Micropump

Abstract: A pump apparatus comprising an enclosure (70) for holding a volume of fluid; an intake one-way valve (46,58) for enabling intake of fluid into the enclosure; a discharge one-way valve (48,64) for enabling discharge of fluid from the enclosure; a diaphragm (28) for cyclically deflectably increasing and decreasing the volume of the enclosure whereby fluid is oscillatingly drawn into the enclosure and discharged therefrom; a heating assembly (30) for selectively oscillatingly applying heat to the diaphragm and terminating application of heat thereto for selectively oscillatingly deflecting the diaphragm.

Description: The invention relates to a pump apparatus according to the preamble of claim 1, to a method of pumping fluid through an enclosure means and to a method of making a pump apparatus. A pump apparatus according to the preamble of claim 1 is known from the US-A-4 895 500. The US-A-4 895 500 discloses a pump apparatus having an enclosure for holding a volume of fluid, an intake one-way valve for enabling intake of fluid into said enclosure, a discharge one-way valve for enabling discharge of fluid from said enclosure, a diaphragm for cyclically deflectable increasing and decreasing said volume of said enclosure to draw fluid into that enclosure and discharge fluid therefrom, and means for deflecting said diaphragm. There are many processes in which a relatively small quantity of fluid, either gas or liquid, must be dispensed in a measured amount. One typical process of this type is the process of liquid chromatography in which a precise amount of liquid in a quantity of e.g. 1 microliter must be dispensed to a separation column. In applications in which such small quantities of fluid are to be dispensed by pump, a difficulty in precise metering arises if the pump chamber is relatively large as compared to the quantity of fluid which is to be dispensed. The construction of pumps with extremely small pumping chambers has heretofore proven to be difficult and expensive. Certain microfabrication techniques for constructing valves are described in U.S. Patents 4,821,997 and 4,824,073 of Zdeblick and in U.S. patent application serial number 560,933, filed July 31, 1990, of Beatty and Beckmann for Control Valve Using Mechanical Beam Buckling, each of which is hereby specifically incorporated by reference for all that is disclosed therein. Summary of the Invention The present invention is directed to a method of constructing a pump apparatus which may readily employ microfabrication techniques and which may achieve the advantages associated with microfabrication such as batch fabrication, low cost, repeatability and the like. The invention is also directed to a pump apparatus which may have a very small dead volume and which may have a quick response and accurate dispensing characteristics. The pump apparatus may employ a diaphragm which is actuated by oscillatory heating and cooling thereof. Thus, the invention provides a pump apparatus having the features of claim 1. The invention further comprises a method of pumping fluid according to claim 9 and a method of making a pump apparatus according to claim 12. Brief Description of the Drawings An illustrative and presently preferred embodiment of the invention is shown in the accompanying drawings in which: Fig. 1 is a cross sectional elevation view of a pump apparatus. Fig. 2 is a cross sectional elevation view of the pump apparatus of Fig. 1 with the diaphragm thereof moving outwardly during pump intake. Fig. 3 is a cross sectional elevation view of the pump apparatus of Fig. 1 with the diaphragm thereof moving inwardly during pump discharge. Fig. 4 is a cross sectional elevation view of an alternative embodiment of a pump assembly. Fig. 5 is a schematic diagram illustrating an assembly for oscillatingly heating a pump diaphragm. Figs. 6-13 are cross sectional elevation views illustrating various stages of wafer formation during the fabrication of one portion of the pump assembly shown in Fig. 1. Fig. 14 is a top plan view of the substrate assembly shown in Fig. 13. Fig. 15 is a bottom plan view of the substrate assembly shown in Fig. 13. Figs. 16-21 are cross sectional elevation views illustrating various stages of wafer formation during the fabrication of another portion of the pump assembly shown in Fig. 1. Fig. 22 is a top plan view of the substrate assembly shown in Fig. 21. Fig. 23 is a bottom plan view of the substrate assembly shown in Fig. 21. Detailed Description of the Preferred Embodiments Fig. 1 illustrates a pump apparatus 10 which includes a first substrate assembly 12 and a second substrate assembly 14. As used herein, "substrate assembly" is meant to include a single substrate member and also a wafer formed from a single substrate member. The first substrate assembly 12 comprises a first substrate member 16 having a first exterior planar surface 18 on one side thereof and a second exterior planar surface 20 on an opposite side thereof. The first substrate member has a cavity 22 provided therein defined by a cavity side wall 24 and bottom wall 26. The cavity has an opening 23 located in the plane of surface 20. A portion of the first member located between the first exterior surface 18 and the bottom wall 26 of the cavity defines a diaphragm 28. A resistor 30 which terminates at terminal pads 32, 34 is embedded in the diaphragm 28 proximate surface 18. The second substrate assembly 14 comprises a second substrate member 40 having a first planar surface 42 on one side thereof and a second planar surface 44 on an opposite thereof which is parallel to surface 42. First and second holes 46, 48 extend through the second member. First and second flappers 52, 54 are associated with the first and second holes in second substrate member 40. The first flapper comprises a generally T-shaped configuration (see Fig. 15) having a branch portion 56 attached to the first surface 42 of substrate member 40 and having a trunk portion 58 positioned in spaced apart, overlying relationship with hole 46. The second flapper comprises a generally T-shaped configuration (see Fig. 14) having a branch portion 62 attached to the second surface 44 of substrate member 40 and having a trunk portion 64 positioned in spaced apart, overlying relationship with hole 48. As shown in Fig. 1, the second surface 20 of the first substrate member 16 is attached to the first surface 42 of the second substrate member 40 providing a sealed enclosure 70 defined by cavity walls 24, 26 and second substrate member first surface 42. The enclosure 70 which is adapted to hold a volume of fluid 71 therein has only two openings which are provided by holes 46 and 48. As shown schematically in Fig. 5, the resistor terminal pads 32, 34 are connected to a power source 80, e.g. a 5 volt battery, which provides electrical energy to heat the resistor 30. The battery is connected to the resistor through an oscillator circuit 82, e.g. a CMOS chip, which oscillates the supply of electrical energy provided to the resistor at a predetermined frequency, e.g. one oscillation cycle per millisecond. During each oscillation cycle the resistor heats during a period when energy is supplied thereto and then cools during a period when energy is not supplied thereto. In use the pump apparatus is connected at surface 44 thereof to a fluid supply line 84 and a fluid discharge line 86, as by conventional conduit attachment means well known in the art. The first hole 46 in substrate member 14 enables fluid communication between the fluid supply line 84 and enclosure 70. The second hole 48 enables fluid communication between the fluid discharge line 86 and enclosure 70. In one embodiment of the invention, which is presently the best mode contemplated, the heating of resistor 30 causes a corresponding heating of diaphragm 28 which causes it to expand and buckle outwardly 92, Fig. 2. As the diaphragm buckles outwardly it causes the volume of enclosure 70 to expand thus drawing fluid into the enclosure through hole 46. As the outward buckling takes place the pressure of fluid in discharge line 86 causes end portion 64 of flapper 54 to be urged into engagement with the second surface 48 of substrate member 14 causing hole 48 to be sealed and thus preventing flow of fluid therethrough. During a period when resistor 30 and diaphragm 28 are cooling the diaphragm contracts and buckles inwardly 94, Fig. 3, causing a reduction of volume in enclosure 70 with a corresponding pressure increase which causes end portion 58 of flapper 52 to be urged into engagement with surface 28 sealing hole 46. This pressure increase in enclosure 70 also urges flapper 54 away from surface 44 thus opening hole 48 and enabling discharge of fluid from enclosure 70. Thus in the embodiment of Figs. 1-3 the resistor heating portion of each oscillation cycle is associated with pump intake and the cooling portion of each oscillation cycle corresponds to pump discharge. Hole 46 and flapper 52 function as a one-way intake valve and hole 48 and flapper 54 function as a one-way discharge valve. The total volume of fluid pumped during a single oscillation cycle may be e.g. 1 nanoliter. In the embodiment of Figs. 1-3 the diaphragm at ambient temperature with no external stress applied thereto may have a generally flat profile or may have a profile which is slightly outwardly convex, i.e. bowing away from enclosure 70. In another embodiment of the invention, as illustrated in Fig.4, the diaphragm in an ambient temperature unstressed state (solid lines) is inwardly convex, i.e. bows toward enclosure 70. In this embodiment heating of the diaphragm causes it to expand in the direction of enclosure 70, as shown in dashed lines, thus decreasing the volume thereof. Cooling of the diaphragm in this embodiment causes it to return to its original shape thus increasing the volume of the cavity. Thus in the embodiment of Fig. 4 the heating portion of each energy oscillation cycle is associated with pump discharge and the cooling portion of each cycle is associated with pump intake. Other means of heating the diaphragm to provide oscillatory movement thereof might also be employed such as application of light energy or microwave energy or inductive heat thereto. A specific method of fabricating a pump apparatus 10 will now be described with reference to Figs. 6-23. A substrate member 100 corresponding to substrate member 14 in Fig. 1 is shown in cross section in Fig. 6. Substrate member 100, which may be a silicon substrate member which may be 400 microns thick, is provided with a first coating layer 102, which may be 0.1 microns thick, as by growing an oxide layer thereon, e.g. a silicon dioxide layer. The technique for growing of an oxide layer on a silicon substrate is well known in the art. Next a second coating layer 104, e.g. a polysilicon coating is deposited over the first coating by a chemical vapor deposit technique well known in the art, Fig. 7. Coating layer 104 may be 2 microns thick. The next step, as illustrated by Fig. 8, is to apply a third coating 106 over the second coating 104. The third coating may be a 0.2 micron thick LPCVD (low pressure chemical vapor deposition) silicon nitride layer which is applied by conventional LPCVD techniques well known in the art. Next holes 110, 112 extending through the three coating layers 102, 104, 106 are patterned and etched on opposite sides of the substrate assembly. The holes may be etched with carbon tetrafluoride (CF₄), Fig. 9. Holes 110, 112 are then extended through the substrate member 100 as by etching with potassium hydroxide/isopropanol/water (KOH/ISO/H₂O) as shown in Fig. 10. Next, as shown in Fig. 11, the third layer 106 is stripped as by using phosphoric acid (H₃PO₄). The portion of the assembly which will become the flappers of the pump apparatus 10 is next patterned and etched as by using CF₄. Initially, as shown by Fig. 12, the etching material removes all of the first and second layers 102, 104 except for T-shaped masked portions thereof. As a second phase in this etching operation the etching solution is allowed to remain in contact with the surface of substrate 100 and the perimeter surface of layer 102 thus causing etching of layer 102 to continue, as illustrated in Figs. 13-15. (Figs. 14 and 15 are top and bottom plan views, respectively, of Fig. 13.) This perimeter etching of layer 102 causes it to be removed from below the overlying third layer 104 so as to expose holes 110, 112. When this perimeter etching of layer 102 has progressed to the point indicated in Figs. 13-15 it is terminated by removal of the etching solution thus providing a substrate assembly corresponding to substrate assembly 14 in Fig. 1. A substrate member 200 corresponding to substrate member 12 of Fig. 1 is shown in cross section in Fig. 16. Substrate member 200 may be a 400 micron thick silicon substrate having a 385 micron thick heavily doped (e.g. 10¹⁸ atoms/cm³ phosphorous doped) upper portion 202 and a 15 micron thick lightly doped (e.g. 10¹⁶ atoms/cm³ phosphorous doped) lower region 204 which may be provided by a conventional epitaxy process well known in the art. As illustrated in Fig. 17 a first coating layer 210 is applied to the substrate 200 which may be a 0.2 micron thick layer of LPCVD silicon nitride (Si₃N 4) . As illustrated by Fig. 18, a hole 212 is patterned and etched in the first layer 210 on the top side of the assembly as by using CF₄ plasma. Next, as illustrated in Fig. 19, hole 212 is extended through the first portion 202 of the substrate 200 so as to provide a cavity 214 therein as by etching the exposed surface thereof with a 1:3:8 solution of hydrofluoric acid, nitric acid and acetic acid. A snaking pattern 216, corresponding in shape to electrical element 30, 32, 34 in Fig. 1, is then etched in the first layer 210 on the bottom side of the assembly as by using CF₄, as illustrated in Fig. 20. Next, as illustrated in dashed lines in Fig. 20, resistors 218 e.g. phosphorus resistors are implanted in the lightly doped portion 204 of the substrate in the surface thereof exposed by the snaking pattern etched in layer 210. This resistor implant may be performed using the technique of ion implantation which is well known in the art. The resistor pattern provided may have a resistance of e.g. 1000 ohms. Next, as illustrated by Fig. 21, the remaining portion of coating layer 210 is stripped away as by using H₃PO₄. Figs. 22 and 23 are top and bottom plan views of Fig. 21 showing the cavity 214 and resistor 218 configurations provided in substrate 200. The top surface of substrate 200 shown in Fig. 22 is then positioned in contact with the bottom surface of substrate 100 shown in Fig. 15 and the two substrates are bonded together as by silicon-silicon fusion bonding, which is well known in the art, so as to provide a pump assembly 10 such as shown in Fig. 1.

Claims: A pump apparatus comprising: enclosure means (70) for holding a volume of fluid; intake one-way valve means (46, 58) operatively associated with said enclosure means for enabling intake of fluid into said enclosure means (70); discharge one-way valve means (48, 64) operatively associated with said enclosure means (70) for enabling discharge of fluid from said enclosure means; diaphragm means (28) operatively associated with said enclosure means (70) for cyclically deflectably increasing and decreasing said volume of said enclosure means (70) whereby fluid is cyclically drawn into said enclosure means and discharged therefrom; and means (30) operatively associated with said diaphragm means (28) for selectively cyclically deflecting said diaphragm means; characterized in that said diaphragm means is formed by microfabrication techniques from a wafer comprising a single substrate layer (200) and at least one coating layer (210); said means (30) for deflecting the diaphragm means is a heating means (30) for selectively cyclically applying heat to said diaphragm means and terminating application of heat thereto; and said heating means comprises resistor means (218) integrally formed with said diaphragm means by microfabrication techniques for heating said diaphragm means in response to an electrical current passed therethrough. The apparatus of claim 1 wherein said diaphragm means (28) consists of a portion of said substrate layer of said wafer. The apparatus of claims 1 wherein said enclosure means comprises a pump body formed from a first substrate assembly (12) having a first surface (18) defining an exterior portion of said diaphragm means (28) and a second surface (20) defining an opening (23) of a pump body cavity (22). The apparatus of claim 3 wherein said diaphragm means (28) interfaces with said pump body cavity (22) at an internal surface portion (26) of said first substrate assembly (12). The apparatus of claim 4 further comprising a second substrate assembly (14) attached to said second surface (20) of said first substrate assembly (12) in overlying relationship with said cavity opening (23). The apparatus of claim 5 wherein at least a portion of at least one of said intake and discharge one-way valve means (46,58 and 48,64) are formed from said second substrate member (14). The apparatus of claim 5 wherein said second substrate assembly (14) comprises a first surface (42) attached to said second surface (20) of said first substrate assembly (12) and a second surface (44) positioned parallel to said first surface (42) of said second substrate assembly (14); and wherein said intake one-way valve means comprises: a first hole (46) extending between said first and second surfaces (42,44) of said second substrate member (14); and a first flapper (52) having a first end (56) attached to said first surface (42) of said second substrate assembly (14) and a second end (58) positioned over said first hole (46) in said second substrate assembly (14) in displaceable relationship therewith. The apparatus of claim 7 wherein said discharge one-way valve means comprises: a second hole (48) extending between said first and second surfaces (42,44) of said second substrate assembly (14); and a second flapper (54) having a first end (62) attached to said second surface (44) of said second substrate assembly (14) and a second end (64) positioned over said second hole (48) in said second substrate assembly (14) in displaceable relationship therewith. A method of pumping fluid through an enclosure means (70) having an intake one-way valve (46) and an outlet one-way valve (64) the method comprising: a) providing a substrate layer (200) which is adapted to form a first layer of an integral wafer; b) applying at least one coating layer (210) to said first substrate member to provide at least a second layer of said integral wafer; c) employing microfabrication techniques to expose opposite surface portions of a single one of said at least two layers of said integral wafer so as to create a pump diaphragm having an integrally formed resistor pattern therein from said single one of said layers in the portion thereof having said opposite exposed surface portions, the diaphragm being operatively associated with said enclosure means (70); d) cyclically heating said pump diaphragm formed from said single layer of said wafer by microfabrication techniques by passing electrical current through said internally formed resistor pattern so as to expand and contract said pump diaphragm to pump fluid through the associated enclosure means (70). The method of claim 9 wherein deflecting the diaphragm (28) in the first direction (92) comprises heating the diaphragm and deflecting the diaphragm in the second direction (94) comprises terminating the heating of the diaphragm. The method of claim 9 wherein deflecting the diaphragm in the second direction (94) comprises heating the diaphragm (28) and deflecting the diaphragm in the first direction (92) comprises terminating the heating of the diaphragm. A method of making a pump apparatus according to one of claims 1 to 7 comprising the steps of forming a cavity (22) with an interfacing diaphragm (28) in a first substrate assembly (12); forming a pair of one-way valves (46, 58; 48, 64) in a second substrate assembly (14); attaching said first substrate assembly (12) to said second substrate assembly (14); attaching a cyclic heat source (34) to the diaphragm (28), wherein the step of forming a pair of one-way valves (46, 58; 48, 64) comprises the steps of: forming a first hole through the second substrate assembly; forming a first flapper having a deflectable free end disposed in alignment with the hole which is flexibly displaceable into sealing relationship with the hole. The method of claim 12, wherein said diaphragm (28) is made of one material, not bimetallic. The method of claim 12 or 13, wherein said valves comprise orifices (46,48) and flappers (56;64) said orifices and flappers being made from the same substrate (40). The method of claim 12 wherein said diaphragm (28; 200) is implanted with a pattern of electrically conductive resistor material (218) through the use of microfabrication techniques.

Inventors: BEATTY CHRISTOPHER C, BEATTY, CHRISTOPHER C.
Applicants: HEWLETT PACKARD CO, HEWLETT-PACKARD COMPANY
Application year: 1991
Main classification: F04B43
IPC codes: F04B43, F15C5