U.S. patent application number 11/106178 was filed with the patent office on 2005-11-03 for high thermal efficiency glass microfluidic channels and method for forming the same.
Invention is credited to Caze, Philippe, Dannoux, Thierry Luc Alain.
Application Number | 20050241815 11/106178 |
Document ID | / |
Family ID | 35185900 |
Filed Date | 2005-11-03 |
United States Patent
Application |
20050241815 |
Kind Code |
A1 |
Caze, Philippe ; et
al. |
November 3, 2005 |
High thermal efficiency glass microfluidic channels and method for
forming the same
Abstract
A microfluidic device includes a formed sheet of glass or glass
ceramic material formed to have one or more first micro channels on
a first surface thereof and one or more second micro channels on a
second surface opposite the first. The second channels are
complementary to the first channels and the first channels are
substantially closed by a first sheet of glass or glass ceramic
material bonded to the first surface of the formed sheet. The
second channels may be substantially closed by a second sheet of a
glass or glass ceramic material bonded to the second surface. The
first and second sheets may also be formed sheets. The device may
be formed by vacuum-forming the formed sheet against a single
surface mold, then bonding a plate to one or both sides of the
formed sheet.
Inventors: |
Caze, Philippe;
(Fontainebleau, FR) ; Dannoux, Thierry Luc Alain;
(Avon, FR) |
Correspondence
Address: |
CORNING INCORPORATED
SP-TI-3-1
CORNING
NY
14831
|
Family ID: |
35185900 |
Appl. No.: |
11/106178 |
Filed: |
April 13, 2005 |
Current U.S.
Class: |
165/170 |
Current CPC
Class: |
B81B 2201/058 20130101;
B01L 2200/12 20130101; B01L 2300/12 20130101; F28F 3/12 20130101;
F28F 2260/02 20130101; F28F 21/006 20130101; B81C 1/00119 20130101;
B01L 3/502707 20130101 |
Class at
Publication: |
165/170 |
International
Class: |
F28F 003/14 |
Foreign Application Data
Date |
Code |
Application Number |
Apr 30, 2004 |
EP |
EP04291114.9 |
Claims
What is claimed is:
1. A microfluidic device comprising a molded sheet of a glass or
glass ceramic material bonded to at least one sheet of a glass or
glass ceramic material so as to form micro channels.
2. The microfluidic device as recited in claim 1 wherein the molded
sheet of a glass or glass ceramic material is bonded between two
sheets, each of a glass or glass ceramic material, so as to form
complementary micro channels.
3. The microfluidic device of claim 2 wherein the molded sheet
comprises a first glass material and the two sheets each comprise a
second glass material, the first glass material having a higher
softening temperature than the second glass material.
4. The microfluidic device of claim 1 wherein the molded sheet
comprises a first glass material and the two sheets each comprise a
second glass material, the first glass material having a higher
softening temperature than the second glass material.
5. The microfluidic device of claim 2 further comprising at least
one through-hole through the molded sheet, said through-hole
establishing fluid communication between an adjacent pair of said
micro channels.
6. The microfluidic device of claim 1 further comprising at least
one through-hole through the molded sheet, said through-hole
establishing fluid communication between an adjacent pair of said
micro channels.
7. The microfluidic device of claim 1 wherein the molded sheet,
between adjacent micro channels separated by said molded sheet, has
a thickness in the range of about 0.2 mm to about 0.7 mm.
8. The microfluidic device of claim 1 wherein the molded sheet,
between adjacent micro channels separated by said molded sheet, has
a thickness in the range of about 0.7 mm to about 3 mm.
9. The microfluidic device of any one of claims 1 wherein said at
least one sheet comprises a second molded sheet.
10. A method of forming a microfluidic device, the method
comprising: providing a mold; positioning a softened sheet of glass
or ceramicizable glass over said mold; applying a differential gas
pressure to said sheet to conform said sheet to said mold, thereby
forming micro channels on at least one surface of said sheet;
substantially closing said micro channels on said at least one
surface of said sheet by bonding a sheet of glass or ceramicizable
glass over said mold.
11. The method of claim 10 further comprising the step of
ceramicizing said plate and said sheet.
12. The method of claim 10 wherein the step of applying a
differential gas pressure to said sheet to conform said sheet to
said mold comprises applying a vacuum to said sheet between said
sheet and said mold.
13. The method of claim 10 wherein the step of positioning a
softened sheet of glass or ceramicizable glass over said mold
comprises rolling out a first soft glass sheet over said mold.
14. The method claim 10 wherein the step of positioning a softened
sheet of glass or ceramicizable glass over said mold comprises
positioning a sheet of glass or ceramicizable glass over said mold
then heating said sheet of glass or ceramicizable glass.
15. The method of claim 10 wherein the step of substantially
closing said micro channels on said at least one surface of said
sheet by bonding a sheet of glass or ceramicizable glass over said
mold comprises rolling out a soft glass sheet onto said conformed
sheet, thereby bonding said soft glass sheet to said conformed
sheet.
Description
CROSS-REFERENCE TO RELATED APPLICATIONS
[0001] This application claims the benefit of priority under 35
U.S.C. .sctn. 119 of European Patent Application Serial No.
EP04291114.9 filed on Apr. 30, 2004.
BACKGROUND OF THE INVENTION
[0002] 1. Field of the Invention
[0003] The present invention relates generally to microfluidic
devices and methods for producing such devices, and particularly to
high-thermal-efficiency glass, glass-ceramic, or ceramic
microchannel or microfludic devices and methods for producing such
devices.
[0004] 2. Technical Background
[0005] Microchannel or microfluidic devices are generally
understood as devices containing fluid passages having a
characteristic dimension that generally lies in the range of 10
micrometers (.mu.m) to 1000 .mu.m in which fluids are directed and
processed in various ways. Such devices have been recognized as
holding great promise for enabling revolutionary changes in
chemical and biological process technology, in particular because
heat and mass transfer rates in microfluidic devices may be
increased by orders of magnitude over rates achievable in
conventional chemical processing systems.
[0006] Fluidic microcircuits in glass or glass-ceramic have the
advantage of generally superior chemical resistance. But glass and
glass-ceramics are relatively poor conductors of heat, and thermal
exchange is a key feature in most chemical synthesis. Accurate and
safe local heat management generally allows chemical processing at
relatively higher concentrations, pressures and temperatures,
leading in most cases to better yields and higher efficiency.
SUMMARY OF THE INVENTION
[0007] The present invention provides a device having microfluidic
channels formed of thin glass, glass-ceramic or ceramic sheet
material possessing good surface characteristics and good strength,
and provides a process for reliably and efficiently producing such
devices and channels. The thin-walled microchannels allow efficient
heat exchange while offering superior chemical durability and heat
resistance. The inventive forming process provides a simplified and
reliable manufacturing process while providing a resulting device
that maximizes thermal exchange.
[0008] According to one embodiment of the present invention, a
microfluidic device includes a formed sheet of glass or glass
ceramic material. The formed sheet is formed to have one or more
first micro channels on a first surface thereof and one or more
second micro channels on a second surface opposite the first. The
second channels are complementary to the first channels. The first
channels are substantially closed by a first sheet of glass or
glass ceramic material bonded to the first surface of the formed
sheet, and the second channels may be substantially closed by a
second sheet of a glass or glass ceramic material bonded to the
second surface. The first or second sheet may also be a formed
sheet if desired.
[0009] According to another embodiment of the present invention, a
method is provided for forming a microfluidic device. The method
includes providing a single-surface mold, positioning a sheet of
glass or ceramicizable glass on the mold, heating the mold and the
sheet, and applying a differential gas pressure to the sheet to
conform the sheet to the mold. The result is the formation of micro
channels on at least one surface of the sheet, generally on both
surfaces. Microchannels are then substantially closed or enclosed
by bonding a plate of glass or ceramicizable glass over at least
one surface of the sheet that includes microchannels.
[0010] According to yet another embodiment of the present
invention, a method is provided for forming a microfluidic device,
the method including the step of rolling out a first soft glass
sheet over a moving mold, the first sheet having a first surface
opposite the mold and a second surface opposite the first surface
and resting on said mold; the method further including vacuum
forming said soft glass sheet to conform said sheet to said mold,
forming thereby a conformed sheet having micro channels on both the
first and second surfaces thereof; the method further including
rolling out a second soft glass sheet onto said first surface of
said conformed sheet, thereby bonding said second soft glass sheet
to said conformed sheet and substantially closing said micro
channels on said first surface; the method further including
releasing said conformed sheet from said mold. The method may
additionally include rolling out a third soft glass sheet onto said
second surface of said conformed sheet, thereby bonding said second
soft glass sheet to said conformed sheet and substantially closing
said micro channels on said second surface.
[0011] It is to be understood that both the foregoing general
description and the following detailed description present
embodiments of the invention, and are intended to provide an
overview or framework for understanding the nature and character of
the invention as it is claimed. The accompanying drawings are
included to provide a further understanding of the invention, and
are incorporated into and constitute a part of this specification.
The drawings illustrate various embodiments of the invention and,
together with the description, serve to explain the principles and
operations of the invention.
BRIEF DESCRIPTION OF THE DRAWINGS
[0012] FIG. 1 is a cross-sectional view of a mold 20 and vacuum box
24 useful in connection with the present invention;
[0013] FIG. 2 is the cross section of FIG. 1 after a thin sheet 30
has been positioned on the mold.
[0014] FIG. 3 is the cross section of FIG. 2 after vacuum forming
of the thin sheet 30 to form a formed sheet 32.
[0015] FIG. 4 is a cross section of the formed sheet 32 of FIG. 3
after it has been released from the mold 20.
[0016] FIG. 5 is a cross section of an assembly 38 including the
formed sheet 32 of FIG. 4 and top plate 34 and bottom plate 36.
[0017] FIG. 6 is a cross section of a microfluidic device 50
according to an embodiment of the present invention, the device 50
having been formed by bonding together the assembly of FIG. 5.
[0018] FIG. 7 is a cross section of the microfluidic device 50 of
FIG. 6 including fluid connectors 52.
[0019] FIG. 8 is a cross section of the microfluidic device of FIG.
6 showing the alternating channels in which a first fluid F1 and a
second fluid F2 may be disposed.
[0020] FIG. 9 is a plan view of a microfluidic circuit design
potentially useful with devices of the present invention, the
design having parallel channels 54 each with two access holes
56.
[0021] FIG. 10 is a plan view of another microfluidic circuit
design potentially useful with devices of the present invention,
the design having two concentric spiraling alternate channels each
with an access hole at the edge of the spiral and at the
center.
[0022] FIG. 11 is a cross section of a microfluidic device 50
including minimized channels 60.
[0023] FIG. 12 is a plan view of another microfluidic circuit
design potentially useful with devices of the present invention,
the design including minimized channels 60.
[0024] FIG. 13 is a cross-sectional view of the formed sheet 32 of
FIG. 4, indicating (within the dashed perimeter 41) a location at
which material may be removed to establish fluid communication
between neighboring alternate channels 43 and 45.
[0025] FIGS. 14A-14F are cross sections illustrating certain of the
steps of a presently preferred inventive method of forming devices
of the present invention.
[0026] FIG. 15 is a cross-section of another embodiment of a
microfluidic device 50, having triangular-shaped channels 40.
DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS
[0027] The present invention provides a device having microfluidic
channels formed of thin glass, glass-ceramic or ceramic sheet
material possessing good surface characteristics and good strength,
and provides a process for reliably and efficiently producing such
devices and channels. The method of the present invention employs
forming by means of differential gas pressure to achieve the
desired thin-walled, high-surface quality microchannels of glass,
glass-ceramic, or ceramic. The resulting thin-walled microchannels
allow efficient heat exchange while offering superior chemical
durability and heat resistance. The inventive forming process
provides a simplified and reliable manufacturing process while
providing a resulting device that maximizes thermal exchange.
[0028] According to the present invention, micro channels are
created by a process that includes closing a three dimensional
glass, glass ceramic or ceramic shape, and not solely by stacking
micro-structured plates. An exemplary process constituting one
aspect of the present invention will be described below with
reference to FIGS. 1-7.
[0029] FIG. 1 shows a cross-section of an apparatus 10 useful in
connection with one aspect of the present invention. The apparatus
10 includes a fluid-circuit mold 20 that has been previously
machined or otherwise formed from a suitable material, such as a
refractory steel plate NS 30/ASI 310, available from
Thyssen-France, 78 Maurepas, France. The mold 20 includes
micro-passages 22 for vacuum distribution. The mold 20 is placed in
a vacuum-sealing structure such as a vacuum box 24 having a surface
or ledge 26 for vacuum sealing surrounding the mold 20. The
interior volume of the vacuum box 24 is connected to a vacuum
source such as a vacuum pump not shown in the figure.
[0030] Prior to use, the mold 20 is coated with a suitable release
agent, such as calcium hydroxide (Alcohol+Disperbick 190 at 0.5%
suspension, for example). Disperbick 190 is readily available from
BYK-Chemie Gmbh, Abelstr. 14 D-46483 Wesel, Gemany.) The relief
agent is desirably sprayed uniformly over the entire surface of the
mold 20.
[0031] As shown in FIG. 2 a thin sheet 30, composed of a suitable
glass material and having a surface area sized to cover the surface
or ledge 26, is then applied to the mold 20. The glass may be
Corning 1737.RTM. for example, available from Corning Incorporated,
Corning N.Y., USA.
[0032] The sheet 30 and the mold 20 are then heated together to a
point above the annealing point of the glass material, and
desirably near but below the softening point thereof. In the case
of Corning 1737.RTM. which has an annealing point of about
721.degree. C. and a softening point of about 925.degree. C., for
example, the mold and sheet may be heated to about 870.degree. C.
over a period of about 20 minutes.
[0033] Vacuum is then applied to the vacuum box 24 for a sufficient
time to cause the sheet 30 to conform to the profile of the mold
20, resulting in formed sheet 32 as represented in FIG. 3. As an
alternative, gas pressure could be applied to the surface of the
thin sheet 30 opposite the mold 20, and the micro-passages 22 could
be used solely to relieve back pressure. As an additional
alternative, positive pressure from outside the mold and vacuum
within the mold could be used at the same time.
[0034] The vacuum forming, in addition to reshaping the thin sheet
30 into a formed sheet 32, also has the effect of redrawing
("vacuum redrawing") the sheet 30, resulting a formed sheet 32 that
is generally thinner than the originally thin sheet 30,
particularly in the areas where material was drawn into the mold.
This vacuum forming process thus allows reliable, repeatable
formation of wall structures as thin as 0.3 mm or less, desirably
in the range of about 0.2 mm to about 0.7 mm or less. On the other
hand, using suitably thick starting sheets, wall structures of
greater thicknesses may also be formed using this process,
including thicknesses in the range of about 0.7 mm to about 3 mm,
which thicknesses may be useful in for use in high pressure or very
high pressure applications.
[0035] After vacuum forming, the mold 20 and formed sheet 32 are
cooled to a temperature sufficiently low to allow the formed sheet
32 to retain its formed shape, but desirably sufficiently high to
allow easy removal from the mold 20. For Corning 1737.RTM., for
example, the sheet 30 may be cooled to about 750.degree. C. over a
2 minute period. A light air pressure is then applied to the vacuum
channels 22 to remove the formed sheet 32 from the mold 20. The
release agent significantly facilitates this step. The resulting
formed sheet 32 is depicted in cross section in FIG. 4.
[0036] Next, top and bottom plates 34 and 36 are positioned against
the formed sheet 32 as shown in the cross section of FIG. 5,
forming an assembly 38. Desirably, any desired input and output
holes are formed through the top plate 34 and/or the bottom plate
36, (and through the formed sheet 32 also, if desired) by drilling,
grinding, or other suitable process, before the assembly 38 is
bonded together. As shown in FIG. 5, the access holes may be formed
in opposite plates as in the case of holes 42 and 44 (on the right
side in the Figure) or, if desired, in the same plate, as in the
case of holes 46 and 48. Access holes may extend, as in the case of
hole 48, through both the top plate 34 and the formed sheet 32.
[0037] The assembly 38 is then bonded to form a microfluidic device
50 having closed or enclosed microchannels or passages 40, as shown
in FIG. 6, with sample access holes 42, 44, 46, and 48. The bonding
of the assembly 38 may desirably be accomplished by glass-to-glass
thermal bonding of Corning 1737.RTM. glass plates to a Corning
1737.RTM. formed sheet, by maintaining the assembly 38 at about
870.degree. C. for about 90 minutes. By drilling or otherwise
forming the access holes prior to bonding, micro cracks and surface
damage from the hole forming process, if any, can be annealed.
[0038] The above-described example of the inventive process is
capable of forming, in the same process step, twin circuits
separated by a thin glass layer. Starting from a 0.5 mm thick
sheet, for example, the thickness of the sidewalls 58 may range
from 0.4 to 0.3 mm, offering little barrier to heat exchange. The
sidewalls may be thicker if desired, by starting with a 0.7 mm or a
1 mm thick sheet.
[0039] Standard fluid connectors 52, shown in FIG. 7, can be
affixed by polymeric bonding or other compatible glass-bonding
means.
[0040] Since the forming process described above easily produces
twin complementary channel patterns on the upper and lower surfaces
of the formed sheet 32, one natural application for microfluidic
devices formed in this manner is heat exchange. Channels one side
of the formed sheet 32 may contain a first fluid F1, while channels
on the other side of the formed sheet 32 may contain a second fluid
F2, as shown in FIG. 8. Because the alternate channels are
separated by a minimally thick sheet of glass, quick and efficient
heat transfer is possible.
[0041] FIG. 9 shows a plan view of one possible orientation of
alternate channels as in FIG. 8 in a microfluidic circuit. The
channels 54 may be positioned in a straight, parallel arrangement,
with access holes 56 provided at each end of each channel. Such
channels can be used for two fluids in alternate channels in
contrary flow, as suggested by the arrows and shading in the
Figure, or in other configurations, such as in parallel flow if
desired, for high-throughput heat exchange.
[0042] FIG. 10 shows a plan view of another possible orientation of
alternate channels such as in FIG. 8. In FIG. 10, two alternate
channels 54 are arranged together in a concentric spiral with
access holes 56 at the outer edge and at the center of the
spiral.
[0043] Microchannel arrangements created by the processes described
herein need not be limited to alternating, non-communicating
channel arrangements such as those shown in FIGS. 9 and 10.
[0044] For example, if desired, the mold on which the formed sheet
32 is formed may be designed to minimize the channel size of some
or all channels on one side of the formed sheet 32, resulting, in
minimized channels 60 interspersed with regular channels 40, such
as shown in the microfluidic device 50 of FIG. 11. The resulting
minimized channels may then be omitted from the fluid circuit
design altogether. If desired, the minimized channels 60 may
alternatively be filled with air, helium or other gas, or even a
partial vacuum to aid in thermally insulating adjacent fluid
circuit channels. Conversely, the minimized channels may also be
filled with water or other fluid if high thermal mass and
relatively high thermal conductivity and temperature uniformity is
desired.
[0045] An embodiment of a device according to the present invention
having minimized channel size on one side of the formed sheet is
shown in plan view in FIG. 12. In this embodiment, minimized
channels 60 are not included in the microfluidic circuit, and the
non-minimized channels 54 are provided with access holes 56. In
embodiments such as the one shown in FIG. 12, it is possible to
close the non-minimized channels with a single plate.
[0046] In another alternative embodiment of microfluidic devices of
the present invention, openings for fluid communication may be
established, as desired, between the fluid channels on one side of
the formed sheet 32 and the complementary fluid channels on the
other side, by removing selected portions of the channel walls
within the formed sheet 32. For example, removal (by grinding,
drilling, or other suitable process) from the formed sheet 32 of
the material within the dashed perimeter 41 shown in FIG. 13 will
establish a fluid connection or through-hole between the
neighboring alternate channels 43 and 45. The removed material need
not extend to any great length along the channels (in the direction
in and out of the Figure), so the formed sheet 32 can substantially
retain its structural integrity.
[0047] Microfluidic devices of the present invention have been
successfully produced using various glass compositions, including
Corning 0211, Corning 7059, Corning 1737, available from Corning
Incorporated, Corning, N.Y., USA, and Glaverbel D 263, available
from Glaverbel Group, 1170 Brussels, Belgium. Of these, Corning
1737 offers the smallest coefficient of thermal expansion of about
37.6.times.10.sup.-7 C. A microfluidic device formed of Corning
1737 is suitable for use with fluid temperatures of up to
650.degree. C. Alumino-boro-silicate glasses, such as Kerablack,
(available from Keraglass, 77 Bagneau sur Loing, France) may also
be used. After the microfluidic device is formed as above, then
Kerablack would by ceramicized into vitroceram, providing an
ultra-low coefficient of thermal expansion of about to
-2.10.sup.-7.
[0048] As yet another embodiment of the present invention, two
glass materials having reasonably close coefficients of thermal
expansion may be used to form a single microfluidic device. For
example, the formed sheet 32 may be formed of Corning 1737 while
the top and bottom sheets 34 and 36 used to close the passages in
the device 50 may be formed of Pyrex 7740 (see FIGS. 5 and 6). The
difference in softening point of these two glass materials of about
100.degree. C. allows thermal sealing at about 780.degree. C. This
lower thermal sealing temperature can potentially help prevent
post-vacuum-forming deformation of formed sheet 32.
[0049] Preferred Manufacturing Process
[0050] The isothermal process described above has been demonstrated
for prototype building and may be suitable for very small-scale
manufacture. One embodiment of a more cost-effective and efficient
industrial process is described below with reference to FIGS.
13A-13F.
[0051] As shown in FIG. 14A, glass gob 70 is delivered from a tank
feeder (not shown) onto two heated rotating rollers 72 and 74. A
soft glass sheet 76 is then rolled out over a moving mold 78 and
vacuum formed immediately, forming a formed sheet 80 as shown in
FIG. 14B, with its thickness reduced relative to the soft glass
sheet 76 by the vacuum redraw. In a second and immediately
following pass, a second soft glass sheet 82 is put over the formed
sheet 80, as shown in FIG. 14C. The second soft glass sheet
immediately closes the upper surface of the formed sheet 80, as
shown in FIG. 14D, forming closed upper channels 90. The upper
channels 90 are thus created and closed quickly, in as short as
about 5 to 10 seconds. The formed sheet with its closed upper
channels 90 is then removed from the mold and placed in inverted
position on a support 82. The previously unclosed complementary
fluid circuit is then covered with a third soft glass sheet 84, as
shown in FIG. 14E, forming closed lower channels 100 and resulting
in the microfluidic device 50 of FIG. 14F.
[0052] For forming 7740 Pyrex, for example, desirable thermal
conditions are 1350.degree. C. glass delivery onto 650.degree. C.
heated rollers and mold. The release agent is desirably carbon
black from acetylene cracking. The thinner the glass sheet, the
higher the roller temperature should be. 0.8 mm rolled and vacuum
formed sheets have been demonstrated, offering less than 0.2 mm
thick glass at the bottom of the formed shape.
[0053] Microfluidic devices of the present invention and produced
by the process of the present invention need not be limited to
designs with near-vertical channel walls. FIG. 15 shows a
cross-sectional view of microfluidic device 50 having triangular
channels 40 therein. This and other configurations are easily
achievable according to the present invention. For example, as a
further extension of the present invention, one formed sheet may be
bonded to another formed sheet to form even higher-aspect-ratio
channels, or to form complex passages between the two sheets.
[0054] The process and method of the present invention allow
repeatable and reliable formation of very thin-walled glass
microchannels. The resulting microfluidic devices of the present
invention are particularly suited to high-throughput microfluidic
heat exchange.
[0055] In comparison with other methods of forming microfluidic
devices, the current invention also allows for the provision of
increased wall surface area between adjacent channels relative to
the cross-sectional area of the channels. The large wall surface
area is mainly attributable to the relatively high channel aspect
ratios (ratios of channel height to channel width) achievable with
the disclosed method, as high as 2:1 or more.
* * * * *