Since the invention of the integrated circuit, the complexity of the devices and the cost of the facilities used to build them have increased dramatically. The first fabrication facility with which I was associated was built at Xerox PARC in the mid-1970s at a cost of approximately $15M ($75M today). Today, the cost of a modern fab is approximately $15B. This cost is justified by the fact that today's chips are much more complex than in earlier times. The number of layers involved has grown to over 100, and the tolerances involved are approaching atomic dimensions.
The high cost of a fab means that in order to be cost-effective, it must be fully loaded. This has led to "silicon foundries," which build chips for a variety of "fabless" semiconductor companies based on a set of physical design libraries supplied by the foundry. Carver Mead and Lynn Conway in their seminal 1980 "Introduction to VLSI Systems" initially proposed this concept, but the Taiwan Semiconductor Company (TSMC), founded in 1987, changed what had been an academic exercise into an industrial norm. Today, a few large fabs throughout the world dominate this business.
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