Electron Scattering at Ru–TiN–Ru Interface Stacks

Electron transport across Ru-TiN–Ru interfaces is quantified using multilayers containing five 10-nm-thick Ru(0001) layers separated by TiN interlayers with nominal thicknesses
${d}_{\text {TiN}}$
ranging from 0.01 to 1.6 nm. The multilayers are deposited by sputtering on Al2O3(0001) substrates at
$700~^{\circ }$
C. Their resistivity parallel to the interfaces increases linearly from
$\rho = {7.8}$
–
${11.2}~\mu \Omega $
-cm with increasing
${d}_{\text {TiN}} =0$
–0.2 nm and saturates at a constant
$\rho = 13.3~\pm ~2.5~\mu \Omega $
-cm for
${d}_{\text {TiN}} \ge 0.4$
nm. The linear increase is attributed to electron impurity scattering at a discontinuous TiN layer while resistivity saturation is associated with parallel conduction in individual Ru layers without coherent transport between Ru layers. The data indicate a critical
${d}_{\text {TiN}} =0.4$
–0.6 nm above which electron transport across Ru-TiN–Ru is completely diffuse, leading to a Ru-TiN–Ru contact resistance that is proportional to the TiN layer thickness. This critical thickness is in good agreement with the onset
${d}_{\text {TiN}} =0.4$
–0.6 nm of a decrease in the out-of-plane X-ray coherence length, the onset at
${d}_{\text {TiN}} =0.4$
nm of a detectable X-ray diffraction (XRD) superlattice peak, and the development of X-ray reflectivity (XRR) superlattice fringes for
${d}_{\text {TiN}} \ge 0.4$
nm.