U.S. patent number 6,322,753 [Application Number 09/308,563] was granted by the patent office on 2001-11-27 for integrated microfluidic element.
This patent grant is currently assigned to Johan Roeraade, M.ang.rten Stjernstrom. Invention is credited to Peter Lindberg, Johan Roeraade, M.ang.rten Stjernstrom, Jean Louis Viovy.
United States Patent |
6,322,753 |
Lindberg , et al. |
November 27, 2001 |
Integrated microfluidic element
Abstract
An integrated microfluidic element (1) composed of two
juxtaposed plates (3, 5) bonded together, wherein at least one
plate (3) has an etched structure or pattern of channels (7) on the
surface facing the other plate (1) to form sealed micro channels
(7), said element having micro spacers or posts (11) distributed
over the etched surface of said one plate outside of said etched
structure or pattern, and walls (9) surrounding said channels (7),
said walls (9) having a height equal to that of said spacers or
posts (11); and a method for the manufacture of such integrated
microfluidic element.
Inventors: |
Lindberg; Peter (Nacka,
SE), Roeraade; Johan (S-147 40 Tumba, SE),
Stjernstrom; M.ang.rten (S-114 54 Stockholm, SE),
Viovy; Jean Louis (Paris, FR) |
Assignee: |
Roeraade; Johan (Tumba,
SE)
Stjernstrom; M.ang.rten (Stockholm, SE)
|
Family
ID: |
20405513 |
Appl.
No.: |
09/308,563 |
Filed: |
June 23, 1999 |
PCT
Filed: |
January 23, 1998 |
PCT No.: |
PCT/SE98/00102 |
371
Date: |
June 23, 1999 |
102(e)
Date: |
June 23, 1999 |
PCT
Pub. No.: |
WO98/32535 |
PCT
Pub. Date: |
July 30, 1998 |
Foreign Application Priority Data
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Jan 24, 1997 [SE] |
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9700205 |
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Current U.S.
Class: |
422/503; 156/108;
156/60; 156/87; 156/99; 216/2 |
Current CPC
Class: |
B01L
3/502707 (20130101); G01N 30/6095 (20130101); B01L
2200/0689 (20130101); B01L 2200/12 (20130101); B01L
2300/0816 (20130101); B01L 2300/0887 (20130101); Y10T
156/10 (20150115) |
Current International
Class: |
B01L
3/00 (20060101); G01N 30/00 (20060101); G01N
30/60 (20060101); B01L 003/00 () |
Field of
Search: |
;422/102,104,99 ;216/2
;156/60,87,99,108 |
References Cited
[Referenced By]
U.S. Patent Documents
Foreign Patent Documents
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WO91/16966 |
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Nov 1991 |
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WO |
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WO93/22055 |
|
Nov 1993 |
|
WO |
|
Other References
"Electrophoresis and microlithography", R.H. Austin et al.,
Analusis, vol. 21 (1993) pp. 235-238. .
"Micromachining a Miniaturized Capillary Electrophoresis-Based
Chemical Analysis System on a Chip" D. Jed Harrison et al.,
Science, vol. 261 (Aug. 13, 1993) pp. 895-897. .
"Glass Chips for High-Speed Capillary Electrophoresis Separations
with Submicrometer Plate Heights" Carlo S. Effenhauser, Anal.
Chem., vol. 65 (1993) pp. 2637-2642. .
"Planar Glass Chips for Capillary Electrophoresis: Repetitive
Sample Injection, Quantitation and Separation Efficiency" Kurt
Seiler et al., Anal. Chem., vol. 65 (1993) pp. 1481-1488. .
"Open Channel Electrochromatography on a Microchip" Stephen C.
Jacobson, Anal. Chem., vol. 66 (1994) pp. 2369-2373. .
"High Speed Separation of Antisense Oligonucleotides on a
Micromachined Capillary Electrophoresis Device" Carlo S.
Effenhauser et al., Anal. Chem., vol. 66 (1994) pp. 2949-2953.
.
"Electroosmotic Pumping and Valveless Control of Fluid Flow within
a Manifold of Capillaries on a Glall Chip" Kurt Seiler, Anal.
Chem., vol. 66 (1994) pp. 3485-3491. .
"Characterization of the electrostatic bonding of silicon and Pyrex
glass" A. Cozma et al., J. Micromech. Microeng., vol. 5 (1995) pp.
98-102. .
"Microchip Capillary Electrophoresis with an Integrated Postcolumn
Reactor" Stephen C. Jacobson et al., Anal. Chem., vol. 66 (1994)
pp. 3472-3476. .
"Micromachining of Capillary Electrophoresis Injectors and
Separators on Glass Chips and Evaluation of Flow at Capillary
Intersections" Zhonghui H. Fan et al., Anal. Chem., vol. 66 (1994)
pp. 177-184. .
"Integrated Capillary Electrophoresis Devices with an Efficient
Postcolumn Reactor in Planar Quartz and Glass Chips" Kari Fluri et
al., Anal. Chem., vol. 68 (1996) pp. 4285-4290. .
"Examination of Glass-Silicon and Glass-Glass Bonding Techniques
for Microfluidic Systems" N.F. Raley et al., SPIE, vol. 2639, pp.
40-45..
|
Primary Examiner: Ludlow; Jan
Attorney, Agent or Firm: Burns, Doane, Swecker & Mathis,
L.L.P.
Claims
What is claimed is:
1. A method for the manufacture of an integrated microfluidic
element (5) composed of two juxtaposed plates (3, 5) bonded
together, wherein at least one plate (3) has an etched structure or
pattern of channels (7) on the surface facing the other plate (1)
to form sealed micro channels (7), characterized by forming,
distributed over the etched surface of said one plate outside of
said etched structure or pattern, micro spacers or posts (11), and
by forming walls (9) surrounding said channels (7), said walls (9)
having a height equal to that of said spacers or posts (11) and
then bonding the two plates (3, 5) together to form said
element.
2. A method according to claim 1, wherein the plates (3, 5) are
bonded together by fusion bonding at an increased temperature not
exceeding the softening temperature of the plates.
3. A method according to claim 2, wherein the plates (3, 5) are
bonded together by field-assisted bonding techniques.
4. A method according to claim 1, wherein the plates (3, 5) are
constituted by materials selected from ordinary glass, quartz and
silicon.
5. A method according to claim 1, wherein also said spacers or
posts (11) and walls (9) are formed by etching.
6. A method according to claim 5, wherein the etching is carried
out in one step to form simultaneously both channels (7) and
spacers or posts (11).
7. A method according to claim 5, wherein the etching is carried
out in two steps, a first step to form the channels (7) and a
second step to form the spacers or posts (11).
8. A method according to claim 1, wherein the juxtaposed surfaces
of the plates (3, 5) before bonding the plates together are covered
by a thin layer to form a channel lining of the desired
properties.
9. A method according to claim 8, wherein said thin layer is formed
by chemical vaporization deposition (CVD).
10. A method according to claim 1, wherein access to the channels
formed is obtained by forming holes (8) in either or both of the
two plates (3, 5).
11. A method according to claim 1, wherein the contact surface
between the plates (3, 5) is less than about 50% of the surface of
each plate.
12. A method according to claim 1, wherein the plates (3, 5) are
bonded together by field-assisted bonding techniques.
13. An integrated microfluidic element (1) composed of two
juxtaposed plates (3, 5) bonded together, wherein at least one
plate (3) has an etched structure or pattern of channels (7) on the
surface facing the other plate (5) to form sealed micro channels
(7), characterized by micro spacers or posts (11) distributed over
the etched surface of said one plate outside of said etched
structure or pattern, and by walls (9) surrounding said channels
(7), said walls (9) having a height equal to that of said spacers
or posts (11).
14. An integrated microfluid element according to claim 13, wherein
the plates (3, 5) are constituted by materials selected from
ordinary glass, quartz or silicon.
15. An integrated microfluid element according to claim 14, wherein
the juxtaposed surfaces of the plates (3, 5) before bonding the
plates together have been covered by a thin layer to give a channel
lining of the desired properties.
16. An integrated microfluid element according to claim 14, wherein
access to the channels is obtained by holes (8) made in either or
both of the two plates (3, 5).
17. An integrated microfluid element according to claim 14, wherein
the contact surface between the plates (3, 5) is less than about
50% of the surface of each plate.
18. An integrated microfluid element according to claim 13, wherein
the juxtaposed surfaces of the plates (3, 5) before bonding the
plates together have been covered by a thin layer to give a channel
lining of the desired properties.
19. An integrated microfluid element according to claim 18, wherein
access to the channels is obtained by holes (8) made in either or
both of the two plates (3, 5).
20. An integrated microfluid element according to claim 18, wherein
the contact surface between the plates (3, 5) is less than about
50% of the surface of each plate.
21. An integrated microfluid element according to claim 13, wherein
access to the channels is obtained by holes (8) made in either or
both of the two plates (3, 5).
22. An integrated microfluid element according to claim 21, wherein
the contact surface between the plates (3, 5) is less than about
50% of the surface of each plate.
23. An integrated microfluid element according to claim 13, wherein
the contact surface between the plates (3, 5) is less than about
50% of the surface of each plate.
Description
The present invention relates to integrated microfluidic elements
and a method for the manufacture thereof. Such elements are often
composed of two juxtaposed plates bonded together, wherein one
plate has an etched structure or pattern of channels on the surface
facing the other plate to form sealed microchannels.
Glass substrates have in recent years been used in the manufacture
of miniaturized analytic electrophoresis instrumentation with
micromachining techniques (Harrison, D. J.; Fluri, K., Seiler, K.;
Fan, Z.; Effenhauser, C. S.; Manz, A., Science, 261 (1993) 895-897.
Effenhauser, C. S.; Manz, A.; Widmer, H. M., Anal. Chem., 65 (1993)
2637-2642. Seiler, K.; Harrison, D. J.; Manz, A.; Anal. Chem., 65
(1993) 1481-1488. Jacobson, S. C.; Hergenroder, R.; Koutny, L. B.;
Ramsey, J. M., Anal. Chem., 66 (1994) 2369-2373. Effenhauser, C.
S.; Paulus, A.; Manz, A.; Widmer, H. M., Anal. Chem., 66 (1994)
2949-2953. Seiler, K.; Fan, Z. H.; Fluri, K.; Harrison, D. J.,
Anal. Chem., 66 (1994) 3485-3491. Jacobson, S. C.; Koutny, L. B.;
Hergenroder, R.; Moore, A. W.; Ramsey, J. M., Anal. Chem., 66
(1994) 3472-3476).
The insulating glass material permits the use of high voltages
which can accomplish fast and efficient separations and its
transparency allows for sensitive on-column optical sample
detection.
Bonding of planar structures is an important step necessary in the
manufacture of micro-instrumentation. For utilization of
microfabricated flow channels in analytical techniques such as
electrophoresis, chromatography, flow injection analysis or
field-flow fractionation, the bond between the structures should
preferably be direct. Thus, adhesives should be avoided that can
clog the capillaries and negatively effect the efficiency or the
liquid flow pattern. Accordingly, an etched structure in for
example glass is by preference sealed to another glass plate by
fusion bonding at a temperature that permits fusion while not
deforming the glass parts, to produce uniformly assembled channel
structures.
It is difficult to manufacture large bonded assemblies without
irregularities, since the demand on the substrate material in terms
of planarity, smoothness and cleanness increases with the area of
the substrate. Furthermore, it is usually essential that the
surfaces are connected under extreme clean room conditions, so that
particle contamination can be eliminated at their interface. Void
formation often occurs in the process cycle when bonding starts at
the same time at various locations. Once a void is generated the
trapped gas cannot be exhausted from its confinement.
The glass material most commonly used in micromachining
laboratories is polished substrates of Pyrex Corning 7740, due to
its compatibility with silicon in terms of thermal expansion. This
expensive material is extensively used for anodic bonding to
silicon in the manufacture of microsensors (Cozma, A.; Puers, B. J.
Micromech. Microeng. 5 (1995) 98-102). However, details on
glass-glass fusion bonding of micromachined structures are very
sparse in the literature. The reported bonding process is
characterized by a low yield which often involves repeated cycles
((Harrison, D. J.; Fluri, K., Seiler, K.; Fan, Z.; Effenhauser, C.
S.; Manz, A., Science, 261 (1993) 895-897), including the use of
weights placed over poorly bonded regions (Fan, Z.; Harrison, D. J.
Anal. Chem 66 (1994) 177-184). Recently, the yield has been
improved by the use of sophisticated polishing and cleaning
instrumentation (Fluri, K.; Fitzpatrick, C.; Chiem, N.; Harrison,
D. J. Anal. Chem 68 (1996) 4285-4290), available only in
specialized micromachining laboratories.
For sample detection purposes, many applications require that one
of the glass substrates is very thin (0.15 -0.20 mm), e.g. when
using high numerical aperture microscope objectives. An important
example of such an application where a high degree of magnification
is required is the direct observation of DNA polymer motion by
fluorescence microscopy. Bonding thin glass introduces additional
problems mainly due to that the commercially available thin cover
glass often is manufactured by a drawing process and therefore not
very planar. Raley et al. reported on a etch-back technique where
first two thicker sheaths of Corning 7740 were bonded together and
subsequently thinning one of the sheaths by etching and several
grinding steps (Raley, N. F.; Davidson, J. C.; Balch, J. W. Proc.
SPIE-Int. Soc. Opt. Eng. 2639 (1995) 40-45). Their best glass-glass
bonding results were reported to be in the order of a 85% area
coverage for 5.times.5 cm to 5.times.18 cm glass specimens with a
original thickness of 800 .mu.m. However, the etch-back technique
is anticipated to depend on how well the etching process can be
optimized.
The present invention has for its main object to provide new
techniques for the provision of integrated microfluidic elements
where the problems encountered with the prior art as illustrated
above are eliminated or at least greatly reduced.
Another object of the invention is to provide a method for the
manufacture of integrated microfluidic elements, wherein entrapment
of gas between the plates to be bonded together can be avoided.
Yet another object of the invention is to provide a method for such
manufacture, wherein the problems encountered in the bonding of two
plates of different thermal coefficents of expansion together will
be largely avoided.
Still another object of the invention is to provide integrated
microfluidic elements free of undesirable voids and less vulnerable
to inconsistencies in thermal coefficients of expansion.
For these and other objects which will be clear from the following
disclosure the invention provides for a method for the manufacture
of an integrated microfluidic element composed of two juxtaposed
plates bonded together, wherein at least one plate has an etched
structure or pattern of channels on the surface facing the other
plate to form sealed microchannels. This method is characterized by
forming, distributed over the etched surface of said one plate
outside of said etched structure or pattern, micro spacers or posts
11, and by forming walls surrounding said channels 9, said walls 9
having a height equal to that of said spacers or posts 11 and then
bonding the two plates 3, 5 together to form said element.
The plates can be bonded together by fusion bonding at an increased
temperature which does not exceed the softening temperature of the
plates.
The plates may also be bonded together by field assisted bonding
methods. The bonding techniques used are not critical to the
invention and any conventional bonding method can be used. An
example of such conventional bonding method is anodic bonding of a
glass plate to a silicon substrate.
The plates used can be constituted by materials used in the art,
such as ordinary glass, silicon, quartz, diamond, carbon, ceramics
or polymers. Particularly useful materials are glass, quartz and
silicon.
It is particularly preferred in the method of the invention to form
also the spacers or posts and the walls simultaneously with the
forming of the structure of pattern of channels by etching.
According to an alternative method the etching can be carried out
in two steps, a first step to form the channels and a second step
to form the spacers or posts. By such alternative method the depth
of the etched sections can be varied.
In some cases it is desired to impart special properties to the
channels formed, and here the juxtaposed surfaces of the plates are
covered by a thin layer before bonding the plates together. Such
layer can be formed e.g. by chemical vaporization deposition (CVD),
and the layer can be constituted by any desired material, such as
silicon nitride, metals, glass etc.
Access to the channels formed in the microfluidic element of the
invention is suitably obtained by the formation of holes in either
or both of the two plates in positions coinciding with the
channels.
To obtain optimal performance of the microfluidic element of the
invention it is preferred that the contact surface between the
plates is less than about 50% of the surface of each plate. This
surface now referred to is the major side surface of the plate
corresponding to the surface of the plate facing the accompanying
juxtaposed plate.
The invention also provides for an integrated microfluidic element
comprising two juxtaposed plates bonded together, wherein at least
one plate has an etched structure or pattern of channels on the
surface facing the other plate to form sealed microchannels. Such
element is characterized by microspacers or posts distributed over
the etched surface of said one plate outside of said etched
structure or pattern, and by walls surrounding said channels. These
walls have a height equal to that of said spacers or posts.
The posts or "lines " are preferably substantially equally
distributed over the etched surface of the plate on areas outside
of the etched structure or pattern.
The present invention as outlined above efficiently reduces or
eliminates the problems associated with the prior art techniques.
Thus, the use of microspacers or posts distributed over the etched
surface of the plate greatly reduces the risk for the formation of
voids or cracks in the plate specimens which can be due to dust
particles, non-planarity and inconsistencies or differencies in
thermal coefficients of expansion. Furthermore, the inventive
concept results in flexible structures of less built-in tension
irrespective of differencies in thermal coefficence of expansion of
the two plates. Finally, less expensive materials can be used, such
as ordinary soda-lime microslide glass which, otherwise, would be
virtually impossible to use applying the conventional methods
presently available.
According to a special embodiment of the invention enabling use of
a variety of substrates or materials in the plates, the surfaces of
the plates facing each other are coated after etching with a thin
layer of quartz (SiO.sub.2), such as by chemical vaporization
deposition (CVD). In this manner the two plates can be joined
together by conventional bonding techniques, such as fusion bonding
at an increased temperature. Such method serves the double purpose
of enabling easy bonding of the two plates together and
simultaneously obtaining a channel lining of a uniform structure.
The thickness of such quartz layer may be from fractions of a
micron up to about 10 microns.
BRIEF DESCRIPTION OF THE DRAWINGS.
The invention will in the following be further described more in
detail by non-limiting examples with reference to the appended
drawing, wherein:
FIG. 1 is a section in sideview of an element according to the
present invention;
FIG. 2 is a plan view of the element of FIG. 1 taken in a plane
along the line A--A in FIG. 1; and
FIG. 3, is the layout of a photomask for a capillary
elektrophoretic chip.
While the invention in the following will be exemplified mainly
with reference to the use of glass plates for the manufacture of
elements in accordance with the present invention it is to be noted
that the invention is in no way limited only to the use of such
glass plates but is applicable to all types of materials suitable
for the intended purpose.
When using glass plates the thickness thereof can vary between
about 0.1 and 1 mm, and the deptch of etching can vary between
about 1 .mu.to about 100 .mu.. The invention greatly facilitates
the use of different materials in the two plates, such as one glass
plate to be combined with a quartz or silicon plate.
EXAMPLE 1
The channel manufacturing process includes the steps of:
simultaneously HF etching a channel 7 and an array of posts 11 in a
glass substrate 3; drilling connection holes 8 to the channel in
the glass substrate 3 and bonding the formed channels 7 with a thin
cover slip 5 at temperatures below the softening point of the glass
(FIG. 1 and 2).
Menzel soda-lime microslide glass plates 3 (76.times.25 mm) with a
thickness of 1 mm (.+-.0.1 mm) were used as substrate for etching
the channels (7). Cover glass plates (0.17 mm) were also obtained
from Menzel. The data given by the manufacturer for the mean
coefficient of thermal expansion are 90.6.times.10.sup.-7 K.sup.-1
and (73-74).times.10.sup.-7 K.sup.-1 for the microslide and cover
slips respectively. The corresponding softening points are
720.degree. C. and 732-736.degree. C.
The photo lithographic mask is made with an ordinary CAD program
and is printed with a photo setter on a transparent film. The
processing chemicals (NH.sub.3, H.sub.2 O.sub.2, HCl, NH.sub.4 F,
HF, VLSI Selectipur.RTM. grade) were all obtained from Merck
(Darmstadt, Germany). All processing solutions were prepared with
de-ionized water from a Milli-Q system (Millipore, Bedford, Mass.)
filtered through 0.2 .mu.m filters (Millipore).
The glass substrates were first carefully cleaned in RCA-1 (5 parts
distilled H.sub.2 O: 1 part NH.sub.3 (25%): 1 H.sub.2 O.sub.2
(20%)) and RCA-2 (6 parts H.sub.2 O: 1 part HCl (37%): 1 part
H.sub.2 O.sub.2 (20%)) for 10 min respectively and dehydrated in an
oven (130.degree. C.) for 20 min. For improved adherence of the
photoresist, the surfaces were first primed by exposing the
substrates with Microposit Primer (Shipley, Marlborough, Mass.)
fumes for 3 min. The glass substrates were then coated with a
positive resist (Microposit S1813 Photo Resist, Shipley) with the
aid of a lint free paper and softbaked in an oven at (90.degree.
C.) for 35 min. Next, UV lithography followed by a 1 min immersion
in a developing bath (Microposit Developer 351, Shipley) and
cleaning in distilled H.sub.2 O the UV exposed parts of the
underlying glass were laid open for subsequent etching. After a
hardbaking step (130.degree. C.) for 45 min, etching was performed
in a vigorously stirred aqueous mixture of 5% buffered HF (7 parts
40% NH.sub.4 F; 1 part 50% HF) and 9.25% conc. HCl for 45-60 min at
room temperature to form channels 7, walls 9 and posts 11. The
resulting etch depth was approximately 80 .mu.m.
Connection holes 8 to the flow channel were manufactured by
drilling the microslide with a carbide-drill steel (0.5 mm
diameter). The remaining drilling dust was removed with ultrasonic,
RCA-1 and RCA-2 rinsing steps. Bonding was performed by first
carefully mating the wafers in a clean hood and placing the
substrates with the cover glass downwards in an oven at 630.degree.
C. for 8 hours. In order to avoid fusion to and replication of
scratches from the underlying support, plates of polished vitreous
carbon were utilized (V25 grade, Le Carbone-Lorraine,
Gennevilliers, France).
EXAMPLE 2
The use of the new bonding technique to manufacture microfluidic
structures is illustrated in this example. The glass channel is
designed for directly observing fluorescent images of individual
DNA polymers undergoing separations, under a high numerical
aperture microscope. The photomask used to manufacture this
capillary electrophoretic chip is shown in FIG. 3 as a layout of
the photomask for the capillary electrophoretic chip. The dark
areas define the channel walls 9 and the posts 11 and the channel
dimensions are 500 .mu.m.times.3 mm for the large channels 17 and
50 .mu.m.times.40 mm for the thin channel. The buffer and sample
reservoirs 21,23, respectively, have a diameter of 2 mm. The square
posts dimensions are 400 .mu.m.times.400 .mu.m.
The photolithographic technique presented here does not involve any
advanced deposition or mask-alignment steps. The process is
facilitated by using a positive resist as a direct etch mask
instead of using the commonly used chromium/gold coating. The
pattern in the photomask is simply transferred by UV lithography to
a film of photosensitive positive resist which, in turn, by the
etching process conveys the geometric shape to the glass substrate.
The positive resist withstands diluted buffered HF etch solution at
least up to 1 hour in room temperature, when concentrated HCl is
added to the solution. This etch time is sufficient to produce deep
etched channel structures in ordinary sodalime microscope slides.
We observed that the lower pH also was beneficial for the etching
process itself. At the used concentration of buffered HF, the
smoothness of the channel walls was significantly improved in
comparison with the case where no HCl addition was made.
Additionally, at higher pH and HF concentrations we observed
crystalline precipitates which was determined to be CaF.sub.2 with
EDAX.
No remaining voids or breakage after the thermal bonding step were
observed when the array of posts was utilized as underpinning
elements. It is suggested that the main reason for this observation
is due to the fact that gases are permitted to be exhausted through
the two-dimensional network of open channels. Thus, gas expansion
in enclosed voids never appears when the substrates are heated.
Additionally, no cracks were introduced during the bonding step due
to mismatch in the thermal expansion coefficients between the
etched substrate and the cover glass material. This problem is also
diminished by the lattice of raised posts, since their higher
degree of flexibility reduces the strain imposed on the interface
between the substrates. This opens the possibility to fusion bond
materials with larger difference in thermal expansion coefficients
such as quartz-glass, silicon-glass etc. and broadens the choice of
glass material for the anodic bonding technique (Cozma, A.; Puers,
B. J. Micromech. Microeng. 5 (1995) 98-102), which also is
performed at elevated temperatures.
It is to be observed that the present invention is not restricted
to the specific embodiments described above but is broadly
applicable, and the invention is not to be construed to be limited
otherwise than specified in the appended patent claims.
* * * * *