Abstract:
A structure and method for implementing a precision inductive component within a high frequency integrated circuit is disclosed. The inductive component has a structure of multiple conductive layers dielectrically insulated from each other and located above an integrated circuit substrate. The inductive component comprises a spiral-like inductive layer made of a first conductive layer. Additionally, a number of additional ground planes, each patterned out of its own selected conductive layer to minimize an induced eddy current therein thus improving Q (quality factor) under high frequency operation, are employed with either a linear or a rotational offset amongst them to effect a corresponding amount of adjustment of an inductance value of the inductive component. A number of specific design cases are presented with their respective inductance and RF performance parameters.

Description:
FIELD OF THE INVENTION 
     The present invention relates generally to the field of data communication. More particularity, the present invention discloses a structure and a corresponding method of implementing an inductive component of accurate inductance value for optical communication circuits operating with an input clock speed of a few to 100 GHz/Sec where an accurate inductance value is often required to achieve a correspondingly accurate operating frequency. Thus, the present invention can be included into many circuits for the implementation of subsystem functions such as counters, timers, frequency multipliers and Phase Locked Loop (PLL) in an optical switch IC (Integrated Circuit) for optical communication. Additional related applications are: Optical communication at 2.48 Gbit/sec (OC48) and 40 Gbit/sec (OC768) data rate, Gigabit Ethernet, 10 Gigabit Ethernet, Blue Tooth technology (2.4 GHz) and wireless LAN (5.2 GHz). At such a high data rate, the hardware infrastructure for a multimedia information super highway is also enabled. 
     BACKGROUND OF THE INVENTION 
     Optical Fiber has been used in voice and data communication for some time now due to its high bandwidth and excellent signal quality resulting from its immunity to electromagnetic interference. The inherent optical data rate from a modulated single-mode laser beam travelling through an optical fiber is expected to well exceed 1000 Gbit/sec. 
     To keep up with the data rate of optical data communications, the associated signal processing IC (Integrated Circuit) need to operate in the multiple GHz (Gegahertz, 1 Gegahertz=10 9  cycles/sec) to hundreds of GHz range of clock frequency. To improve the performance parameters of such high speed circuits, the inclusion of inductive components properly designed for RF (Radio Frequency) operation, another type of stored-energy device in addition to the capacitive component, has become increasingly popular. For example, Yue et al described one type of on-chip spiral inductor with patterned ground shields for Si-Based RF IC&#39;s operating in a frequency range of 1-2 GHz. Here, a single ground plane was employed between a spiral inductor and Silicon substrate to increase the inductor Q (quality factor). Furthermore, the ground plane was patterned in a multiple-finger like structure with slots orthogonal to the inductor spiral to minimize an induced eddy current herein thus associated RF power loss (On-Chip Spiral Inductors with Patterned Ground Shields for Si-Based RF IC&#39;s, C. Patrick Yue et al, IEEE Journal of Solid-State Circuits, Vol. 33, NO. 5, May 1998). For another example, Zhou et al described monolithic transformers and their application in a differential CMOS RF low-noise amplifier where each of the monolithic transformers was implemented as a set of two coplanar, interwound spirals (Monolithic Transformers and Their Application in a Differential CMOS RF Low-Noise Amplifier, Jianjun J. Zhou et al, IEEE Journal of Solid-State Circuits, Vol. 33, NO. 12, December 1998). In U.S. Pat. No. 6,188,295 B1 dated Feb. 13, 2001, Tsai disclosed a multi-layered circuit with a top circuit interconnection layer and a lower patterned inductor layer sandwiched between two ground layers both located below the top circuit interconnection layer. By cutting through or partially notching certain micro-strips of the top circuit interconnection layer either the associated equivalent circuit capacitance is adjusted accordingly or a serially coupled inductance-capacitance circuit is formed. Regardless of these references, however, where a precise inductance value is required of the monolithic inductor for an application, for example an oscillator circuit having a precisely specified output frequency that is controlled by the monolithic inductor, there is a need of a simple systematic method whereby the monolithic inductor can be quickly implemented with low cost of development. 
     SUMMARY 
     The present invention is directed to a new design and method of implementing an inductive component within a high frequency integrated circuit having a structure of multiple conductive layers. 
     The first objective of this invention is for the inductive component to achieve an accurate, pre-determined inductance value. 
     A second objective of this invention is for the method of implementation of the inductive component to be simple, systematic, quick and low cost. 
     A third objective of this invention is for the method of implementation of the inductive component to be extendable to the implementation of a precision transformer component. 
     Other objectives, together with the foregoing are attained in the exercise of the invention in the following description and resulting in the embodiment illustrated in the accompanying drawings. 
    
    
     BRIEF DESCRIPTION OF DRAWINGS 
     The current invention will be better understood and the nature of the objectives set forth above will become apparent when consideration is given to the following detailed description of the preferred embodiments. For clarity of explanation, the detailed description further makes reference to the attached drawings herein: 
     FIG. 1 illustrates the cross section of an integrated circuit having a structure of multiple conductive layers; 
     FIG. 2A is a perspective illustration of a reference design of an inductive component wherein only one ground layer, with linear offset, is employed with an inductive layer to form the inductive component; 
     FIG.  2 B and FIG. 2C are the inductance and return loss characteristics for the design of FIG. 2A; 
     FIG. 3A is a perspective illustration of a first variation of the present invention design of an inductive component wherein two ground layers with linear offset, both located on the same side of an inductive layer, are employed with the inductive layer to form the inductive component; 
     FIG.  3 B and FIG. 3C are the inductance and return loss characteristics for the design of FIG. 3A; 
     FIG. 4A is a perspective illustration of a second variation of the present invention design of an inductive component wherein two ground layers with linear offset, each located on a different side of an inductive layer, are employed with the inductive layer to form the inductive component; 
     FIG.  4 B and FIG. 4C are the inductance and return loss characteristics for the design of FIG. 4A; 
     FIG. 5A is a perspective illustration of a third variation of the present invention design of an inductive component wherein three ground layers with linear offset, all located on the same side of an inductive layer, are employed with the inductive layer to form the inductive component; 
     FIG.  5 B and FIG. 5C are the inductance and return loss characteristics for the design of FIG. 5A; 
     FIG. 6A is a perspective illustration of a fourth variation of the present invention design of an inductive component wherein three ground layers with linear offset, surrounding an inductive layer, are employed with the inductive layer to form the inductive component; 
     FIG.  6 B and FIG. 6C are the inductance and return loss characteristics for the design of FIG. 6A; 
     FIG. 7A is a perspective illustration of a fifth variation of the present invention design of an inductive component wherein two ground layers with rotational offset, both located on the same side of an inductive layer, are employed with the inductive layer to form the inductive component; and 
     FIG.  7 B and FIG. 7C are the inductance and return loss characteristics for the design of FIG.  7 A. 
    
    
     DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS 
     In the following detailed description of the present invention, numerous specific details are set forth in order to provide a thorough understanding of the present invention. However, it will become obvious to those skilled in the art that the present invention may be practiced without these specific details. In other instances, well known methods, procedures, components, and circuitry have not been described in detail to avoid unnecessary obscuring aspects of the present invention. 
     Reference herein to “one embodiment” or an “embodiment” means that a particular feature, structure, or characteristics described in connection with the embodiment can be included in at least one embodiment of the invention. The appearances of the phrase “in one embodiment” in various places in the specification are not necessarily all referring to the same embodiment, nor are separate or alternative embodiments mutually exclusive of other embodiments. 
     FIG. 1 illustrates a cross section of an integrated circuit having an IC substrate SUBS  10  located beneath a structure of multiple conductive layers such as a Polysilicon conductive layer  20 , a metal-1 M1  31 , a metal-2 M2  32 , a metal-3 M3  33 , a metal-4 M4  34 , a metal-5 M5  35  and a metal-6 M6  36 . Typically, an TC, although not shown herein for simplicity, is built in near the top of the IC substrate SUBS  10 . The various conductive layers are insulated from each other with a corresponding number of dielectric layers. For example, the Polysilicon conductive layer  20  is insulated from the metal-1 M1  31  with a dielectric layer ILD of thickness 0.7 μm (10 6  meter), the metal-1 M1  31  is insulated from the metal-2 M2  32  with a dielectric layer IMD 1   a  plus IMD 1   b  and the metal-2 M2  32  is insulated from the metal-3 M3  33  with a dielectric layer IMD 2   a  plus TMD 2   b  (0.1 μm thick), etc. Finally, the metal-6 M6  36  is isolated from others with a dielectric layer PASS  1  plus a top dielectric layer PASS 2 . The corresponding pitch between adjacent metal layers is 1.33 μm as illustrated. With the availability of multiple conductive layers, in this case seven (7) including the Polysilicon conductive layer  20 , an inductive component, operating with an IC located on the IC substrate SUBS  10 , can be implemented in many ways and those will be presently illustrated. 
     FIG. 2A is a perspective illustration of a reference design, called CASE-Ref, commonly used in the art, of an inductive component comprising a spiral inductive coil  48  and a single first ground layer  60 . The spiral inductive coil  48  further comprises an inductive layer  50  shaped into a spiral-like geometry, a feed-through via  52   b  and a cross-over layer  52   a.  Furthermore, the first ground layer  60  is illustrated to be patterned into a multiple-finger like structure with slots orthogonal to the spiral inductive coil  48  to minimize an induced eddy current herein thus associated RF (Radio Frequency) power loss. It is remarked that, to minimize the induced loop current, the first ground layer  60  can be patterned into a variety of other geometries, for example a Swiss-cheese geometry with a plurality of embedded holes should work as well. Also, an cuter frame shorting all the fingers of the first ground layer  60  together is not shown here to avoid unnecessary obscuring details. Furthermore, for simplicity of illustration from now on, in all cases of design of the inductive component a trace TRC of width 8 m and a trace spacing TSP of 2 m will be used. As illustrated with three thick right-pointing arrows, in this case the inductive layer  50  is implemented with metal-4 M4  34 , the cross-over layer  52   a  is implemented with the metal-6 M6  36  and the first ground layer  60  is implanted with the metal-1 M1  31 . To simply and systematically adjust the inductance value of the inductive component, the present invention proposes that, in this ease, tho first ground layer  60  to be linearly offset, with respect to the spiral inductive coil  48 , in a plane parallel to the plane of the inductive layer  50 . This is illustrated with an x-axis and a yaxis located next to the first ground layer  60 . The corresponding change in inductance at a fixed frequency of 15 GHz, as a function of x-offset, with a y-offset =0, is illustrated in FIG.  2 B. 
     FIG. 2B shows that, while a smooth functional characteristics does happen, the corresponding total range of inductance change is very small. That is, a Relative Inductance Range (RIR) of only 
     
       
           RIR =( L   max   −L   min )/ L   max =2.8% 
       
     
     is generated and this is not very useful for practical design applications. Another important parameter of the inductive component under such a high operating frequency is called return loss, or symbolically S 11 . The return loss S 11  is well known in the art and, for example, was defined by Hayward (Introduction to Radio Frequency Design, Wes Hayward, W7ZOI, Chapter 4, P. 116-P. 120). To be a useful inductive component, its return loss S 11  vs. frequency characteristics around an operating center frequency must be a smooth, monotonic curve. Furthermore, at the center frequency, the higher the absolute magnitude of the return loss S 11  the better. Thus, FIG. 2C, the return loss characteristics for the reference design of FIG. 2A at offset x=0 and y=0, does exhibit an acceptable return loss S 11  characteristics of an absolute magnitude equal to 6.8 dB (deciBel) at 15 GHz. 
     FIG. 3A is a perspective illustration of a first variation, called CASE-A, of the present invention design of an inductive component comprising a spiral inductive coil  48  and two ground layers designated a first ground layer  60  and a second ground layer  62 . The two ground layers are both located on the same side of the spiral inductive coil  48 . Like before, the spiral inductive coil  48  further comprises an inductive layer  50  shaped into a spiral-like geometry, a feed-through via  52   b  and a cross-over layer  52   a . Also, the first ground layer  60  and the second ground layer  62  are patterned the same way, being a multiple-finger like structure with slots orthogonal to the spiral inductive coil  48  to minimize an induced loop current herein thus associated RF power loss. As illustrated with four thick right-pointing arrows, now the inductive layer  50  is implemented with metal-4 M4  34 , the cross-over layer  52   a  is implemented with the metal-6 M6  36 , the first ground layer  60  is implemented with the metal-1 M1  31  and the second ground layer  62  is implemented with the Polysilicon conductive layer  20 . Like before, to simply and systematically adjust the inductance value of the inductive component, the present invention proposes that, for CASE-A, the second ground layer  62  to be linearly offset, with respect to the spiral inductive coil  48 , in a plane parallel to the plane of the inductive layer  50 . This is illustrated with an x-axis and a y-axis located next to the second ground layer  62 . The corresponding change in inductance at a fixed frequency of 15 GHz, as a function of both an x-offset and a y-offset, is illustrated in FIG. 3B in the form of a three dimensional perspective plot of piece-wise linearized data. 
     FIG. 3B shows that, in addition to being a family of smooth functional characteristics, a corresponding RIR of around 8.5% that is significantly higher than CASE-Ref (2.8%) is generated and this should be useful for practical design applications. For example, a case where an inductance value of 630 picohenry is needed can be satisfied with, following the direction of a set of four dashed arrows, an offset combination of x=3.5 m and y=8 m. In the mask design phase of the inductive component the task of generating a set of identical ground planes with a systematically increasing amount of x- and y-offsets is quite easy with an expected design time of only about a half day. However, if one were to generate a set of gradually changing spiral geometry of the inductive layer  50  to result in a systematically changing inductance value the mask design phase would be quite tedious and it could take about a week. Additionally, the cost of making a complete mask set for an IC of 0.18 m geometry nowadays is around $300,000 and the subsequent IC processing of the mask set will take about 50 days. However, the cost of making only a mask change for a single conductive layer is only about $2,000 and the subsequent IC processing of the single conductive layer will only take a few days. Therefore, with the technique of the present invention a desired inductance value for the inductive component can be accurately realized with a small amount of time and cost for designing and implementation. 
     FIG. 3C shows the return loss S 11  for CASE-A at various offsets of the second ground layer  62 . The return loss S 11  characteristics are all acceptable with an absolute magnitude around 8 dB at 15 GHz that is significantly better than CASE-Ref (6.8 dB). Additionally, comparing with CASE-Ref, the employment of two ground planes, having an offset between them, between the spiral inductive coil  48  and the IC substrate SUBS  10  is expected to provide an additional advantage of higher level of shielding of radio frequency emission between the inductive component and an IC located on the IC substrate SUBS  10 . 
     FIG. 4A is a perspective illustration of a second variation, called CASE-B, of the present invention design of an inductive component comprising a spiral inductive coil  48  and two ground layers designated a first ground layer  60  and a second ground layer  62 . However, the two ground layers are now located on different sides of the spiral inductive coil  48 . As illustrated with four thick right-pointing arrows, the inductive layer  50  is implemented with the metal-4 M4  34 , the cross-over layer  52   a  is implemented with the metal-5 M5  35 , the first ground layer  60  is implemented with the metal-6 M6  36  and the second ground layer  62  is implemented with the metal-1 M1  31 . Here, the present invention proposes that the second ground layer  62  to be linearly offset with respect to the spiral inductive coil  48 . This is again illustrated with an x-axis and a y-axis located next to the second ground layer  62 . The corresponding change in inductance with an x-offset=0 at a fixed frequency of 15 GHz, as a function of a y-offset, is illustrated in FIG.  4 B. 
     FIG. 4B shows that an RIR of about 4.3% is generated, while still being better than that of CASE-Ref (2.8%), that is only marginally useful for practical design applications. 
     FIG. 4C shows the return loss S 11  for CASE-B at various offsets of the second ground layer  62 . The return loss S 11  characteristics has an absolute magnitude around 9.5 dB at 15 GHz that is significantly better than CASE-Ref (6.8 dB). Additionally, comparing with CASE-Ref, the employment of a first ground layer  60  above the spiral inductive coil  48  is expected to provide an additional advantage of a higher level of shielding of radio frequency emission from the inductive component into a surrounding ambient. This advantage of the present invention can become especially important in an application packaging environment called flip-chip wherein the IC comprising the inductive component is flipped upside down and bonded in intimate contact with other underlying RF radiating electronic circuits. 
     FIG. 5A is a perspective illustration of a third variation, called CASE-C, of the present invention design of an inductive component comprising a spiral inductive coil  48  and three ground layers designated a first ground layer  60 , a second ground layer  62  and a third ground layer  64 . All three ground layers are located on the same side of the spiral inductive coil  48 , between the spiral inductive coil  48  and the IC substrate SUBS  10 . Here, the present invention proposes that the second ground layer  62  to be linearly offset with respect to the spiral inductive coil  48 . The corresponding change in inductance with a y-offset=0 at a fixed frequency of 15 GHz, as a function of an x-offset, is illustrated in FIG.  5 B. 
     FIG. 5B shows that an RIR of about 9.6% is generated, being significantly better than that of CASE-Ref (2.8%), that is useful for practical design applications. 
     FIG. 5C shows the return loss S 11  for CASE-C at various offsets of the second ground layer  62 . The return loss S 11  characteristics has an absolute magnitude around 7.7 dB at 15 GHz that is better than CASE-A (6.8 dB). Additionally, comparing with CASE-Ref, the employment of three ground planes, having an offset between them, between the spiral inductive coil  48  and the IC substrate SUBS  10  is expected to provide a much higher level of shielding of radio frequency emission between the inductive component and an IC located on the IC substrate SUBS  10 . 
     FIG. 6A is a perspective illustration of a fourth variation, called CASE-D, of the present invention design of an inductive component comprising a spiral inductive coil  48  and three ground layers designated a first ground layer  60 , a second ground layer  62  and a third ground layer  64 . The first ground layer  60  is located above the spiral inductive coil  48  while the other two ground layers  62  and  64  are located below the spiral inductive coil  48  but above the IC substrate SUBS  10 . Here, the present invention proposes that the third ground layer  64  to be linearly offset with respect to the spiral inductive coil  48 . The corresponding change in inductance with a y-offset=0 at a fixed frequency of 15 GHz, as a function of an x-offset, is illustrated in FIG.  6 B. 
     FIG. 6B shows that an RIR of about 11.2% is generated, being substantially better than that of CASE-Ref (2.8%), that is quite useful for practical design applications. 
     FIG. 6C shows the return loss S 11  for CASE-D at various offsets of the third ground layer  64 . The return loss S 11  characteristics has an absolute magnitude around 10.7 dB at 15 GHz that is significantly better than CASE-A (6.8 dB). Additionally, this arrangement of the ground planes is expected to provide both a higher level of shielding of radio frequency emission between the inductive component and an IC located on the IC substrate SUBS  10  and a higher level of shielding of radio frequency emission from the inductive component into a surrounding ambient. As remarked before under FIG. 4C, this advantage of the present invention can become especially important in an application packaging environment called flip-chip wherein the IC comprising the inductive component is flipped upside down and bonded in intimate contact with other underlying RF radiating electronic circuits. 
     FIG. 7A is a perspective illustration of a fifth variation, called CASE-A with Rotation, of the present invention design of an inductive component that is identical to CASE-A of FIG. 3A except that the second ground layer  62  is now to be rotationally offset by an angle □ with respect to the spiral inductive coil  48 . The corresponding change in inductance at a fixed frequency of 15 GHz, as a function of □, is illustrated in FIG.  7 B. 
     FIG. 7B shows that an RIR of about 22% is generated, being much better than that of CASE-Ref (2.8%), that is very useful for practical design applications. 
     FIG. 7C shows the return loss S 11  for CASE-D at various offsets of the third ground layer  64 . The return loss S 11  characteristics has an absolute magnitude around 9.6 dB at 15 GHz that is significantly better than CASE-A (6.8 dB). Additionally, this arrangement of the ground planes is expected to provide a higher level of shielding of radio frequency emission between the inductive component and an IC located on the IC substrate SUBS  10 . 
     The following TABLE-1 summarizes the various advantages of the present invention with respect to the CASE-Ref: 
     
       
         
               
               
               
               
               
             
               
               
               
               
               
             
           
               
                   
                 TABLE-1 
               
               
                   
                   
               
               
                   
                   
                 return loss 
                   
                 RF shielding 
               
               
                   
                   
                 magnitude 
                 RF shielding 
                 inductor- 
               
               
                   
                 RIR (%) 
                 S 11 (dB) 
                 inductor-IC 
                 ambient 
               
               
                   
                   
               
             
             
               
                   
               
             
          
           
               
                 CASE-Ref 
                 2.8 
                 6.8 
                 reference 
                 reference 
               
               
                 CASE-A 
                 8.5 
                 8 
                 higher 
                 similar 
               
               
                 linear offset 
               
               
                 CASE-B 
                 4.3 
                 9.5 
                 similar 
                 higher 
               
               
                 linear offset 
               
               
                 CASE-C 
                 9.6 
                 7.7 
                 much higher 
                 similar 
               
               
                 linear offset 
               
               
                 CASE-D 
                 11.2 
                 10.7 
                 higher 
                 higher 
               
               
                 linear offset 
               
               
                 CASE-A 
                 22 
                 9.6 
                 higher 
                 similar 
               
               
                 Rotation 
               
               
                   
               
             
          
         
       
     
     The invention has been described using exemplary preferred embodiments. However, for those skilled in this field, the preferred embodiments can be easily adapted and modified to suit additional applications without departing from the spirit and scope of this invention. For example, it should be clear by now that the scope of the present invention is not limited to the illustrated geometry of the inductive component with a TRC of 8 m and a TSP of 2 m as long as these dimensions are consistent with the subsequent IC processing steps. For another example, for those skilled in the art, the structure and method to implement a precision inductive component as described herein can certainly be extended to a multi-spiral transformer having an accurate set of predetermined inductance values for its individual coils and an accurate set of predetermined coupling coefficients amongst its coils. Thus, it is to be understood that the scope of the invention is not limited to the disclosed embodiments. On the contrary, it is intended to cover various modifications and similar arrangements based upon the same operating principle. The scope of the claims, therefore, should be accorded the broadest interpretations so as to encompass all such modifications and similar arrangements.