Growth of AlSb/Sb Structures for Phase Change Memories via Molecular Beam Epitaxy

Abstract

In programming phase change memory (PCM) cells, reducing the RESET current needed to amorphize the PCM material is one of the critical objectives to improve scaling and reduce energy consumption. PCM cells scaled to ~100 nm in diameter typically show RESET currents in the range of one to a few mA1. Different methods have been taken to reduce the PCM RESET current such as doping the phase change material to reduce electrical conductance and increase Joule heating within the PCM, using GeTe/Sb2Te3 superlattices2 to reduce the thermal conductivity (and conductance)of the PCM, and using ultrathin (<5 nm) PCM films such as monatomic Sb 3that enable higher amorphous phase stability and reduce thermal and electrical conductivity as well. The stochasticity of crystallization, which partially determines the reproducibility of SET state resistance programming, can be drastically reduced if template-directed nucleation at the low-energy interface is provided for ordered or epitaxial crystallization4. AlSb/Sb is a tellurium-free PCM heterostructure that may have the capability of template-directed crystallization. AlSb has a much higher melting temperature (1160°C) as compared to 631°C for Sb; therefore, the resistance programming may be controlled by the melting and crystallization of just the Sb-rich phase. In this work, we present two sets of data essential for the fabrication of an AlSb/Sb PCM stack with directed crystallization of a thin Sb layer, specifically, the results proving the feasibility of epitaxial crystal orientation of Sb on AlSb, Van der Waals – assisted orientation of AlSb on SiO2, and low-current programming of AlSb/Sb duo-layer cell with switching of thin Sb layer in the presence of polycrystalline AlSb.