Abstract:
The present invention relates to inductors with improved inductance and quality factor. In one embodiment, a magnetic thin film inductor is disclosed. In this embodiment, magnetic thin film inductor includes a plurality of elongated conducting regions and magnetic material. The plurality of elongated conducting regions are positioned parallel with each other and at a predetermined spaced distance apart from each other. The magnetic material encases the plurality of conducting regions, wherein when currents are applied to the conductors, current paths in each of the conductors cause the currents to generally flow in the same direction thereby enhancing mutual inductance.

Description:
CROSS REFERENCE TO RELATED CASES  
       [0001]    This application is a divisional application of U.S. application Ser. No. 10/014,045, entitled “Magnetic Thin Film Inductors,” filed Dec. 11, 2001. 
     
    
     
       TECHNICAL FIELD  
         [0002]    The present invention relates generally to magnetic thin film inductors and in particular the present invention relates to magnetic thin film inductors with improved inductance and quality factor at relatively high frequencies.  
         BACKGROUND  
         [0003]    Inductors used in integrated circuits are typically mounted on a substrate of the integrated circuit. An inductor typically comprises conducting material formed in a straight line or spiral shape with magnetic material positioned in close proximity. This type of inductor is typically used in relatively low frequency applications, about 1 giga hertz (GHz) or less. At about 1 GHz, the magnetic material of the prior art typically reaches ferro-magnetic resonance. Inductors operating near and/or beyond their ferro-magnetic resonance frequencies will have poor inductance performance. In particular, they will have a poor quality factor due to relatively high eddy currents and interference. Moreover, existing inductors generally take up a relatively large amount of space. In wireless communication operations, it is desired to have an inductor that is relatively small and can operate at a frequency above 1 giga hertz. Accordingly, it is desired in the art for an inductor design that can operate at a relatively high frequency with high inductance while taking up a relatively small amount of space.  
           [0004]    For the reasons stated above and for other reasons stated below which will become apparent to those skilled in the art upon reading and understanding the present specification, there is a need in the art for an efficient inductor that can operate at relatively high frequencies.  
         SUMMARY  
         [0005]    The above-mentioned problems with existing inductors and other problems are addressed by the present invention and will be understood by reading and studying the following specification.  
           [0006]    In one embodiment, a magnetic thin film inductor is disclosed. The magnetic thin film inductor includes a plurality of elongated conducting regions and magnetic material. The plurality of elongated conducting regions are positioned parallel with each other and at a selected spaced distance apart from each other. The magnetic material encases the plurality of conducting regions, wherein when currents are applied to the conducting regions, current paths in each of the conducting regions cause the currents to generally flow in the same direction thereby enhancing mutual inductance.  
           [0007]    In another embodiment, a magnetic thin film inductor is disclosed that comprises a conducting member having one or more turns and portions of magnetic material. The portions of magnetic material encase the one or more turns of the conducting member. Moreover, each portion of magnetic material encases portions of the one or more turns that conduct current in a substantially uniform direction.  
           [0008]    In another embodiment, a magnetic thin film inductor comprises a conductive member and magnetic material. The conductive member is formed into one or more coils. The magnetic material is formed to encase the one or more coils. The magnetic material has a central opening. The one or more coils extend around the central opening. The magnetic material further has a plurality of gaps.  
           [0009]    In another embodiment, a method of forming a magnetic thin film inductor is disclosed. The method comprises forming a first layer of magnetic material on a substrate. Forming a layer of conducting material overlaying the first layer of magnetic material. Patterning the conductive layer to form two or more generally parallel conducting members, wherein the two or more conductive members are positioned proximate each other. Forming a second layer of magnetic material overlaying the conductive members and portions of the first layer of magnetic material, wherein the conductive members are encased by the first and second layers of magnetic material.  
           [0010]    In another embodiment, a method of forming a magnetic thin film inductor is disclosed. The method comprises forming a first layer of magnetic material on a substrate, forming a layer of conductive material overlaying the first layer of magnetic material and patterning the conductive material to form one or more turns of a conductive member in a predefined shape. Forming a second layer of magnetic material overlaying the one or more turns of the conductive member and the first layer of magnetic material. Removing portions of the first and second layers of magnetic material to form a central opening to the substrate, wherein the first and second layers of magnetic material encase the one or more conducting members that extend around the central opening.  
           [0011]    In another embodiment, a method of operating a magnetic thin film inductor in an integrated circuit is disclosed. The method comprises coupling a current to a plurality of conducting members positioned generally parallel with each other and encased by sections of magnetic material, wherein each section of magnetic material encases a plurality of conducting members in which current is flowing in generally the same direction. 
       
    
    
     BRIEF DESCRIPTION OF THE DRAWINGS  
       [0012]    The present invention can be more easily understood and further advantages and uses thereof more readily apparent, when considered in view of the description of the preferred embodiments and the following figures in which:  
         [0013]    [0013]FIG. 1 is a perspective view of one embodiment of the present invention;  
         [0014]    [0014]FIG. 2 is a cross-sectional view of one embodiment of the present invention;  
         [0015]    [0015]FIG. 3 is a perspective view of one embodiment of the present invention;  
         [0016]    [0016]FIG. 4 is a cross-sectional view of one embodiment of the present invention;  
         [0017]    FIGS.  5 A- 5 G are cross-sectional views illustrating the formation of one embodiment of the present invention;  
         [0018]    [0018]FIG. 6 is a top view of one embodiment of a rectangular inductor of the present invention;  
         [0019]    [0019]FIG. 7 is a top view of another embodiment of a rectangular inductor of the present invention;  
         [0020]    [0020]FIG. 8 is a top view of yet another embodiment of a rectangular inductor of the present invention;  
         [0021]    [0021]FIG. 9 is a top view of one embodiment of a square coil inductor of the present invention;  
         [0022]    [0022]FIG. 10 is a top view of an embodiment of a circular coil inductor of the present invention;  
         [0023]    [0023]FIG. 11 is a top view of an embodiment of an octagonal inductor of the present invention; and  
         [0024]    [0024]FIG. 12 is a top view of one embodiment of an arbitrary shaped coil inductor of the present invention. 
     
    
       [0025]    In accordance with common practice, the various described features are not drawn to scale but are drawn to emphasize specific features relevant to embodiments of the present invention. Reference characters denote like elements throughout figures and text.  
       DETAILED DESCRIPTION  
       [0026]    In the following detailed description of the preferred embodiments, reference is made to the accompanying drawings, which form a part hereof, and in which are shown by way of illustration specific preferred embodiments in which the inventions may be practiced. These embodiments are described in sufficient detail to enable those skilled in the art to practice the invention, and it is to be understood that other embodiments may be utilized and that logical, mechanical and electrical changes may be made without departing from the spirit and scope of the present invention. The following detailed description is, therefore, not to be taken in a limiting sense, and the scope of the present invention is defined only by the claims and equivalents thereof.  
         [0027]    Embodiments of the present invention relates to embodiments of a magnetic thin film inductors with improved inductance and quality factor. In the following description, the term substrate is used to refer generally to any structure on which integrated circuits are formed, and also to such structures during various stages of integrated circuit fabrication. This term includes doped and undoped semiconductors, epitaxial layers of a semiconductor on a supporting semiconductor or insulating material, combinations of such layers, as well as other such structures that are known in the art. Terms of relative position as used in this application are defined based on a plane parallel to the conventional plane or working surface of a wafer or substrate, regardless of the orientation of the wafer or substrate. Terms, such as “on”, “side”, “higher”, “lower”, “over,” “top” and “under” are defined with respect to the conventional plane or working surface being on the top surface of the wafer or substrate, regardless of the orientation of the wafer or substrate.  
         [0028]    An embodiment of a thin film inductor  300  of the present invention is illustrated in FIG. 1. In this embodiment, elongate conducting members  302  (which are positioned parallel with each other and are a selected distance apart from each other) are encased with a magnetic material  304 . In operation each of the conducting members conduct current in the same direction. The magnetic flux  306  created in the magnetic material  304  in response to the currents is illustrated in FIG. 2. FIG. 2 is a cross-sectional illustration of thin film inductor  300 . In particular, FIG. 2 illustrates the current flowing into each of the conducting members  302  and a line of magnetic flux  306  created in response to the currents. In this embodiment, a magnetic flux line created by one of the conducting members  302  combines with the magnetic flux lines of adjacent conducting members  302  to enhance the mutual inductance of the magnetic thin film inductor  300 .  
         [0029]    Another embodiment of a thin film inductor  500  is illustrated in FIG. 3. This embodiment includes conducting members  502  and a magnetic material  504  encasing the conducting members  502 . The magnetic material  504  has gaps  506  (or cutout sections  506 ) that form sections of magnetic material  504 . The gaps reduce eddy currents in the magnetic material  504 . As illustrated, the gaps  506  are positioned generally perpendicular to the path of the conducting members  502 . Stated another way, the conducting members enter and exit each gap generally perpendicular to edges of the sectioned magnetic material  504 . As in the previous embodiment, the currents flowing in the same direction in the conducting members  502  creates magnetic flux lines that enhance the mutual inductance of the magnetic thin film inductor  500 . In another embodiment of the thin film inductor  600 , a layer of insulator  606  (or dielectric  606 ) is positioned between conducting members  602  and an encasing magnetic material  604 . This is illustrated in the cross-section view of FIG. 4. In one embodiment, silicon dioxide is used as the insulator. Although, adding the insulting layer  606  slightly decreases inductance, eddy current loss will also decrease and the overall quality factor of the magnetic thin film inductor  600  will be increased.  
         [0030]    One method of forming a magnetic thin film inductor  700  is illustrated in FIGS.  5 (A-G). Referring to FIG. 5A, this method starts with a clean substrate  702  (silicon oxide or silicon). A first layer of magnetic material  704  is deposited on a working surface  701  of the substrate  702  as illustrated in FIG. 5B. Next a first insulation layer  706  is deposited overlaying the first layer of magnetic material  704 . This is illustrated in FIG. 5C. A conductive layer is then formed overlaying the first insulation layer  706 . The conductive layer is patterned to form the conductive members  708 . This is illustrated in FIG. 5D. In one embodiment, the conductive members  708  is shaped by masking, deposition, and/or etching. Referring to FIG. 5E, a second insulting layer  710  is deposited overlaying the conductive members  708  and portions of the first insulation layer  706 . Portions of second insulation layer  710  and the first insulation layer  706  are etched away as illustrated in FIG. 5F. A second layer of magnetic material  712  is then deposited overlaying the second insulation layer  710  and portions of the first layer of magnetic material  704 . This forms magnetic thin film inductor  700  of FIG. 5G. In addition, the first and second layers of magnetic film  704  and  712  can be a single layer of a magnetic material (as illustrated above) or a multi-layer structure with at least two different types of magnetic material. These magnetic materials are stacked alternatively to achieve the optimized effect.  
         [0031]    As stated above, embodiments of the present invention are applied to inductive devices wherein currents are flowing in relatively straight conducting paths and wherein the conducting material that makes up the conducting paths are encased with magnetic material. However, embodiments of the present invention can also be applied to spiral inductors of different shapes. For example, referring to FIG. 6, an embodiment of a rectangular spiral inductor  800  of the present invention is illustrated. As illustrated, this embodiment includes conducting member  802  formed in the shape of a rectangle. The conducting member  802  is encased with sections of magnetic material  804 ,  806 ,  808 . As illustrated, each section of magnetic material  804 ,  806  and  808  encases a portion of the conducting member in which the current travels in a substantially uniform direction. Moreover, as illustrated, corner portions (portions that curve or bend) of the conducting member  802  are not encased with magnetic material. This significantly reduces the loss due to eddy currents.  
         [0032]    Another embodiment of a spiral rectangular inductor  900  is illustrated in FIG. 7. In this embodiment, the conducting material  902  is formed in a spiral of two paths (two turns or two coils) with sections of magnetic material  904 ,  906  and  908  selectively positioned. Each magnetic material section  904 ,  906  and  908  is encased around portions of the conducting member  902  wherein current flows in the same direction. Although, FIG. 7 only shows the conducting member as being formed in two turns, it will be understood that more than two turns could be formed depending on the amount of inductance desired and that the present invention is not limited to two turns. In another embodiment of a spiral rectangular inductor  1000 , sections of magnetic material  1004 ,  1006  and  1008  are further partitioned into smaller sections. This is illustrated in FIG. 8. By further sectioning the magnetic material  1004 ,  1006  and  1008  eddy currents are further reduced. As illustrated in FIG. 8, the conductors  1002  provide substantially parallel current paths in which current (i) flows in substantially uniform directions where the conductors are encased by the sections of magnetic material  1004 ,  1006  and  1008 .  
         [0033]    Referring to FIG. 9, a square spiral inductor  1100  of one embodiment of the present invention is disclosed. This embodiment includes a conducting member  1102  having two turns and four sections of magnetic material  1104 ,  1106 ,  1108  and  1110  encasing relatively parallel sections of the conducting member  11102 . Although not shown, the sections of magnetic material  11104 ,  1106 ,  1108  and  1110  can each be further sectioned to further reduce the eddy currents, similar to what was illustrated in FIG. 8. Moreover, the number of turns can vary to achieve a desired inductance.  
         [0034]    The embodiments of the present invention can also be applied to other shapes. For example, a circular embodiment of a spiral inductor  1200  is illustrated in FIG. 10. In this embodiment, pie shaped sections of magnetic material  1204  selectively encase conductive member  1202 . As with the other embodiments of the present inventions, in this embodiment each section of magnetic material  1204  encases a section of the conductive member  1202  wherein current is flowing in a substantially uniform direction. Another example of an embodiment of an inductor  1300  is an octagon shape as illustrated in FIG. 11. In this embodiment, pie shaped sections of magnetic material  1304  selectively encase sections of conductive member  1302 .  
         [0035]    Moreover, the present invention can be applied to other shapes including generally regular polygonal shapes such as square, octagonal, hexagonal and circular. In addition, embodiments of the present invention can be applied to arbitrary shapes. For example, referring to FIG. 12, yet another embodiment of an inductor  1400  of the present invention is illustrated. In this embodiment, sections of magnetic material  1404  are selectively positioned to encase sections of conducting member  1402  that are positioned in an arbitrary shape. As with the previous embodiments of the present invention, each magnetic material section  1404  is selectively placed so it encases sections of the conducting member  1400  wherein current in the conducting member  1402  travels in a substantially uniform direction. Moreover, as with the previous embodiments, edges of each section of the magnetic material in which the conducting member  1402  enters and exits are generally perpendicular to a path of the conducting member  1402 .  
         [0036]    In forming embodiments of the present invention, layers of magnetic material are first deposited and then patterned to encase selected portions of the conducting members. In each of the embodiments of an inductor in a spiral formation, a central opening in the layers of magnetic material is formed. This is illustrated in FIGS.  6 - 12 . For example, the conducting member  1402  of FIG. 12 encircles the central opening  1406 . This design allows each section of magnetic material  1404  to encase only a portion of the conducting member  1402  in which current is flowing in relatively the same direction.  
         [0037]    The embodiments of the present invention as illustrated in FIGS.  1 - 12  can employ different types of magnetic material. For example, embodiments of the present invention use soft magnetic materials such as FeNi, FeSiAl and CoNbZr. However, inductors with relatively high ferromagnetic frequency can be achieved in the embodiments of the present invention using magnetic thin films having nano particles that form high resisitivity. Examples of magnetic thin films with high resistivity are FeBN, FeBO, FeBC, FeCoBF, FeSiO, FeHfO, FeCoSiBO, FeSmO, FeAIBO, FeSmBO, FeCoSmO, FeZrO, FeNdO, FeYO, FeMgO, CoFeHfO, CoFeSiN, CoAIO, CoAIPdO, CoFeAlO, CoYO, FeAlO and CoFeBSiO. A typical magnetic film thickness for the present invention is around 0.1 to 1.5 micrometers and a typical insulator thickness is about 1 micrometer. As stated above, some embodiments of the present invention use a combination of layers of different magnetic material to form a finished magnetic layer having desired properties.  
         [0038]    In addition, embodiments of the present invention use nano particles of Fe that are introduced into a matrix of Al 2 O 3  to form the magnetic material. The nano particles create higher resistivity which helps to reduce eddy currents. Moreover, with the use of the FeAlO, experiments have shown a ferromagnetic resonance frequency of approximately 9.5 GHz for a thin film thickness (the thickness of the magnetic material) of about 0.15 micometers can be achieved. In addition, the total length of the spiral embodiments is approximately 1 mm. The ferromagnetic resonance frequency of this embodiment as well as the physical length of this embodiment is within the range desired for wireless communication applications.  
         [0039]    Although specific embodiments have been illustrated and described herein, it will be appreciated by those of ordinary skill in the art that any arrangement, which is calculated to achieve the same purpose, may be substituted for the specific embodiment shown. This application is intended to cover any adaptations or variations of the present invention. Therefore, it is manifestly intended that this invention be limited only by the claims and the equivalents thereof.