Abstract:
A micro-machined valve assembly includes a valve diaphragm that will not adhere to a valve seat during elevated temperature operation. The valve assembly has a valve seat, a diaphragm suspended over the valve seat, the diaphragm configured to contact the valve seat upon the application of an actuating pressure on the diaphragm. The diaphragm has a continuous film of a first material, where a portion of the first material in a region where the diaphragm contacts the valve seat includes a first metallic material. The absence of an adhesive or the addition of the metal layer extends the operating temperature of the valve by preventing adhesion of the diaphragm to the valve seat during high temperature operation. Selection of an appropriate material for the metal layer can improve chemical inertness of valve, thereby reducing the possibility that the material flowing through the valve will react with the metal.

Description:
CROSS-REFERENCE TO RELATED APPLICATION 
     This application is a continuation-in-part of commonly assigned U.S. patent application Ser. No. 09/553,910, entitled “EXTENDED RANGE DIAPHRAGM VALVE AND METHOD OF MAKING SAME,” filed on Apr. 20, 2000 now U.S. Pat. No. 6,412,751, and is hereby incorporated into this document by reference. 
    
    
     BACKGROUND OF THE INVENTION 
     Diaphragm valves are useful in many applications. One such application for a diaphragm valve is in a gas chromatograph that is used to perform chemical analysis. Gas chromatography is useful for determining the chemical composition of various materials. It is useful for analyzing minute quantities of complex mixtures from industrial, biological, environmental, and chemical sources. Gas chromatography is also useful for preparing moderate quantities of highly purified compounds otherwise difficult to separate from the mixture in which they occur. 
     Briefly described, gas chromatography is the process by which the components of a mixture are separated from one another by volatizing the sample into a carrier gas stream that is passed through and over a packed column. A packed column is a tubular gas conduit filled with a bed of packing comprising a 20-200 mesh solid support. The surface of the packing is typically coated with a relatively non-volatile liquid and is known as the stationary phase. Alternatively, the column can be a capillary tube having the stationary phase material coating the inside surface of the tube with no packing material. A carrier gas, such as helium, flows continuously in this column. When a gaseous sample is introduced into an entrance end of the column, the carrier gas carries the sample to the exit, or effluent, end. Different components of the sample under analysis move through the column at different rates due to different affinity and solubility of the components in the sample with respect to the stationary phase, and so appear separately at the effluent end. The time it takes for a specific component to travel from the inlet side of the column to the effluent side of the column is a characteristic of the component. 
     The effluent end is the end at which the components of the sample are detected. The detection is normally achieved by measuring physical or chemical properties of the effluent. The properties measured include thermal conductivity changes, density differences, optical absorption, or ionic detection. For a sample mixture having multiple components, the detector outputs a signal that can be represented by a pulse train having multiple peaks. The position of each peak relates to the type of the components in the mixture while the area of the peak relates to the quantity of that component in the mixture. 
     A gas chromatograph can be logically divided into three components. They are the injector, the column, and the detector. The injector measures and delivers a precise quantity of the sample under analysis into the column. The column separates the components in the sample. The detector detects and quantifies the components in the sample. 
     Because the injector controls the flow of minute quantities of the sample, or gas flow, it is preferably constructed using micro-machining manufacturing techniques. Such techniques allow the injector components to be fabricated to exact dimensions. The sample quantity can be accurately controlled either by a fixed volume or a time injection technique. In fixed volume injection, a fixed volume is first filled with the sample and then injected into the column. For time injection, both the flow rate and the time the sample is allowed to pass onto the column are controlled. In either technique, a set of diaphragm valves is used to control both the carrier, or column, flow and the sample flow. They are used to block and switch direction of the sample flow. 
     In a conventional diaphragm valve, a circular depression is created on a flat surface. Inside the depression are two valve ports that are connected to separate external fluid connections. A diaphragm fabricated of a flexible material is positioned above the valve ports such that there is a gap between the diaphragm and the surface of the valve ports. Application of an actuating pressure to a surface of the diaphragm opposite the valve ports causes the diaphragm to deflect toward, and contact at least one of the valve ports. This position is known as the off, state of the valve because fluid communication between the ports is blocked. Removal of the actuating pressure returns the valve to its relaxed, or on state. In the on state, the flexible diaphragm returns to its relaxed position, away from the valve ports, thereby exposing the ports and allowing the sample to flow therethrough. 
     To improve the blockage of fluid flow in the off state, it is desirable that one of the valve ports be located in the center of the depression. It is also desirable that the centrally located valve port include a valve seat. The valve seat is an annular elevation in the well, below the major surface of the wafer in which the ports are formed, and surrounding the centrally located port. Hence, when actuated, the diaphragm will be pushed against the valve seat when in the off state. The valve seat decreases the contact surface area, thus increasing the pressure of the seal when the valve is in the off state. 
     The flexible diaphragm of a conventional valve can be constructed of a polyimide material such as KAPTON®, which is a registered trademark of the DuPont DeNemours company. The diaphragm may be constructed using either a single layer material, such as KAPTON® HN, VN, FPC, KN, E, EN or A, or may be constructed using a multiple layer material, such as KAPTON® FN, as will be described below. 
     KAPTON® is a compliant material so that it may easily deflect and seal around the valve seat upon application of the actuating pressure. The diaphragm is sandwiched between a silicon die, which includes the valve ports, and a backing glass. The diaphragm is preferably held in place via an adhesive. If the diaphragm is constructed of a single layer material, then a separate adhesive can be used to bond the diaphragm to the silicon die and the backing glass. Alternatively, the diaphragm can be clamped between the silicon die and the backing glass. Further, the valve may be constructed using other materials, such as stainless steel. 
     If the diaphragm is constructed of a multiple layer material, the polyimide material from which the diaphragm is constructed can be coated with material that exhibits an adhesive property when the diaphragm is bonded to the silicon die. For example, the adhesive properties may be introduced by raising the temperature of the material. Furthermore, in the case of a single layer material to which adhesive is applied, it is preferable to apply the adhesive on the surfaces of the diaphragm as a continuous thin sheet before applying the diaphragm to the silicon die, which includes the valve ports, and the backing glass. 
     When implemented as a multiple layer structure, several types of polyimide film are suitable for the diaphragm. While KAPTON® type FN is preferable, other materials may also be used. KAPTON® type FN comprises a composite structure having a KAPTON® type HN core with a TEFLON® FEP fluorocarbon resin on both surfaces. This fluorocarbon resin is heat sealable, and thus provides the adhesion property that is desirable on the surface of the diaphragm to bond the diaphragm to the silicon die and to the backing glass. During fabrication, the diaphragm may be bonded at elevated temperature and pressure in order to reduce fabrication time. The bonding process can be modified by adjusting the bonding parameters, which include time, temperature and pressure. Thus, bonding at a lower temperature and pressure can be achieved by increasing bonding time. Further, other materials may be used instead of KAPTON® type FN for the diaphragm. For example, any flexible material that exhibits the desired properties can be used. 
     When implemented as a single layer structure, an adhesive is applied to the surface of the diaphragm or the diaphragm is clamped in place. 
     Many applications for diaphragm valves require the valves to operate at high temperatures. Because some applications require these valves to normally be maintained in the closed, or off state, the diaphragm is pushed onto the valve seat for extended periods of time. Unfortunately, when using a diaphragm constructed of a material that adopts adhesive properties at elevated temperatures, an increase in operating temperature causes the surface of the diaphragm having the polyimide material to bond to the valve seat. Once this bonding begins to occur, the valve will not operate properly. 
     Therefore, it would be desirable to prevent bonding between the valve seat and the diaphragm. 
     SUMMARY OF THE INVENTION 
     The invention provides an extended range diaphragm valve and method for making same. In one embodiment, the invention is valve assembly, comprising a valve seat, a diaphragm suspended over the valve seat, the diaphragm configured to contact the valve seat upon the application of an actuating pressure on the diaphragm. The diaphragm comprises a continuous film of a first material to which a layer of adhesive is applied, where a portion of the adhesive in a region where the diaphragm contacts the valve seat is removed. 
     In an alternative embodiment, the invention is a valve assembly comprising a valve seat, a diaphragm suspended over the valve seat, the diaphragm configured to contact the valve seat upon the application of an actuating pressure on the diaphragm. The diaphragm comprises a continuous film of a first material, wherein a portion of the first material in a region where the diaphragm contacts the valve seat includes a first metallic material. 
     Other features, methods and advantages in addition to or in lieu of the foregoing are provided by certain embodiments of the invention, as is apparent from the description below with reference to the following drawings. 
    
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS 
       The present invention, as defined in the claims, can be better understood with reference to the following drawings. The components within the drawings are not necessarily to scale relative to each other, emphasis instead being placed upon clearly illustrating the principles of the present invention. 
         FIG. 1  is a schematic view illustrating the basic components of an injector including the valve assembly of the present invention. 
         FIG. 2  is a perspective view illustrating a portion of the valve assembly of FIG.  1 . 
         FIG. 3  is a perspective view illustrating the active port of FIG.  2 . 
         FIG. 4  is a plan view illustrating a portion of the valve assembly shown in FIG.  2 . 
         FIG. 5  is a cross-sectional view of the valve assembly of FIG.  1 . 
         FIG. 6A  is a cross-sectional view illustrating the valve diaphragm of  FIG. 5  in a relaxed position. 
         FIG. 6B  is a cross-sectional view illustrating the valve diaphragm of  FIG. 5  in an extended, or actuated, position. 
         FIG. 7A  is cross-sectional view illustrating a valve diaphragm constructed in accordance with one embodiment of the invention. 
         FIG. 7B  is a cross-sectional view illustrating a valve diaphragm constructed in accordance with an alternative embodiment of the invention. 
         FIG. 7C  is a cross sectional view illustrating a valve diaphragm constructed in accordance with another embodiment of the invention. 
         FIG. 7D  is a plan view illustrating the valve diaphragm of FIG.  7 A. 
         FIG. 8A  is cross-sectional view illustrating a valve diaphragm constructed in accordance with another embodiment of the invention. 
         FIG. 8B  is cross-sectional view illustrating a valve diaphragm constructed in accordance with another embodiment of the invention. 
         FIG. 9A  is cross-sectional view illustrating a valve diaphragm constructed in accordance with another embodiment of the invention. 
         FIG. 9B  is a cross-sectional view illustrating a valve diaphragm constructed in accordance with an alternative embodiment of the invention. 
         FIG. 9C  is a cross sectional view illustrating a valve diaphragm constructed in accordance with another embodiment of the invention. 
         FIG. 10A  is cross-sectional view of a diaphragm valve including a diaphragm constructed in accordance with the embodiment of the invention shown in  FIGS. 7A through 7D . 
         FIG. 10B  is a cross-sectional view illustrating the diaphragm valve constructed in accordance with the embodiment of the invention shown in  FIGS. 8A and 8B . 
         FIG. 10C  is a cross-sectional view illustrating the diaphragm valve constructed in accordance with the embodiment of the invention shown in FIGS.  9 A through  9 C. 
     
    
    
     DETAILED DESCRIPTION OF THE INVENTION 
     Embodiments of the invention to be described hereafter with particular reference to a micro-machined valve fabricated on a silicon wafer is applicable to all diaphragm valves that employ a diaphragm that comes into contact with a valve seat during fabrication and operation. Furthermore, while described below as part of an injector for a gas chromatograph, a diaphragm valve constructed in accordance with the various embodiments of the invention has many different applications and is not intended to be limited to use in a gas chromatograph. Furthermore, the concepts of the invention are applicable to various diaphragm and valve seat materials. 
     Turning now to the drawings,  FIG. 1  is a schematic view illustrating the basic components of an injector  10  of a gas chromatograph. The injector  10  is designed to inject a known volume of a sample into a column by controlling the flow of the sample, and controlling the time during which the sample flows into the column. Only the basic components of the injector  10  are illustrated. Injector  10  includes sample valve  12  and injector valve assembly  100 . Although sample valve  12  and injector valve assembly  100  may be constructed in accordance with the invention, only injector valve assembly  100  (hereafter referred to as valve assembly  100 ) will be explained in detail below. 
     Nominally, valve assembly  100  and sample valve  12  are both in the off state A carrier, such as helium, is introduced through port  17  and flows in two directions. One of the flows goes to port  18  and into a reference column. The other flow goes through path  16 , through port  25  into the analytic column. The analytic column is the column having the stationary phase into which the sample is introduced. Following is an illustration of the manner in which a sample is introduced into the column. 
     Injector  10  includes sample inlet  11  through which a sample to be analyzed is introduced. When sample valve  12  is open and valve assembly  100  is closed, the sample is drawn through paths  13  and  14  into the, sample loop  19 . This is accomplished by energizing solenoid switch  24 , which connects port  15  to vacuum pump  26 . The action of vacuum pump  26  draws the sample into the sample loop  19 . The entire sample path is now filled with the sample. Next, the vacuum pump  26  is deactivated and sample valve  12  is turned off. Next, the solenoid switch  24  connects port  15  to a helium gas source  27 , which is at a higher pressure than the helium pressure at port  17 . Hence, the sample in paths  14  and  19  is compressed. After a stabilization time on the order of 50 msec, the injector valve  100  is opened for a predetermined period of time, referred to as the injection time, allowing the sample to flow into path  16  and out through port  25  into the analytic column. After the injection time has elapsed, the injector valve  100  is again closed, separating the sample flow path from the helium flow path. The solenoid switch  24  again connects port  15  to the vacuum pump  26 . The product of the injection time and the sample flow rate is the injection volume. This process repeats when a new sample is analyzed. 
       FIG. 2  is a perspective view illustrating a portion of the valve assembly  100  of FIG.  1 . Valve assembly  100  is fabricated using micro-machined manufacturing techniques, and a portion of valve assembly  100  is therefore fabricated on a silicon wafer. As shown in  FIG. 2 , valve portion  101  includes wafer surface  103  and wafer surface  105 , which is machined to include a number of ports. Alternatively, the valve assembly  100  can be fabricated from other materials, such as glass or stainless steel. 
     By operation of the valve assembly  100  to be described below, samples will pass through the ports of valve assembly  100 . Wafer surface  105  includes an active port  110 , machined therethrough and a number of passive ports  102  also machined therethrough, preferably oriented as shown in FIG.  2 . The number of ports shown in  FIG. 2  is for example only. More or fewer valve ports may be included in valve assembly  100 . For example, the sample valve  12  of  FIG. 1  has only one passive port whereas the injector valve assembly  100  of  FIG. 1  has two passive ports. Active port  110  is the port that is controlled by the diaphragm constructed in accordance with the invention and to be described in further detail below. 
     Passive ports  102  are holes machined in the wafer surface  105  through which the sample admitted through active port  110  can flow. Alternatively, the sample may enter through passive ports  102  and exit through active port  110 . When the active port  110  is closed, the sample may flow between the passive ports. 
     Active port  110  includes valve seat  115 , which is a raised surface with respect to wafer surface  105 . Ridge  104  is also a raised surface with respect to wafer surface  105 . Wafer surface  105  is recessed with respect to wafer surface  103 . The height of valve seat  115  and ridge  104  falls between wafer surface  105  and wafer surface  103  so that a diaphragm constructed in accordance with the invention can be supported by wafer surface  103  as will be more fully described below with respect to FIG.  5 . 
       FIG. 3  is a perspective view illustrating the active port  110  of FIG.  2 . As illustrated in  FIG. 3 , active port  110  is machined so that it is within the region defined by valve seat  115  on wafer surface  105 . 
       FIG. 4  is a plan view illustrating the portion  101  of valve assembly  100  shown in FIG.  2 . The portion  101  of valve assembly  100  includes wafer surface  103 , which in the preferred embodiment is silicon, into which active port  110  and exit ports  102  are formed. A brief description of the steps used to create the structure of  FIG. 4  follows. Performing a first isotropic wet etching technique on wafer surface  103  forms the structure. 
     The etching step creates a circular depression that includes the area defined by wafer surface  105 , passive ports  102 , ridge  104 , valve seat  115 , and active port  110 . The depression is typically 25 μm deep. The first etch step is followed by a second etch step, which includes only wafer surface  105 . Hence, the upper surface of ridge  104  and the upper surface of valve seat  115  reside above wafer surface  105  but below wafer surface  103 . 
     Etching from a reverse surface of the wafer using anisotropic etching techniques forms active port  110  and passive ports  102 . The ridge  104  is formed so as to prevent the diaphragm from covering the passive ports  102  when the diaphragm contacts the valve seat  115  and the ridge  104 . The ridge  104  allows fluid communication between the passive ports  102 . It is understood that this valve structure can be formed by any other technique, for example but not limited to, etching, cutting, or other micro-machining or diaphragm valve manufacturing techniques. In this manner, a diaphragm, to be described below, having one surface is affixed to the surface  103  will not contact valve seat  115  or ridge  104  unless an actuating pressure is applied to the opposing surface of the diaphragm. 
       FIG. 5  is a cross-sectional view of valve assembly  100  of  FIG. 1. A  glass substrate  106  provides mechanical support for valve assembly  100 . Sample flow channel  107  corresponds to path  14  of FIG.  1  through which the sample under analysis is introduced through sample valve  12  (FIG.  1 ). The carrier flow channel  111  is shown only as a cross-section of the channel because it is fabricated at a right angle to the view shown. A carrier gas, typically helium, flows in channel  111 , which corresponds to the flow path  16  of FIG.  1 . 
     The active port  110  resides in the region defined by the interior portion of valve seat  115 . The surface of valve seat  115  and the surface of ridge  104 , reside at a level higher than the surface  105 , but lower than the silicon wafer surface  103 . When the surface  161  of valve diaphragm  150  rests on the surface of valve seat  115 , fluid communication between the active port  10  and the passive ports  102  is blocked. The ridge  104  supports the diaphragm such that the ports  102  are not blocked. Fluid communication between the passive ports is still possible. The ridge  104  is illustrated using a dashed line to indicate that the ridge does not exist over passive ports  102  (see FIG.  4 ). 
     Glass portions  109  reside over valve diaphragm  150  separated therefrom by spacer  151 . Spacer  151  is preferably constructed using a polyimide material similar to that of the diaphragm  150 . Tube  112  brings actuating pressure to the surface  162  of valve diaphragm  150  opposite surface  161 . As shown in  FIG. 5 , the valve diaphragm  150  is in a relaxed, or non-actuated state, thereby allowing a gap  117  to exist between the surface of valve seat  115  and the surface  161  of valve diaphragm  150 . In this state, fluid communication between the active port  110  and the passive ports  102  is possible. Upon the application of actuating pressure to the surface  162  of valve diaphragm  150  via tube  112 , the valve diaphragm  150  will be deflected so that the surface  161  of valve diaphragm  150  contacts the surface of valve seat  115 , thereby closing valve assembly  100 . In this manner, the flow of material through active port  110  is prevented. 
       FIG. 6A  is a cross-sectional view illustrating the valve diaphragm  150  of  FIG. 5  in a relaxed position. As shown in  FIG. 6A , when valve diaphragm  150  is in a relaxed position, a gap  117  exists between the surface of valve seat  115  and the surface  161  of valve diaphragm  150 . In this manner, a sample introduced to active port  110  can pass through the gap  117  and through the cavity  116  for exit through exit port  102 . 
       FIG. 6B  is a cross-sectional view illustrating the valve diaphragm  150  of  FIG. 5  in an extended, or actuated, position. Upon the application of actuating pressure through tube  112  (not shown in FIG.  6 B), the surface  161  of valve diaphragm  150  comes into contact with the surface of valve seat  115 . In this manner, the gap  117  between the surface  116  of valve diaphragm  150  and the surface of valve seat  115  is eliminated, thereby preventing the flow of material from active port  110  into cavity  116 . In this manner, the valve assembly  100  controls the flow of material through the active port  110 . 
     In conventional valve assemblies, the valve diaphragm  150  that contacts valve seat  115  may comprise a composite material, such as KAPTON® FN. Under elevated temperature and pressure, the outer layer of the KAPTON® FN, which is an FEP thin film, can adhere to glass, silicon (such as the surface of valve seat  115 ) and to itself. In this manner, the valve diaphragm  150  and the spacer  151  can be bonded to the silicon portion  101  and glass portions  109  (see FIG.  5 ). If the diaphragm is implemented as a single layer structure, adhesive is typically applied so the diaphragm can be secured to the silicon portion  101  and glass portions  109 . Single layer diaphragm material includes KAPTON® Type E and EN. Typical adhesives are acrylic, epoxy-amide, epoxy-novolac, phenolicbutyral and phenolic-nitrile, as known to those having ordinary skill in the art. Unfortunately, there is no convenient way to apply the adhesive to the diaphragm without covering the portion of the diaphragm that will contact the valve seat with adhesive. 
     Alternatively, the diaphragm can be clamped between the silicon portion  101  and the glass portions  109 , thereby eliminating the adhesive. 
     Unfortunately, regardless of the construction of the valve diaphragm  150 , when bonding to glass or silicon, the bonding temperature of this film can be below 130° C. under elevated pressure and given sufficient time. This is problematic during the operation of the valve when, in order to volatize a sample, the injector and the valve assembly  100  are heated to temperatures in excess of 130° C. Thus, the diaphragm  150  can soften and cause the adhesive on the valve diaphragm  150  to adhere to the surface of valve seat  115 . 
       FIG. 7A  is cross-sectional view illustrating a valve diaphragm  150  constructed in accordance with one embodiment of the invention. Valve diaphragm  150  comprises a layer of a first material  153 , which can be, for example, the polyimide material KAPTON® HN, over which a metallic material  155  is deposited. The polyimide layer of first material  153  is typically 50 μm thick. The metallic material can be, for example, gold, or a gold containing alloy, and can be applied to a thickness of approximately 100 nanometers (nm) approximately as shown. 
     The thickness of the metallic material  155  is very thin compared to the thickness of the diaphragm, and therefore, will not affect the operation of the diaphragm. In this manner, the metallic material  155 , which is inert and applied over the first material  153 , will not adhere to the valve seat  115  and will not react with most samples. 
     Alternatively, a metallic layer of tantalum, aluminum or nickel may be used instead of gold. The selective deposition of thin metal layers on polyimide material is known to those having ordinary skill in the art. One example is evaporation through a shadow mask. These shadow masks are generally constructed of metal foils having openings. Thus, if the shadow mask is placed between the evaporating source and the diaphragm, only the area of the diaphragm that has direct exposure to the evaporating source will have metal deposited thereon. The rest of the area is in the shadow. Similarly, selective deposition can be effected using a sputtering system. 
       FIG. 7B  is a cross sectional view illustrating a valve diaphragm  170  constructed in accordance with another embodiment of the invention. Valve diaphragm  170  is constructed so that a portion of layer  153  is activated in the region  165 . Those having ordinary skill in the art should understand that such activation can be achieved by processes such as plasma etching of the surface. This activation improves the adhesion of the metallic material  155  to the diaphragm in the region  165  when the deposition of the metal is carried out immediately after the activation process. A shadow mask similar to one that can be used to selectively deposit metal on the diaphragm can be used to control activation only in region  165  of the diaphragm. Here, only the regions that are exposed via the holes in the shadow mask become activated. 
       FIG. 7C  is a cross-sectional view illustrating a valve diaphragm  180  constructed in accordance with another embodiment of the invention. In accordance with this embodiment, after the activation of a portion of layer  153  in the region  165  ( FIG. 7B ) as described above, a second metallic material  157 , preferably comprising a 50 nm layer of nichrome, is applied to layer  153  prior to the application of metallic material  155 . Alternatively, the second metallic material may include a titanium-tungsten alloy, which is used as a standard adhesion material in the integrated circuit manufacturing industry, and may also include titanium and chromium. The second metallic material  157  can be referred to as an “adhesion layer” and may improve the adhesion between the metallic material  155  and the material of layer  153 . When the second metallic material  157  is applied, the gold that comprises the metallic material  155  may be electroplated thereon. As mentioned above, the thickness of the metallic material  155  and the second metallic material  157  are such that operation of the diaphragm is unimpeded. 
       FIG. 7D  is a plan view illustrating the valve diaphragm  150  of FIG.  7 A. Shown is a surface of the material layer  153 , to which a metallic material  155  has been applied in the vicinity of the diaphragm  150  that will contact the valve seat  115 . In this manner the valve assembly  100  constructed in accordance with this embodiment of the invention can be operated at significantly higher temperature than previously possible. When constructed in accordance with that shown in  FIGS. 7A through 7C , the metallic material  155  will contact the valve seat  115 , thereby allowing operation at elevated temperatures. 
     In this manner, a valve diaphragm constructed in accordance with this embodiment of the invention can be fabricated and operated at temperatures significantly higher than 130° C., while eliminating the possibility that the layer  153  will adhere to the surface of valve seat  115 . Alternatively, the metallic material  155  can be applied over any suitable valve diaphragm material. 
       FIG. 8A  is cross-sectional view illustrating a valve diaphragm  190  constructed in accordance with another embodiment of the invention. Valve diaphragm  190  comprises a layer of a first material  193 , which can be, for example, the polyimide material KAPTON® HN or any other material from which a diaphragm can be constructed, over which an adhesive material  192  is deposited. The layer of first material  193  is typically 50 μm thick. The adhesive material  192  is applied as a layer over the first material layer  193  and then removed in the region  194  where the valve diaphragm  193  will contact the valve seat  115 . 
       FIG. 8B  is cross-sectional view illustrating a valve diaphragm  195  constructed in accordance with another embodiment of the invention. Valve diaphragm  195  is similar to the valve diaphragm  190 , but includes a layer of metallic material  155  applied in the region  194  ( FIG. 8A ) where the valve diaphragm  195  will contact the valve seat  115 . The metallic material can be, for example, gold, or a gold containing alloy, and can be applied to a thickness of approximately 100 nanometers (nm) approximately as shown. 
     The thickness of the metallic material  155  is very thin compared to the thickness of the diaphragm, and therefore, will not affect the operation of the diaphragm. In this manner, the metallic material  155 , which is inert and applied over the first material  193  will not adhere to the valve seat  115  and will not react with most samples. 
       FIG. 9A  is cross-sectional view illustrating a valve diaphragm  210  constructed in accordance with another embodiment of the invention. Valve diaphragm  210  includes a layer of a first polyimide material  212 , for example, KAPTON® HN, sandwiched between a first layer  214  and a second layer  216  of an adhesive material, such as TEFLON® FEP. Although shown in  FIG. 8A  as being of equal thickness, typically, the polyimide layer  212  is 50 μm and the FEP layers  214  and  256  are 12.5 μm. 
     In accordance with this embodiment of the invention, a metallic material  155 , preferably comprising a layer of gold 100 nm, thick is applied over polyimide layer  214  approximately as shown. The thickness of the metallic material  155  is very thin compared to the thickness of the diaphragm, and therefore, will not affect the operation of the diaphragm. In this manner, the metallic material  155 , which is inert and applied over layer  214  will not adhere to the valve seat  115  and will not react with most samples. Alternatively, a first metal layer of tantalum, aluminum or nickel may be used instead of gold. To fabricate this embodiment, the layer  214  is covered with a shadow mask, the valve diaphragm  210  is placed in a sputtering system, and the metallic material  155  is deposited by sputtering. Alternatively, the metallic material can be deposited by evaporation through a shadow mask. 
       FIG. 9B  is a cross sectional view illustrating a valve diaphragm  220  constructed in accordance with another embodiment of the invention. Valve diaphragm  220  is constructed so that a portion of layer  214  is activated in the region  165 . As mentioned above, those having ordinary skill in the art should understand that such activation can be achieved by processes such as plasma etching of the surface. As further described above, this activation improves the adhesion of the metallic material  155  to the diaphragm in the region  165 . A shadow mask similar to one that can be used to selectively deposit metal on the diaphragm can be used to control activation only in region  165  of the diaphragm. Here, only the regions that are exposed via the holes in the shadow mask become activated. To fabricate this embodiment, the layer  214  is covered with a shadow mask, the valve diaphragm  210  is placed in a sputtering system, the layer  214  is activated with a plasma, and the metallic material  155  is deposited by sputtering. 
       FIG. 9C  is a cross-sectional view illustrating a valve diaphragm  230  constructed in accordance with another embodiment of the invention. In accordance with this embodiment, after the activation of a portion of layer  214  in the region  165  ( FIG. 8B ) as described above, the second metallic material  157 , preferably comprising a 50 nm layer of nichrome, is applied to layer  214  prior to the application of metallic material  155 . Alternatively, the second metallic material may include a titanium-tungsten alloy, which is used as a standard adhesion material in the integrated circuit manufacturing industry, and may also include titanium and chromium. The second metallic material  157  can be referred to as an “adhesion layer” and may improve the adhesion between the metallic material  155  and the material of layer  214 . When the second metallic material  157  is applied, the gold that comprises the metallic material  155  may be electroplated thereon. As mentioned above, the thickness of the metallic material  155  and the second metallic material  157  are such that operation of the diaphragm is unimpeded. To fabricate this embodiment, the layer  214  is covered with a shadow mask, the valve diaphragm  210  is placed in a sputtering system, the layer  214  is activated with a plasma, the second metallic material  157  is deposited by sputtering, and the metallic material  155  is deposited by sputtering. 
       FIGS. 10A ,  10 B, and  10 C are cross-sectional views illustrating a valve assembly  100  including three alternative embodiments of the construction of the diaphragm valves  150 ,  170  and  180  of  FIGS. 7A ,  7 B and  7 C, respectively; diaphragm valves  190  and  195  of  FIGS. 8A and 8B , respectively, and diaphragm valves  210 ,  220  and  230  of  FIGS. 9A ,  9 B and  9 C, respectively. In  FIG. 10A , the metallic material  155  extends from the center of the valve to just beyond the ridge  104 . In  FIG. 10B , the portion  194  of the valve diaphragm  190  that contacts the valve seat  115  is free of adhesive material  192 . 
     In  FIG. 10C , the first metal layer  155  extends onto the surface  103  of the silicon wafer  101 . In the embodiment shown in  FIG. 10C , any contact between the sample gas and layer  153  of diaphragm  150  is prevented. This may be desirable for certain types of samples. 
     It will be apparent to those skilled in the art that many modifications and variations may be made to the preferred embodiments of the present invention, as set forth above, without departing substantially from the principles of the present invention. For example, the present invention can be used with a number of different micro-machined valve configurations, constructed using materials different from those described herein, and a number of different diaphragm valves. Furthermore, the dimensions provided herein are for example purposes only. All such modifications and variations are intended to be included herein within the scope of the present invention, as defined in the claims that follow.