Electrical Switching Characteristics and Thermal Properties of Tellurium based Chalcogenide Glassy Alloys

Abstract

Chalcogenide compounds have gained considerable research interest in the recent past owing to their capability to transform from an amorphous to crystalline phase and exhibit entirely different electrical properties that can be applied in building new class of memories such as phase-change memories, programmable metallization cells and cross-point devices. The present thesis is focussed on the study of the electrical switching behaviour and thermal properties of Te-based ternary chalcogenide glassy alloys to understand the effect of metallic dopants on switching voltages and their thermal characteristics. A novel approach to prepare chalcogenide glassy alloys has been discussed. In this work, two series of chalcogenide systems, namely Ge-Te-Sn and Si-Te-Bi were chosen to study the electrical and thermal properties of these systems. I-V characteristic studies revealed that all the samples prepared had a smooth memory type switching property. Scanning electron microscopy (SEM) studies on pre- switched and post switched samples revealed the morphological changes on the surface of the sample such as the formation of the crystalline filament between two electrodes during switching. Furthermore, the studies on the sample thickness and temperature dependence on switching voltages revealed the nature of switching mechanism. Differential scanning calorimetric (DSC) studies have been undertaken for the thermal analysis of Ge-Te-Sn and Si-Te-Bi chalcogenide samples. We have investigated the crystallization kinetics of prepared chalcogenide glassy systems. Thermal parameters such as change in specific heat (∆Cp), fragility index (F), thermal stability (∆T), enthalpy (∆Hc) and entropy (∆S) are deduced to interpret distinct material behaviour as a function of composition. Structural evaluation like thermal devitrification studies and morphological changes elucidate on restricted glass formability of the Te-based chalcogenide glass system. Finally, the relationship has been established between the thermal parameters and electrical switching characteristics.