It seems like there has been so much research being done on making circuits and components that are smaller and smaller, but at a certain point we are going to be designing components and boards that are literally just a few atoms wide.
Why is it that companies pour so much money into making say a 4 layer circuit board that is 10 square inches still only a flat 4 layers but maybe 8 square inches, rather than just making an 8 layer board only 5 square inches for example? (8 is still possible and it is done, but why isn't this taken up to say 100 layers or more?)
Also does this same principle apply to IC design? Are ICs usually only a few layers and spread into thin sheets, or are they typically built more vertically?
*Edit: So one thing that has become apparent to me from the comments is the fact that in circuit board design you can only really place components on the outer 2 layers. That would make inner layers unnecessary for anything other than weaving. What about in IC design, something like an intel processor? Are there still special components on the outer two layers, or is a processor more 3D than a circuit board?