Die shrink challenges force innovation in other areas

Why has Intel poured money into developing FinFET’s? Because planar silicon doesn’t scale very effectively past 28nm. Why push into graphene, or carbon nanotubes, or for more mundane advances like 3D chip stacking? Because our ability to shrink feature sizes is hitting a wall. Why research the GreenDroid concept, where certain common functions are implemented directly in semi-programmable hardware? Because die size is something we have lots of. Lithography expert Chris Mack has discussed what he calls the “design gap” — the difference between the chips we could be designing, and the chips that are actually being built.

Potential vs. actual chip sizes

The reason transistor counts have continued to rise on CPUs over the last few years has less to do with the actual core logic and more with the other components we now integrate on-die. We now integrate multiple CPU cores, each with its own cache bank — there’s more cache in an Ivy Bridge-E than the amount of RAM that my $1000 desktop shipped with, back in 1997. And even so, we could be building chips far larger than we do. The race is on to find better ways to build cores rather than simply driving feature size shifts, because the costs are rising too quickly for any company to play forever.

Leading edge foundries over time

There were 19 companies still actively building leading-edge capacity at the 130nm. At 22nm/20nm, there are five (GlobalFoundries ought to be on this list). UMC is going to be active at 20nm eventually, but its ramp is running well behind the primary companies. In 1987, 20 of the top 20 semiconductor companies owned their own leading-edge fabs. In 2010, just seven did. As the cost of moving to new processes skyrockets, and the benefits shrink, there’s going to come a time when even Intel looks at the potential value and says, “Nah.”

Semiconductor factory costs

But this doesn’t mean the death of improvements in silicon. On the contrary, there are potential solutions and improvements that haven’t been explored before, partly because the emphasis and cash have always flowed towards smaller process shrinks. The benefit to finding ways to improve a specific process has always been balanced against the expectation that a smaller node would be available in 18-36 months. As that changes, foundries will find ways to improve the final product in other ways.
