The article and paper don't mention it, but the thermal conductivity of single crystal diamond can be increased another 50% at room temperature by using pure carbon-12. The isotopic uniformity reduces scattering of phonons, which are what transports heat energy in diamond. For a very thin film like this the cost of using isotopically purified carbon shouldn't be that bad.
BTW, the thermal conductivity of C-12 diamond at cryogenic temperature is even higher, reaching something like 41000 W/m K at 104 K.
Isotopically purified silicon has also been considered due to its higher thermal conductivity, but the effect there at room temperature is not nearly as dramatic.
Weirdly, I read UV damage in C-12 diamond is reduced by a factor of 10 vs. natural diamond, I understand because this damage process is mediated by phonons. No relevance to the chip use case (unless UV damage in photolithography could be important?), but I found it interesting.
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