Superconducting Superlattices for Cryogenic Systems

This study presents the development of highly thermally resistive interconnects for cryogenic integrated systems. These interconnects are based on a superconducting superlattice technology to enhance the thermal resistance via phonon interface scattering while maintaining perfect electrical conduction at low temperatures. After the qualification of single TiN and Nb films with critical temperatures of 4.9 K and 8.7 K respectively, superlattices with 5-period TiN/Nb bilayers were fabricated to morphologically, electrically and thermally evaluate the potential of this technology. These characterizations demonstrate an effective critical temperature of 8.4 K and compelling thermal properties at sub-K temperatures with a thermal conductivity of $9.7 \cdot 10^{-7} \mathrm{W} / \mathrm{m} \cdot \mathrm{K}$ at 1 K. The implementation of the super-conducting superlattice into 20 $\mu\mathrm{m}$-diameter interconnects in a two- tier demonstrator is then discussed.