njit-etd2000-029 - New Jersey Institute of Technology

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also proportional to the length of the wire, we find that overall the resistance is also
proportional to the length of the wire, we find that overall the resistance increases by a
factor of two. Since the resistance increases by the same factor as the capacitance
decreases, the time delay stays the same as in the unscaled system. This is bad news.
Although the switching times of the individual devices are reduced by scaling, the delays in
propagating signals between them are not. This suggests that the speed of an integrated
circuit will ultimately be limited by the need for devices to communicate with one another.
We have seen that the current flowing between the devices is reduced by a factor of two,
but the cross sectional area of the wires is reduced by a factor of four. As a result the
current per unit area is twice as large as it was before scaling. Since the decrease in the
cross-sectional area also leads to an increase in resistance, this in turn means that more
heat is generated as the current flows through the wire. The heat causes the ions to vibrate
rapidly, and since they are under constant bombardment from the concentrated flow of
electrons, they may literally be wrenched out of their lattice sites. This movement of the
ions, known as electromigration, may be so severe that all the atoms in a small region are
removed, physically destroying the connection.
This assessment of the effects of scaling the interconnects may seem pessimistic, but in
reality the situation can be much worse. We assumed in our argument that the length of
the interconnect scales down in proportion to the other dimensions, but this is not
necessarily the case. In particular, although great efforts are taken in the layout of the
circuits, there is always a requirement for some long interconnects which pass from one