Abstract:
An embodiment of an electronic device includes first and second semiconductor bodies. The first semiconductor body houses a first conductive strip having a first end portion and a second end portion, and houses a first conduction terminal electrically coupled to the first end portion and facing a surface of the first semiconductor body. The second semiconductor body houses a second conductive strip having a third end portion and a fourth end portion, and houses a second conduction terminal electrically coupled to the third end portion and facing a surface of the second semiconductor body. The first and second semiconductor bodies are arranged relative to one another so that the respective surfaces face one another, and the first conduction terminal and the second conduction terminal are coupled to one another by means of a conductive element so as to form a loop of an inductor.

Description:
PRIORITY CLAIM 
     The instant application claims priority to Italian Patent Application No. TO2011A000804, filed Sep. 9, 2011, which application is incorporated herein by reference in its entirety. 
     TECHNICAL FIELD 
     An embodiment relates to an electronic device, in particular of a semiconductor type, provided with an integrated inductor, and to a manufacturing method. In an embodiment, the electronic device is, in particular, a DC-DC converter. 
     BACKGROUND 
     DC-DC converters have assumed, and continue to assume, increasing importance in a plurality of electronic systems and devices, such as, for example, portable devices like cell phones and laptop computers, which are supplied via batteries. Said electronic devices usually include a plurality of electrical circuits and subcircuits, each of which requires, for its own operation, a level of voltage different from the one supplied by the battery. Furthermore, the voltage of the battery decreases during use thereof, as the power is drawn off. DC-DC converters are used in such applications in so far as they enable a method of generation of one or more controlled voltage levels starting from a variable supply voltage, such as, for example, the voltage supplied by a battery. An advantage of using a DC-DC converters may be a considerable saving of space in so far as it makes up for the need to use as many different supply sources as are different voltage levels required by the various electronic circuits for their operation. In particular, electronic switch-mode DC-DC converters carry out a DC-DC conversion by applying a DC voltage across an inductor for a predetermined period of time (usually in a frequency range of approximately from 100 kHz to 5 MHz) so as to generate a flow of electric current and store magnetic energy in the inductor. When, then, the voltage across the inductor is removed, the energy stored is transferred as output voltage and current of the DC-DC converter in a controlled way. By acting on the duty cycle, i.e., the time ratio of switching-on/switching-off, the output voltage remains regulated even though the load current may vary. This method of conversion is very power efficient (the efficiency is typically between approximately 80% and 95%), unlike other solutions, such as linear methods of conversion, which dissipate more power. 
     The external passive components, such as inductors and capacitors used in integrated DC-DC converters, have a value of impedance that depends upon the switching frequency and upon the power that the converter is designed to supply. In the last few years, DC-DC-converter designers have been increasing said switching frequency so as to be able to reduce the dimensions of the inductors to values such that they can be integrated in the converter package (in order to obtain the so-called “Systems in Package”, or SiPs), or even integrated in the die or chip itself (the so-called “Systems-on-Chip”, SoCs). Reference may be made, for example, to Saibal Roy “Challenges in magnetics for PwrSoC—Development in highfrequency magnetics, materials and integration”, PWR&#39;SoC 2010 Cork, Ireland, which is incorporated by reference. 
     As is known, inductors are formed by a low-resistance metal winding, which surrounds a core, which may be made of magnetic material. To provide a microinductor or an integrated inductor, it is typically necessary to have available low-resistivity metal paths and a magnetic material in the form of thin film. In order to maximize the quality factor Q of the inductor, the magnetic material has low coercivity, high saturation, and good response at high frequencies (&gt;10 MHz). Another requisite of the magnetic material for it to be integrated in current micromachining processes is for it to be compatible with silicon processes. Various materials have been studied and many others are still under study (see, for example, Nian X. Sun “RF Magnetic Films and Their Applications in Integrated Magnetic Devices”, PWR&#39;SoC 2010 Cork, Ireland, which is incorporated by reference. 
     There currently exist a plurality of different approaches for providing an integrated inductor, the best known of which envisages forming a planar loop surrounded by two thin layers of magnetic material defined lithographically. Said method is, for example, known from Donald S. Gardner “Integrated On-chip Inductors With Magnetic Films”, IEEE Transactions On Magnetics, Vol. 43, No. 6, June 2007, which is incorporated by reference. 
     The methods of manufacture of integrated inductors of a known type envisage complete integration of the magnetic material on the die of the DC-DC converter, and thus require that the processes of machining of the magnetic material do not come to affect the previous processes of machining of silicon, in effect reducing the choice of the magnetic materials that can be used to a limited group. 
     SUMMARY 
     An embodiment is an electronic device equipped with an integrated inductor, and a manufacturing method, that overcome one or more drawbacks of the known art. 
     According to an embodiment, two semiconductor bodies are formed, each housing a different portion of an inductor. The semiconductor bodies are coupled to one another with the flip-chip technique so that the portions of the inductor housed by them form, when coupled together, a complete inductor. A first semiconductor body houses circuitry of an electronic device (for example, a DC-DC converter) formed according to manufacturing processes typical of the semiconductor industry, and including, for example, at least some steps from among: implantation and diffusion of dopant elements, lithography and formation of metal and/or insulating layers. The last metal layer of the first semiconductor body (facing the surface of the semiconductor body) forms a first portion of the loop of the inductor. According to an embodiment, the second die houses, in addition to its own portion of the inductor, a magnetic layer adapted to form a magnetic core of the inductor. When coupled together, for example, via conductive solder bumps, the portions of the inductor form a plurality of turns that envelop the magnetic core. The magnetic core is hence enclosed within the inductor winding. 
    
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS 
       One or more embodiments are now described, purely by way of non-limiting example and with reference to the attached drawings, wherein: 
         FIG. 1  is a cross-sectional view of an electronic device including an integrated inductor according to an embodiment; 
         FIG. 2  is a top view of a first die of the electronic device of  FIG. 1  according to an embodiment; 
         FIG. 3  is a top view of a second die of the electronic device of  FIG. 1  according to an embodiment; 
         FIG. 4  is a perspective view of the electronic device of  FIG. 1  according to an embodiment; 
         FIGS. 5-16  show process steps for forming the electronic device of  FIG. 1  according to an embodiment; and 
         FIG. 17  is a top view of the electronic device of  FIG. 1  according to an embodiment. 
     
    
    
     DETAILED DESCRIPTION 
       FIG. 1  shows, in cross-sectional view taken along the line of cross section I- 1  of  FIG. 2 , a DC-DC converter  100 , including an inductor  1  of an integrated type, according to an embodiment. 
     The DC-DC converter  100  includes a first die  2  and a second die  4 , electrically coupled together via conductive contacts  6 , in particular in the form of bumps  7  of metal material. 
     The cross section of the first and second dice  2 ,  4  of  FIG. 1  is parallel to a plane XZ, according to the system of axes illustrated in  FIG. 1 . Views along different planes, for example, parallel to the plane XY, are provided in  FIGS. 2 and 3   
     The first die  2  includes: a substrate  8  of semiconductor material, for example, silicon; a supporting layer  10  (having moreover also the function of electrical insulation), for example, silicon oxide (FOX and/or PMD) with a thickness of approximately between 0.3 μm and 3 μm, for example, approximately 1 μm; one or more strips  12  (a plurality of strips  12  is illustrated in  FIG. 1 ), of conductive material, in particular metal, which extend on top of and in contact with the supporting layer  10 ; and an intermetal layer  14 , of dielectric material, for example, silicon oxide, which extends on top of the supporting layer  10  and surrounds the strips  12  to protect and insulate the strips  12 . 
     As may be seen more clearly in  FIG. 2  (which shows the first die  2  in top plan view), the strips  12  include respective contact portions  12   a  adapted to form electrical-contact regions for the conductive contacts  6 . The contact portions  12   a  are in electrical contact with each respective strip  12 , at terminal portions of the respective strip  12 . According to the embodiment illustrated in  FIG. 2 , each strip has a substantially rectangular shape with rounded corners, and the contact portions  12   a  are formed integral with each respective strip  12 . 
     A different embodiment (not illustrated) envisages that the contact portions  12   a  are formed separately from the strips  12 , and coupled to the latter via conductive paths or other conductive elements (for example, wires). 
     To return to  FIG. 2 , each strip  12  extends in a respective principal direction of extension u. The principal directions of extension u of each strip  12  are substantially parallel to one another. The contact portions  12   a  are arranged at mutually opposite ends  13   a ,  13   b  of each strip  12  in the principal direction of extension u. 
     Each strip  12  extends in the principal direction of extension u (major side of the rectangle that forms the strip  12 ) for a distance of approximately between 0.5 mm and 10 mm, for example, approximately 2 mm. Moreover, each strip  12  extends in a direction v (minor side of the rectangle that forms the strip  12 ), orthogonal to the principal direction of extension u, for a distance of approximately between 50 μm and 200 μm, for example, approximately 100 μm. 
     As may be noted from  FIG. 2 , the strips  12  are arranged to form a series of strips  12  set approximately parallel alongside one another and delimited laterally by strips  12 ′ and  12 ″. The strips  12  are electrically insulated from one another by a portion of the intermetal layer  14  that extends between them. The principal direction of extension u forms an angle θ, with the axis Y, between 0° and 90°, for example, approximately 20°. 
     The strip  12 ′ includes just one contact portion  12   a  formed at the end  13   a , whereas the end  13   b  is without contact portions  12   a . Extending alongside the strip  12 ″ is a conductive region  16  provided with a contact portion  16  similar to the contact portions  12   a . The conductive portion  16  is made of the same material as the strips  12 , and the contact portion  16   a  is approximately the same, as regards dimensional characteristics and material, as the contact portions  12   a.    
     Contact portions  12   a , arranged at the respective ends  13   a  of the strips  12 , are aligned with respect to one another (within the production tolerances) in one and the same first direction of alignment approximately parallel to the axis X; contact portions  12   a , arranged at the respective ends  13   b  of the strips  12 , are aligned with respect to one another and to the contact portion  16   a  (within the production tolerances) in one and the same second direction of alignment approximately parallel to the first direction of alignment. 
     Furthermore, contact portions  12   a  arranged at a respective end  13   a  of a respective strip  12  are aligned, in a direction of alignment substantially parallel to the axis Y, with contact portions  12   a  arranged at a respective end  13   b  of strip  12  immediately set alongside the strip  12  considered. 
     With joint reference to  FIG. 1  and  FIG. 3 , the second die  6  includes a substrate  18  of semiconductor material, for example, silicon, a supporting layer  20  (having also the function of electrical insulator), for example, silicon oxide (FOX and/or PMD), with a thickness of approximately between 0.3 μm and 3 μm, for example, approximately 1 μm, one or more strips  22  (a plurality of strips  22 , equal, in number, to the plurality of strips  12  of  FIG. 2 , is illustrated in  FIG. 3 ), of conductive material, in particular metal, which extend on top of and in contact with the supporting layer  20 , an intermetal layer  24 , of dielectric material, which extends on top of the supporting layer  20  and surrounds the strips  22 , to protect and insulate the strips  22 , an insulation layer  26 , which extends on top of the intermetal layer  24 , and a magnetic layer  30  (not visible in the cross section of  FIG. 1 ), which extends within the insulation layer  26 . The insulation layer  26  and the magnetic layer  30  do not extend at terminal portions  23   a  and  23   b  of the strips  22  where contact portions  22   a  are formed, as described hereinafter. 
     The magnetic layer is, for example, made of a metal alloy having at least one property from among a high saturation magnetic field, low coercivity, good frequency response of magnetic permeability (&gt;10 MHz), and high resistivity. Mixtures or alloys that satisfy one the more of said requisites are, for example, CoZrTa, NiFe, CoFeHfO, CoZrO, CoP, and CoFeSiB. 
     As may be seen more clearly in  FIG. 3  (which shows, in top plan view, the second die  4 ), each strip  22  includes respective contact portions  22   a  adapted to form electrical-contact regions for the conductive contacts  6 . The contact portions  22   a  are in electrical contact with each respective strip  22 , and are formed integral with each respective strip  22  at terminal portions of the respective strip  22 . 
     According to a different embodiment (not illustrated), the contact portions  22   a  are formed separately from the strips  22  and coupled to the latter via conductive paths. 
     According to the embodiment illustrated in  FIG. 3 , each strip  22  has a substantially rectangular shape with rounded corners, and extends in a respective principal direction of extension j. The principal directions of extension j of each strip  22  are substantially parallel to one another and substantially parallel to the axis Y. The contact portions  22   a  are arranged at ends  23   a ,  23   b , mutually opposite in the principal direction of extension j, of each strip  22 . Each strip  22  extends in the principal direction of extension j (major side of the rectangle that forms the strip  22 ) for a distance of approximately between 0.2 mm and 10 mm. Furthermore, each strip  22  extends in a direction k approximately orthogonal to the principal direction of extension j (minor side of the rectangle that forms the strip  22 ) for a distance of approximately between 50 μm and 200 μm, for example, approximately 100 μm. 
     The strips  22  are electrically insulated from one another by a portion of the intermetal layer  24  that extends between them. 
     Contact portions  22   a , arranged at the respective ends  23   a  of the strips  22 , are approximately aligned with respect to one another in one and the same first direction of alignment approximately parallel to the axis X (within the production tolerances); contact portions  22   a , arranged at the respective ends  23   b  of the strips  22 , are approximately aligned with respect to one another in one and the same second direction of alignment approximately parallel to the first direction of alignment (within the production tolerances). 
     With reference to  FIG. 1 , the first and second dice  2 ,  4  face one another so that contact portions  22   a  of the strips  22  of the second die  4  face, and are substantially aligned in the direction Z to, respective contact portions  12   a  of the strips  12  of the first die  2 . The contact portions  12   a  are electrically coupled to the contact portions  22   a  by means of bumps  7 . It is in this way that the inductor  1  is formed, the turns, or loops, of which are formed by the strips  12  and  22  coupled via the bumps  7 . The inductor  1  is provided with a magnetic core (formed by the magnetic layer  30 ) set between the turns. The shape of the magnetic core (i.e., of the magnetic layer  30 ) can be linear, toroidal, or some other shape. 
     The inductor  1  thus formed can be biased by applying a difference of potential between the end  13   b  of the strip  12 ′ (which hence has the function of first biasing terminal of the inductor  1 ) and the conductive region  16  (which hence has the function of second biasing terminal of the inductor  1 ). For this purpose, the first die  2  includes appropriate biasing means (not illustrated) coupled between the ends  13   b  of the strip  12 ′ and the conductive region  16 . 
     As an alternative to what has been illustrated and described so far herein, the first die  2  can include a first biasing terminal not coincident with the end  13   b  of the strip  12 ′ (i.e., distinct from the strip  12 ′), but electrically coupled to the latter via appropriate electrical connections. 
     In general, irrespective of the embodiment of the strips  12 , the first die  2  includes a plurality of devices, and/or active and/or passive components, and/or electronic circuits (designated as a whole by the reference number  33  in  FIG. 1 ), adapted to manage biasing of the inductor  1  and form, together with the inductor  1 , the DC-DC converter  100 . The electronic components  33  that form the electrical circuitry of the inductor DC-DC  100  may be formed according to manufacturing processes of a known type, which are not described in detail herein. In general, the manufacturing process includes some or all of steps of implantation of dopant species, steps of thermal diffusion of the implanted dopant species, steps of lithography and etching, and steps of formation of metal and/or insulating layers. In an embodiment, the last-formed metal layer of the first die  2  forms the strips  12  of the inductor  1 . 
     As may be seen in  FIG. 2 , the first die  2  further includes a plurality of conductive pads  35 , adapted to be contacted by means of wire bonding for receiving/issuing supply signals and/or operative signals of the DC-DC converter  100 . The pads  35  are arranged outside the area in which the strips  12  are formed. According to one embodiment (illustrated in  FIG. 4 ), the second die  4  has a substantially quadrangular shape, with lateral dimensions smaller than the respective dimensions of the first die  2 . In this way, when the first die  2  and the second die  4  are coupled together, the second die  4  extends on top of the first die  2  in an area between the pads  35 . 
       FIG. 4  moreover shows conductive wires  38  electrically coupled to the pads  35 . 
       FIGS. 5-16  show steps of manufacture of the DC-DC converter  100  according to an embodiment, in particular with reference to the steps of manufacture of the inductor  1 . 
       FIG. 5  shows, in cross-sectional view along the line of cross section I-I of  FIG. 2 , the first die  2 . 
     In the step of  FIG. 5 , the first die  2  includes a previously machined substrate  8 , in particular including active and passive electrical and electronic components  33 , designed to form circuitry of a DC-DC converter. The substrate  8 , made of semiconductor material, for example, silicon, can hence include, in a way not illustrated, a plurality of conductive and/or insulating layers (or regions) formed therein or thereover. The steps of machining of the first die  2  are typically carried out in a controlled environment or clean room, according to typical steps of CMOS processes. 
     Then ( FIG. 6 ), formed on a top face  8   a  of the substrate  8 , for example by means of deposition, is the supporting layer  10 , for instance, made of silicon oxide (FOX and/or PMD), with a thickness of approximately between 0.3 μm and 3 μm, for example, approximately 1 μm, having the function of defining a resting base on which to form the strips  12  of the inductor  1 . 
     Next ( FIG. 7 ), a metal layer is deposited to form the last metal level of the first die  2  and defined by means of steps of lithography and etching so as to form the strips  12 , having a shape and dimensions as described previously with reference to  FIG. 2 . 
     The metal layer that forms the strips  12  is made of a material with low conductivity, for example, aluminium or copper, and can be formed using the sputtering technique, or else with techniques of electrodeposition, or with the RDL (redistribution layer) technique. 
     Next ( FIG. 8 ), an intermetal layer  14  of dielectric material, for example, silicon oxide, is deposited on top of the supporting layer  10  and the strips  12 . A subsequent masked etching step enables formation of recesses  42  in the intermetal layer  14 , at the ends  13   a ,  13   b  of the strips  12 , exposing surface portions  44  of the strips  12 . The surface portions  44  of the strips  12  thus exposed form the contact portions  12   a  described previously. 
       FIG. 9  shows, in cross-sectional view along the line of cross section II-II of  FIG. 3 , the second die  4 , including, in this step, just the substrate  18 , made of semiconductor material. The second die  4  can be machined in an environment with class of dustiness lower than the class of dustiness required for machining the first die  2 , and/or on equipment not shared with the ones used for manufacturing the first die  2 . In this way, the subsequent steps of machining of the second die  4  (in particular, the formation of the magnetic layer  30 ) can be carried out independently of the machining steps carried out on the first die  2  without any risk of contamination. 
     Then ( FIG. 10 ), formed on the top face  18   a  of the substrate  18  is the supporting layer  20 , which is made, for example, of silicon oxide (FOX and/or PMD) with a thickness of approximately between 0.3 μm and 3 μm, for example, approximately 1 μm, having the function of defining a resting base on which to form the strips  22  of the inductor  1 . 
     Next, a metal layer forming the last metal level of the second die  4  is deposited. Said metal layer is defined by means of steps of lithography and etching so as to form the strips  22 , which have a shape and dimensions as described previously. The metal layer that forms the strips  22  is made of a material with low conductivity, for example, aluminium or copper, and can be obtained using the sputtering technique, or else with techniques of electrodeposition, or with the RDL (redistribution layer) technique. 
     Then, an intermetal layer  24  of dielectric material, for example, silicon oxide, is deposited on top of the supporting layer  20  and the strips  22 . 
     Next ( FIG. 11 ), formed, by means of deposition or growth, on top of the intermetal layer  24 , is a first intermediate insulation layer  50 , made, for example, of insulating material, such as silicon oxide or silicon nitride. 
     Formed on the first intermediate insulation layer  50  is the magnetic layer  30  (not visible in the cross section of  FIG. 11 ; it is illustrated in  FIGS. 12 and 13 ). 
     The magnetic layer  30  is formed by deposition of a layer of metal alloy (for example, chosen in the group including CoZrTa, NiFe, CoFeHfO, CoZrO, and CoP, CoFeSiB. 
     The methods of deposition of the magnetic layer  30  may be multiple, for example, sputtering, magnetron sputtering, electrodeposition, or any other method. The magnetic material can be deposited in a single layer or else in multiple layers of metal alloy separated by respective layers of insulating material (for example, silicon oxide or else a nitride of one of the components of the magnetic alloy). Alternatively, the magnetic material that forms the magnetic layer  30  can be deposited in the form of nanogranules immersed in a matrix of insulating material (such as, for example, silicon oxide or polymeric material). 
     It has been found that, when the magnetic layer  30  is formed by multiple layers of magnetic alloy separated by respective layers of insulating material, or else the magnetic material that forms the magnetic layer  30  is in the form of nanogranules immersed in insulating material, the parasitic currents in the magnetic layer  30 , during use, are considerably reduced as compared to other structures. 
     If the magnetic layer  30  has not been formed with electrodeposition techniques, a further step of lithography and etching is envisaged to define the shape and dimensions of the magnetic layer  30 . As an alternative to the step of lithography and etching, the magnetic layer  30  can be defined in shape and dimensions using the lift-off technique. 
     As may be seen more clearly in top view in  FIG. 12 , the magnetic layer  30  has dimensions such as to be contained at least partially within the area where the turns  22  extend, so that, when the first and second dice  2 ,  4  are coupled to one another, the magnetic layer  30  extends, for example, exclusively, within the region defined by the strips  12 ,  22  and by the bumps  7 . More in particular, the magnetic layer  30  is formed so that it does not extend at the ends  23   a  and  23   b  of the strips  22  so as to leave exposed the regions where the contact portions  22   a  are then formed. 
       FIG. 13  shows a cross-sectional view of the second die  4  following the manufacturing steps described previously, taken along the line of cross section III-III of  FIG. 12 , where the magnetic layer  30  is shown in section. 
     In  FIG. 14 , to return to the representation in cross section along the line of cross section II-II of  FIG. 3  or  FIG. 12 , there is formed, for example, by means of deposition or growth, a second intermediate insulation layer  52 , made of insulating material, such as, for example, silicon oxide or silicon nitride. The first intermediate insulation layer  50  and the second intermediate insulation layer  52  form the insulation layer  26 . 
     Finally ( FIG. 15 ), by means of successive lithography and etching steps, recesses  56  are formed in the insulation layer  26  at the ends  23   a ,  23   b  of the strips  22  to expose surface portions  58  of the strips  22 . The surface portions  58  of the strips  22  thus exposed form the contact portions  22   a  described previously. 
     The steps of machining of the second die  4  may not require particular precautions as regards contamination of possible electronic components, or of the equipment used, by the magnetic material of which the magnetic layer  30  is made. In fact, the second die  4  may not house electronic components (all the circuitry necessary for operation of the DC-DC converter  100  being housed in the first die  2 ), and the steps of manufacture of the second die  4  can be carried out in places and according to modalities distinct from the steps of manufacture of the first die  2 . 
     At the end of the manufacturing steps according to  FIGS. 5-15 , the second die is coupled ( FIG. 16 ) to the first die (using the flip-chip technique) by means of bumps  7 , which are in electrical contact with both of the contact portions  12   a  and  22   a.    
     The first die  2  includes a first surface  2   a  and a second surface  2   b , opposite to one another. The first surface  2   a  is the exposed surface of the substrate  8 , whereas the second surface  2   b  is the surface (opposite to the first surface  2   a  along the axis Z) obtained at the end of the manufacturing steps described. Likewise, the second die  4  includes a first surface  4   a  and a second surface  4   b , opposite to one another. The first surface  4   a  is the exposed surface of the substrate  18 , whereas the second surface  4   b  is the surface (opposite to the first surface  4   a  along the axis Z) obtained at the end of the manufacturing steps described. 
     During the step described with reference to  FIG. 16 , the first and second dice are coupled together so that the respective second surfaces  2   b  and  4   b  face one another. 
     If it were to prove necessary, given the thickness of the intermetal layer  24  and the insulation layer  26 , the recesses  56  can be partially or completely filled with conductive material, for example, metal, in order to facilitate the contact between the bumps  7  and the surface portions  58  of the strips  22 . Typically, the thickness of the intermetal layer  24  and of the insulation layer  26  is such that this operation not is necessary ( FIG. 15  is not in scale). 
     The bumps  7  can be formed, indifferently, in areas corresponding to the contact portions  12   a  and  22   a  of the first die  2  or of the second die  4  before the step of coupling using the flip-chip technique, and then coupling is carried out. 
     The flip-chip technique is also known in the literature as “Controlled Collapse Chip Connection”, or C4. 
     The flip-chip technique is used in micromachining techniques for intercoupling semiconductor devices, such as, for example, integrated circuits, with external circuitry, typically by soldering respective electrical-contact portions via soldering elements known as “bumps”. 
     The bumps  7  are deposited on the electrical-contact portions (for example, contact portions  12   a ) of a die (for example, the first die  2 ). In order to make a connection between the first and second dice  2 ,  4 , one of the two dice (for example, the second die  4 ) is flipped on the other so that the first and second dice  2 ,  4  face one another and are aligned so that the respective electrical-contact portions  12   a ,  22   a  face one another and are coupled together via the bumps  7 . Then, a step of heating (for example, via ultrasound) such as to melt the bumps  7  partially enables a secure contact to be obtained between the electrical-contact portions  12   a  and  22   a  of the dice  2 ,  4 . 
     In this way, the inductor  1  including a continuous metal loop shaped like a spiral that envelops the magnetic layer  30  is formed, and is insulated electrically from the latter by means of the intermetal layers  14  and  24 , and the insulation layer  26 . 
       FIG. 17  shows, in top plan view, the first and second dice  2 ,  4  coupled together. In particular, the strips  12  and  22  and the magnetic layer  30  are visible in  FIG. 17 . 
     The stacked die thus obtained can be closed in a package using known packaging techniques. And the packaged DC-DC converter may be combined with one or more other components, such as processor (e.g., a microprocessor or microcontroller) to form a system. 
     From an examination of the characteristics of the embodiments according to the present disclosure one or more advantages of the embodiments are evident. 
     In particular, integration of the magnetic inductor, via the flip-chip technique described, may enable reduction to negligible values of the parasitic inductances that must be normally taken into account when an inductor is used outside the integrated circuit and coupled to the latter via paths on a printed circuit board (PCB), or else in the case of a co-packaged inductor, bonding between the IC and the micro-inductor. 
     Furthermore, integration of the inductor enables a drastic reduction of the dimensions of the entire DC-DC converter and the system in which the DC-DC converter is disposed, and at the same time reduction of the costs linked to the assembly of discrete components on a printed circuit. 
     In addition, one or more embodiments described enable reduction of the environmental impact of the manufacturing steps, given the smaller amount of magnetic material used and the better efficiency obtained by an integrated DC-DC conversion system as compared to a discrete one. 
     Finally, it is clear that modifications and variations may be made to what has been described and illustrated herein, without thereby departing from the sphere and spirit of the present disclosure. 
     In particular, it is evident that, even though the manufacturing steps of  FIGS. 5-16  have been described with reference to two dice, said steps can be carried out on an entire wafer to form a plurality of DC-DC converters  100  each provided with a respective inductor  1 . This is followed by dicing to isolate the individual dice. 
     Alternatively, the dice  2  and  4  can be generic semiconductor bodies. 
     In addition, the magnetic layer  30  may not be formed. In this case, the inductor has a dielectric core formed by the intermetal layers  14  and  24 . The insulation layer  26  may be unnecessary in the absence of the magnetic layer  30 . 
     Furthermore, the embodiments described include an inductor having a plurality of turns or loops. But it is evident that said inductor can include just a single turn or loop. 
     Moreover, according to an embodiment a plurality of inductors of the type described can be formed on one and the same die. The plurality of inductors can belong to a respective plurality of electronic devices or else to one and the same electronic device, which uses more than one inductor for its operation (e.g., a multiphase DC-DC converter). 
     Finally, the teachings according to the present disclosure can be extended to generic electronic apparatuses, other than a DC-DC converter, that include one or more inductors. 
     From the foregoing it will be appreciated that, although specific embodiments have been described herein for purposes of illustration, various modifications may be made without deviating from the spirit and scope of the disclosure. Furthermore, where an alternative is disclosed for a particular embodiment, this alternative may also apply to other embodiments even if not specifically stated.