Ph.D. in Information Technology: Final Dissertation
DEIB - Alfa Room
June 13th, 2016
11.00 am
June 13th, 2016
11.00 am
Abstract
On June 13th, 2016 the final dissertation of the candidate of the Ph.D. in Information Technology will be held at DEIB Alfa Room and will start at 11.00 am:
Luca Crespi – XXVIII Cycle
"Characterization and Modeling of Chalcogenide Alloys Stoichiometric Stability during Phase Change Memory Operation"
Advisor: Prof. Andrea Lacaita
Abstract:
This thesis work focuses on the characterization and modeling of stoichiometric instabilities in chalcogenide materials for non-volatile Phase Change Memory, with emphasis on ternary alloys bases on Germanium, Antimony and Tellurium.
Two major device architectures have been investigated, namely, the Wall Architecture, based on the heater electrode concept, where a resistive electrode generates the heat necessary to melt the active material, and the Line Architecture, based on the self-heating concept, where the heat is generated within the active material.
Through an accurate experimental characterization, the architectures have been described in their electrical, thermal, mechanical and mass transport aspects. An electrical characterization, aimed to define the device properties, in terms of electrical current density and temperature profile, has been performed. The results obtained where later used to select the best electrical conditioning to highlight mass transport effects.
After the electrical preparation, the cells have been cut for EDX imaging or exposed to synchrotron light for X-ray fluorescence analysis, in order to acquire elemental maps depicting the atomic profiles. The behavior of the various elements has been studied, highlighting the local variations in material ratio and showing that it qualitatively followed the data already reported in literature.
Once the elemental trends were available, a quantitative numerical model for mass transport was developed. Such model took into account all the mass transport drivers present in a Phase Change Memory, like the electric field, the thermal gradient, the mechanical stress gradient and the material total concentration variation. The model can also take into account the differences of material properties based on the local stoichiometry, and modify the material parameters accordingly, while at the same time keeping all the equations self-consistent.
The developed numerical model has been applied to both Wall and Line Architectures, resulting in a very good match with the experimental atomic profiles, allowing for the calibration of driver's coefficients and atomic diffusivity for each element.
Luca Crespi – XXVIII Cycle
"Characterization and Modeling of Chalcogenide Alloys Stoichiometric Stability during Phase Change Memory Operation"
Advisor: Prof. Andrea Lacaita
Abstract:
This thesis work focuses on the characterization and modeling of stoichiometric instabilities in chalcogenide materials for non-volatile Phase Change Memory, with emphasis on ternary alloys bases on Germanium, Antimony and Tellurium.
Two major device architectures have been investigated, namely, the Wall Architecture, based on the heater electrode concept, where a resistive electrode generates the heat necessary to melt the active material, and the Line Architecture, based on the self-heating concept, where the heat is generated within the active material.
Through an accurate experimental characterization, the architectures have been described in their electrical, thermal, mechanical and mass transport aspects. An electrical characterization, aimed to define the device properties, in terms of electrical current density and temperature profile, has been performed. The results obtained where later used to select the best electrical conditioning to highlight mass transport effects.
After the electrical preparation, the cells have been cut for EDX imaging or exposed to synchrotron light for X-ray fluorescence analysis, in order to acquire elemental maps depicting the atomic profiles. The behavior of the various elements has been studied, highlighting the local variations in material ratio and showing that it qualitatively followed the data already reported in literature.
Once the elemental trends were available, a quantitative numerical model for mass transport was developed. Such model took into account all the mass transport drivers present in a Phase Change Memory, like the electric field, the thermal gradient, the mechanical stress gradient and the material total concentration variation. The model can also take into account the differences of material properties based on the local stoichiometry, and modify the material parameters accordingly, while at the same time keeping all the equations self-consistent.
The developed numerical model has been applied to both Wall and Line Architectures, resulting in a very good match with the experimental atomic profiles, allowing for the calibration of driver's coefficients and atomic diffusivity for each element.
