Memory switching in a type I amorphous chalcogenide |
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Authors: | David D Thornburg |
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Affiliation: | (1) Xerox Palo Alto Research Center, 94304 Palo Alto, California |
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Abstract: | Amorphous chalcogenides may be divided among three classes based upon the changes in local order and bond type on transition
from the amorphous to the crystalline phases. These types include: (I) Stoichiometric compounds which do not undergo significant
changes in local order on crystallization (e.g., As2Se3). (II) Stoichiometric compounds which undergo significant changes in local order on crystallization (e.g., GeTe). (III) Non-stoichiometric
alloys which phase separate on crystallization.
Previous work on memory switching has been performed primarily on type II and type III chalcogenides. The memory switching
process in thin film specimens of a type I chalcogenide, amorphous As2Se3, is examined in this paper. Measurements of the threshold voltage distribution for devices of a given thickness display a
sharp peak at some value VO . A plot of VO as a function of film thickness shows the initiation of switching to be field controlled, suggesting a non-thermal initiation
mechanism. Microscopic examination of switched devices yields evidence for Joule heating, which is enchanced by self-capacitive
energy released during switching subsequent to formation of the low resistance path.
From the thickness dependence of VO and measurements of the failure time of devices biased below threshold, a switching mechanism for this material is deduced
which incorporates spinodal decomposition of metallic As clusters in an insulating matrix. These clusters then chain under
the influence of an applied field and form a low resistance filamentary path. |
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