WO1995008716A2

WO1995008716A2 - Micromachined valve apparatus

Info

Publication number: WO1995008716A2
Application number: PCT/US1994/009319
Authority: WO
Inventors: Cynthia R. Nelson; Fred C. Sittler; Gregory A. Boser
Original assignee: Rosemount Analytical Inc.
Priority date: 1993-09-24
Filing date: 1994-08-18
Publication date: 1995-03-30
Also published as: CN1133080A; JPH09505130A; CA2169826A1; WO1995008716A3

Abstract

A valve controlling fluid flow includes a brittle layer (12) of material having a port opening (30, 32) therein and a valve seat (24A-24F) disposed about a perimeter of the port opening (30, 32). The valve seat (24A-24F) is selectively covered to control fluid flow through the port opening (30, 32). A second layer of material (20) is spaced apart from the brittle layer (12) and has a surface facing the valve seat (24A-24F). A flexible sheet of material (18) sandwiched between the brittle layer of material (12) and the second layer of material (20) includes a diaphragm (22A-22F) actuated by a control force to selectively cover the valve seat (24A-24F) to thereby control fluid flow through the port opening (30, 32). The flexible sheet of material (18) includes a moldable material (64) a portion of which conforms to a contour of the valve seat (24A-24F). The moldable material (64) is preferably joined to a flexible organic material (66).

Description

røCROMACHENED VALVE APPARATUS

BACKGROUND 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 batch 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 input 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^"10 at cc He/sec), the valves of this construction do not satisfy the sealing requirements. 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 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 1 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; Figures 3A through 3F are a sequence of representative views illustrating a second method for making the improved micromachined valve of the present invention; Figures 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 1 illustrates a micromachined valve assembly 10 used in a gas chromatography analysis device, not shown. Generally, the valve assembly 10 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 22A, 22B, 22C, 22D, 22E, and 22F included in the layer 18.

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 photolithography techniques including etchingprocesses, 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 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 10"¹⁰ 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 10 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 10 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 10 and its construction is hereby incorporated by reference. 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 wafer 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 technique illustrated using Teflon FEP film, the valve is heated to a temperature of 265° - 350° Celsius and a pressure of 20-100 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 20 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 remaining on the contoured edges 60.

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 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 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 ther oset polymer includes 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 maximize the degree of ther osetting or cross-linking, a thermoplastic polymer (Kapton-TefIon PFA) is bonded and formed in a vacuum to the polyimide, as illustrated in Figure 5C. If a spin-on, sprayed or cast adhesive, 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. 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 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 liquid, the polyimide molds to the contour 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 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 (applying 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 control ports, for example, port 142 through which a control force is 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 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.

Claims

WHAT IS CLAIMED IS:

1. A micromachined fluid handling device responsive to a control force, comprising: a base layer of material having a surface; and a moveable layer of material having a recess for handling fluid, the recess opening toward the base layer, the movable layer having a perimeter defining the recess, the moveable layer held relative to the base layer such that at least a portion of the perimeter releasably contacts the surface of the base layer as a function of the control force.

2. The micromachined fluid handling device of claim 1 wherein the base layer includes: a first port opening and a first valve seat disposed about a perimeter of the first port opening; and a second port opening and a second valve seat disposed about a perimeter of the second port opening; and wherein the moveable layer includes: a first diaphragm portion regulating fluid flow through the first port opening; and a second diaphragm portion regulating fluid flow through the second port opening; and wherein the recess comprises a channel providing fluidic communication between the first and second port openings.

3. The micromachined fluid handling device of claim 2 wherein the base layer further includes a third port opening and a third valve seat disposed about the third port opening, and wherein the moveable layer includes a third diaphragm portion regulating fluid flow through the third port opening.

4. The micromachined fluid handling device of claim 2 and further comprising channel means for fluidly connecting the first and second port openings, the channel means having a portion of reduced sectional area to induce a pressure differential between the first and second port openings.

5. The micromachined fluid handling device of claim 4 and further comprising a third layer of material held to the base layer on a side opposite the movable layer, the channel means comprising a second channel formed in the third layer.

6. The micromachined fluid handling device of claim 2 wherein the base layer is made of a brittle material.

7. The micromachined ...aid -handling device of claim 1 wherein the moveable layer comprises a flexible organic material bonded to a moldable material, wherein the moldable material faces the surface of the base layer and includes the recess.

8. The micromachined fluid handling device of claim 7 wherein the moldable material comprises a polymer.

9. The micromachined fluid handling device of claim 1 wherein the base layer includes an opening for fluidic communication with the recess and a valve seat disposed about a perimeter of the opening; and wherein the moveable layer includes a diaphragm portion displaced by the control force relative to the valve seat to regulate fluid flow through the opening to the recess.

10. The micromachined fluid handling device of claim 9 wherein the moveable layer includes a release material bonded to a surface of the moveable layer facing the valve seat, the release material releasably engaging the valve seat.

11. The micromachined fluid handling device of claim 9 wherein the moveable layer includes a plug portion mating with the valve seat.

12. A valve regulating fluid flow in response to a control force, comprising: a brittle layer of material having a port opening therein and a " valve seat disposed about a perimeter of the port opening; and a flexible sheet of material held to the brittle layer of material, and including a diaphragm portion actuated by the control force for selectively covering the valve seat to control fluid flow through the port opening, the flexible sheet of material comprising a moldable material proximate the valve seat.

13. The valve of claim 12 wherein the flexible sheet includes a flexible organic material joined to the moldable material.

14. The valve of claim 12 wherein the flexible sheet includes a release material bonded to the moldable material, the release material releasably engaging the valve seat.

15. The valve of claim 14 wherein the flexible sheet includes a plug portion mating with the valve seat, the release material being bonded to and covering the plug portion.