Integrated circuits are used for a wide variety of electronic applications, from simple devices such as wristwatches, to the most complex computer systems. A microelectronic integrated circuit chip (IC) can generally be thought of as a collection of logic cells with electrical interconnections between the cells, formed on a monolithic semiconductor substrate (e.g., silicon). An IC may include a very large number of logic cells and require complicated connections between them. A logic cell, which may also referred to herein as a standard cell or a cell, is a group of one or more circuit elements grouped together to perform a logical function. Logic cell types include, for example, core cells, scan cells and input/output (I/O) cells. Each of the cells of an IC may have one or more pins, each of which in turn may be connected to one or more other pins within the IC by wires. The wires connecting the pins of the IC may also formed on the surface and/or in one or more layers of the chip.
Cell placement in semiconductor fabrication involves a determination of where particular cells should be located in the substrate of an integrated circuit device. Due to the large number of components and the details required by the fabrication process, physical design is not practical without the aid of computers. Many phases of physical design extensively use computer aided design (CAD) tools to automate the physical design process phases have already been partially or fully automated. Automation of the physical design process has increased the level of integration, reduced turn around time and enhanced chip performance.
As IC technologies have improved with smaller device dimensions and faster switching frequencies, and greater integration, power consumption has increased such that power distribution networks in an integrated circuit have become more important. One problem in the power distribution network in an IC that has arisen with the advances in IC technologies relates to voltage drops (also referred to as IR drops) across the power distribution network. Localized voltage drops are caused by switching cells sourcing or sinking currents and drawing power through a resistive power distribution network or grid. Excessive voltage drops in the supply voltage on the power distribution network can reduce switching speeds, reduce noise margins, and cause failures in the electronic devices of the IC. Excessive voltage drops in the supply voltage on the power distribution network may be an indication of poor placement of logic cells with respect to even power distribution. It is desirable to better regulate the voltage supplied to the electronic devices in the integrated circuit over the power distribution network to address the potential voltage drops therein.