Patent Publication Number: US-2021177061-A1

Title: Microfluidic dispensing device having a plurality of ejection chambers

Description:
BACKGROUND 
     Technical Field 
     The present disclosure relates to a microfluidic dispensing device, in particular of inhalable substances, with a plurality of ejection chambers. 
     Description of the Related Art 
     As is known, the desire to accurately control the dispensing of inhalable substances, both for therapeutic purposes and for manufacturing non-medical devices, such as the so-called electronic cigarettes, has led to the development of miniaturized dispensing apparatus that are easily usable. 
     A miniaturized dispensing apparatus for inhalable substances of known type normally comprises a tank, which contains a fluid with the substances to be dispensed in solution, and at least a dispensing chamber, having ejector nozzles and supplied by the tank. An actuator, accommodated in the chamber and driven by a controller, causes a controlled quantity of fluid to be ejected. 
     For example, a miniaturized dispensing apparatus of this type is shown in Italian patent application No. 102018000005372 (corresponding to US patent application US 2019/0350260 A1) and briefly described herein below. 
     In detail,  FIG. 1  shows a miniaturized dispensing apparatus  1 , here an electronic cigarette. The miniaturized dispensing apparatus  1  comprises a casing  2  accommodating a driver  3 , a battery  4  and a microfluidic cartridge  5  of disposable type. 
     More in detail, the casing  2  forms a control chamber  7  and a cartridge chamber  8 . In one embodiment, the control chamber  7  is substantially axial, is open at a first end  2 A of the casing  2  and is closable for example with an aesthetic lid, not shown. The driver  3 , comprising for example an ASIC (Application Specific Integrated Circuit)  6 , may be soldered on a substrate  10 , for example a PCB (Printed Circuit Board) insertable into the control chamber  7  together with the battery  4 . 
     The cartridge chamber  8  is arranged between the control chamber  7  and a second end  2 B of the casing  2  and is accessible through a flip door  11  for inserting and removing the microfluidic cartridges  5 . The cartridge chamber  8  communicates with the outside through inlet holes  13  and a mouthpiece  14 . More precisely, the inlet holes  13  and the mouthpiece  14  are arranged so that suction through the mouthpiece  14  causes the air in the cartridge chamber  8  to return through the inlet holes  13 , the sucked air to pass through the cartridge chamber  8  and the air to subsequently come out through the mouthpiece  14 . 
     Electrical connection lines  15 , for example embedded in the casing  2 , extend between the control chamber  7  and the cartridge chamber  8  to electrically couple the driver  3  and the microfluidic cartridge  5  in the cartridge chamber  8 . 
     The microfluidic cartridge  5  comprises a tank  17 , containing a liquid to be dispensed, and a spray nozzle  18  controlled by the driver  3  and arranged here on an external face of the microfluidic cartridge  5 . 
     In the embodiment shown in  FIGS. 2A and 2B , the spray nozzle  18  comprises a substrate  20  covered by an insulating layer  21 , a chamber layer  23  extending above the insulating layer  21 , and a nozzle plate  25  bonded to the chamber layer  23 . The substrate  20 , the insulating layer  21  and the chamber layer  23  may be, for example, respectively, of semiconductor material, silicon oxide or nitride and a polymeric material such as dry film. The nozzle plate  25  may be of polymeric material or semiconductor material. 
     Supply passages  26  fluidly coupled to the tank  17  ( FIG. 1 ) are formed through the substrate  20 , the insulating layer  21  and the chamber layer  23 . In the embodiment illustrated in  FIGS. 2A and 2B , in particular, the supply passages  26  are circular and concentric. 
     Chambers  30  are formed in the chamber layer  23  along the supply passages  26 , as also shown in  FIG. 2B . In the illustrated embodiment, the chambers  30  are distributed uniformly. Furthermore, the chambers  30  are fluidly coupled to the supply passages  26  through respective microfluidic channels  31  and are delimited on the bottom by the insulating layer  21  and on the top by the nozzle plate  25 . 
     Nozzles  32  are formed in the nozzle plate  25  at each chamber  30  and allow, in use, the liquid nebulized by the chambers  30  to pass and to be mixed with the air flowing from the inlet holes  13  through the cartridge chamber  8  towards the mouthpiece  14 . 
       FIG. 3  shows a possible embodiment of a chamber  30 . Here, the chamber  30  has a parallelepiped shape and is laterally delimited by walls  30 A formed in the chamber layer  23 . 
     A heater  33  is formed here within the insulating layer  21  below the chamber  30 . The heater  33  may be formed, in a non-limiting manner, of polycrystalline silicon, Al, Pt, TiN, TiAlN, TaSiN, TiW. The heater  33  is connected to the driver  3  ( FIG. 1 ) through the electrical connection lines  15 . 
     In use, the ASIC  6  ( FIG. 1 ) generates electrical signals supplied to the heaters  33  of the chambers  30  through the connection lines  15 , allowing the heaters  33  to heat up to a programmed temperature, for example 450° C. The liquid present in the chambers  30 , coming from the tank  17  ( FIG. 1 ) through the supply passages  26  ( FIG. 2A ), is then rapidly heated and forms vapor bubbles such as to push a drop of liquid through each nozzle  32 . As a whole the chambers  30  thus allow vapor “plumes” to be obtained in the cartridge chamber  8 . 
     BRIEF SUMMARY 
     In prior approaches and applications of dispensing devices, to generate sufficient vapor “plumes” for the specific application, a large number of chambers  30  is generally relied on or utilized, for example greater than one thousand. For example, referring to  FIG. 3 , the direct driving of each heater  33  through respective connection lines  15  is thus complex, expensive and generally utilized a large integration area for the arrangement of the contact pads and the difficulty of forming the wire connections. 
     To overcome this problem, it is possible to use a suitable driver, such as the ASIC  6  of  FIG. 1 , and arrange it within the silicon die wherein the microfluidic cartridge  5  is formed. However, this solution is also expensive and cannot be used in all low-cost applications. 
     In various embodiments, the present disclosure provides a dispensing device which overcomes the drawbacks of the prior art. 
     According to the present disclosure, a microfluidic dispensing device, the manufacturing process thereof and a dispensing method are provided. 
     In at least one embodiment, a microfluidic dispensing device is provided that includes a plurality of chambers, each chamber having an inlet configured to receive a liquid to be dispensed and a nozzle configured to emit a drop of liquid, the plurality of chambers forming a sequence of chambers. A plurality of actuators are included, with each actuator being associated with a respective chamber and configured to receive a respective actuation quantity and cause a drop of liquid to be emitted by the nozzle of the respective chamber. A plurality of drop emission detection elements are included, one for each chamber, each drop emission detection element being configured to generate an actuation command upon detecting the emission of a drop of liquid from the nozzle of a respective chamber. The device further includes a sequential activation electric circuit including a plurality of sequential activation elements, one for each chamber, each sequential activation element being coupled to the drop emission detection element associated with the respective chamber and to an actuator associated with a chamber following the respective chamber in the sequence of chambers, each sequential activation element being configured to receive the actuation command from the drop emission detection element associated with the respective chamber and activate the actuator associated with the subsequent chamber in the sequence of chambers. 
     In at least one embodiment, a process for manufacturing a microfluidic dispensing device is provided that includes: forming a plurality of chambers, each chamber having an inlet configured to receive a liquid to be dispensed and a nozzle configured to emit a drop of liquid, the plurality of chambers forming a sequence of chambers; forming a plurality of actuators, each actuator being associated with a respective chamber and configured to receive a respective actuation quantity and cause a drop of liquid to be emitted by the nozzle of the respective chamber; forming a plurality of drop emission detection elements, one for each chamber, each drop emission detection element being configured to generate an actuation command upon detecting the emission of a drop of liquid from the nozzle of a respective chamber; and forming a sequential activation electric circuit, including: a plurality of sequential activation elements, one for each chamber, each sequential activation element being coupled to the drop emission detection element associated with the respective chamber and an actuator associated with a chamber following the respective chamber in the sequence of chambers, each sequential activation element being configured to receive the actuation command from the drop emission detection element associated with the respective chamber and activate the actuator associated with the subsequent chamber in the sequence of chambers. 
     In at least one embodiment, a method for dispensing in a microfluidic dispensing device is provided. The microfluidic dispensing device includes: a plurality of chambers, each chamber having an inlet and a nozzle, the plurality of chambers forming a sequence of chambers; a plurality of actuators, one for each chamber; a plurality of drop emission detection elements, one for each chamber; and a sequential activation electric circuit including: a plurality of sequential activation elements, each sequential activation element being coupled to the drop emission detection element associated with the respective chamber and an actuator associated with a chamber following the respective chamber in the sequence of chambers. The method includes: providing a liquid to be dispensed to the plurality of chambers; activating an actuator of a first chamber of the succession of chambers and causing a drop of liquid to be emitted by the nozzle of the first chamber; detecting the emission of the drop from the first chamber through the sequential activation element associated with the first chamber; and upon detecting the emission of the drop from the first chamber, activating an actuator associated with a chamber following the first chamber through the sequential activation element associated with the first chamber. 
    
    
     
       BRIEF DESCRIPTION OF THE SEVERAL VIEWS OF THE DRAWINGS 
       For a better understanding of the present disclosure, embodiments thereof are now described, purely by way of non-limiting example, with reference to the attached drawings, wherein: 
         FIG. 1  is a longitudinal-section perspective view of a known electronic cigarette; 
         FIG. 2A  is an exploded perspective view of a microfluidic dispensing device usable in the electronic cigarette of  FIG. 1 ; 
         FIG. 2B  is an enlarged perspective view of a portion of the microfluidic dispensing device of  FIG. 2A , with parts removed for clarity; 
         FIG. 3  is a section perspective view of a detail of  FIG. 2A ; 
         FIG. 4A  is a simplified top view of the present microfluidic dispensing device, with parts removed for clarity; 
         FIG. 4B  shows an equivalent scheme of the microfluidic dispensing device of  FIG. 4A ; 
         FIGS. 5 and 6  show different embodiments of the present microfluidic dispensing device, in simplified top views; 
         FIGS. 7A-10A  show cross-sections of the present microfluidic dispensing device, taken along section line VIIA-VIIA of  FIG. 4A , in subsequent manufacturing steps; and 
         FIGS. 7B-10B  show cross-sections of the present microfluidic dispensing device, taken along section line VIIB-VIIB of  FIG. 4A , in subsequent manufacturing steps. 
     
    
    
     DETAILED DESCRIPTION 
     A microfluidic dispensing device  50  usable in a dispensing apparatus, such as an electronic cigarette, an inhaler for medical use, a CPAP (Continuous Positive Airway Pressure) device, for detecting sleep apneas or in different types of apparatus, such as anti-pollution masks and apparatus for detecting leaks of air or other fluids, used in the industrial or automotive field, is described herein below. 
     For understanding the principle underlying the present microfluidic dispensing device, reference be initially made to  FIG. 4B  which shows an equivalent electric circuit, thereafter also referred to as sequential activation circuit. 
     The microfluidic dispensing device  50  comprises a plurality of dispensing cells connected to each other so as to be activated sequentially. In the following figures, only three dispensing cells are shown, referred to as initial cell  49 A, first sequential cell  49 B and second sequential cell  49 C, but it is to be understood that, in general, numerous other dispensing cells are arranged sequentially in succession to the second sequential cell  49 C and activated sequentially, as discussed below. 
     In the following description, since the dispensing cells (except, in part, the initial cell  49 A) have a similar structure, both the dispensing cells and the specific parts will be indicated with the generic number (for example  49  for the dispensing cells), not followed by a letter, when the description in general refers thereto, and with the number and the respective letter (A, B and C) when referring to a specific dispensing cell (here  49 A,  49 B,  49 C) or parts thereof. 
     In the electrical diagram shown in  FIG. 4B , the initial cell  49 A is arranged between a ground line  54  and a first supply line  55  and comprises an initial dispensing chamber  52 A, an initial heater  59 A and an initial drop emission detection element  51 A. An activation pulse I is provided to the first supply line  55  to activate the initial heater  59 A, which is configured to cause a drop to be emitted (similarly to what is described with reference to  FIG. 3 ); upon emitting a drop, the initial drop emission detection element  51 A generates an initial activation signal A. 
     The sequential cells  49 B,  49 C have a structure similar to the initial cell  49 A but also comprise a first, respectively a second switch,  60 B,  60 C, controlled by a preceding cell in the sequence (here the initial cell  49 A and the first sequential cell  49 B, respectively). 
     In detail, the first sequential cell  49 B is arranged between the ground line  54  and a second supply line  56  and comprises a first sequential dispensing chamber  52 B, a first sequential heater  59 B, the first switch  60 B and a first sequential drop emission detection element  51 B. The first sequential heater  59 B and the first switch  60 B are arranged mutually in series between the ground line  54  and the second supply line  56 . As indicated above, the first switch  60 B is controlled by the initial drop emission detection element  51 A and is configured, when receiving the initial activation signal A, to close the current path between the ground line  54  and the second supply line  56  and supply the first sequential heater  59 B. The first sequential heater  59 B is configured, when supplied, to cause a drop to be emitted into the first sequential dispensing chamber  52 B; the first sequential drop emission detection element  51 B is configured, upon detecting a drop, to generate a first activation signal B. 
     The second sequential cell  49 C is arranged between the ground line  54  and the second supply line  56  and comprises a second sequential dispensing chamber  52 C, a second sequential heater  59 C, the second switch  60 C and a second sequential drop emission detection element  51 C. The second sequential heater  59 C and the second switch  60 C are arranged mutually in series between the ground line  54  and the second supply line  56 . The second switch  60 C is controlled by the first sequential drop emission detection element  51 B and is configured, when receiving the first activation signal B, to close the current path between the ground line  54  and the second supply line  56  and supply the second sequential heater  59 C. The second sequential heater  59 C is configured, when supplied, to cause a drop to be emitted into the second sequential dispensing chamber  52 C; the second sequential drop emission detection element  51 C is configured, upon detecting a drop, to generate a second activation signal C to control a third switch  60 D of a subsequent sequential cell, not shown in  FIG. 4B . The heaters ( 59 A- 59 C), acting as actuators for emitting a drop, the drop emission detection elements ( 51 A- 51 C) and the switches ( 60 B- 60 D), comprised in the sequential activation circuit shown in  FIG. 4B , thus allow each cell  49 A- 49 C, when activated for emitting a drop, to generate an activation signal of a subsequent cell in the sequence. Accordingly, a single initial signal (activation pulse I) allows all the sequential cells to be activated automatically and in sequence. 
     The sequential activation described above may be implemented in the manner shown in  FIG. 4A . 
       FIG. 4A  shows again three dispensing chambers (also identified here as initial chamber  52 A, first chamber  52 B and second chamber  52 C). In general, however, as already indicated, the microfluidic dispensing device  50  comprises a large number of dispensing chambers, even a few thousand. 
     In the embodiment shown, the dispensing chambers  52 A,  52 B and  52 C are arranged mutually adjacent, side by side along a line, and are fluidly connected to supply passages in a not-shown manner, for example formed as described above with reference to  FIGS. 2A and 2B  for passages  26 . 
     In  FIG. 4A , the first supply line  55  is coupled to a first voltage source  57 , providing pulse-type voltage, and the second supply line  56  is coupled to a second voltage source  58 , providing direct voltage. In the exemplary embodiment shown, the voltage sources  57 ,  58  are integrated in the microfluidic dispensing device  50  and provide, for example, pulse voltage of 15V and, respectively, direct voltage of 20 V. Alternatively to what shown, the voltage sources  57 ,  58  may be external to the microfluidic dispensing device  50 , and coupled to the supply lines  55 ,  56  through contact pads not shown. 
     The dispensing chambers  52 A- 52 C are equal to each other and may be formed, generally speaking, as shown in  FIG. 3  and described in more detail below with reference to  FIGS. 4 and 10A, 10B ; in particular, each dispensing chamber  52 A,  52 B,  52 C is formed by a compartment overlying a stack of layers forming the heaters  59 A,  59 B,  59 C; furthermore each dispensing chamber  52 A- 52 C accommodates a first and a second conductive region  64 A- 64 C and  65 A- 65 C, contact regions  53 A- 53 C and membranes  71 A,  71 B,  71 C (forming the drop emission detection elements  51 A- 51 C). The conductive regions  64 A- 64 C and  65 A- 65 C, together with the contact regions  53 A- 53 C, form the switches  60 B- 60 D and are electrically coupled to an initial connection track or line  72 A, a first and a second sequential connection track  72 B,  72 C, a first, a second and a third track section  67 B,  67 C,  67 D, which, together with the dispensing chambers  52 A- 52 C and the heaters  59 A- 59 C, form the sequential activation circuit of  FIG. 4B . 
     In detail, the initial heater  59 A associated with the initial chamber  52 A is arranged between and is electrically coupled to a common ground track  62  (connected to the ground line  54 ) and the initial connection track  72 A (connected to the first supply line  55 ). The common ground track  62  and the initial connection track  72 A are formed in the same stack of layers forming the conductive regions  64 A- 64 C and  65 A- 65 C, the connection tracks  72 A- 72 C and the track sections  67 B,  67 C,  67 D. 
     The first conductive region  64 A of the initial chamber  52 A is connected to the common ground track  62  and the second conductive region  65 A of the initial chamber  52 A is connected and contiguous to the first track section  67 B. The first conductive region  64 A of the initial chamber  52 A and the second conductive region  65 A of the initial chamber  52 A are arranged substantially in the initial chamber  52 A, face each other and are electrically separated. 
     The initial membrane  71 A also extends within the initial chamber  52 A, adjacent to the initial heater  59 A, and carries the initial contact region  53 A on the bottom so that this region is vertically superimposed on and spaced, at rest, from the first and the second conductive regions  64 A,  65 A of the initial chamber  52 A. The initial membrane  71 A is configured to deform when a drop is emitted (as described in detail hereinbelow). 
     The initial membrane  71 A thus forms the initial drop detection element  51 A; the initial contact region  53 A, together with the first conductive region  64 A of the initial chamber  52 A and the second conductive region  65 A of the initial chamber  52 A, forms the first switch  60 B of  FIG. 4B . 
     The first sequential heater  59 B associated with the first sequential chamber  52 B is arranged between the second conductive region  65 A of the initial chamber  52 A (through the first track section  67 B) and the first sequential connection track  72 B (connected to the second supply line  56 ); furthermore the first sequential heater  59 B is electrically coupled thereto. 
     Accordingly, the first sequential heater  59 B may be electrically coupled to the common ground line  62  through the first switch  60 B of  FIG. 4B . 
     The first conductive region  64 B of the first sequential chamber  52 B is connected to the common ground track  62  and the second conductive region  65 B of the first sequential chamber  52 B is connected to the second track section  67 C. The first conductive region  64 B of the first sequential chamber  52 B and the second conductive region  65 B of the first sequential chamber  52 B are arranged substantially in the first sequential chamber  52 B, face each other and are electrically separated. 
     The first sequential membrane  71 B also extends within the first sequential chamber  52 B, adjacent to the first sequential heater  59 B and carries the first sequential contact region  53 B on the bottom so that this region is vertically superimposed on and spaced, at rest, from the first and the second conductive regions  64 B,  65 B of the first sequential chamber  52 B. The first sequential membrane  71 B is configured to deform when a drop is emitted (as described in detail hereinbelow). 
     The first sequential membrane  71 B thus forms the first sequential drop detection element  51 B; the first sequential contact region  53 B, together with the first conductive region  64 B of the first sequential chamber  52 B and the second conductive region  65 B of the first sequential chamber  52 B, forms the second switch  60 C of  FIG. 4B . 
     The second sequential heater  59 C associated with the second sequential chamber  52 C is arranged between the second conductive region  65 B of the first sequential chamber  52 B (through the second track section  67 C) and the second sequential connection track  72 C (connected to the second supply line  56 ); furthermore the second sequential heater  59 C is electrically coupled thereto. 
     Accordingly, the second sequential heater  59 C may be electrically coupled to the common ground line  62  through the second switch  60 C of  FIG. 4B . 
     The first conductive region  64 C of the second sequential chamber  52 C is connected to the common ground track  62  and the second conductive region  65 C of the second sequential chamber  52 C is connected to the third track section  67 D. The first conductive region  64 C of the second sequential chamber  52 C and the second conductive region  65 C of the second sequential chamber  52 C are arranged substantially in the second sequential chamber  52 C, face each other and are electrically separated from each other. 
     The second sequential membrane  71 C also extends within the second sequential chamber  52 C, adjacent to the second sequential heater  59 C and carries the second sequential contact  53 C on the bottom region so that this region is vertically superimposed on and spaced, at rest, from the first and the second conductive regions  64 C,  65 C of the second sequential chamber  52 C. The second sequential membrane  71 C is configured to deform when a drop is emitted (as described in detail below). 
     The second sequential membrane  71 C thus forms the second sequential drop detection element  51 C; the second sequential contact region  53 B, together with the first conductive region  64 C of the second sequential chamber  52 C and the second conductive region  65 C of the second sequential chamber  52 C, forms the third switch  60 D for sequentially supplying a subsequent heater in the sequence, not shown here. 
     In use, when it is desired to activate the microfluidic dispensing device  50 , the first voltage source  57  generates the activation signal I. Accordingly, the initial heater  59 A is crossed by a pulse current, heats up and causes a drop to be emitted by the initial chamber  52 A, similarly to what described in Italian patent application No. 102018000005372, mentioned above. The pressure variation associated with the emission of the drop by the initial chamber  52 A causes the deformation of the initial membrane  71 A, which bends towards the first and the second conductive regions  64 A,  65 A of the initial chamber (in a direction perpendicular to the plane of  FIG. 4A ), causing a similar deflection of the initial contact region  53 A which comes into physical and electrical contact with both the first conductive region  64 A and the second conductive region  65 A of the initial chamber  52 A, connecting them and closing the first switch  60 B. 
     Noteworthy, the first switch  60 B remains closed only as long as the initial membrane  71 A is deformed; after the drop has been emitted, the pressure in the initial chamber  52 A decreases and the initial membrane  71 A returns to its rest position, by reopening the first switch  60 B. 
     Closing the first switch  60 B determines the electrical connection of the first sequential heater  59 B to the common ground track  62  through the first track section  67 B. As a result, the first sequential heater  59 B heats up and causes a drop to be emitted by the first sequential chamber  52 B. 
     In turn, the pressure variation associated with the emission of the drop by the first sequential chamber  52 B causes the deformation of the first sequential membrane  71 B and the first sequential contact region  53 B, which comes into physical and electrical contact with both the first conductive region  64 B and the second conductive region  65 B of the first sequential chamber  52 B, connecting them and closing the second switch  60 C. 
     As a result a drop is emitted by the second sequential chamber  52 C and the second sequential membrane  71 C is deformed, similarly to what described above for the initial membrane  71 A and the first sequential membrane  71 B. 
     In this manner, the sequential emission of drops by all the dispensing chambers (not shown) in the microfluidic dispensing device  50  may be obtained. 
     In the microfluidic dispensing device  50  of  FIGS. 4 and 4A , as indicated, all the dispensing chambers  52  are arranged sequentially and are activated in succession. 
     Alternatively, the dispensing chambers  52  may be grouped, so that groups of dispensing cells or dispensing modules are controlled simultaneously, as for example shown in  FIG. 5 or 6 . 
     In detail,  FIG. 5  shows a dispensing device  100  having a plurality of dispensing modules (three in  FIG. 5 ). Each dispensing module comprises a plurality of dispensing chambers  52  formed and arranged in the manner shown in  FIG. 4A ; accordingly, the elements common to  FIG. 4A  have been provided with the same reference numbers and will not be further described. 
     In particular, each dispensing module comprises an initial chamber  52 A and a plurality of sequential chambers (in  FIG. 5 , a first and a second sequential chamber  52 B,  52 C; however, as for the device  50  of  FIG. 4A , generally each dispensing module may comprise a large number of dispensing chambers  42 , for example even a few hundred or a few thousand). 
     In  FIG. 5 , each initial heater  59 A is connected to a respective first voltage source  57 , and all the other heaters (first and second sequential heaters  59 B,  59 C of all the dispensing modules) are connected to the second voltage source  58 . 
     In this manner, for each dispensing module, the respective initial heater  59 A controls the subsequent sequential heaters of the same module, substantially reducing the number of connection wires necessary to control the dispending device  100 . 
     Furthermore, the activation of each dispensing module may take place independently: for example, the dispensing chambers  52  of each dispensing module may be supplied by different liquids contained in different parts of the tank (not shown, similar to tank  17  of  FIG. 1 ) and be activated simultaneously, so as to obtain the simultaneous release and mixing of drops of liquid of different type. 
     Alternatively, the dispensing modules may be activated selectively; for example, in some operating modes, all the dispensing modules are operated; in other operating modes, only some dispensing modules are operated, for example a half or a third. In this manner, dispensing of different selectable quantities of drops may be obtained. Or the dispensing modules may be activated at different times, as may be desired depending on design considerations. 
       FIG. 6  shows a dispensing device  150 , three dispensing modules whereof are shown. 
     Here again, each dispensing module is formed as the group of dispensing chambers  52  shown in  FIG. 4A ; in detail, the first dispensing module is formed by a plurality of dispensing chambers  52 A′,  52 B′,  52 C′, with heaters  59 A′,  59 B′,  59 C′ and a set of drop emission detection elements  51 A′,  51 B′,  51 C′ associated therewith. The second dispensing module is formed by a plurality of dispensing chambers  52 A″,  52 B″,  52 C″, with heaters  59 A″,  59 B″,  59 C″ and a set of drop emission detection elements  51 A″,  51 B″,  51 C″ associated therewith. The third dispensing module is formed by a plurality of dispensing chambers  52 A″′, 52 B″′, 52 C″′, with heaters  59 A″′, 59 B″′, 59 C″′ and a set of drop emission detection elements  51 A″′, 51 B″′, 51 C″′associated therewith. 
     In this embodiment, pairs of initial heaters  59 A are connected to a same first voltage source. In particular,  FIG. 6  shows two initial heaters  59 A′,  59 A″ connected to a same first voltage source, indicated here with  57 ′, through a first pulse supply line  55 ′, and a further initial heater  59 A″′ (together with a subsequent initial heater not shown) is connected to another first voltage source, indicated here with  57 ″, through a second pulse supply line  55 ″. 
     Here again, all the other heaters (first and second sequential heaters  59 B′,  59 C′,  59 B″,  59 C″) are connected to the second voltage source  58 . 
     This solution also allows modules for dispensing fractional quantities of drops or dispensing according to predetermined time sequences to be selectively activated. 
     The manufacturing process of the microfluidic dispensing device  50  of  FIG. 4A  is shown in  FIGS. 7A, 8A, 9A, 10A , as regards the area of the first and second switches  60 B,  60 C and in  FIGS. 7B, 8B, 9B and 10B  as regards the area of the first sequential chamber  52 B. The structures relating to the subsequent switches, the initial chamber  52 A, the second sequential chamber  52 C and the other cells of the sequence (not shown) are formed simultaneously, as apparent to the skilled in the art. The dispensing devices  100  and  150  of  FIGS. 5 and 6  have the same structure and what described herein below also applies thereto. 
     In detail,  FIGS. 7A and 7B  show an intermediate structure  80  relating to the manufacture of the microfluidic dispensing device  50  after the first initial steps. 
     In particular, the intermediate structure  80  of  FIG. 7A  comprises a substrate  200  of semiconductor material, for example silicon, overlaid by a first insulating layer  201 , for example of silicon oxide.  FIG. 7A  also shows metal regions obtained by depositing and shaping a metal layer  202  (for example of copper-doped aluminum—AlCu) on the first insulating layer  201  and including a first metal region  202 A (forming the common ground track  62  and the first conductive region  64 A of the initial chamber  52 A, contiguous to each other and in electrical continuity), a second metal region  202 B (forming the second conductive region  65 A of the initial chamber  52 A and the first track section  67 B), a third metal region  202 C (forming the first conductive region  64 B of the first sequential chamber  52 B), and a fourth metal region  202 D (forming the second conductive region  65 B of the first sequential chamber  52 B and the second track section  67 C).  FIG. 7B  shows part of the third metal region  202 C, forming here part of the first conductive region  64 B of the first sequential chamber  52 B. In this step, in a not-shown manner, the connection tracks  72 A- 72 C are also formed. 
     Furthermore, the intermediate structure  80  comprises portions of a sacrificial layer  203 , for example of silicon oxide, deposited above the metal layer  202  (or, where the latter has been removed, above the first insulating layer  201 ) and defined so as to form ( FIG. 7A ) a first insulating region  203 A, partially covering the first metal region  202 A; a first sacrificial region  203 B (where it is desired to form the first switch  60 B,  FIG. 4A ), between and partially covering the first metal region  202 A and the second metal region  202 B; a second sacrificial region  203 C (where it is desired to form the second switch  60 C,  FIG. 4A ), above and laterally surrounding the second metal region  202 B and arranged between the latter and the fourth metal region  202 D. Furthermore, the sacrificial layer  203  forms ( FIG. 7B ) a second insulating region  203 D, where it is desired to form the first sequential heater  59 B; in  FIG. 7B  the second sacrificial region  203 C is also visible. 
     A resistive layer  204  of material suitable for forming the heaters  59 A- 59 C, for example of polycrystalline silicon, Al, Pt, TiN, TiAlN, TaSiN, TiW, has already been deposited above the sacrificial layer  203  and defined. In  FIG. 7B , the resistive layer  204  forms a heater region  204 A, forming the first sequential heater  59 B; furthermore, it may form a first protective region  204 B, covering the second insulating region  203 A ( FIG. 7A ). 
     A connection layer  205 , for example of metal, such as aluminum, has already been deposited above the resistive layer  204  and defined, so as to form ( FIG. 7A ) a first and a second connection region  205 A,  205 B, overlying, respectively, the first sacrificial region  203 B and the second sacrificial region  203 C and forming the contact regions  53 A,  53 B of  FIG. 4A . The second connection region  205 B is also visible in  FIG. 7B . 
     A first protection layer  206  of dielectric material, for example of SiN, which in  FIGS. 7A and 7B  is continuous and which, in general, is opened where it is desired to form the contacts with the metal layer  202 , has already been deposited above the connection layer  205 , and defined. 
     Above the first protection layer  206 , a heat distribution layer  207 , formed, for example, by a layer of Tantalum (Ta) underlying a succession of layers such as silicon oxynitride (SiON) and tetraethyl orthosilicate (TEOS) with anti-reflective functionality, has already been deposited and defined, so as to form a heat distribution region  207 A ( FIG. 7B ), at the first sequential heater  59 B. 
     Furthermore, above the previous layers, a second protection layer  208 , for example of polymeric material, such as TMMR produced by Tok, Tokyo Ohka Kogyo Co. Inc., which is removed here only above the heat distribution region  207 A ( FIG. 7B ), has already been deposited and defined. 
     Thereafter,  FIGS. 8A and 8B , the first protection layer  206  and the second protection layer  208  are selectively removed to form membrane openings  210  and reach the first sacrificial region  203 B and the second sacrificial region  203 C ( FIG. 7A ) which are then removed through a special etching (for example with hydrofluoric acid) to form a first and a second cavity  211 A,  211 B ( FIG. 8A ) below the first and second contact regions  205 A,  205 B. The second cavity  211 B is also visible in  FIG. 8B . Accordingly, the portions of the protection layers  206 ,  208  above the cavities  211 A,  211 B form the initial membrane  71 A and the first sequential membrane  71 B; the first and second contact regions  205 A,  205 B, forming the contact regions  53 A and  53 B, respectively, are suspended above the first and second metal regions  202 A,  202 B and the third and fourth metal regions  202 C,  202 D, respectively, forming the switches  60 B,  60 C. 
     In practice, in the embodiment shown, the initial membrane  71 A and the first sequential membrane  71 B, as well as the second sequential membrane  71 C, are contiguous to the respective heaters  59 A- 59 C (of which in  FIG. 8B  only the first sequential heater  59 B formed by the heater region  204 A is visible). 
     Thereafter,  FIGS. 9A and 9B , the intermediate structure  80  is covered by a shaping layer  215 , for example of photoresist, which is shaped so as to form a first and a second chamber sacrificial region  215 A,  215 B (at areas of the device  50  where it is desired to form the initial chamber  52 A and the first sequential chamber  52 B) as well as lightening regions  215 C (at portions of the microfluidic dispensing device  50  where it is desired to form lightening cavities). 
     Then,  FIGS. 10A and 10B , a structural layer  216 , for example of TMMF produced by Tok, Tokyo Ohka Kogyo Co. Inc., is deposited and defined so that the structural layer  216  has a chamber opening  217  ( FIG. 10B ) above the area of the intermediate structure  80  where it is desired to form the first sequential chamber  52 B (as well as, in a non-visible manner, the other dispensing chambers  52 . Thereafter, the first and second chamber sacrificial regions  215 A,  215 B are completely removed through the chamber opening  217 , forming the initial chamber  52 A and the first sequential chamber  52 B. The chamber opening  217  also forms a nozzle for the first sequential chamber  52 B. In practice, the structural layer  216  here forms both lateral delimitation walls of the dispensing chambers and a nozzle plate. 
     Final steps, not shown, follow for thinning the intermediate structure  80  and forming rear channels, in a per se known manner, for the fluidic connection of the dispensing chambers to one or more tanks (not shown), obtaining the microfluidic dispensing device  50  of  FIG. 4A . 
     The microfluidic dispensing device  50 ,  100 ,  150  described herein has numerous advantages. 
     In particular, the sequential activation of the cells  49  allow the activation signals which, in one embodiment, may be limited to a single signal for all the cells, to be considerably reduced, obtaining a semi-automatic behavior of the dispensing device. As a result the present microfluidic dispensing device requires little integration area of the contact areas, has small overall dimensions and low cost, therefore it may also be used in small and/or cheap portable apparatus. 
     Furthermore, it is no longer necessary to have a control unit, such as an ASIC, for the activation, reducing system costs, both when the control unit is outside and when it is within the dispensing device. 
     The described microfluidic dispensing device also allows current consumption to be reduced, as the semi-automatic activation mechanism described allows the number of active components, for example transistors, necessary for the operation of the dispensing device, to be reduced. 
     The specific implementation shown in  FIGS. 7A-10B  allows the switches  60 B,  60 C,  60 D to be formed using the same layers used to form other structures, such as the heaters  59 , with simple modifications of masks and possibly adding the steps for forming the membrane openings  210  and removing sacrificial regions, with manufacturing costs comparable to those of the known devices. 
     Finally, it is clear that modifications and variations may be made to the microfluidic dispensing device, the manufacturing process and the dispensing method described and illustrated herein without thereby departing from the scope of the present disclosure, as defined in the attached claims. 
     For example, although the present description refers to a device thermally actuated by heaters, the same solution may also apply to actuations of a different type, for example of a piezoelectric type, wherein a piezoelectric actuator causes the deformation of an actuation membrane for emitting the drop. In this case, part of the actuation membrane might be used to close the switch associated. 
     Furthermore, the spatial arrangement of the dispensing chambers may be any, depending on the application. In particular, they may be arranged side by side on a line, straight or curved, or on a closed line, such as a circumference (for example as in the solution shown in  FIGS. 2A and 2B ), be arranged on one or more lines, for example on multiple concentric circumferences (as also shown in  FIGS. 2A and 2B ). 
     The shape and specific implementation of the dispensing chambers may vary with respect to what shown; in particular, the dispensing chambers may have any geometric shape, different from the rectangular one shown. Furthermore, the implementation shown in  FIGS. 7A-10B  may vary; for example, instead of having an integrated layer forming both the walls delimiting the dispensing chambers and the nozzle plate, a separate nozzle plate may be formed, bonded to the structure forming the dispensing chambers. 
     The shape, size, number and position of the nozzles in each dispensing chamber may differ, depending on the application. 
     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.