Abstract:
An integrated circuit includes a substrate and an inductive device on a first side of the substrate. The integrated circuit includes a first ferromagnetic material on a second side of the substrate opposite the first side.

Description:
BACKGROUND 
     Inductive devices, such as transformers and inductors provided by coils are often included in small scale, medium scale, or very large scale integration (VLSI) circuits. Typically, inductive devices integrated in these circuits use large coil diameters to obtain a good quality factor (i.e., Q-factor). A good Q-factor is especially important for radio frequency (RF) technology applications. Large diameter coils, however, typically use a large percentage of the available substrate area of an integrated circuit and therefore increase production costs. 
     Concentric coils are typically located in parallel to a substrate surface. The coils are fabricated in back end of line (BEOL) processing during a metallization process using suitable metallization material. Typically, the coils may consume 50% or more of the total chip area. In addition, the inductivities achieved from the coils are usually not suitable for applications in which the coils will be used not only for signal transmission but also for power transmission. 
     For these and other reasons, there is a need for the present invention. 
     SUMMARY 
     One embodiment provides an integrated circuit. The integrated circuit includes a substrate and an inductive device on a first side of the substrate. The integrated circuit includes a first ferromagnetic material on a second side of the substrate opposite the first side. 
    
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS 
       The accompanying drawings are included to provide a further understanding of the present invention and are incorporated in and constitute a part of this specification. The drawings illustrate the embodiments of the present invention and together with the description serve to explain the principles of the invention. Other embodiments of the present invention and many of the intended advantages of the present invention will be readily appreciated as they become better understood by reference to the following detailed description. The elements of the drawings are not necessarily to scale relative to each other. Like reference numerals designate corresponding similar parts. 
         FIG. 1  illustrates a cross-sectional view of one embodiment of an integrated circuit including an inductive device encased in ferromagnetic material. 
         FIG. 2  illustrates a cross-sectional view of another embodiment of an integrated circuit including an inductive device encased in ferromagnetic material. 
         FIG. 3  illustrates a cross-sectional view of another embodiment of an integrated circuit including an inductive device encased in ferromagnetic material. 
         FIG. 4  illustrates a cross-sectional view of another embodiment of an integrated circuit including an inductive device encased in ferromagnetic material. 
         FIG. 5  illustrates a cross-sectional view of another embodiment of an integrated circuit including an inductive device encased in ferromagnetic material. 
     
    
    
     DETAILED DESCRIPTION 
     In the following Detailed Description, reference is made to the accompanying drawings, which form a part hereof, and in which is shown by way of illustration specific embodiments in which the invention may be practiced. In this regard, directional terminology, such as “top,” “bottom,” “front,” “back,” “leading,” “trailing,” etc., is used with reference to the orientation of the Figure(s) being described. Because components of embodiments of the present invention can be positioned in a number of different orientations, the directional terminology is used for purposes of illustration and is in no way limiting. It is to be understood that other embodiments may be utilized and structural or logical changes may be made without departing from the scope of the present invention. The following detailed description, therefore, is not to be taken in a limiting sense, and the scope of the present invention is defined by the appended claims. 
       FIG. 1  illustrates a cross-sectional view of one embodiment of an integrated circuit  100   a . Integrated circuit  100   a  includes a substrate  102 , inductive devices  104   a  and  104   b , dielectric material  106 , first ferromagnetic material  108 , and second ferromagnetic material  110 . In other embodiments, integrated circuit  100   a  includes any suitable number of inductive devices. 
     First ferromagnetic material  108  and second ferromagnetic material  110  partially or fully encase or enclose inductive devices  104   a  and  104   b . The ferromagnetic material can be applied using suitable semiconductor processing techniques during front end of line (FEOL) processing and/or back end of line (BEOL) processing. The ferromagnetic material can be positioned above inductive devices  104   a  and  104   b , below inductive devices  104   a  and  104   b , and/or on the sides (inner and outer) of inductive devices  104   a  and  104   b.    
     First ferromagnetic material  108  and second ferromagnetic material  110  confine the magnetic flux inside inductive devices  104   a  and  104   b . The confining of the magnetic flux inside inductive devices  104   a  and  104   b  reduces energy dissipation from inductive devices  104   a  and  104   b  due to leakage fields and magnetic coupling to silicon substrate  102 . By reducing the energy dissipation in this way, the quality factor (i.e., Q-factor) of inductive devices  104   a  and  104   b  is increased. By increasing the Q-factor of inductive devices  104   a  and  104   b , inductive devices  104   a  and  104   b  can be used for both signal transmission and power transmission. 
     Inductive devices  104   a  and  104   b  are formed in metallization layers on substrate  102  using suitable metallization materials. In one embodiment, inductive devices  104   a  and  104   b  are concentric coils providing inductors, transformers, or other suitable devices. Dielectric material  106  surrounds the metal material forming inductive devices  104   a  and  104   b . In one embodiment, substrate  102  is a silicon substrate. The thickness of substrate  102  is less than the diameter of inductive devices  104   a  and  104   b . In one embodiment, grinding is used to reduce the thickness of substrate  102  to between approximately 60-100 μm. 
     Ferromagnetic material, such as Co, Fe, Ni, or other suitable ferromagnetic material is deposited on the backside of substrate  102 . The ferromagnetic material is structured using suitable lithography processes to provide gaps  116  between portions of first ferromagnetic material  108 . Gaps  116  between portions of first ferromagnetic material  108  are provided to prevent eddy currents. Because silicon substrate  102  has a low electrical conductivity, magnetic coupling of the magnetic field of inductive devices  104   a  and  104   b  into substrate  102  is low. Therefore, first ferromagnetic material  108  shields the magnetic field of inductive devices  104   a  and  104   b.    
     Ferromagnetic material, such as Co, Fe, Ni, or other suitable ferromagnetic material is deposited on the top and sides of inductive devices  104   a  and  104   b . In one embodiment, the ferromagnetic material is structured using suitable lithography processes to provide second ferromagnetic material  110 . Second ferromagnetic material  110  includes first portions  112  and second portions  114 . First portions  112  are provided on top of inductive devices  104   a  and  104   b . Second portions  114  are provided on the outer sidewalls of dielectric material  106  surrounding inductive devices  104   a  and  104   b . In one embodiment, second portions  114  are also provided on the inner sidewalls of dielectric material  106  surrounding inductive devices  104   a  and  104   b . In one embodiment, the sidewalls of dielectric material  106  surrounding inductive devices  104   a  and  104   b  are perpendicular to first portions  112 . In another embodiment, the sidewalls of dielectric material  106  surrounding inductive devices  104   a  and  104   b  are sloped. 
       FIG. 2  illustrates a cross-sectional view of another embodiment of an integrated circuit  100   b . Integrated circuit  100   b  includes substrate  102 , first ferromagnetic material  120 , inductive devices  104   a  and  104   b , dielectric material  106 , and second ferromagnetic material  122  and  124 . In this embodiment, first ferromagnetic material  120  is provided between inductive devices  104   a  and  104   b  and substrate  102 . First ferromagnetic material  120  is formed in a metallization layer on substrate  102 . Since first ferromagnetic material  120  is between inductive devices  104   a  and  104   b  and substrate  102 , in this embodiment the thickness of substrate  102  can be greater than the diameter of inductive devices  104   a  and  104   b.    
     Second ferromagnetic material  122  is printed over inductive devices  104   a  and  104   b . In one embodiment, second ferromagnetic material  122  is printed using an inkjet printer or other suitable printer. Next, a galvanic process is used to optimize or enhance the printed ferromagnetic material  122  and to provide ferromagnetic material  124 . The galvanic process is selected to provide a combination of ferromagnetic material  122  and  124  providing desired ferromagnetic properties. Ferromagnetic materials  122  and  124  include first portions  126  and second portions  128 . First portions  126  are provided on top of inductive devices  104   a  and  104   b . Second portions  128  are provided on the outer sidewalls of dielectric material  106  surrounding inductive devices  104   a  and  104   b . In one embodiment, second portions  128  are also provided on the inner sidewalls of dielectric material  106  surrounding inductive devices  104   a  and  104   b . In this embodiment, the sidewalls of dielectric material  106  surrounding inductive devices  104   a  and  104   b  are sloped such that a printer can print ferromagnetic material  122  on the sidewalls. First ferromagnetic material  120  and second ferromagnetic material  122  and  124  provide a similar function as first ferromagnetic material  108  and second ferromagnetic material  110  previously described and illustrated with reference to  FIG. 1 . 
       FIG. 3  illustrates a cross-sectional view of another embodiment of an integrated circuit  100   c . Integrated circuit  100   c  is similar to integrated circuit  100   b  previously described and illustrated with reference to  FIG. 2 , except that in integrated circuit  100   c  first ferromagnetic material  120  is replaced with first ferromagnetic material  108 . First ferromagnetic material  108  is deposited and structured on the backside of wafer  102  as previously described and illustrated with reference to  FIG. 1 . First ferromagnetic material  108  and second ferromagnetic material  122  and  124  provide a similar function as first ferromagnetic material  108  and second ferromagnetic material  110  previously described and illustrated with reference to  FIG. 1 . 
       FIG. 4  illustrates a cross-sectional view of another embodiment of an integrated circuit  100   d . Integrated circuit  100   d  includes substrate  102 , first ferromagnetic material  120 , inductive devices  104   a  and  104   b , a ferromagnetic mold material  130 , and an encapsulating mold material  132 . In this embodiment, first ferromagnetic material  120  is provided between inductive devices  104   a  and  104   b  and substrate  102 . First ferromagnetic material  120  is formed in a metallization layer on substrate  102 . Since first ferromagnetic material  120  is between inductive devices  104   a  and  104   b  and substrate  102 , in this embodiment the thickness of substrate  102  can be greater than the diameter of inductive devices  104   a  and  104   b.    
     In addition, inductive devices  104   a  and  104   b  are encased or enclosed with ferromagnetic mold material  130 . In one embodiment, ferromagnetic mold material  130  includes a suitable molding compound mixed with ferrite or other suitable material to provide a ferromagnetic mold material. The ferromagnetic mold material is applied over the top and sidewalls of dielectric material  106  and inductive devices  104   a  and  104   b  using a suitable molding process. A suitable non-ferromagnetic encapsulation mold material  132  encapsulates ferromagnetic mold material  130  and substrate  102 . First ferromagnetic material  120  and ferromagnetic mold material  130  provide a similar function as first ferromagnetic material  108  and second ferromagnetic material  110  previously described and illustrated with reference to  FIG. 1 . 
       FIG. 5  illustrates a cross-sectional view of another embodiment of an integrated circuit  100   e . Integrated circuit  e  is similar to integrated circuit  100   d  previously described and illustrated with reference to  FIG. 4 , except that in integrated circuit  e  first ferromagnetic material  120  is replaced with first ferromagnetic material  108 . First ferromagnetic material  108  is deposited and structured on the backside of wafer  102  as previously described and illustrated with reference to  FIG. 1 . First ferromagnetic material  108  and ferromagnetic mold material  130  provide a similar function as first ferromagnetic material  108  and second ferromagnetic material  110  previously described and illustrated with reference to  FIG. 1 . 
     Embodiments provide inductive devices embedded in ferromagnetic material. The ferromagnetic material shields the inductive devices thereby increasing the inductivities and Q-factors of the inductive devices. By increasing the Q-factors of the inductive devices, the inductive devices can be used for both signal transmission and power transmission in small scale, medium scale, or very large scale integration circuits. 
     Although specific embodiments have been illustrated and described herein, it will be appreciated by those of ordinary skill in the art that a variety of alternate and/or equivalent implementations may be substituted for the specific embodiments shown and described without departing from the scope of the present invention. This application is intended to cover any adaptations or variations of the specific embodiments discussed herein. Therefore, it is intended that this invention be limited only by the claims and the equivalents thereof.