Phase change materials: From structures to kinetics

2007 ◽  
Vol 22 (9) ◽  
pp. 2368-2375 ◽  
Author(s):  
Wojciech Wełnic ◽  
Johannes A. Kalb ◽  
Daniel Wamwangi ◽  
Christoph Steimer ◽  
Matthias Wuttig
Keyword(s):  
Phase Change ◽  
Crystalline State ◽  
Phase Change Materials ◽  
Vacancy Concentration ◽  
Amorphous State ◽  
Structural Difference ◽  
Relative Difference ◽  
Crystal Nucleation ◽  
Optical Contrast ◽  
Entropy Of Fusion

Phase change materials possess a unique combination of properties, which includes a pronounced property contrast between the amorphous and crystalline state, i.e., high electrical and optical contrast. In particular, the latter observation is indicative of a considerable structural difference between the amorphous and crystalline state, which furthermore is characterized by a very high vacancy concentration unknown from common semiconductors. Through the use of ab initio calculations, this work shows how the electric and optical contrast is correlated with structural differences between the crystalline and the amorphous state and how the vacancy concentration controls the optical properties. Furthermore, crystal nucleation rates and crystal growth velocities of various phase change materials have been determined by atomic force microscopy and differential thermal analysis. In particular, the observation of different recrystallization mechanisms upon laser heating of amorphous marks is explained by the relative difference of just three basic parameters among these alloys, namely, the melt-crystalline interfacial energy, the entropy of fusion, and the glass transition temperature.

Phase Change Materials - From Structures to Kinetics

2006 ◽  
Vol 918 ◽  
Author(s):  
Matthias Wuttig ◽  
Wojciech Welnic ◽  
Ralf Detemple ◽  
Henning Dieker ◽  
Johannes Kalb ◽  
...  
Keyword(s):  
Phase Change ◽  
Crystalline State ◽  
Phase Change Materials ◽  
Amorphous State ◽  
Structural Difference ◽  
Fast Time ◽  
Optical Contrast ◽  
Fast Time Scale ◽  
Kinetics Of ◽  
Structure Properties

AbstractPhase change materials possess a unique combination of properties which include a pronounced property contrast between the amorphous and crystalline state, i.e. a high electrical and optical contrast. In particular the latter observation is indicative for a considerable structural difference between the amorphous and crystalline state. At the same time the crystallization of the amorphous state proceeds on a fast time scale. This raises the question how structure, properties and kinetics are related in phase change alloys. It will be demonstrated that only a small group of covalent semiconductors with octahedral-like coordination has the required property combination. This is related to their thermodynamic properties which govern the kinetics of crystallization.

scholarly journals The Effect of Channel Length on Phase Transition of Phase Change Memory

2018 ◽  
Vol 7 (3.11) ◽  
pp. 25
Author(s):  
M S. A.Aziz ◽  
F H. M.Fauzi ◽  
Z Mohamad ◽  
R I. Alip
Keyword(s):  
Phase Transition ◽  
Silicon Carbide ◽  
Phase Change ◽  
Pulse Width ◽  
Crystalline State ◽  
Phase Change Memory ◽  
Amorphous State ◽  
Channel Length ◽  
Change Memory

The phase transition of germanium antimony tellurium (GST) and the temperature of GST were investigated using COMSOL Multiphysic 5.0 software. Silicon carbide was using as a heater layer in the separate heater structure of PCM. These simulations have a different channel of SiC. The temperature of GST and the phase transition of GST can be obtained from the simulation. From the simulation, the 300 nm channel of SiC can change the GST from amorphous to crystalline state at 0.7V with 100 ns pulse width. The 800 nm channel of SiC can change the GST from amorphous to crystalline state at 1.1V with 100 ns pulse width. Results demonstrated that the channel of SIC can affecting the temperature of GST and the GST changes from amorphous state to crystalline state. As the channel of SiC decreased, the temperature of GST was increased and the GST was change to crystalline state quickly.  

The role of structural order and stiffness in the simultaneous enhancement of optical contrast and thermal stability in phase change materials

2019 ◽  
Vol 7 (14) ◽  
pp. 4132-4142 ◽  
Author(s):  
Qian Li ◽  
Kaicheng Xu ◽  
Xiaoyi Wang ◽  
Haihua Huang ◽  
Liang Ma ◽  
...  
Keyword(s):  
Thermal Stability ◽  
Phase Change ◽  
Energy Saving ◽  
Phase Change Materials ◽  
Photonic Devices ◽  
Optical Contrast ◽  
The Past ◽  
Structural Order ◽  
Perfect Absorbers

In the past several years, phase change materials (PCMs) have been widely applied in energy-saving non-volatile photonic devices, such as active perfect absorbers, nanopixel displays and all-photonic memories.

Origin of the Optical Contrast in Phase-Change Materials

2007 ◽  
Vol 98 (23) ◽  
Author(s):  
Wojciech Wełnic ◽  
Silvana Botti ◽  
Lucia Reining ◽  
Matthias Wuttig
Keyword(s):  
Phase Change ◽  
Phase Change Materials ◽  
Optical Contrast

The Origin of Optical Contrast in Sb 2 Te 3 ‐Based Phase‐Change Materials

2019 ◽  
Vol 257 (1) ◽  
pp. 1900289 ◽  
Author(s):  
Jose C. Martinez ◽  
Li Lu ◽  
Jing Ning ◽  
Weiling Dong ◽  
Tun Cao ◽  
...  
Keyword(s):  
Phase Change ◽  
Phase Change Materials ◽  
Optical Contrast

scholarly journals Investigating Phase Transform Behavior in Indium Selenide Based RAM and Its Validation as a Memory Element

2016 ◽  
Vol 2016 ◽  
pp. 1-7
Author(s):  
Swapnil Sourav ◽  
Amit Krishna Dwivedi ◽  
Aminul Islam
Keyword(s):  
Phase Change ◽  
Phase Change Materials ◽  
Amorphous State ◽  
Random Access ◽  
Random Access Memory ◽  
Indium Selenide ◽  
Access Memory ◽  
Memory Element ◽  
Phase Transform ◽  
Simulation Results

Phase transform properties of Indium Selenide (In2Se3) based Random Access Memory (RAM) have been explored in this paper. Phase change random access memory (PCRAM) is an attractive solid-state nonvolatile memory that possesses potential to meet various current technology demands of memory design. Already reported PCRAM models are mainly based upon Germanium-Antimony-Tellurium (Ge2Sb2Te5 or GST) materials as their prime constituents. However, PCRAM using GST material lacks some important memory attributes required for memory elements such as larger resistance margin between the highly resistive amorphous and highly conductive crystalline states in phase change materials. This paper investigates various electrical and compositional properties of the Indium Selenide (In2Se3) material and also draws comparison with its counterpart mainly focusing on phase transform properties. To achieve this goal, a SPICE model of In2Se3 based PCRAM model has been reported in this work. The reported model has been also validated to act as a memory cell by associating it with a read/write circuit proposed in this work. Simulation results demonstrate impressive retentivity and low power consumption by requiring a set pulse of 208 μA for a duration of 100 μs to set the PCRAM in crystalline state. Similarly, a reset pulse of 11.7 μA for a duration of 20 ns can set the PCRAM in amorphous state. Modeling of In2Se3 based PCRAM has been done in Verilog-A and simulation results have been extensively verified using SPICE simulator.

Characteristics of OUM Phase Change Materials and Devices for High Density Nonvolatile Commodity and Embedded Memory Applications

2003 ◽  
Vol 803 ◽  
Author(s):  
Tyler A. Lowrey ◽  
Stephen J. Hudgens ◽  
Wally Czubatyj ◽  
Charles H. Dennison ◽  
Sergey A. Kostylev ◽  
...  
Keyword(s):  
Phase Change ◽  
Phase Change Materials ◽  
Thermal Environment ◽  
Structural Phase ◽  
Phase Change Memory ◽  
Amorphous State ◽  
Memory Device ◽  
High Density ◽  
Process Technology ◽  
Change Memory

ABSTRACTPhase change memory devices were originally reported by S. R.Ovshinsky [1] in 1968. A 256-bit phase-change memory array based on chalcogenide materials was reported in 1970 [2] Recent advances in phase change materials, memory device designs, and process technology have resulted in significant advances in phase change device performance, and a new memory device, called Ovonic Unified Memory (OUM), has been developed. This paper will discuss various device and materials characteristics of OUM phase change memory materials of interest in applications for nonvolatile high-density memories. These materials are generally Te chalcogenide based, exploiting the congruent crystallization of the FCC phase and the associated reduction in resistivity that results from crystallization from the quenched amorphous state. Data storage is a thermally initiated, rapid, reversible structural phase change in the film. While rewriteable DVD disks employ laser heat to induce the phase change and modulate reflectivity, OUM technology uses a short electrical current pulse to modulate resistivity. The device geometry and thermal environment dictate the power and energy required for memory state programming.

Computer Simulation of the Phase-change Cycle of GST-225

2008 ◽  
Vol 1072 ◽  
Author(s):  
Stephen Elliott ◽  
Jozsef Hegedus
Keyword(s):  
Phase Change ◽  
Homogeneous Nucleation ◽  
Amorphous State ◽  
Crystal Nucleation ◽  
Neutron Diffraction Data ◽  
Structural Units ◽  
Slow Cooling ◽  
Rapid Cooling ◽  
Rocksalt Structure ◽  
First Time

ABSTRACTWe have simulated for the first time, by ab initio molecular dynamics, the complete phase-transformation cycle (liquid-crystal, liquid-amorphous-crystal) of the phase-change (PC) memory material Ge2Sb2Te5 (GST-225). We have observed that rapid cooling of the simulated melt leads to an amorphous product, whereas slow cooling results in the metastable rocksalt crystal. Furthermore, crystallization to the same structure is observed to occur on annealing the quenched amorphous model to temperatures below the melting temperature. The RDF of the energy-relaxed amorphous GST-225 structure agrees very well with experimental neutron-diffraction data, reproducing the shortening of the Ge-Te bond length relative to that in the rocksalt crystal structure observed experimentally.We have observed crystal-nucleation events in the simulated liquid that have been identified as the creation of connected near-regular square fourfold rings, the basic structural units of the rocksalt structure. These crystal nuclei are invariably found to be quenched into the amorphous state on rapid cooling of the simulated melt. This observation therefore explains why GST materials crystallize so readily and why homogeneous nucleation is so facile.

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