Temperature-Dependent Thermal Properties of Phase-Change Memory Electrode Materials

The programming current required to switch a phase-change memory cell depends upon the thermal resistances in the device. In many designs, significant heat loss occurs through the electrode. This letter investigates the thermal properties of a multilayer electrode stack. This material offers greater thermal resistance than single-material electrodes due to the presence of multiple thermal boundary resistances (TBRs), reducing heat loss from the device and potentially lowering the programming current. Picosecond time-domain thermoreflectance interrogates the temperature-dependent thermal conductivity of three as-deposited and postannealed electrode materials: carbon, titanium nitride, and tungsten nitride. These data are used to extract the temperature-dependent, as-deposited, and postannealed TBR in two multilayer electrode stacks: carbon-titanium nitride and tungsten-tungsten nitride. The C-TiN stacks demonstrate an as-deposited TBR of 4.9 m²K/GW, increasing to 11.9 m²K/GW postanneal. The W-WN_x stacks demonstrate an as-deposited TBR of 3.9 m²K/GW, decreasing to 3.6 m² K/GW postanneal. These resistances are equivalent to electrode films with thickness on the order of tens of nanometers.