Abstract:
The subject matter described herein involves a wire bonded integrated circuit (IC) that includes a power distribution grid, or power redistribution bus, within a single layer, e.g. the topmost metallization layer, of the IC chip. Electrical conductors in the power distribution grid are generally L-shaped. Thus, the electrical conductors are arranged generally in symmetrical quadrants within which the electrical conductors extend from one side edge of the IC chip to a generally right-angled corner and then to a second side edge that is adjacent to the first side edge.

Description:
FIELD 
     The subject matter herein relates to distribution of electrical power across an integrated circuit chip through a power grid layer. 
     BACKGROUND 
     An integrated circuit (IC) chip typically includes one or two primary layers of electrical conductors (e.g. aluminum, copper and other conductors), a.k.a. a “power redistribution bus” or power distribution grid, that provide gross distribution of electrical power across the IC chip. The power distribution grid typically transmits the electrical power through other layers of electrical conductors that distribute the electrical power more finely to the various electronic components (e.g. transistors, capacitors, etc.) in the various other layers of the IC chip. 
     Examples of such power distribution grids  100 ,  102  and  104 , specifically for wire bonded IC&#39;s, are shown in FIGS. 1,  2  and  3 , respectively. The power distribution grid  100  (FIG. 1) is similar to the grids  10  and  20  shown in prior art FIGS. 1 and 2 in U.S. Pat. No. 6,111,310. The power distribution grid  100  includes four main electrical conductors  106  arranged to form a square that generally corresponds to an outer perimeter of an IC (not shown) on which the power distribution grid  100  may be formed. The power distribution grid  100  also includes two sets of evenly spaced electrical conductors  108  and  110 , one vertical set (electrical conductors  108 ) and one horizontal set (electrical conductors  110 ), that connect the main electrical conductors  106  on opposite sides of the outer perimeter of the IC. The electrical conductors  108  and  110  are generally perpendicular to each other and have a generally constant width. Additionally, the electrical conductors  108  are typically formed within a different layer of the IC than are the electrical conductors  110 , so the electrical conductors  108  and  110  cannot intersect and cause an electrical short. Also, the electrical conductors  108  and  110  typically supply the electrical power to the IC, and another set of electrical conductors (not shown) disposed in the same two layers of the IC chip as the power electrical conductors  108  and  110  typically supplies the ground. 
     Since the electrical conductors  108  and  110  have a generally constant width, in order to deliver approximately the same current to each region of the IC chip, the current density must be considerably greater in the portion of the electrical conductors  108  and  110  near the periphery of the IC chip than in the center of the IC chip. The greater current density can result in electromigration if the cross-section of the electrical conductors  108  and  110  is too small near the periphery of the IC chip. 
     The power distribution grid  102  shown in FIG. 2 is similar to the power distribution grid  100  (FIG. 1) and to the grid  30  shown in FIG. 3 in U.S. Pat. No. 6,111,310. Similar to the power distribution grid  100 , the power distribution grid  102  includes four main electrical conductors  112  arranged to form a square that generally corresponds to an outer perimeter of an IC (not shown) on which the power distribution grid  102  may be formed. The power distribution grid  100  also includes two sets of non-intersecting electrical conductors  114  and  116  that connect the main electrical conductors  112  on opposite sides of the outer perimeter of the IC chip. The electrical conductors  114  and  116  are generally perpendicular to each other. However, unlike the power distribution grid  100  shown in FIG. 1, the electrical conductors  114  and  116  have a varying width, instead of a constant width. In this manner, the problem with electromigration that may be experienced in the power distribution grid  100  is reduced in the power distribution grid  102 . Additionally, the power distribution grid  102  exhibits less voltage drop than does the power distribution grid  100 , so the power is more evenly distributed across the power distribution grid  102  than across the power distribution grid  100 . The power distribution grid  102  is typically made from conductor material, such as aluminum, that can be formed in relatively wide lines. 
     The power distribution grid  104  shown in FIG. 3 is similar to the power distribution grid  102  (FIG.  2 ), except that the four main electrical conductors  118  (arranged to form a square that generally corresponds to an outer perimeter of an IC) and the two sets of non-intersecting variable-width conductors  120  and  122  are formed from multiple individual generally-constant-width electrical conductors  124 . Having multiple individual electrical conductors  124  allows the power distribution grid  104  to be formed from conductor material, such as copper, that cannot readily be formed in relatively wide lines. Some of the individual electrical conductors  124  extend all the way across the IC chip (not shown), while the others extend only part way from the periphery of the IC chip toward the center of the IC chip. In this manner, the problem with electromigration that may be experienced in the power distribution grid  100  (FIG. 1) is reduced in the power distribution grid  104 , because there are more of the individual electrical conductors  124  to transfer the current near the periphery of the IC chip where there is more current in the power distribution grid  104  than near the center of the IC chip. 
     The power distribution grids  100  (FIG.  1 ),  102  (FIG. 2) and  104  (FIG. 3) require exclusive use of at least two layers of the IC chip, which takes up valuable space within the IC chip and limits the vertical thickness of at least one of these two layers (increasing the layer&#39;s resistance), since a layer that is overlaid by another layer is inherently restricted in its vertical thickness due to physical limitations of chip fabrication processes. On the other hand, if the power distribution grids  100 ,  102  and  104  were made with only one set of electrical conductors (e.g.  108 ,  114  and  120 ) in only one layer of the IC chip, then the power distribution grids  100 ,  102  and  104  would receive current on only two sides of the IC chip, e.g. the top and bottom sides, which requires a relatively tight arrangement of power pins (not shown) on only two sides of the IC chip and results in an unsymmetrical voltage drop from a given point on the IC chip to the nearest main electrical conductor  106  (FIG.  1 ),  112  (FIG. 2) or  118  (FIG. 3) on the periphery of the IC chip. 
     It is with respect to these and other background considerations that the subject matter herein has evolved. 
     SUMMARY 
     The subject matter herein involves a power distribution grid that is formed in only one layer of an IC chip (e.g. the top layer), includes power pins on all four sides of the IC chip and results in a symmetrical voltage drop and current density in both the horizontal and vertical directions across the IC chip for a relatively even power distribution. The IC chip is generally divided into quadrants, each including one corner (top-left, top-right, bottom-right or bottom-left) of the IC chip and about half of the two side edges (top, bottom, left side and right side) that form the corner. Electrical conductors for each quadrant of the power distribution grid are routed from the side edge on one side of the corner of the IC chip to the side edge on the other side of the corner. Generally, the electrical conductors do not intersect each other, so the electrical conductors can be formed in the same layer of the IC chip. 
     In a particular embodiment, the electrical conductors of each quadrant are routed in general L-shapes from one IC chip side edge of the quadrant to the other IC chip side edge of the quadrant on the other side of the corner of the IC chip, without intersecting each other. The L-shaped electrical conductor nearest the corner of the IC chip in the quadrant is the shortest electrical conductor in the quadrant, and the L-shaped electrical conductor nearest the center of the IC chip is the longest electrical conductor in the quadrant. Additionally, the power distribution grid is generally symmetrical about the center point of the IC chip. Additionally, every other one of the L-shaped electrical conductors in each quadrant may be power conductors separated by ground conductors, so that all four side edges of the IC chip may have power and ground pins, resulting in the symmetrical voltage drop and current density and the relatively even power distribution across the IC chip. 
    
    
     A more complete appreciation of the present disclosure and its scope, and the manner in which it achieves the above noted improvements, can be obtained by reference to the following detailed description of presently preferred embodiments taken in connection with the accompanying drawings, which are briefly summarized below, and the appended claims. 
     BRIEF DESCRIPTION OF THE DRAWING 
     FIG. 1 is a plan view of a prior art power distribution grid. 
     FIG. 2 is a plan view of another prior art power distribution grid. 
     FIG. 3 is a plan view of another prior art power distribution grid. 
     FIG. 4 is a plan view of an integrated circuit (IC) chip including a power distribution grid incorporating the present invention. 
     FIG. 5 is a plan view of an integrated circuit (IC) chip including an alternative power distribution grid incorporating the present invention. 
     FIG. 6 is a plan view of another integrated circuit (IC) chip including another alternative power distribution grid incorporating the present invention. 
    
    
     DETAILED DESCRIPTION 
     An integrated circuit (IC) chip  200 , as shown in FIG. 4, includes a power distribution grid, or power redistribution bus,  202  having several L-shaped electrical conductors  204  and a center electrical conductor  206  that extend inward across the IC chip from an outer conductor  207  that connects to power pins  208  at side edges  210  of the IC chip  200  without intersecting each other. The IC chip  200 , including the power distribution grid  202 , is formed using conventional IC chip fabrication techniques. The power pins  208  are typically for wire bonding the IC chip  200  to an external power source (not shown). The electrical conductors  204  and  206  supply electrical power to electronic components (not shown) in the IC chip  200 , typically through a variety of additional conductors  212  in other layers of the IC chip  200 , to enable the functioning of the IC chip  200 . Additionally, the electrical conductors  204  and  206  are typically interleaved with ground electrical conductors (not shown). Furthermore, all of the electrical conductors  204  and  206  (and the ground electrical conductors) are disposed in the same conductor layer (not shown), such as the top metallization layer, of the IC chip  200 . In this manner, the power distribution grid  202  requires a smaller die size for the IC chip  200  and less cost than does the prior art. Additionally, the power pins  208  may be evenly distributed on all of the side edges  210  of the IC chip  200 , rather than having all power pins on only two sides of the IC chip  200 . 
     The center electrical conductor  206  effectively separates the IC chip  200  and power distribution grid  202  into four generally symmetrical quadrants, each bounded by a portion of the center electrical conductor  206  and a portion of two adjacent side edges  210 . The L-shaped electrical conductors  204  are each confined to one quadrant and extend generally perpendicularly from the side edges  210  of the quadrant to a generally right-angled corner  214  without intersecting another L-shaped electrical conductor  204  or the center electrical conductor  206 . In this manner, the voltage drop and current density in both the horizontal and vertical directions across the IC chip  200  are generally symmetrical. Additionally, the symmetry results in a relatively even power distribution across the IC chip  200 . 
     Being in the topmost layer of the IC chip  200 , such as the top metallization layer, the electrical conductors  204  and  206  are as not restricted in their height as they would be if they were disposed in an intermediate layer of the IC chip  200 . The prior art electrical conductors  108  and  110  (FIG.  1 ),  114  and  116  (FIG. 2) and  120  and  122  (FIG.  3 ), on the other hand, have to be disposed in two layers of the IC chip, so that they don&#39;t intersect each other. Therefore, the prior art electrical conductors  108 ,  110 ,  114 ,  116 ,  120  and  122  that are overlaid by another layer of the IC chip are more restricted in their maximum height, due to physical limitations in the fabrication processes by which the IC chips are formed. Such restrictions also limit the conductivity of the electrical conductors  108 ,  110 ,  114 ,  116 ,  120  and  122 . Since the electrical conductors  204  and  206  are not as restricted, however, their conductivity is relatively high, so the power distribution grid  202  can be formed in only one layer. Additionally, the additional conductors  212  and any other signal conductors (not shown) are not formed in the same layer of the IC chip  200  as the electrical conductors  204  and  206 , so the electrical conductors  204  and  206  can be routed in both the horizontal and vertical directions without affecting other conductors. 
     Since the electrical conductors  204  and  206  can be routed both horizontally and vertically, power and ground can be supplied at all four side edges  210  of the IC chip  200 . Thus, current can be supplied to and removed from every point on the IC chip  200  generally in the most efficient manner, i.e. at the nearest side edge  210 , and result in a relatively low overall voltage drop and current density across the IC chip  200 . Furthermore, having the power and ground supplied on all four sides of the IC chip  200  results in the voltage drop and current density being generally symmetrical and distributed relatively evenly across the IC chip  200 . Thus, the power distribution grid  202  allows greater flexibility in placement of the power-consuming electronic components throughout the IC chip  200 , because the more symmetrical, even distribution of voltage and current can handle greater variations in voltage and current changes than can the prior art. Additionally, the greater thickness of the electrical conductors  204  and  206 , resulting in the lower current density and more even distribution, relieves the electromigration problems more efficiently, relative to die size, than does the prior art. 
     Alternative power distribution grids  216  and  218  are shown in FIGS. 5 and 6, respectively. The alternative power distribution grids  216  and  218  have all the same advantages described above with respect to the power distribution grid  202  (FIG.  4 ), but with slight variations in structure. The power distribution grid  216 , for instance, includes the L-shaped electrical conductors  204 , but not the center electrical conductor  206  (FIG.  4 ). The power distribution grid  218 , on the other hand, includes both the L-shaped electrical conductors  204  and the center electrical conductor  206 , but each of the electrical conductors  204  and  206  have a step-tapered width. The widest portions of the electrical conductors  204  and  206  are at the ends near the side edges  210 , and the narrowest portions are at the centers of the electrical conductors  204  and  206 . In this manner, voltage drop, current density and potential electromigration effects are further alleviated or reduced. A further alternative power distribution grid (not shown), which also further alleviates or reduces the voltage drop, current density and potential electromigration effects, may include several individual electrical conductors  124  (FIG. 3) of different lengths most heavily concentrated near the side edges  210 . 
     Presently preferred embodiments of the subject matter herein and its improvements have been described with a degree of particularity. This description has been made by way of preferred example. It should be understood that the scope of the claimed subject matter is defined by the following claims, and should not be unnecessarily limited by the detailed description of the preferred embodiments set forth above.