1,721,004 research outputs found
The race of phase change memories to nanoscale storage and applications
No full textThe successful development of phase change memory technology (PCM) has been one of the most relevant novelties in the field of semiconductor memories of the last years. PCM products at the 45 nm node are being manufactured, mainly driven by applications in cellular phones. In the coming years, the consolidated know-how accumulated over five decades of research activities and more than ten years of industrial experience will further drive the race of resistive storage components to nanoscale, supporting the development of energy-aware, optimized memory systems for both stand-alone and embedded applications. This paper provides an overview of the most recent developments on phase change physics and technology, pointing out the key topics requiring additional investigation and further understandin
Thresold switching and phase transition numerical models for phase change memory simulations
No full textA comprehensive numerical model for chalcogenide glasses is presented, coupling a physically based electrical model able to reproduce the threshold switching with a local nucleation and growth algorithm to account for the phase transition dynamics. The main ingredients of the chalcogenide physics are reviewed and analyzed through simplified analytical models, providing a deeper insight on the origin of the threshold switching mechanism in chalcogenide glasses. A semiconductorlike three-dimensional full-coupled numerical implementation of the proposed model is finally presented and its capabilities to quantitatively reproduce the key elements of the Ge2Sb2Te5chalcogenide physics are demonstrated in the framework of phase change memory device simulations
Intrinsic data retention in nanoscaled phase-change memories - Part I: Monte Carlo model for crystallization and percolation
No full textThe amorphous phase of chalcogenide material in
phase-change memories (PCMs) is subjected to spontaneous and
thermal-activated crystallization. This represents a critical reliability
issue and has to be carefully investigated and modeled for
physically based projection of retention failure up to ten years. A
new three-dimensional percolation model describing the statistical
crystallization behavior in an intrinsic PCM cell for the amorphous
state is developed. With this physical model, the authors
were able to calculate the resistance evolution with time in the
cell and the statistical distribution of retention failure times in
a cell array. From the impact of geometrical parameters on the
cell retention performance, PCM design guidelines to minimize
data-loss effects can be obtained. The model allows the evaluation
of nucleation and growth parameters and statistical extrapolations
of intrinsic retention failure, which will be shown in Part 2
Intrinsic data retenction in nanoscaled phase-change memories - Part II: Statistical analysis and prediction of failure time
No full textThe statistical spread of intrinsic data retention times
in phase-change memory (PCM) cells is studied. Based on the
crystallization and percolation model described in Part 1, the
crystalline grain size in the amorphous volume after data loss is
extracted. From the temperature dependence of grain size, the
authors calculate the statistical shape factor for the distribution
of failure times, allowing a statistical prediction of data retention
in PCM large arrays. The scaling and optimization issues with
respect to failure time statistical spread are finally addressed
Modeling of programming and read performance in phase-change memories - Part II: Program disturb and mixed scaling approach
No full textThe scaling analysis of phase-change memory (PCM) cells is an essential step toward validation as a competitive technology in terms of array density and current consumption. While the current scaling has been addressed in a companion paper, we focus here on the thermal crosstalk, namely, the temperature increase in 1 bit in the array while an adjacent cell is being programmed by a high-current reset pulse. This parasitic heating may lead to partial crystallization in the amorphous phase and to a consequent resistance decrease after cycling. Our analysis shows that the thermal crosstalk strongly depends on the scaling approach used, e.g., isotropic or nonisotropic scaling. A new mixed-scaling option for PCM cells is proposed, which provides the maximum decrease of programming current compatible with the reliability requirements deriving from the thermal crosstalk. The effects of this new scaling approach on the programmed volume and data retention are finally addressed
Modeling and simulation of conduction characteristics and programming operation in nanoscaled phase-change memory cells
No full textMODIFIED RESET STATE FOR ENHANCED READ MARGIN OF PHASE CHANGE MEMORY
No full textSubject matter disclosed herein relates to techniques involving a structural relaxation (SR) phenomenon for increasing resistance of a Reset state of phase change memory
Modeling of programming and read performance in phase-change memories - Part I: cell optimization and scaling
No full textOne of the major concerns for the feasibility of phase-change memories is the reduction of the programming current. To this aim, several efforts have been dedicated both on cell geometry and on material engineering. This paper addresses programming-current minimization by the optimization of the cell geometry and materials, programming-current scaling, and the tradeoff between programming and readout performances of the cell. A general procedure to find the optimum-cell geometry is proposed and applied to a prototype vertical cell. Then, the evolution of program and read performances through technology nodes is analyzed by numerical simulations with the aid of an analytical model, for both the isotropic- and nonisotropic-scaling approaches. The two scaling approaches are discussed and compared in terms of program and read cell performances. Finally, material optimization is considered for further program-read improvement
Study of Cycling-Induced Parameter Variations in Phase Change Memory Cells
No full textThe electrical and thermal parameters of phase change memory (PCM) cells are modified by cycling-induced mechanisms. In this letter, an adaptive cycling procedure is introduced to provide an endurance characterization by keeping the peak temperature at the heater/chalcogenide interface almost constant despite the cell parameters Variations. Experimental results on the PCM wall architecture are collected and explained by considering the reduction of the heater electrical/thermal resistances and the impact of crystallization kinetics variation during cycling
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