Information reliability evaluation of a Ge2Sb2Te5-based phase change memory cell

The information reliability of phase change memory cells at different ambient temperatures has been assessed for the first time. The statistical approach chosen is based on A.N. Kolmogorov’s heuristic theory, which describes the kinetics of isothermal crystallization. We have analyzed the influence of the phase change memory cell size and critical size of crystalline nuclei, which depends on the physicochemical parameters of the material and temperature. The results demonstrate that the information reliability of phase change memory cells of typical dimensions can be sufficiently high up to 100°C. Calculation results are compared to available experimental data.     

Influence of chalcogenide glasses electro physical parameters on threshold voltage for phase-change memory

The simple equations have been derived for main setting parameters of phase-change memory (PCM) devices. The calculations of threshold voltage and delay time are carried out based on emission model for an initial stage of electric breakdown in amorphous semiconductors. The temperature dependences of threshold voltage agree with the experimental data for GST material.     

Influence of the Degree of Crystallinity on the Dispersion of the Optical Parameters of Ge2Sb2Te5 Phase-Change Memory Thin Films

Semiconductors - Abstract—Extensive studies of Ge2Sb2Te5 material are associated with the possibility of producing multilevel nonvolatile elements for high-speed integrated optical functional...     

Retrieval of some parameters of an amorphous chalcogenide semiconductor from the temperature and field dependences of its conductivity

We study the conductivity of amorphous chalcogenide films used in phase-change-memory (PCM) devices which are based on the effect of reversible switching of a semiconductor from the high-(amorphous) to the low-resistivity (crystalline) state under the external electrical actions. Temperature and electric-field dependences are studied for the high fields E ≥ 10⁵ V/cm. It is shown that in this domain, the conductivity is mainly contributed by the field emission of nonequilibrium carriers (holes) from deep levels near the Fermi energy. Based on the developed model, we calculate such parameters as the density of the emission centers and the mean free path of nonequilibrium holes at room temperature. The results of calculations are compared with data obtained by other methods. It is shown that the adopted model adequately describes the basic experimental dependences.     

Phase separation in chalcogenide semiconductors of the Ge-Te system upon thermal cycling

Close-to-eutectic compositions in the Ge-Te system are analyzed and their behavior with repeated heat treatments is studied by means of differential scanning calorimetry and X-ray diffraction. It is shown that repeated heat treatment of the compositions under study leads to phase separation in the material. Assumptions are made about the nature of processes occurring in the materials subjected to heat treatment.     

Electrical conductivity of amorphous films of chalcogenide compounds in high electric fields

Effect of the electric field’s strength and temperature on the electrical conductivity of amorphous thin films of chalcogenide compounds has been studied. It is demonstrated that, at strengths of the electric field exceeding 10⁴ V cm^?1, the current increases exponentially as the voltage is increased. The activation energy of the temperature dependence of the conductivity decreases as the strength of the electric field is increased. A model that satisfactorily describes the experimental data is suggested on the basis of the assumption that the increase in the carrier concentration with the field strength has a dominant effect on the conductivity. The effective carrier’s mobility of ～10^?2 cm² V^?1 s^?1 and the activation length of ～(10–30) nm, which represents the influence of the electric field, are used as characteristic parameters of the model.     

Physical aging of chalcogenide glasses

Physical aging effects are shown to be typical of chalcogenide glasses with an under- or overconstrained network and to influence their physicochemical properties. The natural physical aging of glasses can be accelerated by gamma irradiation or exposure to light.     

Electrical properties and transport mechanisms in phase change memory thin films of quasi-binary-line GeTe–Sb<Subscript>2</Subscript>Te<Subscript>3</Subscript> chalcogenide semiconductors

The temperature dependences of the resistivity and current–voltage (I–V) characteristics of phase change memory thin films based on quasi-binary-line GeTe–Sb₂Te₃ chalcogenide semiconductors Ge₂Sb₂Te₅, GeSb₂Te₅, and GeSb₄Te₇ are investigated. The effect of composition variation along the quasibinary line on the electrical properties and transport mechanisms of the thin films is studied. The existence of three ranges with different I–V characteristics is established. The position and concentration of energy levels controlling carrier transport are estimated. The results obtained show that the electrical properties of the thin films can significantly change during a shift along the quasi-binary line GeTe–Sb₂Te₃, which is important for targeted optimization of the phase change memory technology.     

Deformation of Glassy Selenium above Its Softening Temperature

The strain-time response of glassy selenium is investigated above its softening temperature using an automatic apparatus for thermomechanical studies. The results demonstrate that, in the stress and temperature ranges studied, Se exhibits three types of strain-time responses: elastic, delayed elastic, and viscous flow. The first two responses relax reversibly in the course of elastic recovery. The relaxation of delayed elastic strain shows exponential behavior with a single relaxation time. In contrast to amorphous polymers, Se deformation is a small-scale process involving simple kinetic units.__________Translated from Neorganicheskie Materialy, Vol. 41, No. 5, 2005, pp. 619–622.Original Russian Text Copyright © 2005 by Kozyukhin.     

Phase transitions in thin Ge<Subscript>2</Subscript>Sb<Subscript>2</Subscript>Te<Subscript>5</Subscript> chalcogenide films according to Raman spectroscopy data

Data on the Raman spectra of thin Ge₂Sb₂Te₅ chalcogenide semiconductor films are reported. The study is performed with the purpose of determining the temperatures of phase transitions initiated by laser radiation.