Patent Publication Number: US-2012024389-A1

Title: Integrated electromagnetic actuator, in particular electromagnetic micro-pump for a microfluidic device based on mems technology, and manufacturing process

Description:
BACKGROUND 
     1. Technical Field 
     The present disclosure regards an integrated electromagnetic actuator, a microfluidic device that uses the actuator, a process for manufacturing the actuator and the microfluidic device, and a method for displacing liquid using the actuator. 
     2. Description of the Related Art 
     Known to the art are micropumps for generating a flow of a fluid in a given direction in a channel of a microfluidic device. The micropumps generally comprise a membrane of flexible material, arranged above a portion of the channel, actuated in compression through a piezoelectric actuator. When the piezoelectric actuator causes a deflection of the membrane towards the channel, the fluid present in the channel is moved within the channel itself, for example from a hole for inlet into the channel to a hole for outlet from the channel. However, since the deflection of the membrane caused by a piezoelectric actuator is generally limited in amplitude (given that the displacement of the piezoelectric actuator itself is limited), the piezoelectric actuators are generally driven at a high frequency of vibration, which involves a high consumption of electrical energy. In addition, the piezoelectric actuator is made of generally costly materials, which causes an increase in the manufacturing costs. 
     In order to overcome the aforementioned problems, micropumps with electromagnetic actuation have been proposed, for example in U.S. Application Publication No. 2010/0111726. Said micropumps comprise a substrate  1 , a top plate  2 , a deformable membrane  3  comprising a magnetic material, and a planar winding  4 . The substrate  1  comprises, on a first face, a groove  5 , above which the top plate  2  is mounted. The top plate  2  is provided with an inlet hole  6 , an outlet hole  7 , and a through hole  8 , formed between the inlet hole  6  and the outlet hole  7 , and in communication, when top plate  2  is mounted on the substrate, with the groove  5 . The membrane  3  is arranged on the through hole  8 , in such a way as to close the latter, thus forming a reservoir  9 . The winding  4  is arranged facing a face of the substrate  1  opposite to the face on which the top plate  2  is mounted, in such a way as to be aligned with the reservoir  9 . In use, the winding  4  is traversed by electric current and, as is known, generates a magnetic field, the direction of which depends upon the direction of flow of the current. Since the membrane  3  comprises magnetic material, for magnetic fields of sufficiently high intensity, the membrane  3  can be controlled in deflection so as to approach the substrate  1  or recede therefrom by simply varying the direction of flow of the current in the winding  4 . When the membrane  3  is deflected in such a way that it moves away from the substrate  1 , a negative pressure is created within the reservoir  9 , which causes a movement of the fluid from the inlet hole  6  towards the reservoir  9 , which fills. When the membrane  3  is deflected in such a way that it approaches the substrate  1 , the fluid within the reservoir  9  is compressed and made to come out from the reservoir  9 . To favor outlet of the fluid in the direction of the outlet hole  7  rather than in the direction of the inlet hole  6  (in this way generating an effective flow of the fluid in a preferential direction), the micropump described operates according to the principle of an impedance pump. In detail, the distance between the inlet hole  6  and the reservoir  9 , through the groove  5 , is greater than the distance between the reservoir  9  and the outlet hole  7 . 
     When the membrane  3  oscillates (or vibrates) under the force impressed by the magnetic field generated by the winding  4 , a non-uniform distribution of pressure is generated on the fluid, which is pushed prevalently towards the outlet hole  7 . However, the flow rate that is obtained markedly depends upon the frequency of vibration of the membrane  3 , rendering this micropump subject to pressure problems as the frequency of vibration of the membrane  3  varies, and difficult to modulate. 
     In addition, the need to form a reservoir  9  in a pre-defined position with respect to the inlet hole  6  and outlet hole  7  in order to guarantee a non-uniform distribution of pressure on the fluid to be moved renders this micropump not practical for being integrated in systems of a “lab-on-chip” type. 
     BRIEF SUMMARY 
     Some embodiments of the present disclosure are an integrated electromagnetic actuator, a microfluidic device that uses the actuator, a process for manufacturing the actuator and the microfluidic device, and a method for displacing liquid using the actuator that will be free from the disadvantages of the known art. 
     According to the present disclosure, an integrated electromagnetic actuator, a microfluidic device that uses the actuator, a process for manufacturing the actuator and the microfluidic device, and a method for displacing liquid using the actuator are provided as defined, respectively, in claims  1 ,  12 ,  15 , and  24 . 
     In particular, the actuator comprises: a chamber; a flexible membrane, comprising a region of ferromagnetic material extending above the chamber; a winding; and a core element extending inside the winding. In use, the winding and the core element co-operate in such a way that, when the winding is traversed by a current, a magnetic field is generated with a direction and intensity such as to cause a deflection of the membrane towards the bottom surface of the chamber. 
    
    
     
       BRIEF DESCRIPTION OF THE SEVERAL VIEWS OF THE DRAWINGS 
       For a better understanding of the present disclosure, preferred embodiments thereof are now described, purely by way of non-limiting example, with reference to the attached drawings, wherein: 
         FIG. 1  shows, in cross-sectional view, a micropump with electromagnetic actuation of a known type; 
         FIG. 2  shows, in cross-sectional view, an electromagnetic actuator according to one embodiment of the present disclosure; 
         FIGS. 3   a - 3   c  show, in top plan view, windings belonging to the actuator of  FIG. 2 , according to respective embodiments; 
         FIG. 4  shows, in perspective view, the electromagnetic actuator of  FIG. 2 ; 
         FIGS. 5   a - 5   g  show an operating sequence of a plurality of actuators of  FIGS. 2 and 4 , which operate according to the principle of a three-phase peristaltic pump; 
         FIG. 6  shows in perspective view a portion of the electromagnetic actuator of  FIGS. 2 and 4 ; 
         FIGS. 7-13  show, in cross-sectional view, manufacturing steps for the production of the electromagnetic actuator of  FIG. 2 ; 
         FIG. 14  shows, in perspective view, a microfluidic diagnostic device that integrates an electromagnetic actuator according to one embodiment of the present disclosure; 
         FIG. 15  shows a block diagram of a device for controlled release of drugs that integrates an electromagnetic actuator according to one embodiment of the present disclosure; and 
         FIG. 16  shows, in cross-sectional view, an electromagnetic actuator according to a further embodiment of the present disclosure. 
     
    
    
     DETAILED DESCRIPTION 
       FIG. 2  shows, in lateral cross-sectional view, an actuator  10  of an electromagnetic type according to an embodiment of the present disclosure. In particular, the actuator  10  is a magnetic or electromagnetic actuator. More in particular, the actuator  10  is a micropump configured for being integrated in microfluidic devices. 
     The actuator  10  comprises a substrate  11 , made, for example, of semiconductor material, more in particular silicon. Alternatively, the substrate  11  may be made of plastic material. According to an embodiment of the present disclosure, the substrate  11  can be of a pre-processed type and have, in a way known and not shown in the figure, one or more overlapping regions of semiconductor and/or dielectric and/or metal material. 
     Extending on a face  11   a  of the substrate  11  is a first structural layer  12 , for example made of silicon oxide, arranged in direct contact with the substrate  11  through the face  11   a . Formed within the first structural layer  12  is a winding  14 , or inductor, obtained using MEMS technology. The winding  14  comprises a plurality of concentric and coplanar turns, and is completely integrated within the first structural layer  12 . Each turn of the plurality of turns is made of conductive material and has, in top plan view, a circular shape ( FIG. 3   a ) or a quadrangular shape ( FIG. 3   b ), or a generally polygonal shape ( FIG. 3   c ), or any other shape. The winding  14  is made of conductive material, in particular metal, such as, for example, aluminum, gold, nickel, or an alloy thereof, or any other metal. According to the dimensions and the degree of integration that it is desirable to obtain, the winding  14  can be formed by a number of turns ranging between 1 and 1000, for a total length, in extension, of between 100 μm and 100 m. Each turn is laterally separated from the other turns of the winding  14  by a distance of between 100 nm and 100 μm. Each turn moreover has a width of between 100 nm and 100 μm, and a thickness of between 10 nm and 100 μm. It is evident that the dimensions indicated above for the winding  14  are examples of possible embodiments of the winding  14 . According to further embodiments of the present disclosure, the winding  14  can have dimensions different from the ones indicated, greater or smaller, and/or a number of turns greater than 1000. 
     In order to enable electrical contact of both of the terminals  14 ′,  14 ″ of the winding  14 , a first conductive path  13  and a second conductive path  15  are provided, formed in metal layers different from one another. The first conductive path  13  is in electrical contact with a first terminal portion  14 ′ of the winding  14  belonging to the outermost turn of the winding  14 ; the second conductive path  15  is, instead, in electrical contact with a second terminal portion  14 ″ of the winding  14 , belonging to the innermost turn of the winding  14 . The second conductive path  15  is formed in a metal layer different from the metal layer in which the turns and the first conductive path  13  are formed, in particular in a lower metal layer. 
     The first and second conductive paths  13 ,  15  are connected to biasing means  19 , in particular a current generator, preferably of a type integrated in the substrate  11 . The current generator  19  is configured to generate a flow of current between the first terminal portion  14 ′ and the second terminal portion  14 ″ of the winding  14 . In addition, by alternating the direction of flow of the current within the winding  14 , the direction of the magnetic field generated is altered accordingly. 
     The turns of the winding  14  define a region  16  internal to the winding  14 , in which a core element  18  is arranged, for example made of iron, or cobalt, or nickel, or a mixture thereof, or, in general, any ferromagnetic material. The core element  18  extends completely within the first structural layer  12 . Present above the first structural layer  12  is a chamber or channel, designated by the reference number  20 , laterally delimited by a second structural layer  22 , which is arranged on top of and in direct contact with the first structural layer  12  and which defines side walls  20 ′ of the channel  20 . The second structural layer  22  is made, for example, of photoresist. A photoresist that can be used has a base of acrylic polymers, which possess good characteristics of adhesion and strength. Alternatively, the second structural layer  22  is made of the same material as the first structural layer  12 , in particular silicon oxide. The second structural layer  22  has a thickness h of between 1 μm and 500 μm, for example 20 μm. 
     The channel  20  is moreover delimited at the bottom by the first structural layer  12 , which defines a bottom  20 ″ of the channel  20 . 
     The channel  20  is separated from the winding  14  by a portion  12   d  of the first structural layer  12  having a thickness of between 1 nm and 100 μm, preferably 10 nm. 
     Arranged above the second structural layer  22  is a cover layer  24 , in direct contact with the second structural layer  22  so as to seal the channel  20  hermetically at the top. The cover layer  24  is, for example, an adhesive tape or an adhesive film, or again a layer of material rendered adhesive and coupled to the second structural layer  22  so as to seal the channel  20 . More in particular, the cover layer  24  is made of a transparent polymeric material, preferably bio-compatible, for example chosen in the group comprising polyethylene, glass, Plexiglas, polycarbonate, polydimethylsiloxane (PDMS), or the like. Again, the cover layer  24  is made of a generic elastomeric material or material with elastomeric base, such as, for example, polyurethane. 
     The cover layer  24  has a thickness p preferably of between 1 μm and 100 μm, for example 10 μm. 
     Arranged on top of the cover layer  24  is a passive element  26 , for example made of ferromagnetic material such as iron, or nickel, or cobalt, or a mixture thereof, or any other material with ferromagnetic properties. The passive element  26  is coupled to the cover layer  24  in such a way that the movement of the passive element  26  along an axis  28  substantially perpendicular to the cover layer  24  causes a consequent movement of the cover layer  24  along the axis  28 . 
     The cover layer  24  and the passive element  26  form a membrane layer  27 . 
     The substrate  11  further comprises, in a way not shown in  FIG. 2 , electronic devices designed to supply a current i within the turns of the winding  14 . As is known, the flow of current i in the winding  14  generates a magnetic field defined by a magnetic-field vector having direction and sense that depend upon the direction and sense of the current i (according to the known “right-hand rule”). 
     In the case where the passive element  26  has an own intense magnetic field, for example in the case where the passive element  26  is made of a ferromagnetic material previously magnetized having high value of coercivity and saturation, by alternating the sense of the flow of current within the winding  14 , it is possible to generate a magnetic field with alternating sense that causes the action of respective forces, with senses opposite to one another, on the passive element  26 . These forces are such as to act on the passive element  26  in the direction defined by the axis  28 , parallel to the axis Z and substantially orthogonal to the plane XY in which the cover layer  24  lies, in order to displace the cover layer  24  in both senses of the axis  28 . 
     The cover layer  24 , in its movement along the axis  28 , has degrees of freedom limited by the fact that it is coupled to the second structural layer  22  along peripheral portions  24 ′ of the cover layer  24 . Hence, just a central portion  24 ″ of the cover layer  24  oscillates along the axis  28 , approaching and moving away from the bottom  20 ″ of the channel  20  according to the corresponding movement of the passive element  26 . 
     The winding  14 , the core element  18 , and the passive element  26  form an electromagnetic-actuator element configured for generating, when a current is made to flow in the winding  14  such as to induce a magnetic field, a controlled deformation, or a vibration, of the cover layer  24 . 
       FIG. 4  shows, in perspective view, the actuator  10  described with reference to  FIG. 2 . 
     In use, in order to guarantee a flow of a fluid present in the channel  20  with a preset direction and sense, it is possible to provide a plurality of micropumps  10  along one and the same channel  20  and operate the micropumps  10  as shown in  FIGS. 5   a - 5   g , which show the principle of operation of a three-phase peristaltic pump. 
     In detail,  FIGS. 5   a - 5   g  show, in schematic form, a method for operating a plurality of actuators  10 ; in particular, three actuators  10  are shown, arranged in sequence along a common channel  20 . In this case, each actuator  10  operates as a micropump. For clarity of description, in what follows designated by  10   a  is the actuator  10  appearing on the left in the representation of  FIGS. 5   a - 5   g ; designated by  10   c  is the actuator  10  appearing on the right in the representation of  FIGS. 5   a - 5   g ; and designated by  10   b  is the actuator  10  appearing at the center in the representation of  FIGS. 5   a - 5   g , between the actuator  10   a  and the actuator  10   c.    
       FIG. 5   a  shows a starting step in which the micropumps  10   a - 10   c  are in a resting state, and no current flows in the respective windings  14 . 
     Then ( FIG. 5   b ), current is made to flow in the winding  14  of the actuator  10   a  so as to generate a magnetic field that causes on the passive element  26  of the actuator  10   a  the action of a force directed towards the channel  20 . Consequently, the cover layer  24  of the actuator  10   a  goes down, under the force of the field generated and acting on the passive element  26 , until it comes into contact with the bottom  20 ″ of the channel  20 . There is hence a first displacement of the fluid within the channel  20 . 
     Next ( FIG. 5   c ), while maintaining the cover layer  24  of the actuator  10   a  lowered, in contact with the bottom  20 ″ of the channel  20 , current is made to flow in the winding  14  of the actuator  10   b  so as to generate a magnetic field that causes on the passive element  26  of the actuator  10   b  the action of a force directed towards the channel  20 . Consequently, the cover layer  24  of the actuator  10   b  goes down, until it comes into contact with the bottom  20 ″ of the channel  20 . There is in this case a second displacement of fluid within the channel  20 , with orientation defined by the arrow  30  in  FIG. 5   c . In fact, since the channel  20  is closed by the action of the actuator  10   a , the only sense of flow possible for the fluid is the one defined by the arrow  30 . 
     Then ( FIG. 5   d ), while maintaining the cover layer  24  of the actuator  10   b  lowered, in contact with the bottom  20 ″ of the channel  20 , current is made to flow in the winding  14  of the actuator  10   c  so as to generate a magnetic field that causes on the passive element  26  of the actuator  10   c  the action of a force directed towards the channel  20 . There is also in this case a further displacement of fluid within the channel  20 , with orientation defined by the arrow  30 . 
     As shown in the subsequent  FIGS. 5   e - 5   g , the coating layers  24  of the actuators  10   a - 10   c  are then brought into a position at a distance from the bottom  20 ″ of the channel  20 . By performing this operation in sequence, i.e., bringing in sequence the actuator  10   a , then the actuator  10   b , and finally the actuator  10   c  into a position at a distance from the bottom  20 ″ of the channel  20 , the portion of channel  20 , in the region corresponding to the actuators  10   a - 10   c , is filled with fluid coming from the region appearing to the left of the micropumps  10   a - 10   c . An effective flow of fluid is thus obtained, with orientation defined by the arrow  30 , all along the channel  20 . 
     To bring each actuator  10  back into a resting position it is typically sufficient to interrupt the flow of current in the respective winding  14 . However, in order to prevent any possible problem of stiction of the cover layer  24  to the bottom  20 ″ of the channel  20 , it is possible to favor recession of the cover layer  24  from the bottom  20 ″ of the channel  20  by generating a magnetic field such as to guide the passive element (and hence the cover layer  24 ) in the direction defined by the axis Z so that it recedes from the channel  20 . The magnetic field is generated by causing a current to flow in the winding  14  with sense opposite to that of the current used for attracting the passive element  26  (and hence the cover layer  24 ) towards the channel  20 . This phenomenon is possible thanks to the high residual magnetization that exists in the majority of ferromagnetic materials and can be controlled by choosing as ferromagnetic material of the passive element  26  a material with a coercivity value higher than the respective coercivity value of the core element  18 . In this way, for an appropriate value of the magnetic field in the winding  14 , after reversal of the direction of flow of the current, the magnetic field is found in opposition with respect to the residual magnetic field of the passive element  26 , thus generating a repulsive force. 
     The principle of operation of the actuator  10  described takes into account a plurality of physical phenomena. It is known that the magnetic field orthogonal to the plane in which the winding  14  lies, in the center of the winding  14  and assuming a winding  14  with circular turns, is given by the summation of the contributions of each turn of the winding  14 . As is known, a detailed analysis of the lines of magnetic field, generated by a winding traversed by current, in planes parallel to the plane in which the turn lies and arranged at various distances  6  from the plane in which the turn lies, shows that the magnetic field is not uniform. The non-uniformity is verified also in different points of one and the same plane. It is likewise known that for values of δ&lt;&lt;R (where R is the radius of the innermost turn of the winding  14 ), the magnetic field can be considered, to a first approximation, uniform in the entire cylindrical volume having a height equal to δ and a base width defined by the innermost turn of the winding  14 . 
     The force used to deform the cover layer  24  can be calculated if the shear modulus of the material that forms the cover layer  24  is known. The force of magnetic attraction exerted on the passive element  26  can be derived from the analysis of the energy of magnetic field present in the area between the core element  18  and the passive element  26 . If the thickness of the portion of the first structural layer  12  that separates the channel from the winding  14  and from the core element  18  is neglected, the thickness g of the area is given by g≈h+p. The presence of the core element  18  arranged inside the winding  14  produces, as is known, a gain of the magnetic field (the gain has a variable value, according to the ferromagnetic material used to form the core element  18 , approximately between 10 2  and 10 6 ). For values of g&lt;&lt;R it is possible to consider the magnetic field in the region between the core element  18  and the passive element  26  as a uniform field. 
     Given hereinafter is a numeric example of the magnetic force exerted on a passive element  26  by a winding  14  provided with a core element  18 , and forming an actuator  10  according to the present disclosure. 
     Consider a winding  14  comprising 50 metal turns, in which the innermost turn has a radius R 1 =250 μm and the outermost turn has a radius R 50 =400 μm. The conductive wire with which the winding  14  is made is an aluminum wire (more in detail, an aluminum planar conductive path) having a width of 1.5 μm and a thickness of 1.5 μm. The turns are laterally separated from one another by 1.5 μm. The current i that flows through the winding  14  has a value of approximately 13 mA. It is to be noted that the current is maintained at a low value for reasons of maximum safety in so far as, for nanometric or micrometric dimensions of the turns (height and width), a higher value of current (for example by one or more orders of magnitude) could cause burning of the winding  14 . 
     The core element  18  is made of ferromagnetic material and has a value of magnetic-permeability constant μ m =10 3 . 
     In addition, the thickness of the cover layer is assumed as being p=10 μm and the value of the shear modulus of the cover layer  24  is assumed as being 0.0086 GPa (a polyurethane cover layer  24  is considered in this example). The depth of the channel  20  is assumed as being h=10 μm, and the maximum angle of deformation of the cover layer  24  to come into contact with the bottom  20 ″ of the channel  20  is 45°. 
     The minimum force F M  that must be applied to deform the cover layer  24  can be calculated on the basis of the following formula (1): 
     
       
         
           
             
               
                 
                   
                     
                       F 
                       M 
                     
                     
                       S 
                       L 
                     
                   
                   = 
                   
                     G 
                     · 
                     
                       tg 
                        
                       
                         ( 
                         ϑ 
                         ) 
                       
                     
                   
                 
               
               
                 
                   ( 
                   1 
                   ) 
                 
               
             
           
         
       
     
     where: S L  is the area of a lateral surface of the sectioned cover layer  24  (shown hatched in  FIG. 6 ); G is the shear modulus of the cover layer  24 ; and θ is the angle of deformation of the cover layer  24 . 
     Hence, considering a cover layer having a thickness of 10 μm and a diameter of 500 μm, the value of S L  is given by 2π·500·10=15700 μm 2 . There is hence obtained a value of force F M  necessary for deformation of the cover layer  24  of approximately 0.13 Pa. 
     The value of magnetic field B tot  generated by the winding  14 , for all the turns of the latter, is given by the following formula (2): 
     
       
         
           
             
               
                 
                   
                     B 
                     tot 
                   
                   = 
                   
                     
                       ∑ 
                       
                         n 
                         = 
                         1 
                       
                       50 
                     
                      
                     
                       
                         
                           
                             μ 
                             0 
                           
                            
                           i 
                         
                         
                           2 
                            
                           R 
                         
                       
                        
                       
                         μ 
                         m 
                       
                     
                   
                 
               
               
                 
                   ( 
                   2 
                   ) 
                 
               
             
           
         
       
     
     where we have considered: a winding having 50 turns; a value of current i of 13 mA; turns set at the same distance apart having a minimum radius (innermost turn) R 1 =250 μm and a maximum radius (outermost turn) R 50 =400 μm; a value of air magnetic permeability μ 0 =4π· 10   −7 ; and a value of magnetic permeability of the core element  18  μ m =10 3 . 
     There is thus obtained a value of B tot  of approximately 1.31 T. 
     Given the value of B tot  calculated according to Eq. (2), the force of attraction F A  generated on the cover layer  24  by the passive element  26  is given by the following formula (3): 
     
       
         
           
             
               
                 
                   
                     F 
                     A 
                   
                   = 
                   
                     
                       
                          
                         U 
                       
                       
                          
                         g 
                       
                     
                     = 
                     
                       
                         
                           B 
                           2 
                         
                          
                         A 
                       
                       
                         2 
                          
                         
                           μ 
                           0 
                         
                       
                     
                   
                 
               
               
                 
                   ( 
                   3 
                   ) 
                 
               
             
           
         
       
     
     where U is the magnetic energy contained in the volume defined between the core element  18  and the passive element  26 , given by the following formula (4): 
     
       
         
           
             
               
                 
                   U 
                   = 
                   
                     
                       1 
                       
                         2 
                          
                         
                           μ 
                           0 
                         
                       
                     
                      
                     
                       B 
                       2 
                     
                      
                     gA 
                   
                 
               
               
                 
                   ( 
                   4 
                   ) 
                 
               
             
           
         
       
     
     where g is the distance that separates the core element  18  from the passive element  26 , substantially given by the thickness of the cover layer (p) added to the value of depth of the channel  20  (h); and A is the area of the core element  18 , assumed equal to the area of the passive element  26  (with reference to the values previously indicated, A=π·R 1   2 =π·250 2 =196250 μm 2 ). 
     On the basis of the values previously indicated by way of example, a value of force of attraction F A =0.13 N is obtained. 
     The value of F A  is hence such as to deflect, in use, the cover layer  24  considered. 
     By modifying as desired the values of electric current i, of thickness h of the channel  20 , of thickness p of the cover layer  24 , the material of which the core element  18  and the passive element  26  are made (hence varying their value of magnetic permeability μ m ), the number and size of the turns of the winding  14 , and in general the other parameters involved in the formulas given above, it is possible to vary the value of force applied to the cover layer  24 , consequently varying the characteristics of compression and displacement of the fluid present, in use, in the channel  20 . 
     An estimate of the flow of fluid obtained by applying a value of force F D  as indicated previously can be obtained assuming that, at each pumping cycle, the fluid present in the portion of channel substantially underneath the passive element  26  is completely moved in the same direction, in particular in the direction in which it is desired to obtain the flow of fluid (for example as indicated by the arrow  30  in  FIGS. 5   b - 5   g ). Using a pumping-cycle frequency of 10 Hz, a flow of fluid (in this case the fluid is assumed to be water) of 0.8 μL/min is obtained. 
     It is here pointed out that the value of flow can be easily altered (increased or decreased) by simply varying the value R of the radius of the turns of the winding  14 . In particular, by reducing the value of R the value of the flow is reduced, which is useful in applications that require extremely low rates of flow. 
     It is evident that what has just been described merely exemplifies operation of the actuator  10 . A variation of the pumping characteristics can be obtained by varying other parameters with respect to the ones indicated, or the geometry of the various components of the actuator  10 . For example, it is possible to use turns 4 having a square shape, which best fit the geometry of a rectangular channel. 
       FIGS. 7-13  show successive steps of a process for manufacturing the actuator  10 .  FIGS. 7-13  do not show process steps for manufacturing the current generator  19 , which is provided in a form integrated in the substrate  11  in a known way. 
     As shown in  FIG. 7 , a substrate  11  is provided, for example made of semiconductor material, preferably silicon, or, alternatively, plastic material. The substrate  7  comprises the current generator  19  (here not shown). Then, on the front side  11   a  of the substrate  11 , opposite to the back side  11   b  of the substrate  11 , a first intermediate layer  12   a  is formed, for example made of thermally grown or deposited silicon oxide. 
     Next ( FIG. 8 ), formed on the first intermediate layer  12   a , for example via known deposition techniques, is a layer of conductor material, which is then shaped, via known lithographic and etching techniques in such a way as to form a conductive path  15  extending towards a peripheral region of the substrate  11 . As already described with reference to  FIG. 2 , the conductive path  15  has, in use, the function of forming an electrical connection between the innermost turn of the winding  14  (not yet formed in the process step of  FIG. 8 ) and biasing means external to the winding  14  (here not shown). The conductive path  15  may be made of metal, for example aluminum. Alternatively, the conductive path  15  may be made of doped polysilicon. 
     Then, a second intermediate layer  12   b  is formed on the conductive path  15  and on the first intermediate layer  12   a . Following upon formation of the second intermediate layer  12   b , the latter, if necessary, is planarized. The second intermediate layer  12   b  is preferably made of the same material as the first intermediate layer  12   a , in the example described silicon oxide. 
     Next ( FIG. 9 ), via successive lithographic and etching steps, a contact hole  32  is opened through the second intermediate layer  12   b , until the conductive path  15  is reached. Then a step of formation of a layer of conductive material  34  is carried out on the second intermediate layer  12   b  and within the contact hole  32 , thus forming a conductive path between the conductive path  15  and the layer of conductive material  34 . 
     Then ( FIG. 10 ), via successive lithographic and etching steps, the layer of conductive material  34  is shaped in such a way as to form the winding  14 , comprising a plurality of concentric turns. The innermost turn of the winding  14  is in contact, via a terminal portion of its own, with the contact hole  32  and, via the latter, with the conductive path  15 . 
     According to an embodiment of the present disclosure, the winding  14  has, in top plan view, a circular shape. The innermost turn has, for example, a diameter D I  of between 10 μm and 5000 μm, preferably 500 μm, whilst the outermost turn has a diameter D O  of between 20 μm and 20000 μm, preferably 1600 μm. 
     According to a further embodiment of the present disclosure, the winding  14  has, in top plan view, a square shape. In this case, D I  is the length of the side of the innermost square, whilst D O  is the length of the side of the outermost square. 
     Each turn of the winding  14  has a width of between 0.1 μm and 100 μm, preferably 1 μm. In addition, the turns are spaced from one another by a distance of between 0.1 μm and 100 μm, preferably 1 μm. 
     Then ( FIG. 11 ), formed on the second intermediate layer  12   b  is a third intermediate layer  12   c . The third intermediate layer  12   c  fills the space between the turns of the winding  14  and is made of dielectric material. For example, the third layer  12   c  is made of deposited silicon oxide. Following upon formation of the third intermediate layer, the latter is removed in an area corresponding to a region internally defined by the winding  14 , until the surface of the second intermediate layer  12   b  is exposed. A layer of ferromagnetic material (for example iron, or nickel, or cobalt, or a mixture thereof) is then formed such as to cover the exposed surface of the second intermediate layer  12   b  so as to form the core element  18 . The core element  18  has a thickness approximately equal to the thickness of the turns of the winding  14 , for example between 0.01 μm and 100 μm, preferably 1 μm. Any ferromagnetic material that may be present on the third intermediate layer  12   c  following upon the step of formation of the core element  18  is removed. 
     Next ( FIG. 12 ), formed on the core element  18  of the third intermediate layer  12   c  and of the winding  14  is a fourth intermediate layer  12   d , made of dielectric material, for example silicon oxide. The fourth intermediate layer  12   d  has a thickness of between 1 nm and 100 μm, preferably 10 nm. 
     It is clear that, since the fourth intermediate layer  12   d  forms, at the end of the manufacturing steps, the bottom  20 ″ of the channel  20 , the fourth intermediate layer  12   d  can be made, for reasons that depend upon the particular application of the actuator  10 , of materials different from silicon oxide. For example, it may be made of deposited polymeric layers, transparent plastic substrates, or oxynitride, or may be passivated after its formation. 
     The first  12   a , second  12   b , third  12   c , and fourth  12   d  intermediate layers form the first structural layer  12  of  FIG. 2 . 
     Then, formed on the fourth intermediate layer  12   d  is a second structural layer  22 , for example made of deposited SiO 2 , or dry photoresist formed by means of lamination. Alternatively, the second structural layer  22  can be formed by spinning of photoresist of a liquid type. Then a photolithographic process is carried out to define a channel  20  within the second structural layer  22 . For this purpose, a mask (not shown), defining (in a positive or negative way, according to the photoresist used) the channel  20 , is used for the photolithographic step. A subsequent etching step enables selective removal of portions of the second structural layer  22  until the fourth intermediate layer  12   d  is exposed, thus forming the channel  20  delimited laterally by the second structural layer  22  and at the bottom by the fourth intermediate layer  12   d.    
     The channel  20  is formed substantially in an area corresponding to the core element  18 . For this purpose, alignment marks, of a known type, can be provided. 
     Finally ( FIG. 13 ), a cover layer  24  is set above the channel  20 , in contact with the second structural layer  22 . The cover layer  24  is, for example, as has been said, an adhesive tape or film, of compatible transparent polymeric material. The cover layer  24  may even be a suspended membrane of silicon oxide or of silicon with a thickness sufficiently small as to deflect or deform, for example with a thickness of between 3 nm and 70 nm. It is evident that the smaller the angle required for deformation, the greater may be the thickness of the cover layer  24 . 
     Formed on the cover layer  24 , through sputtering techniques or screen printing or ink jet printing, is the passive element  26 , made of ferromagnetic material, for example iron, or nickel, or cobalt, or a mixture thereof. The passive element  26  is formed substantially in a position corresponding to the core element  18  and vertically aligned therewith. For this purpose, alignment marks (not shown) may be envisaged, so as to enable alignment of the passive element  26  with the core element  18 . The actuator  10  of  FIG. 2  is thus obtained. 
       FIG. 14  shows a perspective view of an integrated device  50 , in particular a diagnostic device, comprising a fluid displacing device  51  including a plurality of actuators  10  of the type previously described. In particular, the fluid displacing device  51  comprises three actuators  10 , which operate as described and shown with reference to  FIGS. 5   a - 5   g . According to the embodiment shown in  FIG. 14 , the winding  14 , the core element  18 , and the passive element of the actuators  10  have a square shape. 
     The diagnostic device  50  comprises a substrate  110  (common to all the actuators  10 , similar to the substrate  11 ) and a first structural layer  120  (which is also common to the actuators  10  and is similar to the first structural layer  12 ), arranged on top of, and in direct contact with, the substrate  110 . The substrate  110  comprises integrated electronic components (shown schematically), in particular designed to form the current generator  19 . 
     Extending over the first structural layer  120  is the second structural layer  220  (which is also common to all the actuators  10  and which is similar to the second structural layer  22 ), in which a channel  53  in fluid communication with each respective channel  20  of each actuator  10  is provided. 
     The first structural layer  120 , in particular in a position corresponding to the bottom  53 ″ of the channel  53 , is, in this case, made of a material compatible with the use of the diagnostic device  50 , for example biocompatible material (e.g., silicon oxide). Alternatively, a non-biocompatible layer may be used, passivated in an area corresponding to the bottom  53 ″ of the channel  53 . Common passivation materials include silanes, albumin, sonicated salmon-sperm DNA, random hexamer oligonucleodites, and the like. In addition, in some applications, it may be desired to functionalize one or more surfaces for immobilizing receptors, for example adding hydroxyl (OH) groups. All these surfaces are referred to as “compatible”, where by this term is meant that the surface is compatible with the assay and with the receptors used in the device. 
     The thickness of the substrate  110  is variable and chosen so as to guarantee at the same time ease of production of the diagnostic device  50  and of the integrated actuators  10  and also resistance to impact of the diagnostic device  50  and of the actuators  10 . 
     The second structural layer  220  has, according to a further embodiment not shown in the figure, a plurality of channels similar to the channel  53 . In the case where a plurality of channels  53  is present, each channel  53  is isolated from other channels  53  by means of the second structural layer  220 . 
     The channel  53  shown in  FIG. 14  has a rectangular shape, in top plan view, and is isolated on all four sides by the second structural layer  220 . Other shapes, different from the rectangular shape, are possible, for example once again shaped like a circular, square, or in general polygonal serpentine, for example with or without rounded corners. In the case of a number channels  53  on one and the same diagnostic device  50 , each channel  53  can in any case have a shape and size different from the shape and size of the other channels  53 , chosen in the design stage according to the need. 
     The channel  53  houses one or more detection regions  52  (for example in the form of “spots” housed in series along the channel  53  and separated from one another by approximately 100 μm), comprising receptor biomolecules deposited in a known way. For example, it is possible to use an automated spotting technique, which substantially envisages the use of a mechanical arm, which, in an automatic way, takes samples of the biological material to be deposited (in liquid solution) and, with micrometric precision, deposits drops of the biological material in the channel  53  to form the detection regions  52 . 
     Typically, each of the drops is of a few picoliters, but the drops can be as large as 1-5 μl, or larger still, according to the application and to the available size of the specimen. Alternatively, the entire surface of a certain region can be covered if desired for the application considered. 
     In addition, the diagnostic device  50  comprises an inlet hole  54  and an outlet hole  56 , formed through the substrate  110  and the first structural layer  120  and designed to form, respectively, an access path (see the arrow  60 ) from the outside of the diagnostic device  50  towards the channel  53  and an outlet path (see the arrow  61 ) from the channel  53  towards the outside of the diagnostic device  50 . 
     The diagnostic device  50  further comprises a cover layer  240 , which covers the channel  53  and forms, at the same time, the cover layer  24  of the actuators  10 . The cover layer  240  has hence characteristics similar to those described with reference to the cover layer  24 . 
     The cover layer  240  is arranged on top of, and in contact with, the second structural layer  220 , and has the function both of supporting the passive element  26  of each actuator  10  and of hermetically sealing the channel  53  at the top. In this way, the single points for access to the channel  53  are the inlet hole  54  and the outlet hole  56 . The cover layer  240  is, for example, made of elastomeric material, in particular transparent to light. In the case where the channel  53  is transparent to light, it is altogether optically accessible from the outside of the diagnostic device  50 , which can be used in fluorescence systems or for visual inspection. In general, it is important for the step of coating of the channel  53  not to damage the receptors or the material deposited in the channel  53 , and hence processes that envisage, for example, thermal treatments at high temperature or using plasma would have to be excluded in the case of heat-sensitive molecules. 
     The inlet and outlet holes  54 ,  56  can be provided with a respective closing element (not shown), for example a plug made of plastic or elastomeric material, which seals the channel  53 . The inlet and outlet holes  54 ,  56  may also be provided with a fast-coupling system for fluidic connections, of a known type, for example of a threaded type or a clamp type. 
     The detection regions  52  comprise, for example, a given type of receptors, such as biomolecules (DNA, RNA, proteins, antigens, antibodies, etc.) or micro-organisms or parts of them (bacteria, viruses, spores, cells, organelles, etc.) or any chemical element used for detecting an analyte. The receptors, provided with specific markers, for example fluorescent markers, are immobilized on the bottom  53 ″ of the channel  53 . According to alternative embodiments, the receptors can be free in solution instead of being immobilized to the device, according to the application for which the diagnostic device  50  is used. However, solid-phase assays are generally preferred since they enable washing away of non-immobilized material and hence increase the sensitivity and simplicity of the detection assays. 
     When these receptors are set in direct contact with a biological specimen to be analyzed comprising molecules capable of combining with the receptors, the combination of the molecules with the receptors activates specific markers, for example fluorescent markers. When the fluorescent markers are activated, they can emit autonomously a light radiation. Alternatively, the fluorescent markers can be induced into a state of light emission by external excitation. Only the activated markers are able to emit light radiation of their own, whereas non-activated markers do not respond to the external excitation (or in any case, in general, do not emit light radiation or emit light at a different wavelength). 
     By operating the actuators  10  according to the steps described with reference to  FIGS. 5   a - 5   g , the biological liquid or the specimen is made to flow from the inlet hole  54  (see the arrow  60 ) along the entire channel  53  (see the arrow  63 ). In this way, the biological liquid comes into contact with the detection regions  52  and then comes out of the channel  53  through the outlet hole  56  (see the arrow  61 ). 
     Detection of the fluorescence can be carried out with the channel  53  emptied, not emptied, or only partially emptied, as desired for the specific application. 
     The manufacturing steps of the diagnostic device  50  correspond to the manufacturing steps of the actuator  10 , shown and described with reference to  FIGS. 7-13 . However, in order to form the inlet and outlet holes  54 ,  56  and the detection regions  52 , further process steps are envisaged. 
     In detail, the inlet hole  54  and outlet hole  56  are formed, for example, after the steps described with reference to  FIG. 12 . For this purpose, on the back side  110   b  of the substrate  110  a mask is formed, designed to define regions in which the inlet hole  54  and outlet hole  56  are to be formed. 
     Next, by means of successive etching steps, the portions of the substrate  110  left exposed by the mask are removed, until the first structural layer  120  is reached. Then, by means of a subsequent etching, portions of the first structural layer  120  are removed until the channel  53  is reached. In the case where the first structural layer  120  is made entirely of silicon oxide, just one etch is sufficient to reach the channel  53 . Alternatively, in the case where the structural layer  120  comprises different materials overlapping on one another, a number of etching steps may be necessary, each of them selective for the type of material to be removed. In addition, the etch can be either of a dry type or of a wet type, as desired. 
     The back side  110   b  of the substrate  110  is thus set in fluid communication with the channel  53  to form the inlet hole  54  and the outlet hole  56 . 
     In the case of a substrate  110  made of silicon and a first structural layer  120  made of silicon oxide, the etching operation for formation of the inlet holes  54  and outlet holes  56  can be plasma etching using alternatively SF 6 , CF 4  or a combination of SF 6  and C 4 F 8 . The step of formation of the holes is preferably compatible with TSV (through silicon via) technology, which enables removal, in a single etching step, of both portions of the substrate  11  and portions of the first structural layer  120 . 
     To form the detection regions  52 , following upon formation of the inlet and outlet holes  54 ,  56 , cleaning of the bottom  53 ″ of the channel  53  is carried out, for example using a piranha solution, i.e., a mixture of sulphuric acid H 2 SO 4  and hydrogen peroxide H 2 O 2 , or, alternatively, an RCA-1 cleaning (sometimes called standard clean SC-1), i.e., a mixture of H 2 O, NH 4 OH, H 2 O 2 , which can be followed by a further cleaning with a second cleaning using a mixture of H 2 O 2 , HCl and H 2 O. There is then carried out a step of cleaning and activation (for example, to expose OH groups) of the bottom  53 ″ of the channel  53 , by means of a mixture of HCl and CH 3 OH, and then a step of functionalization of the bottom  53 ″ of the channel  53  is carried out (for example, by means of silanization). The detection regions  52  are then formed, for example using an automated-spotting technique. Since the bottom  53 ″ of the channel  53  is completely accessible at the top, the spotting step does not involve complex processes of alignment. Since this step is of a known type, it is not described any further herein. 
     In this way, the diagnostic device  50  of  FIG. 14  is formed. 
     According to a further use of the present disclosure, one or more actuators  10  can be integrated in a device for controlled release of drugs  70  (shown in schematic form in  FIG. 15 ). The device for controlled release of drugs  70  comprises a reservoir  72  designed to contain a drug, in liquid solution, which is to be administered to a patient. The reservoir  72  is connected to a release hole  76  of the device  70 , through which the drug is released in the area to be treated. The path of the drug from the reservoir  72  to the release hole  76  occurs through a channel  74  provided with a device for movement of fluid  75 , in particular comprising one or more actuators  10  of the type described with reference to  FIG. 2 , which operate as micropumps according to the steps described with reference to  FIGS. 5   a - 5   g  (of the type already shown and described with reference to the diagnostic device  50  of  FIG. 14 ). 
     By appropriately configuring the dimensions of the channels  20 ,  74  (which are in fluid connection with one another) and/or the force of compression exerted by each actuator  10  on the liquid present, in use, in the channel  20 , it is possible to regulate as required the amount of drug released through the release hole  76 . 
     The process for manufacturing the actuator  10 , described with reference to  FIGS. 7-13 , and/or the diagnostic device  50 , and/or the device for controlled release of drugs  70 , can be implemented at an industrial level by working an entire wafer of semiconductor material, provided on which are a plurality of actuators  10  and/or diagnostic devices  50  and/or devices for controlled release of drugs  70  of the type described previously. In this case, at the end of the manufacturing steps, the wafer is diced into single chips, and the chips are packaged. 
     From an examination of the characteristics of the disclosure provided according to the present disclosure the advantages that it affords emerge clearly. 
     The integrated actuator according to the present disclosure enables management of extremely small flows of liquids. 
     In addition, for manufacturing simplicity, the actuator according to the present disclosure is extremely advantageous from an economic point of view, rendering it suitable for devices of a disposable type. 
     In addition, thanks to the high level of integration and to the use of biocompatible materials, the actuator described can be used in micro-devices that can be implanted for biomedical applications, also in implantable devices. 
     Finally, the use of a core element  18  arranged inside and planar to the winding  14 , enables generation of intense magnetic fields also in the case of low currents applied to the winding  14 . This enables at the same time a considerable energy saving, a reduced heating of the winding  14  by the Joule effect, and a considerable saving in terms of area occupation. In fact, the present applicant has verified that, given the same intensity of magnetic field generated, the solution that envisages a winding  14  provided with a core element  18  according to the present disclosure is of a size considerably smaller than that of a winding  14  without the core element  18 . 
     Finally, it is clear that modifications and variations may be made to the disclosure described and illustrated herein, without thereby departing from the sphere of protection thereof. 
     For example, the passive element  26  can be set underneath the cover layer  24  and fixed with respect thereto. Alternatively, the cover layer  24  itself can comprise ferromagnetic material. In this latter case, the cover layer  24  and the passive element  26  coincide. 
     In addition, the turns of the winding  14  and the core element  18  may not be coplanar but be arranged on different planes (i.e., be provided on different metal layers). 
     In addition, as shown in  FIG. 16 , a shell  90  of ferromagnetic material can be provided (for example, made of the same material as the core element  18 ) surrounding the winding  14  on all or on some of its sides, within the first structural layer  12  and/or above the cover layer  24 , laterally with respect to the passive element  26 . The core element  18  extends within the first structural layer  12  until it comes into contact with the shell  90 . The winding  14  is in any case electrically insulated from the shell  90  by portions of the first structural layer  12  between the shell  90  and the winding  14 . This embodiment presents the advantage of increasing the value of the magnetic field applied to the passive element  26 , given the same conditions, as compared to the embodiment of  FIG. 2 . 
     Finally, the actuator described according to the present disclosure can be used for applications other than those of a micropump. For instance, it can be used, when necessary, for narrowing a channel thus reducing the amount of fluid that flows in the channel and at the same time increasing the pressure thereof locally. In addition, the actuator according to the present disclosure can be used as micro-valve, to interrupt and alternatively enable a flow of a liquid in a channel. 
     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.