Zeitschriftenartikel: „Phase change memory GST“

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S. A.Aziz, M., F. H. M.Fauzi, Z. Mohamad, and R. I. Alip. "The Effect of Channel Length on Phase Transition of Phase Change Memory." International Journal of Engineering & Technology 7, no. 3.11 (2018): 25. http://dx.doi.org/10.14419/ijet.v7i3.11.15923.

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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.

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Golovchak, R., Y. G. Choi, S. Kozyukhin, et al. "Oxygen incorporation into GST phase-change memory matrix." Applied Surface Science 332 (March 2015): 533–41. http://dx.doi.org/10.1016/j.apsusc.2015.01.203.

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3

Behrens, Mario, Andriy Lotnyk, Hagen Bryja, Jürgen W. Gerlach, and Bernd Rauschenbach. "Structural Transitions in Ge2Sb2Te5 Phase Change Memory Thin Films Induced by Nanosecond UV Optical Pulses." Materials 13, no. 9 (2020): 2082. http://dx.doi.org/10.3390/ma13092082.

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Ge-Sb-Te-based phase change memory alloys have recently attracted a lot of attention due to their promising applications in the fields of photonics, non-volatile data storage, and neuromorphic computing. Of particular interest is the understanding of the structural changes and underlying mechanisms induced by short optical pulses. This work reports on structural changes induced by single nanosecond UV laser pulses in amorphous and epitaxial Ge2Sb2Te5 (GST) thin films. The phase changes within the thin films are studied by a combined approach using X-ray diffraction and transmission electron microscopy. The results reveal different phase transitions such as crystalline-to-amorphous phase changes, interface assisted crystallization of the cubic GST phase and structural transformations within crystalline phases. In particular, it is found that crystalline interfaces serve as crystallization templates for epitaxial formation of metastable cubic GST phase upon phase transitions. By varying the laser fluence, GST thin films consisting of multiple phases and different amorphous to crystalline volume ratios can be achieved in this approach, offering a possibility of multilevel data storage and realization of memory devices with very low resistance drift. In addition, this work demonstrates amorphization and crystallization of GST thin films by using only one UV laser with one single pulse duration and one wavelength. Overall, the presented results offer new perspectives on switching pathways in Ge-Sb-Te-based materials and show the potential of epitaxial Ge-Sb-Te thin films for applications in advanced phase change memory concepts.

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Stern, Keren, Yair Keller, Christopher M. Neumann, Eric Pop, and Eilam Yalon. "Temperature-dependent thermal resistance of phase change memory." Applied Physics Letters 120, no. 11 (2022): 113501. http://dx.doi.org/10.1063/5.0081016.

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One of the key challenges of phase change memory (PCM) is its high power consumption during the reset operation, when the phase change material (typically Ge2Sb2Te5, i.e., GST) heats up to ∼900 K or more in order to melt. Here, we study the temperature-dependent behavior of PCM devices by probing the reset power at ambient temperatures from 80 to 400 K. We find that different device structures exhibit contrasting temperature-dependent behavior. The reset power in our confined-type PCM is nearly unchanged with ambient temperature, corresponding to a temperature-dependent thermal resistance, whereas results for mushroom-type PCM from the literature show a linear relation between power and temperature, suggesting a more constant thermal resistance. This discrepancy is ascribed to different temperature distributions and thermal properties of the dominant components of the PCM cell thermal resistance, as shown by electro-thermal modeling. In the confined cell, the thermal boundary resistance of the GST and the thermal conductivity of the bottom electrode dominate the thermal resistance, while for the mushroom cell, the GST thermal conductivity plays a greater role. These findings can help to design more power- and energy-efficient PCM devices by better focusing thermal management efforts on the key components of the device.

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Kim, Sung Soon, Jun Hyun Bae, Woo Hyuck Do, et al. "Thermal Stress Model for Phase Change Random Access Memory." Solid State Phenomena 124-126 (June 2007): 37–40. http://dx.doi.org/10.4028/www.scientific.net/ssp.124-126.37.

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Thermal stress model considering the effect of phase transformation is proposed for Phase-Change Random Access Memory (PRAM). The results of simulation show that the high level of stress is generated on the junction where Ge2Sb2Te5(GST), TiN and SiO2 meet together. The high level of stress can also be observed in the interface between TiN and SiO2. From simulation results, it can be predictable that delamination between GST and TiN can occur during operation of PRAM. It is expected that the simulation model, which has been developed in this research, is very useful tool for PRAM device design.

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Raeis-Hosseini, Niloufar, and Junsuk Rho. "Dual-Functional Nanoscale Devices Using Phase-Change Materials: A Reconfigurable Perfect Absorber with Nonvolatile Resistance-Change Memory Characteristics." Applied Sciences 9, no. 3 (2019): 564. http://dx.doi.org/10.3390/app9030564.

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Integration of metamaterial and nonvolatile memory devices with tunable characteristics is an enthusing area of research. Designing a unique nanoscale prototype to achieve a metasurface with reliable resistive switching properties is an elusive goal. We demonstrate a method to exploit the advantages of a phase-change material (PCM) as a metamaterial light absorber and a nanoscale data storage device. We designed and simulated a metamaterial perfect absorber (MPA) that can be reconfigured by adjusting the visible light properties of a chalcogenide-based PCM. The suggested perfect absorber is based on a Ge2Sb2Te5 (GST) film, and is tuned between two distinct states by heat treatment. Furthermore, we fabricated and characterized a resistive switching memory (ReRAM) device with the same features. The MPA/ReRAM device with a conventional metal/dielectric/metal structure (Ag/GST/Al2O3/Pt) consisted of arrays of Ag squares patterned on a GST thin film and an alumina-coated Pt mirror on a glass substrate. Based on the numerical data, amorphous GST showed perfect absorbance in the visible spectrum, whereas, crystalline GST showed broadband perfect absorbance. The fabricated ReRAM device exhibited uniform, bidirectional, and programmable memory characteristics with a high ON/OFF ratio for nonvolatile memory applications. The elucidated origin of the bipolar resistive switching behavior is assigned to the formation and rupture of conductive filaments.

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Agarwal, Satish C. "Role of potential fluctuations in phase-change GST memory devices." physica status solidi (b) 249, no. 10 (2012): 1956–61. http://dx.doi.org/10.1002/pssb.201200362.

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Xue, Yuan, Sannian Song, Xiaogang Chen, et al. "Enhanced performance of phase change memory by grain size reduction." Journal of Materials Chemistry C 10, no. 9 (2022): 3585–92. http://dx.doi.org/10.1039/d1tc06045g.

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9

Pacco, Antoine, Ju-Geng Lai, Pallavi Puttarame Gowda, et al. "Wet Chemical Recess Etching of Ge₂Sb₂Te₅ for 3D PCRAM Memory Applications." ECS Meeting Abstracts MA2022-01, no. 28 (2022): 1262. http://dx.doi.org/10.1149/ma2022-01281262mtgabs.

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Memory cells comprising a Phase Change Material (PCM) are the building blocks of fast and non-volatile memory devices called Phase Change Random Access Memory (PCRAM) [1-3]. The working principle of this memory involves data retention in the form of a phase (amorphous or crystalline) and the set and reset can be done by Joule heating to induce an amorphous-to-crystalline or crystalline-to-amorphous transition respectively. Some chalcogenide materials experience this thermally driven phase change, GeSbTe (GST) being one of those alloys extensively studied. GST has also been adopted for the fabrication of the 1st generation X-point memory [4] and might be adopted in a 2nd generation X-point memory of a four-layer PCM structure [5]. However, this 2D scaling or stacking of PCRAM is limited by cost and therefore the development of 3D architectures is envisaged for decreasing the cost/bit [6]. A key requirement for the fabrication of this 3D architecture is the conformal deposition and etch-back of GST. Dry plasma etching might be limited to anisotropic recess while isotropic lateral recess is needed. Therefore, wet isotropic etching might be the process of choice. A few chemical solutions have been proposed in previous studies. Cheng et al. showed that GST could be etched in HNO3 but with a very high etch rate and with an unwanted surface composition change due to different oxidation and dissolution rates of the metalloids [7]. Wang et al. demonstrated that basic wet etching solutions led to a slower etch rate and a much smoother surface compared to acidic wet etching solutions [8]. Deng et al. showed a switch in the etch rate order between crystalline and amorphous GST depending on the H2O2 concentration in TMAH [9]. In this work, we present a controllable partial recess solution that leaves the GST surface smooth after recess. Wet recess of amorphous and crystalline blanket films, as well as patterned samples, was initially explored using the commodity chemistries Ammonium Peroxide Mixture (APM) and (Hydrochloric Peroxide Mixture) HPM. The etching of GST in HPM as a function of the H2O2 concentration was monitored by ICPMS and showed a well-controlled etch rate. However, some shortcomings of these H2O2-containing solutions, like roughness and selectivity, lead to a change of oxidizing agent from H2O2 to O3. In the O3-containing solutions, the selectivity towards Al2O3, SiO2, and TiN could be secured. The impact of the dissolved O3 concentration on surface roughness and etch rate as well as the uniformity of this wet etching process were assessed on a single wafer tool. Finally, the bulk and surface GST composition and oxidation post-recess were verified through XPS and ERD. REFERENCES: [1] D. Loke et al., “Breaking the Speed Limits of Phase-Change Memory.” Science, 2012, 336, 6088, 1566. [2] K. Ding et al., “Recipe for ultrafast and persistent phase-change memory materials.” NPG Asia Mater 12, 63, 2020. [3] F. Rao et al., “Reducing the stochasticity of crystal nucleation to enable sub-nanosecond memory writing.” Science, 2017, 358, 6369, 1423. [4] [internet] https://www.techinsights.com/blog/intel-3d-xpoint-memory-die-removed-intel-optanetm-pcm-phase-change-memory [5] [internet] https://www.techinsights.com/blog/memory/intels-2nd-generation-xpoint-memory [6] [internet] https://www.imec-int.com/en/imec-magazine/imec-magazine-october-2017/in-pursuit-of-high-density-storage-class-memory [7] H.Y. Cheng et al., “Wet-Etching Characteristics of Ge2Sb2Te5 Thin Films for Phase-Change Memory.” IEEE Trans. Magn., 41, 2, 2005. [8] L. Wang et al., “Basic Wet-Etching Solutions for Ge2Sb2Te5 Phase Change Material.” J. Electrochem. Soc., 157, H470, 2010. [9] C. Deng et al., “XPS study on the selective wet etching mechanism of GeSbTe phase change thin films with TMAH.” Proc. of SPIE, 8782, 87820N, 2012.

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Yin, You, and Sumio Hosaka. "Crystal Growth Suppression by N-Doping into Chalcogenide for Application to Next-Generation Phase Change Memory." Key Engineering Materials 497 (December 2011): 101–5. http://dx.doi.org/10.4028/www.scientific.net/kem.497.101.

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In this work, we investigate the effect of the N-doping on microstructure and electrical properties of chalcogenide Ge2Sb2Te5(GST) films for application to multilevel-storage phase change memory (PCM). Crystal size can be markedly reduced from 16 nm to 5 nm by N-doping into GST. The crystal growth suppression is believed to be controlled by distributed fine nitride particles. The resistivity of N-GST as a function of annealing temperature exhibits a gradual change due to the crystal growth suppression. The characteristics imply that N-GST is suitable for application to multilevel-storage PCM as the next-generation nonvolatile memory.

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Ren, W., M. Zhong, J. Dai, P. Mukundhan, and M. Zhang. "Phase change memory alloys: GST cell array characterization using picosecond ultrasonics." Microelectronic Engineering 88, no. 5 (2011): 822–26. http://dx.doi.org/10.1016/j.mee.2010.07.016.

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12

Zhu, Yueqin, Zhonghua Zhang, Sannian Song, et al. "Ni-doped GST materials for high speed phase change memory applications." Materials Research Bulletin 64 (April 2015): 333–36. http://dx.doi.org/10.1016/j.materresbull.2015.01.016.

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13

Pan, Yuanchun, Zhen Li, and Zhonglu Guo. "Lattice Thermal Conductivity of mGeTe•nSb2Te3 Phase-Change Materials: A First-Principles Study." Crystals 9, no. 3 (2019): 136. http://dx.doi.org/10.3390/cryst9030136.

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As the most promising materials for phase-change data storage, the pseudobinary mGeTe•nSb2Te3 (GST) chalcogenides have been widely investigated. Nevertheless, an in-depth understanding of the thermal-transport property of GST is still lacking, which is important to achieve overall good performance of the memory devices. Herein, by using first-principles calculations and Boltzmann transport theory, we have systematically studied the lattice thermal conductivity along the out of plane direction of both stable hexagonal and meta-stable rock-salt-like phases of GST, and good agreement with available experiments has been observed. It is revealed that with the increase of the n/m ratio, the lattice thermal conductivity of hexagonal GST increases due to the large contribution from the weak Te-Te bonding, while an inverse trend is observed in meta-stable GST, which is due to the increased number of vacancies that results in the decrease of the lattice thermal conductivity. The size effect on thermal conductivity is also discussed. Our results provide useful information to manipulate the thermal property of GST phase-change materials.

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Wang, Miao, Yegang Lu, Xiang Shen, et al. "Effect of Sb2Se on phase change characteristics of Ge2Sb2Te5." CrystEngComm 17, no. 26 (2015): 4871–76. http://dx.doi.org/10.1039/c5ce00656b.

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In this paper, the effect of Sb2Se on the phase change characteristics of Ge2Sb2Te5 (GST) is systemically studied for applications in phase-change random access memory (PRAM).

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Kim, JunHo, and Ki-Bong Song. "Simulation Study on Heat Conduction of a Nanoscale Phase-Change Random Access Memory Cell." Journal of Nanoscience and Nanotechnology 6, no. 11 (2006): 3474–78. http://dx.doi.org/10.1166/jnn.2006.17963.

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We have investigated heat transfer characteristics of a nano-scale phase-change random access memory (PRAM) cell using finite element method (FEM) simulation. Our PRAM cell is based on ternary chalcogenide alloy, Ge2Sb2Te5 (GST), which is used as a recording layer. For contact area of 100 × 100 nm2, simulations of crystallization and amorphization processes were carried out. Physical quantities such as electric conductivity, thermal conductivity, and specific heat were treated as temperature-dependent parameters. Through many simulations, it is concluded that one can reduce set current by decreasing both electric conductivities of amorphous GST and crystalline GST, and in addition to these conditions by decreasing electric conductivity of molten GST one can also reduce reset current significantly.

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Lei, Xin-Qing, Jia-He Zhu, Da-Wei Wang, and Wen-Sheng Zhao. "Design for Ultrahigh-Density Vertical Phase Change Memory: Proposal and Numerical Investigation." Electronics 11, no. 12 (2022): 1822. http://dx.doi.org/10.3390/electronics11121822.

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The integration level is a significant index that can be used to characterize the performance of non-volatile memory devices. This paper proposes innovative design schemes for high-density integrated phase change memory (PCM). In these schemes, diploid and four-fold memory units, which are composed of nano-strip film GST-based memory cells, are employed to replace the memory unit of a conventional vertical PCM array. As the phase transformation process of the phase change material involves the coupling of electrical and thermal processes, an in-house electrothermal coupling simulator is developed to analyze the performance of the proposed memory cells and arrays. In the simulator, a proven mathematical model is used to describe the phase change mechanism, with a finite element approach implemented for numerical calculations. The characteristics of the GST-strip-based memory cell are simulated first and compared with a conventional vertical cell, with a decrease of 32% in the reset current amplitude achieved. Next, the influences of geometric parameters on the characteristics of memory cell are investigated systematically. After this, the electrothermal characteristics of the proposed vertical PCM arrays are simulated and the results indicate that they possess both excellent performance and scalability. At last, the integration densities of the proposed design schemes are compared with the reference array, with a maximum time of 5.94 achieved.

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Bartlett, Philip N., Sophie L. Benjamin, C. H. (Kees) de Groot, et al. "Non-aqueous electrodeposition of functional semiconducting metal chalcogenides: Ge2Sb2Te5 phase change memory." Materials Horizons 2, no. 4 (2015): 420–26. http://dx.doi.org/10.1039/c5mh00030k.

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LIAO, YUANBAO, JIAJIA WU, LING XU, et al. "FORMATION, STRUCTURE AND PROPERTIES OF HIGHLY ORDERED SUB-30-nm PHASE CHANGE MATERIALS (GST) NANOPARTICLE ARRAYS." Surface Review and Letters 17, no. 04 (2010): 405–10. http://dx.doi.org/10.1142/s0218625x10014259.

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Chalcogenide phase change material Ge1Sb2Te4 (GST) nanoparticle arrays with long-range-order were fabricated by using a monolayer of self-assembled polystyrene (PS) spheres as mask. The morphology of nanoparticle arrays can be controlled via changing RIE processing conditions. Images of atomic force microscopy (AFM) and scanning electron microscopy (SEM) show that highly uniform GST nanoparticle arrays with particle density around 109 cm-2 were formed. The sizes of nanoparticles can be reduced to a tiny diameter in the range of 30–40 nm (top diameter). The GST nanoparticle arrays exhibit a prominent peak near 580 nm in reflectance spectra, which indicates that they possess a photonic band gap. These results confirm that GST nanoparticle arrays have a 2D periodicity and long-range order. The method of nanosphere lithograph may apply to manufacturing of high density memory devices based on phase change-based memory materials.

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Makino, Kotaro, Kosaku Kato, Yuta Saito, et al. "Terahertz spectroscopic characterization of Ge2Sb2Te5 phase change materials for photonics applications." Journal of Materials Chemistry C 7, no. 27 (2019): 8209–15. http://dx.doi.org/10.1039/c9tc01456j.

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Ge–Sb–Te (GST) phase change materials exhibit a metal-to-insulator transition and therefore are expected to be useful for a variety of terahertz wave applications in addition to their primary application in optical and electrical memory devices.

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Sun, Zhi Mei, Yuan Chun Pan, Bai Sheng Sa, and Jian Zhou. "Ab Initio Study on Hexagonal Ge₂Sb₂Te₅-A Phase-Change Material for Nonvolatile Memories." Materials Science Forum 687 (June 2011): 7–11. http://dx.doi.org/10.4028/www.scientific.net/msf.687.7.

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On the basis of ab initio total energy calculations, we have performed an extensive study on the stacking sequence and random occupation of Ge and Sb to make the same layer in stable hexagonal Ge2Sb2Te5 (h-GST), an excellent candidate for phase change random memory applications. The results demonstrate that the atomic arrangements have great effects on lattice parameter c and electronic properties of h-GST. h-GST changes from semiconductor to metallic behavior as varying the atomic sequence.

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Liu, Cheng, Yonghui Zheng, Tianjiao Xin, Yunzhe Zheng, Rui Wang, and Yan Cheng. "The Relationship between Electron Transport and Microstructure in Ge2Sb2Te5 Alloy." Nanomaterials 13, no. 3 (2023): 582. http://dx.doi.org/10.3390/nano13030582.

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Phase-change random-access memory (PCRAM) holds great promise for next-generation information storage applications. As a mature phase change material, Ge2Sb2Te5 alloy (GST) relies on the distinct electrical properties of different states to achieve information storage, but there are relatively few studies on the relationship between electron transport and microstructure. In this work, we found that the first resistance dropping in GST film is related to the increase of carrier concentration, in which the atomic bonding environment changes substantially during the crystallization process. The second resistance dropping is related to the increase of carrier mobility. Besides, during the cubic to the hexagonal phase transition, the nanograins grow significantly from ~50 nm to ~300 nm, which reduces the carrier scattering effect. Our study lays the foundation for precisely controlling the storage states of GST-based PCRAM devices.

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Guo, Pengfei, Andrew Sarangan, and Imad Agha. "A Review of Germanium-Antimony-Telluride Phase Change Materials for Non-Volatile Memories and Optical Modulators." Applied Sciences 9, no. 3 (2019): 530. http://dx.doi.org/10.3390/app9030530.

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Chalcogenide phase change materials based on germanium-antimony-tellurides (GST-PCMs) have shown outstanding properties in non-volatile memory (NVM) technologies due to their high write and read speeds, reversible phase transition, high degree of scalability, low power consumption, good data retention, and multi-level storage capability. However, GST-based PCMs have shown recent promise in other domains, such as in spatial light modulation, beam steering, and neuromorphic computing. This paper reviews the progress in GST-based PCMs and methods for improving the performance within the context of new applications that have come to light in recent years.

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Kang, Shinyoung, Juyoung Lee, Myounggon Kang, and Yunheub Song. "Achievement of Gradual Conductance Characteristics Based on Interfacial Phase-Change Memory for Artificial Synapse Applications." Electronics 9, no. 8 (2020): 1268. http://dx.doi.org/10.3390/electronics9081268.

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In this paper, gradual and symmetrical long-term potentiation (LTP) and long-term depression (LTD) were achieved by applying the optimal electrical pulse condition of the interfacial phase-change memory (iPCM) based on a superlattice (SL) structure fabricated by stacking GeTe/Sb2Te3 alternately to implement an artificial synapse in neuromorphic computing. Furthermore, conventional phase-change random access memory (PCRAM) based on a Ge–Sb–Te (GST) alloy with an identical bottom electrode contact size was fabricated to compare the electrical characteristics. The results showed a reduction in the reset energy consumption of the GeTe/Sb2Te3 (GT/ST) iPCM by more than 69% of the GST alloy for each bottom electrode contact size. Additionally, the GT/ST iPCM achieved gradual conductance tuning and 90.6% symmetry between LTP and LTD with a relatively unsophisticated pulse scheme. Based on the above results, GT/ST iPCM is anticipated to be exploitable as a synaptic device used for brain-inspired computing and to be utilized for next-generation non-volatile memory.

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Alip, Rosalena Irma, Ryota Kobayashi, Yu Long Zhang, Zulfakri bin Mohamad, You Yin, and Sumio Hosaka. "A Novel Phase Change Memory with a Separate Heater Characterized by Constant Resistance for Multilevel Storage." Key Engineering Materials 534 (January 2013): 136–40. http://dx.doi.org/10.4028/www.scientific.net/kem.534.136.

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A novel phase change memory structure with a separate heater was proposed for a multilevel storage. Finite element analysis was conducted to investigate the possibility of multilevel storage. 100 ns SET pulses, with an increasing amplitude from 0.5 V to 3 V, were applied for heating the phase change layer, Ge2Se2T5 (GST). From the simulation result, it was exhibited that the temperature in the GST layer increased gradually when an increasing pulse is applied to the separate heater layer (N-TiSi3). This implies that crystallization is well controlled by changing the amplitude of the applied SET pulse. The gradual increase in the temperature leads to gradual resistance drop, depending strongly on the capping material. The gradual resistance drop will allow multilevel storage for the memory device.

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Kim, Yewon, Byeol Han, Yu-Jin Kim, et al. "Atomic layer deposition and tellurization of Ge–Sb film for phase-change memory applications." RSC Advances 9, no. 30 (2019): 17291–98. http://dx.doi.org/10.1039/c9ra02188d.

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We studied the atomic layer deposition (ALD) and the tellurization of Ge–Sb films to prepare conformal crystalline Ge–Sb–Te (GST) films and to achieve void-free gap filling for emerging phase-change memory applications.

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Qiao, Yang, Jin Zhao, Haodong Sun, et al. "Pt Modified Sb2Te3 Alloy Ensuring High−Performance Phase Change Memory." Nanomaterials 12, no. 12 (2022): 1996. http://dx.doi.org/10.3390/nano12121996.

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Phase change memory (PCM), due to the advantages in capacity and endurance, has the opportunity to become the next generation of general−purpose memory. However, operation speed and data retention are still bottlenecks for PCM development. The most direct way to solve this problem is to find a material with high speed and good thermal stability. In this paper, platinum doping is proposed to improve performance. The 10-year data retention temperature of the doped material is up to 104 °C; the device achieves an operation speed of 6 ns and more than 3 × 105 operation cycles. An excellent performance was derived from the reduced grain size (10 nm) and the smaller density change rate (4.76%), which are less than those of Ge2Sb2Te5 (GST) and Sb2Te3. Hence, platinum doping is an effective approach to improve the performance of PCM and provide both good thermal stability and high operation speed.

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Chao, Der-Sheng, Yi-Chan Chen, Fred Chen, et al. "Enhanced Thermal Efficiency in Phase-Change Memory Cell by Double GST Thermally Confined Structure." IEEE Electron Device Letters 28, no. 10 (2007): 871–73. http://dx.doi.org/10.1109/led.2007.906084.

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Ahn, Jun-Ku, Kyoung-Woo Park, Sung-Gi Hur, et al. "Metalorganic chemical vapor deposition of non-GST chalcogenide materials for phase change memory applications." Journal of Materials Chemistry 20, no. 9 (2010): 1751. http://dx.doi.org/10.1039/b922398c.

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Sourav, Swapnil, Amit Krishna Dwivedi, and Aminul Islam. "Investigating Phase Transform Behavior in Indium Selenide Based RAM and Its Validation as a Memory Element." Journal of Materials 2016 (September 22, 2016): 1–7. http://dx.doi.org/10.1155/2016/6123268.

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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.

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Antolini, Alessio, Eleonora Franchi Scarselli, Antonio Gnudi, et al. "Characterization and Programming Algorithm of Phase Change Memory Cells for Analog In-Memory Computing." Materials 14, no. 7 (2021): 1624. http://dx.doi.org/10.3390/ma14071624.

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In this paper, a thorough characterization of phase-change memory (PCM) cells was carried out, aimed at evaluating and optimizing their performance as enabling devices for analog in-memory computing (AIMC) applications. Exploiting the features of programming pulses, we discuss strategies to reduce undesired phenomena that afflict PCM cells and are particularly harmful in analog computations, such as low-frequency noise, time drift, and cell-to-cell variability of the conductance. The test vehicle is an embedded PCM (ePCM) provided by STMicroelectronics and designed in 90-nm smart power BCD technology with a Ge-rich Ge-Sb-Te (GST) alloy for automotive applications. On the basis of the results of the characterization of a large number of cells, we propose an iterative algorithm to allow multi-level cell conductance programming, and its performances for AIMC applications are discussed. Results for a group of 512 cells programmed with four different conductance levels are presented, showing an initial conductance spread under 6%, relative current noise less than 9% in most cases, and a relative conductance drift of 15% in the worst case after 14 h from the application of the programming sequence.

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Nguyen, Huu Tan, Andrzej Kusiak, Jean Luc Battaglia, et al. "Thermal Properties of In-Sb-Te Thin Films for Phase Change Memory Application." Advances in Science and Technology 95 (October 2014): 113–19. http://dx.doi.org/10.4028/www.scientific.net/ast.95.113.

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Phase change memories (PCM) are typically based on compounds of the Ge-Sb-Te (GST) ternary system. Nevertheless, a major drawback of PCM devices based on GST is the low crystallization temperature, which prevents the fulfillment of automotive-level or military-grade requirements (125°C continuous operation). To overcome this limitation, alloys belonging to the In-Sb-Te (IST) system have been proposed, which have demonstrated high crystallization temperature, and fast switching. Thermal properties of the chalcogenide alloy and of its interfaces within the PCM cell are key parameters versus the programming current, reliability and optimized scaling of PCM devices. The Modulated Photothermal Radiometry (MPTR) technique was implemented to measure the thermal conductivity of IST thin films as well as the thermal boundary resistance at the interface with other surrounding materials (a metal and a dielectric). The experiment was carried outin situfrom room temperature up to 550°C in order to investigate the intrinsic thermal properties at different temperatures and the significant structural rearrangement upon the phase transition. Two different stoichiometries for the IST ternary alloy were deposited by Metal Organic Chemical Vapor Deposition (MOCVD) on a Si substrate covered with thermal SiO2and then capped with a Platinum layer that acts as an optical and thermal transducer. Additional data from Raman and XRD lead to complementary analysis.

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Shao, Mingyue, Yang Qiao, Yuan Xue, Sannian Song, Zhitang Song, and Xiaodan Li. "Advantages of Ta-Doped Sb3Te1 Materials for Phase Change Memory Applications." Nanomaterials 13, no. 4 (2023): 633. http://dx.doi.org/10.3390/nano13040633.

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Phase change memory (PCM), a typical representative of new storage technologies, offers significant advantages in terms of capacity and endurance. However, among the research on phase change materials, thermal stability and switching speed performance have always been the direction where breakthroughs are needed. In this research, as a high-speed and good thermal stability material, Ta was proposed to be doped in Sb3Te1 alloy to improve the phase transition performance and electrical properties. The characterization shows that Ta-doped Sb3Te1 can crystallize at temperatures up to 232 °C and devices can operate at speeds of 6 ns and 8 × 104 operation cycles. The reduction of grain size and the density change rate (3.39%) show excellent performances, which are both smaller than that of Ge2Sb2Te5 (GST) and Sb3Te1. These properties conclusively demonstrate that Ta incorporation of Sb3Te1 alloy is a material with better thermal stability and faster crystallization rates for PCM applications.

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Inoue, Nobuki, and Hisao Nakamura. "Structural transition pathway and bipolar switching of the GeTe–Sb2Te3 superlattice as interfacial phase-change memory." Faraday Discussions 213 (2019): 303–19. http://dx.doi.org/10.1039/c8fd00093j.

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Noor, Nafisa, Sadid Muneer, Raihan Sayeed Khan, Anna Gorbenko, and Helena Silva. "Amorphized length and variability in phase-change memory line cells." Beilstein Journal of Nanotechnology 11 (October 29, 2020): 1644–54. http://dx.doi.org/10.3762/bjnano.11.147.

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The dimensions of amorphized regions in phase-change memory cells are critical parameters to design devices for different applications. However, these dimensions are difficult to be determined by direct imaging. In this work, the length of amorphized regions in multiple identical Ge2Sb2Te5 (GST) line cells was extracted from electrical measurements. After each cell was programmed to an amorphous state, a sequence of increasing-amplitude post-reset voltage pulses separated by low-amplitude read DC sweeps was applied. When a post-reset voltage pulse with sufficient amplitude was applied to a given cell, the measured current and the post-pulse resistance increased drastically, indicating that the cell re-amorphized after threshold switching, melting, and quenching. The amorphized length was calculated using the measured voltage at which the threshold switching occurred and the expected drifted threshold field at that time. The measured threshold voltage values and, hence, the extracted amorphized length, generally increase linearly with the programmed resistance levels. However, significant variability arises from the intrinsically unique crystallization and amorphization processes in these devices. For example, cells programmed to an amorphous resistance of approx. 50 MΩ show threshold voltage values of 5.5–7.5 V, corresponding to amorphized length values of 290–395 nm. This unpredictable programming feature in phase-change memory devices can be utilized in hardware security applications.

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Li, Tao, Liang Cai Wu, Zhi Tang Song, San Nian Song, Feng Rao, and Bo Liu. "Carbon-Doped Sb-Rich Ge-Sb-Te Phase Change Material for High Speed and High Thermal Stability Phase Change Memory Applications." Materials Science Forum 898 (June 2017): 1834–38. http://dx.doi.org/10.4028/www.scientific.net/msf.898.1834.

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Carbon-doped Sb-rich Ge-Sb-Te (Sb-CGST) is proved to be a promising candidate for phase change memory because of it high crystallization temperature (higher than 200°C) and 10-year data retention temperature (higher than 120°C). The carbon-doped Sb-rich Ge-Sb-Te (Sb-CGST) films were deposited on SiO2/Si (100) substrate by RF magnetron co-sputtering using CGST alloy target (a GST target containing 16 at. % C) and Sb targets at room temperature. The content of Sb in the films was controlled by adjusting the sputtering power ratio of CGST and Sb. The results showed that both of these two properties increase firstly and then decreases with increasing the content of Sb, which are superior to that of Ge2Sb2Te5. Furthermore, Sb-CGST based PCM cells were fabricated to investigate the property of material. 6ns pulse could realize SET operation, and 3.2 x 10-11J energy can realize RESET operation.

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Kim, Myoung Sub, Jin Hyung Jun, Jin Ho Oh, et al. "Electrical Switching Characteristics of Nitrogen Doped Ge₂Sb₂Te₅ Based Phase Change Random Access Memory Cell." Solid State Phenomena 124-126 (June 2007): 21–24. http://dx.doi.org/10.4028/www.scientific.net/ssp.124-126.21.

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Ge2Sb2Te5 (GST) has been widely studied for PRAM as reversible phase change material. GST is expected to reduce RESET (crystalline → amorphous) operation power, which is one of important issues for PRAM technology. In order to investigate the effect of nitrogen doping on electrical switching characteristics, we fabricated two kinds of PRAM cells with nitrogen-doped (N-doped) and un-doped GST, which were different bottom electrode contact size (0.80~1.00 ). N-doped GST PRAM cells have higher dynamic resistance with small sized bottom electrode contact and lower RESET voltage (about 1.2 V, 50 ns) than un-doped GST PRAM cells (about 1.6 V, 50 ns). The resistance switching ratio (RRESET to RSET) was about 100. The results of this study indicate that nitrogen doping into GST film and smaller size of bottom electrode contact reduce RESET power for PRAM operation.

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Oh, Sang Ho, Kyungjoon Baek, Sung Kyu Son, et al. "In situ TEM observation of void formation and migration in phase change memory devices with confined nanoscale Ge2Sb2Te5." Nanoscale Advances 2, no. 9 (2020): 3841–48. http://dx.doi.org/10.1039/d0na00223b.

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Yoon, Jong Moon, Hu Young Jeong, Sung Hoon Hong, et al. "Large-area, scalable fabrication of conical TiN/GST/TiN nanoarray for low-power phase change memory." J. Mater. Chem. 22, no. 4 (2012): 1347–51. http://dx.doi.org/10.1039/c1jm14190b.

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Chen, Yimin, Nan Han, Fanshuo Kong, et al. "Kinetics features of 2D confined Ge₂Sb₂Te₅ ultrathin film." Applied Physics Letters 121, no. 6 (2022): 061904. http://dx.doi.org/10.1063/5.0100570.

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Ge2Sb2Te5 (GST) films of 7 nm thickness in the multilayer structure of [GST 7 nm/W 6 nm]20 have been fabricated, and their crystallization kinetics is studied via ultrafast differential scanning calorimetry and a generalized Mauro–Yue–Ellison–Gupta–Allan viscosity model. A distinct fragile-to-strong crossover (FSC) transition behavior, which is beneficial to balance the contradiction between good thermal stability nearby glass transition temperature Tg and fast crystal crystallization speed around melting temperature, is found in this 2D confined GST ultrathin film with the FSC transition temperature of 1.25 Tg. The above analyses are helpful to understand the kinetics features of an ultrathin GST material in a low-dimensional phase-change device for neuro-inspired in-memory computing.

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Pathak, Anushmita, Shivendra Kumar Pandey, and Jitendra Kumar Behera. "Optical band-gap evolution and local structural change in Ge₂Sb₂Te₅ phase change material." Journal of Physics: Conference Series 2426, no. 1 (2023): 012045. http://dx.doi.org/10.1088/1742-6596/2426/1/012045.

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Abstract The amorphous to crystalline phase transition in Ge2Sb2Te5 (GST) phase change material is investigated using XRD and the systematic variation in the optical band-gap (Eg ) and structural disorder (B 1/2) employing UV-Vis-NIR spectroscopy. The amorphous phase is observed to have Eg value of 0.708 eV while crystalline phase (200 °C) shows 0.442 eV. Variation in B 1/2 slope of 13.4 % is noted around the crystallization temperature (150 °C), depicting structural disorder reduction and hence structural ordering in the material forming the cubic phase. The change in the optical band-gap and local structural disorder upon crystallization occurs due to alternation in the atomic bonding configurations, which is explored using XPS technique. The findings reveal Ge-Te (~1218.35 eV binding energy) and Sb-Te (~528.8 eV) bonds in the amorphous phases. However, their bond lengths increase (hence binding energy reduces) as the annealing temperature rises, demonstrating phase switching occurs upon reaching the crystallization temperature. Insight into the optical band-gap, local structural disorder, and atomic arrangement governs many vital features of phase change material, such as fast crystallization speed, better thermal stability, high endurance, and large resistance contrast, which provide the path for non-volatile memory and nanophotonic applications.

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Hamada, Seiti, Takafumi Horiike, Tomohiro Uno, et al. "Evaluation of Ge_xSb_yTe_z Film Grown by Chemical Vapor Deposition." Materials Science Forum 725 (July 2012): 289–92. http://dx.doi.org/10.4028/www.scientific.net/msf.725.289.

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This paper describes structure evaluation of GexSbyTez (GST) film fabricated by chemical vapor deposition (CVD). We successfully established composition controlled GST CVD with smooth surface by applying appropriate deposition conditions. By increasing Ge flow rate or reducing substrate temperature, the average grain size was reduced and the film flatness was improved. As the results, we succeeded to obtain the extremely smooth surface, and also to fill a finite hole with conformal film deposition. All GexSbyTez films showed FCC or amorphous crystalline structures, both are utilized in the proposed phase change random access memory (PRAM), in spite of the wide range of composition control. We believe these CVD-GST films are useful for PRAM applications.

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Kashem, Md Tashfiq Bin, Jake Scoggin, Helena Silva, and Ali Gokirmak. "(Digital Presentation) Finite Element Modeling of Thermoelectric Effects in Phase Change Memory Cells." ECS Meeting Abstracts MA2022-01, no. 18 (2022): 1031. http://dx.doi.org/10.1149/ma2022-01181031mtgabs.

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Phase change memory (PCM) is a high-speed high-endurance non-volatile electronic memory technology which utilizes the electrical resistivity difference between the amorphous and the crystalline phases of phase change materials, such as Ge2Sb2Te5 (GST), to store information [1]. PCM cells are switched by short duration electrical pulses by melting a small volume to transition to dielectric amorphous phase (reset) or heating above glass-transition temperature to crystallize (set). The cells experience extremely large thermal gradients (~ 50 K/nm) and high current densities (~50 MA/cm2) during reset. Hence thermoelectric (TE) contributions are very significant both in bulk and at the material and solid-liquid interfaces [2]. In this work, we performed finite element simulations of mushroom PCM cells and analyzed contributions of Joule heating (symmetric) and thermoelectric heat (asymmetric) during reset and set operations using COMSOL Multiphysics. A field effect transistor (FET), modeled using a circuit model, is used as an access device. We self-consistently solve for current continuity, heat transport (Fig. 1) and phase changes in the materials, including temperature, electric-field and phase-dependent electrical and thermal conductivity, thermal boundary resistances and latent heat of fusion, along with temperature dependent stochastic nucleation, growth and grain-boundary amorphization, accounting for all energy exchanges [3-6]. Thermoelectric heat exchanges are due to generation and recombination of electrons and holes as well as the kinetic energy absorbed or released by the transported free charge carriers [7]. These energy exchanges can take place at material interfaces (Peltier heat) or in bulk material (Thomson heat). Discontinuity of Seebeck coefficient and temperature (due to thermal boundary resistances) make TE contributions very significant in PCM devices. Our simulation results show the significance of the TE contributions on the reset behavior of PCM devices (Fig. 2). Self-heating at the bottom TiN-GST interface is substantially higher for one of the current polarities, giving rise to an over-sized mushroom in the case of negative polarity, for the same reset pulse amplitude. The negative polarity case (over-reset cell) cannot be set with the same set pulse as the positive polarity case. From the power consumption and peak current requirement point of view, it is advantageous to have higher TE heating inside the mushroom and its interfaces. TE cooling away from the mushroom interfaces is advantageous for reduced thermal cross-talk and write-disturb on the neighboring cells. However, thermal gradients also need to be kept under consideration for reliability perspective. Acknowledgement: Md Tashfiq Bin Kashem acknowledges support from General Electric through a Graduate Fellowship for Innovation. This work is supported through US National Science Foundation (NSF) award # 1710468. References: [1] S. W. Fong, et al., IEEE Trans. Elect. Dev., vol. 64, p. 4374 (2017). [2] A. Faraclas, et al., IEEE Trans. Elect. Dev., vol. 61, p. 372 (2014). [3] Z. Woods, et al., IEEE Trans. Elect. Dev., vol. 64, p. 4466 (2017). [4] Z. Woods, et al., IEEE Trans. Elect. Dev., vol. 64, p. 4472 (2017). [5] J. Scoggin, et al., Appl. Phys. Lett., vol. 112, p. 193502 (2018). [6] J. Scoggin, et al., Appl. Phys. Lett., vol. 114, p. 043502 (2019). [7] G. Bakan et al., Sci. Rep., vol. 3, p. 2724 (2013). Figure 1

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Kashem, Md Tashfiq Bin, Jake Scoggin, Ali Gokirmak, and Helena Silva. "(Digital Presentation) Electrothermal Modeling of Interfacial Phase Change Memory." ECS Meeting Abstracts MA2022-01, no. 18 (2022): 1032. http://dx.doi.org/10.1149/ma2022-01181032mtgabs.

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Phase change memory (PCM) is a high-speed non-volatile memory that utilizes the reversible and fast transition between highly conductive crystalline phase and highly resistive (dielectric) amorphous phase of the phase change material to store information and the large electrical resistivity contrast between the two phases for retrieval of the stored data [1,2]. One of the main challenges for PCM is the large power required to heat the active region above crystallization or melting temperature. Lower energy and higher speed operations have been demonstrated with thin film superlattice stacks of phase change materials known as interfacial phase change memory (iPCM) [3-6]. The mechanisms behind the improved performance of iPCM are still under investigation but recent work indicates similar crystallization and melt-quench operation of these devices [5]. In this work, we perform electrothermal finite element simulations of reset and set operations on iPCM structures consisting of alternately stacked Ge2Sb2Te5 (GST) and GeTe layers using COMSOL multiphysics [7-10]. Electrical pulses are applied for reset and set processes utilizing an internal circuit model where a transistor is used as an access device. Coupled electric current and heat transfer physics are employed to incorporate Joule heating and thermoelectric effects (Thomson heat within a single material and Peltier heat at material interfaces) with temperature dependent Seebeck coefficients, thermal conductivities, electrical resistivities, heat capacities and thermal boundary resistances (TBR) for each material / material pairs. Latent heat of fusion is included in the amorphous-crystalline and solid-liquid transitions [10], giving rise to heat release at the crystal-amorphous boundaries during crystal growth and heat absorption at the grain boundaries during amorphization. Grain boundaries and material interfaces have high energy sites, making them easier to melt, described as heterogeneous melting [10]. iPCM [5] structures utilize engineered interfaces formed between nanometer scale thin-film stacks, promoting amorphization through increased number of material interfaces and reduced thermal conduction due to TBR. Furthermore, the melting temperature, electrical conductivity and Seebeck coefficient of the different materials within an iPCM device differ. Hence, such layered structures may have the advantage of melting of only one of the alternating layers assisted by local heating or cooling due to Peltier effect at the interfaces. Our results on iPCM and conventional PCM structures of same dimensions and geometry (20 nm wide, 150 nm high pore-cells) show ~ 50% reduction in reset times and more consistent set times for iPCM cells due to lesser variations in grain sizes and location of boundaries. Acknowledgment: This work is partially supported by the National Science Foundation under award DMR-1710468. References: [1] S. W. Fong et al., IEEE Trans. Electron Devices 64, 4374 (2017). [2] G. W. Burr et al., IEEE J. Emerg. Sel. Topics Circuits Syst. 6, 146 (2016). [3] J. Tominaga et al., physica status solidi (RRL) 13, 1800539 (2019). [4], K. V. Mitrofanov et al., Japanese Journal of Applied Physics 57, 04FE06 (2018). [5] K. L. Okabe et al., Journal of Applied Physics 125, 184501 (2019). [6] T. Ohyanagi et al., AIP Advances 6, 105104 (2016). [7] Z. Woods et al., IEEE Trans. Electron Devices 64, 4466 (2017). [8] Z. Woods et al., IEEE Trans. Electron Devices 64, 4472 (2017). [9] J. Scoggin et al., Applied Physics Letters 112, 193502 (2018). [10] J. Scoggin et al., Applied Physics Letters 114, 043502 (2019).

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Kiouseloglou, Athanasios, Gabriele Navarro, Veronique Sousa, et al. "A Novel Programming Technique to Boost Low-Resistance State Performance in Ge-Rich GST Phase Change Memory." IEEE Transactions on Electron Devices 61, no. 5 (2014): 1246–54. http://dx.doi.org/10.1109/ted.2014.2310497.

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Yamamoto, Takuya, Shogo Hatayama, Yun-Heub Song та Yuji Sutou. "Influence of Thomson effect on amorphization in phase-change memory: dimensional analysis based on Buckingham’s П theorem for Ge₂Sb₂Te₅". Materials Research Express 8, № 11 (2021): 115902. http://dx.doi.org/10.1088/2053-1591/ac3953.

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To evaluate the Thomson effect on the temperature increase in Ge2Sb2Te5 (GST)-based phase-change random access memory (PCRAM), we created new dimensionless numbers based on Buckingham’s П theorem. The influence of the Thomson effect on the temperature increase depends on the dominant factor of electrical resistance in a PCRAM cell. When the effect is dominated by the volumetric resistance of the phase-change material C = ρ c Δ x / σ ≪ O ( 1 ) , the dimensionless evaluation number is B = μ T σ Δ ϕ k , where ρ c is the contact resistance, Δx is the thickness of PCM, σ and k are the electrical and thermal conductivities, μ T is the Thomson coefficient, and Δϕ is the voltage. When the contact resistance cannot be ignored, the evaluation number is B/(1 + C). The characteristics of hexagonal-type crystalline GST in a PCRAM cell were numerically investigated using the defined dimensionless parameters. Although the contact resistance of GST exceeded the volumetric resistance across the temperature range, the ratio of contact resistance to the whole resistance reduced with increasing temperature. Moreover, increasing the temperature of GST enhanced the influence of the Thomson effect on the temperature distribution. At high temperatures, the Thomson effect suppressed the temperature increase by approximately 10%–20%.

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Meng, Yingjie, Yimin Chen, Kexin Peng, et al. "GeTe ultrathin film based phase-change memory with extreme thermal stability, fast SET speed, and low RESET power energy." AIP Advances 13, no. 3 (2023): 035205. http://dx.doi.org/10.1063/5.0138286.

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We designed the phase-change memory (PCM) cell based on ultrathin GeTe film (∼10 nm) and homemade nanoscale electrode filling craft to improve data retention ability and reduce programming energy, respectively. It was found that the temperature for ten years’ data retention of this ultrathin GeTe film is 160 ± 32.8 °C, which is much higher than that of conventional Ge2Sb2Te5 (GST, 83 ± 20.6 °C) film. Benefit to the nature of fragile-to-strong crossover behavior in GeTe supercooled liquids that was confined in a two-dimension structure, a fast SET speed of 6 ns is also detected in this ultrathin GeTe PCM. Moreover, the RESET power consumption of this ultrathin GeTe PCM is measured as 1.8 ± 0.5 nJ, and it is much lower than that of GST PCM (16.5 ± 1.5 nJ), which is attributed to the nanoscale electrode of the devices. The above-mentioned improvements enable the application of ultrathin GeTe PCM in neuromorphic computing.

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Zhang, Dan, Yifeng Hu, Haipeng You, et al. "High Reliability and Fast-Speed Phase-Change Memory Based on Sb70Se30/SiO2 Multilayer Thin Films." Advances in Materials Science and Engineering 2018 (June 21, 2018): 1–6. http://dx.doi.org/10.1155/2018/9693015.

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Sb70Se30/SiO2 multilayer thin films were applied to improve the thermal stability by RF magnetron sputtering on SiO2/Si (100) substrates. The characteristics of Sb70Se30/SiO2 multilayer thin films were investigated in terms of crystallization temperature, ten years of data retention, and energy bandgap. It is observed that the crystallization temperature, 10-year data retention, and resistance of Sb70Se30/SiO2 multilayer composite thin films exhibited a higher value, suggesting that Sb70Se30/SiO2 multilayer composite thin films have superior thermal stability. The AFM measurement suggests that the SbSe (1 nm)/SiO (9 nm) multilayer thin films possess a smaller surface roughness (RMS = 0.23 nm). Besides, it was found that the phase-change time of SbSe (1 nm)/SiO (9 nm) multilayer thin films was shorter than that of GST in the process of crystallization and amorphization.

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Hira, Takashi, Takayuki Uchiyama, Kenta Kuwamura, Yuya Kihara, Tasuku Yawatari, and Toshiharu Saiki. "Switching the Localized Surface Plasmon Resonance of Single Gold Nanorods with a Phase-Change Material and the Implementation of a Cellular Automata Algorithm Using a Plasmon Particle Array." Advances in Optical Technologies 2015 (February 2, 2015): 1–5. http://dx.doi.org/10.1155/2015/150791.

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We investigate the modulation of the localized surface plasmon resonance (LSPR) of a gold nanorod (AuNR) using a GeSbTe film as an active medium. We demonstrate high-contrast switching of LSPR in an AuNR/GST/Au thin film sandwich structure upon phase change. To go beyond this single-particle switching functionality, we consider a plasmon particle system interacting with a phase-change material (PCM) to discuss the possibility of parallel processing devices with memory functionality, exploiting the plasticity and threshold behavior that are inherent characteristics of PCMs. We demonstrate that the temporal and spatial evolution of a plasmon-PCM array system can be equivalent to a cellular automata algorithm.

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Kashem, Md Tashfiq Bin, Sadid Muneer, Lhacene Adnane, Faruk Dirisaglik, Ali Gokirmak, and Helena Silva. "(Digital Presentation) Calculation of the Energy Band Diagram and Estimation of Electronic Transport Parameters of Metastable Amorphous Ge₂Sb₂Te₅." ECS Meeting Abstracts MA2022-01, no. 18 (2022): 1043. http://dx.doi.org/10.1149/ma2022-01181043mtgabs.

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Phase change memory (PCM) is a high speed, high density non-volatile resistive memory technology that utilizes different phases (crystalline and amorphous) of phase change materials such as Ge2Sb2Te5 (GST) to store information [1]. Here, the material undergoes two types of reversible switching phenomena: (i) Ovonic Threshold Switching (OTS), which causes the amorphous phase of the material to switch from a highly resistive state to conductive state with application of high electric fields, resulting in current flow and (ii) Ovonic Memory Switching (OMS), which is due to the change of the phase of the material between amorphous and crystalline phases induced by heating [2]. Even though PCM entered high volume manufacturing, the electronic properties of the phase change materials are still not well understood [3,4]. In this work, we construct the energy band diagram of amorphous GST as a function of temperature using a temperature dependent model of effective activation energy of conduction in metastable amorphous GST [5], which we obtained from high-speed experiments on GST line-cells [6]. Assuming the bandgap energy to linearly decrease with temperature [7,8] and p-type conduction (based on positive Seebeck coefficients measured in a wide temperature range [9]) , we determine a temperature dependent Fermi energy level from 0K to melting temperature, Tmelt ~ 858 K. Liquid GST is expected to become metallic (bandgap collapsing to 0) at ~ 894K, based on the experimental results. We also estimate the carrier concentration at Tmelt utilizing the latent heat of fusion (126 kJ/kg) [10] to be pmelt = 1.47 x 1022 cm-3. Using the melt resistivity measured on GST thin film, we calculate the carrier mobility at melting point as µmelt ~0.187 cm2/V-s, close to the previously reported value of 0.15 cm2/V-s based on crystalline state mobility and a density of states calculation [2]. Assuming a weak temperature dependence of the mobility [5], we obtain the carrier concentration of ~3.37× 1017 cm-3 at room temperature which lies within the ~1017-1018 cm-3 range estimated in a former study [3]. Finally, we calculate conduction activation energy of as-deposited amorphous GST from temperature dependent Seebeck coefficient measured simultaneously with the resistance [9]. The activation energy varies as a parabolic function of temperature where it starts from 0 eV at 0 K, reaches a peak of ~0.257 eV near glass transition temperature (~400 K) with the room temperature value of ~0.24 eV and becomes 0 eV again at ~810 K. We also utilize the Seebeck coefficient measurements along with the band edges and Fermi energy level information from the energy band diagram to calculate the ratio of minority carrier concentration to the total carrier concentration as a function of temperature; this is useful to predict the temperature beyond which bipolar conduction becomes significant. Acknowledgment: Analysis is performed with the support of US National Science Foundation (NSF) award ECCS 1711626. The experimental data used for this analysis were collected with the support of US NSF DMR-1710468 on devices fabricated with the support of US Department of Energy Office of Basic Energy Sciences. References: [1] S. W. Fong et al., IEEE Trans. Electron Devices, vol. 64, no. 11, pp. 4374–4385, 2017. [2] A. Pirovano et al., IEEE Trans. Electron Devices, vol. 51, no. 3, pp. 452–459, 2004. [3] T. Kato et al., Japanese J. Appl. Physics, vol. 44, no. 10, pp. 7340–7344, 2005. [4] M. Schumacher et al., Sci. Rep., vol. 6, no. June, pp. 1–11, 2016. [5] S. Muneer et al., AIP Adv., vol. 8, no. 6, p. 65314, Jun. 2018. [6] F. Dirisaglik et al., Nanoscale, vol. 7, no. 40, pp. 16625–16630, 2015. [7] E. M. Vinod et al., J. Non. Cryst. Solids, vol. 356, no. 41–42, pp. 2172–2174, 2010. [8] Y. Kim et al., Appl. Phys. Lett., vol. 90, no. 17, pp. 1–4, 2007. [9] L. Adnane et al., J. Appl. Phys., vol. 122, no. 12, 2017. [10] Z. Fan et al., Japanese J. Appl. Physics, vol. 42, no. 2 B, pp. 800–803, 2003.

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Cueto, O., C. Jahan, V. Sousa, et al. "Analysis by simulation of amorphization current in phase change memory applied to pillar and GST confined type cells." Microelectronic Engineering 88, no. 5 (2011): 827–32. http://dx.doi.org/10.1016/j.mee.2010.09.022.

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