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The disorder‐to‐order (crystallization) process in phase‐change materials determines the speed and storage polymorphism of phase‐change memory devices. Only by clarifying the fine‐structure variation can the devices be insightfully designed, and encode and store information. As essential phase‐change parent materials, the crystallized Sb–Te binary system is generally considered to have the cationic/anionic site occupied by Sb/Te atoms. Here, direct atomic identification and simulation demonstrate that the ultrafast crystallization speed of Sb–Te materials is due to the random nature of lattice site occupation by different classes of atoms with the resulting octahedral motifs having high similarity to the amorphous state. It is further proved that after atomic ordering with disordered chemical occupation, chemical ordering takes place, which results in different storage states with different resistance values. These new insights into the complicated route from disorder to order will play an essential role in designing neuromorphic devices with varying polymorphisms. [ABSTRACT FROM AUTHOR]

The magnetostructural phase transition in Fe50Al50 alloy with chemically ordered paramagnetic B2 and disordered ferromagnetic (FM) A2 phase has applications in spintronics such as phase-change magnetic memory and magnonic devices. We first conducted a systematic first-principles density functional theory study of the A2 and B2 phases in the Fe50Al50 alloy. A theoretical understanding of this equiatomic alloy's electronic and spin-dynamical properties leads us to the experimental exploration of the FM A2 phase. Therefore, we deposit the 50 nm Fe50Al50 alloy thin film using sputtering and investigate the influence of the Ta buffer layer on its structural and magnetic properties. Our results reveal that the film with a buffer layer exhibits the A2 phase with appreciably higher saturation magnetization (848 emu/cc) than the film without a buffer layer (576 emu/cc). However, the surface roughness and Gilbert damping (α) slightly increase with the presence of the buffer layer from 0.41 to 0.56 nm and 4.35 × 10−3–4.94 × 10−3, respectively. The enhancement in α is due to extrinsic contributions induced by surface inhomogeneities. [ABSTRACT FROM AUTHOR]

Thermal stability and phase transition rate are two important issues that restrict the engineering applications of phase change memories. In this paper, GeSb/Sb multilayer films were prepared by multilayer stacking, and their phase transition properties were investigated. GeSb/Sb multilayer films had higher crystallization temperature, better data retention, and lower resistance drift than pure Sb films, which indicated that they had excellent thermal stability and accuracy of resistance identification. The test results of X‐ray diffraction and atomic force microscopy showed that GeSb spacer layers could inhibit grain growth of Sb film layers, thus reducing the roughness and potential fluctuation of the film surface. X‐ray reflectivity experiments showed that the GeSb/Sb multilayer films before and after crystallization had small volume changes. The devices based on [GeSb(7 nm)/Sb(3 nm)]8 multilayer films could achieve reversible resistive transition operation between SET and RESET at a pulse width of 10 ns, showing satisfactory transition rate and operational power consumption. The low resistance drift and ultra‐fast phase transition speed make GeSb/Sb multilayer films one of the promising choices for phase change memories. [ABSTRACT FROM AUTHOR]

Phase-change memory (PCM), recently developed as the storage-class memory in a computer system, is a new non-volatile memory technology. In addition, the applications of PCM in a non-von Neumann computing, such as neuromorphic computing and in-memory computing, are being investigated. Although PCM-based devices have been extensively studied, several concerns regarding the electrical, thermal, and structural dynamics of phase-change devices remain. In this article, aiming at PCM devices, a comprehensive review of PCM materials is provided, including the primary PCM device mechanics that underpin read and write operations, physics-based modeling initiatives and experimental characterization of the many features examined in nanoscale PCM devices. Finally, this review will propose a prognosis on a few unsolved challenges and highlight research areas of further investigation. We certify that the submitted manuscript is truly original, unpublished, and not being considered for publication elsewhere. [ABSTRACT FROM AUTHOR]

[Display omitted] Interfacial Phase Change Memory (iPCM) retrench unnecessary power consumption due to wasted heat generated during phase change by reducing unnecessary entropic loss. In this study, an advanced iPCM (GeTe/Ti-Sb 2 Te 3 Superlattice) is synthesized by doping Ti into Sb 2 Te 3. Structural analysis and density functional theory (DFT) calculations confirm that bonding distortion and structurally well-confined layers contribute to improve phase change properties in iPCM. Ti-Sb 2 Te 3 acts as an effective thermal barrier to localize the generated heat inside active region, which leads to reduction of switching energy. Since Ge-Te bonds adjacent to short and strong Ti-Te bonds are more elongated than the bonds near Sb-Te, it is easier for Ge atoms to break the bond with Te due to strengthened Peierls distortions (R long /R short) during phase change process. Properties of advanced iPCM (cycling endurance, write speed/energy) exceed previous records. Moreover, well-confined multi-level states are obtained with advanced iPCM, showing potential as a neuromorphic memory. Our work paves the way for designing superlattice based PCM by controlling confinement layers. [ABSTRACT FROM AUTHOR]

In order to validate the flexible storage potential, [Ge 2 Sb 2 Te 5 (3 nm)/Sb(7 nm)] 5 superlattice-like phase change films on flexible polyetheretherketone substrates were prepared by magnetron sputtering. The phase transition behavior and the effect of different bending cycles on the properties were investigated. Compared with conventional rigid Si/SiO 2 substrate, [Ge 2 Sb 2 Te 5 (3 nm)/Sb(7 nm)] 5 films based on a flexible substrate possessed better thermal stability and surface adhesion. The superlattice-like structure was confirmed by transmission electron microscopy. PCM devices based on polyetheretherketone substrates were fabricated and the electrical conversion characteristics before and after bending were verified and compared. [ABSTRACT FROM AUTHOR]

We discuss inline electrical testing to monitor the baseline of Analog Computing hardware using Phase Change Memory (PCM) technology. Tightening the PCM resistance distribution is necessary to meet analog computation requirement. A new yield methodology is introduced. A study of heater process variation, which will affect the heater height and the PCM resistance, will be discussed. [ABSTRACT FROM AUTHOR]

High density phase change memory array requires both minimized critical dimension (CD) and maximized process window for the phase change material layer. High in-wafer uniformity of the nanoscale patterning of chalcogenides material is challenging given the optical proximity effect (OPE) in the lithography process and the micro-loading effect in the etching process. In this study, we demonstrate an approach to fabricate high density phase change material arrays with half-pitch down to around 70 nm by the co-optimization of lithography and plasma etching process. The focused-energy matrix was performed to improve the pattern process window of phase change material on a 12-inch wafer. A variety of patternings from an isolated line to a dense pitch line were investigated using immersion lithography system. The collapse of the edge line is observed due to the OPE induced shrinkage in linewidth, which is deteriorative as the patterning density increases. The sub-resolution assist feature (SRAF) was placed to increase the width of the lines at both edges of each patterning by taking advantage of the optical interference between the main features and the assistant features. The survival of the line at the edges is confirmed with around a 70 nm half-pitch feature in various arrays. A uniform etching profile across the pitch line pattern of phase change material was demonstrated in which the micro-loading effect and the plasma etching damage were significantly suppressed by co-optimizing the etching parameters. The results pave the way to achieve high density device arrays with improved uniformity and reliability for mass storage applications. [ABSTRACT FROM AUTHOR]

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. [ABSTRACT FROM AUTHOR]

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. [ABSTRACT FROM AUTHOR]

Phase change memory (PCM) is an exceptional universal memory innovation that offers qualities like fast speed and non-volatility. But major obstacle still exists in achieving better thermal stability and rapid switching at the same time. Therefore, it is crucial to investigate new materials with enhanced properties. To overcome the contrast of access time between storage systems and memories, storage class memory concept based on emerging nonvolatile memory technology has been introduced. Resistive switching has gained much awareness in last decade due to its application in PCM technologies. Investigation of resistive switching on novel Te (1−x) (GeSe 0.5)Sc x (x = 0, 0.05, 0.1, 0.15) quaternary alloy has been analyzed in this paper. Material has revealed electrical resistivity contrast of ∼103 orders of magnitude that offers better thermal stability than the majority of other phase transition alloys. Additionally, current-voltage (I-V) properties and voltage dependent threshold switching support an incredibly fast threshold switching operation. Switching is observed at 18–30 V and threshold voltage has been noticed to decrease (10–12 V) with increasing temperature. From XPS study, it can be observed that binding energy is shifting towards lower energies by 0.25 eV. Sc makes the GeTeSe parent material appealing for next-generation high-speed, non-volatile, and improved thermal stability memory applications. [Display omitted] • Electrical resistivity contrast of ∼103 orders of magnitude. • Better thermal stability than the majority of other phase transition alloys. • Switching is observed at 18-30 V and threshold voltage has been noticed to decrease (10-12 V) with increasing temperature. • The barrier-cluster model is used to interpret compensating effect in thermally controlled resistive switching and d.c. conduction. • Sc makes the GeTeSe appealing for next-generation high-speed, non-volatilememory applications. [ABSTRACT FROM AUTHOR]

To solve the problems of complex structure, poor reliability, and low intelligence of existing fan clutches for large hybrid vehicles, this paper proposes a new adaptive shape memory alloy intelligent fan clutch for large hybrid vehicle motor cooling. Based on the pure shear shape memory alloy thermodynamic effects, the relationship between shape memory alloy spring recovery force and temperature has been established; based on the shape memory alloy spring thermal drive characteristics and clutch construction dimensions, clutch torque transmission equations have been established. The shape memory alloy fan clutch transmission characteristics were quantitatively analyzed in terms of temperature, torque, rotational speed, and slip rate. The results show that the shape memory alloy fan clutch model based on the finite element method (FEM) and the established transmission model can accurately describe the mechanical characteristics of the shape memory alloy phase change process and the clutch torque transmission characteristics. When the clutch input speed is 3000 rad/min and the temperature is 100 °C, the output torque is 19.04 N·m, the speed is 2877.2 rad/min, and the slip rate is 4.3%. Due to the shape memory effect of shape memory alloy, the clutch can intelligently adjust the fan speed by sensing the ambient temperature. A fan clutch can satisfy the heat dissipation requirement of a large hybrid vehicle's transmission system under complicated road conditions. [ABSTRACT FROM AUTHOR]

Via in situ transmission electron microscopy, we observed on nanoscale unconventional structural evolution during two-dimensional (2D) phase transitions in a Sb 2 Te 3 /TiTe 2 phase-change heterostructure (PCH), which reduces amorphous relxation and crystallization stochasiticity to facilitate rapid and reliable memory programming. [Display omitted] Phase-change heterostructure (PCH) holds great promise for overcoming the low-precision bottleneck that limits multibit storage and parallel computing in conventional phase-change random-access memory. However, the origin of high-accuracy control of electrical resistance achieved in programming PCH memory devices has yet to be established. Via in situ transmission electron microscopy, here we unveil the unusual microscopic processes during the order–disorder phase transitions driven by electrical pulse in a Sb 2 Te 3 /TiTe 2 PCH architecture. The template-modulated phase transition is confirmed to be two-dimensional (2D) in nature. The structural transformation path and dynamics in the confined Sb 2 Te 3 sublayers are found to be profoundly changed with respect to those in bulk monolithic Sb 2 Te 3 , leading to markedly suppressed amorphous relaxation and substantially reduced crystallization stochasticity, both highly desirable for swift and accurate device operations. Our atomic-scale observations provide direct evidence of, and much-needed insight into, the working mechanisms that may enable superior 2D phase-change electronic devices. [ABSTRACT FROM AUTHOR]

Ambient humidity has an important impact on the performance of flexible electronic devices, and wearable electronic devices will inevitably involve a high humidity environment. To investigate the impact of humidification on flexible phase-change memory, we prepared Sb phase-change film and memory device unit with polyether ether ketone as substrate, and studied the effect of humidification on the properties of the film and device. The results show that the effective transition from an amorphous to a crystalline state can still be achieved by the film after soaking in water for 55 min, and the phase transition temperature increases with the increase of soaking time. Water molecules refine the film grains, resulting in increased crystalline resistance. Sb is a hydrophilic material, and its hydrophilicity decreases after crystallization. The reversible conversion of SET-RESET can be realized under different pulse widths even after the phase change memory device is soaked in water and bent many times. This study shows that antimony-based flexible phase change memory has certain deformation self-healing ability and moisture resistance, which provides a way to expand its application environment. [Display omitted] [ABSTRACT FROM AUTHOR]

In this paper, the flexible phase change behavior of Ge 2 Sb 2 Te 5 /Mg 35 Sb 65 superlattice-like memory based on PEEK substrate is investigated in detail. The flexible memory has good thermal stability (T c ∼270.4 °C), resistance to bending (more than 2 ×104 bending times), low resistance drift (less than 25% of the Ge 2 Sb 2 Te 5 film), stable amorphous to crystalline resistance ratio (∼2 orders of magnitude) and ultra-fast information access speed (∼5 ns). Bending refines the grain of the film and widens the band gap. This study provides a potential option for flexible information storage electronics. • Ge 2 Sb 2 Te 5 /Mg 35 Sb 65 superlattice-like films on PEEK substrates possess good thermal stability and mechanical bending durability. • After several bending cycles, the FPCM can even complete the ultrafast phase transition within 5 ns. [ABSTRACT FROM AUTHOR]

Ge-Sb-Te (GST) thin films are emerging materials for various non-volatile memory applications. The compounds contain a huge number of vacancies that play important roles in structural and electronic transitions. Control of disorder and understanding the structural transformations in GST thin films are of great importance for the design and reliability of phase change memory devices. In this work, in situ heating atomic-resolution transmission electron microscopy is used to observe structural transformations from vacancy disordered (fcc) to layered ordered (vacancy-ordered (vo)) and van der Waals-bonded trigonal (vdW t)) structures. Starting from 160 °C, randomly distributed vacancies in fcc grains gradually accumulate into vacancy layers. Further heating to 220 and 240 °C results in the formation of vdW t-domains within the vo-GST grains and the formation of large <001>-oriented t-grains, in a good agreement with outcomes on in situ XRD heating of epitaxial vo-GST thin film. Moreover, vo and fcc GST structures can coexist with vdW t-structure in one grain. Full transformation to 〈 11 2 ¯ 0 〉 -oriented t-grains occurs at 280 °C. Unlike other grains, the 〈001〉 t-grains show abnormal grain growth behaviour, while the electron beam irradiation accelerates the growth. Detailed characterizations of vo-grains reveal transient structures that indicate shear transformation mechanism and different defects as well as chemical changes during the transformations. Overall, this study provides new insights to understand the phase transition mechanisms and to optimize the microstructure in thin GST layers. [Display omitted] [ABSTRACT FROM AUTHOR]

One central task of developing nonvolatile phase change memory (PCM) is to improve its scalability for high‐density data integration. In this work, by first‐principles molecular dynamics, to date the thinnest PCM material possible (0.8 nm), namely, a monolayer Sb2Te3, is proposed. Importantly, its SET (crystallization) process is a fast one‐step transition from amorphous to hexagonal phase without the usual intermediate cubic phase. An increased spatial localization of electrons due to geometrical confinement is found to be beneficial for keeping the data nonvolatile in the amorphous phase at the 2D limit. The substrate and superstrate can be utilized to control the phase change behavior: e.g., with passivated SiO2 (001) surfaces or hexagonal Boron Nitride, the monolayer Sb2Te3 can reach SET recrystallization in 0.54 ns or even as fast as 0.12 ns, but with unpassivated SiO2 (001), this would not be possible. Besides, working with small volume PCM materials is also a natural way to lower power consumption. Therefore, the proposed PCM working process at the 2D limit will be an important potential strategy of scaling the current PCM materials for ultrahigh‐density data storage. [ABSTRACT FROM AUTHOR]

One central task of developing nonvolatile phase change memory (PCM) is to improve its scalability for high‐density data integration. In this work, by first‐principles molecular dynamics, to date the thinnest PCM material possible (0.8 nm), namely, a monolayer Sb2Te3, is proposed. Importantly, its SET (crystallization) process is a fast one‐step transition from amorphous to hexagonal phase without the usual intermediate cubic phase. An increased spatial localization of electrons due to geometrical confinement is found to be beneficial for keeping the data nonvolatile in the amorphous phase at the 2D limit. The substrate and superstrate can be utilized to control the phase change behavior: e.g., with passivated SiO2 (001) surfaces or hexagonal Boron Nitride, the monolayer Sb2Te3 can reach SET recrystallization in 0.54 ns or even as fast as 0.12 ns, but with unpassivated SiO2 (001), this would not be possible. Besides, working with small volume PCM materials is also a natural way to lower power consumption. Therefore, the proposed PCM working process at the 2D limit will be an important potential strategy of scaling the current PCM materials for ultrahigh‐density data storage. [ABSTRACT FROM AUTHOR]

The superlattice-like Sn 15 Sb 85 /Ti phase change films were fabricated by magnetron sputtering, and the effects of Ti layer on the phase change properties and crystal structure of the Sn 15 Sb 85 films were systematically researched. With the addition of Ti layers, the crystallization temperature of the films increased, indicating their thermal stability and data retention were improved. X-ray diffraction results reflect that the presence of Ti layers restrains grain growth and refines grain size. X-ray photoelectron spectroscopy analysis reveals that the incorporation of Ti layers enhances the interatomic binding energy and improves the stability. X-ray reflectivity analysis and atomic force microscopy indicate that the Sn 15 Sb 85 /Ti films have smaller volume change and smoother surface than pure Sn 15 Sb 85 films, implying the better interfacial property and reliability. The T-type phase change memory cell based on Sn 15 Sb 85 /Ti thin film has faster operation speed (100 ns) and lower power consumption (2.6 ×10−12 J) than the conventional Ge 2 Sb 2 Te 5 material. The results show that the superlattice-like Sn 15 Sb 85 /Ti film will be a potential candidate with outstanding properties in thermostability and power consumption. • Proposing the Sn 15 Sb 85 /Ti thin film with superlattice-like structure. • Performance optimization and structural analysis of film. • PCM cells based on Sn 15 Sb 85 /Ti film was prepared and tested. [ABSTRACT FROM AUTHOR]

Phase-change memory utilizing amorphous-to-crystalline phase-change processes for reset-to-set operation as a nonvolatile memory has been recently commercialized as a storage class memory. Unfortunately, designing new phase-change materials (PCMs) with low phase-change energy and sufficient thermal stability is difficult because phase-change energy and thermal stability decrease simultaneously as the amorphous phase destabilizes. This issue arising from the trade-off relationship between stability and energy consumption can be solved by reducing the entropic loss of phase-change energy as apparent in crystalline-to-crystalline phase-change process of a GeTe/Sb2Te3 superlattice structure. A paradigm shift in atomic crystallography has been recently produced using a quasi-crystal, which is a new type of atomic ordering symmetry without any linear translational symmetry. This paper introduces a novel class of PCMs based on a quasicrystalline-to-approximant crystalline phase-change process, whose phase-change energy and thermal stability are simultaneously enhanced compared to those of the GeTe/Sb2Te3 superlattice structure. This report includes a new concept that reduces entropic loss using a quasicrystalline state and takes the first step in the development of new PCMs with significantly low phase-change energy and considerably high thermal stability. [ABSTRACT FROM AUTHOR]

Highlights • Two FAC and SP heating strategies are designed for a PCM-based power battery pack. • Several evaluation factors are developed to compare the performance of the strategies. • The FAC strategy has been optimized by constructing a "close-ended" hot air cycle. • The SP heating strategy demonstrates the best heating performance. Abstract Constructing a complete battery thermal management (BTM) system consisting of both the heating and cooling functionalities is critical to guarantee the cycling life and safety of the power battery pack. In this work, we focus on the neglected issue of replenishing a cooling system with a heating functionality in a standardized power battery module. Two kinds of heating strategies, including forced air convection (FAC) heating and silicone plate (SP) heating are developed and then optimized on an advanced phase change material (PCM)-cooling based battery module. The experimental results show that the performance of the FAC heating strategies can be optimized by constructing a "close-ended" battery pack and increasing the fan number to recycle the waste heat and uniform the air flow field, respectively. The strategy of SP heating at 90 W demonstrates the most effective heating performance. For instance, an acceptable heating time of 632 s and a second lowest temperature difference of 3.55 °C can be obtained, resulting in a highest comprehensive evaluation factor of 0.42, much higher than those of other heating strategies (0.29–0.32). These encouraging results may raise concerns about constructing suitable cooling and heating functionalities simultaneously in a BTM system to realize a target oriented use, particularly those targeting various harsh operating environments. [ABSTRACT FROM AUTHOR]

Multilevel storage and resistance drift are two challenges in phase-change memories. Here, we report that [C(5 nm)/Sb 2 Te 3 (12 nm)] 5 phase-change heterostructure film has multilevel phase change properties and low resistance drift. The addition of carbon broke the Sb 2 Te 3 bond and formed new C-Sb and C-Te bonds. The reliability of phase-change heterostructure was demonstrated by transmission electron microscopy. The amorphous resistance drift index of C/Sb 2 Te 3 film was reduced effectively which may be caused by the structure relaxation. In addition, PCM devices based on C/Sb 2 Te 3 phase-change heterostructure films also confirmed the potential of multilevel storage. This research provided a new method to realize multilevel phase-change memories with low resistance drift. • [C(5 nm)/Sb 2 Te 3 (12 nm)] 5 (C/ST) phase-change heterostructure (PCH) films were prepared by magnetron sputtering. • C/ST film has two resistance changes and low resistance drift index. • The clear multilayer structure confirms the good reliability of superlattice structure. • The PCM devices based on C/ST PCH film exhibit three stable storage states and has low power consumption. [ABSTRACT FROM AUTHOR]

Phase transformations between cubic and rhombohedral states of phase-change chalcogenide materials have been considered to result in small resistance drift, fast read/write speeds, and low power consumption in phase-change memory devices. However, it is difficult to observe such dynamic processes by experiments. Especially, the ultra-fast speed of, and ultra-small area affected during, the displacive transformation involved in the phase transformations, lead to a lack of direct evidence for studying the transformation mechanism. Here, we directly observed the reversible displacive transformations in Yttrium-doped Sb 2 Te 3 (Y-Sb 2 Te 3) by ab initio molecular-dynamics (AIMD) simulations. The forward displacive transformation, from the cubic to the rhombohedral phase, can be spontaneously realized through a two-step transformation, the shearing, and contraction between Te-Sb-Te-Sb-Te building blocks. On the other hand, the backward transformation, from the rhombohedral to the cubic phase, requires high-temperature heating (above 900 K) and atomic diffusion. The diffusion of cation-site Sb atoms into interstitial sites, located in the interlayers of building blocks, triggers the backward transformation; thus, it is diffusion-assisted. Moreover, the enhancement of thermostability of the cubic phase by Y dopants promotes the backward transformation. This study can improve the understanding of the displacive transformations in phase-change materials and may offer new insights into developing phase-change memory devices based on Sb 2 Te 3. [Display omitted] [ABSTRACT FROM AUTHOR]

Tellurium based materials possess a low temperature phase change transition. Sometimes they cannot be obtained in an amorphous state under normal conditions. Thus they can be used as an active element in phase change memory devices. Our study is dedicated to the synthesis of tellurium based materials using the systems (GeTe3)100-xInx, x = 5 mol %, 10 mol %, 15 mol % and 20 mol % and (GeTe4)100-xInx, x = 5 mol %, 10 mol %, 15 mol % and 20 mol %, the deposition of thin films on their ground and the investigation of their morphology, topology and structure aiming to obtain new knowledge for evaluation of the possibility for application of these materials in phase change memory devices. [ABSTRACT FROM AUTHOR]

Thermal properties, mechanism and kinetics of crystallization for Ge2Sb2Te5 thin films were investigated. The parameters of amorphous-crystalline phase transition for Ge2Sb2Te5 thin films were determined. Kinetic triplet (effective activation energy, preexponential factor and reaction model) for the crystallization process of Ge2Sb2Te5 thin films was established. The model of GST filmcrystallization was proposed. Obtained kinetic parameters for Ge2Sb2Te5 films allowed predicting data processing and storage times of the phase change memory cell. It was found that Ge2Sb2Te5 thin film can provide the data processing time of the phase change memory cell about nanoseconds, which is comparable with that of the random access memory. [ABSTRACT FROM AUTHOR]

The synthesis of SnSe 2 thin films, for phase change memory applications, generally require selenization and higher temperature. However, there are many critical problems associated with selenization, such as use of highly toxic H 2 Se/Se gas at high temperature, slow reaction rate and non-uniform composition of thin films. To overcome these problems, a novel and relatively low temperature synthesis of SnSe 2 thin films has been reported here. Selenium rich Sn 30 Se 70 (prepared by melt quenching technique) has been thermally evaporated in presence of Ar followed by vacuum annealing at 200 °C. An attempt has been made to elucidate the structural, optical and electrical properties of these thin films. X-ray diffraction and UV–Vis studies confirmed a phase change from orthorhombic SnSe to hexagonal SnSe 2 followed by improvement in crystallinity (from ≈ 5 nm to 15 nm) and a red shift in optical band gap on annealing. Electrical studies revealed that SnSe phase have single thermal and photo activation energies in temperature range from −20 °C to 100 °C. A large contrast (four orders) in dark-conductivity [(3.19 ± 0.02) × 10 −5 Ω − 1 c m − 1 to (5.16 ± 0.02) × 10 −1 Ω − 1 c m − 1 ] between two phases of Sn 30 Se 70 , suggests its use in phase change memory devices. The SnSe 2 phase is observed to be highly stable in the presence of visible light as compared to SnSe. [ABSTRACT FROM AUTHOR]

GeSbTe alloys have the ability of rapidly transforming between amorphous and crystalline phases. Therefore, they can be used in the non-volatile phase change memory. Recently, a vacancy-ordered cubic Ge 2 Sb 2 Te 5 ( VOC GST) phase change material where the vacancies are highly ordered in the (111) plane, has been experimentally demonstrated by STEM. However, studies are mainly on the structural characterization, rather than on the phase change behavior and possible applications of the VOC GST. Here, using first-principles molecular dynamic simulations, we study the melt-quenched amorphization process and its possible applications. We find that the VOC GST exhibits a quasi-two-dimensional amorphization process that is triggered by the diffusion of Ge atoms but not others. A partial amorphous ( P-amor ) phase is obtained, which can act as an intermediate state between the pure amorphous and pure crystalline phases for possible ternary-state data storage. [ABSTRACT FROM AUTHOR]

ZnxSbyTez thin films are deposited on quartz or glass substrates by the electron beam evaporation technique in an ultra-high vacuum. A prototype phase change memory device using the ZST (ZnxSbyTez) thin film is fabricated. The current-voltage test results of the device show the threshold voltage of ZST531 (Zn5.18Sb3.75Te1.10 at.%) is 2.4 V, which is similar to that of the device based on pure Ge2Sb2Te5. It is shown that the phase-change device with the ZST film is able to perform several reading and writing cycles and the off/on resistance ratio is nearly 10 under pulse voltage. The switching performance of the device is also investigated. Most importantly, the results of the in situ resistance measurements show that the increase of crystallization temperature and the higher 10-year data retention temperature are as high as 300 °C and 191 °C, respectively. This indicates that the ZnxSbyTez material is quite stable, and thus appropriate for use in phase-change memory. [ABSTRACT FROM AUTHOR]

[Display omitted] • The prepared CPCM exhibits excellent flexibility at room temperature. • FCPCM possesses high enthalpy, high thermal conductivity and electrical conductivity. • FCPCM has wide temperature range of flexibility and shape memory properties. • FCPCM is available for fast heating with low current. • For thermal therapy, FCPCM applied to the face and knees, elbows, waist, back, etc. Thermotherapy is often preferable to medication and surgery because of its mild side effects and noninvasiveness. However, current research methods are unable to improve the efficiency of pre-treatment resulting in unportable use, and poor room temperature flexibility has become its critical limitation. Herein, a novel conductive flexible composite phase-change material (CPCM) was prepared for high-performance thermotherapy. Styrene ethylene butylene styrene (SEBS) and expanded graphite (EG) absorb paraffin (PA) and silicone oil onto a three-dimensional network. The CPCM possesses a high energy storage density (100.8–164.5 J/g) and sufficient volume conductivity (383.76 S·m−1) and can improve the thermal conductivity to 1600 % relative to pure PA. Moreover, it is flexible and possesses shape memory at both room temperature and the phase change temperature (44 ℃). The hardness of the material is 44.5 HA at room temperature and can be reduced to 2.0 HA after phase transition. When heated electrically, it heated threefold faster than when heated by hot air. The material was tested by volunteers and was found to maintain a temperature above 40 °C for more than 30 min. The utilization of this CPCM in thermotherapy is a promising low-cost and environmentally friendly strategy. [ABSTRACT FROM AUTHOR]

Phase-change random access memory has been served as a bridge across the memory wall within the conventional von Neumann computing architecture, owing to its excellent non-volatility and rapid switching. Nitrogen doping in Ge 2 Sb 2 Te 5 -like phase-change materials (PCMs) was a routine method for enhancing non-volatility of amorphous phases, although sacrificing crystallization speed markedly. Here we introduced N element into Sc 0.3 Sb 2 Te 3 PCM that possesses sub-nanosecond crystallization speed, trying to cope with stability/reliability issues raised by backend thermal-budget processing. However, we observed an abnormal deterioration in thermal stability of N-doped amorphous Sc 0.3 Sb 2 Te 3 films. As compared to the undoped counterparts, they exhibit a weakened fragile-to-strong crossover in viscosity that gives rise to a higher atomic mobility at elevated temperatures while a less rigid vitreous network at low temperatures. Therefore, N doping leads to an accelerated crystal growth rate and a higher steady-state nucleation rate in heterogeneous manner, causing a faster crystallization, whereas the kinetic suffocation contributed by original Sc element as approaching room temperature must have been partially counteracted by N dopant. This acceleration in crystallization kinetics delivers N-doped Sc 0.3 Sb 2 Te 3 as a promising candidate in working memory. [Display omitted] [ABSTRACT FROM AUTHOR]

Scanning probe phase-change memory (SPPCM) has been widely considered as one of the most promising candidates for next-generation data storage devices due to its fast switching time, low power consumption, and potential for ultra-high density. Development of a comprehensive model able to accurately describe all the physical processes involved in SPPCM operations is therefore vital to provide researchers with an effective route for device optimization. In this paper, we introduce a pseudo-three-dimensional model to simulate the electrothermal and phase-transition phenomena observed during the SPPCM writing process by simultaneously solving Laplace’s equation to model the electrical process, the classical heat transfer equation, and a rate equation to model phase transitions. The crystalline bit region of a typical probe system and the resulting current-voltage curve obtained from simulations of the writing process showed good agreement with experimental results obtained under an equivalent configuration, demonstrating the validity of the proposed model. [ABSTRACT FROM AUTHOR]

[Display omitted] • Design strategy of phase change material properties are developed for low-energy memory application. • Low operation energy condition is explored automatically through Bayesian optimization. • Operation energy is lowered by decreasing thermal conductivity, ratio of volume resistance to contact resistance and phase change temperature. • According to the developed design strategy, operation energy of typical Ge-Sb-Te can be decreased to less than 1/100 in phase change memory application. Aiming at reducing energy consumptions in data writing, the development of new memory materials is highly required. To develop new phase change materials (PCMs) with extremely low operation energy used in non-volatile memory, such as storage-class memory, we performed Bayesian optimization for the physical properties of PCMs through numerical simulations. In this numerical simulation, the electrical potential and temperature distribution were solved simultaneously. It was found that a PCM with low thermal conductivity, low melting temperature, and low ratio of contact resistance to volumetric resistance results in a low operation energy of a PCM-based memory application. Finally, we developed a design strategy for PCMs. New PCMs should be developed by lowering the operation energy E , described as E = κ (1 + C)Δ T /Δ z , where κ is the thermal conductivity of the PCM, Δ T is the melting temperature, C is the ratio of contact resistance to the volumetric resistance, and Δ z is the thickness of the PCM. The present results clarify the relationship between thermal and electrical properties for lowering operation energy ever hidden in previous studies. According to the design strategy, an operation energy in phase change memory application can be decreased to less than 1/100 compared with conventional Ge-Sb-Te compounds. [ABSTRACT FROM AUTHOR]

Highlights: [•] Phase change behavior of Sb-rich Ga–Sb–Se was studied for phase change memory. [•] Sb-rich Ga–Sb–Se films possess crystallization temperature higher than 225°C. [•] Sb-rich Ga–Sb–Se film has retention ability in excess of 135°C for 10years. [•] Compared with Ge2Sb2Te5, Ga10Sb60Se30 has fast crystallization speed. [ABSTRACT FROM AUTHOR]

Conduction and switching in the phase-change memory (PCM) strongly depend on the transport mechanisms in the disordered amorphous phase. To predict the programming characteristics and the scaling behavior of PCM, accurate models for transport in the amorphous phase considering the local disorder are essential. This paper presents a numerical model to study the subthreshold conduction in the amorphous state of PCM. The nonhomogeneous active material is described through a potential energy landscape, dictating the local barrier for electron hopping. The model shows strong percolation effects in the amorphous cap of the high resistance state, thus accounting for the observed relationship between the electrical and physical thicknesses of the amorphous cap and for the observed thickness dependence of resistance. The model is finally used to describe the programming characteristics with better accuracy in the transition regime from set to reset, which is critical for multilevel cell applications. [ABSTRACT FROM PUBLISHER]

The programming speed in a phase change memory (PCM) relies on the kinetics of crystallization in the pulsed regime. To predict the programming speed and retention of a PCM, a careful understanding and modeling of crystallization in the phase change material is essential. In this paper, we study crystallization kinetics directly in PCM devices. From thermal annealing and pulsed-set experiments, we extract the temperature dependence of the crystallization in a wide temperature range between 170^\circC and the melting point (about 620^\circC). Our results indicate two markedly different activation energies below/above 300^\circC, thus providing evidence for a non-Arrhenius crystallization kinetics in PCM. [ABSTRACT FROM PUBLISHER]

GeSbTe (GST) is a technologically important phase-change material for data storage, where the fast reversible phase transition between crystalline and amorphous states is used for recording information. The encoding is achieved by the large contrast in physical properties between the two states. Ge vacancies (V) and Sb antisite atoms (Sb) are primary point defects in crystalline GST. The effect of V and Sb on the atomic arrangements in amorphous GST is unknown, which, however, has significant effects on the performance of GST. In this work, by means of ab initio molecular dynamics calculations, the atomic arrangements in amorphous ideal and defective GST have been investigated. The results show that the amorphous structure of GST with Sb ( St-GST) or with V ( V-GST) has the same cubic framework and close chemical ordering to ideal GST, and hence similar fast reversible phase transition behavior is expected in the defective phases. Furthermore, the presence of Sb or V in the crystalline phase will result in much more Ge atoms in a tetrahedral geometry as well as in a fourfold octahedral environment in the amorphous state. Especially in V-GST, around 36 % Ge atoms occupy a fourfold octahedral geometry. As fourfold octahedral Ge atoms can enhance the large contrast in physical properties between the crystalline and amorphous phases, introducing Ge vacancies would be an efficient way to improve the performance of GST phase-change materials. [ABSTRACT FROM AUTHOR]

A phase-change (PC) memory model that keeps track of the detailed cooling profile in the RESET process is described in this brief. By physically calculating the final crystal fraction resulting from the thermal dynamic of the PC material during the RESET process, the final resistance of the memory cell can be more accurately determined. The proposed model has been implemented in Verilog-A language and verified by experimental data. [ABSTRACT FROM AUTHOR]

To address the scalability of phase change memory (PCM), we study a 1-D thickness scaling effect on threshold switching voltage (Vth), Vth drift, high resistance state (RESET) resistance (RRESET) drift, and crystallization temperature (Tcrys). We use a pseudo three-terminal device to accurately correlate the amorphous region thickness to the observed characteristics. The pseudo 3-terminal device is a fully functional PCM cell and enables 1-D thickness scaling study down to 6 nm without the need for ultrafine lithography. Vth scales down to 0.65–0.5 V (at 25 ^ \circ\C–75 ^\circ\C) for 6-nm-thick \Ge2\Sb2\Te5 (GST), showing that stable read operation is possible in scaled PCM devices. The Vth drift measurement suggests that Vth drift can be attributed to threshold switching field (Eth) drift, whereas Vth0, i.e., Vth at zero thickness, stays almost constant. RRESET drift shows no dependence on the amorphous GST thickness. Tcrys is \sim\!\175 \ ^\circ\C for the device with 6-nm-thick GST, compared with \sim\!\145 \ ^\circ\C of thick GST. From the 1-D scaling study, no significant hurdles against scaling are found down to 6 nm. Further study of scaling effect on endurance and development of scalable selection device is needed to assess the ultimate scalability of PCM. [ABSTRACT FROM PUBLISHER]

GeSh nanowires (NWs) have been grown using a vapor-liquid-solid approach for the fabrication of electrically operated phase-change random access memory device. The NWs are 40-100 nm in diameter and have approximately 90% Sb for fast crystallization. Memory devices show an on/off resistance ratio of 104, reset programming current of 0.7 mA, and set programming current of 60 nA. [ABSTRACT FROM AUTHOR]

[Display omitted] • GeSb/HfO 2 superlattice-like films were prepared by magnetron sputtering. • The thermal stability of GeSb/HfO 2 is greatly improved. • Under the influence of HfO 2 , the grain size of the film decreases to 3.34 nm. • The density of the film decreased to 4.27% before and after phase transition. • The energy required for RESET operation of Ge 1 Sb 9 /HfO 2 superlattice-like film is low. This paper focused the effect of the recombination of HfO 2 on the phase change behavior and crystalline properties of Ge 1 Sb 9 /HfO 2 superlattice-like phase change films. Compared with pure Ge 1 Sb 9 , the Ge 1 Sb 9 /HfO 2 superlattice-like film has higher crystallization temperature, better data retention ability and larger activation energy, indicating excellent thermal stability. With the increase of HfO 2 thickness ratio, the band gap becomes wider. Atomic force microscopy and X-ray diffraction tests illustrate that HfO 2 composite layers can inhibit the growth of grain, reduce the grain size and have a smoother surface. X-ray reflectivity tests show that Ge 1 Sb 9 /HfO 2 film has a small volume fluctuation during the crystallization process. Raman spectroscopy is used to observe the molecular vibration. Phase change memory devices based on Ge 1 Sb 9 /HfO 2 thin film are fabricated to evaluate its electrical performance. The results reveal that HfO 2 composite layers play a significant role in improving thermal stability, refining grain size and reducing power consumption on Ge 1 Sb 9 phase change film. [ABSTRACT FROM AUTHOR]

In this paper, the phase transition mechanism and device conversion performance of the Sb/GeTe superlattice-like films were studied and showed improved amorphous thermal stability and resistance drift compared to the pure Sb films. Transmission electron microscopy showed that the Sb layer plays a leading role in the crystallization process, forming a large number of Sb grains. The metallic behavior of the Sb/GeTe thin films was confirmed by density functional theory calculations. The thermal conductivity of the crystalline film was found to be higher than that of the amorphous film, and the thermal conductivity of the Sb/GeTe film was lower than that of the other monolayer films. In the Sb/GeTe film, the Sb–Sb and Ge–Te bonds were the main bond structures, and some Sb–Te bonds were formed at the layer interfaces, enhancing the stability of the film. Laser picosecond measurements showed that Sb/GeTe film had a higher crystallization rate than the GeTe film. The phase change memory devices based on the Sb/GeTe thin films were found to have lower operational power consumption and higher transition speed. These results showed that the Sb/GeTe thin film explored in this study was a promising phase change storage thin film with excellent performance. ● The coupling effect of multiple interfaces in Sb/GeTe superlattice films were investigated in detail. ● The redistribution of the atoms after crystallization was observed. ● The energy band structure of the Sb/GeTe superlattice films was obtained by density functional theory calculations. ● The interface coupling improved the phase transition behavior and the phase transition performance. [ABSTRACT FROM AUTHOR]

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. [ABSTRACT FROM AUTHOR]

Phase-change electrical probe memory has recently attained considerable attention owing to its profound potential for next-generation mass and archival storage devices. To encourage more talented researchers to enter this field and thereby advance this technology, this paper first introduces approaches to induce the phase transformation of chalcogenide alloy by probe tip, considered as the root of phase-change electrical probe memory. Subsequently the design rule of an optimized architecture of phase-change electrical probe memory is proposed based on a previously developed electrothermal and phase kinetic model, followed by a summary of the state-of-the-art phase-change electrical probe memory and an outlook for its future prospects. [ABSTRACT FROM AUTHOR]