Nanoscale crystallization of phase change Ge₂Sb₂Te₅ film with AFM lithography

Abstract

We have made nanoindents on Ge(2)Sb(2)Te(5)(GST) films using electric field-assisted atomic force microscope (AFM) lithography. GST shows increase of material density and electric conductivity as it changes from amorphous to crystalline phases. By applying electric field between AFM probe-tip and GST surface, nanoscale crystallization could be induced on tip contact area. As the crystallized GST exhibits increase of material density, that is to say depression of volume, nanoindented surface with crystallization is created on host amorphous GST (a-GST) film. For the AFM lithography, a highly conductive tip, which showed voltage-switching characteristics in current-voltage spectroscopy of GST film, was found to be very suitable for recording and sensing crystallized nanoindents on the GST film. By varying sample bias voltages, we performed nanoscale crystallization, and measured the nanostructured film in AFM conductance-image (C-image) mode and topography-image (T-image) mode, simultaneously. Two types of crystallized wires were fabricated on (a-GST) film. Type-I was sensed in only C-image, whereas Type-II was sensed in both C-image and T-image. These nanowires are discussed in terms of crystallization of GST and sensitivity of current (or topography) sensing. By repeated lithography, larger size of nanoindented wires were also produced, which indicates line-dimension controllability of AFM lithography.

Nanoscale multilevel switching in Ge2Sb2Te5thin film with conductive atomic force microscopy

“…In our works, the thickness of the GST sample is 50 nm, the threshold switching and memory switching occurred at around 2 V and 7.2 V, respectively (shown in figure 7). In the works by Kim et al [14,15], the thickness of the GST sample was 150-200 nm and the scanning voltage was lower than 10 V. In our previous works [24], the thickness of the GST sample was 50 nm, and the scanning voltage was lower than 2 V. Then we considered that the highest scanning voltage did not reach the memory switching voltage, only the threshold switching was observed.…”

“…However, the former switching is a pure electronic process induced by high electric field, while the latter is a structural change process caused by the Joule heat. In previous reports, only one switching process was observed [14,15]. Moreover, nanoscale conductive marks were produced by applying IV-spectra on the amorphous GST thin film, and related characteristics are considered.…”

Evaluating Adoption, Impact, and Factors Driving Adoption for TREWS, a Machine Learning-Based Sepsis Alerting System

“…Population characteristics and overall adoption rates (Study question 1) were estimated using all patient encounters with an alert or sepsis diagnosis during this period. Based on a refinement of the criteria used in the third sepsis consensus definition (Sepsis-3) 30 and the CDC Adult Sepsis Event Toolkit sepsis criteria 61 , sepsis cases were retrospectively identified using EHR-based sepsis phenotyping, which identifies patients with sepsis based on clinical symptoms and orders indicating suspected infection and related acute organ dysfunction within 48 hours of each other, while also adjusting for the effects of confounding comorbidities on these criteria 34,35 .…”

Nanothermal characterization of amorphous and crystalline phases in chalcogenide thin films with scanning thermal microscopy

“…5,6 Finding stoichiometries that promote a fast crystallization time, lower threshold switching voltage/current between states, and improved high-cycle reliability are of particular interest. 7 Although various scanning probe microscopy (SPM) techniques have been employed to study these materials by electrical 1,[8][9][10][11] and nanomechanical 12,13 means, there lacks a quantitative, non-destructive characterization method to investigate local nanoscale thermal properties of PCM that is a critical factor for their switching energy and read/write dynamics. Several methods are currently employed to study thermal properties, such as Raman spectroscopy and IR spectroscopy, however, these have a spatial resolution limited to the micron scale.…”