MICROFLUIDIC DEVICE FOR SPRAYING SMALL DROPS OF LIQUIDS

Abstract

A microfluidic device provided in a body accommodating a fluid containment chamber. A fluidic access channel and a drop emission channel are formed in the body and are in fluidic connection with the fluid containment chamber to form a fluidic path towards the body outside through a nozzle having an outlet section. An actuator is operatively coupled to the fluid containment chamber and is configured to cause ejection of fluid drops through the drop emission channel in an operating condition of the microfluidic device. The drop emission channel comprises a portion of reduced section having a smaller area than the outlet section of the nozzle.

Claims

1. A method, comprising: forming a fluid containment chamber in a semiconductor body; forming a nozzle that is partially offset from the fluid containment chamber, the nozzle having an outlet section having a first area, the nozzle being in fluid communication with the fluid containment chamber by a fluid path, the fluid path having a second area, the second area being smaller than the first area; and forming an actuator operatively coupled to the fluid containment chamber and configured to cause ejection of drops of fluid through the nozzle.

2. The method according to claim 1 wherein the nozzle comprises forming a plurality of nozzles, each nozzle being partially offset from the fluid containment chamber, the plurality of nozzles having outlet sections having first areas, each of the plurality of nozzles being in fluid communication with the fluid containment chamber by a plurality of fluid paths having second areas, the second areas being smaller than the first area.

3. The method according to claim 2 wherein forming the plurality of nozzles comprises forming the plurality of nozzles to partially overlap edges of the fluid containment chamber.

4. The method according to claim 1 wherein forming the fluid containment chamber comprises forming a fluid containment chamber having a tapered inlet.

5. A method, comprising: forming a fluid containment chamber in a body; forming a drop emission channel including a nozzle having an opening at an outer surface of the body that is configured to expel fluid, wherein the opening of the nozzle partially overlaps the fluid containment chamber and partially overlaps a portion of the body that does not include the fluid containment chamber; and forming an actuator operatively coupled to the fluid containment chamber and configured to cause ejection of drops of fluid through the nozzle.

6. The method according to claim 5 wherein forming the drop emission channel including the nozzle having the opening at the outer surface of the body comprises forming a plurality of drop emission channels, each including a respective nozzle having a respective opening at the outer surface of the body.

7. The method according to claim 6 wherein the openings of the nozzles partially overlap the fluid containment chamber and partially overlap a portion of the body that does not include the fluid containment chamber.

8. The method according to claim 5 wherein forming the fluid containment chamber comprises forming a fluid containment chamber having a tapered inlet.

9. The method according to claim 5, further comprising forming the fluid containment chamber in a semiconductor body.

10. A method, comprising: forming a fluid containment chamber in a first body; and forming a plurality of drop emission channels in a second body, coupling the first body with the second body so that the plurality of drop emission channels are in fluid communication with the fluid containment chamber, wherein each of the plurality of drop emission channels include a nozzle having an opening at an outer surface of the second body that is configured to expel fluid, wherein the openings of the nozzles partially overlap the fluid containment chamber and partially overlap portions of the first body that do not include the fluid containment chamber.

11. The method according to claim 10, further comprising providing an actuator in a chamber of the second body, the actuator coupled to a membrane at a surface of the fluid containment chamber in the first body.

12. The method according to claim 11 wherein coupling the first body with the second body encloses the actuator in the chamber.

13. The method according to claim 11 wherein the actuator is a piezoelectric actuator.

14. The method according to claim 10 wherein the plurality of drop emission channels are arranged at a perimeter of the fluid containment chamber.

15. The method according to claim 10 wherein the plurality of drop emission channels are arranged equidistant from each other at a perimeter of the fluid containment chamber.

16. The method according to claim 10 wherein the plurality of drop emission channels are arranged at a perimeter of the fluid containment chamber.

17. The method according to claim 10 wherein the first and second bodies include semiconductor material.

18. The method according to claim 10 wherein the first body is a semiconductor body.

Description

BRIEF DESCRIPTION OF THE SEVERAL VIEWS OF THE DRAWINGS

[0021] For a better understanding of the present disclosure, preferred embodiments thereof are now described, purely by way of non-limiting example, with reference to the attached drawings, wherein:

[0022] FIG. 1 is a perspective cross-section of a chamber of a known microfluidic device of a thermal type;

[0023] FIGS. 2A-2E show the operation of the chamber of FIG. 1;

[0024] FIG. 3 is a cross-section of a chamber of a known microfluidic device of a piezoelectric type;

[0025] FIG. 4 is a simplified top plan view, with parts in see-through view, of the chamber of the microfluidic device of a thermal type of FIG. 1;

[0026] FIG. 5 is a simplified top plan view, with parts in see-through view, of one embodiment of the present microfluidic device of a thermal type;

[0027] FIG. 6 is a perspective cross-section, taken along section plane VI-VI of FIG. 5, of a cell of the microfluidic device of FIG. 5;

[0028] FIG. 7 is a cross-section of the chamber of FIG. 5, taken along section plane VII-VII;

[0029] FIG. 8 is a cross-section of the chamber of FIG. 5, taken along section plane VIII-VIII;

[0030] FIG. 9 shows schematically in perspective view the generation of a drop in the known cell of FIG. 1;

[0031] FIG. 10 shows schematically in perspective view the generation of a drop in the cell of FIG. 5;

[0032] FIG. 11 is a simplified top plan view of a portion of an embodiment of the present device, comprising a plurality of cells;

[0033] FIGS. 12A-12D are simplified top plan views of different embodiments of the chamber of FIG. 5; and

[0034] FIGS. 13A and 13B are cross-sections, similar to FIG. 3, of a part of cell of a different embodiment of the present microfluidic device, with actuation of a piezoelectric type.

DETAILED DESCRIPTION

[0035] The present device is based upon the principle of forming a portion of the drop emission channel with an effective cross-section having a smaller area than the cross-section of the rest of the drop emission channel. This is obtained by forming a part of the drop emission channel (for example, the nozzle) partially offset with respect to the rest of the drop emission channel, overlying it or underlying it. In practice, in the present device, the area of the nozzle and the area of the rest of the drop emission channel have a non-zero intersection which has a smaller area than the entire nozzle area. In this way, it is possible to obtain a choking in the drop emission channel, i.e., a useful drop emission area which is smaller than the one achievable with existing or future manufacturing techniques.

[0036] The above principle is highlighted by comparing FIGS. 4 and 5, which show, respectively, in a simplified way, the position of the nozzle with respect to the fluid containment chamber in the case of a microfluidic device with thermal generation according to the prior art and according to an embodiment of the present device.

[0037] In FIG. 4, representing in a simplified way the cell 11 of FIG. 1 and thus using the same reference numbers, the nozzle 15 is arranged substantially centered with respect to the top of the fluid containment chamber 19 and of the heater 20.

[0038] FIG. 5 shows in a simplified way a cell 51 of a microfluidic device 50. The cell 51 is formed in a body 100 of micrometric dimensions and comprises a fluid containment chamber 52, a fluidic inlet 66 connected to a fluid supply channel 67, a heater 53, and a drop emission channel, here formed by a nozzle 54. The nozzle 54 is arranged offset with respect to the fluid containment chamber 52, and precisely its cross-section (base area) is no longer comprised within the area of the fluid containment chamber 52, but an intersection area between the two areas exists, designated by 57 and represented hatched in FIG. 5, and is of a smaller size than the area of the nozzle 54, such that the size of the intersection area is less than the size of the nozzle opening.

[0039] The cell 51 may be manufactured as shown in FIGS. 6-8. Here, the device 50 is formed by a substrate 60, for example of semiconductor material, covered by an insulating layer 61, for example of silicon oxide. A chamber layer 63 extends over the insulating layer 61, for example of polymeric material such as dry film.

[0040] In the cell 51, a heater 53 is formed within the insulating layer 61 and forms an actuator. The fluid containment chamber 52 is formed within the chamber layer 63, above the heater 62, facing the insulating layer 61. The fluid containment chamber 52 here has a parallelepipedal shape with approximately rectangular base, parallel to a plane XY of a Cartesian system XYZ, with a height (in the direction Z) smaller than the thickness of the chamber layer 63. The fluid containment chamber 52 is laterally delimited by walls 65 that define a lateral surface of the fluid containment chamber 52. The fluidic access 66, formed in the chamber layer 63, connects the fluid containment chamber 52 with a fluid supply channel 67, schematically represented in FIG. 5 and visible in the cross-section of FIG. 7. The fluidic access 66 may have the shape shown schematically in FIG. 5, with a first portion 66A, which is wider, contiguous to the fluid supply channel 67, and a second portion 66B, which is narrower, contiguous to the fluid containment chamber 52. In the first portion 66A, columns (not shown) may be present for preventing large particles from blocking the fluidic access 66.

[0041] The nozzle 54, which here has a cylindrical shape with circular base, is formed in the top part of the chamber layer 63 and is arranged at one corner of the fluid containment chamber 52, so that a portion of the surface of the walls 65 extends through its base area. In particular, the intersection 54 here has an area that is approximately one quarter of the base area of the nozzle 54.

[0042] The cell 51 may be manufactured by initially forming, on the substrate 60, a sacrificial structure having a shape corresponding to the fluid containment chamber 52, of the fluidic access 66, and of the fluid supply channel 67, then depositing polymeric material intended to form the chamber layer 63. In particular, the chamber layer 63 may be formed using lamination and reflow techniques, in a per se known way in the microinjector technique. Next, the chamber layer 63 is perforated, via selective etching and using common photolithographic techniques, to form the nozzle 54.

[0043] Alternatively, the chamber layer 63 may be separately molded and bonded on the insulating layer 61, or formed in a dug silicon structure, bonded to the insulating layer 61. According to a different embodiment, the chamber layer 63 may be formed by two separate layers or regions, glued together.

[0044] The intersection 54 causes the useful area of the nozzle 54 to be reduced as compared to its physical dimensions obtainable with the current lithographic definition processes, and allows obtainment of drops of smaller dimensions as compared to devices micromachined using the same technology, as shown also in the simulations of FIGS. 9 and 10, showing, respectively, generation of a drop of a same fluid with the cell 11 of FIG. 4 and with the cell 51 of FIG. 5.

[0045] The fluid containment chamber 52 may form part of an array of drop-generation chambers 52 arranged side by side and connected to a same fluid supply channel 67, as shown in FIG. 11, to form a nebulizer 70.

[0046] The nozzle 54 and the fluid containment chamber 52 may have different shapes and mutual arrangements. For example, the fluid containment chamber 52 may have a cylindrical or polyhedral shape as desired, whether regular or irregular, with the nozzle arranged so as to intersect (in top plan view) the circumference or perimeter of the base. Further, a number of nozzles may be provided for each fluid containment chamber.

[0047] For example, FIG. 12A shows a cell 51A formed in a body 150 of micrometric dimensions having a fluid containment chamber 52A with a square base, with a nozzle 54.sup.1-54.sup.4 arranged on each corner thereof. In this way, the intersection 57 between each nozzle 54.sup.1-54.sup.4 and the fluid containment chamber 52A has a smaller area than the respective nozzle 54.sup.1-54.sup.4, which thus emits a drop of reduced size, but as a whole the four intersections have an area approximately equal to a known cell 11, thus improving the density of the drops emitted by each fluid containment chamber 52A.

[0048] FIG. 12B shows a cell 51B having a fluid containment chamber 52B with a base that also here is square, with protuberances 80 extending from each corner of the square along the diagonals. The cell 51B of FIG. 12B comprises four nozzles 54.sup.1-54.sup.4, partially overlapping the protuberances 80. The nozzles 54.sup.1-54.sup.4 may have a greater diameter than the width of the protuberances 80, since the latter may have smaller dimensions than the nozzles, due to the different manufacturing techniques.

[0049] FIG. 12C shows a cell 51C having a star-shaped fluid containment chamber 52C having five points, on each whereof a respective nozzle 54.sup.1-54.sup.5 is formed.

[0050] FIG. 12D shows a cell 51D having a fluid containment chamber 52D of a triangular shape having three vertices on which nozzles 54.sup.1-54.sup.3 are formed.

[0051] Also in the cells 51B-51D a reduction in volume of the drops emitted is then obtained, without excessively penalizing the emitted liquid density.

[0052] FIG. 13A shows a portion of a cell 99 of a microfluidic device 90 of a piezoelectric type. The microfluidic device 90 has the same base structure as the microfluidic device 30 of FIG. 3 and has thus been represented only in part, using the same reference numbers, and differs from the embodiment of FIG. 3 as regards the configuration of the drop emission channel, here designated by 91. In detail, in the microfluidic device 90, the drop emission channel 91 comprises, in addition to the through channel 41, the openings 42, 46, and the hole 48 in the nozzle plate 36 (the latter items being referred to hereinafter as first hole 48 and first plate 36), a second hole 92. The second hole 92 is arranged partially offset to the first hole 48 so as to form an intersection having a smaller area than the holes 48, 92, as described for the intersection 57 of FIG. 5. The second hole 92 is here formed in a second nozzle plate 93 bonded to the nozzle plate 36 (designated hereinafter as first nozzle plate 36), and the drop emission nozzle, here designated by 95, is formed by the two holes 48, 92. Thereby, the drop emission nozzle 95 is formed by two channel portions that are partially not aligned, reducing the outlet section of the liquid drop expelled from the chamber 31 as a result of the deflection of the membrane 37, like the drop-generation cell 52 of FIG. 5.

[0053] FIG. 13B shows a microfluidic device 96 of a piezoelectric type similar to the microfluidic device 90 of FIG. 13A. Unlike this, the microfluidic device 96 has a single nozzle plate (here designated by 43′). The drop emission channel, here designated by 91′, has a nozzle 97 formed by a hole 48′ in the nozzle plate 43′ that is offset with respect to the through channel 41 in the third region 38. In this way, the nozzle 97 has an effective cross-section of small dimensions, like the microfluidic device 90 of FIG. 13A.

[0054] Finally, it is clear that modifications and variations may be made to the microfluidic device described and illustrated herein, without thereby departing from the scope of the present disclosure. For example, the different embodiments described may be combined so as to provide further solutions.

[0055] Further, the shape of the nozzle base may differ from the one shown; for example, it may be oval or polygonal.

[0056] In the microfluidic device with piezoelectric actuation, the reduction of the useful section could be obtained at the inlet mouth of the through channel 41, by appropriately staggering the mouth of the channel 41 with respect to the fluid containment chamber 31.

[0057] Further, also in the microfluidic device with piezoelectric actuation, the fluid containment chamber 35 may have any shape, for example a polyhedral shape having a base with projecting vertices, points, or portions. Also in this case, the fluidic path may comprise a plurality of nozzles partially overlapping the projecting vertices, points, or portions, so as to form intersections of reduced area.

[0058] Also for the microfluidic device with piezoelectric actuation, it is possible to arrange a plurality of cells of the type shown in FIGS. 13A and 13B, alongside each other, with inlet channels 40 connected to a common supply channel, for forming a nebulizer.

[0059] Further, in all the microfluidic devices, the fluid containment chamber may have a cylindrical shape with circular or oval base, and the nozzle or nozzles may be arranged straddling the circumference of the circular or oval base.

[0060] The various embodiments described above can be combined to provide further embodiments. These and other changes can be made to the embodiments in light of the above-detailed description. In general, in the following claims, the terms used should not be construed to limit the claims to the specific embodiments disclosed in the specification and the claims, but should be construed to include all possible embodiments along with the full scope of equivalents to which such claims are entitled. Accordingly, the claims are not limited by the disclosure.