Interface-Dominated Thermal Transport in Sb₂Te₃/TiTe₂ Superlattices

The high energy consumption of phase change memory remains one of the biggest hurdles toward its widespread implementation. Most phase change materials demonstrate a high contrast in thermal conductivity between the amorphous and crystalline phases with the latter having the higher value. This is detrimental, as a high thermal conductivity will allow heat, meant to drive the phase change, to diffuse into the surrounding structures, increasing the energy demand even further. In order to address this high contrast, the Sb₂Te₃/TiTe₂ superlattice is studied using a bottom-up approach: starting with the individual materials, before studying full superlattices. X-ray diffraction is used to study the structure and stability, while time-domain thermoreflectance gives insight into the thermal transport characteristics of these materials and their superlattice. Incoherent diffuse phonon transport is found to be responsible for heat flow in both Sb₂Te₃ and TiTe₂. The combination of both materials into a superlattice reduces the thermal conductivity contrast by 92% from 0.69 W m^-1 K^-1 to 0.05 W m^-1 K^-1. Room-temperature measurements indicate that in a superlattice composed of 5 nm Sb₂Te₃ and 3 nm TiTe₂ layers the thermal conductivity remains approximately 0.2 W m^-1 K^-1 for both phases. The creation of this superlattice effectively eliminates the thermal conductivity contrast, preventing unwanted heat dissipation during phase transitions. This work shows that superlattice engineering can play an important role in managing the energy consumption of phase change memory devices.