It is a combination of things, of which cooling is one. A more fundamental and challenging physical limit is increased loss due to higher frequency (which is wh

It is a combination of things, of which cooling is one. A more fundamental and challenging physical limit is increased loss due to higher frequency (which is why chip voltage needs to be increased). It gets to the point where too much signal loss occurs across "long" lines between parts of the chip. This is why using plasmonics in ICs is an active field of research; the hope is to be able to use optics for long distance interconnects inside the processor.