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Title: Reversible electrical breakdown in amorphous chalcogenides
Author: Irfan, A. Y.
ISNI:       0000 0004 2737 4491
Awarding Body: University of Greenwich
Current Institution: University of Greenwich
Date of Award: 1974
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An investigation has been made of reversible electrical breakdown in amorphous chalcogenides with particular attention being paid to the on-state properties of Si12 Te48As30Ge10 glass threshold switches. Apparatus is described for the preparation of well-characterised materials and flash-evaporated thin-film switching devices. Measurements have been made of the current-voltage characteristics, including the effect of variation of thermal boundary conditions on the stability and form of the on-state behaviour. All tested devices have been found to undergo a forming process which is attributed to structural changes in the device material. These structural changes have been substantiated by measurements on virgin and formed devices of (i) off-state resistance as a function of number of switching operations, (ii) off-state resistance as a function of electrode contact area, (iii) device conductance versus frequency and (v) the effect of uniaxial pressure on device off-state current. The results satisfy a model for a formed device in which there is a highly conducting and inhomogeneous filamentary region surrounded by a low-conducting glass. It is shown that when the thermal conductivity of the device electrode material is two or three orders of magnitude greater than that of the switching glass, the magnitude of the minimum holding voltage is proportional to the square root of the thermal conductivity of the electrode material. This observation is consistent with a thermal constriction model where the minimum holding voltage is the sum of the voltage drops across the filament constrictions at electrode/glass interfaces. The holding current is shown to be a linear function of ambient temperature and extrapolates to zero at a temperature similar to that for a threshold voltage - temperature plot. Photographic recordings of the current-voltage characteristics of the switching devices have shown that the on-state of a formed device consists of several distinct branches depending on the switching history of the device and the electrode materials. The multiply-branched on-state is interpreted in terms of sequential forming of current channels between tellurium-crystallite clusters and the electrodes. Several mechanisms are discussed to explain the origin of these current channels and the localized thermal breakdown mechanism is considered to be the most favourable one.
Supervisor: Williams, J. L. Sponsor: Not available
Qualification Name: Thesis (Ph.D.) Qualification Level: Doctoral
EThOS ID:  DOI: Not available
Keywords: QC Physics