Phd in PHYSICS

Thesis title: Study of phase-change materials for low-energy devices

This PhD thesis explores recent advancements in phase-change materials (PCMs), a class of materials employed in phase-change memories (PCMs) for neuromorphic applications. While PCMs offer energy-efficient switching, the fabrication of nanoscale devices faces challenges such as resistance drift and atomic migration during cycling. A promising strategy to mitigate these issues involves the design of phase-change heterostructures (PCHs), where the phase-change material is confined by a carefully selected material. This work investigates the feasibility of such heterostructures and their potential for practical implementation. The study begins with a broad overview of PCMs and PCHs, highlighting their current limitations and recent advancements. A key focus is placed on novel heterostructures based on Ge₂Sb₂Te₅ and GeTe, confined by TiTe₂. Computational simulations indicate that these heterostructures can be experimentally realized and exhibit promising switching properties. Additionally, a heterostructure composed of pure Sb confined by TiTe₂ is analyzed, revealing ultrafast recrystallization dynamics that could be advantageous for memory applications. Beyond PCHs, this thesis contributes to the study of thin Bi films, in collaboration with RWTH Aachen University. By varying the film thickness, the work examines Peierls distortions and bonding mechanisms, demonstrating that the electronic and structural properties of Bi can be tuned, transitioning from covalent to metavalent bonding. Furthermore, a collaboration with STMicroelectronics involves TCAD simulations of Ge₂Sb₂Te₅-based memory cells, enabling the development and calibration of models to accurately reproduce device behavior. Overall, this research advances the understanding of PCHs as a viable approach for in-memory and neuromorphic computing, while also proposing new strategies for optimizing PCM-based devices. The findings highlight the significant potential of PCHs and suggest further experimental and computational investigations to refine and expand their applicability.