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Carbon-doped Ge2Sb2Te5 (CGST) is a potential candidate in phase change random access memory (PCRAM) with superb thermal stability and ultrahigh cycle endurance. Direct observation of the microstructure evolution of CGST is desirable to uncover the phase transformation mechanism on the relationship of nucleation/crystalline behaviors of the crystalline phase at elevated temperatures and the pristine amorphous phase at room temperature. Here, we investigate the structural evolution of CGST using combined in situ techniques. Our in situ x-ray diffraction and ellipsometry results demonstrate that CGST exhibits a much higher phase transition temperature than undoped one. Temperature-dependent in situ transmission electron microscopy observations further reveal that carbon doping plays a critical role in tailoring the properties of GST by tuning the stochasticity of nucleation/crystallization, stabilizing amorphous and crystalline GST via isolating and refining the grain size at room temperature and elevated temperature. Our work provides detailed information for understanding the microscopic origin of crystallization kinetics of carbon-doped phase change materials toward high-performance PCRAM. [ABSTRACT FROM AUTHOR]

Ge 2 Sb 2 Te 5 (GST), a phase change material, generally exhibits two-step crystallization (amorphous → fcc → hcp) to store and process data. The present study reports the crystallization behavior and bonding mechanism of Ga-doped GST thin films with thermal annealing. Ga doping results in the formation of Ga–Te bonds and shows no bonding with other host elements (Ge and Sb), which changes the bonding mechanism and leads to one-step crystallization (amorphous → fcc). The optical transmission contrast confirmed the thermal stabilization of the fcc phase with thermal annealing. These findings suggest that Ga doping into GST thin films has thermally stabilized the metastable fcc phase and suppressed the hcp phase, hence posing it as a potential candidate for phase change memory applications with fast processing speed and low power consumption. [ABSTRACT FROM AUTHOR]

The dielectric function evolution and electronic bandgap manipulation by silicon (Si) doping for Sb 2 Te 3 phase change films have been investigated by temperature dependent spectroscopic ellipsometry measurements. During the phase change from amorphous to rhombohedral structures, the significant contrast of electronic band structure for pure Sb 2 Te 3 and Si-doped Sb 2 Te 3 (SST) films as functions of temperature (210–620 K) and Si concentration (0%–12%) has been systematically studied by analyzing the dielectric functions, Tauc gap energy, and partial spectral weight integral. The distinct differences can be mainly attributed to the increment of structure order degree, originated from the change of local bonding arrangement. Based upon the evolutions of Tauc gap energy and partial spectral weight integral with increasing temperature for all four samples, it can be concluded that Si doping can inhibit the crystallization of amorphous films and accelerate the phase change process by serving as nanoscale heaters, which is helpful in improving the thermal stability of amorphous films. The elevated crystallization temperature and phase change rate by Si doping contribute to the dependability and endurance for SST-based phase change memory. The present data provide an important direction on the physical mechanism investigation of Si doping Sb 2 Te 3 by optical techniques. [ABSTRACT FROM AUTHOR]

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]

Material properties of Ga–Sb binary alloy thin films deposited under ultra-high vacuum conditions were studied for analog phase change memory (PCM) applications. Crystallization of this alloy was shown to occur in the temperature range of 180–264 °C, with activation energy >2.5 eV depending on the composition. X-ray diffraction (XRD) studies showed phase separation upon crystallization into two phases, Ga-doped A7 antimony and cubic zinc-blende GaSb. Synchrotron in situ XRD analysis revealed that crystallization into the A7 phase is accompanied by Ga out-diffusion from the grains. X-ray absorption fine structure studies of the local structure of these alloys demonstrated a bond length decrease with a stable coordination number of 4 upon amorphous-to-crystalline phase transformation. Mushroom cell structures built with Ga–Sb alloys on ø110 nm TiN heater show a phase change material resistance switching behavior with resistance ratio >100 under electrical pulse measurements. TEM and Energy Dispersive Spectroscopy (EDS) studies of the Ga–Sb cells after ∼100 switching cycles revealed that partial SET or intermediate resistance states are attained by the variation of the grain size of the material as well as the Ga content in the A7 phase. A mechanism for a reversible composition control is proposed for analog cell performance. These results indicate that Te-free Ga–Sb binary alloys are potential candidates for analog PCM applications. [ABSTRACT FROM AUTHOR]

This work presents the optimization of the crystallization behavior and reliability of Sn15Sb85 thin films by doping Sm element. The phase transition behaviors induced by thermal were investigated by in situ resistance measurement. With the addition of Sm element, Sn15Sb85 film exhibits the superior crystallization temperature (232 °C) and data conservation (172.32 °C for 10 years), larger activation energy of crystallization (4.91 eV) and crystalline resistance (∼103 Ω), which contributes to the increased thermal stability of the amorphous state and decrease in the programming energy. The Sm-doping can broaden the energy band gap from 0.55 to 1.07 eV. The amorphous Sm and Sn compositions could retard grain growth and refine grain size from 21.13 to 11.13 nm, combining with x-ray diffraction and x-ray photoelectron spectroscopy. The surface morphology of Sn15Sb85 film becomes smoother after Sm doping as determined by atomic force microscopy images, resulting in the improved interfacial reliability. Phase change memory devices based on Sm0.095(Sn15Sb85)0.905 films can successfully achieve the complete SET and RESET reversible operation process with high operating speed (200 ns) and low power consumption (1.6 × 10−10 J). The results suggest that doping the proper concentration of Sm element will be an effectual solution to adapt and optimize the crystallization properties of Sn15Sb85 phase change material. [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]

Operation speed, data retention, thickness variation, and resistance drift are main shortages for conventional Ge2Sb2Te5 based phase change memory (PCM). In this Letter, we propose a type of ultrathin amorphous carbon (a-C)/Sb2Te multilayer nanostructures with semiconductor process compatibility, which has high speed and excellent reliability in terms of data retention (131 °C for 10-year), thickness variation (1.52%), and resistance drift (0.0095). The PCM devices based on [a-C (1 nm)/Sb2Te (7 nm)]5 multilayer nanostructures exhibit a fast operation speed of 5 ns. The SET/RESET resistance ratio remains constant over 105 cycles by more than two orders of magnitude. The excellent performance of a-C/Sb2Te multilayer nanostructures makes it a promising storage medium to expand the applications of PCM, such as automotive electronics. [ABSTRACT FROM AUTHOR]

Research works on phase change random access memory (PCRAM) based on Ge–Sb–Te (GST) phase change materials have achieved exciting progress, but the industrialization of PCRAM still faces big challenges, including unsatisfied endurance property or unexpected cell structure failure during fabrication. Here, we investigate the impact of the thermal budget in back-end-of-line (BEOL) process on the microstructure evolution of carbon doped GST (CGST) cells. We demonstrate that the as-deposited amorphous CGST in the confined memory cell will transform to face centered-cubic (FCC) phase with uniform grain size during high temperature up to 400 °C in the BEOL process. However, if there is much more unexpected thermal budget during the BEOL process, the FCC-CGST grains will further grow and transform to highly ⟨0001⟩ oriented single crystalline hexagonal (HEX) GST, together with the formation of voids, leading to the structure failure of the storage cells. By virtue of the advanced spherical aberration corrected transmission electron microscopy (Cs-TEM), we find that there are randomly stacked seven-layered and nine-layered atomic arrangements in single crystalline HEX-GST, corresponding to the chemical stoichiometry of Ge2Sb2Te5 and Ge1Sb2Te4, respectively. Interestingly, twin crystal with the coexistence of vacancy-ordered FCC-GST and HEX-GST on the different twin boundary is observed, indicating that the twin crystals play a critical role in the coalescence and the growth of FCC-GST. This work not only sheds light on the structure failure mechanism of GST cell but also provided additional insight into the formation of HEX-phase in a confined GST memory cell. [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]

Organic‐inorganic hybrid multifunctional materials have received significant attention due to their potential applications in smart devices such as phase‐change memory (PCM), resistive random‐access memory (ReRAM). Yet, devices application requires achieving a balance between fast switching speeds, long‐term stability, and high cycling endurance in materials still facing difficulties. Herein, we report two hybrid phase transition compounds: (CMQ)BiCl5(CMQ=Chloromethyl Quinuclidin‐3‐one) (1) and (FMQ)2SbBr5(FMQ=Fluoromethyl Quinuclidin‐3‐one) (2), both two compounds exhibit high phase transition temperature, dual‐stable behavior in dielectric during reversible phase transition process. Notably, 1 exhibit small dielectric change after multiple dielectric state switching. Furthermore, investigate the influence of halogen substitution (F to Cl) for compound properties, which show an Increasing transition temperature (9 K) and raising structural dimension (0D to 1D). Additionally, using first principles, analyze the electronic structure of 1 and find that it has a 3.4 eV wide bandgap, closing to GaN semiconductor (3.4 eV). This work provides a new insight into developing the next‐generation phase transition compounds and chemical modification enhances material performance. [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]

Models of the amorphous phase of the GeTe compound have been generated by depositing individual atoms on a substrate by molecular dynamics simulations. This material is of interest for applications in phase change memories. The kinetic energy of the atoms impinging on the surface is in the range 1.5–10 eV which is typical of magnetron sputtering growth. The simulations with up to 8000 atoms exploit a machine learning potential devised previously by the group. The structural properties of the films depend very little on the energy of the impinging atoms in the range 1.5–10 eV and they are also very similar to those of amorphous models generated by quenching from the melt, but for a larger fraction of GeGe bonds and Ge atoms in tetrahedral geometries in the films. The crystal nucleation and growth are then simulated at 600 K which is close to the temperature of maximal crystal growth velocity exploited in the memory devices. Despite the structural differences mentioned above, the kinetics of crystallization at 600 K is very similar for the as‐deposited and melt‐quenched amorphous models. [ABSTRACT FROM AUTHOR]

The effects of yttrium dopants on the phase change behavior and microstructure of Sn15Sb85 films have been systematically investigated. The yttrium-doped Sn15Sb85 film has the higher phase transition temperature, ten year data retention ability and crystallization activation energy, which represent a great improvement in thermal stability and data retention. X-ray diffraction, transmission electron microscopy and x-ray photoelectron spectroscopy reveal that the amorphous Sn and Y components restrict the grain growth and decrease the grain size. Raman mode typically associated with Sb is altered when the substance crystallized. Atomic force microscopy results show that the surface morphology of the doped films becomes smoother. T-shaped phase change storage cells based on yttrium-doped Sn15Sb85 films exhibit the lower power consumption. The results demonstrate that the crystallization characteristics of Sn15Sb85 film can be tuned and optimized through the yttrium dopant for the excellent performances of phase change memory. [ABSTRACT FROM AUTHOR]

Balancing operation speed and thermal stability is a big challenge in phase change memory (PCM). In this work, a carbon (C) and chromium (Cr) co-doped Sb2Te strategy has been proposed for achieving high operation speed and high stability in PCM applications. In general, doping with the appropriate Cr element is beneficial to improve thermal stability, but it will sacrifice its operation speed. C-doping can enhance thermal stability and retain its fast phase transition properties due to the carbon elements tend to form agglomerates in the host that ameliorate disorder of the amorphous phase without loss of the phase transition rate. Intriguingly, the as-prepared C1.19Cr0.23Sb2Te material exhibits good data retention (T10-year @ 155.0 °C) and low-volume change rate (1.8%), as well as fast switching speed (4 ns) and good endurance (>1 × 105 cycles). This research indicates that C and Cr co-doping is an effective method to achieve excellent stability of phase-change materials without sacrificing the phase-transition rate of Sb2Te materials. [ABSTRACT FROM AUTHOR]

Ge-rich GeSbTe alloys allowed overcoming temperature limitations of phase-change memory technology. In this paper, we present a thorough investigation of the structural evolution and the crystallization process of these alloys as a function of increasing temperature in annealing. We highlight the progressive rearrangement of the structure toward the demixing of Ge and GeSbTe phases. In particular, we show the stability of Sb–Te units and the development of Ge–Te bonds around these features. We observe the formation of a transient GeSbTe phase, which is driven by crystallization phenomena, leading to a gradual diffusion and expulsion of Ge. Therefore, the system moves toward the complete separation of Ge and Ge2Sb2Te5 stable phases. Furthermore, we investigate the effect of N-doping in Ge-rich GeSbTe, which induces the formation of Ge–N bonds. Such features are demonstrated to be responsible for a delayed structural reorganization to higher temperatures, thus affecting the entire process of crystallization and phase separation in the alloy. [ABSTRACT FROM AUTHOR]

Cu2GeTe3 (CGT) is a promising phase change material for phase change random access memory (PCRAM) applications because of its high thermal stability in the amorphous phase and its capability to undergo rapid phase change. In this paper, the electrical conduction mechanism of a CGT memory device fabricated using W electrodes (W/CGT) was investigated using current–voltage (I–V) measurements and angle resolved hard x-ray photoelectron spectroscopy (AR-HAXPES). The I–V characteristics of the W/CGT memory device were found to display non-linear behavior in the RESET (amorphous) state, while linear behavior was observed in the SET (crystalline) state, indicating that the W/CGT memory device exhibited Schottky conduction in the RESET state, but Ohmic conduction in the SET state. The effective Schottky barrier height was found to increase linearly as the ideality factor decreased to unity with the ideal W/CGT Schottky barrier height in the RESET state estimated to be 0.33 eV, a value in good agreement with the directly measured Schottky barrier height of 0.35 eV between W and amorphous CGT by AR-HAXPES measurements. These results suggest that the interface between the metal electrode and the phase change material plays an important role in PCRAM devices, and its comprehensive understanding is necessary for future application development. [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 considered as a leading candidate for next generation data storage as well as emerging computing device, but the advancement has been hampered by high switching energy due to the melting process and amorphous relaxation induced large resistance drift. Polymorphic crystal-crystal transition without amorphization in metal dichalcogenides (TMDs) could be employed to solve these issues. Yet, the mechanism is still controversy. A melting-free PCM made of two dimensional (2D) MoTe2, which exhibits unipolar resistive switching (RS) and multi-level states with substantially reduced resistance drift via joule heating, is reported in this work. The device is first prepared based on the temperature dependence of Raman spectrum and electrical transport investigations on MoTe2 films. Significantly improved device performances on energy efficiency, switching speed, and memory window are further achieved by electrode size scaling down, indicating the key role of localized heating. Then, device scale transmission electron microscopy images reveal that the resistive switching stems from the transition between semiconducting 2H phase and metallic 1T′ phase. An entropy induced Te vacancies model is proposed to explain the reversible phase change mechanism in the MoTe2 based device. This study paves the way for further development of PCM based on atomically thin 2D TMDs, aiming for high density storage-class memory and high-precision neuromorphic computing. [ABSTRACT FROM AUTHOR]

The effect of yttrium doping on the phase transition properties and crystal structure of Ge1Sb9 thin films was studied. Y-doped Ge1Sb9 thin films have higher crystallization temperature (218 °C) and data retention capacity (141.2 °C for 10 years), revealing that Y doping improves amorphous thermal stability. X-ray diffraction and X-ray photoelectron spectroscopy analysis show that the addition of yttrium could inhibit grain growth and restrict the grain size due to the formation of amorphous Y and Ge components. X-ray reflectivity results show that yttrium doping results in less volume change, which predicts the enhanced performance stability of the device. A T-shaped phase change memory cell based on the Y0.26(Ge1Sb9)0.74 films exhibits a faster operation speed (100 ns) and lower power consumption (2.4 × 10−10 J) than traditional Ge2Sb2Te5 materials. The results reveal that Y-doped Ge1Sb9 is a phase change memory material with good structural properties and device performance. [ABSTRACT FROM AUTHOR]

Innovative nanocomposites consisting of [(GeTe)4 nm/C1 nm]10 multilayers (MLs) deposited by magnetron sputtering are integrated in phase‐change memory (PCM) test devices with a "wall structure." Scanning transmission electron microscopy (STEM) shows that an ML structure, with crystallized GeTe layers, is kept after integration in as‐fabricated devices and also after an additional annealing of the devices at 425 °C. The programming current (RESET current) required to reach the high resistance state of [(GeTe)4 nm/C1 nm]10 ML devices decreases by 45% after annealing at 425 °C. The reduction in RESET current is 55% and the reduction in drift coefficient is about 40% in ML devices annealed at 425 °C compared to similar devices incorporating Ge2Sb2Te5. STEM imaging, coupled with nano‐beam electron diffraction and electron energy loss spectroscopy, of ML devices in the high resistance state shows that the RESET current reduction after annealing is correlated to a reduction of the amorphized volume. [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]

We have fabricated GaSb/Ge2Sb2Te5 (GST) superlattice-like structure thin films for phase change memory by magnetron sputtering method, and investigated their phase transition behavior and electrical properties. The experimental results show that increasing the thickness ratio of the GaSb layer to the GST layer can increase the crystallization temperature and reduce the threshold voltage, which is conducive to improving the thermal stability of the GaSb/GST thin films. By analyzing the differences in morphology, thickness and element distribution during phase transition, it is found that the volume of the GaSb layer decreases with the increase of annealing temperature, while the volume of the GST layer expands gradually. However, the volume change range of GaSb/GST thin films is not obvious. Controlling the volume change of the GaSb/GST thin films during phase transition can prolong the service life of the device. By observing the diffusion of interface elements in GaSb/GST superlattice films during annealing, we have found that the interface mixing of Ge element is the most obvious, and Te element have a clear trend of aggregation to adjacent GaSb layers. [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]

In this study, In48.9Sb15.5Te35.6 (IST) was introduced as a stable interlayer to improve the weak amorphous thermal stability and large resistance drift of Sb films. The results showed that Sb atoms tend to bond with In atoms to form In–Sb bonds at the multilayer interfaces, thus improving the thermal stability of multilayer films. Compared with Sb films, Sb/IST had a higher phase transition temperature (∼196 °C) and crystallization activation energy (∼2.23 eV). The surface scratch test revealed that the adhesion of the Sb/IST multilayer film to the substrate was stronger. The separation of the interfaces reduced the phase transition range and made the density change smaller before and after crystallization (∼3.1%). Grain refinement resulted in a decrease in resistance drift and electrostatic potential on the film surface for the Sb/IST film. A phase change memory device based on the Sb/IST multilayer film successfully realized the reversible operation of SET and RESET. The feasibility of the Sb/IST multilayer films as a kind of phase change material with high stability and low resistance drift was verified. [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 phase transformation properties of C/Sb composite multilayer films based on flexible substrates were studied. After different times of bending, the flexible films can still achieve amorphous to crystalline phase transition, but the crystalline resistance increases to different degrees. When the bending times are less than 15000 times, the deformation makes the grain fine, the surface of the film tends to be flat, the surface electric field effect is weakened, and the resistance drift is reduced. When the bending times are higher than 15000 times, cracks begin to appear in the film, and the cracks' depth and width increase with the bending times. The distribution of C and Sb elements at the crack was analyzed by scanning electronic microscope energy spectrum. The phase change memory device of C/Sb composite multilayer film based on flexible PEEK substrate has been made, and the rapid reversible resistance transition (∼10 ns) in various complex states has been successfully achieved. This research provides a new idea for flexible information storage. • The addition of carbon increases the phase transition temperature and improves the thermal stability of pure antimony. • Complete the phase transition in the case of external bending and internal bending. • After 80,000 bending, the phase transition can still be completed, showing good bending resistance. • The device made of composite material realizes the SET-RESET process at the pulse width of 10ns. [ABSTRACT FROM AUTHOR]

[Display omitted] • [C(3 nm)/Sb 7 Se 3 (3 nm)] 5 Superlattice-like film exhibits high comprehensive performance in phase change memory. • C3/SS3 SLL film has a high crystallization temperature (∼240 ℃) and a ten-year data retention temperature (∼170 ℃). • The PCM based on C3/SS3 SLL film has ultrafast operating speed (∼6 ns) and low power consumption (∼2.18 × 10-11 J). • The addition of carbon nanolayers has formed C-Sb and C-Se bonds, which have been verified by experiments and simulations. The C/Sb 7 Se 3 superlattice-like film was prepared by magnetron sputtering technology, and the effects of carbon nanolayers on the film and device properties were studied. The C/Sb 7 Se 3 superlattice-like films show excellent thermal stability and data retention, especially the [C(3 nm)/Sb 7 Se 3 (3 nm)] 5 film. The analysis of transmission electron microscopy and x-ray diffraction reveal that the high-quality multilayer structure of [C(3 nm)/Sb 7 Se 3 (3 nm)] 5 is maintained. The segmentation of phase change material by amorphous carbon layer reduces the size of crystalline region, thus accelerates the crystallization rate. Element mapping indicates that C atoms and Se atoms in the annealed [C(3 nm)/Sb 7 Se 3 (3 nm)] 5 films show obvious interlayer diffusion. The results of x-ray photoelectron spectroscopy and density functional theory manifest that atomic diffusion results in the formation of strong C-Sb and C-Se bonds in the phase transition layer and C atom prefers to occupying interstitial site in the center of the periodic structural unit of Sb 2 Se 3 phase. Carbon atoms can effectively suppress grain growth and gradually move to the boundary of the grain, refining grain size, thus improving the stability of the amorphous phase. This study indicates that carbon nanolayers play an important role in improving the thermal stability and operation speed, reducing power consumption and resistance drift in Sb 7 Se 3 films. [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]

The crystallization mechanism of In2S3-doped Sb thin films is studied in detail to verify the potential application in phase change memory. Here, we observe directly that two different crystallization behaviors can exist in In–S–Sb thin layers by using aberration-corrected scanning transmission electron microscopy. The difference between Sb53.3(In2S3)46.7 and Sb30.9(In2S3)69.1 materials is induced by phase separation. The crystallization mechanism of the Sb53.3(In2S3)46.7 material is related to the formation of the nanocomposite structure with continuous precipitation of Sb nanocrystals. The crystallization characteristic of the Sb30.9(In2S3)69.1 material originates from the diffusion-driven In–S/In–S–Sb interface formation that acts as a "n–p" heterojunction, thereby resulting in the "depletion layer effect" and decreasing the carrier density to 7.42 × 1020 cm−3 at 280 °C. Sb30.9(In2S3)69.1 shows good bipolar-type resistance switching characteristics as the conventional Ge2Sb2Te5. This work provides clear experimental evidence to deepen the understanding of the crystallization mechanism for indium chalcogenides alloyed with Sb films, contributing to the improved control of the phase change behavior to establish high-performance multi-level nonvolatile memory and neuromorphic synaptic systems. [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]

We measure heterogeneous power dissipation in phase change memory (PCM) films of 11 and 22 nm thin Ge2Sb2Te5 (GST) by scanning Joule expansion microscopy (SJEM), with sub-50nm spatial and ~0.2 K temperature resolution. The heterogeneous Joule and Peltier effects are explained using a finite element analysis (FEA) model with a mixture of hexagonal close-packed and face-centered cubic GST phases. Transfer length method measurements and effective media theory calculations yield the GST resistivity, GST-TiW contact resistivity, and crystal fraction of the GST films at different annealing temperatures. Further comparison of SJEM measurements and FEA modeling also predicts the thermopower of thin GST films. These measurements of nanometer-scale Joule, thermoelectric, and interface effects in PCM films could lead to energy-efficient designs of highly scaled PCM technology. [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]

We demonstrate the potential of using plasma profiling time‐of‐flight mass spectrometry (PP‐TOFMS) to accelerate process developments for phase‐change random access memory (PCRAM) applications, which require advanced materials with composition‐driven properties. We assess the performances of PP‐TOFMS for the chemical depth‐profiling of GeSbTe phase change materials, first after deposition steps to investigate the top surface layer and the incorporation of silicon into the amorphous matrix, then after the thermal annealing step to refine in situ capping strategies, and finally in close loop with etching process steps. Comparison of reference‐free semiquantitative PP‐TOFMS analysis based on ion beam ratio with Rutherford backscattering spectrometry shows remarkable agreement (~10% relative). PP‐TOFMS proves to be a fast screening tool, which allows process monitoring and selection of samples that indeed need more complex analysis. [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]

The single layer Zn 44 Sb 39 Se 17 thin film, being fabricated by Sb 70 Se 30 and Zn using co-sputtering method, exhibits double phase change transition. The double phase change processes are mainly attributed to the crystallization of the Sb and ZnSb phases. The potential operating temperature for ten years of two phase change processes are 64 °C and 179 °C, of which the good stability of the second phase change can be sufficient for the autoelectronic applications. Meanwhile we also discovered the Zn 44 Sb 39 Se 17 thin film presents apparent low power consumption in comparison with Ge 2 Sb 2 Te 5 and other reported Sb-Se based phase change materials. Image, graphical abstract [ABSTRACT FROM AUTHOR]

[Display omitted] • Three resistance states with clear distinction are obtained in indium selenide phase-change thin films. • Amorphous indium selenide thin films crystallize at two different temperatures to form two crystalline phases. • Reversible switch between three resistance states as fast as 60 ns is implemented in In 2 Se 3 -based PCM cells. • Successive crystallization in indium selenide thin films is applicable to multi-level phase-change memory. Increasing the storage density of phase-change memory is a challenging subject towards the universal memory commercialization. Multi-level data storage can be implemented in phase-change memory cells by designing multiple stages of crystallization of phase-change materials, which is favorable to push forward the application of phase-change memory in storage-class memory and the emerging in-memory computing. Here, the structure and properties of In 2 Se 3 phase-change thin films with multi-level phase transitions are investigated. The In 2 Se 3 thin films changes resistance states twice upon heating with high crystallization temperature and good thermal stability. The amorphous In 2 Se 3 thin films undergo partial crystallization of the Se phase followed by crystallization of the γ-In 2 Se 3 phase, with successive stages of crystallization accounting for the three distinct levels of resistivity. The phase-change memory cell based on In 2 Se 3 thin films shows a continuous switching process of high resistance state, intermediate resistance state and low resistance state with low drift coefficient in SET-RESET operations at a speed as fast as 60 ns, and the RESET power is as low as 311 pJ, indicating that the In 2 Se 3 thin films have good performance of three-state storage property and can effectively improve the memory density. [ABSTRACT FROM AUTHOR]

We present thermodynamic crystallization and melting models and calculate phase change velocities in Ge2Sb2Te5 based on kinetic and thermodynamic parameters with a focus on the impacts of grain boundary melting. The calculated phase change velocities are strong functions of grain size, with smaller grains beginning to melt at lower temperatures. Phase change velocities are continuous functions of temperature which determine crystallization and melting rates. Hence, set and reset times as well as power and peak current requirements for switching are strong functions of grain size. Grain boundary amorphization can lead to a sufficient increase in cell resistance for small-grain phase change materials even if the whole active region does not completely amorphize. Isolated grains left in the amorphous regions, the quenched-in nuclei, facilitate templated crystal growth and significantly reduce set times for phase change memory cells. We demonstrate the significance of heterogeneous melting through 2-D electrothermal simulations coupled with a dynamic material phase change model. Our results show reset and set times on the order of ∼1 ns for 30 nm wide confined nanocrystalline (7.5 nm–25 nm radius crystals) phase change memory cells. [ABSTRACT FROM AUTHOR]

We have investigated the effect of thermal annealing on the structure of single and stacked phase change memory films based on SnSe and GaSb. Samples were prepared by pulsed laser deposition and investigated by X-ray absorption spectroscopy (XAS) and X-ray diffraction (XRD) methods. Electrical resistance versus temperature investigations showed crystallisation temperatures of 292°C and 198°C for SnSe and GaSb single films, respectively. Above the transition temperature, GaSb crystallises into a face-centered cubic structure, whereas SnSe has an orthorhombic arrangement. Annealing at three temperatures (160°C, 250°C and 350°C) of the SnSe\GaSb stacked films promotes bond breaking, atom diffusion between the two layers and formation of new phases. At 160°C, GaSb films crystallise partially and no effect is observed on the crystallinity of SnSe films. After 250°C, rhombohedral SnSb emerges in addition to GaSb complete crystallisation. A major, completely new, body-centered orthorhombic unindexed quaternary Ga-Sn-Sb-Se phase formation was observed in the samples annealed at 350°C. The GaSb crystallites are fully dissolved and we have observed the formation of a minor hexagonal SnSe2 phase. The analysis of EXAFS data, measured at Se and Ga K-edges, revealed changes in the local atomic environment as a function of the annealing temperature. A tetrahedral configuration is obtained for the Ga atoms in both as-deposited and annealed samples, whereas Se is mostly bivalent in the amorphous samples and has an octahedral arrangement in crystalline SnSe. Our results show that inter-layer diffusion should always be considered and evaluated when designing memory cells composed of stacked phase change chalcogenide films. [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]