Fig. 4. Annealing effect on the in-plane thermal conductivity.

SSTR measured in-plane thermal conductivity of our annealed Cu films as a function of a, b thickness, c annealing temperature, and d grain size. Figure 4b is the magnified version of Fig. 4a for the thickness of ≈57 nm or greater. The thickness of the films is indicated with arrows in Fig. 4c, d. Figure 4c features trace lines for film thicknesses of 27, 43, and 57 nm, highlighting thermal conductivity trends with annealing. The appearance of grain boundary segregation during annealing reduces the thermal conductivity of 27 nm Cu.