Patent Publication Number: US-2006017539-A1

Title: Low-loss inductor device and fabrication method thereof

Description:
CROSS-REFERENCE TO RELATED APPLICATIONS  
      This application claims priority under 35 U.S.C. § 119 from Korean Patent Application 2004-56468, filed on Jul. 20, 2004, the entire contents of which are incorporated herein by reference.  
     BACKGROUND OF THE INVENTION  
      1. Field of the Invention  
      The present invention relates to an inductor device and, more particularly, to an inductor device and a fabrication method thereof capable of minimizing the loss of the inductor.  
      2. Description of the Related Art  
      The Micro-electro-mechanical system (MEMS) is the technology of implementing mechanical and/or electrical devices by using the semiconductor process. For example, the inductor device can be fabricated by use of the MEMS technology.  
      The inductor device is fabricated to supply magnetic fluxes or fields to a device requiring the magnetic fluxes or fields such as a capacitor in an LC resonance circuit. Therefore, a consideration factor in the inductor fabrication is to design an inductor device to supply all magnetic fluxes generated in the inductor to a device requiring the magnetic fluxes, but not to the other devices.  
      Therefore, two of the factors to consider in an inductor device are inductance and a quality factor. Currently, the inductance has been satisfactorily achieved to some extent, but the quality factor has not been achieved up to a desired value due to the substrate loss and the electric current limitation caused by DC resistance which occurs in an inductor device.  
      For example, as shown in  FIG. 1 , the conventional inductor device has an inductor L ( 102 ) integrated and formed on the substrate  100 , so the parasitic effect is caused between the inductor  102  and the substrate  100  due to the direct contact of the inductor  102  with the substrate  100 . The inductance of the inductor  102  becomes lowered due to the parasitic effect. In order to solve the problem of low inductance as above, an expensive low-dielectric substance has to be used.  
      In consideration of the cost and the problem of low inductance due to the parasitic effect, there has been proposed a method of fabricating an inductor device having air gaps. However, the inductor device with the air gaps formed can have a high quality factor Q and inductance, but requires a highly difficult process. Further, the inductor device with the air gaps formed has an adhesion problem when the wet etching process is carried out for floating the structure in the air.  
     SUMMARY OF THE INVENTION  
      The present invention has been developed in order to solve the above drawbacks and other problems associated with the conventional arrangement. A first aspect of the present invention is to provide an inductor device having a high quality factor Q and inductance by minimizing substrate losses occurring in the inductor device.  
      A second aspect of the present invention is to provide an inductor device having a flat dual structure.  
      A third aspect of the present invention is to provide an inductor device fabrication method capable of forming an air gap of more than a few hundred μm.  
      A fourth aspect of the present invention is to provide an inductor device capable of protecting an inductor from outside.  
      The foregoing and other aspects and advantages are substantially realized by providing an inductor device, comprising a substrate etched away at predetermined intervals; first and second inductors formed on the top and bottom of the substrate, respectively; and a protection package for shielding at least one of the first and the second inductors from outside.  
      The first and second inductors are formed in a symmetrical structure with respect to the substrate, and the inductor device further comprises connection parts for electrically connecting the first and second inductors.  
      The inductor device may further comprise air gaps between the substrate, the first inductor, and the second inductor in order for the first and the second inductors to be exposed in the air.  
      The inductor device may further comprise a further protection package for shielding the other of the first and the second inductors from outside, and the further protection package has an electrode layer formed thereon at predetermined positions to supply electric currents to the inductor device.  
      Further, an inductor device fabrication method comprises forming a first inductor on top of a substrate, and forming a second inductor on a bottom of the substrate; etching away the substrate at predetermined intervals; and forming a protection package for hermetically sealing at least one of the first inductor and the second inductor for shielding the at least one of the first inductor and the second inductor from outside.  
      The substrate may be etched away by, for example, dry etching.  
    
    
     BRIEF DESCRIPTION OF THE DRAWINGS  
      The above aspects and features of the present invention will be more apparent by describing exemplary embodiments of the present invention with reference to the accompanying drawings, in which:  
       FIG. 1  is a view for showing an inductor device fabricated according to a general method;  
       FIGS. 2A and 2B  are views for showing an inductor device according to an embodiment of the present invention; and  
       FIGS. 3A through 3P  are views for illustrating a process of fabricating an inductor device according to an embodiment of the present invention. 
    
    
     DETAILED DESCRIPTION OF EXEMPLARY EMBODIMENTS  
      Hereinafter, the present invention will be described with reference to the accompanying drawings.  
       FIGS. 2A and 2B  are views for showing an exemplary inductor device according to an embodiment of the present invention. The inductor device has a substrate  202 , and first and second inductors  206  and  204  formed in a symmetrical structure on the upper and lower sides of the substrate  202 . Further, the inductor device has a connection part  208  for connecting the first inductor  206  and the second inductor  204 . As stated above, the inductor device forms a dual structure of the first and second inductors  206  and  204 , so as to have a high inductance.  
       FIG. 2A  is an inductor device not hermetically sealed, and  FIG. 2B  is a view for showing an inductor device hermetically sealed by protection packages  200  and  210 .  
      The protection package  200  of  FIG. 2A  is fabricated in glass, and the substrate  202  is fabricated in silicon Si. The first and second inductors  206  and  204  are fabricated in metal substances such as cooper Cu and the like. The inductor device has air gaps formed therein so that the first and second inductors  206  and  204  float from the substrate  202 . The quality factors of the first and second inductors  206  and  204  can be improved due to the floating of the first and second inductors  206  and  204  from the substrate  202 .  
       FIG. 2B  shows that the first and second inductors  206  and  204  can be safely secured from external shocks since the first and second inductors  206  and  204  are hermetically sealed with the first and second protection packages  210  and  200 . Further, electrode layers  212  are formed so that the first and second inductors  204  and  206  actually can be used.  
      Hereinafter, detailed description will be made on the inductor device fabrication process according to an embodiment of the present invention with reference to  FIGS. 3A-3P .  
       FIG. 3A  is a view for showing a substrate  202  and a seed layer  300  coated on the top of the substrate  202 . The seed layer  300  is made of a metal substance such as Titanium Ti, Chromium Cr, or the like. Description will be made later on the reason why the seed layer  300  is coated on the top of the substrate  202 .  
       FIG. 3B  is a view for showing photosensitive solution  302  coated on a region formed on the top of the seed layer  300 . The shape of the first inductor is determined depending on a region on which the photosensitive solution  302  is coated.  
       FIG. 3C  is a view for showing the electroplating of a metal substance on a region on which the photosensitive solution  302  is not coated. The electroplating of the metal substance forms the first inductor  206 . In general, copper Cu is used as the metal substance, but copper can be replaced with any conductive substance depending on a user&#39;s requirement. The seed layer  300  performs a function of improving adhesive power of the metal substance (first inductor)  206  and the substrate  202 . That is, if the seed layer  300  does not exist, the adhesive power of the metal substance  206  and the substrate  202  is deteriorated.  
       FIG. 3D  is a view for showing the etching of the photosensitive solution  302  coated in  FIG. 3B  and the seed layer  300  coated in  FIG. 3A . The etching of the photosensitive solution  302  forms the first inductor  206  of the inductor device. Hereinafter, description will be made on a process of hermetically sealing the first inductor  206  with the first protection package  210 .  FIG. 3D  also shows the first protection package  210  to hermetically seal the first inductor  206 . As stated above, the first protection package  210  is made of glass, but can be made of a different substance depending on the user&#39;s requirement.  
       FIG. 3E  is a view for hermetically sealing the first inductor  206  with the first protection package  210 . The first inductor  206  is hermetically sealed with the first protection package  210  by anodic bonding. In order to carry out the anodic bonding, a negative voltage is applied to the top of the first protection package  210  and a positive voltage is applied to the bottom of the substrate  202 . For the sake of brevity, a detailed description of the carrying-out of the anodic bonding will be omitted. The first inductor  206  is hermetically sealed with the first protection package  210  by the anodic bonding.  
      As shown in  FIG. 3F , the substrate  202  is polished as much as a certain thickness. In general, the Chemical Mechanical Polishing (CMP) is used to polish the substrate  202 . The flatness of the substrate  202  can be improved by the polishing of the substrate  202  by the CMP.  
      As shown in  FIG. 3G , a portion of the substrate  202  is etched away to allow formation of a connection part  208  electrically connecting the first and second inductors  206  and  204 . Further,  FIG. 3G  shows the etching of two regions to allow formation of two connection parts  208 .  
      In  FIG. 3H , the regions etched away in  FIG. 3G  are electroplated with a metal substance to form the regions as the connection parts  208 . The electroplating process is the same as shown in  FIG. 3C . Hereinafter, description will be made on a process of forming the second inductor  204 .  
      In  FIG. 3I , the second inductor  204  is formed. The process of forming the second inductor  204  is the same as the process carried out in  FIGS. 3A  to  3 D.  
      In  FIG. 3J , the photosensitive solution (PR)  306  is coated on a portion of the second inductor  204 .  FIG. 3J  shows three regions, that is, both end portions and a middle portion, coated with the photosensitive solution  306 , for example. Further, a metal substance  304  is coated on the top of the first protection package  210 . The metal substance can be replaced with the same substance as the metal substance  300  coated on the top of the substrate  202  of  FIG. 3A . Further, the process of coating the metal substance  304  can be omitted depending on user&#39;s requirement, or performed at one of the next steps to be carried out.  
      In  FIG. 3K , a dry release is used to etch away the regions not coated with the photosensitive solution  306 . In particular, the dry release etches away the substrate  202  not coated with the photosensitive solution  306 . Further, portions of the first and second inductors  206  and  204  can be etched away as the dry release is carried out. The dry-release process floats the first and second inductors  206  and  204  in the air.  
      In  FIG. 3I , the photosensitive solution  306  coated in  FIG. 3J  is removed.  
      In  FIG. 3M , the second protection package  200  is used to hermetically seal the second inductor  204 . The process of hermetically sealing the second inductor  204  is the same as the process of hermetically sealing the first inductor  206 .  
      In  FIG. 3N , electrodes are formed to supply electric currents to the first and second inductors  206  and  204 . The electroplating is carried out to form the electrodes by filling a metal substance  212  in recess portions of the first protection package  210 .  
      In  FIG. 3O , the photosensitive solution  310  is coated on portions of the metal substance  212  to form the electrode layer  212  as in  FIG. 2B .  
       FIG. 3P  shows a process of forming the first protection package for protecting the first inductor. Further, if the metal substance  212  is etched away, the photosensitive solution  310  coated in  FIG. 3O  is eliminated.  
       FIGS. 3A-3P  show a process of forming the first protection package for protecting the first inductor, but, depending on the user&#39;s requirement, the process can be omitted that forms the first protection package for protecting the first inductor as in  FIG. 2A . That is, only the second protection package would be formed to protect the second inductor.  
      The process for an inductor device according to the fabrication method of the present invention enables the inductor device to have high inductance and quality factor. Further, the method enables the inductor device to have air gaps of more than a few hundred μm formed therein. The method employs the dry-etching process instead of the much more difficult wet-etching process, enabling the flat and dual-structured inductors to be easily fabricated. The formation of the protection packages can protect the inductors from external shocks.  
      The foregoing embodiments and advantages are merely exemplary and are not to be construed as limiting the present invention. The present teaching can be readily applied to other types of apparatuses. Also, the description of the embodiments of the present invention is intended to be illustrative, and not to limit the scope of the claims, and many alternatives, modifications, and variations will be apparent to those skilled in the art.