Well, unless one devises a way to break up atoms + rearrange those in such a way as to turn protons, neutrons, quarks etc. into compute machinery, we're stuck with individual atoms (or small groups of those) as the smallest possible building blocks. And thus Moore's law will hit a brick wall at some point. 3D structures (stacks w/ many layers of transistors & interconnect) will help, but make thermal issues more difficult than they already are.

Kind of like (iirc) the tip of a scanning tunneling microscope might be used to pick up & manipulate individual atoms.

Self-organizing materials like DNA might make that process easier, not scale it down further.

Read up on Molecular Nanotechnology.

Perhaps the thermal issues could be solved with LK99 :)