Ultra-low Energy Phase Change Memory with Improved Thermal Stability by Tailoring the Local Structure through Ag Doping (original) (raw)
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Fast and scalable memory characteristics of Ge-doped SbTe phase change materials
physica status solidi (b), 2012
Phase change memory (PCM) has opportunities of various applications on the premise of its high performance operations, which are still to develop with innovations such as change of a memory material. In respects of high-speed and high-scalability memory characteristics, d-phase Ge-doped SbTe (GeST) materials stand as highly promising candidates. An overview of the material and device characteristics of these materials is presented primarily based on our recent experimental and computational studies and with a particular regard to their Sb-to-Te ratio (STR) dependence. TEM images of the d-phase GeST microstructures of varying STR and a highly scaled PCM cell with a d-phase GeST of high STR.
Characteristics of Phase Change Memory Devices based on Ge-doped SbTe and its derivative
2007
As a promising candidate for a phase change material of a highly fast and scalable non-volatile memory, Ge-doped SbTe with a certain range of Sb and Te content has interesting material properties such as a low melting temperature, fast crystallization with a high crystallization temperature, and a low electrical resistivity. Using test vehicles based on a cell structure with a contact pore of 100 to 200nm in size, Ge-doped SbTe of two different compositions (Sb/Te atomic ratio of 4.53 and 2.08) were examined and compared with Ge 2 Sb 2 Te 5 in term of important device characteristics such as SET speed, SET resistance as well as RESET current. Between the two compositions, Gedoped SbTe of the higher Sb content was found superior by far in SET speed, which is considered to arise from fast growth-dominated crystallization characteristics of the material combined with the nature of a SET process within the device that does not necessarily require nucleation of crystallites in the presence of movable inter-phase boundaries. Ge-doped SbTe of the higher Sb content was also shown to provide a higher SET speed by more than two orders of magnitude and a lower SET resistance by about one tenth than Ge 2 Sb 2 Te 5. As for RESET current, the material was observed to require a higher current than Ge 2 Sb 2 Te 5 for a stable operation but there appears much room for improvement with a proper understanding of the apparently incomplete RESET at a much lower current level than the one for a stable RESET. Lastly, a derivative of Ge-doped SbTe of the higher Sb/Te content was formed by addition of nitrogen, which turned out to provide an effective means to reduction in RESET current without significantly decreasing SET speed.
Si 3.5 Sb 2 Te 3 Phase Change Material for Low-Power Phase Change Memory Application
Chinese Physics Letters, 2010
Ga 2 Te 3 films show a higher crystallization temperature, wider band gap, better data retention ability ͑keeping the amorphous state at 112°C for ten years͒, and higher room-temperature resistivity of the crystalline state as compared with Ge 2 Sb 2 Te 5 . Ga 2 Te 3 phase change memory cells with an effective diameter of 1 m also show fast switching speed. The set operation was done by a 400 ns-2.4 V pulse, and the reset operation was done by a 30 ns-5.5 V pulse. The dynamic switching ratio between the OFF and ON states is over than 10 3 .
Global and local structures of the Ge-Sb-Te ternary alloy system for a phase-change memory device
Physical Review B, 2006
A detailed theoretical investigation on the global and local structures of the Ge-Sb-Te͑GST͒ ternary alloy system for the phase-change memory is presented. We examine the cohesive energy of the ͑GeTe͒ n ͑Sb 2 Te 3 ͒ m homologous series as well as the dependence of the energy on the atomic distribution. We show that the cohesive energy decreases with increasing vacancy concentration and the vacancies repel each other to minimize the number of dangling bonds. In Ge 2 Sb 2 Te 5 , Sb and Ge atoms favor two-dimensional ͑layered͒ and three-dimensional ͑agglomerated͒ arrangements, respectively. In Ge 1 Sb 2 Te 4 , on the other hand, Ge atoms tend to form a two-dimensional layered structure. Possible structural building blocks of the GST system are proposed based on the density-functional theory total energy calculations.
Journal of Thermal Analysis and Calorimetry, 2016
The influence of different amounts of Bi, Ti and In on the thermal properties and crystallization kinetics of Ge 2 Sb 2 Te 5 thin films for phase change memory devices was investigated. Temperatures and heat effects of crystallization were evaluated for all investigated compositions. Joint utilization of model-free Ozawa-Flynn-Wall and model-fitting Coates-Redfern methods allowed to estimate effective activation energies and pre-exponential factors for crystallization processes of amorphous films as functions of conversion, and determine reaction models. It was found that crystallization process most adequately can be described by the second-or third-order reaction. Storage and data processing times of the phase change memory cells on the basis of investigated materials were calculated with using of determined kinetic triplets of crystallization processes. Calculations showed that crystallization time decreases nearly on the order of magnitude for Ge 2 Sb 2 Te 5 ?1 mass% In in comparison with undoped Ge 2 Sb 2 Te 5. On the other hand, compositions with 0.5 and 3 mass% In allow to increase sufficiently storage time. Introduction of Ti does not significantly affect data processing time of phase change memory cell; however, it decreases storage time. Ge 2 Sb 2 Te 5 ?0.5 mass% Bi composition have the most suitable kinetic parameters for phase change memory among the studied thin films.
physica status solidi (RRL) – Rapid Research Letters, 2020
Chalcogenide materials play essential roles in modern nonvolatile memory technology in the form of both phase‐change memory (PCM) and selector devices. Herein, Bi–Te binary alloys are explored as an alternative candidate for superlattice (SL) or interfacial PCM (iPCM). GeTe/Bi4Te3 (GT/BT) SL exhibits similar structural features to conventional GeTe/Sb2Te3 (GT/ST) SL, such as highly oriented crystal grains and intermixing. Furthermore, preliminary device measurements show that Ge–Bi–Te (GBT) SL switches in a similar manner to conventional Ge–Sb–Te (GST), suggesting that they may be a promising candidate for memory applications. In addition, Bi2Te3/Sb2Te3 (BT/ST) heterostructure films have been successfully fabricated and show clear interface stacking at the atomic level. Although the BT/ST heterostructure is ostensibly a p–n junction, rectifying behavior is not observed in current (I)–voltage (V) measurements due to the existence of a large number of carriers in both layers. Finally,...
Journal of Applied Physics, 2008
We present chemical state information on contamination-free Ge 2 Sb 2 Te 5 thin film using high-resolution x-ray photoelectron spectroscopy ͑HRXPS͒ and the corresponding theoretical understanding of the chemical states, on both amorphous and metastable phases, illuminating the phase-change mechanism of the system. HRXPS data revealed that the Sb 4d shallow core level was split into two components having different binding energies and that the spin-orbit splitting feature of the Ge 3d level was enhanced as the system became metastable. Negligible change was observed in the Te 4d shallow core level, and in contrary to the previous report's prediction less change in valance band spectra was observed. The results imply that Sb movement is also involved in the phase-change mechanism and that acquisition of shallow core-level spectra can be a useful measure for understanding phase-change mechanism. Hydrogenated SbTe 6 octahedral-like cluster model was introduced to schematically interpret the generation of the two components in the Sb 4d level in metastable state, having an isotropic six-bonds configuration, and an anistropic six-bonds ͑three-short and three-elongated bonds͒ configuration. The amorphous state was modeled to have three-short bonds configuration. Finally, Stibnite-like building block model was used to show that the existence of the above two configurations for Sb atoms is feasible in the Ge 2 Sb 2 Te 5 system.