INTEGRATED CIRCUITS (ICs) are simply circuits whose components are formed simultaneously on a single piece of semiconducting material. Instead of wiring together the discrete components of a circuit — such as resistors, capacitors, inductors, diodes and transistors — the IC designer arranges for them to be produced and electrically interconnected as a single ‘chip’. There are many advantages in so doing: the devices need no packaging, the interconnections and spacing between components can be very small (usually a few μm) and their small size means they can be mass produced in very large quantities very cheaply. In addition, the simultaneous formation of transistors in ICs means they are naturally closely matched, leading to improved circuit performance, especially for operational and differential amplifiers. The evolution of ICs based on silicon has been rapid and continuous. Figure 10.1 shows the trend with time in the best production processes for the minimum width of ‘features’ such as conductors, gates and so forth, components/mm2 and components/chip, all on a logarithmic scale.
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