U.S. patent application number 10/074962 was filed with the patent office on 2003-08-14 for micro-fluidic anti-microbial filter.
Invention is credited to Cho, Steven T., Christianson, Harlow B..
Application Number | 20030150791 10/074962 |
Document ID | / |
Family ID | 27659995 |
Filed Date | 2003-08-14 |
United States Patent
Application |
20030150791 |
Kind Code |
A1 |
Cho, Steven T. ; et
al. |
August 14, 2003 |
Micro-fluidic anti-microbial filter
Abstract
An anti-microbial filter (105) for a micro-fluidic system (100)
includes a silicon-based filter membrane (213) having holes (218)
formed therein. The membrane (213) is formed on a substrate (211).
One side of the filter membrane (213) has an anti-microbial coating
(216) between the holes (218) on the filter membrane (213) and the
other side can include filter supports formed from a silicon
substrate. A method for making the anti-microbial filter (105)
includes forming a filter membrane (213) on a substrate (211),
forming holes (218) in the membrane (213) by providing a filter
mask (215) and etching holes (218) through holes (222) in the mask
(215). Then portions of the substrate (211) are removed from the
filter membrane (213) using a masking and etching process to expose
the holes (218). An anti-microbial coating is applied to the
membrane (213) adjacent the holes (218).
Inventors: |
Cho, Steven T.;
(Castroville, CA) ; Christianson, Harlow B.; (San
Jose, CA) |
Correspondence
Address: |
STEVEN F. WEINSTOCK
ABBOTT LABORATORIES
100 ABBOTT PARK ROAD
DEPT. 377/AP6A
ABBOTT PARK
IL
60064-6008
US
|
Family ID: |
27659995 |
Appl. No.: |
10/074962 |
Filed: |
February 13, 2002 |
Current U.S.
Class: |
210/321.84 ;
210/490; 210/500.26; 216/2; 216/56 |
Current CPC
Class: |
B01D 67/003 20130101;
B01D 69/02 20130101; A61L 2/022 20130101; B01D 71/027 20130101;
B01D 63/087 20130101; B01D 67/0088 20130101; B01D 2325/48 20130101;
B01D 61/18 20130101 |
Class at
Publication: |
210/321.84 ;
210/500.26; 210/490; 216/2; 216/56 |
International
Class: |
B01D 063/08 |
Claims
What is claimed is:
1. A method for making an anti-microbial filter for a micro-fluidic
system, the method comprising the steps of: providing a substrate;
forming a filter membrane of a filter material on the substrate;
and forming a plurality of holes through the filter membrane by
providing a filter mask having a plurality of holes therein over
the filter membrane by depositing a plurality of spacers on the
filter material such that a part of each of the spacers contacts
the filter material to define said plurality of recesses and holes
in the filter mask, depositing filter mask material partially
around the spacers and on the filter material such that the part of
each of the spacers that contacts the surface of the filter
material prevents the filter mask material from continuously coming
between the spacers and the filter material and thereby defines one
of the plurality of holes in the filter mask, removing the
plurality of spacers to form the plurality of recesses and holes in
the filter mask, and forming the plurality of holes in the filter
membrane in registration with the plurality of recesses and holes
in the filter mask respectively; and removing at least a portion of
the substrate to expose at least some of the holes in the filter
membrane.
2. The method according to claim 1, wherein the step of forming the
filter membrane further comprises the step of: diffusing filter
material into a predetermined depth of the substrate, wherein the
predetermined depth of the diffusion of the filter material into
the substrate corresponds to a predetermined thickness of the
filter membrane.
3. The method according to claim 1, wherein the step of forming the
filter membrane further comprises the step of: depositing the
filter membrane on the substrate.
4. The method according to claim 1, wherein the step of forming the
plurality of holes in the filter membrane comprises the steps of:
providing a filter mask having a plurality of recesses therein over
the filter membrane; and forming the plurality of holes in the
filter membrane in registration with the plurality of holes in the
filter mask.
5. The method according to claim 1, wherein the step of removing
the plurality of spacers further comprises the step of: dissolving
the plurality of spacers.
6. The method according to claim 1, wherein the step of removing
the plurality of spacers further comprises the step of:
disintegrating the plurality of spacers.
7. The method according to claim 1, wherein the step of forming the
plurality of holes in the filter membrane comprises the step of:
etching the filter membrane through the recesses in filter
mask.
8. The method according to claim 1 comprising the step of:
depositing an anti-microbial coating between the holes on the
filter membrane.
9. The method according to claim 9 wherein the anti-microbial
coating contains silver.
10. The method according to claim 4, wherein the plurality of holes
in the filter membrane are formed by etching the filter membrane
through the recesses in filter mask.
11. The method according to claim 10, wherein the etching step
includes reactive ion etching.
12 An anti-microbial filter adapted for a micro-fluidic system
comprising: a filter membrane formed of a silicon-based material
and having a plurality of holes formed therethrough.
13. The anti-microbial filter according to claim 12 further
comprising: a silicon support structure connected to the filter
membrane and extending from the filter membrane.
14. The anti-microbial filter according to claim 26 further
comprising: an anti-microbial coating disposed between the holes on
the filter membrane.
15. A method for making an anti-microbial filter for a
micro-fluidic system, the method comprising the steps of: providing
a substrate; forming a filter membrane of a filter material on the
substrate; forming a plurality of holes in the filter membrane; and
removing at least a portion of the substrate to expose the
plurality of holes in the filter membrane.
Description
FIELD OF THE INVENTION
[0001] The present invention generally relates to filters for
purification of fluids. More particularly, the present invention
relates to a micro-fluidic anti-microbial filter.
BACKGROUND OF THE INVENTION
[0002] MEMS technology integrates electrical components and
mechanical components on a common silicon substrate by using
micro-fabrication technology. Integrated circuit (IC) fabrication
processes, such as photolithography processes and other
microelectronic processes, form the electrical components. The IC
fabrication processes typically use materials such as silicon,
glass, and polymers. Micro-machining processes, compatible with the
IC processes, selectively etch away areas of the IC or add new
structural layers to the IC to form the mechanical components. The
integration of silicon-based microelectronics with micro-machining
technology permits complete electro-mechanical systems to be
fabricated on a single chip. Such single chip systems integrate the
computational ability of microelectronics with the mechanical
sensing and control capabilities of micro-machining to provide
smart devices.
[0003] One type of MEMS is a micro-fluidic system. Micro-fluidic
systems include components such as channels, reservoirs, mixers,
pumps, valves, chambers, cavities, reaction chambers, heaters,
fluidic interconnects, diffusers, nozzles, and other micro-fluidic
components. These micro-fluidic components typically have
dimensions between a few micrometers and a few hundreds of
micrometers. These small dimensions minimize the physical size, the
power consumption, the response time and the waste of the
micro-fluidic system. Such micro-fluidic systems may provide
wearable miniature devices located either outside or inside a human
body or an animal body.
[0004] Applications for micro-fluidic systems include genetic,
chemical, biochemical, pharmaceutical, biomedical, chromatography,
IC cooling, ink-jet printer head, medical, radiological,
environmental, as well as any devices that require liquid or gas
filled cavities for operation. Such application may involve
processes related to analysis, synthesis and purification. The
medical applications include diagnostic and patient management such
as implanted drug dispensing systems. The environmental
applications include detecting hazardous materials or conditions
such as air or water pollutants, chemical agents, biological
organisms or radiological conditions. The genetic applications
include testing and/or analysis of DNA.
[0005] An anti-microbial filter is a device that filters out
microorganisms in a fluidic system. Anti-microbial filters are
typically used for fluid purification, such as in air, water and
drug delivery systems. In drug delivery systems, anti-microbial
filters are used to prevent microorganisms in a human or an animal
body from reaching the fluid source of the drug delivery. Some
anti-microbial filters are made with holes that are large enough to
permit fluid to flow through the filter in one direction, but small
enough to prevent the microorganisms from moving through the filter
in the opposite direction. Anti-microbial filters may also have a
coating, such as silver, disposed on the downstream side of the
filter that prevents some microorganisms from adhering to the
filter and kills other microorganisms that contact the coating.
Some anti-microbial filters have a long, narrow, winding path,
otherwise known as a torturous path, which permits fluid to flow in
one direction through the path while inhibiting the flow of
microorganisms in the opposite direction. Anti-microbial filters
have been made on a macro scale. However, making anti-microbial
filters on a micro scale presents special challenges, such as the
construction of very small holes with precision while being cost
effective, manufacturable and reliable.
[0006] Accordingly, it would be desirable to have an anti-microbial
filter that is small enough to be used in a micro-fluidic system.
The anti-microbial filter would be constructed using
micro-machining processes to permit it to be integrated into a
micro-fluidic system. The micro-machining process would be precise
and cost effective. Thus, the anti-microbial filter would be easy
to manufacture and of high quality.
SUMMARY OF THE INVENTION
[0007] According to one aspect of the present invention, an
anti-microbial filter adapted for a micro-fluidic system includes a
filter membrane formed of a silicon-based material having a
plurality of holes formed therein.
[0008] According to another aspect of the present invention, a
support structure is connected to and extends from a first side of
the filter membrane.
[0009] According to another aspect of the present invention, an
anti-microbial coating is disposed between the holes on the filter
membrane.
[0010] According to another aspect of the present invention, the
micro-fluidic system includes a fluid source adapted to contain
fluid, a fluid sink fluidly connected to the fluid source and
adapted to receive the fluid, and the anti-microbial filter fluidly
connected to the fluid source and the fluid sink.
[0011] According to another aspect of the present invention, the
micro-fluidic system further includes an upstream channel fluidly
connecting the fluid source to the anti-microbial filter and a
downstream channel fluidly connecting the fluid sink to the
anti-microbial filter.
[0012] According to another aspect of the present invention, a
method for making an anti-microbial filter includes the steps of
providing a substrate, forming the filter membrane on the
substrate, forming the plurality of holes in the filter membrane,
and removing at least a portion of the substrate to expose the
plurality of holes in the filter membrane.
[0013] According to another aspect of the present invention, the
step of forming the filter membrane further includes the step of
diffusing filter material into a predetermined depth of the
substrate, wherein the predetermined depth of the diffusion of the
filter material into the substrate corresponds to a predetermined
thickness of the filter membrane.
[0014] According to another aspect of the present invention, the
step of forming the filter membrane further includes the step of
depositing the filter membrane on the substrate.
[0015] According to another aspect of the present invention, the
step of forming the plurality of holes in the filter membrane
further includes the steps of providing a filter mask, having a
plurality of holes, over the filter membrane, and forming the
plurality of holes in the filter membrane corresponding to the
plurality of holes in the filter mask.
[0016] According to another aspect of the present invention, the
step of providing the filter mask further comprises the steps of
depositing a plurality of spacers on the filter material, wherein a
part of the plurality of spacers contacts the filter material,
depositing filter mask material partially around the spacers and on
the filter material, wherein the part of the plurality of spacers
that contacts the surface of the filter material prevents the
filter mask material from coming between the part of the plurality
of spacers and the filter material, and removing the plurality of
spacers to form the plurality of holes in the filter mask, wherein
each spacer that contacts the filter material corresponds to each
hole in the filter mask.
[0017] According to another aspect of the present invention, the
step of removing the plurality of spacers further comprises the
step of dissolving the plurality of spacers.
[0018] According to another aspect of the present invention, the
step of removing the plurality of spacers further includes the step
of disintegrating the plurality of spacers.
[0019] According to another aspect of the present invention, the
step of forming the plurality of holes in the filter membrane
further comprises the step of etching the filter membrane through
the holes in filter mask.
[0020] According to another aspect of the present invention, the
step of removing at least a portion of the substrate further
comprises the step of removing portions of the substrate from the
filter membrane, wherein the remaining portions of the substrate
that contact the filter membrane provide the support structure for
the filter membrane.
[0021] According to another aspect of the present invention, the
step of removing at least a portion of the substrate further
comprises the step of removing the entire substrate from the filter
membrane.
[0022] According to another aspect of the present invention, an
anti-microbial coating is deposited between the holes on the filter
membrane.
[0023] These and other aspects of the present invention are further
described with reference to the following detailed description and
the accompanying figures, wherein the same reference numbers are
assigned to the same features or elements illustrated in different
figures. Note that the figures may not be drawn to scale. Further,
there may be other embodiments of the present invention explicitly
or implicitly described in the specification that are not
specifically illustrated in the figures and vise versa.
BRIEF DESCRIPTION OF THE DRAWINGS
[0024] FIG. 1 illustrates a micro-fluidic system having an
anti-microbial filter in accordance with a preferred embodiment of
the present invention.
[0025] FIGS. 2A-K illustrate, in a sequence of cross-sectional
views, a micro-machined fabrication process for making the
anti-microbial filter of FIG. 1 according to the present
invention.
[0026] FIG. 3 illustrates a flowchart describing a method for
making the anti-microbial filter using the micro-machined
fabrication process of FIGS. 2A-2K.
[0027] FIG. 4 is a top plan view of the anti-microbial filter of
FIG. 1.
[0028] FIG. 5 is a front elevation view of the anti-microbial
filter of FIG. 1.
[0029] FIG. 6 is a right side elevation view of the anti-microbial
filter of FIG. 1.
[0030] FIG. 7 is a plan view of the bottom of the anti-microbial
filter of FIG. 1.
[0031] FIG. 8 illustrates an elevation view of a semiconductor
construction for the upstream channel, the anti-microbial filter
and the downstream channel according to a first embodiment of the
present invention.
[0032] FIG. 9 illustrates an elevation view of a semiconductor
construction for the fluid source and the anti-microbial filter
according to a second embodiment of the present invention.
[0033] FIG. 10 illustrates an elevation view of a semiconductor
construction for the anti-microbial filter and the fluid sink
according to a third embodiment of the present invention.
DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS
[0034] FIG. 1 illustrates a micro-fluidic system 100 having an
anti-microbial filter 105 in accordance with a preferred embodiment
of the present invention. The micro-fluidic system 100 is
constructed using the MEMS technology described above. The
micro-fluidic system 100 generally includes a fluid source 101, an
upstream channel 103, the anti-microbial filter 105, a downstream
channel 107, a fluid sink 109, and fluid 113. The fluid source 101
is fluidly connected to the fluid sink 109 through the upstream
channel 103 and the downstream channel 107. The direction of fluid
flow 111 in the micro-fluidic system 100 is from the fluid source
101 to the fluid sink 109. The anti-microbial filter 105 filters
out microorganisms in the micro-fluidic system. In the preferred
embodiment of the present invention, the anti-microbial filter 105
prevents microorganisms from moving from the downstream channel 107
or the fluid sink 109 to the upstream channel 103 or the fluid
source 101. The anti-microbial filter 105 may filter fluid flowing
between two micro-fluidic components. Preferably, the
anti-microbial filter 105 filters fluid flowing between the
upstream channel 103 and the downstream channel 107. Alternatively,
the anti-microbial filter 105 may filter fluid flowing between the
fluid source 101 and the upstream channel 103, or between the
downstream channel 107 and the fluid sink 109, or between the fluid
source 101 and the fluid sink 109 without the upstream channel 103
or the downstream channel 107.
[0035] The fluid source 101 contains the fluid 113 and represents
any of the micro-fluidic components described above, including but
not limited to reservoirs, mixers, and chambers. Similarly, the
fluid sink 109 receives the fluid 113 and generically represents
any of the micro-fluidic components described above.
[0036] The upstream channel 103 and the downstream channel 107
carry the fluid 113 between the fluid source 101 and the fluid sink
109. The upstream channel 103 and the downstream channel 107 may be
formed as two separate channels connected by the anti-microbial
filter 105 or as one integral channel having the anti-microbial
filter 105 disposed therein. The fluid 113 flows from the fluid
source 101 to the fluid sink 109 responsive to pressure exerted on
the fluid 113. The pressure exerted on the fluid 113 may be
supplied from an external source or an internal source relative to
the micro-fluidic system 100. Examples of the external source of
pressure include, without limitation, gravity and rotating
mechanisms. An example of the internal source of pressure includes,
without limitation, a pump. Preferably, the pump is also a
component of the micro-fluidic system 100.
[0037] The fluid 113 may have any appropriate state that permits
fluid flow, such as a liquid state or a gas state. The fluid 113
represents any composition of matter appropriate for applications
of the micro-fluidic system 100, as described above. Examples of
fluids 113 include, without limitation, chemical, bodily,
hazardous, biological, and radiological fluids. Biological fluids
may be any biologically derived analytical sample, including,
without limitation, blood, plasma, serum, lymph, saliva, tears,
cerebrospinal fluid, urine, sweat, semen, and plant and vegetable
extracts.
[0038] The micro-fluidic system 100 in FIG. 1 represents a relative
simple system for the sake of clarity. In practice, the
micro-fluidic system 100 may be a very complex system having many
and/or duplicated micro-fluidic components, such as multiple
anti-microbial filters 105. The micro-fluidic system 100,
performing complex or parallel functions, typically needs many
anti-microbial filters 105, such as greater than ten anti-microbial
filters 105, to filter the fluids 113 moving throughout different
parts of the micro-fluidic system 100 at the same time or different
times. Therefore, it is desirable for the anti-microbial filters
105 to be compact, reliable, simple to fabricate, and easily
integrated with the rest of the micro-fluidic system 100.
[0039] FIGS. 2A-2K illustrate, in a sequence of cross-sectional
views, a micro-machined fabrication process for making the
anti-microbial filter 105 of FIG. 1 in accordance with the
preferred embodiment of the present invention. The FIGS. 2A-2K
illustrate various materials being added or being removed to create
the features of the anti-microbial filter 105. FIG. 3 illustrates a
flowchart describing a method for making the anti-microbial filter
105 using the micro-machined fabrication process, as shown in FIGS.
2A-2K. The method includes a sequence of steps 302-312, inclusive.
The steps 302-312 shown in FIG. 3 correspond to the cross-sectional
views of FIGS. 2A-2K, respectively. Next, each of the steps in FIG.
3 and the corresponding cross-sectional view in FIGS. 2A-2K are
described in detail.
[0040] At step 302 in FIG. 3, corresponding to FIG. 2A, a substrate
211 is provided. The substrate 211 may be formed of any material
that is compatible with the micro machined fabrication process.
Preferably, the substrate 211 is made of silicon. The substrate 211
is constructed using methods that are well known in the art of
semiconductor manufacturing processing. The substrate 211 generally
provides the foundation or platform on which to build the
anti-microbial filter 105. The substrate 211 may have a thickness
in the range of one to hundreds of microns, and is preferably 3
micrometers thick. In the preferred embodiment of the present
invention, the substrate 211 also provides structural support for
the anti-microbial filter 105, as a finished device, in the
MEMS.
[0041] At step 303 in FIG. 3, corresponding to FIG. 2B, substrate
mask material 200 is deposited on the first, preferably bottom,
side of the substrate 211. The substrate mask material 200 may be
formed of any material that is compatible with the micro machined
fabrication process. Preferably, the substrate mask material 200 is
silicon dioxide. Preferably, the substrate 202 and the substrate
mask material 200 are provided together as a manufactured wafer.
The substrate mask material 200 may be deposited on the substrate
211 using a variety of methods that are well known in the art of
semiconductor manufacturing processing. The substrate mask material
200 may have a thickness in the range of hundreds to thousands of
angstroms thick, and is preferably 1000 angstroms thick. The
substrate mask material may be deposited on the substrate 211 using
a variety of methods that are well known in the art of
semiconductor manufacturing processes. The substrate mask material
200 is used later in the micro-machining process to form a
substrate mask 212 for the substrate 211.
[0042] At step 304 in FIG. 3, corresponding to FIG. 2C, filter
material 201 is formed on the second, top side of the substrate
211. The filter material 201 may be formed of any material that is
compatible with the micro machined fabrication process. In the
preferred embodiment, the filter material 201 is deposited on the
substrate 211 using deposition processes such as electrochemical,
ultrasonic spray, aerosol, or spin-on, that are well known in the
art of semiconductor processing. Alternatively, the filter material
201 may be formed on the surface of the substrate 211 by doping the
top surface of the substrate 211 with a silicon compatible
material, such as boron. In this case, the thickness of the filter
material corresponds to the depth of penetration of the filter
material 201 into the surface of the substrate 211. When the filter
material 201 is deposited, preferably, the filter material 201 is
polysilicon, but may also be nitride, epitaxy, and the like. The
filter material 201 may have a thickness in the range of 0.1-100
micrometers, and is preferably 3-5 micrometers thick. The filter
material 201 is used later in the micro-machining process to form a
filter membrane 213 for the anti-microbial filter 105, as a
finished device, in the MEMS.
[0043] At step 305 in FIG. 3, corresponding to FIG. 2D, openings
220 are formed in the substrate mask material 200 to form the
substrate mask 212. The openings 220 may otherwise be known as
recesses, wells, cavities, and the like. The openings 220 are
formed in the substrate mask material 200 using a variety of
methods, such as photo-resist with an etch process, that are well
known in the art of semiconductor processing. The openings 220
extend through the substrate mask material 200 to the bottom
surface of the substrate 211 so that portions of the bottom surface
of the substrate are exposed. The openings 220 formed in the
substrate mask 212 define areas on the bottom side of the substrate
211 that are removed later to form the filter supports. The
openings 220 may be formed after any step in the method in FIG. 3
or after any sequence in FIGS. 2B-2K that is appropriate or
desirable because the formation of the openings is not dependent on
another step. However, the openings 220 need to be formed in the
substrate mask material before the openings 224 can be formed in
the substrate 211 to form the filter supports (see FIG. 2I).
[0044] At step 306 in FIG. 3, corresponding to in FIG. 2E, spacers
214 are deposited on the top surface of the filter material. The
spacers 214 may be formed of any material that is compatible with
the micro machined fabrication process. Preferably, the spacers are
formed of polystyrene, but may also be formed of silica, polymeric,
carboxylate (COOH) polystyrene, and the like. The spacers 214 may
have any shape and size. Preferably, the spacers 214 are spheres
having a diameter in the submicron range. Alternatively, the
spacers 214 may be cubes, ovals, and irregular or random shapes.
The spacers 214 may be solid or hollow. The spacers 214 deposited
on the filter material preferably each have the same or nearly
similar shapes and sizes, but may also have different shapes and
sizes. In the preferred embodiment of the present invention, the
spacers 214 are spheres having part number P0002100N from Bangs
Lab, 9025 Technology Drive, Fishers, Ind. 46038-2886. In the
preferred embodiment, the spacers 214 are deposited on the
substrate 211 using deposition process such as electrochemical,
ultrasonic spray, aerosol, or spin-on, that are well known in the
art of semiconductor processing. The spacers 214 are preferably
deposited as a single layer of spacers 214 arranged in a
side-by-side relationship, but may also be deposited as multiple
layers if desired and appropriate. The spacers 214 may be deposited
in a random or predetermined pattern, as desired and appropriate.
Preferably, the spacers 214 are carried in a liquid during the
deposition process, leaving only the spacers 214 when the liquid
dries. The spacers 214 naturally adhere to the surface of the
filter material 201 made of polysilicon, but may be made to be
attracted to the filter material by using the electrophoresis
deposition process, described above, which also increases the
density of the spacers 214. The spacers 214 may have any diameter
or thickness in the range of 0.05-0.5 micrometers, and are
preferably 0.2 micrometers thick. As best seen in FIG. 7H, the
spacers 214 are used later in the micro-machining process to form
holes 222 in a filter mask 215 for the anti-microbial filter 105.
Generally, the diameter of the spacers 214 corresponds to the
diameter of the holes 222 in the filter mask 215 that, in turn,
correspond to the holes 218 in the filter membrane 213 of the
anti-microbial filter 105. Therefore, special consideration should
be given to the size of the spacers 214 because the size of each
spacer 214 indirectly relates to the size of the microorganisms
that need to be filtered.
[0045] At step 307 in FIG. 3, corresponding to FIG. 2F, filter mask
material is deposited around the spacers 214 on the filter
material. Preferably, the filter mask material does not completely
cover the spacers 214. Further, the filter mask material does not
come between the spacers 214 and the filter material 201 where the
spacers 214 contact the filter material. In practice, the filter
mask material extends about one-half way underneath the spheres
because of the curved shape of the spheres against the relatively
flat surface of the substrate and the method of deposition used.
This relatively imprecise application of the filter mask material
is acceptable because the end goal is to have holes 218 in the
filter membrane 213 that correspond to the diameter of the spacers
214, as is described later with the remaining steps. The filter
mask 215 may be formed of any material that is compatible with the
micro machined fabrication process. In the preferred embodiment,
the filter mask material is deposited on the filter material 201
using deposition processes such as electrochemical, ultrasonic
spray, aerosol, or spin-on, that are well known in the art of
semiconductor processing. Preferably, the filter mask 215 is formed
of material that does not permit ions to pass through it. Hence,
the filter mask 215 may be formed from most refractory metals such
as titanium, chrome, tungsten, platinum, nickel, and the like. The
filter mask material may have a thickness in the range of 0.05-0.3
micrometers, and is preferably 0.05 micrometers thick. The filter
mask material is used later in the micro-machining process to form
a filter mask 215 for the anti-microbial filter 105.
[0046] At step 308 in FIG. 3, corresponding to FIG. 2G, the spacers
214 are removed to form holes 222 in the filter mask material to
provide the filter mask 215, otherwise called a filter template.
The spacers 214 may be removed using any method that is compatible
with the micro machined fabrication process. Preferably, the
spacers 214 are removed by dissolving the spacers 214 with
solutions, such as an acid solution, a base solution or an
oxidizing solution. For example, hydrogen peroxide and sulfuric
acid each dissolve spacers 214 formed of a polymeric material.
Also, for example, acetone can dissolve spacers 214 formed of
organics. Alternatively, the spacers 214 may be removed by
disintegrating the spacers 214 using processes, including but not
limited to ultrasound, ethylenediamine-pyrocatechol-water (EDP),
and the like. In practice, since the filter mask material extends
about one-half way underneath the spacers 214, as described in step
307, the holes 222 in the filter mask material have a diameter of
about one-half the diameter of the spacers 214. In the preferred
embodiment of the present invention, it is interesting to note that
the process forms the holes 222 in the filter mask 215 by removing
an element (i.e., the spacers 214), formed of one material, from
the filter mask material, formed of a different material. This
preferred method of forming the holes in the filter mask 215 is in
contrast to more expensive, time consuming and less precise methods
of forming holes in a filter mask, such as by an electron beam,
deep ultraviolet light, x-ray, or photolithography.
[0047] At step 309 in FIG. 3, corresponding to FIG. 2H, holes 218
are formed in the filter material using the filter mask 215 to form
the filter membrane 213. The holes 218 extend through the thickness
of the filter material. The holes 218 may be formed using any
process that is compatible with semiconductor manufacturing
processing. In the preferred embodiment of the present invention, a
directionally controlled etching process is used to form the holes
218. Preferably, a reactive ion etching (RIE) process is used, but
other processes such as ion beam milling may also be used. During
the RIE process, ions bombard the filter mask 215. Because of the
material of the filter mask 215, as described above in step 307,
the ions bounce off the filter mask 215. However, the holes 222
formed in the filter mask 215, as described in step 308, permit the
ions to pass through the holes 222 to reach the filter material on
the opposite side of the filter mask. The ions react with the
filter material to cause the filter material to be selectively
removed, as is well known in the art of semiconductor manufacturing
processing, to create the holes 218 in the filter material. The
speed of formation of the holes 218 and depth of the holes 218 is
dependent upon factors such as the intensity and duration of the
ion bombardment as well as the filter material. The holes 218
formed in the filter membrane 213 tend to be a little larger than
the holes 222 in the filter mask 215 by about one-half the
dimension of the spacers 214 due to a bleed through or fringe
effect of the ions passing through the holes 222 in the filter mask
215. Since, the holes 222 formed in the filter mask 215, have a
diameter about one-half the diameter of the spacers 214, the holes
218 in the filter material having a dimension approximately equal
to the dimension of the spacers 214. The holes 218 in the filter
material are sized appropriately to effectively filter out unwanted
microorganisms.
[0048] At step 310 in FIG. 3, corresponding to FIG. 2I, holes 224
are formed in the substrate 211 to form the filter supports. The
use of filter supports is optional and depends on the structural
and material integrity of the filter membrane 213, as well as the
construction and material of the MEMS that the filter membrane 213
is integrated with. The holes 224 may be formed using any process
that is compatible with semiconductor manufacturing processing, as
is well known in the art. The holes 224 extend through the
thickness of the substrate 211 and correspond to the openings 220
formed in the substrate mask material 200, as described in step
305. The holes 224 in the substrate 211 expose the holes 218 in the
filter membrane 213. By selectively removing the substrate material
to form the holes 224, the substrate material that remains forms
the filter supports. The number and location of the filter supports
may vary as desired and appropriate.
[0049] At step 311 in FIG. 3, corresponding to FIG. 2J, the filter
mask material and the substrate mask material are removed using
methods that are well known in the art of semiconductor
manufacturing processing.
[0050] At step 312 in FIG. 3, corresponding to FIG. 2K, a coating
216 is deposited on the side of the filter membrane 213 that is
remote from the filter supports. The coating 216, otherwise known
as a film, may be deposited using any process that is compatible
with semiconductor manufacturing processing, such as
electrochemical, ultrasonic spray, aerosol, or spin-on, that are
well known in the art of semiconductor processing. Preferably, the
coating 216 is formed of a material that does not permit
microorganisms to adhere to it and/or kills microorganisms that
contact the coating 216. Preferably, the coating 216 is formed of
silver. The coating 216 may have a thickness in the range of 0.05
to several microns thick, and is preferably 0.1 micrometers thick.
Preferably, the coating 216 is deposited on the downstream side of
the filter membrane 213. When fluid flows through the filter
membrane 213, the pressure of the fluid typically keeps the
microorganisms from moving upstream against the pressure of the
fluid to reach the fluid source. However, when or if the pressure
of the fluid flow stops, the microorganisms may try to move, by
migration or diffusion, upstream through the filter membrane 213.
In this case, the coating 216 prevents or inhibits such movement.
Depending on the application for the filter membrane 213, the
coating 216 is optional.
[0051] The steps described above advantageously produce an
anti-microbial filter 105 that is small enough to be used in the
micro-fluidic system 100. The anti-microbial filter 105 is
constructed using micro-machining processes to permit it to be
integrated into the micro-fluidic system 100. The anti-microbial
filter 105 has precisely defined hole sizes that are cost effective
and easy to manufacture. The filter 105 reliably filters out
unwanted microorganisms. In the preferred embodiment of the present
invention, the anti-microbial filter 105 is used in miniature or
micro-sized intravenous or implanted drug delivery systems.
[0052] FIGS. 4-7 illustrate the top, front, right and bottom views
of the anti-microbial filter 105 respectively. FIGS. 5 and 6 show
the coating 216 disposed on the filter membrane 213 that is formed
on the substrate 211. FIGS. 4 and 7 show the holes 218 formed in
the anti-microbial filter 105. FIG. 7 shows the substrate 211
formed as filter supports comprising a wall along the perimeter of
the filter 105 and six posts inside the perimeter of the filter
105. FIG. 4 shows the filter supports with dashed lines because
they are hidden in this view.
[0053] The size and shape of the anti-microbial filter 105, as
viewed in the FIG. 4 and FIG. 7, may vary as desired and
appropriate for a particular application. The shape of the
anti-microbial filter 105, as viewed in FIGS. 4 and 7, may be
square, rectangular, round, oval, a shape having any number of
sides, as well as any irregular shape. In the preferred embodiment
of the present invention, the size of the anti-microbial filter
105, as viewed in FIGS. 4 and 7, is in the range of tens of microns
to several millimeters and is preferably 1 mm.times.1 mm. In the
preferred embodiment of the present invention, the thickness of the
anti-microbial filter 105, as viewed in the elevation views FIGS. 5
and 6, is in the range of 0.1 and 50 micrometers and is preferably
3 micrometers.
[0054] Next, FIGS. 8, 9 and 10 are described together. FIG. 8
illustrates an elevation view of a semiconductor construction for
the upstream channel 103, the anti-microbial filter 105 and the
downstream channel 107 in accordance with one embodiment of the
present invention. FIG. 9 illustrates an elevation view of a
semiconductor construction for the fluid source 101 and the
anti-microbial filter 105, in accordance with another embodiment of
the present invention. FIG. 10 illustrates an elevation view of a
semiconductor construction for the anti-microbial filter 105 and
the fluid sink 109, in accordance with another embodiment of the
present invention.
[0055] Generally, in FIGS. 8, 9 and 10, the upstream channel 103,
the downstream channel 107, the anti-microbial filter 105, the
fluid source 101 and the fluid sink 109 are formed using
micro-machining processes and materials compatible with
semiconductor construction. Preferably, the semiconductor
construction is planar to permit the upstream channel 103, the
downstream channel 107, the anti-microbial filter 105, the fluid
source 101 and the fluid sink 109 to be assembled in a stacked
arrangement using known assembly processes and materials. Any of
the individual elements may be integrated with each other, if
desired and appropriate for a particular application. The coating
216 on the anti-microbial filter 105 is orientated to be on the
downstrearn side of the anti-microbial filter 105 to prevent
microorganisms from moving upstream through the filter 105.
[0056] In FIG. 8, the upstream channel 103 and the downstream
channel 107 represent a fluid channel, preferably formed in
semiconductor material, using micro-machining techniques.
Preferably, the fluid flows into the right side of the upstream
channel 103, but may alternatively flow into the left side of the
upstream channel 103 (as shown by dashed lines) or into both the
right and left sides of the upstream channel 103. Likewise, the
fluid flows out of the left side of the downstream channel 107, but
may alternatively flow out of the right side of the downstream
channel 107 (as shown by dashed lines) or out of both the left and
right sides of the downstream channel 107. The anti-microbial
filter 105 is disposed between the upstream channel 103 and the
downstream channel 107. The substrate 211 forming the filter
support contacts the upstream channel 103. The coating 216 on the
filter membrane 213 contacts the downstream channel 107.
[0057] In FIG. 9, the fluid source 101 directly contacts the
anti-microbial filter 105, without having the upstream channel 103
disposed between the fluid source 101 and the anti-microbial filter
105. In this case, the substrate 211 forming the filter support
contacts the fluid source 101.
[0058] In FIG. 10, the fluid sink 109 directly contacts the
anti-microbial filter 105, without having the downstream channel
107 disposed between the fluid sink 107 and the anti-microbial
filter 105. In this case, the coating 216 contacts the fluid sink
107.
[0059] Hence, while the present invention has been described with
reference to various illustrative embodiments thereof, the present
invention is not intended that the invention be limited to these
specific embodiments. Those skilled in the art will recognize that
variations, modifications and combinations of the disclosed subject
matter can be made without departing from the spirit and scope of
the invention as set forth in the appended claims.
* * * * *