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Memory switching phenomenon in Ag-(As-S-Ge) superionic chalcogenides based structures


Author: Ion Stratan
Degree:doctor of physics and mathematics
Speciality: 01.04.10 - Semiconductors physics and engineering
Year:2011
Scientific adviser: Dumitru Ţiuleanu
doctor habilitat, professor, Technical University of Moldova
Institution: Technical University of Moldova
Scientific council: DH 02-01.04.10-27.03.08
Institute of Applied Physics of the ASM

Status

The thesis was presented on the 25 February, 2011
Approved by NCAA on the 31 March, 2011

Abstract

Adobe PDF document0.41 Mb / in romanian

Keywords

Chalcogenide glasses, photodissolution, kinetics, solid electrolyte, switching, programmable metallization.

Summary

The thesis is devoted to the complex study of the process of formation of superionic materials via silver photodissolution (PD) in As-S-Ge ternary chalcogenide glasses (ChG), development and characterization of nonvolatile memory cells based on these solids.

It is proposed and realized a new method of study of the kinetics of the metal (Ag) photodissolution process in chalcogenides glasses. The method consists on indirect evaluation of the thickness of the unreacted silver layer by monitoring the change which occurs in the transmittance of the Ag/ChG structure in the IR spectra as PD proceeds.

The thorough investigation of PD kinetics of Ag in ChG, as well as of optical transmittance spectra evolution of Ag/ChG structures, were pointed out some new peculiarities of this unique process, influenced by temperature and chemical composition of ChG. For the first time were experimentally confirmed calculations and theoretical conclusions of Elliott concerning the ionic-electronic mechanism of the solid electrolyte formation via Ag PD in ChG.

For the first time were systematically studied the process of Ag photodissolution in As-SGe ternary ChG and formation of quaternary solid electrolytes. This study revealed the compositional dependences of the superionic material formation process. The memory switching structures have been manufactured and characterized using prepared solid electrolytes.Were pointed out the influence of the geometry of the structure as well as the chemical composition of the solid electrolyte and the temperature on the switching threshold and other parameters of the nonvolatile memory structures. It was found that the (GeS4)0.33 (AsS3)0.67 based solid electrolyte exhibits the optimal properties to be used in electronic memory switches.

It was developed a new device for detection of toxic gases, which combines the solid electrolyte based electronic switcher with a chalcogenide chemical sensor. The thesis consists of introduction, four base chapters and conclusions. It has 107 text pages, 51 figures, 3 tables and 123 references. The main results were published in 13 scientific papers.