Low Energy Order-To-Disorder Transition Pathways In Phase-Change Nanowires
type: CreativeWork
description: Phase change memory (PCM) can reversibly transform between the amorphous and crystalline phase within nanoseconds, making it a promising candidate for non-volatile memory (NVM) applications. The conventional method to realize the crystal−amorphous transformation in PCM is to heat the material above its melting point by an electrical pulse, after which it is quenched by sudden removal of the pulse. However, such a method requires very large current densities, which results in massive parasitic heat losses and also accelerated failure of the device. On the other hand, it has been recently shown that resistance switching in PCM systems such as superlattices and nanowires can occur at much lower current densities, where the temperature of the material always stays below its melting point. In-situ transmission electron microscopy (TEM) studies on nanowires, with a growth direction aligned with the dislocation slip system, have shown that the resistance change occurs by a dislocation-templated amorphization process. However, the resistance switching mechanism in superlattices, which consist of periodically alternating layers of two different PCM materials, has been much debated with many studies claiming it to be an order-to-order transition.In this study, we attempt to further lower the current density for the crystal-amorphous transformation by multiple strategies: pre-inducing defects in the nanowire by a size-mismatched dopant, synthesizing self-assembled compositionally modulated superlattice nanowires, and lastly by utilizing an unconventional flat phonon mode based amorphization mechanism in In2Se3 nanowires. Furthermore, we utilize TEM extensively to correlate the structural and electrical resistance changes in these nanowires, which reveal several interesting characteristics. The resistance switching mechanism in the superlattice nanowires is found to be an order-disorder transition, contrary to what is proposed in literature. Ab-initio simulations indicate that …
abstract: Phase change memory (PCM) can reversibly transform between the amorphous and crystalline phase within nanoseconds, making it a promising candidate for non-volatile memory (NVM) applications. The conventional method to realize the crystal−amorphous transformation in PCM is to heat the material above its melting point by an electrical pulse, after which it is quenched by sudden removal of the pulse. However, such a method requires very large current densities, which results in massive parasitic heat losses and also accelerated failure of the device. On the other hand, it has been recently shown that resistance switching in PCM systems such as superlattices and nanowires can occur at much lower current densities, where the temperature of the material always stays below its melting point. In-situ transmission electron microscopy (TEM) studies on nanowires, with a growth direction aligned with the dislocation slip system, have shown that the resistance change occurs by a dislocation-templated amorphization process. However, the resistance switching mechanism in superlattices, which consist of periodically alternating layers of two different PCM materials, has been much debated with many studies claiming it to be an order-to-order transition.In this study, we attempt to further lower the current density for the crystal-amorphous transformation by multiple strategies: pre-inducing defects in the nanowire by a size-mismatched dopant, synthesizing self-assembled compositionally modulated superlattice nanowires, and lastly by utilizing an unconventional flat phonon mode based amorphization mechanism in In2Se3 nanowires. Furthermore, we utilize TEM extensively to correlate the structural and electrical resistance changes in these nanowires, which reveal several interesting characteristics. The resistance switching mechanism in the superlattice nanowires is found to be an order-disorder transition, contrary to what is proposed in literature. Ab-initio simulations indicate that …
author: Modi, Gaurav
language: en
date published: 2022
date modified: 2026-07-24T03:46:55Z
provider: University of Pennsylvania
publisher: Networked Digital Library of Theses and Dissertations
type: WebPage
source organization: University of Pennsylvania