In situ TEM study of crystallization and chemical changes in an oxidized uncapped Ge2Sb2Te5 film

Abstract

Ge2Sb2Te5 (GST-225) has been the most used active material in nonvolatile phase-change memory devices. Understanding the kinetics and dynamics involved in crystallization is critical for the optimization of materials and devices. A GST-225 thin film of 20 nm thickness was prepared by sputtering directly onto a Protochip and left uncapped and exposed to atmosphere for approximately 1 year. Early stages of crystallization and growth of the film have been studied inside the TEM from room temperature to 140 °C. The morphological and structural transformations have been studied by a Cs-corrected environmental TEM, and images have been recorded using a high-speed low electron dose camera (Gatan K3 IS). The amorphous to crystalline transformation has been observed at ∼35 °C. From the large field, high-resolution images obtained using the Gatan K3 IS camera early crystallization can be detected and nucleation rates and growth velocities can be obtained.

Asymmetric nanoparticle oxidation observed in-situ by the evolution of diffraction contrast

“…When coupled with aberration correction, TEM performed in bright-field conditions can allow for real-time tracking of atomic movement and facet reconstruction at exposed crystalline surfaces to provide information on nanoparticle evolution with unprecedented temporal and spatial resolution. This has been helped significantly by the development of next-generation direct electron detection cameras that can image at incredibly high speeds and low electron dose rates [5][6][7][8][9]. Further, the increased field of view in such cameras increases the chances of detecting and tracking the dynamical evolution of a nanoparticle of interest.…”

An experimental study of Ge diffusion through Ge2Sb2Te5

“…11,20,21 It is commonly accepted that these variations in resistivity observed at temperatures ranging from room temperature to some 200°C result from Ge diffusion via these grain boundaries and from the subsequent atomic rearrangements at the grain boundaries. 18,22,23 In summary, several types of diffusivity would be needed to describe and simulate the atomic mechanisms involved in the forming, SET and RESET operations of PCM cells, as well as to predict the observed degradations (drifts or failures) of PCM cells based on GST alloys, over time. Unfortunately, the literature is poor in data relevant to the diffusion of Ge in GST alloys.…”

Measuring Electrical Resistivity at the Nanoscale in Phase-Change Materials

“…To understand the operation of devices, different in situ techniques have been developed to monitor the phase transition, notably in transmission electron microscopy (TEM) . A distinction needs to be made between in situ experiments that heat the whole specimen, usually thin films, to provoke the phase change − and operando experiments that aim to be closer to the actual operation of devices by injecting current pulses in situ . , However, all depend on structural or chemical analysis and do not probe directly the local electrical properties. Here we present a method based on operando electron holography to determine the local resistance with nanometer spatial resolution.…”