My guess is we'll probably need something like graphene. Gallium Arsenide seems more like a 10 year stop-gap than a 50 year revolution. The problem is we can't get any "smaller", because we enter the quantum world and that's something entirely different. However, with graphene we can keep the transistors the same, but raise the clock speeds each generation, perhaps up to 1 TeraHerz or more, with a Moore's Law-like rate of improvement in performance.
Yeah, transistor size might reach their top pretty soon, but with 3D circuits and new materials speeds will continue to increase.
I would bet that improvements will become less predictable, though. Unfortunately, investors really dislike unpredictability, so R&D spending will probably drop.
Yeah, I don't think 1 THz is achievable, but we can likely do substantially better than 4 Ghz, even when we can't go smaller. Then there are also gains to be made from building bigger, building in 3 dimensions, decreasing waste heat, etc. I suspect that innovation with chips will get bumpier, but likely overall maintain the pace of innovation for a couple decades more - which is all we need to get into really interesting territory re AI and other things.
