Abstract:
A micromachined coupler for coupling a capillary having a first size to an orifice having a shape and a second size, has a body which has a shape conforming the shape of the cavity into which the body must fit. A through hole is defined through the body. The through hole has a size conforming to the first size of the capillary. The capillary is disposable into the through hole so that the capillary is communicated to the orifice without the first and second sizes necessarily being the same. The cavity and the body have conforming slanting surfaces, and in particular the cavity and the body define truncated pyramidal shapes. The cavity and the body each have a truncated pyramidal shape. The pyramidal shape may be square, triangular, or conical. A method of fabricating the micromachined coupler is achieved either by micromaching or micromolding.

Description:
RELATED APPLICATIONS 
     The present application is related to U.S. Provisional Patent Application serial No. 60/124,244 filed on Mar. 12, 1999. 
    
    
     BACKGROUND OF THE INVENTION 
     1. Field of the Invention 
     The invention relates to the field of fluidics and in particular to coupling devices used in microfluidic circuits. 
     2. Description of the Prior Art 
     Rapidly developing Micro Electro Mechanical Systems (MEMS) technology makes micro fluidic systems very attractive for many applications, such as micro heat exchangers, micro chromatographs, biochemical detectors, micro mass spectrometers, micro reactors, and micro fluid control systems (e.g., microchannels, micro valves, micro pumps, and micro flow meters). It is quite challenging to transfer fluids between a micro fluidic system and its macroscopic environment because of micron-scale dimensions. There is no effective and simple way to apply conventional fluidic couplers to microscale fluidic systems at this time. Currently, to achieve coupling, a tube with an inside diameter significantly larger than the size of the inlet or outlet is directly glued to the opening. The yield of this approach is usually very low due to tube misalignment and inlet or outlet blockage by excessive glue. In addition, the permissible number of couplings for a micro fluidic system is limited by the relatively large size of the tubing used, and may not be adequate for the system. Furthermore, such a coupling generally cannot withstand high pressures required in many applications. 
     In order to adapt to the rapidly growing demand for micro fluidic systems, a novel, low-cost, and highly reliable coupling technique is required. The micromachined fluidic couplers proposed and developed at the Caltech Micromachining Laboratory can fulfill this requirement. 
     BRIEF SUMMARY OF THE INVENTION 
     The invention comprises a micromachined coupler for coupling a capillary having a first size to an orifice having a shape and a second size. The invention in particular comprises a substrate, and a cavity defined in the substrate defining the orifice. A body is provide which has a shape conforming the shape of the cavity. A through hole is defined through the body. The through hole has a size conforming to the first size of the capillary. The capillary is disposable into the through hole so that the capillary of the first size is coupled to the orifice of the second size without the first and second sizes necessarily being the same. 
     The cavity and the body have conforming slanting surfaces, and in particular the cavity and the body define truncated pyramidal shapes. The cavity and the body each have a truncated square pyramidal shape, a truncated triangular pyramidal shape, or a truncated conical shape. 
     The micromachined coupler may further comprise a tubing stopper defined in the through hole and/or a shoulder defined on a surface of the coupler for bonding to the substrate outside of the cavity. 
     Typically the size of the orifice is different than the size of the capillary. 
     The invention is also characterized as a method of fabricating a micromachined coupler for coupling a capillary having a first size to an orifice having a shape and a second size comprising the steps of masking a substrate from which will a body of the micromachined coupler will be formed. The masking forms a pattern to define a pyramidal structure in the substrate. The masked substrate is anisotropically etched to form the pyramidal structure including a pit in the pyramidal structure. A surface of substrate opposite the pyramidal structure is then provided with a patterned mask. A prismatic hole is defined through the substrate and communicated with the pit to provide a through hole through the substrate. 
     The step of anisotropically etching the masked substrate to form the pyramidal structure forms a simple truncated structure or a truncated structure with a basal shoulder. 
     In one embodiment the step of defining a prismatic hole through the substrate does not completely remove the pit so that a tubing stop is formed by a remaining portion of the pit. The method further comprises the step of disposing a capillary into the prismatic hole in a sealed relationship therewith. 
     The step of anisotropically etching the masked substrate to form the pyramidal structure forms a square, triangular or conical truncated structure. 
     The invention is still further defined as a method of fabricating a micromachined coupler for coupling a capillary having a first size to an orifice having a shape and a second size comprising the steps of defining a truncated pyramidal cavity in a micromachined mold. A material is disposed or deposited in the truncated pyramidal cavity to form a body of the coupler. A prismatic hole of a first size is defined through the body to define a through hole by deep reactive ion etching. 
     In another embodiment the method further comprises the step of defining by deep reactive ion etching a prismatic hole of a second size in the body aligned with the prismatic hole of the first size to define a tubing stop in the prismatic hole of the first size. 
     The invention now having been briefly summarized, turn to the following drawings wherein the invention may be better visualized and where like elements are reference by like numerals. 
    
    
     BRIEF DESCRIPTION OF THE DRAWINGS 
     FIG. 1 is a diagrammatic perspective view of a microfluidic system coupled with capillaries by means of micromachined fluidic couplers. 
     FIG. 2 is a diagrammatic side cross-sectional view of a coupling of a capillary to the microfluidic system according to the invention as shown in the right side of the drawing and as shown in a conventional coupling without the benefit of the coupler of the invention in the left half of the drawing. 
     FIG. 3 a  is a plan top view of a single inlet or outlet pit shown in enlarged scale. 
     FIG. 3 b  is a cross-sectional view of the pit of FIG. 3 a  as seen through lines  3 — 3  of FIG. 3 a.    
     FIG. 4 is a three-quarter perspective, exploded view of the coupler of the invention shown in combination with the outlet/inlet of the fluidic system and capillary. 
     FIGS. 5 a  and  5   b  cross-sectional diagrammatic side views of the coupler of the invention fitted into inlets/outlets of different diameters or sizes. 
     FIGS. 6 a  and  6   a ′ are the side cross-sectional view and top plan view respectively of a first embodiment of the coupler. 
     FIGS. 6 b  and  6   b ′ are the side cross-sectional view and top plan view respectively of a second embodiment of the coupler. 
     FIGS. 6 c  and  6   c ′ are the side cross-sectional view and top plan view respectively of a third embodiment of the coupler. 
     FIG. 7 is a diagrammatic side cross-sectional view of still another embodiment of the coupler. 
     FIGS. 8 a,    8   b,    8   c  and  8   d  are cross-sectional side views of the invention illustrating the fabrication of the embodiment of FIGS. 6 c  and  6   c′.    
     FIG. 9 is a side cross-sectional view of a coupler of the embodiment of FIGS. 6 c  and  6   c ′ shown bonded to a substrate through a bonding layer. 
     FIGS. 10 a,    10   b,    10   c  and  10   d  illustrate the fabrication steps of molding a coupler. 
     FIG. 11 is a side cross-sectional view which shows the coupler of FIG. 7 fitted to a microfluidic system with small straight inlets and outlets. 
     FIGS. 12 a,    12   b,    12   c  and  12   d  are side cross-sectional views which illustrate the fabrication of a coupler of FIG.  7 . 
    
    
     The invention and various ones of its embodiments now having been illustrated in the above drawings, turn to the following detailed description of the preferred embodiments. 
     DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS 
     Micro fluidic couplers based on micromachining technology have been developed in the Caltech Micromachining Laboratory. By using the uniquely designed couplers, it is possible to easily align capillaries of different sizes to the inlet or outlet of a micro fluidic system. The couplers are strongly bonded directly to a fluidic system. For example, a thin layer of bonding material is applied between the mating surfaces. This coupling technique requires minimal preparation time and is low in complexity, yet provides a robust and high yield interconnect for micro fluidic systems. In addition, the fabrication cost for the couplers is inexpensive because of batch processing. 
     Micromachined fluidic couplers  10  are used to connect fluidic capillaries  12  to a microfluidic system  14  with inlets  16  and outlets  18 , hidden from view by couplers  10  in the depiction of FIG. 1, but explicitly shown in FIG. 2, that may differ from the capillaries  12  in both shape and size. By using such couplers  10 , a fluidic interconnection with multiple channels is built for the microfluidic system  14  as shown in the diagrammatic perspective view FIG.  1 . 
     In general, it is impractical to connect a fluidic capillary  12  directly to the inlet  16  or outlet  18  due to their different shapes and sizes. An intermediate object, i.e. a micromachined coupler  10 , must be introduced to achieve such a coupling. The coupler  10  is designed in such a way that a capillary  12  can be tightly placed into the size-matched hole  20  in the center of the coupler  10  and the coupler  10  can be conformably fitted into the size-matched inlet  16  or outlet  18  defined in substrate  22  as shown in the right half of FIG.  2 . 
     For example, the inlets  16  and outlets  18  in a fluidic system  14  built on a silicon chip or substrate  22  are the pits  26  usually etched into ( 100 ) silicon with an anisotropic wet etch (i.e. KOH, TMAH and EDP) through square openings  24  in the etching mask  28  as shown in FIGS. 3 a  and  3   b.  Such a pit  26  has the pyramidal shape bonded by four ( 111 ) planes as shown in FIGS. 3 a  and  3   b,  and there is yet no effective way to connect a capillary directly to such an inlet  16  or outlet  18 . However, a coupler  10  with the truncated pyramidal shape bonded by four ( 111 ) side walls can now be applied to make such a connection as shown in FIG.  4 . With the similar pyramidal shape formed by an anisotropic wet etching, the coupler  10  can be conformably fitted into the inlet  16  or outlet  18 . A capillary  12  can be placed tightly in the size-matched hole  20  etched in the center of the coupler  10  using deep reactive ion etching (DRIE). Later capillary  12  and coupler  10  can be firmly bonded together by various bonding techniques, such as gluing, polymer film bonding, indium solder bonding, or Au eutectic bonding. 
     Also, as shown in FIGS. 5 a  and  5   b,  a single coupler  10  can be used for an inlet  16  or outlet  18  with various diameters by a variable fitting depth inherent in the design of coupler  10 . 
     Another embodiment of the invention is realized in a truncated pyramidal coupler  10  as shown in FIGS. 6 a,    6   b  and  6   c  and FIGS. 6 a ′,  6   b ′ and  6   c ′. FIGS. 6 a  and  6   a ′ as mentioned before show the simplest design in which a single through-hole  20  on the axis of symmetry of the truncated pyramidal shape is provided. The embodiment of FIGS. 6 b  and  6   b ′ have the same outside shape as coupler  10  of FIG. 6 a  and  6   a ′, but has a tubing stopper  30  inside hole  20  defined as lower circumferential lip in which a hole  32  is defined which has a smaller diameter than hole  20  through the body of coupler  10 . FIGS. 6 c  and  6   c ′ depict a third embodiment which has a shoulder  34 , which can be bonded to the chip substrate  22  of the micro fluidic system  14  to secure the coupling thereto. 
     The micromachined fluidic couplers  10  can be made for inlets  16  and outlets  18  with many other shapes. As shown in FIG. 7, an alignment post  36  made in the same shape as the inlet  16  or outlet  18  can be fitted into the opening  38 , and the adjacent, large flat bonding area  40  can be bonded to the chip substrate  22  of the micro fluidic system  14 . As discussed before, the capillary tubing  12  can be put into the center hole  20  and then bonded to the coupler  10 . A stopper  30  is illustrated in FIG. 7, but may be eliminated if desired. 
     With micromachined couplers  10 , the coupling process becomes less complicated. First, by using the uniquely designed micromachined couplers  10 , small capillaries  12  are easily aligned with the inlets  16  and outlets  18  of a micro fluidic system  14 . Second, by coating a thin layer of bonding material on the surfaces of coupler  10 , micromachined coupler  10  can readily be bonded to a fluidic system  14 . Third, by applying existing bonding techniques such as gluing, polymer film bonding, indium solder bonding, or Au eutectic bonding, a strong coupling can be formed between capillaries  12  and the micro fluidic system  14 . Therefore, this coupling process can provide robust, high-yield fluidic interconnection with minimal preparation time and complexity. 
     The micromachined fluidic couplers  10  can be made from different materials (i.e silicon, metal, and even polymers) that are employed in microfabrication processes By using a batch micromachining process, a large quantity of couplers  10  can be fabricated in a single manufacturing run. Truncated couplers  10  of FIGS. 6 a,    6   b  and  6   c  are designed for the inlet/outlet pits  26  formed by silicon anisotropic wet etching. Post couplers  10  of FIG. 7 are designed for the inlet/outlet pits  26  with any other shapes such as circular pits, rectangular pits, or even triangular pits. Alignment post  36  is manufactured to have a conforming shape to that of the circular pits, rectangular pits, or even triangular pit. 
     Consider now the method of manufacture of a silicon truncated pyramidal coupler  10  as shown in FIGS. 6 c  and  6   c ′. A similar manufacturing process can be used to fabricate the other described embodiments. Silicon truncated pyramidal coupler  10  is fabricated by standard silicon anisotropic wet etching and deep reactive ion etching (DRIE). The process flow is shown in FIGS. 8 a,    8   b,    8   c  and  8   d.  Starting with a &lt;100&gt; silicon prime wafer  22 , a patterned layer of mask material  28  is grown for the following silicon anisotropic wet etch and DRIE. By using a silicon anisotropic wet etch a pyramidal island  42  with a small pit  44  in the center is created on the front side of the wafer  22 . By DRE on the backside  48  of the wafer  22 , a circular pit  20  is etched all the way through to meet the pit  44  on the front side to define hole  32  and stopper  30 . Masking layer  28  is removed. A layer of bonding material is coated before or after the DRE step of FIG. 8 c.  A capillary tube  12 , coated with a thin layer of bonding material, is placed in the size-matched hole  20  and bonded to the coupler  10 . 
     By using the truncated pyramidal silicon couplers  10 , robust, high-yield fluidic interconnection can be easily established. The coupling can be self-aligned by fitting the truncated pyramidal couplers into the shape-matched inlet/outlet pits  26  created by anisotropic etching as shown in FIG.  9 . With a thin layer  50  of bonding material coated on the surfaces, existing bonding techniques (such as gluing, indium solder bonding, or Si—Au eutectic bonding) can be used to bond the couplers  10  to a fluidic system  14 . Strong coupling can be achieved, which allows for high pressures. In addition, the self-aligning feature leads to a high-yield coupling. 
     The truncated pyramidal coupler  10  can also be molded with other materials such plastic, indium solder, and electroplated metals. First, the mold is fabricated on a silicon wafer  52  by an anisotropic wet etch. Then the body  54  truncated pyramidal-shape coupler  10  is molded or electroplated in the silicon mold  52 . Later, the center pit  20  is made by electrode discharge machining (EDM), laser drilling or mechanical drilling. After releasing from the silicon mold  52 , a layer  56  of bonding material is coated on the surface of the coupler  10 . Finally, a capillary tube  12 , coated with a thin layer of glue, is placed in the size-matched hole  20  to bond to the coupler  10 . 
     Post couplers  10  of FIG. 7 are designed for a microfluidic system  14  with small straight inlets and outlets shown in FIG.  11 . By inserting the alignment post  36  into an inlet  16  or outlet  18  of matching size, the coupler  10  and tubing  12  are automatically aligned to the inlet/outlet  16 / 18 . With the strong bond formed by the bonding material and large bonding surface, the coupling can withstand very high pressures. 
     Post coupler  10  is fabricated on a silicon wafer  22  by etching three times via DRIE. The process flow is shown in FIGS. 12 a.  Starting from a flat wafer  22  in FIG. 12 a,  a 200 to 300 μm deep pit  60  is etched on the front side  58 , and then an 50 to 100 μm high alignment post  36  is masked and formed on the front side by etching down the unmasked area  62  as shown in FIG. 12 b.  The post  36  is designed such that its size closely matches that of the inlets/outlets  16 / 18 . On the backside  64 , a pit  66  is etched down all the way to meet pit  60  through front side  58  as shown in FIG. 12 c.  The size of the pit  66  on the backside  64  is chosen to closely match the size of the tubing  12 . After coating with a bonding layer, a tube  12  is inserted into the pit  66  through the backside  64  and then bonded to the coupler  10  as shown in FIG. 12 d.    
     Many alterations and modifications may be made by those having ordinary skill in the art without departing from the spirit and scope of the invention. Therefore, it must be understood that the illustrated embodiment has been set forth only for the purposes of example and that it should not be taken as limiting the invention as defined by the following claims. For example, notwithstanding the fact that the elements of a claim are set forth below in a certain combination, it must be expressly understood that the invention includes other combinations of fewer, more or different elements, which are disclosed in above even when not initially claimed in such combinations. 
     The words used in this specification to describe the invention and its various embodiments are to be understood not only in the sense of their commonly defined meanings, but to include by special definition in this specification structure, material or acts beyond the scope of the commonly defined meanings. Thus if an element can be understood in the context of this specification as including more than one meaning, then its use in a claim must be understood as being generic to all possible meanings supported by the specification and by the word itself. 
     The definitions of the words or elements of the following claims are, therefore, defined in this specification to include not only the combination of elements which are literally set forth, but all equivalent structure, material or acts for performing substantially the same function in substantially the same way to obtain substantially the same result. In this sense it is therefore contemplated that an equivalent substitution of two or more elements may be made for any one of the elements in the claims below or that a single element may be substituted for two or more elements in a claim. 
     Insubstantial changes from the claimed subject matter as viewed by a person with ordinary skill in the art, now known or later devised, are expressly contemplated as being equivalently within the scope of the claims. Therefore, obvious substitutions now or later known to one with ordinary skill in the art are defined to be within the scope of the defined elements. 
     The claims are thus to be understood to include what is specifically illustrated and described above, what is conceptionally equivalent, what can be obviously substituted and also what essentially incorporates the essential idea of the invention.