Low Thermal Conductivity Phase Change Memory Superlattices

TL;DR

This paper demonstrates that doping Sb2Te3-GeTe superlattices with titanium significantly reduces thermal conductivity, enabling faster, lower-voltage phase change memory switching with improved energy efficiency.

Contribution

The study introduces Ti doping in Sb2Te3-GeTe superlattices to lower thermal conductivity and enhance phase change memory performance, a novel approach for energy-efficient memory devices.

Findings

Ti doping halves switching energy compared to undoped superlattices.

Thermally optimized superlattice has a thermal conductivity of 0.25 W/m.K.

Prototype devices switch faster and at lower voltage.

Abstract

Phase change memory devices are typically reset by melt-quenching a material to radically lower its electrical conductance. The high power and concomitantly high current density required to reset phase change materials is the major issue that limits the access times of 3D phase change memory architectures. Phase change superlattices were developed to lower the reset energy by confining the phase transition to the interface between two different phase change materials. However, the high thermal conductivity of the superlattices means that heat is poorly confined within the phase change material, and most of the thermal energy is wasted to the surrounding materials. Here, we identified Ti as a useful dopant for substantially lowering the thermal conductivity of Sb2Te3-GeTe superlattices whilst also stabilising the layered structure from unwanted disordering. We demonstrate via laser heating that lowering the thermal conductivity by doping the Sb2Te3 layers with Ti halves the switching energy compared to superlattices that only use interfacial phase change transitions and strain engineering. The thermally optimized superlattice has (0 0 l) crystallographic orientation yet a thermal conductivity of just 0.25 W/m.K in the "on" (set) state. Prototype phase change memory devices that incorporate this Ti-doped superlattice switch faster and and at a substantially lower voltage than the undoped superlattice. During switching the Ti-doped Sb2Te3 layers remain stable within the superlattice and only the Ge atoms are active and undergo interfacial phase transitions. In conclusion, we show the potential of thermally optimised Sb2Te3-GeTe superlattices for a new generation of energy-efficient electrical and optical phase change memory.