Abstract:
An internal filter includes a lower substrate and an upper substrate. Fluid passages are formed by etching grooves into the surface(s) of the upper and/or lower substrates, and/or in one or more intermediate layers. The filter pores extending between the fluid passages are formed by etching second grooves that fluidly connect the fluid passages. Two or more sets of the one or two intermediate layers can be implemented to provide additional filter passages and/or pores. Each set can be connected to a separate fluid source and/or a separate microfluidic device. In another internal filter, the inlet and outlet passages and the filter pores are formed on the same upper or lower substrate. The inlet and outlet passages are partially formed in a first step. In a second step, the inlet and outlet passages are completed at the same time that the filter pores are formed.

Description:
BACKGROUND OF THE INVENTION  
       [0001]     1. Field of Invention  
         [0002]     This invention relates to systems and methods for fabricating internal die filters.  
         [0003]     2. Description of Related Art  
         [0004]     In a wide range of fluid processing applications, including those in the printing, medical, chemical, biochemical, genetic, automotive and energy fields, it is necessary to separate particles out of the fluid. For example, foreign particles or internally-generated particles may interfere with the subsequent intended use of the fluid, by potentially obstructing a small fluidic passageway in a critical region. Alternatively, the particles generated in the process may be a desired product. Consequently, it is necessary or desirable to capture such particles.  
         [0005]     In particular, there is a class of devices, called microfluidic devices, in which a fluid enters the device and is then processed in some way by the device. Such microfluidic devices typically have an inlet for the fluid, a fluid processing region, and small fluidic passageways which bring the fluid from the inlet to the fluid processing region, and optionally, from the processing region to an outlet.  
         [0006]     In some applications, a filter is fabricated which is internal to the microfluidic device. Such an internal filter is used in addition to or instead of an external filter. An advantage of the internal filter is that it may be placed immediately adjacent to the fluid processing region, either upstream of or downstream of the fluid processing region. Placing the internal filter in such upstream locations catches unwanted particles which might pass through the external filter, if used, as well as particles which developed downstream of the external filter to the device. A challenge for the internal filter is to form many fluidically parallel filter pore passageways so that fluid can be processed with high throughput and all necessary particles caught without causing too high a fluid impedance as the filter loads up with particles.  
         [0007]     U.S. Pat. No. 4,639,748 to Drake et al, which is incorporated herein by reference in its entirety, discloses one exemplary embodiment of a particular fabrication method for an internal filter with fluidically parallel filter pores usable in a thermal ink jet printhead. The method disclosed in the 748 patent uses a sequence of anisotropic, isotropic, and anisotropic chemical etches in a silicon wafer to form the major fluid passageways within the device, as well as to form the filter pores.  
       SUMMARY OF THE INVENTION  
       [0008]     One limitation of the fabrication process described in the incorporated 748 patent is that the material of the device surrounding the fluid passageways and filter pores needs to be single crystal silicon or other material compatible with orientation-dependent chemical etching. This process dictates that 1) the fluid passageways must be straight when seen from the etched surface, 2) each individual fluid passageway must be uniform along its length, 3) intersecting fluid passageways must be at right angles to each other, and 4) the fluid passageways must be substantially triangular in cross-section.  
         [0009]     A second limitation of the fabrication process described in the incorporated 748 patent is that the some of the chemical etch steps need to be carefully controlled in terms of bath composition, temperature, and/or duration, in order to prevent overetching or underetching of the critical features.  
         [0010]     This invention provides systems and methods that eliminate one or more of the limitations of the incorporated 748 patent.  
         [0011]     This invention separately provides systems, methods and materials that do not require tight process control methods and materials that are less expensive.  
         [0012]     This invention separately provides systems and methods that eliminate one or more of the geometric limitations of the incorporated 748 patent.  
         [0013]     This invention separately provides internal filter as having many fluidically parallel filter pore passageways.  
         [0014]     This invention separately provides an internal filter that has multiple stages of filtering within the microfluidic device.  
         [0015]     This invention separately provides an internal filter that can be provided in downstream locations relative to a fluid processing region or device.  
         [0016]     In various exemplary embodiments, an internal filter according to this invention includes a lower substrate, an upper substrate and two intermediate layers. Fluid passages are formed by etching (or the like) through the thickness of a first one of the intermediate layers. The filter pores extending between the fluid passages are formed by etching (or the like) through the thickness of the second one of the two intermediate layers. In various exemplary embodiments, two or more sets of the two intermediate layers can be implemented to provide additional filter passages and/or pores.  
         [0017]     In various other exemplary embodiments, an internal filter according to this invention includes a lower substrate and an upper substrate. Both the inlet and outlet passages and the filter pores are formed on the same upper or lower substrate. In these exemplary embodiments, the inlet and outlet passages are partially formed in a first step. Then, in a second step, the inlet and outlet passages are completed at the same time that the filter pores are formed.  
         [0018]     In various other exemplary embodiments, discrete internal filters can each be connected to a separate fluid source and/or a separate microfluidic device or the like. In various other exemplary embodiments, two or more internal filters can be connected in series. In these exemplary embodiments, the outlet side passage of an upstream internal filter is the inlet side passage for a downstream internal filter. In various exemplary embodiments, one or more of the above-described internal filters can be provided at each of one or more locations downstream of a fluid processing region or device. Placing the internal filter downstream of the fluid processing region catches wanted or unwanted particles which are generated in the fluid processing region or device.  
         [0019]     These and other features and advantages of this invention are described in, or are apparent from, the following detailed description of various exemplary embodiments of the systems and methods according to this invention. 
     
    
     BRIEF DESCRIPTION OF THE DRAWINGS  
       [0020]     Various exemplary embodiments of this invention will be described in detail, with reference to the following figures, wherein:  
         [0021]      FIG. 1  is a top plan view of various exemplary embodiments of an internal filter with interleaved comb fluid pathways connected by multiple sets of filter pores in accordance with this invention;  
         [0022]      FIG. 2  is a first cross-sectional view of a first exemplary embodiment of the internal filter shown in  FIG. 1 ;  
         [0023]      FIG. 3  is a second cross-sectional view of the first exemplary embodiment of the internal filter shown in  FIG. 2 ;  
         [0024]      FIG. 4  is a first cross-sectional view of a second exemplary embodiment of an internal filter corresponding to the top plan view shown in  FIG. 1 ;  
         [0025]      FIG. 5  is a second cross-sectional view of the second exemplary embodiment of the internal filter shown in  FIG. 4 ;  
         [0026]      FIG. 6  is a first cross-sectional view of a third exemplary embodiment of an internal filter corresponding to the top plan view shown in  FIG. 1 ;  
         [0027]      FIG. 7  is a second cross-sectional view of the third exemplary embodiment of the internal filter shown in  FIG. 6 ;  
         [0028]      FIG. 8  is a first cross-sectional view of a fourth exemplary embodiment of an internal filter corresponding to the top plan view shown in  FIG. 1 ;  
         [0029]      FIG. 9  is a second cross-sectional view of the fourth exemplary embodiment of the internal filter shown in  FIG. 8 ;  
         [0030]      FIGS. 10 and 11  illustrate a substrate processed according to a first step of one exemplary embodiment of a method for making a fifth exemplary embodiment of an internal filter according to this invention;  
         [0031]      FIGS. 12 and 13  illustrate a second step of one exemplary embodiment of the method for forming the fifth exemplary embodiment of the internal filter according to this invention;  
         [0032]      FIGS. 14 and 15  illustrate a substrate processed according to a first step of one exemplary embodiment of a method for making a sixth exemplary embodiment of an internal filter according to this invention;  
         [0033]      FIGS. 16 and 17  illustrate a second step of one exemplary embodiment of the method for forming the sixth exemplary embodiment of the internal filter according to this invention;  
         [0034]      FIG. 18  is a first cross-sectional view of a seventh exemplary embodiment of an internal filter corresponding to the top plan view shown in  FIG. 1 ;  
         [0035]      FIG. 19  is a second cross-sectional view of the seventh exemplary embodiment of the internal filter shown in  FIG. 18 ;  
         [0036]      FIG. 20  is a first cross-sectional view of a variation of the seventh exemplary embodiment of an internal filter corresponding to the top plan view shown in  FIG. 18 ;  
         [0037]      FIG. 21  is a second cross-sectional view of the variation of the seventh exemplary embodiment of the internal filter shown in  FIG. 20 ;  
         [0038]      FIG. 22  is a top plan view illustrating an eighth exemplary embodiment of an internal filter according to this invention; and  
         [0039]      FIG. 23  is a top plan view illustrating a ninth exemplary embodiment of an internal filter according to this invention. 
     
    
     DETAILED DESCRIPTION OF EXEMPLARY EMBODIMENTS  
       [0040]      FIG. 1  is a top plan view of a first exemplary embodiment of an internal filter  100  having interleaved comb fluid pathways  110  and  120  connected by multiple sets of filter pores  130  in accordance with this invention. As shown in  FIG. 1 , the inlet side passageway  110  has a plurality of extensions  112  that are configured in a comb pattern and may be placed, for example, near the fluid inlet to the microfluidic device. The outlet side passageway  120  has a plurality of extensions  122  that are also configured in a comb pattern. The fluid passes from the extensions  112  of the inlet side passageway  110  to the extensions  122  of the outlet side passageway  120  through the filter pores  130 .  
         [0041]     The fluid in the outlet side passageway  120  has a substantial number of particles removed relative to the fluid in the inlet side passageway  110 . The removed particles are those of a size and shape such that cannot pass through the filter pores  130 . The fluid may then pass from the outlet side passageway  120  to the fluid processing region of the microfluidic device. It should be appreciated that, when particles are generated in the fluid processing region of the microfluidic device, the internal filter is fabricated downstream of the fluid processing region. In this case, the fluid coming from the processing region would enter the inlet side passageway  110  and the particles would be trapped in the filter pores  130 , with the fluid proceeding to the outlet side passageway  120 .  
         [0042]      FIG. 2  is a first cross-sectional view of a first exemplary embodiment of the internal filter shown in  FIG. 1 .  FIGS. 2 and 3  show the pores  130  made in an upper substrate while the major passages are made in a lower substrate. This cross-sectional view is taken along the line II-II shown in  FIG. 1 . As shown in  FIG. 2 , the filter pores  130  are etched into a single upper substrate  140 , which is made of crystal silicon or other material compatible with orientation-dependent chemical etching. As shown in  FIG. 2 , the extensions  112  of the inlet side passageways  110  and the extensions  122  of the outlet side passageways  120  are etched into a single lower substrate  150 , which is made of crystal silicon or other material compatible with orientation-dependent chemical etching. As shown in FIG.  2 , the fluid passes from the wider extensions  112  of the inlet side passageways  110  through the narrower filter pores  130  and into the wider extensions  122  of the outlet side passageways  120 .  
         [0043]      FIG. 3  is a second cross-sectional view of the first exemplary embodiment of the internal filter shown in  FIG. 1 . This cross-sectional view is taken along the line III-III of  FIG. 1 . The triangular shape of the channels  110 ,  112 ,  120 ,  122  and  130  resulting from the orientation-dependent etching process can be seen in the cross section of the inlet side passageways  110  and the outlet side passageways  120  and of the filter pores  130  shown in  FIG. 3 . The triangular shape of the extensions  112  and  122  can be seen in  FIG. 2 . The inlet side passageways  110 , the outlet side passageways  120  and the extensions  112  and  122  are deeper and wider than the filter pores  130  in order to minimize fluid impedance, while still having filter pores  130  that are small enough to catch small particles.  
         [0044]      FIG. 4  is a first cross-sectional view of a second exemplary embodiment of the internal filter shown in  FIG. 1 . This cross-sectional view is taken along the line II-II shown in  FIG. 1 . In contrast,  FIG. 5  is a second cross-sectional view of the second exemplary embodiment of the internal filter shown in  FIG. 1 . This cross-section view is taken along the line III-III shown in  FIG. 1  As shown in  FIGS. 4 and 5 , in this exemplary embodiment, the substrates  140  and  150  are masked to expose regions corresponding to the inlet and outlet side passages  110  and  120 , and the filter pores  130 , respectively. The substrates  140  and  150  are then reactive ion etched or the like to form the inlet side passages  110  and the outlet side passages  120 , and the filter pores  130 , respectively.  
         [0045]      FIG. 6  is a first cross-sectional view of a third exemplary embodiment of the internal filter shown in  FIG. 1 . This cross-sectional view is taken along the line II-II shown in  FIG. 1 . In contrast,  FIG. 7  is a second cross-sectional view of the third exemplary embodiment of the internal filter shown in  FIG. 1 . This cross-section view is taken along the line III-III shown in  FIG. 1 . It should be appreciated that, in various exemplary embodiments, the internal filter  200  shown in  FIGS. 6 and 7  was manufactured by exposing and developing one or more photosensitive materials, such as polymide, SU-8, polyarylene ether, and the like. As shown in  FIG. 6 , the filter pores  230  are formed in an upper layer  240 , while the inlet side passageway  210  and extensions  212  and the outlet side passageway  220  and extensions  222  are formed in a lower layer  250 . The upper and lower layers  240  and  250  are separate from each other. The upper and lower layers  240  and  250  are then bonded together and to each of an upper substrate  260  and a lower substrate  270 .  
         [0046]     The processes used to expose and develop the photosensitive materials, and thus to form the structures shown in  FIGS. 2-7 , are easier to control than the similar processes used in the incorporated 748 patent. Orientation-dependent etching of silicon in a single substrate, such as in  FIGS. 2 and 3 , is self terminating and essentially stops when the etch planes intersect at a point. This is why the cross-section is triangular. The reactive ion etching process used to form the structures shown in  FIGS. 4 and 5  etches at a relatively slow rate that does not depend on the crystal planes of the substrate. As a result, the depth and shape of the etched structures can be more easily controlled. Furthermore, the processes used to form the structures shown in  FIGS. 6 and 7  are easy to use and control because the passages formed in each layer are formed through the whole layer. Therefore, passage depth does not need to be controlled. Also, the processes for exposing and developing photosensitive materials do not limit the internal filter to geometries with only two layers of passages.  
         [0047]      FIG. 8  is a first cross-sectional view of a fourth exemplary embodiment of the internal filter shown in  FIG. 1  according to this invention. This cross-sectional view is also taken along the line II-II shown in  FIG. 1 . In contrast,  FIG. 9  is a second cross-sectional view of the fourth exemplary embodiment the internal filter shown in  FIG. 1 . This cross-section view is also taken along the line III-III shown in  FIG. 1 . As shown in  FIGS. 8 and 9 , in addition to the upper layer  240  and the lower layer  250  shown in  FIGS. 6 and 7 , an additional filter pore layer  280  and an additional inlet and outlet passageway layer  290  is added. This doubles the number of filter pores in parallel with relatively little increase in space used in the device.  
         [0048]     In various other exemplary embodiments, methods for fabricating fifth and sixth exemplary embodiment of the internal filter with interleaved comb fluid pathways connected by multiple sets of filter pores according to this invention do not etch into top and bottom substrates, as in the first and second embodiments, nor do they etch completely through the upper and lower layers  240  and  250 , as in the fifth and sixth exemplary embodiments. In fact, the upper and lower layers  240  and  250  are not even used in this third exemplary embodiment. Rather, these exemplary embodiments of the methods for fabricating the fifth and sixth exemplary embodiments of the internal filter use orientation-dependent etching, reactive ion etching and/or some other appropriate technique.  
         [0049]     Using reactive ion etching and/or some other appropriate technique, passages of different widths and depths can be obtained in a single substrate by using multiple steps.  FIGS. 10 and 11  illustrate a substrate processed according to a first step of one exemplary embodiment of the method for making the fifth exemplary embodiment of the internal filter according to this invention. In particular,  FIG. 10  shows the substrate when taken on a view corresponding to the line II-II of  FIG. 1 , while  FIG. 11  corresponds to a view taken along the line III-III shown in  FIG. 1 .  
         [0050]     As shown in  FIGS. 10 and 11 , in this first step of this exemplary embodiment of the method for forming the fifth exemplary embodiment of the internal filter, the substrate  300  is masked to expose regions corresponding to the inlet and outlet side passages  320  and  330 . The substrate  330  is then reactive ion etched or the like to begin forming the inlet side passages  310  and the outlet side passages  320 . In particular, it should be appreciated that, after this first step, as shown in  FIG. 10 , the inlet side passages  310  and the outlet side passages  320  are only partially formed.  
         [0051]     The regions of the substrate  300  corresponding to the filter pores  330  are then exposed by removing corresponding portions of the mask. A second reactive ion etching or the like step is used to form the filter pores  330  and to deepen the inlet side passageways  310  and the outlet side passageways  320 . In particular,  FIG. 12  shows the substrate  330  and an upper substrate  340  after this second step when taken on a view corresponding to the line II-II of  FIG. 1 . Similarly,  FIG. 13  shows the substrate  300  and the upper substrate  340  after this second step when taken of a view corresponding to the line III-III of  FIG. 1 . That is,  FIGS. 12 and 13  show the substrate  330  after the second reactive ion etching step is performed and the upper substrate  340  is bonded in place. It should be appreciated that plasma, deep silicon or other types of etching can also be used to perform the method for fabricating the third exemplary embodiment of the internal filter according to this invention.  
         [0052]     Using orientation-dependent etching and/or some other appropriate technique, passages of different widths and depths can be obtained in a single substrate by using multiple steps.  FIGS. 14 and 15  illustrate a substrate processed according to a first step of one exemplary embodiment of the method for making the sixth exemplary embodiment of the internal filter according to this invention. In particular,  FIG. 14  shows the substrate when taken on a view corresponding to the line II-II of  FIG. 1 , while  FIG. 15  corresponds to a view taken along the line III-III shown in  FIG. 1 .  
         [0053]     As shown in  FIGS. 14 and 15 , in this first step of this exemplary embodiment of the method for forming the fifth exemplary embodiment of the internal filter, the substrate  400  is masked to expose regions corresponding to the inlet and outlet side passages  420  and  430 . The substrate  430  is then orientation-dependent etched or the like to begin forming the inlet side passages  410  and the outlet side passages  420 . In particular, it should be appreciated that, after this first step, as shown in  FIG. 14 , the inlet side passages  410  and the outlet side passages  420  are only partially formed.  
         [0054]     The regions of the substrate  400  corresponding to the filter pores  430  are then exposed by removing corresponding portions of the mask. A second orientation-dependent etching or the like step is used to form the filter pores  430  and to deepen the inlet side passageways  410  and the outlet side passageways  420 . In particular,  FIG. 16  shows the substrate  400  and an upper substrate  340  after this second step when taken on a view corresponding to the line II-II of  FIG. 1 . Similarly,  FIG. 17  shows the substrate  400  and the upper substrate  440  after this second step when taken of a view corresponding to the line III-III of  FIG. 1 . That is,  FIGS. 16 and 17  show the substrate  400  after the second orientation-dependent etching step is performed and the upper substrate  440  is bonded in place.  
         [0055]      FIG. 18  is a first cross-sectional view of a seventh exemplary embodiment of the internal filter shown in  FIG. 1 . This cross-sectional view is taken along the line II-II shown in  FIG. 1 . In contrast,  FIG. 19  is a second cross-sectional view of the seventh exemplary embodiment of the internal filter shown in  FIG. 1 . This cross-section view is taken along the line III-III shown in  FIG. 1 . It should be appreciated that, in various exemplary embodiments, the internal filter  500  shown in  FIGS. 18 and 19  was manufactured by reactive ion etching or the like a substrate  540  and by additionally exposing and developing one or more photosensitive materials, such as polymide, SU-8, polyarylene ether, and the like, used to form an intermediate layer  550 .  
         [0056]     As shown in  FIGS. 18 and 19 , the filter pores  530  are formed in an intermediate layer  550  and the inlet side passageway  510  and extensions  512  and the outlet side passageway  520  and extensions  522  are formed in the lower substrate  540 . The intermediate layer  550  is separate from the lower and upper substrates  540  and  560 . The substrate  550  is then bonded to each of the upper substrate  560  and the lower substrate  540 . Of course, it should be appreciated that, the upper and lower substrates are so only in  FIGS. 18 and 19 . In use, the lower substrate  540  can be above the upper substrate  560  and the intermediate layer  550 .  
         [0057]      FIG. 20  is a first cross-sectional view of a variation of the seventh exemplary embodiment of the internal filter shown in  FIG. 18 . This cross-sectional view is taken along the line II-II shown in  FIG. 1 .  FIG. 21  is a second cross-sectional view of the variation of the seventh exemplary embodiment of the internal filter shown in  FIG. 18 . This cross-section view is taken along the line III-III shown in  FIG. 1 . It should be appreciated that, in various exemplary embodiments, the internal filter  500  shown in  FIGS. 20 and 21  was manufactured by reactive ion etching or the like the substrate  540  and by additionally exposing and developing one or more photosensitive materials, such as polymide, SU-8, polyarylene ether, and the like, used to form the intermediate layer  550 .  
         [0058]     As shown in  FIGS. 20 and 21 , the filter pores  530  are formed in an intermediate layer  550  and the inlet side passageway  510  and extensions  512  are formed in the lower substrate  540 . In contrast, the outlet side passage-way  520  and extensions  522  are formed in the upper substrate  560 . The intermediate layer  550  is separate from the lower and upper substrates  540  and  560 . The substrate  550  is then bonded to each of the upper substrate  560  and the lower substrate  540 . Of course, it should be appreciated that, the upper and lower substrates are so only in  FIGS. 20 and 21 . In use, the lower substrate  540  can be above the upper substrate  560  and the intermediate layer  550 .  
         [0059]     It should be appreciated that plasma etching, deep silicon etching, precision injection molding of plastic materials, coining, electroforming, air abrasive blasting, laser ablation or known or later-developed methods for fabricating the internal filter with interleaved comb fluid pathways connected by multiple sets of filter pores, shown in  FIGS. 2-21  can be used, as appropriate, to form the first-third exemplary embodiments of the internal filter according to this invention.  
         [0060]     It should also be appreciated that different fabrication methods can be used for different layers or substrates of the various exemplary embodiments of the internal filter according to this invention. For example, photosensitive material exposure and development processes can be used to fabricate the inlet side passageways and outlet side passageways in a separate layer, which is then bonded to a lower substrate, and the filter pores can be reactive ion etched into an upper substrate.  
         [0061]     One limitation of the internal filter with interleaved comb fluid pathways connected by multiple sets of filter pores shown in  FIG. 1  is that there is only one inlet side passage-way  110  and only one outlet side passageway  120 . This limits the types of fluids the device may handle simultaneously to one. There are many applications, such as color printing, where the internal filter needs to handle multiple sources or multiple fluid processing sites independently.  
         [0062]      FIG. 22  shows an eighth exemplary embodiment of an internal filter with interleaved comb fluid pathways connected by multiple sets of filter pores according to this invention. As shown in  FIG. 22 , in this eighth exemplary embodiment, the multiple sets of filter pores are configured in alternate positions to support multiple independent fluid sources and/or multiple independent fluid sinks. As shown in  FIG. 22 , the inlet side passageway  610  and the outlet side passageway  620  are used for one type of fluid, for example, a yellow-colored ink. The other inlet side passages  630 ,  650  and  670 , and the other outlet side passages  640 ,  660  and  680  are used for other types of fluid, for example, cyan-, magenta- and black-colored inks respectively. It should be appreciated that the internal filter can be fabricated so that the multiple independent fluid sources are connected to separate layers, instead of in the configuration shown in  FIG. 22 .  
         [0063]     Of course, it should be appreciated that, in  FIG. 22 , in various exemplary embodiments, each of the inlet side passageways  610 ,  630 ,  650  and  670  could instead be connected to the same fluid source or upstream fluid processing device, while each of the outlet side passageways  620 ,  640 ,  660  and  680  is connected to a different fluid sink, such as a fluid collection device or a downstream fluid processing device. In this way, different filtered streams can be directed to different outlet side devices. If the filter pores  690  for each of the different sets of inlet and outlet side passageways  610 - 620 ,  630 - 640 ,  650 - 660  and  670 - 680  are differently sized so that different size particles are allowed to pass through the corresponding pores  690 , the fluid streams output from the outlet side passageways  620 ,  640 ,  660  and  680  will have different sets of particles in the fluid and/or will have different fluid properties or parameters depending on which particles are filtered from that fluid. Accordingly, it should be appreciated that the plurality of inlet side passageways  610 ,  630 ,  650  and  670  can be different portions of a single inlet side passageway.  
         [0064]     Of course, it should also be appreciated that, in  FIG. 22 , in various exemplary embodiments, each of the inlet side passageways  610 ,  630 ,  650  and  670  could be connected to a different fluid source or upstream fluid processing device, while each of the outlet side passageways  620 ,  640 ,  660  and  680  is connected to the same fluid sink, such as a fluid collection device or a downstream fluid processing device. In this way, different input streams can be combined before being forwarded to the same outlet side devices, with each different input stream being filtered in a manner appropriate for that input fluid stream. Accordingly, it should be appreciated that the plurality of outlet side passageways  620 ,  630 ,  660  and  680  can be different portions of a single outlet side passageway.  
         [0065]     That is, if each different input fluid stream has particles that are different sizes, the filter pores  690  for each of the different sets of inlet and outlet side passageways  610 - 620 ,  630 - 640 ,  650 - 660  and  670 - 680  can be differently sized so that each different input fluid stream is appropriately filtered. In this way, particles of the same size in different input streams can be differently filtered, such that particles of a given size that need to be removed from one input fluid stream can be removed, while particles of that given size of a different input fluid stream that need to be allowed to pass through to the outlet stream are not filtered from that input fluid stream. If the fluid were filtered after being combined, this differential filtering would not be possible.  
         [0066]     The variation of the seventh exemplary embodiment that is shown in  FIGS. 20 and 21  allows more freedom in placing the inlet and outlet side passageways  510  and  520  relative to each other. For example, instead of the position shown in  FIG. 21 , the outlet side passageway  520  could be placed vertically over the inlet side passageway  510 . Furthermore, if this variation of the seventh exemplary embodiment were used with the eighth exemplary embodiment shown in  FIG. 22 , two or more inlet side passageways  510  could be provided in the lower substrate  540 , with different ones of the first passages  512  connected to different ones of the two or more inlet side passageways  510 . Similarly, two or more outlet side passageways  520  could be provided in the upper substrate  560 , with different ones of the second passages  522  connected to different ones of the two or more outlet side passageways  520 . In this case, some of the pores  530  could be omitted so that some first passages  512  are not connected to adjacent second passages  522 . Consequently, two or more of the separate structures shown in  FIG. 22  could be formed in an overlapping or interleaved manner in the same region of the internal filter.  
         [0067]      FIG. 23  illustrates a ninth exemplary embodiment of an internal filter with interleaved comb fluid pathways connected by multiple sets of filter pores, according to this invention. As shown in  FIG. 23 , in this ninth exemplary embodiment, the multiple sets of filter pores are configured in alternate positions to provide a second stage of filtering for particles of different sizes. As shown in  FIG. 23 , fluid enters through the inlet side passage  710 , passes through the large filter pores  720  and into the center passage  730 . The fluid then passes from the center passage  730  through a set of smaller filter pores  740  and into the outlet side passage  750 . Smaller particles not trapped in the larger filter pores  720  are trapped in the smaller filter pores  740 .  
         [0068]     It should be appreciated that the filter locations shown in  FIG. 23  can also be used to provide filtering before and after fluid processing which is performed in the center passage  730 . Alternately, the center passage can be split into two portions with a fluid processing structure connected between the two portions of the center passage  730 .  
         [0069]     While particular embodiments have been described, alternatives, modifications, variations, improvements, and substantial equivalents that are or may be presently unforeseen may arise to applicants or others skilled in the art. Accordingly, the exemplary embodiments of the invention, as set forth above, are intended to be illustrative, not limiting. Various changes may be made without departing from the spirit and scope of the invention. Therefore, the appended claims as filed and as they may be amended are intended to embrace all such alternatives, modifications, variations, improvements, and substantial equivalents.