Abstract:
An exemplary method for making a micropump device is disclosed as providing inter alia a substrate ( 300 ), an inlet opening ( 310 ), and outlet opening ( 340 ), a pump chamber ( 370 ) and flapper valves ( 350, 360 ). The fluid inlet channel ( 310 ) is generally configured to flow a fluid through/around the inlet opening flapper valve ( 350 ). The outlet opening flapper valve ( 360 ) generally provides means for preventing or otherwise decreasing the incidence of outlet fluid re-entering either the pumping cavity ( 370 ) and/or the fluid inlet channel ( 310 ). Accordingly, the reduction of backflow generally tends to enhance overall pumping efficiency. Disclosed features and specifications may be variously controlled, adapted or otherwise optionally modified to improve micropump operation in any microfluidic application. Exemplary embodiments of the present invention representatively provide for substantially self-priming gas/liquid micropumps that may be readily integrated with existing portable ceramic technologies for the improvement of device package form factors, weights and other manufacturing and/or device performance metrics.

Description:
FIELD OF INVENTION  
         [0001]    The present invention relates to micropumps, and more particularly, in one representative and exemplary embodiment, to piezoelectrically actuated, high aspect ratio micropumps having integrated check valves for improved performance, efficiency and production cost savings in microfluidic applications.  
         BACKGROUND  
         [0002]    Development of microfluidic technology has generally been driven by parallel ontological advancements in the commercial electronics industry with the ever-increasing demand for sophisticated devices having reduced part counts, weights, form factors and power consumption while improving or otherwise maintaining overall device performance. In particular, advancement of microfluidic technology has met with some success in the areas of packaging and the development of novel architectures directed to achieving many of these aims at relatively low fabrication cost.  
           [0003]    The development of microfluidic systems, based on for example, multilayer laminate substrates with highly integrated functionality, have been of particular interest. Monolithic substrates formed from laminated ceramic have been generally shown to provide structures that are relatively inert or otherwise stable to most chemical reactions as well as tolerant to high temperatures. Additionally, monolithic substrates typically provide for miniaturization of device components, thereby improving circuit and/or fluidic channel integration density. Potential applications for integrated microfluidic devices include, for example, fluidic management of a variety of Microsystems for life science and portable fuel cell applications. One representative application includes the use of ceramic materials to form micro-channels and/or cavities within a laminate structure to define, for example, a high aspect ratio micropump.  
           [0004]    Conventional pumps and pumping designs have been used in several applications; however, many of these are generally too cumbersome and complex for application with microfluidic systems. For example, existing designs typically employ numerous discrete components externally assembled or otherwise connected together with plumbing and/or component hardware to produce ad hoc pumping systems. Consequently, conventional designs have generally not been regarded as suitable for integration with portable ceramic technologies or in various applications requiring, for example, reduced form factor, weight or other desired performance and/or fabrication process metrics. Moreover, previous attempts with integrating microfluidic pumps in laminated substrates have met with considerable difficulties in producing reliable fluidic connections and/or hermetic seals capable of withstanding manufacturing processes and/or operational stress while maintaining or otherwise reducing production costs. Accordingly, despite the efforts of prior art pump designs to miniaturize and more densely integrate components for use in microfluidic systems, there remains a need for high aspect ratio micropumps having integrated check valves suitably adapted for incorporation with, for example, a monolithic device package.  
         SUMMARY OF THE INVENTION  
         [0005]    In various representative aspects, the present invention provides a system and method for fluid transport in microfluidic systems. A representative design is disclosed as comprising a fluid inlet opening, a fluid outlet opening, a pumping cavity, a reservoir cavity, a check valve substantially enclosed within each of the cavities, and means for moving fluid through the device. An integrated high aspect ratio micropump, in accordance with one embodiment of the present invention, may be formed utilizing multilayer ceramic technology in which check valves are integrated into a laminated ceramic structure; however, the disclosed system and method may be readily and more generally adapted for use in any fluid transport system. For example, the present invention may embody a device and/or method for providing integrated pumping and/or valving systems for use in fuel cell fuel delivery and/or partitioning applications.  
           [0006]    One representative advantage of the present invention would allow for improved process control and manufacturing of integrated micropump systems at substantially lower cost. Additional advantages of the present invention will be set forth in the Detailed Description which follows and may be obvious from the Detailed Description or may be learned by practice of exemplary embodiments of the invention. Still other advantages of the invention may be realized by means of any of the instrumentalities, methods or combinations particularly pointed out in the claims. 
       
    
    
     BRIEF DESCRIPTION OF THE DRAWINGS  
       [0007]    Representative elements, operational features, applications and/or advantages of the present invention reside inter alia in the details of construction and operation as more fully hereafter depicted, described and claimed—reference being had to the accompanying drawings forming a part hereof, wherein like numerals refer to like parts throughout. Other elements, operational features, applications and/or advantages will become apparent to skilled artisans in light of certain exemplary embodiments recited in the detailed description, wherein:  
         [0008]    [0008]FIG. 1 representatively depicts a cross-section, elevation view of a package substrate in accordance with an exemplary embodiment of the present invention;  
         [0009]    [0009]FIG. 2 representatively illustrates one exemplary method for depositing check valves within the package substrate depicted in FIG. 1; and  
         [0010]    [0010]FIG. 3 representatively depicts a cross-section, elevation view of an assembled and substantially sealed micropump device package in accordance with another embodiment of the present invention. 
     
    
       [0011]    Those skilled in the art will appreciate that elements in the Figures are illustrated for simplicity and clarity and have not necessarily been drawn to scale. For example, the dimensions of some of the elements in the Figures may be exaggerated relative to other elements to help improve understanding of various embodiments of the present invention.  
       DETAILED DESCRIPTION OF EXEMPLARY EMBODIMENTS  
       [0012]    The following descriptions are of exemplary embodiments of the invention and the inventors&#39; conceptions of the best mode and are not intended to limit the scope, applicability or configuration of the invention in any way. Rather, the following description is intended to provide convenient illustrations for implementing various embodiments of the invention. As will become apparent, changes may be made in the function and/or arrangement of any of the elements described in the disclosed exemplary embodiments without departing from the spirit and scope of the invention.  
         [0013]    Various representative implementations of the present invention may be applied to any system and/or method for fluid transport. As used herein, the terms “fluid”, “fluidic” and/or any contextual, variational or combinative referent thereof, are generally intended to include anything that may be regarded as at least being susceptible to characterization as generally referring to a gas, a liquid, a plasma and/or any matter, substance or combination of compounds substantially not in a solid or otherwise effectively immobile condensed phase. As used herein, the terms “inlet” and “outlet” are generally not used interchangeably. For example, “inlet” may generally be understood to comprise any cross-sectional area or component feature of a device, the flux through which tends to translate fluid from a volume element substantially external to the device to a volume element substantially internal to the device; whereas “outlet” may be generally understood as referring to any cross-sectional area or component feature of a device, the flux through which tends to translate fluid from a volume element substantially internal to the device to a volume element substantially external to the device. On the other hand, as used herein, the terms “liquid” and “gas” may generally be used interchangeably and may also be understood to comprise, in generic application, any fluid and/or any translationally mobile phase of matter. As used herein, the term “purged”, as well as any contextual or combinative referent or variant thereof, is generally intended to include any method, technique or process for moving a volume element of fluid through the outlet of a device so as to dispose or otherwise positionally locate the “purged” volume element external to the device. Additionally, as used herein, the terms “valve” and “valving”, as well as any contextual or combinative referents or variants thereof, are generally intended to include any method, technique, process, apparatus, device and/or system suitably adapted to control, affect or otherwise parameterize fluid flow scalar quantities (e.g., volume, density, viscosity, etc.) and/or fluid flow vector quantities (i.e., direction, velocity, acceleration, jerk, etc.). Additionally, as used herein, the terms “pump” and “pumping”, or any contextual or combinative referents or variants thereof, are generally intended to include any method, technique, process, apparatus, device and/or system suitably adapted to flow or otherwise translate a fluid volume element from a first location to a second location.  
         [0014]    A detailed description of an exemplary application, namely a system and method for making a micropump in a laminar device package is provided as a specific enabling disclosure that may be readily generalized by skilled artisans to any application of the disclosed system and method for microfluidic transport in accordance with various embodiments of the present invention. Moreover, skilled artisans will appreciate that the principles of the present invention may be employed to ascertain and/or realize any number of other benefits associated with fluid transport such as, but not limited to: improvement of pumping efficiency; reduction of device weight; reduction of device form factor; improved sample loading in microfluidic assays; improvement in sample throughput; sample multiplexing and/or parallel sample processing; integration with micro-array techniques and/or systems; microfluidic sample transport; pumping of fuel and/or fuel components in a fuel cell system and/or device; and any other applications now known or hereafter developed or otherwise described in the art.  
         [0015]    In one representative application, in accordance with an exemplary embodiment of the present invention, a laminar micropump system, as generally depicted in FIG. 3, is disclosed. The system generally includes at least one substantially flexible, or otherwise at least partially deformable, material comprising, for example, a flapper valve  350 ,  360 . The disclosed valving system, in certain representative embodiments, may include features to control the effective magnitude of cross-sectional area presented for fluid acceptance in order to at least partially control or otherwise parameterize fluid flux through said inlet opening  310  and/or outlet opening  340 . For example, inlet opening  310  and/or outlet opening  340  may comprise a taper, a flare, a constriction, a plurality of corrugations, a bend, a pinch, an oblique plane of fluid acceptance (e.g., wherein inlet opening  310  and/or outlet opening  340  facial alignment generally may be other than normal to the instantaneous vector of fluid flow) or such other means, features and/or methods now known, subsequently developed or otherwise hereafter described in the art.  
         [0016]    The operation of flapper valves  350 ,  360  generally provide passive means for substantially preventing or otherwise controlling or restricting the backflow of purged outlet fluid into reservoir chamber  330  and/or pumping chamber  370 . For example, outlet flapper valve  360  generally permits fluid flow when the flow vector (e.g., the direction of fluid pressure; also termed the “fluid transport gradient”) corresponds to translation of fluid volume elements away from inlet opening  310  through fluidic channels  320  toward outlet opening  340 . Additionally, outlet flapper valve  360 , in accordance with representative aspects of the present invention, conjunctively provides for effective prevention of fluid flow to outlet opening  340  when the instantaneous fluid transport gradient corresponds to translation of fluid volume elements away from outlet opening  340  through fluidic channels  320  toward inlet opening  310  (e.g., “backflow”). In an alternative exemplary embodiment, reservoir chamber  330  and/or pumping chamber  370  may further or alternatively comprise a mixing chamber, a reaction chamber and/or a fuel reformer chamber (in the case of application of the present invention, for example, to fuel cell systems).  
         [0017]    One exemplary implementation of the present invention may be manufactured from the substrate representatively illustrated in FIG. 1, wherein a laminar substrate  300  is provided for the fabrication of a piezo-driven micropump. Outlet opening  310  is suitably configured to provide a path for fluid transport to pumping chamber  370 . Fluidic channel  320  provides fluidic communication between pumping chamber  370  and reservoir chamber  330 . Reservoir chamber  330  is generally configured to provide effective fluidic communication to outlet opening  340 . Skilled artisans, however, will appreciate that other channel configurations and/or circuit geometries may be employed in order to define inter alia various fluidic transport paths, for example, in a laminar substrate in accordance with various other embodiments of the present invention.  
         [0018]    In one representative embodiment, openings for disposing flapper valves  350 ,  360  are defined in substrate  300  such that flapper valves  350 ,  360  may be suitably deposited in pumping chamber  370  and reservoir chamber  330  respectively, from substantially the same surface of substrate  300  presented during fabrication as depicted, for example, in FIG. 2. One exemplary benefit of the disclosed method of same-side device assembly resides in fewer process fabrication/control steps resulting in substantially lowered cost of production.  
         [0019]    Other means for providing substantially passive valving function other than that of a flapper valve include, for example: a slit (e.g., duckbill valve), a plunger, a shuttle, a rotary stop-cock, a one-way flow gate or any other device feature, method or means for substantially passive valving now known, subsequently developed or hereafter described in the art. The same may be alternatively, conjunctively or sequentially used in various embodiments of the present invention. Skilled artisans will appreciate that the term “passive”, as it may refer to valving devices and/or function, generally connotes the ability of a valve and/or valve device feature so characterized, to actuate the operation of restriction, constriction and/or dilation of fluid inlet acceptance and/or fluid outlet purging in effective correspondence to the forces nominally inherent to the translation of fluid volume elements through the valve device. That is to say, when the fluid flow is in a first direction, the fluidic forces operate to actuate the valve into a first conformation (i.e., substantially open); and, when the fluid flow is in a second direction (e.g., for a binary valve, generally given as the “opposite direction”), the fluidic forces operate to actuate the valve into a second conformation (i.e., substantially closed).  
         [0020]    In various exemplary embodiments, flapper valves  350 ,  360  may be fabricated from silicone, silicone-based rubber, rubber, metal, metal alloy, polymer or such other materials whether now known or subsequently discovered or otherwise hereafter described in the art. In an exemplary application where passive check valves  350 ,  360  comprise flapper valves, as generally depicted, for example, in FIG. 2, the valves may comprise a silicone-based rubber material. Additionally, flapper valves  350 ,  360  may optionally comprise means for attachment, such as, for example, an extension tab having a substantially annular retaining ring for securing or otherwise at least partially immobilizing flapper valve  350 ,  360  within device package substrate  300 . Various other attachment means and/or packaging features for retaining, localizing or otherwise disposing check valves known in the art may be used as well. For example, the following retaining means may be conjunctively, alternatively or sequentially employed: adhesives, organic epoxies, a mechanical anchor, press-fit clips, solder, clamps, seals, adaptors and/or such other retention, connection or attachment devices, means and/or methods, whether now known or otherwise hereafter described in the art.  
         [0021]    [0021]FIG. 3 generally depicts two passive flapper valves  350 ,  360  disposed within an exemplary monolithic package substrate  300 . The device package  300  generally comprises an input microfluidic channel  310 , an output microfluidic channel  340  and pump actuator element  380 . In one representative embodiment, pump actuator may comprise a piezoelectric micropump element  380 . In an exemplary embodiment, piezoelectric element  380  may be secured to the package substrate  300  by, for example, solder  390 . Accordingly, substrate  300  may comprise solder-wettable features  305  that are generally provided to permit secure solder attachment of piezoelectric element  380  and/or cover  375  to substrate  300 . Various other means for attaching piezoelectric element  380  and/or cover  375  to package substrate  300  may include, for example: epoxy, adhesive and/or such other attachment means and/or methods whether now known or hereafter described in the art. In yet another exemplary embodiment of the present invention, piezoelectric element  380  may alternatively be integrated within the package substrate; for example, between ceramic layers in a position substantially internal to the device as the package is built up.  
         [0022]    As electric current is supplied to the package, piezoelectric element  380  operates as a deformable diaphragm membrane whose deformation (e.g., “stroke volume”) causes oscillating over- and under-pressures in pump chamber  370 . Pump chamber  370 , in an exemplary embodiment, may be bounded by, for example, two passive check valves  350 ,  360 . The pump actuation mechanism  380  need not be limited to piezoelectric actuation, but may alternatively, sequentially or conjunctively be driven by electrostatic or thermopneumatic actuation or such other means and/or methods now known, subsequently derived or otherwise hereafter described in the art.  
         [0023]    During the movement of the diaphragm element (i.e., piezoelectric element  380 ) in a direction which tends to enlarge the pump chamber volume, an under-pressure is generated in pump chamber  370  causing fluid to flow through inlet channel  310  in a flow direction which causes pump flapper valve  350  to distend toward piezoelectric element  380  thereby permitting fluid to flow around flapper valve  350  to enter into pump chamber  370 . Since the fluid transport gradient during the under-pressure stroke is anti-parallel to the fluid flow acceptance conformation of reservoir flapper valve  360 , flapper valve  360  seals so as to at least partial reduce the occurrence of fluid disposed in outlet channel  340  re-entering via fluidic channel  320  into pump chamber  370  (e.g., backflow). Accordingly, this component of the pump cycle is termed the “supply mode” or the “supply stroke”.  
         [0024]    In the alternate and next phase of the stroke cycle, the movement of the diaphragm element  380  in a direction which tends to reduce the pump chamber volume causes an over-pressure to be generated in pump chamber  370 , thereby flowing fluid through outlet opening  340  as a result of fluid flowing out of pump chamber  370  into fluidic channel  320  in a flow direction which causes reservoir flapper valve  360  to distend toward, for example, cover plate  375  thereby permitting fluid to flow around flapper valve  370  to enter into reservoir chamber  330  and subsequently into outlet channel  340 . Since the fluid transport gradient during the over-pressure stroke is anti-parallel to the fluid flow acceptance conformation of pump flapper valve  350 , flapper valve  350  seals so as to at least partial reduce the occurrence of fluid disposed in pump chamber  370  from back-flowing into the inlet channel  310 . Accordingly, this component of the pump cycle is termed the “pumping mode” or the “delivery stroke”.  
         [0025]    The volume of the pump chamber upon relaxation of the actuation diaphragm is known as the dead volume V 0  and the volume the actuation membrane deflects during a pump cycle generally defines the stroke volume ΔV. The ratio between the stroke volume and dead volume may be used to express the compression ratio ε. Due in part to the relatively small stroke of micro-actuators and the relatively large dead volume, the compression ratio  
       ɛ   =       Δ                 V       V   0                             
 
         [0026]    is usually relatively small.  
         [0027]    The pressure cycles (e.g., “pressure waves”) generated from the actuation supply and pump modes typically operate to switch the valves. In the limit of the pump chamber  370  being filled with an ideally incompressible fluid, the pressure waves would ideally propagate from the actuation diaphragm to the valves with no net pressure loss—in which case, the compression ratio is generally not regarded as an important metric of pump performance and/or efficiency. However, where the fluid medium is not ideally incompressible, there exists a compressibility factor κ&gt;0 which may be employed to characterize the tendency of a real fluid to dampen the propagation of the actuation pressure wave Δp. If the pressure change Δp falls below a certain value p′ (e.g., the threshold pressure differential for actuation of a valve), the pump generally will not properly operate. Accordingly, a minimum condition for operation of any micropump may be expressed as |Δp|≧|p′|.  
         [0028]    Given the compressibility κ of a liquid, the pressure change Δp may be calculated (if the volume change ΔV induced by the actuator is known) in accordance with the equation V 0 +ΔV=V 0 (1−κΔp). If this expression is substituted into those previously presented, the compressibility ratio ε for liquid micropumps may be expressed as ε liquid ≧κ|p′|. Accordingly, a threshold valve actuation pressure p′ of 1 kPa in combination with the compression ratio for water κ water  (5*10 −9  m 2 /N) would yield a minimum compression ratio ε water  of 510 −6 . In this case, where the stroke volume ΔV is assumed to be 50 nl, the dead volume V 0  generally may not exceed 10 ml. Skilled artisans, however, will appreciate that the preceding example will generally only hold true where the pump chamber  370  is completely filled with liquid and no degassing and/or bubble occlusion occurs during micropump operation and therefore provides a first-order approximation for the determination of operational parameters and/or design specifications.  
         [0029]    In the case of a gas pump, assuming an ideal gas having an adiabatic coefficient of γ (1.4 for air), at atmospheric pressure p 0  and an actuation pressure wave of magnitude Δp, the following expression may be obtained:  
           p   0   V   0   γ =( p   0   +Δp )( V   0   +ΔV ) γ   
         [0030]    Accordingly, it may be shown that the criterion for the compression ratio of a gas micropump may be similarly derived as  
         ɛ   gas     ≥         (       p   0         p   0     -          p   ′              )       1   γ       -   1                           
 
         [0031]    and, in the case of isothermal state transitions, the adiabatic coefficient γ may be taken as equal to unity. For the device previously presented for the micropumping of water (e.g., p′=1 kPa and ΔV=50 nl), the dead volume V 0  for the same system adapted for the micropumping of air must generally not exceed 5 μl.  
         [0032]    In conventional micropump operation, gas bubbles may often remain in the pump chamber during the priming procedure and/or the liquid may even volatized in response to temperature changes during operation. In these cases, the expression for the compression ratio of a liquid ε liquid ≧κ|p′| will no longer hold true since the compressibility of the gas bubble is generally much larger than the compressibility of the liquid. Depending on the volume of the gas bubble, the actuation pressure wave will be dampened in an amount that may be calculated if the volume of the gas bubble is substituted for the dead volume in the appropriate equation presented vide supra. If the gas bubble volume becomes so large that the actuation pressure wave falls below the threshold valve actuation pressure, the micropump will fail. Consequently, in the limit of the entire pump chamber volume being filled with a gas, the operational design criteria for liquid self-priming pumps converges to the design criteria for those of gas micropumps.  
         [0033]    Additionally, in practical applications, the design criteria may even need to be more stringent to account for higher-order fluid dynamics. For example, self-priming liquid micropumps must typically suck the liquid meniscus from the inlet  310  into the pump chamber  370 , thereby increasing the threshold critical pressure p′ in parity with the surface tension of the meniscus at the juncture between and/or within, for example, the microfluidic channels and the microfluidic valves. Those skilled in the art will recognize that other fluid dynamics and/or parametric contributions may require consideration in the determination of optimal operational specifications for a micropump in accordance with the present invention as they may be employed in a variety of practical applications and/or operating environments. The same shall be regarded as within the scope and ambit of the present invention.  
         [0034]    In the foregoing specification, the invention has been described with reference to specific exemplary embodiments; however, it will be appreciated that various modifications and changes may be made without departing from the scope of the present invention as set forth in the claims below. The specification and figures are to be regarded in an illustrative manner, rather than a restrictive one and all such modifications are intended to be included within the scope of the present invention. Accordingly, the scope of the invention should be determined by the claims appended hereto and their legal equivalents rather than by merely the examples described above. For example, the steps recited in any method or process claims may be executed in any order and are not limited to the specific order presented in the claims. Additionally, the components and/or elements recited in any apparatus claims may be assembled or otherwise operationally configured in a variety of permutations to produce substantially the same result as the present invention and are accordingly not limited to the specific configuration recited in the claims.  
         [0035]    Benefits, other advantages and solutions to problems have been described above with regard to particular embodiments; however, any benefit, advantage, solution to problems or any element that may cause any particular benefit, advantage or solution to occur or to become more pronounced are not to be construed as critical, required or essential features or components of any or all the claims.  
         [0036]    As used herein, the terms “comprises”, “comprising”, or any variation thereof, are intended to reference a non-exclusive inclusion, such that a process, method, article, composition or apparatus that comprises a list of elements does not include only those elements recited, but may also include other elements not expressly listed or inherent to such process, method, article, composition or apparatus. Other combinations and/or modifications of the above-described structures, arrangements, applications, proportions, elements, materials or components used in the practice of the present invention, in addition to those not specifically recited, may be varied or otherwise particularly adapted by those skilled in the art to specific environments, manufacturing specifications, design parameters or other operating requirements without departing from the general principles of the same.