Abstract: Threshold switching in amorphous chalcogenides underpins the operation of Ovonic Threshold Switching (OTS) selectors and phase-change memory (PCM) devices used in high-density cross-point memory architectures. Despite extensive macroscopic and microscopic characterisations, a direct physical linkage between threshold switching behaviour and the topology of the amorphous network remains unresolved. This thesis addresses this gap by systematically investigating the role of amorphous network connectivity in governing threshold switching dynamics in GexTe100−x systems. Time-resolved transient electrical measurements were performed on GeTe, GeTe4, and GeTe6 devices across nanosecond and sub-nanosecond timescales. Key switching parameters, including threshold voltage, delay time, and holding voltage, were extracted under controlled excitation spanning sub-threshold to super-threshold regimes. GeTe4 exhibits stable and repeatable switching, with delay times of ~10 ns, reducible to ~300 ps under moderate overvoltage, consistent with its near-isostatic network configuration. Comparative analysis of GeTe6 and GeTe devices reveals that Te-rich GeTe6, characterised by a floppy and weakly constrained network, enables faster and lower-power switching than rigid GeTe. Raman spectroscopic measurements confirm enhanced vibrational flexibility in Te-rich compositions, establishing a direct correlation between vibrational dynamics and electrical switching behaviour. Overvoltage-dependent delay time characteristics further demonstrate a strong dependence of threshold switching dynamics on Te-Te connectivity. This work establishes threshold switching as a topology-driven non-equilibrium phenomenon in amorphous semiconductors. Reduced amorphous network connectivity promotes topological softening and localised excitations regions, facilitating rapid formation of transient conductive pathways under electrical or optical stimulation. By integrating constraint theory, vibrational analysis, and ultrafast electrical measurements, the thesis identifies amorphous network connectivity as the key determinant of threshold switching behaviour. These findings provide both fundamental insight and practical design principles for engineering high-speed, low-power selector materials, with implications for next-generation memory and neuromorphic computing technologies.

Event Details
Title: Unravelling the Role of Tellurium Network Connectivity in Sub-nanosecond Threshold Switching Dynamics of Amorphous GexTe100−x Devices (PhD Viva Voce)
Date: April 08, 2026 at 03:00 PM
Venue: Google Meet (http://meet.google.com/msh-ymjq-nrb)
Speaker: Mr. Sakthikumaran (EE18D040)
Guide: Dr. Anbarasu Manivannan
Type: PHD seminar

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