Interconnect is also the technical
term for a
wire that connects
transistors in an
integrated circuit. The number of interconnect layers used in
digital integrated circuits has increased with increased
circuit complexity. A modern
microprocessor may have seven interconnect layers, with the uppermost layers devoted to
clock and
power distribution. The most common interconnect materials are (in order of decreasing resistivity)
polysilicon,
aluminum, and
copper.
In the past, interconnects could often be considered perfect wires with no degrading effects on a circuit. As digital integrated circuits have evolved, parasitic interconnect capacitance has become an important, and perhaps even dominant source of switching delay. Circuit designers must also contend with capacitive crosstalk between interconnects that can incorrectly switch the binary level of a node. As clocking speeds rise in the GHz range, transmission line effects in the interconnects make circuit design even more laborious.