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Title: Memory switching processes in chalcogenide glasses
Author: El-Khishin, Ahmed Tawfik
Awarding Body: University of Edinburgh
Current Institution: University of Edinburgh
Date of Award: 1979
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The aim of this work was to investigate the processes iInvolved in the memory switching phenomenon in chalcogenide glasses. The experimental study was performed using the stable memory switching composition Ge15Te815b252 although some trials were made on compositions from the pseudo-binary As 2T83 + GeTe. The experimental study included characterization of the materials by measurement of their electrical conductivity as a function of temperature and electric field. The lock-on time to establish a memory on-state was measured as a function of pulse parameters, ambient temperature, device geometry, parallel capacitance and substrate thermal conductivity. The results were consistent with a high temperature filament leading to the growth of a crystalline filament. The capacitive discharge energy was found to play an essential role in the memory switching process indicating the thermal nature of the on-state even during the first nanoseconds of the switching event. The measurements of the lock-on time as a function of device diameter and substrate thermal conductivity indicated that the filament temperature may not be critically dependent on the substrate thermal properties while the device diameter had a substantial effect on the filament temperature. The results of the study of the effect of illumination on lock-on time (to check non-thermal mechanisms) were not conclusive. However, It was found that the effect of the electric field is to inhibit nucleation. Thus the decrease of the lock-on time with the amplitude of the applied pulse was explained in terms of the effect of the capacitive discharge energy and not an electric field enhanced nucleation rate. The memory performance of the different compositions from the pseudo binary As2Te3 + GeTe was correlated to the glass transition temperature, crystallization temperature and the composition of the crystalline filament. The discussed processes were related to the device failure mechanisms and operating conditions in order to improve the device lifetime and its reliability.
Supervisor: Not available Sponsor: Not available
Qualification Name: Thesis (Ph.D.) Qualification Level: Doctoral
EThOS ID:  DOI: Not available