MICROFLUIDIC DEVICE FOR SPRAYING VERY SMALL DROPS OF LIQUIDS

A microfluidic device has a chamber; a fluidic access channel in fluidic connection with the chamber; a plurality of nozzle apertures in fluidic connection with the chamber; and an actuator, operatively coupled to the fluid containment chamber and configured to cause ejection of drops of fluid through the nozzle apertures in an operating condition of the microfluidic device. The chamber has an elongated shape, with a length and a maximum width, wherein an aspect ratio between the length and the maximum width of the chamber is at least 3:1. The nozzle apertures are configured to generate, in use, a plurality of drops having a total drop volume, wherein a ratio total drop volume to a chamber volume is at least 15%.

BACKGROUND

Technical Field

The present disclosure relates to an improved microfluidic device for spraying very small drops of liquids.

Description of the Related Art

As is known, for spraying inks and/or perfumes as well as in e-cigarettes or in inhalation medical devices, the use has been proposed of microfluidic devices of small dimensions, which may be obtained with microelectronic manufacturing techniques.

The delivery of known or unknown composition fluid is feasible with modified design, ink jet structures, described for example in US 2015/367014, US 2014/14310633 (corresponding to U.S. Pat. No. 9,174,445), US 2015/0367356 or US 2015/367641.

In addition, WO 2004/085835A1 discloses a liquid ejecting apparatus and a manufacturing method thereof using a PZT bulk technology, wherein a thick metal plate is worked to form liquid passages and a chamber and a piezoelectric/electrostrictive element is fixed to the metal plate. Ejection is obtained by the piezoelectric/electrostrictive element that generates a pressure wave.

Another piezoelectric inkjet head is disclosed in US 2009/009565. However, in some applications, such as in nebulizer applications, it is desired to spray drops of very small dimensions, as small as 1μm. However, current semiconductor technologies allow manufacture of nozzles with diameters greater than 6 μm.

To solve this issue, for example, US2018/0141074 discloses a microfluidic device formed in a body accommodating a fluid containment chamber. An exemplary embodiment is shown inFIGS.1and2. Here, a chamber1formed in a body5is coupled to a fluid access channel2and to a drop emission channel or nozzle3formed in a nozzle plate (not visible, overlying the chamber1). The drop emission channel3overlies the chamber1and is partially offset thereto, to define an intersection area4having smaller dimension than the hole area and thus defining an effective exit area. A heater8is formed in the body5under the chamber1and is configured to heat the fluid in the chamber1so as to generate a drop that is emitted through the drop emission channel3.

Thus, small drops may be obtained. In particular, the dimensions of the drops (diameter/volume) are directly linked to the nozzle diameter, as shown inFIG.2plotting the volume of the emitted drops as a function of the diameter of the nozzle (the effective exit area inFIG.1).

US 2019/350260 discloses a similar microfluidic dispenser wherein small drops are obtained using offset nozzles openings having different shapes and arranged at different positions.

This solution has been successful in reducing the dimensions of the emitted drops but has caused further challenges regarding the operation of the device, in particular when it is desired to spray a high number of very small drops with high frequency.

In particular, for obtaining a sufficient volume of emitted fluid, test structures comprising a plurality of apertures arranged on the periphery of the chamber have been studied. However, it has been seen that this architecture may not be thermally efficient.

In fact, for example, microfluidic devices with peripheral offset nozzles with a diameter of 6 μm, configured to obtain drops of about 0.28 pL (picoliters) have been studied. This results in a drop volume that is less than 1% of the chamber volume, and thus of fluid contained in the chamber (for example, 50 pL). Therefore, a much higher volume of fluid is heated than the volume of the actually ejected fluid. Consequently, it has been observed that heat energy builds up very quickly in the chamber and may cause the die, accommodating a plurality of adjacent chambers, to overheat.

In some cases, boiling of the fluid has been observed even before it enters the chambers, globally depriming the system. Therefore, in devices comprising many chambers each connected to a plurality of nozzles, with ignition at high frequency (even higher than 1 kHz), the risk of a failure of the entire device due to global depriming exists. In addition, depriming may occur very quickly, destroying the device.

Various embodiments of the present disclosure provide an improved microfluidic device solving the problems of the prior art.

BRIEF SUMMARY

According to the present disclosure, there are provided a microfluidic device and a manufacturing process thereof.

DETAILED DESCRIPTION

Hereinbelow, embodiments of a microfluidic device will be described in detail. In the ensuing description, spatial indications such as “upper”, “lower”, “on”, “over”, “under”, “top”, “bottom”, and so on are to be interpreted according to the discussed Figures and are not limitative.

FIGS.3-4show a microfluidic device10manufactured using micro-manufacturing steps, as discussed more in detail hereinafter.

The microfluidic device10has a general structure shown inFIG.3and is formed in a body11including a substrate12, an insulating layer13, a chamber layer14, and a nozzle layer15.

The substrate12, the insulating layer13, the chamber layer14and the nozzle layer extend over each other in a height direction, parallel to a vertical axis (first axis Z of a Cartesian reference system XYZ).

The substrate12is for example of semiconductor material, such as monocrystalline silicon. The insulating layer13is for example a multilayer including silicon oxide, silicon nitride and other insulating layers. The substrate12and the insulating layer form a base body portion22. The chamber layer14is for example a polymeric material such as dry film. The nozzle layer15may be formed by semiconductor material, such as monocrystalline silicon or a polymeric material such as dry film, as discussed hereinbelow. The chamber layer14forms a plurality of chambers17, one chamber17being shown inFIGS.3and4. The chambers17are laterally delimited by lateral walls16formed by the chamber layer14; in addition, the chambers17are delimited by a bottom base17A formed by the insulating layer13and by an upper base17B formed by the nozzle layer15. The bottom base17A and upper base17B extend along a first direction and a second direction, respectively, the second direction transverse to the first direction.

The insulating layer13accommodates a plurality of actuators, here heaters18(one shown). The heaters18are arranged below the chambers17, one heater18for each chamber17. However, in the alternative, more heater portions18may be arranged under each chamber17.

Each heater18is coupled to a firing circuit, not shown, through connection lines19.

Inlets20extend through the chamber layer14from opposite sides of the chamber17. The inlets20connect the chamber17with a fluid supply channel not shown here.

A plurality of nozzle openings23extend through the nozzle layer17along the periphery of each chamber17. Specifically, as clearly visible inFIG.4, the nozzle openings23partially overlay the chamber17and fluidically connect the chamber17with the outside of the microfluidic device10, for the ejection of liquid drops.

In order to reduce the exit area of the drops, as shown in the enlarged detail inFIG.4, the nozzle openings23form each an intersection area34similar to intersection area4ofFIG.1.

In the embodiment shown inFIG.4, the lateral walls16of the chamber17extend along a rectangle and the chamber17has a parallelepipedal shape with rectangular bottom base17A, extending parallel to plane XY of the Cartesian reference system XYZ. In the top view ofFIG.4, the bottom base17A of the chamber17has long sides much longer than the short sides.

In particular, the length of the long sides of the bottom base17C is greater than twice the length of the short sides; in the embodiment shown inFIG.4, the long sides of the rectangular bottom base17C are four times longer than the short sides.

In the embodiment ofFIG.4, the inlets20open in the chamber17at the short sides of the chamber17. The nozzle openings23extend adjacent and partially intersecting (e.g., overlapping) the long sides.

The nozzle openings23are designed to have small intersection areas34in which the nozzle openings23and the chamber17overlap. Thereby, the drop volume is reduced, as visible from the plot ofFIG.5showing the relationship between drop diameter and the effective exit area, that is the intersection area. Here, the interesting area is the one comprised between 0.2 and 0.5 μm2.

In the shown example, the nozzle openings23have a triangular, almost isosceles shape, with an acute angle corner intersecting the chamber17and forming intersection area34. Thereby, for a triangle height Ht (FIG.4) of 6 μm, feasible with the present technology, an intersection area34of about 0.32 μm2may be obtained, and consequently, a drop volume of about 0.02 pl.

In the microfluidic device10, the chamber17and the nozzle openings23are designed in order to have a volume ratio between drop volume and chamber volume that is higher than 15%.

From study of the Applicant, it has been observed that, by designing the chamber17so as to maximize its perimeter (thereby, to have a higher number of small nozzle openings23) while reducing the volume of the chamber17, less overheating is obtained.

In particular, it has been demonstrated that, with a volume ratio higher than 15%, a constant high flow of liquid from the inlets20to the nozzle openings23may be obtained, eliminating stationary liquid in the chamber17and thus chamber deprime.

For example, this may be obtained for a chamber17having a width W=6 μm, a length L=12 μm and thus a volume of 1008 μm3, eight nozzle openings23(with a total volume of emitted drops of 0.16 pL). The same ratio may be obtained with chambers17having an area that is an entire multiple n of the base chamber area and a number of nozzle openings23equal to4n:

FIG.6shows a device10including three groups of emitting portions25, each formed by a plurality of chambers17(here five), adjacent to each other.

Here each chamber17is formed by four basic cells (as indicated by the dashed lines) and thus has sixteen nozzle openings23.

The heaters18of the chambers17of a same group of emitting portions25are connected together, as indicated inFIG.6by lines26. In particular, as shown, the heaters18of a same group of emitting portions25are coupled between a firing circuit, supplying firing pulses Vo, e.g., 10V, and ground.

According to an embodiment of the present microfluidic device, a small intersection area may be obtained by forming small dimension features in the lateral wall16of the chamber17, instead of in the nozzle layer15. In fact, Applicant's tests have shown that alignment of the nozzle openings23with respect to the chambers17may be sometimes difficult In addition, in some instances, drilling of very small nozzle openings23in the nozzle layer15, e.g., by laser, has been proved challenging and does not always bring to the formation of openings with constant dimension; in rare cases, partially closed nozzles were observed, thereby resulting in uneven intersection areas and not optimal behavior.

Specifically, according to this embodiment, the lateral wall16is not smooth and straight, but has a plurality of protrusions of very small dimensions. Each nozzle opening has here an area (in top plan view) comparable with the chamber area and extend almost entirely offset with respect to an adjacent chamber17except for at the chamber protrusions, thereby defining a plurality of nozzle apertures of very small area.

For example,FIGS.7-9show three different shapes of chambers and nozzle apertures that allow to obtain very small intersection areas in a simple way, using current macromachining techniques.

FIGS.7and8shows a microfluidic device100comprising a chamber layer114.

Chamber layer114forms a plurality of chambers117(four visible) having here a generally rectangular area in top plan view (parallel to the plane XY). The chambers117are delimited by lateral walls116formed by the chamber layer114. The lateral walls116of each chamber17form a plurality of protrusions130(FIG.8) adjacent to each other, extending inside the chamber117and separated a corresponding plurality of indentations131.

Heaters118extend below the chambers117and are represented by dotted lines. The protrusions130have here a generally square shape, with sides, e.g., of about 2.5-2.6 μm.

A nozzle layer115(represented by hatched lines) extends on the chamber layer114and upwardly closes the chambers117. The nozzle layer115has openings132offset to the chambers117, but intersecting (e.g., overlapping) the indentations131.

In particular, the openings132are vertically aligned to portions119of the chamber layer114extending between pairs of adjacent chambers117.

In more detail, each nozzle opening23extends between two adjacent chambers17and intersects the indentations131of the two adjacent chambers23at two different portions of its periphery.

Thereby, the openings23may have a large area, even larger than the chambers; therefore they may be obtained in a simple way and with high size accuracy.

Here, also the openings132are rectangular in top plan view.

Thereby the openings132and the indentations131form intersection areas134(FIG.8) of very small dimensions, and in particular, of a few μm2.

For example, if the openings132extend up to almost the entire length of the indentations131(along a second axis Y of the Cartesian reference system XYZ, parallel to the width dimension of the chambers117) an exit area of 1.5×2.6 μm2may be obtained for each cavity131.

The intersection areas134are exit areas for a fluid contained in the chamber117, in an operating condition of the microfluidic device100. Thereby, the microfluidic device100is able to generate very small drops at each chamber117and, after application of a voltage pulse V to the heaters118(analogously to what shown inFIG.6), an aerosol of many, very small drops is obtained.

By virtue of the elongated shape of the chambers117(here having a length, along a third axis X of the Cartesian reference system XYZ, that is about four times the width, along the second axis Y), a volume ratio greater than 15% may be obtained, thereby providing reliable operation of the microfluidic device100, without overheating or depriming of the microfluidic device100.

FIG.7also shows inlets120as well as pillars133formed in the inlets120to block any impurity possibly dragged by the entering liquid.

FIG.9shows a different shape of the chambers (here indicated by217) and of the openings (here indicated by232) in the nozzle layer215.

Here the chambers217have a generally oval or elliptic base area. Also here, the chambers217are delimited by lateral walls216forming a plurality of adjacent protrusions230and a corresponding plurality of indentations231. In addition, also here each chamber217has a greater dimension (length, measured along the third axis X) that is about twice the shorter dimension (width, measured along the second axis Y).

For example, the chambers217may have an elliptical shape with a first semiaxis length of 60 μm and a second semiaxis length of about 20 μm.

The heater, indicated here by218, may have here again rectangular shape.

The protrusions230and the indentations231have here pointed tips.

A nozzle layer215(also represented by hatched lines) extends on the chamber layer214and has openings232that, in top plan view, are generally countershaped to the chambers217. In particular, the openings232are elongated in a direction parallel to the third axis X and have an arcuate, concave shape. Thus, in different cross-sections taken along the third axis X, the width of openings232is decreasing from the end (near one inlet220of the chambers217) toward a central portion of each opening232, and then increasing again toward the other end. The openings232also here at least partially extend over the protrusions230and the indentations231.

FIG.10shows another shape of the chambers (here indicated by317) and of the openings (here indicated by332) in the nozzle layer315. Here, the chambers317have a general rectangular shape, in top plan view (parallel to plane XY) with point-tipped protrusions330separated by similarly shaped indentations331.

The openings332have a generally constant width (in a direction parallel to the second axis Y) with enlarged ends, with an aspect ratio of at least 3:1.

In general, in further embodiments, the shape of the chambers, of the openings, of the projections and of the indentations therebetween may widely vary, as long as the openings have micrometric intersection areas with the indentations.

The microfluidic device100ofFIGS.7-10may be manufactured as discussed below with reference toFIGS.11-28.

In these Figures, the manufacturing of a single microfluidic device100is described; in general however, many microfluidic devices are manufactured in a single wafer and separated at an intermediate or a final step, in a manner known in the art, even if not discussed in detail.

FIG.11shows a portion of a wafer400that has already been worked to form the heaters and the electrical connection structures.

In detail,FIG.13, the wafer400comprises a substrate401, for example of monocrystalline silicon, covered by an insulating layer413accommodating heaters418. The substrate401and the insulating layer413form a base body portion422.

Here, the insulating layer413is a multilayer including, e.g., an oxide layer450, for example of thermal oxide; a first intermediate dielectric layer451, for example BPSG (BoroPhosphoSilicate Glass); a second intermediate dielectric layer452, for example silicon nitride; and a protection layer454, for example USG (Undoped Silicon Glass).

A heater418, for example of TaSiN or TaA1N, extend between the first and the second intermediate dielectric layers451and452.

A metal layer453, for example Tantalium, extends here on the second intermediate dielectric layer452and forms a heat distribution layer. In some applications, however, the metal layer453may be missing.

The protection layer454covers the metal layer453and accommodates electric connection lines419(FIG.12), of conductive material, for example of Al, that are connected to the heaters418in openings (not visible) in the protection layer454and in the metal layer453and couple the heaters418to pads (not represented, for simplicity), arranged on the periphery of the microfluidic device.

The protection layer454is shaped to form chamber cavities455at locations where the chambers are to be formed. In particular, each chamber cavity455overlies a respective heater418. The shape of the chamber cavities455may be the same as the desired shape of the chambers or any, for example rectangular; in general, the area of the each first chamber cavity455is smaller than the chamber area.

In addition, the protection layer454forms tank connection cavities456(FIG.11), each extending near groups of first chamber cavities455, as explained better later on, and pad cavities457(FIG.11) overlying the pads (not shown).

Then,FIGS.14-17, a lower chamber layer460is deposited and defined. The lower chamber layer460is for example of a photosensitive dry material that is spinned and defined to delimit lower chamber openings461vertically arranged over and in prosecution to the chamber cavities455, but slightly larger, as visible inFIG.17.

The lower chamber openings461are for example shaped as shown inFIG.9and visible in the enlarged detail ofFIG.16. In particular, the lower chamber openings461are delimited by a wall forming lower indentations466separated by lower protrusions467(FIG.16).

In addition, the lower chamber layer460is shaped to form lower pillar portions464(FIGS.15and16).

The lower chamber layer460is also removed to form lower tank connection openings462over the tank connection cavities456ofFIG.11and to form lower pad opening463over the pad cavities457, as shown inFIG.14.

The lower chamber layer460is then baked and hardened.

InFIGS.18-21, an upper chamber layer470is deposited and defined. The upper chamber layer470is for example of a photosensitive dry material, the same or different from the lower chamber layer460. The upper chamber layer470is, e.g., spinned and defined to delimit upper chamber openings471vertically arranged over and in prosecution (e.g., fluidically connected) to the lower chamber openings461. The lower and upper chamber layers460,470form chamber layer414.

As visible in the top plan view ofFIG.19, the upper chamber openings471have a similar shape to the lower chamber openings461, but are slightly larger. In particular, the upper chamber openings471have upper indentations476that extend deeper in the lateral walls416than the lower indentations266and upper protrusions477that are about aligned with the lower protrusions467, as also visible by the dashed portions inFIG.20.

In addition, the upper chamber layer470is shaped to form upper pillar portions474(FIG.19), vertically aligned to the lower pillar portions464.

As indicated inFIG.20, the upper chamber openings471and the lower chamber openings461form chambers417; the upper protrusions477and the lower protrusions467form chamber protrusions430; the upper indentations476and the lower indentations466form chamber indentations431; the upper pillar portions474and the lower pillar portions464form pillars433(FIG.19).

As can be seen in particular inFIG.19, the lower and upper chamber layers460,470also form inlets420.

The upper chamber layer470also form upper tank connection openings472over the lower tank connection openings462ofFIG.15as well as upper pad openings473over the lower pad openings463ofFIG.14, as shown inFIG.18.

The upper chamber layer470is then baked and hardened.

Then,FIGS.21-22, the substrate401is dry etched to remove the semiconductor material of the substrate401under the tank connection openings472,462. Thereby, fluid supply channels480are formed. The fluid supply channels480extend through the entire thickness of substrate401, laterally to the chambers417, and in fluid connection with the inlets420.

InFIGS.23-26, a nozzle layer415is deposited and defined. The nozzle layer415is, e.g., of a photosensitive dry film, that may be the same or different from the lower and upper chamber layers460,470. The nozzle layer415is laminated and defined according to standard photolithographic techniques to form openings432, shaped as shown inFIGS.9and24.

The openings432are offset with respect to the chambers417, as explained with reference toFIG.9and visible also inFIGS.26-27, so that the nozzle layer415cover most of the area of the chambers417except for, at least, part of the chamber indentations431, forming intersection areas434(FIG.27).

The nozzle layer415also upwardly covers the inlets420and the fluid supply channels480and is removed over the lower and upper pad openings463,473(pad openings483,FIG.23), to allow electrical connection to the electric connection lines419(FIG.12).

Therefore, as visible inFIGS.26-28and indicated by arrows L, fluid entering the fluid supply channels480from a lower face482of the substrate401may reach the inlets420and the chambers417, be heated by the heaters418, causing generation of bubbles, and be ejected through the intersection areas434, analogously to the operation described in above cited patent application US 2018/0141074.

In particular, as shown by the arrows S inFIG.27, by virtue of the small dimensions of the intersection areas434, many small drops are ejected, ensuring a high total volume of the sprayed liquid with very small diameter drops.

Since the small features determining the dimension of the ejected drops are formed in the lower and upper chamber layers460,470, in particular in the upper chamber layer470, which may be defined in a simple way, using standard, reliable and well known photolithographic techniques, manufacturing of the microfluidic device100is simple and reliable.

The obtained geometry is thus well controlled and the microfluidic device100is able to operate in a desired manner.

By forming the chambers417so as to have smaller areas at the lower chamber openings461than at the upper chamber openings471, better ejection conditions may be obtained; in addition, the resulting chamber417is more easily complying the volume ratio of 15% discussed above, all the other geometrical aspects being equal.

According to a different embodiment, the nozzle layer15ofFIG.3is formed by a separate wafer, that is bonded to the wafer accommodating the chambers17, as discussed below with reference toFIGS.29-40.

With reference toFIG.29, a microfluidic device500comprises a lower wafer600and an upper wafer650.

The lower wafer600basically comprise the same structures as wafer400ofFIGS.21-22. Accordingly, the same elements are identified by reference numbers increased by200with respect to the correspondent elements inFIGS.21-22and are not described in detail again.

In particular, the chamber layer, here identified by number614, may be formed by a single layer, e.g., of a polymeric material, as shown, or by a multiple layer, analogously to lower and upper chamber layers460,470ofFIG.20. The chamber layer614forms chamber617delimited by a lateral wall616.

Upper wafer650is a semiconductor wafer shaped to form a plurality of nozzle openings623, extending for the entire thickness of the upper wafer650.

In particular, here, each nozzle opening623comprises a smaller section portion655and a larger section portion656.

Specifically, the upper wafer650has a lower main surface660, facing the lower wafer600, and an upper main surface661, opposite the lower main surface660. The smaller section portions655of the nozzle openings623extend from the upper main surface661; the larger section portions656extend from the lower main surface660and directly face the lower wafer600.

The smaller section portions655of the nozzle openings623may have a circular cross-section, with a diameter of about 2 μm; the larger section portions656may also have a circular cross-section, with a diameter of about 3 μm, and be concentric to the smaller section portions655.

The microfluidic device500ofFIG.29is manufactured as described below, with reference toFIGS.30-40.

Initially,FIG.30, a starting substrate700is used. Starting substrate700comprises a first semiconductor layer701, an intermediate layer702of insulating material, and a second semiconductor layer703. For example, first semiconductor layer701may be silicon with a thickness of about 400 μm, intermediate layer702may be silicon oxide with a thickness of about 1 μm, and second semiconductor layer703may be silicon with a thickness of about 5-10 μm.

InFIG.31, the second semiconductor layer703is etched using known photolithographic techniques to form the smaller section portions655of the nozzle openings623.

The smaller section portions655of the nozzle openings623may have the shapes shown inFIGS.7-10. In the alternative, they may be arranged according the so-called showerhead arrangement, as shown inFIG.32, or in any other arrangement.

Then,FIG.33, thermal oxidation is performed; thus an etch stop layer705covers the surface of the second semiconductor layer703, including inside the smaller section portions655of the nozzle openings623. The etch stop layer705may be, e.g., 0.4 μm thick.

InFIG.34, a structural layer706of silicon is epitaxially grown on the etch stop layer705and then planarized, e.g., by CMP (Chemical Mechanical Polishing). The structural layer706grows on the thin covering layer705and may extend in the smaller section portions655of the nozzle openings623. The final thickness of the structural layer706may be 10 μm.

Then, the structural layer706is etched using a mask to form the larger portion sections656of the nozzle openings623.

Since the larger portion sections656are vertically centered with the smaller section portions655of the nozzle openings623, etching stops on the etch stop layer705and removes the silicon within the smaller section portions655.

FIG.35shows the resulting starting substrate700in a partially cut-away perspective view where intermediate layer702and etch stop layer705are not visible.

Simultaneously, before or after working the starting wafer700, the first wafer600is worked to obtain the structure ofFIG.36. In a not visible manner, also fluid supply channels (680inFIG.40) have already been formed.

Then,FIG.37, the starting wafer700is turned upside down and bonded to the lower wafer600. Here, the chamber layer614acts as an adhesion layer that is directly bonded to the structural layer706, with the first semiconductor layer701arranged at the top.

Thereafter, the starting wafer700is thinned, e.g., by grinding the first semiconductor layer701, as shown by the dashed lines. For example, the first semiconductor layer701may be reduced to a thickness of about 40 μm.

InFIG.38, the first semiconductor layer701is completely removed, for example by dry etch; in addition, also the exposed portions of the intermediate layer702and of the etch stop layer705are removed by dry etch. The upper wafer650is thus obtained.

Thereby, the microfluidic device500ofFIGS.29and38is obtained.FIGS.39and40show prospective views of the microfluidic device500, showing the relative position of the chambers617and the nozzle apertures623, as well as of fluid supply channels680, inlets420and pillars633.

With the process ofFIGS.29-40, small features may be easily defined. In particular, in case of nozzle openings623forming a showerhead pattern, with a plurality of nozzle openings623for each chamber617, small dimensions may be obtained by dry etching the starting wafer700, in an easily definable way.

The same steps may however be used to form large dimension nozzle openings623, with small features formed in the chamber layer614as an alternative to the deposition of a photosensitive dry film, as discussed with reference toFIGS.11-28.

Finally, it is clear that numerous variations and modifications may be made to the microfluidic device and the manufacturing steps described and illustrated herein, all falling within the scope of the disclosure.

For example, the various embodiments described above can be combined to provide further embodiments.

In particular, the heaters18,418,618may be replaced by actuators operating according to a different principle; for example actuators of a piezoelectric material, for example PZT (Pb, Zr, TiO3) may be used, e.g., as disclosed in US2019/0358955.

The shape of the chambers17,417and617may widely vary, so as the shape of the protrusions130,230,430and indentations131,231,431.

A microfluidic device (1;100;500) may be summarized as including a chamber (17;117;217;317;417;617); a fluidic access channel (20;120;420,480;620,680) in fluidic connection with the chamber; a plurality of nozzle apertures (34;134;434;623) in fluidic connection with the chamber; and an actuator (18;418;618), operatively coupled to the fluid containment chamber and configured to cause ejection of drops of fluid through the nozzle apertures in an operating condition of the microfluidic device, wherein the chamber (17;117;217;317;417;617) has an elongated shape, with a length and a maximum width, wherein an aspect ratio between the length and the maximum width of the chamber is at least 3:1.

The chamber (17;117;217;317;417;617) may have a rectangular or oval base shape.

The chamber (17;117;217;317;417;617) may be delimited by a first base (17A), a second base (17B) and a lateral wall (16;116;216;416), the first and second bases extending along a first and a second direction, the second direction transverse to the first direction, the first and second directions defining the chamber length and the chamber maximum width, respectively, the lateral wall extending along a third direction, transverse to the first and second directions and defining a chamber height.

The chamber (17;117;217;317;417;617) may have a chamber volume and the nozzle apertures (34;134;434;623) may be configured to generate, in use, a plurality of drops having a total drop volume, wherein a ratio total drop volume to chamber volume is at least 15%.

The microfluidic device may include a base body portion (22;422), a chamber layer (14;114;414;614) and a nozzle layer (15;115;215;315;415;650), the base body portion forming the first base (17A) and accommodating the actuator (18;418;618), the chamber layer forming the lateral wall (16;116;216;416;616) and the nozzle layer forming the second base (17B) of the chamber (17;117;217;317;417;617).

The lateral wall (16;116;216;416) may form a plurality of indentations (131;231;

331;431) and protrusions (130;230;330;430), and the nozzle layer (15;115;215;315;415) may include at least one nozzle opening (132;232;332;432) offset with respect to the chamber (17;117;217;317;417) and intersecting the indentations at intersection areas forming the nozzle apertures (34;134;434).

The chamber layer (414) may include a first layer (460) extending on the base body (422) portion and a second layer (470), extending on the first layer, the first layer delimiting a lower chamber aperture (461), the second layer delimiting an upper chamber aperture (471), the lower chamber aperture having a smaller area than the upper chamber aperture.

The chamber layer (14;114;214;314;414) and the nozzle layer (15;115;215;315;415) may be polymeric layers.

The nozzle layer (650) may be silicon wafer.

Each nozzle aperture (623) may include a larger section portion (656) facing the chamber (617) and a smaller section portion (655) in prosecution of the larger section portion and extending from an outer surface (661) of the nozzle plate (650).

The nozzle apertures (623) may be arranged in a showerhead arrangement above the chamber (617).

A process for manufacturing a microfluidic device may be summarized as including forming a chamber (17;117;217;317;417;617); forming a fluidic access channel (20;120;420,480;620,680) in fluidic connection with the chamber; forming a plurality of nozzle apertures (34;134;434;623) in fluidic connection with the chamber; and forming an actuator (18;418;618), operatively coupled to the fluid containment chamber and configured to cause ejection of drops of fluid through the nozzle apertures in an operating condition of the microfluidic device, wherein the chamber (17;117;217;317;417;617) has an elongated shape, with a length and a maximum width, wherein an aspect ratio between the length and the maximum width of the chamber is at least 3:1.

Forming an actuator (18;418;618) may include forming the actuator in a base body portion (22;422); forming a chamber (17;117;217;317;417;617) may include forming a chamber layer (14;114;414;614) on the base body portion, with the chamber overlying the actuator, the base body portion forming a first base (17A) of the chamber and the chamber layer forming a lateral wall of the chamber; and forming a plurality of nozzle apertures (34;134;434;623) may include forming a nozzle layer (15;115;215;315;415;650) on the chamber layer and forming at least one opening that at least partially overlies the chamber, the nozzle layer covering the chamber and forming a second base (17B) of the chamber.

Forming a chamber layer (114;214;314;414) may include shaping the lateral wall (116;216;316;416) to form a plurality of indentations (131;231;331;431) and protrusions (130;230;330;430), and forming at least one opening comprises forming a nozzle opening (132;232;332;432) offset with respect to the chamber and intersecting the indentations at intersection areas, thereby forming the nozzle apertures (34;134;434).

Forming a chamber layer (414,614) may include forming a first layer (460) on the base body portion (422), the first layer defining a first chamber aperture (461); forming a second layer (470) on the first layer, the second layer defining a second chamber aperture (471), the first chamber aperture having a smaller area than the second chamber aperture.

The chamber layers (14;114;214;314;414) and the nozzle layer (15;115;215;315;415) may be polymeric layers.

Forming a nozzle layer may include forming first opening portions (655) in a semiconductor wafer (700); forming second opening portions (656) in the semiconductor wafer over the first opening portions, the second opening portions having larger area than the first opening portions and extending in prosecution to the first opening portions; bonding the semiconductor wafer (700) to the chamber layer (614), with the second opening portions facing the chamber; and thinning the semiconductor wafer to expose the first opening portions.

The first opening portions (655) extend for a partial thickness of a starting wafer (700) of semiconductor material; after forming first opening portions, an etch stop layer (702) may be grown on the starting wafer, a semiconductor layer (706) may be grown on the etch stop layer, thereby forming the semiconductor wafer (700), and the second opening portions are formed in the semiconductor layer; and thinning the semiconductor wafer may include removing the starting wafer up to the first opening portions.

A microfluidic MEMS device (1;100;500) may also be summarized as including:

a plurality of chambers (17;117;217;317;417;617), the chambers (17;117;217;317;417;617) having an elongated shape, with a length and a maximum width, wherein an aspect ratio between the length and the maximum width of the chambers is at least 3:1;

a fluidic access channel (20;120;420,480;620,680) for each chamber, in fluidic connection with a respective chamber;

a plurality of nozzle apertures (34;134;434;623) for each chamber, in fluidic connection with the respective chamber;

an actuator (18;418;618) for each chamber, operatively coupled to the respective chamber and configured to cause ejection of drops of fluid through the nozzle apertures in an operating condition of the microfluidic MEMS device;

a chamber layer (14;114;414;614) and a nozzle layer (15;115;215;315;415;650), overlying each other, the chamber layer forming the plurality of chambers and the nozzle layer forming a plurality of nozzle openings (132;232;332;432),

each chamber being delimited by a lateral wall (16;116;216;416) having a plurality of indentations (131;231;331;431) and protrusions (130;230;330;430); and the nozzle openings (132;232;332;432) being offset with respect to the chambers (17;117;217;317;417), with each nozzle opening extending between two adjacent chambers and intersecting the indentations of the two adjacent chambers at intersection areas forming the nozzle apertures (34;134;434).

The chamber (17;117;217;317;417;617) may have a rectangular or oval base shape.

The chamber (17;117;217;317;417;617) may be delimited by a first base (17A), a second base (17B) and the lateral wall (16;116;216;416), the first and second bases extending along a first and a second direction, the second direction transverse to the first direction, the first and second directions defining the chamber length and the chamber maximum width, respectively, the lateral wall extending along a third direction, transverse to the first and second directions and defining a chamber height.

The chamber (17;117;217;317;417;617) may have a chamber volume and the nozzle apertures (34;134;434;623) may be configured to generate, in use, a plurality of drops having a total drop volume, and a ratio total drop volume to chamber volume is at least 15%.

The microfluidic device may further include a base body portion (22;422) the base body portion forming the first base (17A) and accommodating the actuator (18;418;618), and the nozzle layer forming the second base (17B) of the chamber (17;117;217;317;417;617).

The chamber layer (414) may include a first layer (460) and a second layer (470), extending on the first layer, the first layer delimiting a lower chamber aperture (461), the second layer delimiting an upper chamber aperture (471), the lower chamber aperture having a smaller area than the upper chamber aperture.

The first layer (460) may extend on the base body portion (422). The chamber layer (14;114;214;314;414) and the nozzle layer (15;115;215;315;415) may be polymeric layers or the chamber layer (14;114;214;314;414) may be a polymeric layer and the nozzle layer (650) may be a silicon wafer.

The actuator may be a heater (18;418;618).

The nozzle openings (232;332;432) may have a larger area than the chambers (217;317;417).

A process for manufacturing a microfluidic MEMS device may be summarized as including:

forming a plurality of chambers (17;117;217;317;417;617), the chambers (17;117;217;317;417;617) having an elongated shape, with a length and a maximum width, wherein an aspect ratio between the length and the maximum width of the chambers is at least 3:1;

forming a fluidic access channel (20;120;420,480;620,680) for each chamber, in fluidic connection with a respective chamber;

forming a plurality of nozzle apertures (34;134;434;623) for each chamber, in fluidic connection with the respective chamber; and

forming an actuator (18;418;618) for each chamber, operatively coupled to the respective chamber and configured to cause ejection of drops of fluid through the nozzle apertures in an operating condition of the microfluidic MEMS device,

wherein forming a plurality of chambers comprises forming a chamber layer (14;114;414;614) and forming a lateral wall (16;116;216;416) for each chamber, the lateral walls delimiting each a respective chamber and having a plurality of indentations (131;231;331;431) and protrusions (130;230;330;430),

forming a plurality of nozzle apertures comprises forming a nozzle layer (15;115;215;315;415;650) on the chamber layer and forming a plurality of the nozzle openings (132;232;332;432) in the nozzle layer, and

the nozzle openings (132;232;332;432) being offset with respect to the chambers (17;117;217;317;417), with each nozzle opening extending between two adjacent chambers and intersecting the indentations of the two adjacent chambers at intersection areas forming the nozzle apertures (34;134;434).

Forming an actuator (18;418;618) may include forming the actuator in a base body portion (22;422); and

the chamber layer (14;114;414;614) may be formed on the base body portion, with the chamber overlying the actuator, the base body portion forming a first base (17A) of the chamber and the nozzle layer covering the chamber and forming a second base (17B) of the chamber.

Forming a chamber layer (414,614) may include:

forming a first layer (460) on the base body portion (422), the first layer defining a first chamber aperture (461);

forming a second layer (470) on the first layer, the second layer defining a second chamber aperture (471), the first chamber aperture having a smaller area than the second chamber aperture.

The chamber layers (14;114;214;314;414) and the nozzle layer (15;115;215;315;415) may be polymeric layers.

The nozzle openings (132;232;332;432) may have a larger area than the chambers.

A microfluidic MEMS device (1;100;500) may also be summarized as including:

a chamber (17;117;217;317;417;617);

a fluidic access channel (20;120;420,480;620,680) in fluidic connection with the chamber;

a plurality of nozzle apertures (34;134;434;623) in fluidic connection with the chamber; and

an actuator (18;418;618), operatively coupled to the fluid containment chamber and configured to cause ejection of drops of fluid through the nozzle apertures in an operating condition of the microfluidic device,

the chamber (17;117;217;317;417;617) having an elongated shape, with a length and a maximum width, the length being greater than the width,

a chamber layer (14;114;414;614);

a nozzle layer (15;115;215;315;415;650), overlying the chamber layer,

wherein the chamber layer forms a lateral wall (16;116;216;416) of the chamber and the nozzle layer forms at least one a nozzle opening (132;232;332;432);

the lateral wall (16;116;216;416) forming a plurality of indentations (131;231;331;431) and a plurality of protrusions (130;230;330;430),

the nozzle opening (132;232;332;432) being offset with respect to the chamber (17;117;217;317;417) and intersecting the indentations at intersection areas forming the nozzle apertures (34;134;434);

the chamber layer (414) comprises a first layer (460) and a second layer (470), extending on the first layer, the first layer delimiting a lower chamber aperture (461), the second layer delimiting an upper chamber aperture (471), the lower chamber aperture having a smaller area than the upper chamber aperture.

Another microfluidic MEMS device (1;100;500) may be summarized as including:

a chamber (17;117;217;317;417;617);

a fluidic access channel (20;120;420,480;620,680) in fluidic connection with the chamber;

a plurality of nozzle apertures (34;134;434;623) in fluidic connection with the chamber; and

an actuator (18;418;618), operatively coupled to the fluid containment chamber and configured to cause ejection of drops of fluid through the nozzle apertures in an operating condition of the microfluidic device,

the chamber (17;117;217;317;417;617) having an elongated shape, with a length and a maximum width, the length being greater than the width,

a chamber layer (14;114;414;614);

a nozzle layer (15;115;215;315;415;650), overlying the chamber layer,

wherein the chamber layer forms a lateral wall (16;116;216;416) of the chamber and the nozzle layer forms at least one a nozzle opening (132;232;332;432);

the lateral wall (16;116;216;416) forming a plurality of indentations (131;231;331;431) and a plurality of protrusions (130;230;330;430), the nozzle opening (132;232;332;432) being offset with respect to the chamber (17;117;217;317;417) and intersecting the indentations at intersection areas forming the nozzle apertures (34;134;434);

wherein each nozzle aperture (623) may comprise a larger section portion (656) facing the chamber (617) and a smaller section portion (655) in prosecution of the larger section portion and extending from an outer surface (661) of the nozzle plate (650).

The nozzle apertures (623) may be arranged in a showerhead arrangement above the chamber (617).

A process for manufacturing a microfluidic MEMS device may be summarized as including:

forming a chamber (17;117;217;317;417;617) having an elongated shape, with a length and a maximum width, the length being greater than the width, forming a fluidic access channel (20;120;420,480;620,680) in fluidic connection with the chamber;

forming a plurality of nozzle apertures (34;134;434;623) in fluidic connection with the chamber; and

forming an actuator (18;418;618), operatively coupled to the fluid containment chamber and configured to cause ejection of drops of fluid through the nozzle apertures in an operating condition of the microfluidic device,

forming a chamber (17;117;217;317;417;617) comprises forming a chamber layer (14;114;414;614) and forming a lateral wall (16;116;216;416) in the chamber layer, the lateral wall having a plurality of indentations (131;231;331;431) and protrusions (130;230;330;430);

forming a plurality of nozzle apertures (34;134;434;623) comprises forming at least one nozzle opening (132;232;332;432) offset with respect to the chamber and intersecting the indentations at intersection areas, thereby forming the nozzle apertures (34;134;434), and

forming a chamber layer (414,614) comprises forming a first layer (460) on the base body portion (422), the first layer defining a first chamber aperture (461), and forming a second layer (470) on the first layer, the second layer defining a second chamber aperture (471), the first chamber aperture having a smaller area than the second chamber aperture.

Another process for manufacturing a microfluidic MEMS device may be summarized as including:

forming a chamber (17;117;217;317;417;617) having an elongated shape, with a length and a maximum width, the length being greater than the width, forming a fluidic access channel (20;120;420,480;620,680) in fluidic connection with the chamber;

forming a plurality of nozzle apertures (34;134;434;623) in fluidic connection with the chamber; and

forming an actuator (18;418;618), operatively coupled to the fluid containment chamber and configured to cause ejection of drops of fluid through the nozzle apertures in an operating condition of the microfluidic device,

forming a chamber (17;117;217;317;417;617) comprises forming a chamber layer (14;114;414;614) and forming a lateral wall (16;116;216;416) in the chamber layer, the lateral wall having a plurality of indentations (131;231;331;431) and protrusions (130;230;330;430);

forming a plurality of nozzle apertures (34;134;434;623) comprises forming at least one nozzle opening (132;232;332;432) offset with respect to the chamber and intersecting the indentations at intersection areas, thereby forming the nozzle apertures (34;134;434), and

wherein forming a nozzle layer may comprise:

forming first opening portions (655) in a semiconductor wafer (700);

forming second opening portions (656) in the semiconductor wafer over the first opening portions, the second opening portions having larger area than the first opening portions and extending in prosecution to the first opening portions;

bonding the semiconductor wafer (700) to the chamber layer (614), with the second opening portions facing the chamber; and

thinning the semiconductor wafer to expose the first opening portions.

The first opening portions (655) may extend for a partial thickness of a starting wafer (700) of semiconductor material and the process may further comprise:

after forming first opening portions, growing an etch stop layer (702) on the starting wafer, growing a semiconductor layer (706) on the etch stop layer, thereby forming the semiconductor wafer (700), and forming the second opening portions in the semiconductor layer;

wherein thinning the semiconductor wafer may comprise removing the starting wafer up to the first opening portions.