The history of semiconductors and Moore’s Law follows a long and somewhat meandering path. Conte, a professor at the schools of computer science and engineering at Georgia Institute of Technology, points out that computing has not always been tied to shrinking transistors. “The phenomenon is only about three decades old,” he points out. Prior to the 1970s, high-performance computers, such as the CRAY-1, were built using discrete emitter-coupled logic-based components. “It wasn’t really until the mid-1980s that the performance and cost of microprocessors started to eclipse these technologies,” he notes.
At that point, engineers developing high-performance systems began to gravitate toward Moore’s Law and adopt a focus on microprocessors. However, the big returns did not last long. By the mid-1990s, “The delays in the wires on-chip outpaced the delays due to transistor speeds,” Conte explains. This created a “wire-delay wall” that engineers circumvented by using parallelism behind the scenes. Simply put: the technology extracted and executed instructions in parallel, but independent, groups. This was known as the “superscalar era,” and the Intel Pentium Pro microprocessor, while not the first system to use this method, demonstrated the success of this approach.
Around the mid-2000s, engineers hit a power wall. Because the power in CMOS transistors is proportional to the operating frequency, when the power density reached 200W/cm2, cooling became imperative. “You can cool the system, but the cost of cooling something hotter than 150 watts resembles a step function, because 150 watts is about the limit for relatively inexpensive forced-air cooling technology,” Conte explains. The bottom line? Energy consumption and performance would not scale in the same way. “We had been hiding the problem from programmers. But now we couldn’t do that with CMOS,” he adds.
No longer could engineers pack more transistors onto a wafer with the same gains. This eventually led to reducing the frequency of the processor core and introducing multicore processors. Still, the problem didn’t go away. As transistors became smaller—hitting approximately 65nm in 2006 —performance and economic gains continued to subside, and as nodes dropped to 22nm and 14nm, the problem grew worse.
What is more, all of this has contributed to fabrication facilities becoming incredibly expensive to build, and semiconductors becoming far more expensive to manufacture. Today, there are only four major semiconductor manufacturers globally: Intel, TSMC, GlobalFoundries, and Samsung. That is down from nearly two dozen two decades ago.
To be sure, the semiconductor industry is approaching the physical limitations of CMOS transistors. Although alternative technologies are now in the research and development stage—including carbon nanotubes and tunneling field effect transistors (TFETs)—there is no evidence these next-gen technologies will actually pay off in a major way. Even if they do usher in further performance gains, they can at best stretch Moore’s Law by a generation or two.