njit-etd2000-029 - New Jersey Institute of Technology

components, whereas discrete devices have to be individually connected to form a circuit,
a process that is both expensive and unreliable. This means that an integrated circuit
manufacturer who wants to remain competitive has been forced to follow, if not lead the
way, in producing ever more complex circuits on a single chip. The other key factor is
performance. Small transistors operate faster than larger ones and at the same time are
more reliable since the electrical contacts within an integrated circuit are far less likely to
fail than the conventional soldered joints used to attach discrete components on to a
circuit board.
At the same time as the circuit size has been increasing, the size of the individual
components has decreased substantially. This has been achieved primarily by progressively
refining the photolithographic techniques, allowing finer structures to be resolved. The
benefits of this reduction in size are easy to appreciate. If we reduce all of the dimensions
by a factor of two, then four times as many devices can be squeezed on to the same area
as before. Since the cost of a circuit is effectively governed by the surface area that it
occupies, this reduces the cost per function by a factor of four. There is also a second
major incentive to reduce the size of the individual components, and that is the effect it has
on the speed of the operation of the devices. The speed of a MOSFET is governed by the
time it takes an electron to cross the gate region. By reducing this distance by a factor of
two we therefore also obtain a similar increase in the performance of the devices. These
advantages of reduced cost, smaller size and increased performance have fuelled the rapid
increase in the number of electronic devices that can be placed on a single chip.