Ferroelectricity in Few Layer α−In2Se3 Flakes

This thesis explores the first steps toward realizing multiferroic memory devices based on two-dimensional (2D) ferroelectric materials, with a focus on In2Se3. Motivated by the scaling challenges of conventional semiconductor technology and the promise of van der Waals heterostructures, the project aimed to isolate few-layer In2Se3, establish fabrication protocols for graphene-based devices, and attempt nanoscale characterization of ferroelectric properties. Through iterative optimization of mechanical exfoliation, bi- and tri-layer In2Se3 flakes were successfully obtained on Si/SiO$2 substrates. Atomic force microscopy (AFM) confirmed their thickness, while piezoresponse force microscopy (PFM) was attempted to probe ferroelectric domains. Although PFM on thin flakes proved difficult—often leading to tip degradation due to leakage currents—these trials emphasized the critical role of substrate engineering and highlighted the need for upgraded measurement infrastructure to achieve...Show moreThis thesis explores the first steps toward realizing multiferroic memory devices based on two-dimensional (2D) ferroelectric materials, with a focus on In2Se3. Motivated by the scaling challenges of conventional semiconductor technology and the promise of van der Waals heterostructures, the project aimed to isolate few-layer In2Se3, establish fabrication protocols for graphene-based devices, and attempt nanoscale characterization of ferroelectric properties. Through iterative optimization of mechanical exfoliation, bi- and tri-layer In2Se3 flakes were successfully obtained on Si/SiO$2 substrates. Atomic force microscopy (AFM) confirmed their thickness, while piezoresponse force microscopy (PFM) was attempted to probe ferroelectric domains. Although PFM on thin flakes proved difficult—often leading to tip degradation due to leakage currents—these trials emphasized the critical role of substrate engineering and highlighted the need for upgraded measurement infrastructure to achieve reproducible results. Device fabrication advanced to the stage of contacted graphene Hall bars. Extensive work on electron-beam lithography dosing, resist preparation, and metal lift-off yielded a reliable process for producing clean, reproducible contacts. Transfer of In2Se3 onto graphene was initiated but not completed due to time constraints and geometric limitations of available flakes. Preliminary cryostat measurements of graphene devices were attempted but were hindered by back-gate leakage, pointing to necessary refinements in device architecture. Despite these challenges, the work establishes a foundation for future studies. It demonstrates the feasibility of obtaining atomically thin In2Se3, outlines a solid fabrication workflow, and identifies the technical setbacks in ferroelectric characterization and device testing. These insights provide a workflow for progressing toward functional In2Se3/graphene heterostructures, with the ultimate goal of demonstrating ferroelectric gating and, in the long term, enabling multiferroic memory devices.Show less

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Ferroelectricity in Few Layer α−In2Se3 Flakes