We have considered the resistance linear and constant. However, at high frequencies skin effect comes to play, and resistance becomes frequency dependent. The increased resistance at high frequencies may cause extra attenuation and thus distortion of the signals being transmitted over the wire.

Aluminum is the interconnect material mostly used in ICs because of its low cost and compatibility with the standard CMOS process. Present technology uses copper increasingly because of its low resistivity and better immunity against electro migration. Polysilicon should only be used for local interconnect. Although the sheet resistance of diffusion layer (n+, p+) is comparable to that of polysilicon, the use of diffusion wires should be avoided due its large capacitance and the associated RC delay.