Note: Descriptions are shown in the official language in which they were submitted.
WO 95/08716 PCT/US94109319
~ 2169826
MICROMACHINED VALVE APPARATUS
~3ACKGROUND OF THE INVENTION
The present invention relates to miniature,
micromachined valves. More particularly, the present
invention provides an improved valve seat that is helium
hermetic in addition to a valve assembly that provides
a small accurate sample volume of gas.
Various miniature, micromachined valves have
been advanced in the prior art. In U.S. Patent No.
4,869,282, the valves are micromachined to make valve
passageways and openings in a silicon layer during batc.
processes utilizing known micromachining techniques,
such as photolithography and etching techniques. If
glass layers are used, the channels or passageways can
be molded in place. An organic diaphragm layer,
preferably a polyimide such as Kapton~, manufactured by
DuPont, is fused to the silicon layer around a perimeter
of a cavity. The organic diaphragm film functions as a
valve diaphragm selectively sealing the valve seat and
preventing gas flow through the port opening.
One particular disadvantage of the valves
having construction as described above and as taught in
U.s. Patent 4,869,282 is that the valves tend to leak a
small amount when the valves are in the "closed" state.
For many applications, the small amount of leakage is
insignificant and the valves of that construction
operate satisfactorily. However, in other applications,
such as a sample control valve connected to an inpL
port of mass spectrometer where a high vacuum must be-
maintained on one side of the valve and where the valve
must make a helium hermetic seal (10-l atm cc He/sec),
the valves of this construction do not satisfy the
sealing requirements.
r
WO95/08716 PCT~S94/09319
6q 8~6 -2-
SUMMARY OF THE INVENTION
A valve controlling fluid flow includes a
brittle layer of material having a port opening therein
and a valve seat formed about a perimeter of the port
opening. The valve seat is selectively covered to
control fluid flow through the port opening. A flexible
sheet of material held to the brittle layer of material
to form a diaphragm is actuated through a control force
to selectively cover the valve seat and control fluid
flow through the port opening. The flexible sheet of
material includes a moldable material, at least a
portion of which molds to a contour of the valve seat.
The moldable material is preferably joined to a flexible
organic material.
Preferably, the flexible organic material
comprises Kapton film, while various thermoplastic and
thermoset polymers can be used for the moldable
material. For instance, Teflon FEP and Teflon PFA both
manufactured by Dupont are suitable thermoplastic
polymers that mold well through the use of suitable heat
and pressure, while ~castable~ thermosetting polymers
such as high-planarity spin-on polyimides molded to the
valve seats during fabrication also work very well. For
the aforementioned polymers in one fabrication
technique, a release material such as gold without an
adhesion layer is patterned on the valve seat wafer and
then bonded to a surface of the polymer during the
molding process to prevent adhesion of the polymer to
the valve seat.
The present invention further includes a
micromachined valve assembly that can accurately provide
a small metered volume of gas heretofore not provided in
the prior art. In a first preferred embodiment, the
WO95/08716 PCT~S94/09319
~ 6982~
valve assembly includes a ,brittle layer of material
having a first and second port opening with a
corresponding valve seat formed about a perimeter of
each port opening. A second layer of material is spaced
apart from the brittle layer, and a flexible sheet of
material is sandwiched between the brittle layer of
material. The flexible sheet of material includes first
and second diaphragm portions that selectively cover the
first and second valve seats. The flexible sheet
further includes a channel, preferably formed therein,
that fluidly communicates with the first and second port
openings .
In the preferred embodiment, the channel also
fluidly communicates with a third port opening having a
third valve seat about its perimeter formed in the
brittle layer. A third diaphragm portion of the
flexible sheet further controls fluid flow through the
third port opening by selectively covering the third
valve seat. The valve assembly provides a metered small
sample of gas by diverting a portion of the gas to be
tested into the channel formed in the flexible sheet by
uncovering the first and second valve seats with the
third port opening closed. By then closing the first
and second port openings and subsequently uncovering the
third port opening, the metered sample of gas entrapped
within the channel is provided to a selected instrument
or device.
BRIEF DESCRIPTION OF THE DRAWINGS
Figure l is an exploded view of a gas
chromatograph valve assembly;
Figures 2A through 2C are a sequence of
representative views illustrating a method for making an
improved micromachined valve of the present invention;
.
WO95/08716PCT~S94/09319
.
2~ 69&26
Figures 3A through 3F are a sequence of
representative vi~ws illustrating a second method for
making the improved micromachined valve of the present
invention;
5Figures 4A through 4D are a sequence of
representative views illustrating a third method for
making the improved micromachined valve of the present
invention;
Figures 5A through 5E are a sequence of
representative views illustrating a fourth method for
making the improved micromachined valve of the present
invention;
Figure 6 is an exploded view of a valve
assembly of present invention for providing a selected
sample volume of a test gas and illustrating a fifth
method for making the improved micromachined valve of
the present invention;
Figure 7 is a sectional view of the valve
assembly of Figure 6 taken along lines 7--7 and
including a stop layer; and
Figure 8 is a schematic representation of the
valve assembly of Figure 6.
DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS
Figure l illustrates a micromachined valve
assembly l0 used in a gas chromatography analysis
device, not shown. Generally, the valve assembly l0
comprises a sandwich construction of several individual
layers bonded together, including a valve seat wafer or
layer 12 having an upper valve seat surface 14, a
flexible layer 18, and a stop layer 20 having means for
controlling deflection of individual diaphragm portions
WO95/08716 2 1 6 9 8 2 6 PCT~S94/09319
-5-
22A, 22B, 22C, 22D, 22E, and 22F included in the layer
lB.
Each of the diaphragm portions 22A-22D are
aligned with corresponding valve seats 24A, 24B, 24C,
24D, 24E and 24F formed on the upper surface valve seat
surface 14. Each diaphragm portion 22A-22F seals two
valve ports indicated at 30 and 32 in each of the valve
seats 24A-24F, respectively. The valve ports 30 and 32
fluidly connect to a lower channeling layer 34, which
interconnects each of the valve sections as illustrated
by arrows 38.
Actuation gas flow through the valve assembly
10 is controlled through ports 40A, 40B, 40C, 40D, 40E
and 40F which typically control deflection of each of
the diaphragm portions 22A-22F with suitable pressure
differentials applied thereto. Channels 50, 51, 52, 53,
54, and 55 formed in the layer 20 and additional
channels formed in an upper layer 56 direct actuating
fluid to the control ports 40A-40F.
When the valve assembly 10 is made, the Layers
are micromachined, such as through the use of known
photolithographytechniques includingetchingprocesses,
or through the use of electrostatic discharge machining
(EDM), or, if glass layers are utilized, through the use
of molding or laser machining processes when the glass
layers are formed to create any necessary channels.
The materials can be any desired semi-
conductor material or other brittle materials that are
non-reactive to the gases used. Silicon is a useful
material for the valve seat layer 12, stop layer 20, the
channeling layer 34, and the upper layer 56. Other
materials such as glass or sapphire also can be used for
,.
WO95/08716 PCT~S94109319
69 ~6 -6-
one or more of the layers. The layers do not have to be
all one type of material.
The valve assembly of the prior art, although
suitable for substantially controlling gas flow did not
provide a helium hermetic seal (a seal on the order of
lO10 atm cc He/sec). In the past, both uncoated and
metal-coated flexible organic material, such as Kapton
manufactured by Dupont, had been used as the diaphragm,
the remainder of the flexible layer being sealed to the
silicon layer with a relatively low temperature glass
frit, but this construction did not produce a helium
leak type seal. In general, the present invention can
provide a helium leak type seal by providing a moldable
material that retains its molded shape during valve
operation. The moldable material, such as a thermoset
or a thermoplastic polymer material, is joined or bonded
to the flexible organic material. A release layer
joined to the moldable material defines the diaphragm
portion of the combined flexible organic/moldable
material, the release material contacting the valve seat
when in the valve is closed. The release layer isolates
the moldable material from the valve seat and prevents
adhesion of the moldable material to the valve seat.
The valve assembly lO incorporates bonding
techniques and materials of the layer 18 of the present
invention described below with reference to any set of
the sequence drawings of Figures 2A-2C, 3A-3F, 4A-4D and
5A-5E, or the exploded view of Figure 6. The valve
assembly lO is used herein for illustrative purposes and
is but one useful embodiment. U.S. patent 4,869,282
which describes operation of the valve assembly lO and
its construction is hereby incorporated by reference.
WO95/08716 ~ 825 PCT~S94/09319
--7--
Referring to Figure 2A, the layer 12 is etched
to provide ports 30 and 32. Preferably, to improve
sealing characteristics, the ports 30 and 32 are
provided with contoured edges 60; however, the
contoured edges 60 are not necessary. A release
material 62, such as gold, that resists adhesion to the
layer 12 and bonds to a moldable material 64, such as a
thermoplastic Teflon FEP film manufactured by Dupont, is
patterned to the valve seat 24 with suitable sputtering,
evaporation, or electroless plating methods. The
patterned moldable material 64 is typically already
joined to a flexible organic material 66 (i.e.
colaminated), such as Kapton manufactured by Dupont.
The patterned flexible layer 18 is then bonded to
surface 14 of the valve seat layer 12. In addition to
colaminated film, Dupont also manufactures both Teflon
FEP and Kapton films separately, which can be used.
Referring to Figure 2B, the patterned organic
material/moldable material layer 18 is bonded to the
stop wafer 20. If desired, an additional static bonding
layer 61 of suitable material such as Teflon FEP film
may be used between the organic material 66 and the stop
layer 20. The stop layer 20 includes the control port
40, which is used during valve operation to control
displacement of the diaphragm portion. The completed
wa~er stack is then diced, and individual valves are die
attached to a housing, not shown, using a suitable
bonding material.
To provide helium hermetic seals, the moldable
material 64 is then molded to the valve seat 24 as
illustrated in Figure 2B by heating the valve and
applying pressure, a fabrication technique hereinafter
referred to as "thermoformed". In the fabrication
WO95/08716 PCT~S94109319
~2~ 6q~6 -8-
technique illustrated using Teflon FEP film, the valve
is heated to a temperature of 265 - 350 Celsius and a
pressure of 20-lO0 psi is applied across the diaphragm
portion 22 through the control port 40. The thermoform
fabrication technique provides a flexible diaphragm
portion 22 which is formed to the contour of the valve
seat 24. The patterned release layer 62 prevents
adhesion of the moldable material 64 to the valve seat
24 and the contoured edges 60 during valve operation.
A prototype valve using Teflon FEP film for
layer 64 was observed to maintain a helium hermetic seal
of the valve seat 24 after repeated cycling at
temperatures of approximately 80 Celsius. An increased
operating temperature can be achieved with other
suitable thermoplastic moldable materials for layer 64,
such as Teflon PFA film manufactured by Dupont. Using
Teflon PFA film an increased pressure and temperature
may be necessary during the thermoforming fabrication
technique to properly mold the diaphragm to the valve
seat.
Figures 3A through 3F illustrate an
alternative method for forming a valve assembly of the
present invention. Beginning with the layer 12 etched
with the desired ports 30 and 32 as illustrated in
Figure 3A, the release material 62 is patterned on the
surface of the layer 12 to define the valve seat 24 in
the diaphragm area and on the contoured edges 60, if
provided, as illustrated in Figure 3B. The flexible
organic material/moldable material diaphragm 18
described above is then layered on top of the release
material 62 and bonded to the top surface of the layer
12 about the outer perimeter of the valve seat 24, as
illustrated in Figure 3C. In Figure 3D, the stop layer
WO95/08716 2 1 6 9 ~ 26 PCT~S94/09319
_g _
is then bonded to the flexible organic
material/moldable material sheet 18, if desired, with
the static bonding layer 61. Heat and gas pressure as
described above are applied according to the thermoform
fabrication technique to form the moldable material 64
to the valve seat 24 and contoured edges 60, as
illustrated in Figure 3E. After the heat and pressure
of the thermoform fabrication technique have been
removed, a suitable pressure is applied to the ports 30
and 32 to lift the diaphragm portion 22 from the valve
seat 24, as illustrated in Figure 3F. Since the
moldable material 64 bonds well with the release
material 62, while release material 62 bonds poorly with
the layer 12 due to the absence of an adhesion layer,
the release material 62 is transferred from the layer 12
to the moldable material 64 with some fragments 65
possibly re~; n; ng on the contoured edges ~0.
The process outlined above with reference to
Figures 3A - 3F provides a release layer 62 which is
much smoother than that described with reference to
Figures 2A - 2C, and which more accurately replicates
the contour of the valve seat 24.
Figures 4A through 4D provide yet another
method for producing the valve assembly of the present
invention. Referring to Figure 4A, the layer 12 is
etched to provide a thin web of material 70 (25
micrometers) in each of the ports 30 and 32. If
desired, the thin webs of material 70 can be recessed by
etching the silicon on both sides in order to provide
contoured edges 60. Alternatively, etching can occur
solely from the bottom side of the layer 12, whereupon
contoured edges will be absent. The release layer 62 is
patterned on the layer 12 including each of the webs 70
WOg~/08716 PCT~S94/09319
~ ~q ~
--10--
to define the valve seat 24. The flexible organic
material/moldable material diaphragm 18 described above
is then layered on top of the release material 62 and
formed and bonded in a vacuum to the top surfaces of
layer 12 and release material 62 at which time the layer
64 is molded to the contour of the valve seat 24. In
Figure 4C, the stop layer 20 is then bonded to the
flexible organic material/moldable material diaphragm 18
with a suitable bonding material 61 such as a Teflon
film or spun-on polyimide adhesive. The webs 70 are
then removed through plasma etching. A suitable
differential pressure is applied to the ports 30 and 32
to lift the diaphragm portion 22 away from the layer 12,
as illustrated in Figure 4D. The process illustrated in
Figures 4A through 4D produce a diaphragm portion 22
having a plug portion 73 mating with the valve seat 24
that is fully coated or encapsulated with the release
material 62 resulting in a more durable diaphragm
surface, which flows less at elevated temperatures,
since the moldable material 64 is partially constrained.
The release layer 62 provides a metal diffusion layer or
barrier to the process gas stream.
Figures 5A-5E illustrate yet another method
for producing the valve assembly of the present
invention. Referring to Figure 5A, the layer 12 is
etched to provide the thin web of material 70 (25
micrometers) in each of the ports 30 and 32. If
desired, the thin webs of material 70 can be recessed by
etching the silicon on both sides in order to provide
contoured edges 60. The release layer 62 is patterned
on the layer 12 including each of the webs 70 to define
the valve seat 24. In this method, the moldable
material 64 includes a thermoset solvent based polymer
W095J08716 ~ PCT~94/09319
72, such as a high planarity spin-on polyimide, which is
spun-on as a liquid and "cast" (solidified) onto and
molded to the patterned valve seat 24, as illustrated in
Figure 5B. Spin-on, sprayed or cast polyepoxyimide or
similar polymers can be used. Another possible
thermosetpolymerincludes Benzocyclobutene manufactured
by Dow Chemical Company. Preferably, an adhesion
promoter such as aluminum-oxide, is provided between the
release material 62 and the polyimide layer 72 since
adhesion of the polyimide as well as benzocyclobutene to
the release layer 62 such as gold is typically poor.
Following hard baking at 300-350 Celsius,
necessary to m~; m; ze the degree of thermosetting or
cross-linking, a thermoplastic polymer (Kapton-Teflon
PFA) is bonded and formed in a vacuum to the polyimide,
as illustrated in Figure 5C. If a spin-on, sprayed or
cast adhe=,ve, such as polyimide or polyepoxyimide
adhesive is used, the use of the thermoplastic adhesive
can be avoided with the resulting diaphragm portion 22
being harder, and more durable with less material flow
during high temperature service.
In Figure 5D, the stop layer 20 is then bonded
to the flexible organic material/moldable material
diaphragm 18 with a static bonding layer 61 of
thermoplastic Teflon FEP film, Teflon PFA film, or
thermoset polyepoxyimide adhesive. The webs 70 are
removed through plasma etching. A suitable pressure is
applied to the ports 30 and 32 to lift the flexible
diaphragm portion 22 away from the layer 12, as
illustrated in Figure 5E. The method described with
reference to Figures 5A-5E also produces the plug
portion 73 that is fully coated with the release
material 62.
WO95/08716 PCT~S94/09319
69 8~6 -12-
Figure 6 illustrates yet another method for
producing a valve assembly of the present invention and
in particular a sample volume valve assembly 100 capable
of providing a nanoliter sample volume of gas or other
fluid. The sample injection valve 100 includes a silicon
layer 101 micromachined to provide three valve seats
102A, 102B and 102C with ports 113, 119 and 125,
respectively. A second silicon layer 104 is etched to
provide a channel 106 connecting ports 113 and 119 in
layer 101. The channel 106 includes a portion 108 with
reduced sectional area sufficient to provide a pressure
differential between portions 110 and 112 of channel 102
when gas is forced therethrough. A branch channel 111
fluidly connects the channel portion 110 to port 113 in
the valve seat 102A, while a similar branch channel 115
fluidly connects the channel portion 112 to port 119 in
the valve seat 102C.
A release layer 114 such as gold is deposited
on each seat 102A-102C to define the diaphragm area for
20 each of the corresponding valves. Each valve seat 102A-
102C initially includes a web similar to the web 70
illustrated in Figure 5C.
A solvent based polyimide or polyepoxyimide
adhesive, such as IP542 Adhesive manufactured by Cemota,
69390 Vernaison, France, is spun-on, sprayed or cast on
the silicon layer 101 over the valve seats 102A-102C and
the corresponding webs and then baked for a suitable
duration to remove the solvent. Since the polyimide is
a initially li~uid, the polyimide molds to the contour
30 of the valve seats. The baked polyimide film 116 which
is left on the silicon layer 101 is patterned using a
NiChrome mask to remove material from a continuous
portion 103 by plasma etching, thereby to form a small
WO95/08716 2 1 6 9 ~ 2 6 PCT~S94/09319
,
-13-
channel 118 that intersects with each of the valve seats
- 102A-102C, thereby selectively fluidly connecting ports
113, 119, and a port 125 of valve seat 102B when the
corresponding valve diaphragms are operated. The
channel 118 defines the sample volume produced by the
injection valve. In the embodiment illustrated, the
channel 118 is masked and etched to provide a small
volume of a sample gas, for example, a nanoliter.
A flexible organic film 121 such as Kapton is
then stretched about a suitable fixture, not shown, and
the solvent based polyimide adhesive 123, is then spun-
on the flexible organic film 121 and baked to produce a
composite film indicated generally at 120. The
composite film 120 is then bonded (applylng heat and
pressure to the flexible organic film 121) to the etched
polyimide layer 116 to form a layer 117. Since mating
surfaces of both the layer 116 and the film 118 are a
type of polyimide, the resulting layer 117 is uniform
with the channel 118 encapsulated without filling in the
etched area. Characteristics of the polymer material
123 include being able to pattern and remove a portion
of the material and then bond the polymer with another
suitable polymer without filling in the portion that was
removed.
The webs of each valve seat 102A-102C are then
plasma etched and a suitable stop layer 140 (Figure 7),
similar to stop layer 20 in Figures 2C, 3F, 4D and 5E is
bonded to the Kapton-adhesive composite. The stop layer
140 is used to limit the deflection of the flexible
diaphragm portions 117A, 117B and 117C away from each of
the valve seats 102A-102C and includes con~rol ports,
for example, port 142 through which a control force is
WO95/08716 PCT~S94/0~319
~ 6q ~ 14-
provided to initiate deflection of the diaphragm
portions 117B.
Operation of the valve assembly 100 is
illustrated schematically in Figure 8. A gas source 130
is connected to the channel 106 at an end 132. The gas
flows through the channel 106 to a vent provided at the
opposite end 134 of the channel 106. When a sample of
the gas is desired, the corresponding diaphragm portions
117A and 117C for valves seats 102A and 102C are
displaced allowing a portion of the gas to flow through
the channel 118 etched in the layer 117 and the ports
113 and 119. This sample of gas enters the channel 118
due to the pressure differential across the reduced
sectional area portion 108 of the main channel 106. The
diaphragm portions 117A and 117C above valve seats 102A
and 102C are then actuated to close the corresponding
ports 113 and 119 so that the sample of the gas is
entrapped within the channel 118. The diaphragm portion
117B above the valve seat 102B is then displaced so that
the sample of gas exits the channel 118 through the port
125 provided in the valve seat 102B.
In the embodiment illustrated, the control
force for the flexible diaphragm on the valve seats 102A
and 102C is a low pressure provided on the surface of
the flexible organic material 121. The difference
between the low pressure and the high pressure in
channel 106 lifts the diaphragm 117 away from the
corresponding valve seat. The valve assembly 100 is
particularly well suited for use with ion mass
spectrometers where a small volume of gas, for example
less than 100 nanoliters, is provided for testing. The
valve assembly 100 provides a helium hermetic seal
across large pressure differentials thereby eliminating
WO95/08716 ~l 69826 PCT~S94/09319
-15-
the complexity associated with multistage pressure
reduction.
Referring to Figure 7, when used with an ion
mass spectrometer 143, the port 125 opens to the ion
mass spectrometer assembly 143. Since the ion mass
spectrometer 143 operates at very low pressures (10-6
atm), it is difficult to displace diaphragm 117B using
differential pressure. Instead, other means for
displacing the diaphragm 117B, such as an actuator 144
which pulls upon the flexible diaphragm 117, or
hydraulic fluid activated by a piston can be used.
Although the present invention has been
described with reference to preferred embodiments,
workers skiLled in the art will recognize that changes
may be made in form and detail without departing from
the spirit and scope of the invention.
