Control valve utilizing mechanical beam buckling

Abstract: A valve apparatus (10) for controlling fluid flow comprising a substrate (12) having a first aperture (26) extending therethrough for defining a first fluid flow path; a beam (72) having first and second terminal end portions (82, 84) mounted in fixed relationship with the substrate (12) and having a bucklingly displaceable intermediate portion (86) positioned in overlying relationship with the aperture (26) for covering and uncovering the aperture for preventing or enabling fluid flow through the aperture; and a temperature control assembly (144, 148, 96, 98) for selectively controlling the temperature of the beam for selectively bucklingly displacing the intermediate portion (86) of the beam for controlling fluid flow through the aperture (26).

Description: The present invention relates generally to control valves and, more particularly to a micro control valve which utilizes mechanical beam buckling to open and close a valve orifice. In many fluid flow control applications, especially in pneumatic flow control applications, it is desirable to use a control valve which may be actuated quickly and with relatively low energy consumption in response to an electronic control signal. It is also desirable in many applications that the control valve have a relatively small dead volume. Various applications for valves having such characteristics are described in U.S. Patents 4,821,997 and 4,824,073. A problem with the above described valve of U.S. Patent 4,824,073 and 4,821,997 is that the fabrication process, including the encapsulation of a volume of fluid within a sealed enclosure involves a large number of process steps. It would thus be generally desirable to provide a micro control valve for use in a wide variety of applications including those described for the micro valve of U.S. Patents 4,824,073 and 4,821,997 but which is more easily fabricated and less expensive to produce than the micro valves described in those patents. EP-A-0339528 discloses a valve apparatus with a thermally-actuated beam or membrane on a substrate with heating means which cause the beam to close a valve aperture. This document corresponds to the introductory part of the present claim 1. In EP-A-0339528, the aperture remains closed until further heating means are actuated. The present invention is directed to a valve apparatus for controlling fluid flow. The valve comprises a substrate having an aperture extending therethrough which defines a fluid flow path. A beam having first and second terminal end portions is mounted in fixed relationship with the substrate. A bucklingly displaceable intermediate portion of the beam is positioned in overlying relationship with the aperture for covering and uncovering the aperture for preventing or enabling fluid flow through the aperture. A temperature control assembly is used to control the temperature of the beam so as to selectively bucklingly displace the intermediate portion of the beam to control fluid flow through the aperture. The phrase "buckling displacement" as used herein refers to lateral displacement which occurs at an intermediate portion of a beam which is fixed at both ends as a result of a change in the longitudinal dimension of the beam. The temperature control assembly may include a relatively low power electrical power source which provides energy to a resistor positioned near the beam or, alternatively, which passes a current through the beam to heat the beam. According to a first aspect of the present invention, there is provided a valve apparatus for controlling fluid flow comprising: a substrate having an aperture extending therethrough for defining a fluid flow path; beam means having first and second terminal end portions mounted in fixed relationship with said substrate and having a bucklingly displaceable intermediate portion positioned in overlying relationship with said aperture for covering and uncovering said aperture for preventing or enabling fluid flow through said aperture; and temperature control means for selectively controlling the temperature of said beam means for selectively bucklingly displacing said intermediate portion of said beam means for controlling fluid flow through said aperture, wherein heating the beam displaces it from a first position where fluid is prevented from flowing, to a second position where fluid is able to flow, characterised in that means are provided which enable a fluid pressure to be exerted on the side of the beam means remote from the substrate, the arrangement being such that, in the first position of the beam means, said pressure-exerting means urges said intermediate portion against said aperture, and in that said beam means comprises a first surface which is positioned remote from said substrate and a second surface disposed generally parallel to said first surface and positioned proximate to said substrate; said beam means having: an inwardly buckled position wherein said intermediate portion is positioned in sealed covering relationship with said aperture and wherein said first surface of said beam means has a generally concave contour; an outwardly buckled position wherein said intermediate portion is positioned in relatively widely spaced apart, uncovering relationship with said aperture and wherein said first surface of said beam means has a generally convex contour; and a neutral position wherein said intermediate portion is positioned in relatively narrowly spaced apart, uncovering relationship with said aperture and wherein said first surface of said beam means has a relatively flat contour. According to a second aspect of the present invention, there is provided a method of making a control valve for controlling fluid flow comprising a valve apparatus as defined in the preceding paragraph, the method comprising the steps of: coating a substrate with at least one layer of coating material; forming a beam from a portion of said coating layer, leaving opposite end portions of said beam integrally attached to said substrate; forming an orifice extending through said substrate layer which is positioned below a midportion of said beam; and providing an assembly for controllably heating the beam member. An illustrative and presently preferred embodiment of the invention is shown in the accompanying drawings in which: Fig.1 is a top plan view of a microvalve; Fig.2 is a cross-sectional elevation view of the microvalve of Fig.1 with a beam portion thereof in an undeformed position associated with a partially open state of the valve. Fig.3 is a cross-sectional elevation view of the microvalve of Fig.1 with a beam portion thereof in a first buckled position associated with a closed state of the valve. Fig.4 is a cross-sectional elevation view of the microvalve of Fig.1 with a beam portion thereof in a second buckled position associated with a fully open state of the valve. Fig.5 is a cross-sectional elevation view of the microvalve of Fig.1 in use in a fluid flow line with electronic control devices associated with the valve shown schematically. Figs. 6-13 are cross-sectional elevation views illustrating various stages of the fabrication of a single wafer control valve of the type shown in Fig.1. Fig.14 is a bottom plan view of the fabrication stage shown in Fig.13. Fig.15 is a top plan view of a further stage of fabrication of a single wafer valve. Figs.16 & 17 are cross-sectional elevation views of subsequent fabrication stages. Figs. 1-5 illustrate a microvalve 110 which includes a single substrate 112 having a top surface 114, a bottom surface 116, and an aperture 118 extending from the top surface to the bottom surface. A beam 120 having a top surface 122, a bottom surface 124, a first end portion 126, a second end portion 128, and an intermediate portion 130 is attached to the top surface of substrate 112 by bonding material 132 provided at the end portions 126, 128 of the beam. The thickness of the bonding material 132 is such that a small gap is provided between the bottom surface 124 of the beam and the top surface 114 of the substrate along the intermediate portion 130 of the beam when the beam is in an unstressed state at ambient temperature. In one exemplary embodiment, the substrate 112 has a length of 4mm, a width of 6mm, and a thickness of 0.38mm, and the aperture extending therethrough has an opening area of 0.4mm² and may be constructed from silicon. The beam may have a length of lmm, a width of 0.4mm, and a thickness of 0.015mm, and may be constructed from nickel. Fig.5 illustrates use of the microvalve 110 in a supply line 134 having an upstream portion 135 and a downstream portion 136 which may be, for example, portions of a nitrogen supply line for a gas chromatograph. As further illustrated in Fig.5, electrical current supply lines 140, 142 are attached to opposite ends 126, 128 of beam 120 and are operably connected at the other ends thereof to an electrical power source 144 which may be a relatively low-power battery, e.g. a 5-volt battery. One of the current supply lines, e.g. 140, may pass through an electronic switching unit 145 which is operably controlled by a controller unit 148 which provides a control signal to the switching unit 145 through lead 146. The control unit 148 in turn receives signals from a flow monitor unit 152 located in flow line 134 downstream from the microvalve 110. The monitor 152 may be a conventional flow rate monitor or a pressure monitor which provides a signal indicative of a predetermined flow parameter such as flow rate or static pressure to controller 148. Controller 148 may be an EPROM chip programmed to compare the monitor signal value to a predetermine target value and to generate a control signal to open or close the control valve in response to deviations in the monitor signal from that target value. When the beam 120 is in a relatively low temperature state, e.g. ambient temperature, the beam would ordinarily occupy a flat configuration as illustrated in Fig.2. However, as illustrated in Fig.3, due to upstream pressure in line 134, e.g. a pressure of 50 psig, the intermediate portion 130 of the beam is urged against the upper surface of the substrate 112 at the periphery of aperture 118 acting to close the aperture and prevent fluid flow therethrough. When electric current is passed through the beam, the resistance of the beam causes its temperature to become elevated, thereby causing the beam to buckle upwardly to the position illustrated in Fig.4 in uncovered relationship with aperture 118, enabling flow through aperture 118. In one preferred embodiment of the invention, the electrical energy supplied to the beam may be modulated so as to gradually open or close aperture 118 to maintain a selected flow rate or to maintain another selected flow parameter at a constant value. A method of fabricating a one-wafer embodiment of a microvalve 110 of the type illustrated in Figs. 1-4 will now be described with reference to Figs. 6-17. As illustrated in Fig.6, initially a silicon (Si) substrate 200 is provided which may be either a P or N-type silicon substrate which may have a thickness of approximately 400 microns. Next, as illustrated in Fig.7, an oxide (siO₂) 210 is deposited on the silicon substrate 200 to a thickness of between 0.05 microns to 5 microns. Next, as illustrated in Fig.8, silicon nitride (Si₃N₄) 220 is deposited to a thickness of between 500 and 5000 angstroms (A) using low-pressure chemical vapour deposit (LPCVD). Next, as illustrated in Fig.9, a top surface layer of titanium 230 is sputter-deposited to a thickness of between 200 and 2000 A. Next, as illustrated in Fig.10, a layer of nickel (Ni) 240 is electrodeposited on top of the titanium layer to a thickness of between 1 and 100 microns. Next, a flow hole is patterned on the back side of the wafer using a mask of corresponding shape. Next, as illustrated in Fig.11, a first portion of a hole 250 is etched through the silicon nitride and silicon oxide layer using CF-4 plasma. Next, as illustrated in Fig.12, a further portion of hole 250 is etched through the silicon substrate 200 through the use of a solution of potassium hydroxide (KOH), isopropyl alcohol (ISO), and water. Next, as illustrated in Fig.13, the inside layers of silicon nitride and silicon oxide 220, 210 are etched using CF-4 plasma to complete the flow hole 250. Fig.14 is a bottom plan view illustrating the position of the etched flow hole on the wafer. Next, as illustrated in Fig.16 and in solid lines in Fig.15, the nickel layer 240 is etched using ferric chloric to provide a generally I-shaped pattern. In one preferred embodiment, parallel channels 241, 243 are etched in each end portion of the I-shaped nickel pattern in order to form separate terminal pad portions 242, 244 of the nickel layer from the remainder of the nickel layer for enabling the underlying titanium layer to act as a heating resistor, as discussed in further detail below. Next, as illustrated in Fig.17 and in dashed lines in Fig.15, the exposed portion of the titanium layer, except for the area exposed by channels 241, 243, is etched using dilute hydrofluoric acid. The etching of the titanium is allowed to continue sufficiently to undercut the midportion of the I-shaped nickel layer to the point indicated by the dashed lines in Fig.15. The etching of the titanium layer thus provides an orifice extending entirely through substrate 200 and coatings 210 and 220, which opening is overlaid by a span of nickel of layer 240 which is bonded at either end to the titanium layer 230. Each of the pad regions in the nickel layer are connected to leads of an electrical power source either by direct contact of the leads with the upper, exposed surfaces of the pads or, more conventionally through means of a via (not shown) extending vertically through the wafer and contacting an associated nickel pad; the via in turn being attached to a lead of an electrical power supply. In this embodiment, since the nickel layer is substantially thicker than the titanium layer, an electrical current passed through the spanning beam portion of the nickel would create little resistance. However, due to the fact that an electrical current applied to the pad regions of the nickel layer must pass through the titanium layer, and due to the fact that the titanium layer is substantially thinner than the nickel layer, the titanium layer is heated by the passage of the electrical current and acts to heat the nickel beam to produce the necessary buckling action therein. As previously mentioned, other embodiments in which the electrical current is passed through a relatively high-resistance beam enables direct heating of the beam by the electrical current. Other means for heating the beam, such as application of light energy or microwave energy thereto or inductive heating thereof might also be employed.

Claims: A valve apparatus (110) for controlling fluid flow comprising: a substrate (112) having an aperture (118) extending therethrough for defining a fluid flow path; beam means (120) having first and second terminal end portions (126,128) mounted in fixed relationship with said substrate and having a bucklingly displaceable intermediate portion (130) positioned in overlying relationship with said aperture for covering and uncovering said aperture for preventing or enabling fluid flow through said aperture; and temperature control means (144,148) for selectively controlling the temperature of said beam means for selectively bucklingly displacing said intermediate portion of said beam means for controlling fluid flow through said aperture, wherein heating the beam means displaces it from a first position where fluid is prevented from flowing, to a second position where fluid is able to flow, characterised in that: said beam means comprises a first surface (122) which is positioned remote from said substrate (112) and a second surface (124) disposed generally parallel to said first surface and positioned proximate to said substrate; means (135) are provided which enable a fluid pressure to be exerted on said first surface of the beam means remote from the substrate, the arrangement being such that, in the first position of the beam means, said pressure-exerting means urges said intermediate portion (130) in sealed covering relationship with said aperture (118); said beam means (120) having: (a) an inwardly buckled position, corresponding to said first position, corresponding to said first position, wherein said first surface (122) of said beam means has a generally concave contour; (b) an outwardly buckled position wherein said intermediate portion (130) is positioned in relatively widely spaced apart, uncovering relationship with said aperture (118) and wherein said first surface (122) of said beam means has a generally convex contour; and (c) in an unstressed state, a neutral position wherein said intermediate portion (130) is positioned in relatively narrowly spaced apart, uncovering relationship with said aperture (118) and wherein said first surface (122) of said beam means has a relatively flat contour. A valve apparatus (110) according to claim 1, wherein the pressure-exerting means is the upstream portion of a fluid supply line (134). A valve apparatus (110) according to claim 2, said valve apparatus being installed in a flow line (134) having a relatively higher pressure upstream end (135) and a relatively lower pressure downsteam end (136) with said first surface (122) of said beam means positioned relatively upstream from said second surface (124) thereof;. wherein said fluid pressure in said flow line normally holds said beam means in said inwardly buckled position during a relatively low temperature state of said beam means; and wherein said beam means is deflectable from said inwardly buckled position to said outwardly buckled position through application of heat to said beam means by said temperature control means (144,148). A valve apparatus according to any preceding claim, said substrate comprising a silicon substrate and wherein said beam means is integrally connected to said substrate. A valve apparatus according to any preceding claim, wherein the electrical energy supplied to the heating means can be modulated so as to gradually open or close said aperture to maintain a selected flow rate or to maintain another selected flow parameter at a constant value. A valve apparatus according to any preceding claim wherein the heating means passes an electric current through the beam means. A method of making a control valve for controlling fluid flow comprising a valve apparatus according to any preceding claim, the method comprising the steps of: coating a substrate (200) with at least one layer of coating material (240); forming a beam from a portion of said coating layer, leaving opposite end portions of said beam integrally attached to said substrate; forming an orifice (250) extending through said substrate layer which is positioned below a midportion of said beam; and providing an assembly for controllably heating the beam member.

Inventors: BEATTY CHRISTOPHER C, BECKMANN JEROME E, BEATTY, CHRISTOPHER C., BECKMANN, JEROME E.
Applicants: HEWLETT PACKARD CO, HEWLETT-PACKARD COMPANY
Application year: 1991
Main classification: F16K7
IPC codes: F15C5, F16K7, F16K31, F16K99