Crystallization properties of melt-quenched Ge-rich GeSbTe thin films for phase change memory applications

S M S Privitera,I López García,M C Cyrille,V Sousa,C Sabbione,G Navarro,E Rimini,C Bongiorno,E Carria

doi:10.1063/5.0023696

Abstract

The crystallization process of melt quenched Ge-rich GeSbTe films, with composition optimized for memory applications, has been studied by optical reflectance measurements. The optical properties have been related to the structure and composition by means of the effective medium approximation. The compositional variations have been investigated by transmission electron microscopy and electron energy loss spectroscopy. Amorphous materials prepared by melt-quenching with different laser energy densities have been studied. For the energy density of 1.5 J cm−2, a uniform amorphous layer, with embedded Ge crystalline grains, is obtained. The film exhibits a crystallization temperature of 275 °C and no relevant phase separation during crystallization. For a lower energy density of 1 J cm−2, only half of the film thickness is quenched to the amorphous phase, with Ge depletion. The crystallization temperature of the Ge depleted film is 245 °C, and a partial phase separation occurs.

Highlights

One of the most promising non-volatile memory technologies is based on phase change materials (PCMs)
The crystallization process of melt quenched Ge-rich GeSbTe films, with composition optimized for memory applications, has been studied by optical reflectance measurements
Several PCMs working at a temperature compatible with automotive applications have already been selected

Summary

Introduction

One of the most promising non-volatile memory technologies is based on phase change materials (PCMs). In the particular case of Ge-rich GST, it has been shown that during the initial seasoning procedure, Ge segregates at the periphery of the liquid zone, impoverishing the melted volume Such a stoichiometry modification seems to occur only during the initialization process, leading to a stable active cell. Atomic diffusion, with the subsequent stoichiometry variation, may be a factor playing a relevant role in the endurance, especially when the device is made by two different compositions and operates at high temperatures For this reason, the crystallization of the as deposited amorphous film, characterized by the formation of pure Ge crystalline grains as studied recently, may be markedly different in the case of melt quenched materials in which Ge atoms tend to segregate outside the liquid zone

Methods

Results

Conclusion