Abstract:
Integrated circuit inductors achieve high quality factors by replacing a single conductive strand having a first cross-sectional area with a plurality of conductive strands having a combined second cross-sectional area that is smaller than the first cross-sectional area and a combined periphery that is greater than a periphery of the single conductive strand. The dimensions of the plurality of the conductive strands are greater than a skin depth at a desired operating frequency. This results in slightly higher dc resistance, but significantly lower ac resistance. The conductive strands are electrically coupled in parallel and extend side-by-side across an integrated circuit substrate. These strands include a plurality of crossing strand segments that enable the respective strand to be repeatedly transposed from one side of the plurality of strands to another side of the plurality of strands without electrical interruption. In some embodiments, the plurality of strands extend side-by-side in a horizontal plane that is at least substantially parallel to a surface of the integrated circuit substrate. In these embodiments, the crossing strand segments may be treated as cross-over/under strand segments.

Description:
FIELD OF THE INVENTION 
     The present invention relates to integrated circuit devices and, more particularly, to integrated circuit devices having passive energy storage elements thereon. 
     BACKGROUND OF THE INVENTION 
     Conventional integrated circuit device fabrication methods have typically not included techniques to form high quality factor (Q) inductors on integrated circuit substrates. For microwave and wireless communication applications, it may be advantageous to integrate high-Q inductors on bulk silicon, silicon-on-insulator (SOI) or silicon-on-sapphire (SOS) substrates. The quality factor (Q) is expressed by the equation Q=ωL/R, where ω represents resonant frequency, L represents inductance and R represents resistance. Attempts to fabricate high-Q inductors have typically been limited by the fact that conventional wiring interconnect technologies frequently result in conductors and vias having relatively high series resistance when summed together along the length of the inductor. Moreover, integrated circuit inductors may generate magnetic fields that are strongly coupled to an underlying semiconductor substrate, which may act as a lossy conductor having a large skin depth. As will be understood by those skilled in the art, such strong coupling may generate eddy currents within the substrate and these currents act in opposition to currents established in the inductor. Accordingly, strong coupling between an inductor and a semiconductor substrate may operate to reduce the inductance L of the inductor and cause energy loss. 
     Attempts have been made to fabricate integrated circuit inductors having high quality factors. One such attempt is disclosed in U.S. Pat. No. 6,114,937 to Burghartz et al., which is entitled “Integrated Circuit Spiral Inductor.” In particular, the &#39;937 patent discloses a spiral inductor having a spiral metal coil that is deposited into a trench formed in a dielectric layer, which extends over a substrate. The metal coil is enclosed in ferromagnetic liner and cap layers, and is connected to an underpass contact through a metal filled via in the dielectric layer. The spiral inductor also includes ferromagnetic core lines surrounded by the metal spiral coil (see, e.g., &#39;937 patent, FIG. 13). Another attempt is disclosed in U.S. Pat. No. 5,446,311 to Ewen et al., which is entitled “High-Q Inductors in Silicon Technology Within Expensive Metallization.” In particular, the &#39;311 patent discloses an inductor structure that is formed using multiple metallization levels in a conventional integrated circuit technology in which inductor turns utilize the multiple levels to reduce the inductor resistance (see, e.g., &#39;311 patent, FIG. 3). U.S. Pat. Nos. 5,892,425, 5,936,299, 6,160,303 and 6,348,391 also disclose a variety of integrated circuit inductors. 
     Notwithstanding these attempts to develop inductors that are suitable for fabrication on integrated circuit substrates, there continues to be a need for inductors having high quality factors. There also continues to be a need for inductors that may be fabricated using process techniques that yield inductors having highly reproducible quality factors. 
     SUMMARY OF THE INVENTION 
     Integrated circuit inductors according to embodiments of the present invention achieve high quality factors by replacing a single conductive strand having a first cross-sectional area with a plurality of conductive strands having a combined second cross-sectional area that is smaller than the first cross-sectional area and a combined periphery that is greater than a periphery of the single conductive strand. The dimensions of the plurality of the conductive strands are greater than a skin depth at a desired operating frequency. In particular, embodiments of the present invention include a plurality of strands of conductive traces (e.g., metal traces) that are electrically coupled in parallel and extend side-by-side across an integrated circuit substrate. This substrate may be, for example, a bulk semiconductor substrate (e.g., silicon chip), an silicon-on-insulator (SOI) substrate or a silicon-on-sapphire (SOS) substrate. Each of the plurality of strands also includes a plurality of crossing strand segments that enable the respective strand to be repeatedly transposed from one side of the plurality of strands to another side of the plurality of strands without electrical interruption. In some embodiments, the plurality of strands extend side-by-side in a horizontal plane that is at least substantially parallel to a surface of the integrated circuit substrate. In these embodiments, the crossing strand segments may be treated as crossover/under strand segments. In other embodiments, the plurality of strands extend side-by-side in a vertical plane that is at least substantially orthogonal to a surface of said integrated circuit substrate. According to preferred aspects of these embodiments, the plurality of strands are electrically insulated from each other over at least a majority of their length. 
     Each of the plurality of strands of conductive traces may include a corresponding plurality of primary strand segments that are electrically linked together end-to-end by a corresponding plurality of the crossing strand segments. The primary strand segments and the crossing strand segments may be formed on different levels of metallization (e.g., metal N and metal N+1 in a process having at least two levels of metallization). To provide electrical continuity, the primary strand segments and the crossing strand segments for each respective strand are electrically coupled together by conductive vias that extend through an electrically insulating layer disposed between the different levels of metallization. 
     In other embodiments, an inductor having a high quality factor includes an integrated circuit substrate and a plurality of first strands of conductive traces that are electrically coupled in parallel and extend side-by-side across the integrated circuit substrate. Each of the plurality of first strands includes a respective plurality of crossing strand segments at a first level of metallization that enable the respective first strand to be repeatedly transposed from one side of the plurality of first strands to another side of the plurality of first strands without electrical interruption. Each of the plurality of first strands also includes a corresponding plurality of primary strand segments that are electrically linked together end-to-end by a corresponding plurality of the crossing strand segments. The crossing and primary strand segments associated with each of the plurality of first strands may be electrically coupled together by conductive vias that extend through an electrically insulating layer disposed between the different levels of metallization. A plurality of second strands of conductive traces are also provided. These second strands are electrically coupled in parallel and extend side-by-side across the integrated circuit substrate. In some embodiments, these second strands may extend directly above or below the first strands. Each of the plurality of second strands includes a respective plurality of jumper strand segments at a second level of metallization that enable the respective second strand to electrically jump a plurality of the crossing strand segments associated with the plurality of first strands. These jumper strand segments may be contiguous with the primary strand segments that make up the first strands. 
     According to still further embodiments of the present invention, an inductor includes a semiconductor substrate and a plurality of strands of conductive traces that are electrically coupled in parallel and extend side-by-side across the semiconductor substrate in a horizontal plane that is at least substantially parallel to a surface of the semiconductor substrate. In these embodiments, each of the plurality of strands includes a plurality of crossing strand segments that enable the respective strand to be repeatedly transposed from one side of the plurality of strands to another side of the plurality of strands without electrical interruption. To reduce lossy eddy currents in the substrate, a plurality of alternating N-well and P-well regions are disposed side-by-side therein. These well regions, which extend underneath the plurality of strands, are preferably elongate regions that extend in a direction at least substantially orthogonal to the plurality of strands. 
    
    
     BRIEF DESCRIPTION OF THE DRAWINGS 
     FIG. 1A is a plan view of a multi-strand inductor according to an embodiment of the present invention. 
     FIG. 1B is a cross-section view of the inductor of FIG. 1A, taken along lines  1 B- 1 B′. 
     FIG. 1C is a cross-section view of the inductor of FIG. 1A, taken along lines  1 C- 1 C′. 
     FIG. 1D is a cross-section view of the inductor of FIG. 1A, taken along lines  1 D- 1 D′. 
     FIG. 1E is a cross-section view of the inductor of FIG. 1A, taken along lines  1 E- 1 E′. 
     FIG. 1F is a plan view of a multi-strand inductor according to another embodiment of the present invention. 
     FIG. 2 is a plan view of a multi-strand inductor according to another embodiment of the present invention. 
     FIG. 3A is a plan view of an inductor having multiple strands of conductive traces that are substantially concentric, according to another embodiment of the present invention. 
     FIG. 3B is a plan view of primary strand segments that can be used to partially define the inductor of FIG.  3 A. 
     FIG. 3C is a plan view of crossing strand segments that can be used to facilitate transposition of the conductive traces illustrated by FIG.  3 B. 
     FIG. 3D is a plan view of conductive vias that can be used to interconnect the crossing strand segments and primary strand segments illustrated by FIGS. 3B and 3C. 
     FIG. 4A is a plan view of alternating N-type and P-type well regions that operate to reduce eddy currents within a semiconductor substrate when used in conjunction with an inductor according to an embodiment of the present invention. 
     FIG. 4B is an enlarged plan view of a highlighted portion of FIG.  4 A. 
    
    
     DESCRIPTION OF PREFERRED EMBODIMENTS 
     The present invention now will be described more fully herein with reference to the accompanying drawings, in which preferred embodiments of the invention are shown. This invention may, however, be embodied in many different forms and should not be construed as being limited to the embodiments set forth herein; rather, these embodiments are provided so that this disclosure will be thorough and complete, and will fully convey the scope of the invention to those skilled in the art. Like reference numerals refer to like elements throughout. 
     Referring now to FIGS. 1A-1E, an integrated circuit inductor  10  according to one embodiment of the present invention will be described. The illustrated inductor  10  utilizes two levels of metallization, however, inductors according to alternative embodiments of the present invention may utilize a greater number of metallization layers. The regions of the inductor  10  associated with first and second levels of metallization are illustrated by reference numerals  10   a  and  10   b , respectively. In a fabrication process requiring two or more levels of metallization, the first level of metallization may be patterned below or above the second level of metallization. The first and second levels of metallization may be consecutive levels of metallization or one or more intervening levels of metallization may also be present between the first and second levels of metallization. For purposes of discussion herein, the first level of metallization (M 1 ) will be treated as the lowest level of metallization utilized in the fabrication process and the second level of metallization (M 2 ) will be treated as the next higher level of metallization relative to the first level of metallization (M 1 ). 
     The inductor  10  of FIGS. 1A-1E includes a plurality of first strands of conductive traces that extend side-by-side across an integrated circuit substrate. In some embodiments, this integrated circuit substrate may include a bulk semiconductor substrate layer  14  of predetermined conductivity type (e.g., P-type, N-type), as shown in FIGS. 1B-1E. The plurality of first strands of conductive traces are illustrated as five (5) strands  1 - 5  that are electrically coupled in parallel. Inductors having more or less strands may also be used. A portion of the first strand  1  is illustrated as including two primary strand segments at the second level of metallization M 2  and one crossing strand segment at the first level of metallization M 1 . These two primary strand segments are shown as  1   a  and  1   c - 1   g  on the right hand side of FIG.  1 A. The crossing strand segment is illustrated as a cross-under strand segment  1   b ′ on the left side of FIG.  1 A. Conductive vias Al and A 2  electrically connect strand segments  1   a  and  1   c  (at M 2 ) to opposite ends of the cross-under stand segment  1   b ′ (at M 1 ). A portion of the second strand  2  is illustrated as including two primary strand segments at the second level of metallization M 2  and one crossing strand segment at the first level of metallization M 1 . These two primary strand segments are shown as segments  2   a - 2   c  and  2   e - 2   g  on the right hand side of FIG.  1 A. The crossing strand segment is illustrated as a cross-under strand segment  2   d ′ on the left side of FIG.  1 A. Conductive vias A 1  and A 2  electrically connect strand segments  2   c  and  2   e  (at M 2 ) to opposite ends of the cross-under stand segment  2   d ′ (at M 1 ). A portion of the third strand  3  is illustrated as including two primary strand segments at the second level of metallization M 2  and one crossing strand segment at the first level of metallization M 1 . These two primary strand segments are shown as segments  3   a - 3   e  and  3   g  on the right hand side of FIG.  1 A. The crossing strand segment is illustrated as a cross-under strand segment  3   f ′ on the left side of FIG.  1 A. Conductive vias A 1  and A 2  electrically connect strand segments  3   e  and  3   g  (at M 2 ) to opposite ends of the cross-under stand segment  3   f ′ (at M 1 ). A portion of the fourth strand  4  is illustrated as including a primary strand segment at the second level of metallization M 2 . This primary strand segment is shown as segments  4   a - 4   g  on the right hand side of FIG. 1A. A portion of the fifth strand  5  is illustrated as including a primary strand segment at the second level of metallization M 2 . This primary strand segment is shown as segments  5   a - 5   g  on the right hand side of FIG.  1 A. 
     The inductor  10  of FIGS. 1A-1E also includes a plurality of second strands of conductive traces that extend side-by-side across the integrated circuit substrate. The plurality of second strands of conductive traces are illustrated as five (5) strands  1 ′- 5 ′ that are electrically coupled in parallel. A portion of the first strand  1 ′ is illustrated as including primary strand segments  1   a ′,  1   c ′ and  1   e ′ and crossing strand segment  1   b ′ at the first level of metallization M 1 , and jumper strand segment  1   d  at the second level of metallization M 2 . A portion of the second strand  2 ′ is illustrated as including primary strand segments  2   a ′,  2   c ′ and  2   e ′ and crossing strand segment  2   d ′ at the first level of metallization M 1  and jumper strand segment  2   b  at the second level of metallization M 2 . A portion of the third strand  3 ′ is illustrated as including primary strand segments  3   a ′,  3   c ′,  3   e ′ and  3   g ′ and crossing strand segment  3   f ′ at the first level of metallization M 1  and jumper strand segments  3   b  and  3   d  at the second level of metallization M 2 . A portion of the fourth strand  4 ′ is illustrated as including primary strand segments  4   a ′,  4   c ′,  4   e ′ at the first level of metallization M 1  and jumper strand segments  4   b  and  4   d  at the second level of metallization M 2 . A portion of the fifth strand  5 ′ is illustrated as including primary strand segments  5   a ′,  5   c ′,  5   e ′ at the first level of metallization M 1  and jumper strand segments  5   b  and  5   d  at the second level of metallization M 2 . 
     FIGS. 1B-1E illustrate cross-sectional views of the inductor of FIG. 1A, taken along respective cross-sectional lines ( 1 B- 1 B′ to  1 E- 1 E′). In FIG. 1B, the crossing segment  2   d ′ is illustrated as being disposed on a first electrically insulating layer  16 . This crossing segment  2   d ′ is electrically coupled to the primary segments  2   c  and  2   e  by a pair of conductive vias, shown as A 1  and A 2 . These primary segments  2   c  and  2   e  are patterned on a second electrically insulating layer  18 . The illustrated portions of the primary segments include jumper strand segments  1   d ,  5   d ,  4   d ,  3   d . In FIG. 1C, the conductive vias B 1 , C 1 , D 1  and E 1  are illustrated as joining the segments  1   c ′,  5   c ′,  4   c ′ and  3   c ′ to the jumper strand segments  1   d ,  5   d ,  4   d ,  3   d . The segments  2   c  and  2   c ′ are also illustrated In FIG. 1D, the segments  1   c - 5   c  associated with the second level of metallization (M 2 ) are illustrated as extending opposite the segments  1   c - 5   c  associated with the first level of metallization (M 1 ). In FIG. 1E, the conductive vias B 2 -E 2  are illustrated as electrically connecting segments  1   e ′ and  3   e ′- 5   e ′ at the first level of metallization (M 1 ) to the jumper strand segments  1   d  and  3   d - 5   d  at the second level of metallization (M 2 ). 
     Accordingly, the inductor of FIGS. 1A-1E includes a semiconductor substrate layer  14  and a plurality of first strands of conductive traces  1 - 5  that are electrically coupled in parallel and extend side-by-side across the substrate layer  14 . Each of the plurality of first strands of conductive traces  1 - 5  includes a respective plurality of crossing strand segments at a first level of metallization (see, e.g.,  1   b ′,  2   d ′ and  3   f ′). These crossing strand segments enable each respective first strand to be repeatedly transposed from one side of the plurality of first strands to another side of the plurality of first strands without electrical interruption. For example, the crossing strand segment  1   b ′ enables the strand  1  to be transposed from one side of the plurality of first strands  1 - 5  (shown as the right side) to another side of the plurality of first strands  1 - 5  (shown as the left side) without electrical interruption. A plurality of second strands of conductive traces  1 ′- 5 ′ are also provided. These second strands of conductive traces  1 ′- 5 ′ are also electrically coupled in parallel and extend side-by-side across the substrate  14  . Each of the plurality of second strands of conductive traces  1 ′- 5 ′ includes a plurality of jumper strand segments at a second level of metallization. For example, strand  5 ′ includes jumper strand segments  5   b ,  5   d  and  5   f . These jumper strand segments are contiguous with portions of the overlapping strand  5 . In this manner, strands  5  and  5 ′ are electrically connected together at multiple locations along their length. 
     Referring now to FIG. 1F, a multi-strand inductor  12  according to another embodiment of the present invention includes multiple strands  1 ″- 5 ″ that are formed at a second level of metallization (M 2 ). Like the embodiment of FIGS. 1A-1E, these strands  1 ″- 5 ″ are electrically coupled in parallel and extend side-by-side across an integrated circuit substrate. Crossing strand segments, including segments  1   i - 3   i  and similar segments (not shown) on the left side of FIG. 1F, enable each respective strand to be repeatedly transposed from one side of the plurality of strands  1 ″- 5 ″ to another side of the plurality of strands  1 ″- 5 ″ without electrical interruption. 
     FIG. 2 illustrates a multi-strand inductor  20  according to another embodiment of the present invention. In this embodiment, a plurality of strands of conductive traces are provided. These strands of conductive traces are electrically coupled in parallel and extend side-by-side across a substrate. Each of the plurality of strands includes a plurality of crossing strand segments that enable the respective strand to be repeatedly transposed from one side of the plurality of strands to another side of the plurality of strands without electrical interruption. The regions of the inductor  20  associated with first and second levels of metallization are illustrated by reference numerals  20   a  and  20   b , respectively. A first strand  1  is illustrated as including primary strand segments  1   a  and  1   c - 1   e  at the second level of metallization (M 2 ) and crossing strand segment  1   b ′ at the first level of metallization (M 1 ). A second strand  2  is illustrated as including primary strand segments  2   a - 2   c  and  2   e  at the second level of metallization (M 2 ) and crossing strand segment  2   d ′ at the first level of metallization (M 1 ). These first and second strands  1  and  2  constitute a plurality of strands that are periodically transposed with each other from one side of the pair of strands  1 - 2  to an opposite side of the pair of strands  1 - 2 . A third strand  3  is illustrated as including primary strand segments  3   a  and  3   d - 3   e  at the second level of metallization (M 2 ) and crossing strand segment  3   b ′ at the first level of metallization (M 1 ). A fourth strand  4  is illustrated as including primary strand segments  4   a - 4   c  and  4   e  at the second level of metallization (M 2 ) and crossing strand segment  4   d ′ at the first level of metallization (M 1 ). These third and fourth strands  3  and  4  also constitute a separate plurality of strands that are periodically transposed with each other from one side of the pair of strands  3 - 4  to an opposite side of the pair of strands  3 - 4 . 
     Referring now to the right side of FIG. 2, a first pair of strands  1 ′ and  2 ′ and a second pair of strands  3 ′ and  4 ′ are illustrated. The strand  1 ′ includes primary strand segments  1   a ′,  1   c ′ and  1   e ′ and crossing strand segment  1   b ′ at level M 1  and jumper strand segment  1   d  at level M 2 . The strand  2 ′ includes primary strand segments  2   a ′,  2   c ′ and  2   e ′ and crossing strand segment  2   d ′ at level M 1  and jumper strand segment  2   b  at level M 2 . The strand  3 ′ includes primary strand segments  3   a ′,  3   c ′ and  3   e ′ and crossing strand segment  3   b ′ at level M 1  and jumper strand segment  3   d  at level M 2 . The strand  4 ′ includes primary strand segments  4   a ′,  4   c ′ and  4   e ′ and crossing strand segment  4   d ′ at level M 1  and jumper strand segment  4   b  at level M 2 . 
     Referring now to FIGS. 3A-3D, an inductor  30  according to another embodiment of the present invention will be described. This inductor  30 , which is similar to the inductor embodiment  12  of FIG. 1F, includes a plurality of primary strand segments, shown as  32   a ,  32   b  and  32   c , that are substantially concentric. Crossing and jumper strand segments are also provided to enable the transposition of the primary strand segments  32   a ,  32   b  and  32   c . As illustrated best by FIG. 3B, the primary strands  32   a ,  32   b  and  32   c  are patterned at a first level of metallization (M 1 ). In FIG. 3C, the crossing strand segments are identified by the reference numbers  32   a ′,  32   b ′ and  32   c ′ and the jumper strand segments are identified by the reference numbers  32   a ″,  32   b ″ and  32   c ″. These crossing and jumper strand segments may be formed at a second level of metallization (M 2 ). These primary, crossing and jumper strand segments are electrically connected together by conductive vias. These conductive vias are illustrated as Va, Vb or Vc in FIG. 3D, depending on whether the via is associated with a first strand (segments  32   a - 32   a ″), a second strand (segments  32   b - 32   b ″) or a third strand (segments  32   c - 32   c ″). 
     In FIG. 4A, a plan view of alternating N-type and P-type well regions  40  is provided. These alternating well regions provide a high resistance path in a semiconductor substrate (e.g., bulk semiconductor substrate). This high resistance path operates to reduce eddy currents within a semiconductor substrate when used in conjunction with an inductor according to an embodiment of the present invention. An exemplary inductor may include a plurality of primary strand segments  42  that are concentrically arranged. These N-type and P-type well regions are preferably elongate regions that extend in a lengthwise direction. This lengthwise direction is at least substantially orthogonal (e.g., ≧45°) to the plurality of primary strand segments. In FIG. 4B, which represents an enlarged plan view of a portion of the alternating regions illustrated by FIG. 4A, the P-type well regions are illustrated as being electrically coupled together at multiple locations. These P-type well regions may be formed within a deeper N-type well region. Eddy current losses can also be reduced by defining an inductor using uppermost levels of metallization that are relatively distant from the substrate. 
     In the drawings and specification, there have been disclosed typical preferred embodiments of the invention and, although specific terms are employed, they are used in a generic and descriptive sense only and not for purposes of limitation, the scope of the invention being set forth in the following claims.