ULSI stands for Ultra Large Scale Integration which refers to the chips with complexity of more than One million transistors. The term was coined when the critical dimensions of patterns in the chips hovered in the range of 0.25 micrometers, which have now reduced even further to less than 100nm marking a transition from the micron-scale to nano-scale. At such a scale, various issues which did not affect performance of devices at a higher scale like interconnects (RC delays etc.), conductivity requirements and material properties become very critical and cannot be ignored at any stage.
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