In Dec, 2005, Fujitsu announced that they were able to connect carbon nanotube bumps to the miniature electrode of a high power transistor. Carbon nanotubes have thermal conductivity of 1400W/(m-K) - a level much higher than that of metal(4), and because it is possible to connect carbon nanotube-based bumps very near to the heat-generating miniature electrodes, Fujitsu successfully achieved the high amplification of flip-chips with heat dissipation levels equivalent to face-up structures.
Existing cooling technology
Reversible computing paper talking about limiting heat generation This can be done as well as spacing out the system to be less dense.
Article exploring limits of computing
Another PHd dissertation that analyses the future limits to computing and cooling
Typical passive emission 3.5 * 10 ** 22 flux bits/s cm**2 (about 100W per square centimeter)
Drexler's fractal plumbing 3.8 * 10 ** 24 flux bits/s cm**2 (about 10-100KW of heat removed per square centimeter)
Slow atomic ballistic (theoretical 1 m/s coolant) flux 10 ** 26 bits/s cm**2
Fast atomic ballistic (theoretical relativistic speed coolant) flux 3 * 10 ** 33 bits/s cm**2
Quantum maximum 5 * 10 ** 40 flux bits/s cm**2
Existing cooling is at about 1KW per square centimeter using microchannels with force d liquid convection (David Tuckerman)