  Phase change memory (PCM) is a rapidly growing technology that not only
offers advancements in storage-class memories but also enables in-memory data
storage and processing towards overcoming the von Neumann bottleneck. In PCMs,
the primary mechanism for data storage is thermal excitation. However, there is
a limited body of research regarding the thermal properties of PCMs at length
scales close to the memory cell dimension and, thus, the impact of interfaces
on PCM operation is unknown. Our work presents a new paradigm to manage thermal
transport in memory cells by manipulating the interfacial thermal resistance
between the phase change unit and the electrodes without incorporating
additional insulating layers. Experimental measurements show a substantial
change in thermal boundary resistance as GST transitions from one
crystallographic structure (cubic) to another (hexagonal) and as the thickness
of tungsten contacts is reduced from five to two nanometers. Simulations reveal
that interfacial resistance between the phase change unit and its adjacent
layer can reduce the reset current for 20 and 120 nm diameter devices by up to
~40% and ~50%, respectively. The resultant phase-dependent and geometric
effects on thermal boundary resistance dictate that the effective thermal
conductivity of the phase change unit can be reduced by a factor of four,
presenting a new opportunity to reduce operating currents in PCMs.
