3D holograms may be
generated and projected into the photosensitive monomer to generate
3D structures (without the need for Z-stage adjustment).
[0043] FIG. 6 shows another exemplary embodiment of a microfluidic
system 100 of the present invention, integrated with a larger
P.mu.SL system (not shown) to enable materials flexibility, i.e.
fabricating multi-materials components, with multiple materials in
either the same layer or across layers. This allows a broad range
of materials to be used with P.mu.SL to include metals, ceramics
and a range of polymers. FIG. 6 shows in particular a P.mu.SL bath
vessel 101 having a cylinder 102 and a piston 103. The top of the
cylinder is open and contains a photosensitive resin. The top of
the piston 103 is shown as the fabrication stage and is connected
to a z-stage 104 for lowering/elevating the fabricated part,
typically in a layer-by-layer process. The cylinder 102 walls may
be optically transparent so as to enable illumination by image
projectors (not shown). The system 100 is shown having an inlet 108
fluidically connected to at least two different photosensitive
resin sources 106 to 107, which are connected to supply the vessel
with different photosensitive liquids. A control valve 109 is shown
connected to a computer 105 (or other controller) for controlling
injection of resin into the bath vessel. An outlet port 110 is also
shown for exhausting photosensitive liquid from the hath container,
so that the vessel may be emptied of a first photosensitive liquid
used to produce a first feature of a fabricated structure prior to
tilling with a second photosensitive liquid used to produce a
second feature of the fabricated structure. And a control valve 111
is also shown connected to the computer 105 for controlling flow
out of the vessel.
[0044] FIG. 6 also shown a membrane 112 which may be positioned at
the liquid surface, so as to enable laminar flow when resin is
moved in and out of the vessel. The membrane is preferably
optically transparent, as well as flexible so as to deform when
fluid is moving in/out and eliminate liquid free surface
disturbance. Optionally, the membrane may be gas permeable. Example
material types include PDMS, glass, quartz, and other clear
flexible polymers. It is notable that if an FSL is used, the
membrane may or may not be used since the FSL would cover the free
surface in place of the membrane. However, since the FSL is a thin
film structure it can also be deposited on the membrane 112, such
as in combination with radical inhibition layer.
[0045] FIG. 7 shows a top view of another embodiment of the
microfluidic system integrated into the P.mu.SL of the present
invention. In particular, a bath vessel 200 used in a P.mu.SL
system and adapted to contain a photosensitive resin therein is
shown having multiple inlet, and outlet ports 201-206 connected
along its walls, and preferably near the liquid surface. The
injection or inlet ports are indicated at 201-203, and the exhaust
or outlet ports are indicated at 204-206. Each of the inlet ports
are in fluidic communication with one or more different types of
photosensitive resin reservoir or sources to provide the vessel
basin 200' with the desired material. In one particular embodiment,
each inlet port may be connected with a unique material, while in
an alternative embodiment, each inlet port may be connected to each
of the various types of resins available.
[0046] And FIG. 8 shows a combined system 300 having the features
of a multiple projection system for 3D holographic fabrication and
an integrated microfluidic system for multiple material delivery.
In particular, three projection systems 321-322 are shown, which
project two-dimensional images into the fabrication zone
characterized by a bath vessel 301. Similar to FIG. 36, the system
includes a P.mu.SL bath vessel 301 having a cylinder 302 and a
piston 303. The top of the cylinder is open and contains a
photosensitive resin. The top of the piston 303 is shown as the
fabrication stage and is connected to a z-stage 304 for
lowering/elevating the fabricated part, typically in a
layer-by-layer process. The cylinder 302 walls may be optically
transparent. And ports 308 and 310 are connected to the bath vessel
and controlled by valves 309 and 311, respectively. Furthermore a
computer 305 controls the z-stage 304 and the valves 309, 311.
While not shown in FIG. 8, each of the projections systems 301-301
may incorporate a FSL such that the image projected into the
fabrication zone is a near-field image. And similar to the membrane
112 of FIG. 6, FIG. 8 also shows a membrane 312 positioned at the
liquid surface.
[0047] While particular embodiments and parameters have been
described and/or illustrated, such are not intended to be limiting.
Modifications and changes may become apparent to those skilled in
the art, and it is intended that the invention be limited only by
the scope of the appended claims.
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