Integrated Circuit Signal Delay

Technologies for designing and building microelectronics-based computational equipment have been steadily advancing ever since the first commercial discrete circuits (ICs) were introduced in the late 1950s (1) (monolithic integrated circuits were introduced in the 1960s). As predicted by Moore's law in the 1960s (2), integrated-circuit density has been doubling approximately every 18 months, and this doubling in size has been accompanied by a similar exponential increase in circuit speed (or more precisely, clock frequency). These trends of steadily increasing circuit size and clock frequency are illustrated in Figs. 1(a) and 1(b), respectively. As a result of this amazing revolution in semiconductor technology, it is not unusual for modern integrated circuits to contain over 10 million switching elements (i.e., transistors) packed into a chip area as large as 500 mm 2 (3–5). This truly exceptional technologi