In 1974 Robert Dennard came up with a scaling theory that drew on Moore's Law to promise ever-faster microprocessors. If from one generation to the next the transistor length shrinks by a factor of about 0.7, the transistor budget doubles, speed goes up by 40%, total chip power remains the same, and a legion of other good things continues to be bestowed on the semiconductor industry.
Unfortunately Dennard scaling petered out at 90 nm. Clock rates stagnated and power budgets have grown at each process node. Many traditional tricks just don't work any more. For instance, shrinking transistors meant thinner gate oxide thicknesses, but once those hit 1.2 nm (about the size of five adjacent silicon atoms), tunneling created unacceptable levels of leakage. Semiconductor engineers replaced the silicon-dioxide insulator (with a dielectric constant of 3.9) with other materials like hafnium dioxide (dielectric constant = 25), to allow for somewhat thicker insulation. Voltages had to go down, but are limited by subthreshold leakages as the transistors' threshold voltage must inevitably decline. More leakage means greater power dissipation. A lot of innovative work is being done, like the use of 3D finFETs, but the Moore's manna of yore has, to a large extent, dried up.
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