Abstract:
Disclosed are novel methods and apparatus for efficiently providing power buses and bump patterns with reduced inductance and/or resistance. In an embodiment, an apparatus is disclosed. The apparatus includes a plurality of power and ground bus pairs. Each power and ground bus pair may have a power bus and a ground bus. The apparatus further includes a first power bus from a first pair of the plurality of power and ground bus pairs. The first power bus may include a plurality of power bumps. The apparatus also includes a first ground bus from the first pair of the plurality of power and ground bus pairs. The first ground bus may include a plurality of ground bumps. Each of the plurality of power/ground bumps may be substantially equidistance from any immediately neighboring ground bump of the first ground bus.

Description:
FIELD OF INVENTION  
         [0001]    The present invention generally relates to power distribution in integrated circuits (ICs). More specifically, an embodiment of the present invention relates to a low inductance and resistance power bus and bump pattern.  
         BACKGROUND OF INVENTION  
         [0002]    As the functionality requirements of today&#39;s electronic products increase, the IC designs associated with these products also become increasingly more complicated. Examples of such IC designs include very large-scale integration (VLSI) circuits such as microprocessor chips (including those provided by Sun Microsystems, Inc., of Palo Alto, Calif.). As these designs become more compact, in part, to incorporate additional functionality in the same floor space, voltage variations at the transistor level quickly become a significant problem for designers. More specifically, a challenging issue facing today&#39;s IC designers is reducing direct current (DC) and alternating current (AC) voltage variations at the transistors of IC chips.  
           [0003]    In AC voltage variations, the voltage variation is directly proportional to inductance and rate of current variation. Thus, as the current swings increase, so do the voltage variations. Large current swings may result, for example, from clock-gating (i.e., turning off/on) various blocks in a chip, high switching instruction and data patterns, and wide instruction and data buses. In DC voltage variations, the voltage variation is generally directly proportional to the resistance of a given path. Thus, as the resistance in a path increases, so does the voltage drop in that path.  
           [0004]    Accordingly, problems associated with the prior art include increased power consumption and decreased performance due in part to unstable and/or unpredictable voltage levels at transistors of a chip. Also, having an unstable and/or unpredictable voltage at the transistor level may decrease the reliability of a chip.  
           [0005]    Another issue facing today&#39;s IC designers is that the current bump placement techniques may require that bumps be located over alpha sensitive circuitry because nearly all bumps contain lead, which omits alpha particles. This is highly undesirable because alpha particles can interfere with the operation of an IC.  
           [0006]    [0006]FIG. 1 illustrates an exemplarily cross-sectional view of a power grid  100  in accordance with the prior art. A first power bus  102  has bumps  104   a ,  104   b , and  104   c  thereon. A ground bus  106  has bumps  108   a ,  108   b , and  108   c  thereon. A second power bus  110  includes bumps  112   a ,  112   b , and  112   c . As illustrated in FIG. 1, the ground bus  106  may be located between the first power bus  102  and the second power bus  110 . Alternatively, a power bus may be located between two ground buses (not shown). As illustrated in FIG. 1, bumps from different buses are substantially aligned. For example, the bump  104   a  is aligned with bumps  108   a  and  112   a.    
         SUMMARY OF INVENTION  
         [0007]    The present invention provides novel methods and apparatus for reducing DC and/or AC voltage variations at the transistor level of IC chips, in part, by creating novel power and ground bump patterns and/or novel power and ground grids. In an embodiment, these patterns and grids may be located at the top metal layer of an IC, which attaches to bumps. In another embodiments, the novel power and ground bump patterns and/or novel power and ground grids may be referred to as low resistance, low inductance power structures (LRLIPSs). In yet another embodiment, the LRLIPS may reduce the resistance and/or inductance of the power and ground grid of a VLSI design.  
           [0008]    In a further embodiment, an apparatus is disclosed. The apparatus includes a plurality of power and ground bus pairs. Each power and ground bus pair may have a power bus and a ground bus. Each bus within each power and ground bus pair may be closer in distance to each other than to a bus from a different power and ground bus pair. The apparatus further includes a first power bus from a first pair of the plurality of power and ground bus pairs. The first power bus may include a plurality of power bumps. The apparatus also includes a first ground bus from the first pair of the plurality of power and ground bus pairs. The first ground bus may include a plurality of ground bumps. Each of the plurality of power bumps may be substantially equidistance from any immediately neighboring ground bump of the first ground bus. Also, each of the plurality of ground bumps may be substantially equidistance from any immediately neighboring power bump of the first power bus. 
       
    
    
     BRIEF DESCRIPTION OF DRAWINGS  
       [0009]    The present invention may be better understood and its numerous objects, features, and advantages made apparent to those skilled in the art by reference to the accompanying drawings in which:  
         [0010]    [0010]FIG. 1 illustrates an exemplarily cross-sectional view of a power grid  100  in accordance with the prior art;  
         [0011]    [0011]FIG. 2 illustrates a cross-sectional view of a power grid  200  in accordance with an embodiment of the present invention; and  
         [0012]    [0012]FIG. 3 illustrates an exemplarily cross-sectional view of an extended power grid  300  in accordance with an embodiment of the present invention. 
     
    
       [0013]    The use of the same reference symbols in different drawings indicates similar or identical items.  
       DETAILED DESCRIPTION  
       [0014]    In the following description, numerous details are set forth. It will be apparent, however, to one skilled in the art that embodiments of the invention may be practiced without these specific details. In other instances, well-known structures, devices, and techniques have not been shown in detail, in order to avoid obscuring the understanding of the description. The description is thus to be regarded as illustrative instead of limiting.  
         [0015]    Reference in the specification to “one embodiment” or “an embodiment” means that a particular feature, structure, or characteristic described in connection with the embodiment is included in at least an 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.  
         [0016]    [0016]FIG. 2 illustrates an exemplarily cross-sectional view of a power grid  200  in accordance with an embodiment of the present invention. The power grid  200  includes a first power bus  202  and a second power bus  206  each having wires  203   a - e  and  207   a - e , respectively. In an embodiment, the wires within each set of wires ( 203   a - e  and  207   a - e ) may be separated with any type of dielectric. As illustrated, in accordance with one embodiment, the wires (e.g.,  203   a - e  and  207   a - e ) may be electrically coupled by, for example, utilizing connectors  205  and  209  (shown throughout wires  203   a - e  and  207   a - e , respectively). In an embodiment, it is envisioned that these connectors (e.g.,  205  and/or  209 ) may be an integral part of the wires (e.g.,  203   a - e  and/or  207   a - e ), instead of a separate structure. In one embodiment, the wires (e.g.,  203   a - e  and/or  207   a - e ) and/or connectors (e.g.,  205  and/or  209 ) may be constructed utilizing the same material. In an embodiment, the wires (e.g.,  203   a - e  and/or  207   a - e ) and/or connectors (e.g.,  205  and/or  209 ) may be constructed by using material selected from a group including copper, aluminum, silver, gold, other types of conductive substances, and/or any combination thereof.  
         [0017]    The first and second power buses ( 202  and  206 ) each have bumps  204   a - b  and  208   a - b , respectively. The power grid  200  further includes a first ground bus  210  and a second ground bus  214  each having bumps  212   a - c  and  216   a - c , respectively. In one embodiment, any pair of adjacent power and ground buses may be as close to each other as possible without causing a short. It is envisioned that the distance between adjacent power and ground buses may depend on the technology utilized to implement the circuitry. For example, the minimum distance between adjacent power and ground buses may be 30 microns in one technology and 10 in another.  
         [0018]    Also, it is envisioned that by decreasing the distance between each power and ground bus pair the mutual inductance is increased, thereby decreasing overall inductance of a design. Lowering inductance is envisioned to be greatly beneficial for certain applications, especially where higher frequencies (currently, exceeding 2 GHz in some designs) are utilized. In an embodiment, the lower inductance permits increased speeds for a design in addition to improving reliability. The Formula (1) below illustrates the effects of reducing the mutual inductance more specifically.  
           L   total   =L   1   +L   2 −(2 *L   mutal )  (Formula 1)  
         [0019]    In Formula 1, L 1  and L 2  are the inductances associated with circuits  1  and  2 , L mutual  is the mutual inductance of circuits  1  and  2 , and L total  is the total inductance for circuits  1  and  2 ). In an embodiment, the circuits  1  and  2  may be adjacent power and ground buses, respectively. It is also envisioned that the total inductance may be reduced by lowering the inductance of each circuit. For example, in an embodiment, the power and/or ground buses may be made wider in width and/or shorter in length. However, depending on the available floor space and/or associate costs, it may be more desirable to reduce the total inductance (L total ) by increasing the mutual inductance (L mutual ). Accordingly, in an embodiment, it is desirable to decrease the gap between paired power and ground buses without causing a short and/or negatively affecting the signal carrying capabilities of the adjacent buses (for example, through varying electrical fields associated with the adjacent buses and the like). In such an embodiment, it is envisioned that the inductance of a power and ground grid is lowered without changing the resistance associated therewith.  
         [0020]    As illustrated in FIG. 2, the bumps from different power buses may be substantially aligned (for example, vertically), in an embodiment. For example the bump  204   a  of the first power bus  202  may be aligned with the bump  208   a  of the second power bus  206 . Similarly, in an embodiment, the bumps from the ground buses may be aligned. For example, the bump  212   b  of the first ground bus  210  may be aligned with the bump  216   b  of the second ground bus  214 . In an embodiment, the bumps of a power bus may be equidistance from bumps of an adjacent ground bus. For example, the distance from the bump  204   a  to the bumps  212   a  and  212   b  may be substantially equal. Similarly, in an embodiment, the bumps of a ground bus may be substantially equidistance from bumps of an adjacent power bus. For example, the distance from the bump  212   b  to the bumps  204   a  and  204   b  may be substantially equal.  
         [0021]    [0021]FIG. 3 illustrates an exemplarily cross-sectional view of an extended power grid  300  in accordance with an embodiment of the present invention. The power grid  300  includes a first power bus  202  having a bump  204   a  and wires  203   a - e . The power grid  300  further includes a first ground bus  210  having a bump  212   a  and wires  211   a - e . As illustrated, the bumps  204   a  and  212   a  may not be vertically aligned (such as discussed with respect to FIG. 2). In an embodiment, the wires within each set of wires ( 203   a - e  and  211   a - e ) may be separated with any type of dielectric. As illustrated in FIG. 3, in accordance with one embodiment, the wires (e.g.,  203   a - e  and  211   a - e ) may be electrically coupled by, for example, utilizing connectors  205  and  213  (shown throughout wires  203   a - e  and  211   a - e , respectively). In another embodiment, it is envisioned that the wires  203   a - e  and  211   a - e  may each be a single wire (e.g.,  203  and  211 ). It is also envisioned that process limitations may require a set of wires instead of a single wire.  
         [0022]    In a further embodiment, it is envisioned that these connectors (e.g.,  205  and/or  213 ) may be an integral part of the wires (e.g.,  203   a - e  and/or  211   a - e ), instead of a separate structure. In one embodiment, the wires (e.g.,  203   a - e  and/or  211   a - e ) and/or connectors (e.g.,  205  and/or  213 ) may be constructed utilizing the same material. In an embodiment, the wires (e.g.,  203   a - e  and/or  211   a - e ) and/or connectors (e.g.,  205  and/or  213 ) may be constructed by using material selected from a group including copper, aluminum, silver, gold, other types of conductive substances, and/or any combination thereof.  
         [0023]    The power grid  300  additionally includes extended wires  302   a - b  and  304   a - b . As illustrated in FIG. 3, in accordance with one embodiment, the wires (e.g.,  302   a - b  and  203   a - e ) may be electrically coupled by, for example, utilizing connectors  303  (shown throughout wires  302   a - b ). Similarly, in accordance with one embodiment, the wires (e.g.,  304   a - b  and  211   a - e ) may be electrically coupled by, for example, utilizing connectors  305  (shown throughout wires  304   a - b ). In an embodiment, it is envisioned that these connectors (e.g.,  303  and/or  305 ) may be an integral part of the wires (e.g.,  302   a - b  and/or  304   a - b ), instead of a separate structure. In another embodiment, the wires (e.g.,  302   a - b  and/or  304   a - b ) and/or connectors (e.g.,  303  and/or  305 ) may be constructed utilizing the same material. In yet another embodiment, the wires (e.g.,  302   a - b  and/or  304   a - b ) and/or connectors (e.g.,  303  and/or  305 ) may be constructed by using material selected from a group including copper, aluminum, silver, gold, other types of conductive substances, and/or any combination thereof.  
         [0024]    It is envisioned that the set of wires  203   a - e  of the first power bus  202  may be extended (e.g., utilizing the extended wires  302   a - b ) on an opposite side from the first ground bus  210 . And, the set of wires  211   a - e  may be extended (e.g., utilizing the extended wires  304   a - b ) on an opposite side from the first power bus  202 . Such extension of the wire sets  203   a - e  and  211   a - e  by, for example, the extended wires  302   a - b  and  304   a - b , respectively, will not cause shorting in embodiments where the wire sets are brought as close to each other as possible, in part, to reduce the total inductance (see, e.g., the discussion with respect to FIG. 2). The total inductance is reduced for one or both of the following two reasons: (1) the reduced self-inductance (e.g., by introducing wider conductance paths), and/or (2) the increased mutual inductance (see, e.g., FIG. 3). The effect is envisioned to provide a wider power and/or ground bus, depending on which bus(es) are widened by adding wires. Also, in accordance with one embodiment of the present invention, it is envisioned that the mutual inductance between, for example, the extended wires  304   a - b  and an adjoining power grid (not shown) may be increased, whereas the mutual inductance between the set of wires  211   a - e  and the adjoining power grid may be reduced.  
         [0025]    Accordingly, in an embodiment of the present invention, wire sets may be extended by adding one or more wires on an opposite side of the wire set from the neighboring power/ground bus. For example, with respect to FIG. 2, if the second power bus  206  and the second ground bus  214  are considered as a pair of power and ground buses, then wire set  207   a - e  may be extended by adding wires on the opposite side from the second ground bus  214 . Similarly, wires  215   a - e  may be extended by adding wires on the opposite side from the second power bus  206 .  
         [0026]    In one embodiment, the extension of the wire sets may result in reduction of resistance associated with the power and/or ground buses. The reduction in resistance may reduce the voltage variation due to DC, which is also known as the IR drop (where I is for current and R is for resistance and the multiplication of the two result in voltage in accordance with the Ohm&#39;s law, i.e., V=I*R). An advantage of LRLIPS, in accordance with an embodiment of the present invention, is that the power and ground grid has the ability to be adjusted to any resistance value without changing the bump pattern. For example, a power and ground grid with very little resistance may be designed, but such a design may leave very little room to route global signals.  
         [0027]    Therefore, LRLIPS, in accordance with an embodiment of the present invention, permits striking of a right balance of power and ground resistance and global signal tracking. In addition, in an embodiment, localized power and ground grids may be adjusted so as to tune a given IC to have the same IR drop in all transistors without changing the power and ground bumps.  
         [0028]    Furthermore, reduction in inductance of a power grid reduces the voltage variations due to AC, which is also known as L*(di/dt) (where L stands for inductance and di/dt indicates the rate of change in current (i) over time (t)). The di/dt is largely determined by the architecture, frequency, and power of an IC. The inductance, L, may be reduced with LRLIPS, in accordance with an embodiment of the present invention, since the power and ground grids are so close and tightly coupled together (see, e.g., the discussion with respect to FIG. 2). It is envisioned that, in an embodiment, having a lower inductance power and ground grid will reduce voltage variations due to variations of current with respect to time. These current variations may be difficult to predict and estimate in cases where they are dependant on instruction and data patterns. Thus, by reducing the inductance (L) of a given power and ground grid, certain embodiments of the present invention dampen the effects of large current variations, thereby reducing large voltage variations, which in turn improves reliability and circuit performance.  
         [0029]    It is envisioned that in an embodiment having a stable and predictable voltage at all transistors is paramount in achieving maximum performance and minimum power consumption. In addition, having a stable and predictable voltage at all transistor will increase reliability of an IC (e.g., if not enough guard band was allotted for voltage variation in the power budget estimates).  
         [0030]    Additionally, in an embodiment, the present invention provides the flexibility of removing individual power and ground bumps without increasing voltage drops or modifying the overall power and ground bump structure. This would be useful when an individual bump is, for example, over an Alpha sensitive circuit. This is especially valuable because nearly all bumps may contain lead (lead emits Alpha particles). In a further embodiment, a widened metal may be utilized to compensate for the voltage drop associated with removing a bump. In addition, LRLIPS, in accordance with one embodiment of the present invention, does not impact the yield or the manufacturability of the VLSI chip. According, LRLIPS, in accordance with an embodiment of the present invention, may allow an IC to perform faster, reduce the overall IC power consumption, and/or provide some combination of these performance and power benefits.  
         [0031]    Moreover, an IC may perform faster by having the minimum voltage at the transistors that is higher, so the transistor would switch faster at the low voltage corner. In particular, the minimum voltage would be higher since the budget for AC and DC voltage drops will be lower (i.e., Vtran=Vsupply−Vac_drop−Vdc_drop, where Vtran is the voltage at the transistor, Vsupply is the supply voltage, Vac_drop is the voltage associated with an AC drop, and Vdc_drop is the voltage associated with a DC drop). Alternately, in an embodiment, the voltage at the transistor may be left the same (e.g., resulting in the same performance) and the Vsupply lowered to reduce the overall power consumption.  
         [0032]    Accordingly, in one embodiment, the bump pattern may be diagonal to reduce cheesing of package power planes. Thus, reducing resistance (R) and inductance (L) on, for example, a ceramic package. Such an embodiment is envisioned to also reduce the overall voltage drops.  
         [0033]    The foregoing description has been directed to specific embodiments. It will be apparent to those with ordinary skill in the art that modifications may be made to the described embodiments, with the attainment of all or some of the advantages. For example, the embodiments of the present invention may be applied equally well to any device with a power and/or ground grid. Therefore, it is the object of the appended claims to cover all such variations and modifications as come within the spirit and scope of the embodiments of the present invention.