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Crystallization (set) time is a key bottleneck to achieve high-speed programming in phase change memory (PCM). Overcoming this limitation requires a deeper understanding of the solidification processes within nanoscale device configuration. This study explores crystallization dynamics in Ge2Sb2Te5 by measuring the transient resistance and power during the set process in confined PCM cells with nanosecond resolution. The transient resistance probes the phase, while the power can be used to evaluate temperature, thus uncovering details of the phase change dynamics. Our findings reveal a notable trend indicating that solidification from the melt results in faster crystallization compared with annealing the glassy state. Moreover, we observed notable differences in the solidification dynamics during set (crystallization) and reset (amorphization) pulses. Our nanosecond transient measurement methodology proves valuable in revealing crucial aspects of PCM crystallization dynamics, holding the potential to enable higher-speed programming. [ABSTRACT FROM AUTHOR]

Due to the growing demand for miniaturization and energy efficiency in modern electronic devices, there is a renewed interest for optoelectronic memories and sensors based on 2D materials. In particular, the molybdenum ditelluride (MoTe 2) is one of the most promising materials for applications in nonvolatile phase-change memory devices, as its properties can be controlled by visible-light illumination. Among the several ways to synthesize MoTe 2 , the molybdenum oxide tellurization through isothermal close space sublimation (CSS) annealing in gas atmosphere is a simple and low-cost effective method for large-scale production of devices based on this layered material. Therefore, the understanding of the physical properties of MoTe 2 thin films produced by this technique is crucial for future applications. Surprisingly, our results indicate that there is a photoinduced growth of the crystalline phase of tellurium on the 1T ′ -MoTe 2 matrix even when the power density of the laser is low. From Raman spectroscopy investigations, we were able to show that nanometer-sized tellurium crystallites work as seed sites for the photocrystallization of tellurium. By assuming that the overall crystallization process is described by a kinetic approach that is based on the Kolmogorov–Johnson–Mehl–Avrami theory, our results indicate that the process is governed by an anisotropic organization of the tellurium atoms in helical structures during the crystal growth. [ABSTRACT FROM AUTHOR]

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]

Recently, nanostructuration has been proposed to improve the performance of phase change memories. This is the case of superlattices composed of amorphous carbon and crystalline germanium telluride, which we have investigated by molecular dynamics. For this, a modified Stillinger–Weber potential is adapted to reproduce their stiffness contrast/impedance ratio. In order to study the effect of the interface interaction, two sets of parameters are used to model the interfaces with different interactions between the two materials using the properties of the softer material or the average properties between the two creating an adaptation of impedance across the layers. The effects of interface roughness and carbon diffusion at grain boundaries are studied. Using equilibrium molecular dynamics as well as the propagation of wave-packets, we show first that without impedance adaptation, the anisotropy is high, and the roughness has a marked impact on the properties. However, the introduction of impedance adaptation destroys those effects on the thermal conductivity. Finally, we show that the periodic texturing of the interface increases the transmission of in-plane transverse phonons. [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]

In the domain of phase change memories (PCMs), intensive research is conducted to reduce the programming cycle cost. The RESET operation is done by melting the PCM and then quenching the liquid phase to put it back to the amorphous state. In most of the devices, the heating is realized by the Joule effect with a titanium nitride (TiN) component put in contact with the PCM itself. One of the crucial points to improve the efficiency of this technology is to characterize the thermal contact between TiN and PCM. Having a low thermal resistance between the heater and the PCM ensures the heat transfer between the two is as efficient as possible. In this work, the interfacial thermal resistance between Ge-doped G 2 Sb 2 Te 5 (GeGST)/TiN in multilayer systems has been characterized, and the influence of the compressive stress exerted by the TiN layers on the GeGST crystallization has been highlighted. [ABSTRACT FROM AUTHOR]

We mimic bacterial learning and memory abilities in tungsten based two-sided single layers of WSeO, WSeS, WSeSe, and WSeTe, where the thickness of the material represents the growth in time. We aim to create a quantum memristor like system to show learning and memory abilities of bacteria with time while it grows. Its governing equation is derived, and it was found to be similar to the gene regulatory response model of the bacteria. Polarization is calculated from the Berry phase theory to plot its relation with the degauss parameter in time, which leads to bow-tie like memory switches similar to phase-change memories. We attribute this behavior to a specific bacteria, that is, Geobacter metallireducens. Mimicking bacteria's learning and memory abilities will open a way to merge physical intelligence with quantum computing computationally. [ABSTRACT FROM AUTHOR]

Herein, a low RESET current 1T1R mushroom‐cell phase‐change memory (PCM) device that uses fiber‐textured homostructure GeSbTe (GST) grown on highly oriented TiTe2 seed layer is reported. The homostructure device outperformed the industry standard device, that uses doped polycrystalline GST, on most figures of merit. The homostructure devices are also benchmarked against superlattice (SL) PCM devices with 10 periods of 5/5 nm GST/Sb2Te3 grown on the TiTe2 seed layer, and are found to have same low RESET current. It is also observed by transmission electron microscopy that the alternating layers of GST/Sb2Te3 and TiTe2/Sb2Te3 in SL devices are intermixed in the switched region after the devices are cycled with RESET/SET pulses. Additionally, when the SL device is left in the SET state, the intermixed switched region crystallinity is textured and exhibits van der Waals gaps. The SL PCM devices require a precise layered structure that is hard to yield on a full wafer scale. In contrast, fiber‐textured homostructure PCM cells reported here are easily manufacturable, while providing similarly low RESET current and low‐resistance drift, which makes this device suitable for analog artificial intelligence computation. [ABSTRACT FROM AUTHOR]

A single Sb phase demonstrates potential for use in phase change memory devices. However, the rapid crystallization of Sb at room temperature imposes limitations on its practical application. To overcome this issue, Sb is alloyed with Se using a reactive co-sputtering deposition technique, employing both Sb and Sb2Se3 sputter targets. This process results in the formation of Sb-rich Se thin films with varying compositions. Compared to pure Sb, the Sb-rich Se thin films exhibit enhanced thermal stability due to the formation of Sb–Se bonds and reduced resistance drift. In particular, the Sb86.6Se13.4 thin film demonstrates an exceptionally low resistance drift coefficient (0.004), a high crystallization temperature (Tc = 195 °C), a high 10-year data retention temperature (116.3 °C), and a large crystallization activation energy (3.29 eV). Microstructural analysis of the Sb86.6Se13.4 reveals the formation of a trigonal Sb phase with (012) texture at 250 °C, while Sb18Se and Sb2Se3 phases form at 300 °C. Conversely, the Sb98.3Se1.7 thin film shows the formation of the single Sb phase with (001) texture, a Tc of 145 °C, and a low resistance drift coefficient (0.011). Overall, this study demonstrates that the alloying strategy is a viable approach for enhancing thermal stability and reducing resistance drift in Sb-based phase-change materials. [ABSTRACT FROM AUTHOR]

Multi-level phase-change can not only increase the storage density of phase-change memory, but also has important applications in neuromorphic computing. However, its realization is still very challenging. Here, we study the phase-change behaviors of four bilayer films, Sb7Se3(x nm)/Ge50Te50(90 nm), with x = 30, 50, 70, and 100. The expected three-level phase change is not observed at all. Raman and XRD characterizations reveal the occurrence of interlayer coupling between Sb7Se3 and Ge50Te50 layers. De-coupling structure films, Sb7Se3(x nm)/Si(50 nm)/Ge50Te50(90 nm), are proposed and prepared, where the amorphous Si layer serves as de-coupling the interlayer coupling. Three-level phase change is observed in all de-coupling Sb7Se3(x nm)/Si(50 nm)/Ge50Te50(90 nm) films. Our works demonstrate the effect of interlayer coupling on multi-level phase-change, and the de-coupling idea provides a design way for multi-level phase-change materials. [ABSTRACT FROM AUTHOR]

Crystallization determines the programming speed of phase‐change memory devices; while, the nucleation phenomenon of many phase‐change materials (PCMs) is not entirely understood, especially concerning the atomic structures and dynamic behaviors of the subcritical nuclei. This is undoubtedly an insurmountable challenge for scandium antimony telluride (ScxSb2Te3) PCM as its subnanosecond‐crystallization nature impedes the real‐time observation of the transient nucleation process. To solve the puzzle, atomic probe tomography and transmission electron microscopy are employed to circumvent the technical difficulties; for the first time, the atomistic information of the heterogeneous nuclei in ScxSb2Te3 is unveiled, such as enriched Sc ≈ 25 at% in core composition, ≈1.0 nm in geometric size, and ≈1023–1024 m−3 in spatial density. The unique nanoscale chemical inhomogeneity ensures the unusual stabilities and dynamics of the early‐stage nuclei, reinforcing them to survive the melt‐quenching action and greatly suppressing the nucleating randomness, thereby facilitating simultaneous and prompt crystal growth throughout the amorphous phase to achieve ultrafast crystallization. The present study offers a new insight into the nonclassical pathways, which will improve understanding and promote better regulation of the nucleation phenomenon in functional materials. [ABSTRACT FROM AUTHOR]

Phase change memory (PCM) technology is a strong contender for the next‐generation memory in today's data‐centric era. In3SbTe2 (IST) phase change material is recently explored due to its good thermal stability, rapid electrical switching, and significant resistance contrast for multibit storage. However, the main concern in PCM devices is the high‐energy usage during the phase switching process. Herein, a thin oxide (HfO2) layer is inserted between the IST active layer and bottom electrode in PCM device. Such a device exhibits amorphous‐to‐crystalline phase switching (crystallization or SET operation) at a lower voltage of (2.1 ± 0.1) V and 66% reduction in energy consumption compared to the device using only IST active layer. Higher temperature of 688 K is acquired in the device with the oxide layer demonstrating that the Joule heat is effectively confined by the oxide layer assisting the crystallization process in the active layer at a less voltage. Such a device also exhibits a significant resistance contrast of ≈2 orders magnitude, allowing for stable data storage. These results reveal that the switching performance of PCM device using IST phase change material is improved by the oxide layer, which is beneficial for energy‐efficient, nonvolatile data storage applications. [ABSTRACT FROM AUTHOR]

Phase-change memory (PCM) is one of the leading candidates for the next generation nonvolatile memory. As a growth-dominated crystalline material, Sb2Te3 is of rapid crystallization speed while its poor thermal stability limits its application. Doping Ti can significantly enhance its amorphous stability but inevitably slows down its crystallization speed. How to balance the contradiction between thermal stability and operation speed remains challenging. In this work, we proposed a gradient Ti-doped Sb2Te3 phase-change material and device. This gradient doping strategy compensates for the negative effect of Ti doping on the crystallization rate of Sb2Te3 via the template effect of the lower doping concentration layer. Very small lattice mismatch between the Sb2Te3 layers with different Ti doping concentrations is verified by x-ray diffraction characterization. The crystallization temperature of a gradient Ti-doped Sb2Te3 thin film is raised up to 172.6 °C and the same 50 ns operation speed as a pure Sb2Te3 device is achieved in the corresponding PCM device. Furthermore, the gradient distribution of Ti elements and the corresponding progressive crystallization phenomenon are verified by transmission electron microscopy revealing the microscopic origin of rapid crystallization speed. Therefore, with our gradient doping strategy, the amorphous stability is improved without sacrificing the crystallization speed in PCM. [ABSTRACT FROM AUTHOR]

We report the thermal conductivity of amorphous, cubic, and hexagonal Ge2Sb2Te5 using time-domain thermoreflectance from 80 to 500 K. The measured thermal conductivities are 0.20 W m−1 K−1 for amorphous Ge2Sb2Te5, 0.63 W m−1 K−1 for the cubic phase, and 1.45 W m−1 K−1 for the hexagonal phase at room temperature. For amorphous Ge2Sb2Te5, the thermal conductivity increases monotonically with temperature when T < 300 K, showing a typical glass-like temperature dependence, and increases dramatically after heating up to 435 K due to partial crystallization to the cubic phase. For hexagonal Ge2Sb2Te5, electronic contribution to thermal conductivity is significant. The lattice thermal conductivity of the hexagonal phase shows a relatively low value of 0.47 W m−1 K−1 at room temperature and has a temperature dependence of T−1 when T > 100 K, suggesting that phonon–phonon scattering dominates its lattice thermal conductivity. Although cubic Ge2Sb2Te5 has a similar grain size to hexagonal Ge2Sb2Te5, its thermal conductivity shows a glass-like trend like that of the amorphous phase, indicating a high concentration of vacancies that strongly scatter heat-carrying phonons. These thermal transport mechanisms of Ge2Sb2Te5 polymorphs help improve the thermal design of phase change memory devices for more energy-efficient non-volatile memory. [ABSTRACT FROM AUTHOR]

Phase change memory devices are a leading candidate for non-volatile memory arrays, as artificial synapses in neuromorphic circuits, and for in-memory computing. These applications are hampered by a large cycle-to-cycle variation of resistance that is likely associated with the crystallization mechanism of phase change materials. This work presents a direct observation by transmission electron microscopy of the crystallization process during the SET operation of the GeTe 100 nm mushroom cell. The process proceeded purely by growth from the periphery of the amorphous dome without nucleation. It is invariably associated with partial melting of the GeTe layer. The growth-dominated SET operation can completely crystallize the GeTe functional layer only by a gradual sweep down of the voltage across the device. The experimental results were correlated with a finite element model of heat and charge flow and the crystallization dynamics. [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]

Nitrogen doping in chalcogenide materials represents a promising way for the improvement of material properties. Indeed, N doping in GeSbTe phase-change alloys have demonstrated to greatly enhance thermal stability of their amorphous phase, necessary to ensure the data retention of the final phase-change memory device. Although it is suggested that the N doping in such alloys leads to the preferential formation of Ge-N bonds, further questions concerning the bonding, in particular, Sb-N and Te-N, and the structural arrangement remain unclear. In this paper, we present a study of as-deposited elemental Ge, Sb, and Te systems and their nitrides (i.e., GeN, SbN, and TeN alloys), using a large range of N content from 0 up to about 50 at. %. The as-deposited alloys are investigated by Fourier transform infrared and Raman spectroscopy. We identify the active vibrational modes associated with the formation of Ge-N, Sb-N, and Te-N bonds, highlighting the impact of N incorporation on the structure of these elemental systems. We further qualitatively compare the GeN, SbN, and TeN experimental spectra with the "ab initio" simulations of the related ideal nitride structures. Finally, the analysis of elemental nitride layers is extended to N-doped GeSbTe alloys, providing deeper understanding of nitrogen bonding in such ternary systems, employed in memory technology. [ABSTRACT FROM AUTHOR]

The increased demand of high‐performance computing systems has exposed the inherent limitations of the current state‐of‐the‐art von Neumann architecture. Therefore, developing alternate computing primitives that can offer faster computing speed with low energy expenditure is critical. In this context, while several non‐volatile memory (NVM) devices such as synaptic transistors, spintronic devices, phase change memory (PCM), and memristors have been demonstrated in the past, their two‐terminal nature necessitates additional peripheral elements that increase area and energy overhead. Recently, a new multiterminal device prototype known as a memtransistor has shown tremendous potential to overcome these limitations through exceptional control of the gate electrostatics as enabled by 2D channel materials. In this perspective, a brief overview of recent developments in 2D‐memtransistor devices is provided, including their fundamental operational mechanisms and the role of defects in enabling multiple NVM states and optical photoresponse. An overview of their implementation in the context of neuromorphic, probabilistic, information security, and edge‐sensing primitives is also provided. Finally, a futuristic perspective is provided looking toward their successful large‐scale technological integration. [ABSTRACT FROM AUTHOR]

Neural architecture search (NAS), as a subfield of automated machine learning, can design neural network models with better performance than manual design. However, the energy and time consumptions of conventional software‐based NAS are huge, hindering its development and applications. Herein, 4 Mb phase change memory (PCM) chips are first fabricated that enable two key in‐memory computing operations—in‐memory multiply‐accumulate (MAC) and in‐memory rank for efficient NAS. The impacts of the coating layer material are systematically analyzed for the blade‐type heating electrode on the device uniformity and in turn NAS performance. The random weights in the searched network architecture can be fine‐tuned in the last stage. With 512 × 512 arrays based on 40 nm CMOS process, the PCM‐based NAS has achieved 25–53× smaller model size and better performance than manually designed networks and improved the energy and time efficiency by 4779× and 123×, respectively, compared with NAS running on graphic processing unit (GPU). This work can expand the hardware accelerated in‐memory operators, and significantly extend the applications of in‐memory computing enabled by nonvolatile memory in advanced machine learning tasks. [ABSTRACT FROM AUTHOR]

Recently, phase change chalcogenides, such as monochalcogenides, are reported as switching materials for conduction‐bridge‐based memristors. However, the switching mechanism focused on the formation and rupture of an Ag filament during the SET and RESET, neglecting the contributions of the phase change phenomenon and the distribution and re‐distribution of germanium vacancies defects. The different thicknesses of germanium telluride (GeTe)‐based Ag/GeTe/Pt devices are investigated and the effectiveness of phase loops and defect loops future application in neuromorphic computing are explored. GeTe‐based devices with thicknesses of 70, 100, and 200 nm, are fabricated and their electrical characteristics are investigated. Highly reproducible phase change and defect‐based characteristics for a 100 nm‐thick GeTe device are obtained. However, 70 and 200 nm‐thick devices are unfavorable for the reliable memory characteristics. Upon further analysis of the Ag/GeTe/Pt device with 100 nm of GeTe, it is discovered that a state‐of‐the‐art dependency of phase loops and defect loops exists on the starting and stopping voltage sweeps applied on the top Ag electrode. These findings allow for a deeper understanding of the switching mechanism of monochalcogenide‐based conduction‐bridge memristors. [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]

Thermal processes play a crucial role in a variety of applications ranging from thermoelectrics, to thermal barrier coatings for turbines to memory devices, where materials with low thermal conductivity κ are essential for energy savings. By comparing two phase‐change materials, Ge2Sb2Te5$\left(\text{Ge}\right)_{2} \left(\text{Sb}\right)_{2} \left(\text{Te}\right)_{5}$ and Ga2Te3$\left(\text{Ga}\right)_{2} \left(\text{Te}\right)_{3}$, that have very similar thermal conductivities despite very different structures and bond strengths, it is argued that their phonon‐glass electron‐crystal properties stem from randomly oriented nonbonding lone–pair orbitals subtended at chalcogen atoms surrounding intrinsic vacancies. [ABSTRACT FROM AUTHOR]

Amorphous materials specifically chalcogenide glasses (Se, Te, and Sb alloys) are promising materials for fabrication of different solid-state devices and their characteristics can further be improved by doping with rare-earth element. Current study deals with phase transformation, thermal stability, and crystallization kinetics of Er-doped quaternary chalcogenide system which were synthesized using melt quenching technique. In this study, Ge17Sb8Se75−xErx (x = 0, 0.4, 0.8, and 1.0) alloy has been examined from differential scanning calorimetry data wherein the stability and kinetics is studied at variable heating rates. As a standard procedure, non-isothermal conditions were used throughout the kinetic and crystallization studies for understanding the variation in glass transition temperature, melting temperature, thermal stability factor, activation energy of glass transition, and crystallization wherein besides the role of chalcogen element, the doping concentration of rare-earth Er is also understood. Furthermore, devitrification resistance was also analyzed based on activation energy for crystallization. The synthesized Er-doped GeSbSe system shows an increase in transition temperature, melting temperature, thermal stability, and glass-forming ability when the concentration of Er and heating rate increases as compared to the pure alloy. Furthermore, decrease in the activation energy has been observed for Er-doped quaternary chalcogenide system. These observations indicate the potential of Er-GeSbSe chalcogenide glass as phase change memory material and other applications which needs high thermal stability. [ABSTRACT FROM AUTHOR]

The crystallization rate is an important factor for the application of phase change materials as memory devices, which, thus, motivates a strong interest in the underlying crystallization processes. We analyzed the crystallization kinetics of as-deposited amorphous Ge2Sb2Te5 by differential scanning calorimetry, revealing that the thermal treatment below the crystallization onset temperature effectively enhances the crystallization rate compared to the as-deposited samples. Variable resolution fluctuation electron microscopy was carried out to characterize the corresponding amorphous structure of the as-deposited films and the differently annealed states regarding their medium-range order (MRO). As a result, relatively large MRO correlation lengths in the range of 3–4 nm were observed, whereas the MRO volume fraction doubled after longer annealing treatments, demonstrating the importance of MRO and MRO tuning for optimizing the properties of amorphous phase change materials. The increased volume fraction of the MRO seems to also favor an increased nanoindentation hardness. [ABSTRACT FROM AUTHOR]

Though phase-change materials (PCMs) are regarded as constituent part of next-generation phase-change memory and other unfolding optoelectronic applications, the kinetics study of glass transition and crystallization, significant property in switching remains obscure in high-temperature region. Hence, this paper reports the investigation of glass transition and crystallization kinetics of Te (1-x) (GeSe 0.5)Y x (TGSY) chalcogenide glass using differential scanning calorimetry (DSC) at heating rates 5, 10, 15, 20 °C/min. The effect of increasing Y quantity has been described by connecting structural relaxation kinematics during glass transition phenomena and devitrification while crystallization in chalcogenide glasses with their varied physicochemical characteristics. The inclusion of Y causes a discernible rise in the crystallization rate. The system is compatible with a strong glass-forming liquid, according to the Te (1-x) (GeSe 0.5) Y x material fragility index. According to the average values of the kinetic exponent factors, there is heterogeneous nucleation for the investigated composition, which is subsequently followed by a two- or three-dimensional crystal growth phenomenon. Different glass stability criteria have been discussed based on the relationship between the characteristic temperatures. The C ZW and C LX criteria were found to be inappropriate for discussing glass stability (GS) for the studied compositions based on the heating rate and composition dependencies of all criteria. The C YL criteria of Yuan et al. is the finest and it demonstrates the optimal ability for evaluating the GS, according to the data that was extracted from several GS criteria and their relative change parameters. By adding Y, thermal stability parameter and enthalpy emitted during the transition of glass and crystalline phases have been found to have an inverse relationship. All studied properties can conclude the application of studied material in phase-change material devices. [ABSTRACT FROM AUTHOR]

Superlattices made of alternating blocks of the phase change compound Sb 2 Te 3 and of TiTe 2 confining layers have been recently proposed for applications in neuromorphic devices. The Sb 2 Te 3 /TiTe 2 heterostructure allows for a better control of multiple intermediate resistance states and for a lower drift with time of the electrical resistance of the amorphous phase. However, Sb 2 Te 3 suffers from a low data retention due to a low crystallization temperature T x . Substituting Sb 2 Te 3 with a phase change compound with a higher T x , such as GeTe, seems an interesting option in this respect. Nanoconfinement might, however, alters the crystallization kinetics with respect to the bulk. In this work, we investigated the crystallization process of GeTe nanoconfined in geometries mimicking GeTe/TiTe 2 superlattices by means of molecular dynamics simulations with a machine learning potential. The simulations reveal that nanoconfinement induces a mild reduction in the crystal growth velocities which would not hinder the application of GeTe/TiTe 2 heterostructures in neuromorphic devices with superior data retention. [ABSTRACT FROM AUTHOR]

The scandium doped antimony tellurides (ScxSb2Te3), as promising phase-change memory materials, possess the merits of ultrafast crystallization speed and ultralow resistance drift, of the amorphous phases, ensuring the development of cache-type universal memory and high-accuracy computing chip. There is keenness to further explore the annealing effect in the crystalline ScxSb2Te3 phases to seek a potential metal–insulator transition (MIT) in electrical conduction, by which more intermediate resistance states of superior stability can be generated to enhance the programming contrast and accuracy. In this work, we have identified the metastable rock salt ScxSb2Te3 as an Anderson-type insulator and verified that the MIT occurs in its stable rhombohedral grains when lattice vacancies are highly ordered into the van der Waals-like gaps. The Sc dopant can exert profound influence on retarding the vacancy-ordering procedure, even completely prohibiting the MIT for the Sc-rich compounds. Our work suggests that tuning Sc content in ScxSb2Te3 alloys provides a simple route to engineer the material microstructures and electrical properties for the desired memory and computing performances. [ABSTRACT FROM AUTHOR]

Though phase-change materials (PCMs) are regarded as constituent part of next-generation phase-change memory and other unfolding optoelectronic applications, the kinetics study of glass transition and crystallization, significant property in switching remains obscure in high-temperature region. Hence, this paper reports the investigation of glass transition and crystallization kinetics of Te (1-x) (GeSe 0.5)Y x (TGSY) chalcogenide glass using differential scanning calorimetry (DSC) at heating rates 5, 10, 15, 20 °C/min. The effect of increasing Y quantity has been described by connecting structural relaxation kinematics during glass transition phenomena and devitrification while crystallization in chalcogenide glasses with their varied physicochemical characteristics. The inclusion of Y causes a discernible rise in the crystallization rate. The system is compatible with a strong glass-forming liquid, according to the Te (1-x) (GeSe 0.5) Y x material fragility index. According to the average values of the kinetic exponent factors, there is heterogeneous nucleation for the investigated composition, which is subsequently followed by a two- or three-dimensional crystal growth phenomenon. Different glass stability criteria have been discussed based on the relationship between the characteristic temperatures. The C ZW and C LX criteria were found to be inappropriate for discussing glass stability (GS) for the studied compositions based on the heating rate and composition dependencies of all criteria. The C YL criteria of Yuan et al. is the finest and it demonstrates the optimal ability for evaluating the GS, according to the data that was extracted from several GS criteria and their relative change parameters. By adding Y, thermal stability parameter and enthalpy emitted during the transition of glass and crystalline phases have been found to have an inverse relationship. All studied properties can conclude the application of studied material in phase-change material devices. [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]

The crystalline–amorphous–crystalline transition process of an oxygen-tuned Sb phase-change material has been obtained by employing ab initio molecular dynamic calculations. By analyzing the local atomic arrangement and the electron structure of the SbO system, the intrinsic mechanism is explored to comprehend the material function: (1) ultrafast crystallization and difficulty in creating a glassy state of a pure Sb material might be caused by the resonance bonding of linear arrangement Sb atoms in the rhombohedral phase; (2) the impurity oxygen atoms break the medium and long-range linear arrangement of the Sb network by steric effects and change the electronic structure of these Sb atoms bonded to oxygen atoms, i.e., the obvious increase in electron localization and the great decrease in state distribution around the Fermi surface due to the high electronegativity of oxygen. These factors set an effective barrier for crystallization and improve the amorphous stability and, thus, data retention. The present research and scheme provide important insights into the engineering and manipulation of a phase-change material through first-principles calculations toward non-volatile phase change memory. [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]

We investigated the microstructure and texture of completely crystalline Ge–Cu–Te thin films, focusing on the grain orientation, grain boundary character distribution and morphology, and their correlation with electrical and optical behaviors, as phase-change materials for application in phase change memory (PCM). In this study, the preferred {111} orientation was observed in thin films annealed at 300 °C, which is favorable for improving carrier mobility. As the annealing temperature increases to 400 °C, the grain orientation evolves into a random distribution, which is beneficial for improving optical reflectivity. The corresponding orientation evolution mechanism involves the effects of work function, surface energy, and different stress states during annealing. In addition, a high fraction of high angle grain boundaries mixed with a fraction of 60°〈111〉 and 30°〈110〉 grain boundaries is prevalent in the crystalline thin films, which is related to the great thermal stress and orientation randomization in the crystalline thin films. For completely crystallized thin films, the cross-section grain growth, accompanying numerous stacking faults and dislocations, has already spanned the entire thin films thickness direction. This work shows that the grain orientation of phase change materials can be highly impacted by thermal circumstances, which is expected to shed light on the phase-change thin film growth. [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]

Phase-change materials (PCMs), which can transition reversibly between crystalline and amorphous phases, have shown great promise for next-generation memory devices due to their nonvolatility, rapid switching periods, and random-access capability. Several groups have investigated phase-change nanowires for memory applications in recent years. The ability to regulate the scale of nanostructures remains one of the most significant obstacles in nanoscience. Herein, we describe the growth and characterization of germanium telluride (GeTe) nanowires, which are essential for phase-change memory devices. GeTe nanowires were produced by combining thermal evaporation and vapor–liquid–solid (VLS) techniques, using 8 nm Au nanoparticles as the metal catalyst. The influence of various growth parameters, including inert gas flow rate, working pressure, growth temperature, growth duration, and growth substrate, was examined. Ar gas flow rate of 30 sccm and working pressure of 75 Torr produced the narrowest GeTe nanowires horizontally grown on a Si substrate. Using scanning electron microscopy, the dimensions, and morphology of GeTe nanowires were analyzed. Transmission electron microscopy and energy-dispersive x-ray spectroscopy were utilized to conduct structural and chemical analyses. Using a SiO2/Si substrate produced GeTe nanowires that were thicker and lengthier. The current–voltage characteristics of GeTe nanowires were investigated, confirming the amorphous nature of GeTe nanowires using conductive atomic force microscopy. In addition, the effects of the VLS mechanism and the Gibbs–Thomson effect were analyzed, which enables the optimization of nanowires for numerous applications, such as memory and reservoir computing. [ABSTRACT FROM AUTHOR]

In this paper, the Sm-doped Ge10Sb90 films were proposed and the effect of Sm doping on the crystal structure and electrical properties were investigated. The crystallization process of materials with different Sm concentrations was carried out by an in situ resistance measurement system, demonstrating that doping Sm can significantly improve the amorphous resistance, thermal stability, and bandgap of Ge10Sb90 film and alleviate the structural relaxation. X-ray diffraction, x-ray photoelectron spectroscopy, and transmission electron microscopy show that the appropriate content of Sm doping can hinder the grain growth process, limiting the grain size to a certain extent. The phase change memory devices with Sm-doped Ge10Sb90 were prepared based on the CMOS process, and their electrical properties were evaluated. The outcomes indicate that Sm doping can remarkably ameliorate the high RESET current required for Sb-rich Ge10Sb90 films during erasing/writing operation. [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]

The effect of graphite carbon nanolayers on the phase change performance and microstructure of Zn15Sb85 film was systematically studied. After the addition of graphite carbon nanolayers, superlattice-like films exhibit better thermal stability and data retention, especially [C(4 nm)/Zn15Sb85(10 nm)]5 superlattice-like film. The phase change memory based on [C(4 nm)/Zn15Sb85(10 nm)]5 has fast operating speed and ultralow power consumption. During the aging process, the electronic structure of [C(4 nm)/Zn15Sb85(10 nm)]5 superlattice-like film remains almost unchanged. The results of x-ray diffraction and transmission electron microscopy indicate that the addition of graphite carbon nanolayers reduces the grain size. The formation of new C–Sb and C–Zn bonds was speculated through energy dispersion spectroscopy and x-ray photoelectron spectroscopy. The results indicate that graphite carbon nanolayers play an important role in improving the thermal stability, operating speed, reducing power consumption, and resistance drift of Zn15Sb85 films. [ABSTRACT FROM AUTHOR]

Non-volatile memory, which can simultaneously store data and compute in memory, is a promising candidate to break through "memory bottleneck". However, its operation speed and thermal stability are still contradictory and difficult to meet the requirement of in-memory computing especially in high-temperature applications. In this work, optoelectronic hybrid phase-change memory based on Cr doped Ge 2 Sb 2 Te 5 material is proposed, where the picosecond laser is used to perform the information recording/erasing operation based on the reversible phase-change characteristics while resistance signal is detected to realize the information readout. Results imply that the Cr doped Ge 2 Sb 2 Te 5 film with Cr concentration of 10.7 at. % has high crystallization temperature (289 °C) and ten-year data-retention temperature (221 °C), low density-change rate (2.3%) and small resistance drift coefficients (0.022 at 85 °C, 0.056 at 120 °C, 0.070 at 150 °C, and 0.00131 for the laser induced SET state). The corresponding memory device has the SET/RESET operation speeds of as fast as 1820 ps/13 ps accompanied by the RESET/SET resistance ratio of higher than two orders of magnitude. The structural analyses indicate that Cr doping can suppress the growth of grains and reduce the grain size, improving the thermal stability of amorphous Ge 2 Sb 2 Te 5 thin film while the octahedral/defective octahedral motif ensures its fast phase-change speed. Therefore, Cr doped Ge 2 Sb 2 Te 5 based optoelectronic hybrid phase-change memory with superior thermal stability and ultrafast operation speed may be one of the promising solutions for in-memory computing. [ABSTRACT FROM AUTHOR]

Phase change memories (PCRAM) are often made of chalcogenide alloys in the form of multilayer systems (MLS). The mostly used alloys are Ge2Sb2Te5 and Ge‐rich Ge2Sb2Te5. The current article reports on the thermal characterization of very thin (<5 nm) Ge‐rich Ge2Sb2Te5/Ge2Sb2Te5 MLS by modulated photothermal radiometry (MPTR). The MPTR method allows for the investigation of such samples by determining, with an inverse method, the total thermal resistance of the stack deposited on the substrate. With the measurement of the total thermal resistance, it is possible to determine the thermal conductivity of the deposit and the interfacial thermal resistances between layers. The interfacial thermal resistance between Ge‐rich Ge2Sb2Te5/Ge2Sb2Te5 is characterized, which is an important parameter to reduce the energy cost of the PCRAM functioning. It is also possible to highlight a decrease in interface quality inside the MLS after the beginning of the phase transition around 250 °C. [ABSTRACT FROM AUTHOR]

The doping with Cu in the Sb-Se material system can effectively reduce power consumption and improve data retention ability of the PCRAM (Phase-Change Random-Access Memory) material. However, no thermodynamic study of the Cu-Sb-Se system has been reported. Therefore, in this work the Cu-Sb-Se system was modeled using the CALPHAD (CALculation of PHAse Diagrams) method. The excess Gibbs energies of solution phases, including liquid and FCC were expressed by the Redlich-Kister polynomial. Two-sublattice model (Cu,Se)2Se was used to describe the solid solution of binary intermetallic compounds, i.e. α-Cu2Se and β-Cu2Se in Cu-Sb-Se ternary system. The compounds, e.g. η(Cu2Sb), β(Cu3Sb), Sb2Se3, α-CuSe, β-CuSe, Pe(Cu3SbSe4) and C(CuSb3Se5) were described as stoichiometric compounds. The temperature of the eutectic reaction γ(Cu17Sb3) = (Cu) + δ(Cu4Sb) in the Cu-Sb system and the temperature of the invariant reaction L1 = L2 + (Sb) in the Sb-Se system were adjusted. A set of self-consistent thermodynamic parameters for the Cu-Sb-Se system was obtained, and the 623, 673, 723, 773, 873 and 973 K isothermal sections, and the liquidus projection and invariant reactions for this ternary system have been calculated. [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]

The concept of metric dimension has many applications, including optimizing sensor placement in networks and identifying influential persons in social networks, which aids in effective resource allocation and focused interventions; finding the source of a spread in an arrangement; canonically labeling graphs; and inserting typical information in low-dimensional Euclidean spaces. In a graph G, the set S⊆V(G) of minimum vertices from which all other verticescan be uniquely determined by the distances to the vertices in S is called the resolving set. The cardinality of the resolving set is called the metric dimension. The set S is called fault-tolerant resolving set if S\{v} is still a resolving set of G. The minimum cardinality of such a set S is called fault-tolerant metric dimension of G. GeSbTe super lattice is the latest chemical compound to have electronic material that is capable of non-volatile storing phase change memories with minimum energy usage. In this work, we calculate the resolving set (fault tolerant resolving set) to find the metric dimension(fault-tolerant metric dimension) for the molecular structure of the GeSbTe lattice. The results may be useful in comparing network structure and categorizing the structure of the GeSbTe lattice. [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]

Combination of nonvolatile storage and in-memory computing promises to break through the "memory bottleneck" that computing device adopts von Neumann architecture with individual computing and memory unit. Thus, the advanced nonvolatile memory device with ultrafast operation speed is urgently required. Here, the optoelectronic hybrid phase-change memory based on the Ge2Sb2Te5 material is proposed, where the picosecond laser induced reversible phase-change is utilized to write and erase the information while the resistance difference is adopted to realize the accurate information readout. Due to the significant difference in resistance between crystalline and amorphous states, a partial crystallization strategy can be adopted to achieve ultrafast SET operation. Results indicate that SET operation speed of the Ge2Sb2Te5 film and device unit can be as fast as 52 and 130 ps, respectively, while the RESET speed reaches 13 ps. In parallel, the resistance ratio of RESET to SET state is still as high as two orders of magnitude. By using partial crystallization strategy, the phase-change induced by picosecond laser only occurs from amorphous to face-centered-cubic crystalline state with low crystallinity and the defective octahedral motif is observed in the Ge2Sb2Te5 film, which is beneficial to achieve the ultrafast operation speed. At the same time, the ordered clusters existed in the as-deposited and picosecond laser induced RESET films can accelerate the nucleation process of the Ge2Sb2Te5 film, which is one of the important reasons for achieving ultrafast SET speed. The optoelectronic hybrid phase-change memory with ultrafast operation speed may be one of the promising solutions for the in-memory computing. [ABSTRACT FROM AUTHOR]

In the present work, Te(1−x)(GeSe0.5)Scx were synthesized via a melt-quenching technique and characterized by means of X-ray diffractometry, scanning electron microscopy, and energy-dispersive X-ray spectroscopy for structural, morphological, and elemental analysis, respectively. The dielectric parameters and electrical conductivity were determined to determine the applicability of the synthesized material for use in electronic applications. Temperature and frequency dependence of the dielectric constant, ac conductivity, and dielectric loss of the Te(1−x)(GeSe0.5)Scx (0 ≤ x ≤ 0.15) (x = 0, 0.05, 0.1, 0.15) chalcogenide alloy were explored in the frequency range of 1 Hz–1 MHz and below the glass transition temperature (Tg) in a temperature range of 302–422 K. It was observed that there was a decrease in both the dielectric loss and constant with an increase in frequency and decrease in temperature. Investigation of the dielectric loss was based on Guintini's model of dielectric dispersion, which is based on the correlated barrier hopping (CBH) model and explained by orientational polarization. A Cole–Cole plot was utilized for determination of some factors, such as distribution parameter, activation energy and molecular relaxation time. The AC conductivity was found to follow the power law (Aωs) and the frequency exponent s ≤ 1 was noted to reduce with an increase in temperature, which concluded that the CBH model is appropriate for defining the AC conductivity of the prepared samples. The incorporation of Sc tended to increase the localized states density in the tails and, accordingly, there was an increase in the ac conductivity. Hence, the studied material is a promising candidate for phase-change memory applications. [ABSTRACT FROM AUTHOR]

Reversible switching of room‐temperature electrical resistivity due to crystal‐amorphous transition is demonstrated in various chalcogenides for development of non‐volatile phase change memory. However, such reversible thermal switching of room‐temperature electrical resistivity has not reported in transition metal oxides so far, despite their enormous studies on the electrical conduction like metal‐insulator transition and colossal magnetoresistance effect. In this study, a thermally reversible switching of room‐temperature electrical resistivity is reported with gigantic variation in a layered nickelate Sr2.5Bi0.5NiO5 (1201‐SBNO) composed of (Sr1.5Bi0.5)O2 rock‐salt and SrNiO3 perovskite layers via unique crystalline phase changes between the conducting 1201‐SBNO with ordered (O‐1201), disordered Sr/Bi arrangements in the (Sr1.5Bi0.5)O2 layer (D‐1201), and insulating oxygen‐deficient double perovskite Sr2BiNiO4.5 (d‐perovskite). The O‐1201 is reentrant by high‐temperature annealing of ≈1000 °C through crystalline phase change into the D‐1201 and d‐perovskite, resulting in the thermally reversible switching of room‐temperature electrical resistivity with 102‐ and 109‐fold variation, respectively. The 1201‐SBNO is the first oxide to show the thermally reversible switching of room‐temperature electrical resistivity via the crystalline phase changes, providing a new perspective on the electrical conduction for transition metal oxides. [ABSTRACT FROM AUTHOR]

Phase change memory (PCM) and ovonic threshold switching (OTS) materials using chalcogenide glass are essential elements in advanced 3D memory chips. The mid‐gap states, induced by the disorder and defects in the glass, are the physical mechanisms of the electrical switching behavior, while the origin of these trap states is still under debate and the medium‐range clusters that break the global octet rule, such as over‐coordinated atoms, are known to be responsible in various glass. Here, it is discovered that a large fraction of over‐coordinated clusters fails to generate mid‐gap states, which are probably caused by hypervalent bonding, a multi‐centered covalent bond participated by delocalized lone‐pair electrons. This is confirmed by the pressure‐driven simulations of amorphous GeSe models, in which it is found that octahedral motifs and hypervalent bonds prevent the over‐coordinated medium‐range clusters from providing excessive electrons. In practical applications, compatible dopants can be used to change the number of hypervalent bonds, thus controlling the number of mid‐gap states and consequently the performance of PCM and OTS materials. These results reveal the origin of mid‐gap states in chalcogenide glasses, enabling extensive control in the development of pioneering electrical switching materials. [ABSTRACT FROM AUTHOR]

This work systematically investigates the improvement in phase change properties and crystallization mechanism of Sb films after Y doping. Compared with the pure Sb thin films, Sb51Y49 has a higher crystallizing temperature (203 ℃) and longer failure time (766 s), indicating that Y doping can enhance the thermal stability of the material in the amorphous state effectively. Y exists in an amorphous state and has an inhibitory effect on grain growth, resulting in smaller grain sizes in Y-doped Sb films. The crystallization mechanism was investigated using the Johnson–Mehl–Avrami model, and the crystallization mechanism of the Sb films before and after Y-doping is unchanged and always dominated by growth, a property that is favorable for achieving fast phase transitions. The phase change cells based on Sb51Y49 films exhibit a lower energy consumption (3.5 × 10–11 J) than the conventional Ge2Sb2Te5 material. The findings demonstrate the potential of Y-doped Sb as a phase change material with excellent crystallization rate and energy consumption performance. [ABSTRACT FROM AUTHOR]

Memristive devices, which are materials systems with two or three electrodes separated by an insulating or semiconducting material, are becoming increasingly important in various applications. They are already being used as non-volatile electronic memory and are expected to have a market size of up to 5.6 billion USD by 2026. Recent research has shown that memristors have potential for applications in brain-inspired neuromorphic engineering, cryptography, and 5G/6G telecommunications. The versatility of memristors lies in the materials used, as different materials have different electrical characteristics and figures-of-merit. Intense research is necessary to optimize the properties of memristors and discover new functionalities, such as mechanical, optical, and thermal properties. This special issue of Advanced Functional Materials contains 20 articles written by leading scientists in the field, covering various aspects of materials for memristors and proposing innovative applications. The articles discuss the use of different materials, including 2D materials like MoS2, hexagonal boron nitride (hBN), and graphene oxide, as well as materials with dipoles like ferroelectric and piezoelectric materials, nanowire electronics, and phase change memory and organic memory. [Extracted from the article]

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]