One method of making a chip 'tougher' is to physically increase the size of the semiconductor elements (e.g. transistors, FETs). This would seem incompatible with highly-integrated ICs.
This is true. For radiation hardening for space, this is exactly what is required for anything more harsh than LEO. And as a consequence, the generation of processors and memory typically used are 10-20 years behind the current state of the art. That's simply the price of reliability in harsh environments!