US 11,745,493 B2

1
ULTRA-CONFORMAL MICROPRINT ANI
ULTRA-CONFORMAL MICROPRINT
TRANSFERRING

EMENT REGARDING FEDERALLY
SPONSORED RESEARCH

This invention was made with United States Government
support from the National Institute of Standards and Tech-
nology (NIST), an agency of the United States Department
of Commerce. The Government has certain rights in the
invention. Licensing inquiries may be directed to the Tech-
nology Partnerships Office, NIST, Gaithersburg, MD,
20899; voice (301) 975-2573; email tpo@nist.gov.

BRIEF DESCRIPTION

Disclosed is an ultra-conformal microprint composite for
making an ultra-conformal microprint by ultra-conformal
microprint transferring that includes: a microprint substrate;
a glassy composite ultra-conformally disposed on the micro-
print substrate, the glassy composite including: a glassy
transfer layer in a glass state including: corn syrup; and
sugar disposed in the corn syrup; and a transfer moiety
disposed on the glassy transfer layer and arranged as a
microstructure.

Disclosed is a process for making an ultra-conformal
microprint by ultra-conformal microprint transferring that
includes: disposing a transfer moiety arranged in a micro-
structure on a transfer substrate; disposing a glassy transfer
layer on the transfer moiety; forming a glassy composite
comprising the glassy transfer layer and transfer moiety with
maintaining the microstructure of the transfer moiety in the
glassy transfer layer; removing the glassy composite from
the transfer substrate while maintaining the microstructure
of the transfer moiety in the glassy transfer layer; disposing
the glassy composite on a microprint substrate; ultra-con-
formally covering the microprint substrate with the glassy
composite while maintaining the microstructure of the trans-
fer moiety in the glassy transfer layer so that the micro-
structure is disposed on the microprint substrate; and remov-
ing the glassy transfer layer while leaving the transfer
moiety disposed in the microstructure on the microprint
substrate to form the ultra-conformal microprint comprising
the transfer moiety arranged in the microstructure on the
microprint substrate.

BRIEF DESCRIPTION OF THE DRAWINGS

The following description should not be considered lim- 5

iting in any way. With reference to the accompanying
drawings, like elements are numbered alike.

FIG. 1 shows a perspective view of an ultra-conformal
microprint in panel A, a plan view of the ultra-conformal
microprint in panel B, and a cross-section along line A~A
indicated in panel B of the ultra-conformal microprint in
panel C:

FIG. 2 shows a perspective view of a microprint substrate
in panel A, a plan view of the microprint substrate in panel
B, and a cross-section along line A-A indicated in panel B
of the microprint substrate in panel

FIG. 3 shows a plan view of a plurality of transfer
moieties disposed on a sacrificial layer or on a transfer
substrate with the transfer moieties arranged as a micro-
structure;

FIG. 4 shows, in panel A, a cross-section along line A-A
of the article shown in FIG. 3 for transfer moieties disposed

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6:

2

on the sacrificial layer, a glassy composite disposed on the
crificial layer in panel B, removal of sacrificial layer for
separation of the transfer substrate from the glassy compos-
ite in panel C, and the glassy composite removed from the
transfer substrate in panel D;

FIG. 5 shows a glassy composite partially disposed on
microprint substrate in panel A, partial ultra-conformal
disposition of glassy composite on microprint substrate in
panel B. and ultra-conformal disposition of glassy compos-
ite on microprint substrate to form ultra-conformal micro-
print composite in panel C;

FIG. 6 shows a perspective view of an ultra-conformal
microprint composite before removal of the glassy transfer
layer to form the ultra-conformal microprint shown in FIG.

FIG. 7 shows a longitudinal cross-section of the ultra-
conformal microprint composite shown in FIG. 6 before
removal of the glassy transfer layer to form the ultra-
conformal microprint shown in FIG. 1;

FIG. 8 shows, in panel A, a cross-section along line A-A
of the article shown in FIG. 3 for transfer moieties disposed
on the transfer substrate, and panel B shows a cross-section
along line B-B of the article shown in FIG. 3 for transfer
moieties disposed on the transfer substrate;

FIG. 9 shows, in panel A, a cross-section along line A-A
of the article shown in FIG. 3 for transfer moieties disposed.
on a sacrificial layer on the transfer substrate, and panel B
shows a cross-section along line B-B of the article shown in
FIG. 3 for the transfer moieties disposed on a sacrificial
layer on the transfer substrate.

FIG. 10 shows a cross-section of a glassy composite
formed by disposal of a gl: transfer layer to embed the
transfer moiety in the glassy transfer layer starting with
transfer moiety disposed on the transfer substrate in accord
with the article shown in FIG. 8, and panel B shows the
glassy composite removed from the transfer substrate;

FIG. 11 shows, in panel A, a cross-section along line A-A
of the article shown in FIG, 3 for transfer moieties disposed.
on the transfer substrate and disposed in sacrificial layer, a
glassy composite disposed on the sacrificial layer in panel B,
removal of sacrificial layer for separation of the transfer
substrate from the glassy composite in panel C, and the
glassy composite removed from the transfer substrate in
panel D;

FIG. 12 shows, in panel A, a microprint substrate having
an arbitrary shape with a plurality of curved surfaces and a
trench on which is disposed a plurality of native moieties
and that receives disposition of glassy composite; panel B
shows ultra-conformal disposition of glassy composite on
microprint substrate to form ultra-conformal microprint
composite; and in panel C ultra-conformal microprint after
removal of glassy composite from microprint substrate;

FIG. 13 shows, in panel A, an ultra-conformal microprint
that includes a plurality of gold strips disposed as transfer
moieties over a trench on a microprint substrate; panel B
shows a zoomed view of the ultra-conformal microprint
shown in panel A; panel C shows an ultra-conformal micro-
print that includes a plurality of magnetic dots disposed as
transfer moieties in a recessed feature on a microprint
substrate; panel D shows a zoomed view of the ultra-
conformal microprint shown in panel C; panel E shows an
ultra-conformal microprint that includes a plurality of metal-
lic dots disposed as transfer moieties on a hair strand as a
microprint substrate; and panel F shows an ultra-conformal
microprint that includes a plurality of letters made from thin
layers of metal disposed as transfer moieties on a hair strand
as a microprint substrate;



U.S. Patent Sep. 5, 2023 Sheet 13 of 18 US 11,745,493 B2

(A) 20 262 208 242 va (B)

Acc Spot Magn Det WD
{0.00 kv 3.0. 500 SE 5.1

Acc Spot Magn Det : Acc Spot Magn Det WO
998k 20 {00x SE 75 98h 3.0 5000 SE 75

Acc Spot Magn Det WO Acc. Spot Magn
SOT kv30 1200x SE 75 S.00ky 30 2000 SE 75

FIG. 13


US 11,745,493 B2

9

dissolve in water but that dissolves in some other solvent in
which glassy transfer layer 206 does not dissolve.

In an embodiment, a process for making ultra-conformal
microprint 200 by ultra-conformal microprint transferring
includes forming microstructure 210 including transfer moi-
ety 202 on sacrificial layer 203 that optionally can be
disposed on transfer substrate 201. Glassy transfer layer 206
is disposed on microstructure 210 to form glassy composite
207, and sacrificial layer 203 is dissolved in a first solvent.
Glassy composite 207 is disposed on microprint substrate
208. Contact of glassy composite 207 with microprint sub-
strate 208 can be increased by heating glassy composite 207
to a temperature greater than glass transition temperature Tg
of glassy transfer layer 206 such that the glassy transfer layer
206 reflows to ultra-conformally cover microprint substrate
208. By ultra-conformally covering microprint substrate 208
with glassy composite 207, microstructure 210 is disposed
‘on microprint substrate 208 maintaining the configuration of
microstructure 210 as formed on sacrificial layer 203 even

when microprint substrate 208 has a highly non-planar 2

surface that can include local areas of high curvature that are
too high in curvature to be conformally coated by a mechani-
cally less compliant transfer material than glassy transfer
layer 206. By exceeding a glass transition point of glassy
transfer layer 206, glassy composite 207 flows ultra-confor-
mally to fully conform to whatever container or surface on
which glassy composite 207 is disposed. By slowing
increasing a temperature of glassy composite 207 to become
greater than glass transition temperature Tg, microstructure
210 in glassy composite 207 moves with glassy transfer
layer 206 so that microprint substrate 208 is ultra-confor-
mally coated. Following ultra-conformal disposition of
glassy composite 207 on microprint substrate 208, glassy
transfer layer 206 is cooled below glass transition tempera-
ture Tg and solidifies as a glass after which glassy composite
207 is contacted with a solvent to dissolve glassy transfer
layer 206 to remove glassy transfer layer 206 from micro-
print substrate 208 and leave microstructure 210 on micro-
print substrate 208 as ultra-conformal microprint 200. To
avoid cracking of glassy transfer layer 206 during cooling,
a cooling rate can be controlled at a selected rate.

It is contemplated that the first solvent for removal of
sacrificial layer 203 from glassy transfer layer 206 and the
second solvent for removal of giassy transfer layer 206 from
microprint substrate 208 are selected such that the first
solvent dissolves sacrificial layer 203 but not glassy transfer
layer 206, and the second solvent dissolves glassy transfer
layer 206. In addition, if glassy transfer layer 206 is in a
liquid state for disposal on microstructure 210 on sacrificial

layer 203 or transfer substrate 201, the solvent, e.g. water, 5

in the liquid composition for glassy transfer layer 206 does
not dissolve sacrificial layer 203.

In an embodiment, native moiety 211 is disposed on
microprint substrate 208 prior to glassy composite 207 being

disposed on microprint substrate 208, wherein glassy com- 5

posite 207 is disposed on native moiety 211 or on both
microprint substrate and native moiety. Native moiety 211
can remain or subsequently be removed from microprint
substrate 208 after removal of glassy transfer layer 206 from
microprint substrate 208.

Native moiety 211 can include various materials, e.g.,
silicon, or other semiconductors, metals, glass, ceramic,
paper, plastics or other flexible polymeric materials, textiles,
fibers, biological materials such as skin, hair, tissue, organs
and cells and the like. Exemplary native moieties 211
include microspheres, wires, optical fibers or components,
electronic components. Native moiety 211 can have an

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arbitrary shape and size. It is contemplated that the shape of
native moiety 211 can be round, polygonal, irregular, and the
like to provide a cross-sectional shape this is symmetric or
asymmetric with a selected degree of anisotropy. Further,
native moiety 211 can be electrically insulating, semicon-
ductive, or conductive. In an embodiment, native moieties
202 are magnetic, ferromagnetic, paramagnetic, nonmag-
netic, or a combination thereof. A largest dimension of
native moiety 211 can be from 1 nm to 1 cm, specifically
from 10 nm to 1 mm, and more specifically from 100 nm to
100 micron. Moreover, native moiety 211 can have curva-
tures too extreme to be coated using conventional transfer
materials, and native moiety geometry can include over-
hangs or undercuts that can be contacted with a reflowable
transfer material. In an embodiment, native moiety 211
includes polystyrene microspheres of 4.5 micrometer diam-
eter (see e.g., FIGS. 15,17,18).

Depending on a geometry of microprint substrate 208,
heating glassy composite 207 on microprint substrate 208
can be conducted under a vacuum or partial vacuum envi-
ronment to remove trapped air pockets in recessed regions,
eg., trench 212 or blind hole 214, of microprint substrate
208 that could prevent glassy composite 207 from fully
flowing in trench 212 or blind hole 214.

In an embodiment, glassy transfer layer 206 is disposed
‘on microstructure 210 that is disposed on sacrificial layer
203 by placing a solid piece of glassy transfer layer 206 on
microstructure 210 and heating glassy transfer layer 206 to
reflow and contact microstructure 210 to form glassy com-
posite 207 on sacrificial layer 203. In an embodiment,
forming glassy composite 207 on sacrificial layer 203
includes solvating glassy transfer layer 206 in a second
solvent to form a liquid composition for disposal on micro-
structure 210 on sacrificial layer 203; forming a temporary
containment barrier around a periphery of sacrificial layer
203 on which is disposed microstructure 210; and pouring
dissolved glassy transfer layer 206 on microstructure 210
and sacrificial layer 203. The temporary containment barrier
keeps glassy transfer layer 206 from flowing off of sacrificial
layer 203 and can be, e.g., a material that is wrapped around
a periphery of sacrificial layer 203. The second solvent used
to solvate glassy transfer layer 206 can evaporated by
heating glassy composite 207, or flowing a gas over sacri-
ficial layer 203 to increase evaporation of the second solvent
from glassy composite 207 on sacrificial layer 203, or
waiting long enough for evaporation of the second solvent
from glassy composite 207. In the case of heat assisted
evaporation, the glassy composite can be allowed to cool
slowly to avoid possible cracking.

Forming glassy composite 207 on sacrificial layer 203
alternatively can include a drop of liquid composition for
glassy transfer layer 206 that can be spin-coated over
microstructure 210 on microprint substrate 208 or solid
glassy transfer layer 206 can be heated to soften glassy
transfer layer 206 but not liquify it and with subsequent
mechanical pushing or stretching glassy transfer layer 206
can be spread over microstructure 210 on sacrificial layer
203.

The process for making ultra-conformal microprint 200
also can include a transfer substrate that is itself non-planar
since the glassy transfer layer can be made to ultra-confor-
mally coat the transfer substrate and the transfer moieties
just as it can ultra-conformally coat the microprint substrate.
A spatially patterned transfer substrate that may have delib-
erately fashioned local embossed or recessed regions would
create an inversely patterned glass transfer layer that could
then be used to selectively transfer print only onto certain



U.S. Patent Sep. 5, 2023 Sheet 4 of 18 US 11,745,493 B2

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OQ QO OQ | 203
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US 11,745,493 B2

3

FIG. 14 shows full wraparound covering of a hair with
gold dots;

FIG. 15 shows hollow cylinders disposed on a planar
microprint substrate in panel A and hollow cylinders dis-
posed on a sphere in panel B;

FIG. 16 shows metallic dots as transfer moieties on a
microprint substrate that includes a sharp right-angled pro-
tuberance extending from a surface of the microprint sub-
strate in panel A for an arc-shaped protuberance and panel B
for a cylinder-shaped protuberance;

FIG. 17 shows metallic dots as transfer moieties on a
microprint substrate that includes a planar surface and a
plurality of native moieties arranged in an array in panel A
and a zoomed view of a local cluster of such native moieties
in panel

FIG. 18 shows metallic dots that include different metals
and different shapes including gold disks and nickel annular
rings as transfer moieties on a microprint substrate and
disposed on a spherical native moiety in panel A and a
zoomed out view of such in panel B.

DETAILED DESCRIPTION.

A detailed description of one or more embodiments is
presented herein by way of exemplification and not limita-
tion.

It has been discovered that a ultra-conformal microprint
200 and process for ultra-conformal microprint transferring
provides transference of microstructures created on transfer
substrate 201 onto a microprint substrate 208, wherein the
microprint substrate 208 can be a highly nonplanar (e.g..
discontinuous or curved) or incompatible with conventional
fabrication processes. The ultra-conformal microprint trans:
ferring involves disposing a glassy transfer layer 206 on the
transfer substrate 201 and forming a glassy composite 207
that includes transfer moiety 202 disposed in the glassy
composite 207. The glassy composite 207 is removed
together from the transfer substrate 201 and disposed on the
microprint substrate 208. The glassy transfer layer 206 has
a glass transition temperature Tg so that the glassy compos-
ite 207 can be ultra-conformally disposed on the microprint
substrate 208. It is contemplated that ultra-conformal dis-
posal of glassy composite 207 on microprint substrate 208
can cover corners, protuberances, holes, vias, or trenches,
disposed on microprint substrate 208. Finally, the glassy
transfer layer 206 is miscible in a solvent to be removed
from microprint substrate 208 and leave the transfer moiety
202 arranged in a microstructure on microprint substrate 208
as ultra-conformal microprint 200.

Ultra-conformal microprint transferring makes ultra-con- 5

formal microprint 200. In an embodiment, with reference to
FIG. 1, ultra-conformal microprint 200 includes: a plurality
of transfer moiety 202 disposed as microstructure 210 on
microprint substrate 208.

With reference to FIG. 2, microprint substrate 208 s

receives glassy composite 207 for transfer of transfer moiety
202 thereon. Microprint substrate 208 can include various
materials, e.g., a semiconductor (¢.g., silicon and the like
including a binary semiconductor, ternary semiconductor,
and the like), metal, glass, ceramic, paper, polymer, textile,
fiber, biological material (e.g., skin, hair, tissue, organs, and
cells), and the like. Exemplary microprint substrates 208
include microfibers, microspheres, and all manner of non-
planar surfaces with high curvatures for which pattern
transfer is difficult or impossible via other methods. Micro-
print substrate 208 can have an arbitrary shape and size. It
is contemplated that the shape of microprint substrate 208

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4

can be round, polygonal, irregular, and the like to provide a
cross-sectional shape this is symmetric or asymmetric with
a selected degree of anisotropy. A surface of microprint
substrate 208 can be planar or curved and can have an
embossed feature (e.g., a protuberance such as a post or
ridge) or recessed feature (e.g., as an aperture, hole, trench
and the like), wherein the recessed or embossed feature can
have an arbitrary largest linear dimension and arbitrary
shortest linear dimension along a radius, length, width, or
height of the recessed or embossed feature, as applicable to
a geometry of the microprint substrate 208. A largest dimen-
sion of microprint substrate 208 can be from 10 nm to 10 m,
specifically from 100 nm to 10 cm, and more specifically
from 1 jum (also indicated as micron) to 10 mm. Further,
microprint substrate 208 can be flexible, hard, or sofi, can
have rough or smooth surfaces, or can be made from
materials incompatible with conventional semiconductor
processing. In an embodiment, microprint substrate 208
includes a strand of human hair. In another embodiment,
microprint substrate 208 includes a polystyrene micro-
sphere.

Transfer moiety 202 can include various materials, e.g.
silicon or other semiconductor materials, metals, glasses
plastics, polymers, pharmaceuticals, dyes and the like.
Exemplary transfer moieties 202 include metallic, glass and
polymeric microstructures and mixtures thereof, of arbitrary
complexity including even fully functional optical or elec-
tronic components. Transfer moiety 202 can have an arbi-
trary shape and size. It is contemplated that the shape of
transfer moiety 202 can be round, polygonal. irregular, and
the like to provide a cross-sectional shape this is symmetric
or asymmetric with a selected degree of anisotropy. Further,
transfer moiety 202 can be electrically insulating, semicon-
ductive, or conductive. In an embodiment, transfer moieties
202 are magnetic, ferromagnetic, paramagnetic, nonmag-
netic, or a combination thereof. A largest dimension of
transfer moiety 202 can be from 1 nm to 10 cm, specifically
from 10 nm to 1 cm, and more specifically from 10 nm to
1 mm. Moreover, transfer moiety 202 can be made from
materials incompatible with conventional semiconductor
processing and can be made from fragile materials, even
those that may be too fragile to pick up via conventional
methods since the transfer process described here can
involve gentle processing. In an embodiment, transfer moi-
ety 202 includes metallic disks, magnetic dots, and ultrathin
materials (e.g., as shown in FIG. 135) that are thin and
fragile to be not mechanically self-supporting in air, pre-
cluding their being picked up and placed onto a substrate by
conventional acts or articles.

It should be appreciated that ultra-conformal microprint
composite 209 can be formed and used to make ultra-
conformal microprint 200. In an embodiment, ultra-confor-
mal microprint composite 209 for making ultra-conformal
microprint 200 by ultra-conformal microprint transferring
includes: microprint substrate 208; glassy composite 207
ultra-conformally disposed on microprint substrate 208,
glassy composite 207 including: glassy transfer layer 206 in
a glass state including: corn syrup; and sugar disposed in the
corn syrup; and transfer moiety 202 disposed on, or embed-
ded in surface of glassy transfer layer 206 and arranged as
microstructure 210.

Transfer moiety 202 are disposed on microprint substrate
208 and arranged in microstructure 210. The arrangement of
transfer moieties can provide properties of microstructure
210 or ultra-conformal microprint 200 or modifying prop-
erties of microprint substrate 208. Exemplary microstruc-
tures 210 include selected arrangements of metallic wires



US 11,745,493 B2

15

were exposed to the light were then developed away in
photoresist developer to leave behind a photoresist stencil
rhe stencil mask was fully exposed to the light so that
it was subsequently dissolved away in photoresist developer.

Metals that formed the transfer moieties were evaporated
onto this substrate, and the residual photoresist including the
stencil mask was then removed through being developed
away in photoresist developer that also removed deposited
‘metal that was coating it. This left behind metal patterns only
in the positions and geometries of the holes of the stencil
mask on the sacrificial photoresist layer, forming the desired
transfer moieties in the desired microstructure. This was
then coated by pouring a sugar-com syrup glassy material
over it and the solvent (in this case water) was evaporated
from the glassy material by heating. The substrate was then
placed in acetone to dissolve away the sacrificial photoresist
layer and separate the glassy composite containing the
transfer moieties in the microstructure, which was then
placed onto various microprint substrates that had been
prepatterned with demonstrative surface features or native
moieties. To achieve ultra-conformal coating, this glassy
composites on the microprint substrates were then gently
heated to allow for reflow of the glassy transfer material,
which reflowed together with the embedded transfer moi-

eties over the microprint substrate. After dissolution of the 2:

glassy transfer material in water, the transfer moieties in
their microstructure remained behind on the microprint
substrates. Scanning electron microscope images of ultra-
conformal microprints 200 that were made according to this
procedure are shown in FIG. 13, FIG. 14, FIG. 15, FIG. 16,
FIG. 17, and FIG. 18, showing microstructure 210 formed
‘on various shaped microprint substrates 208.

While one or more embodiments have been shown and
described, modifications and substitutions may be made
thereto without departing from the spirit and scope of the
invention. Accordingly, it is to be understood that the present
invention has been described by way of illustrations and not
limitation, Embodiments herein can be used independently
or can be combined.

All ranges disclosed herein are inclusive of the endpoints,
and the endpoints are independently combinable with each
other, The ranges are continuous and thus contain every
value and subset thereof in the range. Unless otherwise
stated or contextually inapplicable, all percentages, when
expressing a quantity, are weight percentages. The
suflix “(s)” as used herein is intended to include both the
ingular and the plural of the term that it modifies, thereby
including at least one of that term (e.g., the colorant(s)
includes at least one colorants). “Optional” or “optionally”
means that the subsequently described event or circumstance
can or cannot occur, and that the description includes
instances where the event occurs and instances where it does
not. As used herein, “combination” is inclusive of blends,
mixtures, alloys, reaction products, and the like.

As used herein, “a combination thereof” refers to a 5

combination comprising at least one of the named constitu-
ents, components, compounds, or elements, optionally
together with one or more of the same class of constituents,
components, compounds, or elements.

Al references are incorporated herein by reference.

The use of the terms “a” and “an” and “the” and similar
referents in the context of describing the invention (espe-
cially in the context of the following claims) are to be
construed to cover both the singular and the plural, unless
otherwise indicated herein or clearly contradicted by con-
text. “Or” means “and/or.” It should further be noted that the

terms “first,” “second,” “primary,

secondary,” and the like

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0

16

herein do not denote any order, quantity, or importance, but
rather are used to distinguish one element from another. The
modifier “about” used in connection with a quantity is
inclusive of the stated value and has the meaning dictated by
the context (¢.g,, it includes the degree of error associated
with measurement of the particular quantity), The conjunc-
tion “or” is used to link objects of a list or alternatives and
is not disjunctive; rather the elements can be used separately
or can be combined together under appropriate circum-
stances.

What is claimed is:
1. A process for making an ultra-conformal microprint
200 by ultra-conformal microprint transferring, the process
comprising:
disposing a transfer moiety 202 arranged in a microstruc-
ture 210 on transfer substrate 201;

disposing a glassy transfer layer 206 on the transfer
moiety 202;

forming a glassy composite 207 comprising the glassy
transfer layer 206 and transfer moiety 202 with main-
taining the microstructure 210 of the transfer moiety
202 in the glassy transfer layer 206;

removing the glassy composite 207 from the transfer
substrate 201 while maintaining the microstructure 210
of the transfer moiety 202 in the glassy transfer layer
206;

disposing the glassy composite 207 on a microprint
substrate 208;

ultra-conformally covering the microprint substrate 208
with the glassy composite 207 while maintaining the
microstructure 210 of the transfer moiety 202 in the
glassy transfer layer 206 so that the microstructure 210
is disposed on the microprint substrate 208; and

removing the glassy transfer layer 206 by dissolving the
glassy transfer layer while leaving the transfer moiety
202 disposed in the microstructure 210 on the micro-
print substrate 208 to form the ultra-conformal micro-
print 200 comprising the transfer moiety 202 arranged
in the microstructure 210 on the microprint substrate
208.

2. The process of claim 1, further comprising:

forming a sacrificial layer 203 on the transfer substrate
201 prior to disposing the transfer moiety 202 and the
glassy transfer layer 206 on the transfer substrate 201;

disposing the transfer moiety 202 arranged in the micro-
structure 210 on the sacrificial layer 203; and

forming the glassy composite 207 on the sacrificial layer
203 to form the glassy composite 207 on the sacrificial
layer 203 such that the sacrificial layer 203 is inter-
posed between the transfer substrate 201 and the glassy
transfer layer 206.

3. The process of claim 2, further comprising:

removing the sacrificial layer 203 to separate the glassy

composite 207 from the transfer substrate 201 prior to
removing the glassy composite 207 from the transfer
substrate 201 while maintaining the microstructure 210
of the transfer moiety 202 in the glassy transfer layer
206.

4. The process of claim 3, further comprising:

contacting the sacrificial layer 203, while disposed on the

transfer substrate 201, with a first solvent that removes
the sacrificial layer 203 to separate the glassy compos-
ite 207 from the transfer substrate 201,

wherein the glassy transfer layer 206 is immiscible in the

first solvent.



US 11,745,493 B2

7

high curvatures that may have radii of curvature of less than
10 micron, less than 1 micron, or less than 0.1 micron.

Removing glassy transfer layer 206 while leaving transfer
moiety 202 disposed in microstructure 210 on microprint
substrate 208 to form ultra-conformal microprint 200
includes dissolving the glassy transfer layer in a solvent that
does not dissolve the transfer moieties and does not dissolve
the microprint substrate. In one embodiment this solvent
may be water, allowing a non-toxic and chemically gentle
process that enables microprint transferal of mechanically or
chemically fragile transfer moieties or transferal onto fragile
microprint substrates that can include a living biological
surface.

In an embodiment, with reference to, e.g., FIG. 3, FIG. 4,
FIG. 9, and FIG. 11, the process for ultra-conformal micro-
print transferring further includes forming sacrificial layer
203 on transfer substrate 201 prior to disposing transfer
moiety 202 and glassy transfer layer 206 on transfer sub-
strate 201 by spin coating a sacrificial material such as

photoresist onto the transfer substrate; disposing transfer 2

moiety 202 arranged in microstructure 210 on sacrificial
layer 203 by microfabrication on the sacrificial layer; and
forming glassy composite 207 on sacrificial layer 203 to
form glassy composite 207 on sacrificial layer 203 such that
sacrificial layer 203 is interposed between transfer substrate
201 and glassy transfer layer 206 by steps performed in
absence of a sacrificial layer.

In an embodiment, with reference to, ¢.g., FIG. 3, FIG. 4,
FIG. 9, and FIG. 11, the process for ultra-conformal micro-
print transferring further includes removing sacrificial layer
203 to separate glassy composite 207 from transfer substrate
201 prior to removing glassy composite 207 from transfer
substrate 201 while maintaining microstructure 210 of trans-
fer moiety 202 in glassy transfer layer 206 by using acetone
to dissolve a photoresist sacrificial layer when using a
sugar-based glassy layer that is insoluble in acetone.

In an embodiment, the process for ultra-conformal micro-
print transferring further includes contacting sacrificial layer
203, while disposed on transfer substrate 201, with a first
solvent that removes sacrificial layer 203 to separate glassy
composite 207 from transfer substrate 201 by soaking the
transfer substrate together with the sacrificial and glassy
layers in a container with the solvent, wherein glassy trans-
fer layer 206 is immiscible in the first solvent. In an
embodiment, the process for ultra-conformal microprint
transferring further includes contacting glassy transfer layer
206, while disposed on microprint substrate 208, with a
second solvent that removes glassy transfer layer 206 from
microprint substrate 208 and leaves transfer moiety 202

disposed in microstructure 210 on microprint substrate 208 5

by soaking the microprint substrate together with the glassy
transfer layer in a solvent that dissolves the glassy transfer
layer but does not dissolve the transfer moieties or the
microprint substrate.

Inan embodiment, with reference to, e.
12, the process for ultra-conformal microprint transferring
further includes heating glassy transfer layer 206 to flow
glassy transfer layer 206 onto microstructure 210 to form
glassy composite 207 on transfer substrate 201 by placing
the transfer substrate on a hotplate or in an oven or in a
vacuum oven or with a heat gun. In an embodiment, the
process for ultra-conformal microprint transferring further
includes heating glassy composite 207 to flow glassy trans-
fer layer 206 with transfer moiety 202 on microprint sub-
strate 208 to ultra-conformally cover glassy composite 207
on the microprint substrate 208 by placing the microprint
substrate on a hotplate or in an oven or in a vacuum oven or

FIG. 5 and FIG. s

&

&

8

using a heat gun. To avoid cracking of glassy transfer layer
on cooling, a controlled slow cooling can be performed.
In an embodiment, a process for ultra-conformal micro-
print transferring to make ultra-conformal microprint 200
includes spin coating a material that is immiscible in water
but miscible in some other solvent and that forms sacrificial
layer 203 on transfer substrate 201 (e.g.. a silicon wafer).
‘The sacrificial layer 203 can be, e.g.. a hard-baked photo-
resist that is soluble in acetone. On sacrificial layer 203,
microstructure 210 of transfer moiety 202 are disposed, e.g.
by a procedure that does not destroy sacrificial layer 203. A
composition for glassy transfer layer 206 that includes water
and sugar is poured over sacrificial layer 203 and transfer
substrate 201 and cured by heating glassy transfer layer 206
to evaporate water from glassy transfer layer 206 to form
glassy composite 207 disposed on sacrificial layer 203,
wherein glassy composite 207 is insoluble in acetone but is
water soluble. Transfer substrate 201 with sacrificial layer
203 and glassy composite 207 are contacted with acetone to
remove sacrificial layer 203 from transfer substrate 201 and
glassy composite 207 without dissolving glassy composite
207 in which remain disposed transfer moiety 202 arranged
as microstructure 210. Glassy composite 207 is disposed on
microprint substrate 208 with microstructure 210 in contact

5 with microprint substrate 208. Optionally, glassy composite

207 is heated above glass transition temperature Tg of glassy
transfer layer 206 but below a temperature for destruction of
microstructure 210, transfer moiety 202, or microprint sub-
strate 208 so that glassy transfer layer 206 ultra-conformally
flows around microprint substrate 208 to form ultra-confor-
mal microprint composite 209. It is contemplated that glassy
transfer layer 206 ultra-conformally enters and coats a
recess, through hole, blind hole, and the like in microprint
substrate 208. Heating can be performed in a vacuum to
avoid trapped air that could prevent glassy composite 207
from being disposed in the recess. Ultra-conformal micro-
print composite 209 is contacted with solvent, e.g., water, to
remove glassy transfer layer 206 from microprint substrate
208 and leave microstructure 210 on transfer moiety 202 to
form ultra-conformal microprint 200.

‘A composition for glassy transfer layer 206 can be pre-
pared by combining sugar, corn syrup, and water, heating the
composition to caramelization, and cooling the composition
to form the material to be used for forming the glassy
transfer layer 206. A ratio of components in glassy transfer
layer 206 can be varied to provide a selectively tailored glass
transition temperature Tg of glassy transfer layer 206. An
exemplary composition includes sugar:com syrup: water in a
2:1:1 ratio by volume, heated until golden brown, and
cooled. The resulting solid can be dissolved in water (e.g.,
1:1 solid:water by volume) to obtain a liquid form of the
material that can easily envelop the transfer moieties and be
used to form, after water evaporation, the solid glassy
composite 207. Without wishing to be bound by theory, it is
believed that while unadulterated sugar can be melted,
unadulterated sugar crystallizes into a non-smooth material
that can transfer large, macro-sized structures of transfer
moiety 202 but that can affect precision of pattern transfer of
microstructure 210. Inclusion of corn syrup in glassy trans-
fer layer 206 prevents crystallization of sugar to provide a
smooth composition. The composition for making glassy
transfer layer 206 can include sugar, corn syrup, or other
glassy materials that have low glass transition temperatures.
The glassy material can be dissolved in water but that does
not dissolve in solvents (e.g., acetone) that are used to
dissolve sacrificial layer 203. Further, sacrificial layer 203
can be a photoresist or another material that does not



U.S. Patent Sep. 5, 2023 Sheet 17 of 18 US 11,745,493 B2

(A)

dpm {0K SE2

§9mm 30.00KX

=

I

fm (000K SE2
133m SO00KX

FIG. 17


U.S. Patent Sep. 5, 2023 Sheet 9 of 18 US 11,745,493 B2

(A) iN mn

© © O o

Lm
Z Lt
Lo
20

(B) \ m

2000000008 x
1 Lent

FIG. 9


U.S. Patent Sep. 5, 2023 Sheet 6 of 18 US 11,745,493 B2

208

FIG. 6


U.S. Patent Sep. 5, 2023 Sheet 5 of 18
(A)
207 v me
208
ar 20
(B)
202
206
O
208 b
(C) A 27
202
28
210
206

FIG. 5

US 11,745,493 B2

26


US 11,745,493 B2

Sheet 18 of 18

Sep. 5, 2023

U.S. Patent

a rr—“—i—S—_
CC

-

Q0KX

00

{ym

W SE
{

dna
Gdmm 000KX

un {00K S62

i

FIG. 18


U.S. Patent Sep. 5, 2023 Sheet 8 of 18 US 11,745,493 B2

(A) iN 2
O Oo oo 6
pa
i
L
240
(B) \ 202
OoOooooo0o00 0
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FIG. 8


US 11,745,493 B2

11

regions of the microprint substrate, corresponding to those
regions where the embossed sections of the transfer layer
make contact with the microprint substrate. To ensure ultra-
conformal contact only for those embossed regions the
glassy layer can be heated to near to its glass transition
temperature such that it only partially reflows onto the
microprint substrate around the embossed contact regions.

Glassy transfer layer 206 can include various materials,
e.g., a carbohydrate, an amorphous agent, an additive, and
the like. Exemplary carbohydrates include a sugar such as
sucrose, corn syrup, and the like. Exemplary amorphous
agents include a water soluble polymer such as starch,
including corn starch. Exemplary additives include fat, trans
fat, protein, carboxylic acid (¢.g., malic acid, citric acid,
acetic acid, fumaric acid, lactic acid, tartaric acid and the
like), gelatin, emulsifier, stabilizer, thickener, anticaking
agent, preservative, antioxidant, leavening agent, acidulant
(e.g. phosphoric acid, and the like), and the like. In an
embodiment, glassy transfer layer 206 includes sucrose and

corn syrup. Com syrup can be made from starch and can 2

include maltose or higher oligosaccharides. Without wishing
to be bound by theory, it is believed that the com syrup
prevents crystallization of the sugar in glassy transfer layer
206. A relative amount of sugar in the corn syrup is selected
to provide glassy transfer layer 206 with a glass transition
temperature Tg and arbitrary range of viscosity, wherein
glass transition temperature Tg of glassy transfer layer 206
provides gradual and reversible transition as an amorphous
material so that glassy transfer layer 206 transitions from a
hard and brittle glassy state into a viscous or rubbery state
and finally a low viscosity liquid as a temperature of glassy
transfer layer 206 increases. In this respect, glass transition
temperature Tg of glassy transfer layer 206 can be from 1°
C. to 200° C., specifically from 10° C. to 150° C., and more
specifically from 25° C. to 100° C.

Glassy transfer layer 206 can have an arbitrary shape and
size. It is contemplated that the shape of glassy transfer layer
206 can be round, polygonal, irregular, and the like to
provide a cross-sectional shape this is symmetric or asym-
metric with a selected degree of anisotropy. A surface of
glassy transfer layer 206 can be planar or curved and can
have a recessed or embossed feature such as an aperture,
hole, trench, post, ridge and the like, wherein the recessed or
embossed feature can have an arbitrary largest linear dimen-
sion and arbitrary shortest linear dimension along a radius,
length, width, or height of the recessed feature, as applicable
to a geometry of the glassy transfer layer 206. A largest
dimension of glassy transfer layer 206 can be from 1 micron
to 10 m, specifically from 100 micron to 1 m, and more

specifically from 1 mm to 10 cm. Further, if a thin glassy s

transfer layer 206 is used, a temporary surrounding or
backing material such as, e.g. tape could be temporarily
attached to the glass transfer layer to add mechanical sta-
bility or provide a convenient method of holding the glass

transfer layer when the glass transfer layer is transferred

from transfer substrate to microprint substrate. In an
embodiment, glassy transfer layer 206 includes a caramel-
ized sugar and corn syrup mixture. In another embodiment,
glass transfer layer includes a commercial Jolly Ranchers
hard candy, including all incorporated colorings, scents,
flavorings and additives dissolved in water and then solidi-
fied on transfer substrate.

Glassy composite 207 is formed by disposing transfer
moiety 202 in glassy transfer layer 206, wherein glassy
composite 207 can have an arbitrary shape and size in which
glassy transfer layer 206 in glassy composite 207 conforms
to a shape of transfer substrate 201 sacrificial layer 203, and

12

transfer moiety 202 thereon. It is contemplated that the
shape of glassy composite 207 can be round, polygonal,
irregular, and the like to provide a cross-sectional shape this
is symmetric or asymmetric with a selected degree of
anisotropy. A surface of glassy composite 207 can be planar
or curved and can have a recessed or embossed feature such
as an aperture, hole, trench, post, ridge and the like, wherein
the recessed or embossed feature can have an arbitrary
largest linear dimension and arbitrary shortest linear dimen-
sion along a radius, length, width, or height of the recessed
feature, as applicable to a geometry of the glassy composite
207. A largest dimension of glassy composite 207 can be
from 100 nm to 10 m, specifically from 1 micron to I m, and
more specifically from 1 mm to 10 cm. In an embodiment,
glassy composite 207 includes a sugar and corn syrup
mixture with an array of gold microdisks embedded in its
surface.

It is contemplated that sacrificial layer 203 is miscible in
a first solvent, and glassy transfer layer 206 is miscible in a
second solvent for which the microprint substrate 208 and
the transfer moiety 202 are immiscible. The first solvent can
include an organic solvent, e.g., acetone, toluene, benzene,
and the like. The second solvent can include a water, an
alcohol (¢.g., methanol, ethanol, and the like), and the like.

Transfer substrate 201 receives sacrificial layer 203 or
microstructure 210. Transfer substrate 201 can include vari-
icon or other semiconductors, metals,
quartz, plastics or other polymeric materials, and the
‘xemplary transfer substrates 201 include substrates on
which the transfer moieties can be readily fabricated such a
silicon or glass or quartz or polymeric materials. Transfer
substrate 201 can have an arbitrary shape and size. It is
contemplated that the shape of transfer substrate 201 can be
round, polygonal, irregular, and the like to provide a cross-
sectional shape this is symmetric or asymmetric with a
selected degree of anisotropy. A surface of transfer substrate
201 can be planar or curved and can have a recessed or
embossed feature such as an aperture, hole, trench, post,
ridge and the like, wherein the recessed or embossed feature
can have an arbitrary largest linear dimension and arbitrary
shortest linear dimension along a radius, length, width, or
height of the recessed feature, as applicable to a geometry of
the transfer substrate 201. A largest dimension of transfer
substrate 201 can be from 1 micron to 10 m, specifically
from 100 micron to 1 m cm, and more specifically from 1
mm to 10 cm. In an embodiment, transfer substrate 201
includes a 3" silicon wafer.

Further, because of the ability to controllably soften the
glassy transfer layer by raising its temperature to near to its
glass transition such that it is either flexible or flowable, the
ultra-conformal process herein is compatible with roll-to-
roll manufacturing techniques. With transfer moieties dis-
posed on one layer of material that is wound round one roll,
the glassy transfer layer can be applied by pressing or rolling
that roll into or over the softened glassy transfer material, or
by rolling the roll such that the transfer substrate and transfer
moieties thereon through a trough containing a lique-
fied version of the glassy transfer material which then
solidifies onto the rolled material as it emerges from the
liquid in the trough and subsequently cools, or as any solvent
in the liquefied glassy transfer material evaporates. The
glassy transfer material can be transferred via rolling contact
pressure onto a second roll around which is wound a flexible
microprint substrate which is subsequently passed through a
trough of solvent that dissolves away the glassy transfer
layer leaving the transfer moieties in their microstructure on
the microprint substrate that is then fed off the second roll.



United States Patent

US0117454:

93

(12) (0) Patent No.: US 11,745,493 B2
Zabow (45) Date of Patent: Sep. 5, 2023
(54) ULTRA-CONFORMAL MICROPRINT AND (56) References Cited
ULTRA-CONFORMAL MICROPRINT
TRANSFERRING U.S. PATENT DOCUMENTS
. 10,533,080 B2* 1/2020 Kim ........ ... B81C 1/00373
(71) Applicant: Government of the United States of
America, as represented by the OTHER PUBLICATIONS
Secretary of Commerce, Gaithersburg,
MD (US) Carlson, A., et al., “Transfer Printing Techniques for Materials
\s bly and Micro/Nanodevice Fabrication”, Advanced Materi-
(72) Inventor: Gary Zabow, Boulder, CO (US) s, 2012, p. 5284-5318, vol. 24.
(73) Assignee: GOVERNMENT OF THE THE * cited by examiner
UNITED STATES OF AMERICA, AS

ay)

(22)

(65)

(1)

(52)

(58)

REPRESENTED BY THE
SECRETARY OF COMMERCE,
Gaithersburg, MD (US)

Subject to any disclaimer, the term of this
patent is extended or adjusted under 35
U.S.C. 154(b) by 258 days.

Appl. No.: 16/988,017

Filed: Aug. 7, 2020

Prior Publication Data

US 2022/0040970 Al Feb. 10, 2022

Int. Cl.
B41M 3/00 (2006.01)
BALF 19/08 (2006.01)

.. B41F 19/08 (2013.01); B41M 3/00
(2013.01); BOSD 2203/35 (2013.01)
lassification Search

B41M 3/00

See application file for complete search history.

{Ay

Primary Examiner —Dah-Wei D. Yuan

Assistant Examiner — Kristen A Dagenais

(74) Attorney, Agent, or Firm — Office of Chief Counsel
for National Institute of Standards and Technology

(57) ABSTRACT

‘A process for making an ultra-conformal microprint by
ultra-conformal microprint transferring includes: disposing
a transfer moiety arranged in a microstructure on a transfer
substrate; disposing a glassy transfer layer on the transfer
moiety; forming a glassy composite; removing the glassy
composite from the transfer substrate while maintaining the
microstructure of the transfer moiety in the glassy transfer
layer; disposing the glassy composite on a microprint sub-
strate; ultra-conformally covering the microprint substrate
with the glassy composite by heating the glassy composite
so that it flows while maintaining the microstructure of the
transfer moiety in the glassy transfer layer so that the
microstructure is disposed on the microprint substrate; and
removing the glassy transfer layer while leaving the transfer
moiety disposed in the microstructure on the microprint
substrate to form the ultra-conformal microprint including
the transfer moiety arranged in the microstructure on the
microprint substrate.

12 Claims, 18 Drawing Sheets



U.S. Patent Sep. 5, 2023 Sheet 11 of 18 US 11,745,493 B2

(A)
210
{ m2
C) O { > 7 8
N01
(B) 210
202
ee)
Nd. \. > Nad. 203 jor
N20
C 20
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—O—0 o— a ja
1
(D) x

210 06
N\ .< np 29



U.S. Patent Sep. 5, 2023 Sheet 10 of 18 US 11,745,493 B2

(A)
210
\ 4 a2
QO Oo oo 6 |*
Lu
y
<
(8)
ane
QO ao o o
\

FIG. 10


U.S. Patent Sep. 5, 2023 Sheet 7 of 18 US 11,745,493 B2

209
Ss
210 _ , 207
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| 'o ee:
O O 1-08
O O O Q L208
2 La m \

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US 11,745,493 B2

5

that can include electronic circuitry or spatially periodic
arrays of transfer moieties whose materials and spatial
arrangements might endow special optical, mechanical, or
‘metamaterial properties to the microprint substrate, or might
provide special surface textures that might impart particular
hydrophobicities or other particular chemical functionalities
to the microprint substrate hydrophobic. A largest dimension
of microstructure 210 can be from 10 nm to 10 m, specifi-
cally from 100 nm to 10 cm, and more specifically from 1
micron to 10 mm. Moreover, microstructure 210 can include
individual or spatially arranged arrays of complex prefab-
ricated optical or electronic components. In an embodiment,
microstructure 210 includes arrays of gold and of magnetic
particles.

Ultra-conformal microprint 200 can be made in various
ways. In an embodiment, with reference to FIG. 3, FIG. 4,
FIG. 5, FIG. 6, FIG. 7, FIG. 8, FIG. 9, FIG. 10, FIG. 11, and
FIG. 12, a process for making ultra-conformal microprint
200 by ultra-conformal microprint transferring includes

disposing transfer moiety 202 arranged in microstructure 2

210 on transfer substrate 201 (e.g., FIG. 3, FIG. 8); dispos-
ing glassy transfer layer 206 on transfer moiety 202 (e.g.,
FIG. 4, FIG. 10, FIG. 11); forming glassy composite 207
comprising glassy transfer layer 206 and transfer moiety 202
with maintaining microstructure 210 of transfer moiety 202
in glassy transfer layer 206 (e.g., FIG. 4, FIG. 10, FIG. 11);
removing glassy composite 207 from transfer substrate 201
while maintaining microstructure 210 of transfer moiety 202
in glassy transfer layer 206 (e.g., FIG. 4, FIG. 10, FIG. 11);
disposing glassy composite 207 on microprint substrate 208
(eg., FIG. 5, FIG. 12); ultra-conformally covering micro-
print substrate 208 with glassy composite 207 while main-
taining microstructure 210 of transfer moiety 202 in glassy
transfer layer 206 so that microstructure 210 is disposed on
microprint substrate 208 (e.g., FIG. 5, FIG. 6, FIG. 7, FIG.
12); and removing glassy transfer layer 206 while leaving
transfer moiety 202 disposed in microstructure 210 on
microprint substrate 208 to form ultra-conformal microprint
200 including transfer moiety 202 arranged in microstruc
ture 210 on microprint substrate 208 (e.g., FIG. 1, FIG. 5,
FIG. 12).

As used herein, “maintaining” the microstructure implies
that the geometrical patterning and spacing between the
moieties comprising the microstructure are unaltered until
they are placed in contact with the microprint substrate when
they either remain unaltered, or if transferred to a microprint
substrate of different surface profile to that of the transfer
substrate or sacrificial layer, such that stretching or com-
pressing is required to accommodate the new surface profile,

that the majority of the relative spatial orderings between 5

moieties compromising the microstructure remains unal-
tered even as the physical spacing between those moieties
may locally shrink or expand by locally differing amounts
(e.g., as per FIG. 13 c where the ordering is maintained even

though the spacing between moieties is locally increased to

accommodate the increased total surface area of the micro-
print substrate arising from the extra area introduced by the
vertical walls of the recessed feature 214).

In the process for ultra-conformal microprint transferring,
disposing transfer moiety 202 arranged in microstructure
210 on transfer substrate 201 or sacrificial layer 203 includes
microfabricating transfer moieties 202 directly onto transfer
substrate 201 or sacrificial layer 203 in microstructure 210;
manually or robotically placing transfer moieties onto the
transfer substrate 201 or sacrificial layer 203; self-assem-
bling prefabricated transfer moieties into microstructure 210
on transfer substrate 201 or sacrificial layer 203; or depos-

&

&

at

6

iting transfer moieties formed via a chemical precipitation
reaction or a direct chemical reaction with the transfer
substrate. The transfer substrate can be chemically function-
alized for formation of the microstructure thereon. In some
embodiments, transfer moieties and microstructure are
formed by subtractive removing of material in certain loca-
tions from a surface layer of the transfer substrate to leave
behind a transfer moiety in a microstructure.

Disposing glassy transfer layer 206 on transfer moiety
202 can include: dissolving the glassy transfer layer in a
solvent to obtain a liquid form that is poured or spin coated
over the transfer substrate 201 or sacrificial layer 203
including transfer moieties, or into which the transfer sub-
strate may be dip coated, and subsequently evaporating the
solvent, optionally with heating provided to accelerate, to
solidify the glassy transfer layer; softening a solid glassy
transfer layer, mechanically pressing or stretching it over the
transfer substrate; or heating the glassy transfer layer so that
it can be flowed over the transfer substrate without any
added solvent and allowing to cool and solidify.

Forming glassy composite 207 includes disposing glassy
transfer layer over transfer moieties or solidifying glass
transfer layer around transfer moieties.

Removing glassy composite 207 from transfer substrate
201 while maintaining microstructure 210 of transfer moiety
202 in glassy transfer layer 206 includes dissolving sacrifi-
cial layer 203 with a solvent that dissolves the sacrificial
layer but not the glassy composite layer, or when in an
absence of sacrificial layer 203, mechanically peeling or
delaminating the glassy composite layer off of the transfer
substrate.

Disposing glassy composite 207 on microprint substrate
208 includes placing the glassy transfer layer on of the
microprint substrate or placing the microprint substrate on
top of the glassy transfer layer. A spacer can support a side
of the glassy transfer layer to aid in subsequent ultra-
conformal covering.

Ultra-conformally covering microprint substrate 208 with
glassy composite 207 includes increasing the temperature to
or greater than glass transition temperature Tg of the glassy
composite such that it softens flows over the microprint
substrate. A spacer can be used to proceed processing
directionally from one side of the microprint substrate to the
other. The process can be performed under partial or com-
plete vacuum to remove gas that can be present in a recess
in the microprint substrate. The composition of the glassy
composite can have a reduced vapor pressure to avoid
bubbling, or a partial vacuum can be used to remove gas
before returning to atmospheric pressure to avoid bubbling.
As used herein, ultra-conformal (and variants thereof,
including ultra-conformally) refers to disposition of a mate-
rial onto microprint substrate 208 that can include a sharp-
cornered recessed or embossed feature, corner, edge, curved
surface, and the like, wherein the disposition of the material
proceeds at all surfaces of microprint substrate 208 to
provide a ultra-conformal layer with physical characteristics
that lack gaps or voids that have a volume larger than 10°°
jum? within the bulk phase of the ultra-conformal layer. The
ultra-conformal layer can have a uniform thickness or non-
uniform thickness at any surface of the ultra-conformal
layer. Ultra-conformal layers can have a uniform composi-
tion throughout the layer or may have a composition that
varies through all or a portion of the layer, based on a
composition of the glassy transfer layer 206 and transfer
moiety 202 disposed in the glassy composite 207. Ultra-
conformal surface covering can be advantageous for sur-
faces or surface features that have sharp angles or locally



US 11,745,493 B2

17

5. The process of claim 4, further comprising:

contacting the glassy transfer layer 206, while disposed
on the microprint substrate 208, with a second solvent
that removes the glassy transfer layer 206 from the
microprint substrate 208 and leaves the transfer moiety
202 disposed in the microstructure 210 on the micro-
print substrate 208.

6. The process of claim 1, further comprising:

heating the glassy transfer layer 206 to flow the glassy
transfer layer 206 onto the microstructure 210 to form
the glassy composite 207 on the transfer substrate 201.

7. The process of claim 1, further comprisin;

heating the glassy composite 207 to flow the glassy
transfer layer 206 with the transfer moiety 202 on the
microprint substrate 208 to ultra-conformally cover the
glassy composite 207 on the microprint substrate 208.

8. The process of claim 1, wherein the glassy transfer

layer 206 has a glass transition temperature.
9. The process of claim 8, wherein the glass transition

temperature of the glassy transfer layer 206 is from 1° C.to 2

50°C.

10. The process of claim 1, wherein the glassy transfer
layer 206 is miscible in a second solvent for which the
microprint substrate 208 and the transfer moiety 202 are
immiscible.

11. The process of claim 10, wherein the second solvent
that the glassy transfer layer 206 is miscible comprises
water.

12. The process of claim 1, wherein the transfer moiety
202 comprises a largest linear dimension that is less than 1

um.

0

5

18


U.S. Patent Sep. 5, 2023 Sheet 3 of 18 US 11,745,493 B2

1

202 203 of 204
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U.S. Patent Sep. 5, 2023 Sheet 14 of 18 US 11,745,493 B2

Acc. Spot Nag
5.00kv 30. 80x SE 247



U.S. Patent Sep. 5, 2023 Sheet 16 of 18 US 11,745,493 B2

200 208 vats 202
(A)

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2t5 2b 2

SW SE2
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U.S. Patent Sep. 5, 2023 Sheet 2 of 18 US 11,745,493 B2

ed
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US 11,745,493 B2

13

Depending on a design, ultra-conformal microprint trans-
ferring can include additional roller steps. In a roll-to-roll
process, a largest dimension of either the transfer substrate,
glassy transfer later, transfer moieties and their microstruc-
ture, glassy composite, or microprint substrate is arbitrarily
selectable, ie., no upper limit on size is discernable.

Ultra-conformal microprint 200 has numerous advanta-
geous and unexpected benefits and uses including placing
electronic, magnetic, conductive, optical, or other compo-
nents into surface regions that would not otherwise be
readily, or economically, accessible. The process for making
ultra-conformal microprint 200 can be used in applications
involving flexible electronics such as wearable sensors to
transfer electronic patterns onto a flexible substrate. Because
ultra-conformal microprint transferring can use water as the
second solvent to remove away glassy transfer layer 206
from microprint substrate 208 at room temperature under
ambient conditions, ultra-conformal microprint transferring
can directly or indirectly transfer print microstructure 210
onto a biological surface, including tissues, cells, muscles,
bones, skin, and the like.

Ultra-conformal microprint transferring can ultra-confor-
mally cover surfaces of high curvature, and ultra-conformal
microprint transferring can transfer print metallic or non-
metallic patterns as microstructure 210 around optical fibers,
providing spectral control of fiber-guided light propagation
and fiber optic sensing through interactions between trans-
ferred patterns microstructure 210 on microprint substrate
208 and conditions in a surrounding medium. Ultra-confor-
mal microprint transferring can transfer periodic arrays of
patterns as microstructure 210 to transfer print diffraction
gratings onto other optical elements that can be transmissive
or reflective or onto planar or curved surfaces of microprint
substrate 208. Arrays can include patterned structures of
microstructure 210 that are optical or microwave metasur-
faces, which can be transferred onto different surfaces for
optical control. Patterns of magnetic elements as microstruc-
ture 210 can be transferred to provide magnetic control over
surfaces of microprint substrate 208, which might include
flexible surfaces or thin fibers, providing ultra-conformal
microprint 200 to be magnetically guided, bent, twisted, and
the like. Metallic patterns of microstructure 210 can be
ultra-conformally transferred to pattern RF antennae on
novel-shaped surfaces of microprint substrate 208.

It is contemplated that ultra-conformal transferring of
arrays of metallic islands or grids of metallic wires as
microstructure 210 can be wrappedly disposed around sur-
faces (e.g., microelectronic components) of microprint sub-
strate 208 to provide a local Faraday cage RF shield.

Microstructure 210 can be subjected to ultra-conformal s

microprint transferring onto microprint substrate 208 to
provide microprint substrate 208 with properties such as
anti-reflection, thermal or wetting properties, or decreased
radar detection,

‘Advantageously, ultra-conformal microprint transferring 5

solves conventional problems of micropatterning on highly
curved surfaces. Ultra-conformal microprint transferring
can form microstructure 210 on microprint substrate 208
where transfer printing is desirable but under which direct
printing onto microprint substrate 208 by conventional
means is infeasible due to processing conditions that could
destroy or adversely impact microprint substrate 208 or
microstructure 210, Such conventional conditions can
include processing temperature; chemical exposure; shape,
size, surface flatness, material hardness, surface roughness,
surface optical property requirements of processing tools,
vacuum processing, thermal expansion mismatches, and the

&

14

like. Ultra-conformal microprint transferring can be used for
transferring microstructure 210 such as electronics for
heads-up displays onto windshields, helmet visors, glasses,
and the like such that, e.g., map or text data can be displayed
thereon. Ultra-conformal microprint transferring can be used
for transferring functional layers as microstructure 210 on
microprint substrate 208 that can include a consumer object
such as a cell phone, pen, and the like. Ultra-conformal
microprint transferring can be used for transferring optical
or holographic micropatterns as microstructure 210 on
microprint substrate 208 that can include drugs to prevent
counterfeits.

Ultra-conformal microprint transferring can use water as
the second solvent at room temperature. Ultra-conformal
microprint transferring is gentle on microprint substrate 208,
providing repetition of ultra-conformal microprint transfer-
ring to build layers of patterned materials and structures, or
allowing the transferred structures to be used to guide
further processing on the microprint substrate by ultra-
conformal microprint transferring a stencil mask, for
example, onto the microprint substrate.

Beneficially, ultra-conformal microprint transferring can
be used for deformation of microstructure 210 before being
disposed on microprint substrate 208 by heating glassy
composite 207 to near glass transition temperature Tg of
glassy transfer layer 206. In this manner, an array as
microstructure 210 can have a selected periodicity, wherein
the periodicity subsequently can be changed before glassy
composite 207 is disposed on microprint substrate 208. In an
embodiment, a diffraction grating pattern of wires as micro-
structure 210 can be stretched in glassy composite 207 to
change effective diffraction angles of microstructure 210 in
glassy composite 207, or such grating or other metamaterial
patterning could be locally stretched or twisted to locally
impart different optical properties before glassy composite
207 is disposed on microprint substrate 208. As a result,
ultra-conformal microprint transferring is efficient and can
allow complex patterns to be created in an absence of
complex processing equipment.

In contrast to conventional transfer printing techniques,
ultra-conformal microprint transferring prints micropatterns
around surfaces with very tight radii of curvature, sharp
corners, undercuts, holes, protrusions, uneven surfaces, and
rough surfaces. Ultra-conformal microprint transferring
involves glassy composite 207 that can reflow, stretch, or
deform on microprint substrate 208, wherein glassy com-
posite 207 ultra-conformally matches surfaces of microprint
substrate 208 having high curvature or tight radii.

The articles and processes herein are illustrated further by
the following Example, which is non-limiting.

EXAMPLE

Various ultra-conformal microprints 200 were made by
ultra-conformal microprint transferring. Here, ultra-confor-
mal microprint transferring included an initial silicon wafer
substrate that was first spin coated with a photoresist layer
to be used as a sacrificial layer. This photoresist layer was
partially hard-baked so that it would not subsequently dis-
solve in photoresist developer but would still dissolve in
acetone. It was also coated with a thin passivating layer, for
example, by exposure to reactive C,F, gas to yield a thin
per-fluorinated coating, to prevent subsequent dissolution in
photoresist solvent that was present in a second layer of
photoresist that was subsequently spin coated over this first
layer of photoresist. The second layer of photoresist was
then patterned via optical lithography and those regions that



U.S. Patent Sep. 5, 2023 Sheet 1 of 18 US 11,745,493 B2



U.S. Patent Sep. 5, 2023 Sheet 12 of 18 US 11,745,493 B2

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U.S. Patent Sep. 5, 2023 Sheet 15 of 18 US 11,745,493 B2

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