Sinomenine regulates circTRPM7-related pathway to inhibit gastric cancer cell growth and metastasis.

Sinomenine has been found to have antitumor effects in a variety of cancers, including gastric cancer. Circular RNA (circRNA) is an important regulator of gastric cancer progression. However, it is not known whether Sinomenine mediates gastric cancer processes by regulating circRNA-related pathways. Quantitative real-time PCR was used to measure the expression of circTRPM7, microRNA-145-5p (miR-145-5p), and pre-B-cell leukemia homeobox 3 (PBX3). MTT assay, colony formation assay, EdU assay, transwell assay, wound-healing assay, and flow cytometry were used to detect cell proliferation, migration, invasion, and apoptosis. The expression of related proteins was detected by Western blot. Mechanically, the interaction of miR-145-5p with circTRPM7/PBX3 was validated by dual-luciferase reporter assay and RIP assay. Our study showed that circTRPM7 expression was reduced in Sinomenine-treated gastric cancer cells. Moreover, overexpression of circTRPM7 upregulated the growth and metastasis of Sinomenine-treated gastric cancer cells. CircTRPM7 could sponge miR-145-5p, and miR-145-5p reversed the effect of circTRPM7 on the growth and metastasis of Sinomenine-treated gastric cancer cells. PBX3 was the target of miR-145-5p, and knockdown of PBX3 could restore the in-miR-145-5p promotion effect on the malignant behavior of Sinomenine-treated gastric cancer cells. To sum up, our data indicated that Sinomenine played an antitumor role in gastric cancer cells via circTRPM7/miR-145-5p/PBX3 axis.

Elemental electrical switch enabling phase segregation-free operation.

Nonvolatile phase-change memory has been successfully commercialized, but further density scaling below 10 nanometers requires compositionally and structurally homogeneous materials for both the memory cell and the associated vertically stacked two-terminal access switch. The selector switches are mostly amorphous-chalcogenide Ovonic threshold switches (OTSs), operating with a nonlinear current response above a threshold voltage in the amorphous state. However, they currently suffer from the chemical complexity introduced by the quaternary or even more diverse chalcogenide compositions used. We present a single-element tellurium (Te) volatile switch with a large (≥11 megaamperes per square centimeter) drive current density, ~103 ON/OFF current ratio, and faster than 20 nanosecond switching speed. The low OFF current arises from the existence of a ~0.95­electron volt Schottky barrier at the Te­electrode interface, whereas a transient, voltage pulse­induced crystal-liquid melting transition of the pure Te leads to a high ON current. Our discovery of a single-element electrical switch may help realize denser memory chips.

12-state multi-level cell storage implemented in a 128 Mb phase change memory chip.

128 Mb Phase Change Memory (PCM) chips show potential for many applications in artificial intelligence. A PCM cell often has a sandwich structure that consists of a TiN bottom electrode, a phase change material, and a top metal. TiN films prepared by atomic layer deposition have high thermal stability, and a WN coating layer on the TiN electrode can prevent oxidation in the electric and thermal field, achieving high endurance of the TiN electrode over 1011 cycles. In the phase change material of carbon-doped Ge2Te2Te5 (CGST), C-C chains and C clusters precipitate at the Ge2Te2Te5 (GST) grain boundaries, which effectively refines the grain size of GST. The C confinement enhances the Ge/Sb atomic migration barrier and suppresses the composition segregation in the Reset/Set operation process and the atomic relaxation of the CGST material. As a result, the endurance and conductivity-drift of the PCM chip were enhanced. Finally, stability over 5 × 108 cycles and 12 multi-level stable states were achieved in the 128 Mb PCM chip. This work presents a step towards the realization of large-scale and energy-efficient neuromorphic computing systems.

Correction: 12-state multi-level cell storage implemented in a 128 Mb phase change memory chip.

Correction for '12-state multi-level cell storage implemented in a 128 Mb phase change memory chip' by Zhitang Song et al., Nanoscale, 2021, DOI: 10.1039/d1nr00100k.

Ta-Doped Sb2Te Allows Ultrafast Phase-Change Memory with Excellent High-Temperature Operation Characteristics.

Phase-change memory (PCM) has considerable promise for new applications based on von Neumann and emerging neuromorphic computing systems. However, a key challenge in harnessing the advantages of PCM devices is achieving high-speed operation of these devices at elevated temperatures, which is critical for the efficient processing and reliable storage of data at full capacity. Herein, we report a novel PCM device based on Ta-doped antimony telluride (Sb2Te), which exhibits both high-speed characteristics and excellent high-temperature characteristics, with an operation speed of 2 ns, endurance of > 106 cycles, and reversible switching at 140 °C. The high coordination number of Ta and the strong bonds between Ta and Sb/Te atoms contribute to the robustness of the amorphous structure, which improves the thermal stability. Furthermore, the small grains in the three-dimensional limit lead to an increased energy efficiency and a reduced risk of layer segregation, reducing the power consumption and improving the long-term endurance. Our findings for this new Ta-Sb2Te material system can facilitate the development of PCMs with improved performance and novel applications.

Five new additions to the genus Spathaspora (Saccharomycetales, Debaryomycetaceae) from southwest China.

Spathaspora is an important genus of d-xylose-fermenting yeasts that are poorly studied in China. During recent yeast collections in Yunnan Province in China, 13 isolates of Spathaspora were obtained from rotting wood and all represent undescribed taxa. Based on morphological and phylogenetic analyses (ITS and nuc 28S), five new species are proposed: Spathaspora elongata, Sp. mengyangensis, Sp. jiuxiensis, Sp. parajiuxiensis and Sp. rosae. Our results indicate a high species diversity of Spathaspora waiting to be discovered in rotting wood from tropical and subtropical southwest China. In addition, the two Candida species, C. jeffriesii and C. materiae, which are members of the Spathaspora clade based on phylogeny, are transferred to Spathaspora as new combinations.

Ultrahigh drive current and large selectivity in GeS selector.

Selector devices are indispensable components of large-scale nonvolatile memory and neuromorphic array systems. Besides the conventional silicon transistor, two-terminal ovonic threshold switching device with much higher scalability is currently the most industrially favored selector technology. However, current ovonic threshold switching devices rely heavily on intricate control of material stoichiometry and generally suffer from toxic and complex dopants. Here, we report on a selector with a large drive current density of 34 MA cm-2 and a ~106 high nonlinearity, realized in an environment-friendly and earth-abundant sulfide binary semiconductor, GeS. Both experiments and first-principles calculations reveal Ge pyramid-dominated network and high density of near-valence band trap states in amorphous GeS. The high-drive current capacity is associated with the strong Ge-S covalency and the high nonlinearity could arise from the synergy of the mid-gap traps assisted electronic transition and local Ge-Ge chain growth as well as locally enhanced bond alignment under high electric field.

Three new Scheffersomyces species associated with insects and rotting wood in China.

Three species of Scheffersomyces were identified during a diversity study of yeasts. All three are associated with insects and rotting wood in China. Phylogenetic analyses of a genomic dataset combining ITS and nrLSU revealed that these new collections are distinct from known species, thus three new species are introduced i.e. S. jinghongensis, S. paraergatensis, and S. anoplophorae. In our phylogenetic analyses, Scheffersomyces jinghongensis possesses a strong independent lineage and is closely related to S. titanus. S. paraergatensis is closely related to S. ergatensis, while S. anoplophorae is related to S. stambukii. Several differences in physiological traits and molecular data indicate that S. jinghongensis, S. paraergatensis, and S. anoplophorae are three newly identified species.

Microscopic Mechanism of Carbon-Dopant Manipulating Device Performance in CGeSbTe-Based Phase Change Random Access Memory.

Carbon (C)-doped Ge2Sb2Te5 material is a potential candidate in phase change random access memory (PCRAM) because of its superb thermal stability and ultrahigh cycle endurance. Unfortunately, the role and distribution evolution of C-dopant is still not fully understood, especially in practical industrial devices. In this report, with the aid of advanced spherical aberration corrected transmission electron microscopy, the mechanism of microstructure evolution manipulated by C-dopant is clearly defined. The grain-inner C atoms distinctly increase cationic migration energy barriers, which is the fundamental reason for promoting the thermal stability of metastable face-centered-cubic phase and postponing its transition to the hexagonal structure. By current pulses stimulation, the stochastic grain-outer C clusters tend to aggregate in the active area by breaking C-Ge bonding; thus, grain growth and elemental segregation are effectively suppressed to improve device reliability, for example, lower SET resistance, shorter SET time, and enlarged RESET/SET ratio. In short, the visual distribution variations of C-dopant can manipulate the performance of the PCRAM device, having much broader implications for optimizing its microstructure transition and understanding C-doped material system.

Crystal-Like Glassy Structure in Sc-Doped BiSbTe Ensuring Excellent Speed and Power Efficiency in Phase Change Memory.

Phase change memory (PCM) is regarded as a promising technology for storage-class memory and neuromorphic computing, owing to the excellent performances in operation speed, data retention, endurance, and controllable crystallization dynamics, whereas the high power consumption of PCM remains to be a short-board characteristic that limits its extensive applications. Here, Sc-doped Bi0.5Sb1.5Te3 has been proposed for high-speed and low-power PCM applications. An operation speed of 6 ns and a threshold current of 0.7 mA have been achieved in 190 nm Sc0.23Bi0.5Sb1.5Te3 PCM, which consumes lower power than GeSbTe and ScSbTe PCM. A good endurance of 5 × 105 has been achieved, which is attributed to the small volume change of 4% during phase change and a good homogeneity phase in the crystalline state. The structure of amorphous Sc0.23Bi0.5Sb1.5Te3 has been characterized by experimental and theoretical methods, showing the existence of a large amount of crystal-like structural factions, which can efficiently minimize the atomic movements required for crystallization and subsequently improve the operation speed and power efficiency. The low diffusivity of Sc and Bi at room temperature and the rapidly increased diffusivity of Bi at elevated temperatures are fundamental for the high data retention of 94 °C and the fast crystallization in Sc0.23Bi0.5Sb1.5Te3. The combination of high atomic mobility and minimized atomic movements during crystallization ensures the high speed and low power consumption of Sc0.23Bi0.5Sb1.5Te3 PCM, which can promote its application to energy-efficient systems, that is, AI chips and wearable electronics.

Observation of van der Waals reconfiguration in superlattice phase change materials.

Phase change memory (PCM) is a leading candidate for nonvolatile memory applications in the big data era. However, the high power consumption, caused by melting GeTe-Sb2Te3-like phase change materials, hinders their applications. A significant step is the proposal to spatially separate GeTe and Sb2Te3 in the form of a superlattice, enabling a higher operating speed and better cyclability at reduced switching energy. However, the physical origin is under intensive debate. Recently, the swapping of the SbTe terminating layers nearest to the van der Waals (vdWs) gap has been claimed to be the mechanism for the superlattice. Here, we reported a direct atomic-scale chemical identification of two kinds of vdWs reconfigurations together with atomic simulations. The vdWs reconfigurations, which occurred at the GeTe and Sb2Te3 boundary, were demonstrated to change the electrical properties and turn this semiconductor into a conductor, leading to the resistance contrast. Besides, strong intermixing of Ge and Sb atoms was directly observed; in the most severe cases, ∼50% of Ge in the GeTe layer diffused into the adjacent Sb2Te3 layer. Our work paves the way for deeper understanding of the phase transition of the GeTe/Sb2Te3 superlattice and the future design of non-volatile memories towards dynamic random access-like memories.

Direct atomic insight into the role of dopants in phase-change materials.

Doping is indispensable to tailor phase-change materials (PCM) in optical and electronic data storage. Very few experimental studies, however, have provided quantitative information on the distribution of dopants on the atomic-scale. Here, we present atom-resolved images of Ag and In dopants in Sb2Te-based (AIST) PCM using electron microscopy and atom-probe tomography. Combing these with DFT calculations and chemical-bonding analysis, we unambiguously determine the dopants' role upon recrystallization. Composition profiles corroborate the substitution of Sb by In and Ag, and the segregation of excessive Ag into grain boundaries. While In is bonded covalently to neighboring Te, Ag binds ionically. Moreover, In doping accelerates the crystallization and hence operation while Ag doping limits the random diffusion of In atoms and enhances the thermal stability of the amorphous phase.

Sc-Centered Octahedron Enables High-Speed Phase Change Memory with Improved Data Retention and Reduced Power Consumption.

Phase change memory (PCM) with advantages of high operation speed, multilevel storage capability, spiking-time-dependent plasticity, etc., has wide application scenarios in both Von Neumann systems and neuromorphic systems. In the automotive application, intelligent system not only needs high efficiency to handle massive data processing but also good robustness to retain the existing data against high working temperature. In this work, Sc-doped GeTe is developed for PCM, which has achieved 120 °C data retention for 10 years, 6 ns operation speed, and 7 nJ low power consumption. The high data retention is attributed to the high coordination number of Sc and its strong bonds with Te atoms in the amorphous phase, which enhances the robustness of the atomic matrices. Sc-centered octahedrons in amorphous state provide a nucleation center, leading to fast crystallization. In the crystalline phase, Sc atoms occupy Ge vacancies to form a homogenous GeTe-like rhombohedral phase. The strong covalent-like Sc-Te bonds weaken the neighboring Ge-Te bonds, lowering energy for melting. Together with the increased energy efficiency originated from confined grain size, the reduced power consumption has been achieved. The improvements in data retention, speed, and power efficiency have made Sc-doped GeTe a promising candidate for high-performance automobile electronics application.

Thermal Barrier Phase Change Memory.

Phase change memory is widely considered as the most promising candidate as storage class memory (SCM), bridging the performance gaps between dynamic random access memory and flash. However, high required operation current remains the major limitation for the SCM application, even after using defect engineering materials, for example, Ti-doped Sb2Te3. Here, we demonstrate that ∼87% current can be reduced by spatially separating Sb2Te3 and TiTe2 layers, thanks to semimetallic TiTe2 serving as a thermal barrier in the reset process. Moreover, the stable crystalline TiTe2 layer provides an ordered interface to speed up the crystallization process of the amorphous Sb2Te3 layer, enabling ∼10 ns ultrafast crystallization speed. An outstanding device lifetime, up to ∼2 × 107 cycles, has been obtained, which is twice as long as that of alloy-based cells. Correlative electron microscopy and atom probe tomography provide evidence that the TiTe2/Sb2Te3 multilayer can keep a layer-stacked structure, avoiding phase segregation found in alloys and strong element intermixing in the GeTe/Sb2Te3 superlattice, which enables excellent cyclability. This study suggests that adding a semimetallic layer in the phase change layer, such as TiTe2 and TiSe2, can yield a phase change memory with superior properties.

Electrical switching properties and structural characteristics of GeSe-GeTe films.

Germanium chalcogenides, especially GeSe and GeTe alloys, have recently gained popularity because of their Ovonic threshold (volatile) and memory (non-volatile) switching properties, with great potential for electric storage applications. Materials designed in a pseudo-binary way may possess superior properties in their phase transition, e.g. GeTe-Sb2Te3 materials, and bring about revolutionary advances in optical storage. However, to date, the electrical switching behaviors of films of pseudo-binary GeSe-GeTe have not yet been studied, and neither have the structural characteristics. Herein, we present both the thermally and electrically induced switching behaviors of GeSe-GeTe film, as well as the structural evolution due to composition tuning. The crystallization temperature of GeSe-GeTe films increases with GeSe content quite sensitively. An atom-resolved picture of the GeSe-GeTe alloy with a state-of-the-art atomic mapping technology has been presented, where a randomly mixed arrangement of Se and Te atoms is determined unambiguously in Ge50Se13Te34 with a GeTe-like rhombohedral structure. The local structural motifs in GeSe-GeTe, more specifically, sixfold coordinated octahedra with a distinguished degree of Peierls distortion and geometric variety, are essential to understand its electric properties. GeSe-GeTe alloy, Ge50Se13Te34, based memory cells have been fabricated, showing a fast memory switching behavior and excellent retention of 10 years at 208 °C.

Atomic scale insight into the effects of Aluminum doped Sb2Te for phase change memory application.

To date, the unpleasant trade-off between crystallization speed and thermal stability for most phase change materials is detrimental to achieve phase change memory (PCM) with both features of high-speed and good-retention. However, it is proved that Al doping in Sb2Te, served as storage media in PCM, favors both a high writing speed (6 ns) and a good retention (103 °C), as well as a low power consumption. Judging by experimental and theoretical investigations, doped Al atoms prefer to replace Sb in Sb2Te lattice, strongly bonded with 6 Te atoms, to form a homogeneous phase. While in amorphous Al doped Sb2Te (AST), Al atoms are in tetrahedral environment, firmly bonded with four Sb/Te atoms. The strong bonding in Al centered tetrahedron in amorphous AST can obstruct the collective motion of Sb atoms near the matrix boundary, leading to the improvement in thermal stability and the confinement in grain size.

Reducing the stochasticity of crystal nucleation to enable subnanosecond memory writing.

Operation speed is a key challenge in phase-change random-access memory (PCRAM) technology, especially for achieving subnanosecond high-speed cache memory. Commercialized PCRAM products are limited by the tens of nanoseconds writing speed, originating from the stochastic crystal nucleation during the crystallization of amorphous germanium antimony telluride (Ge2Sb2Te5). Here, we demonstrate an alloying strategy to speed up the crystallization kinetics. The scandium antimony telluride (Sc0.2Sb2Te3) compound that we designed allows a writing speed of only 700 picoseconds without preprogramming in a large conventional PCRAM device. This ultrafast crystallization stems from the reduced stochasticity of nucleation through geometrically matched and robust scandium telluride (ScTe) chemical bonds that stabilize crystal precursors in the amorphous state. Controlling nucleation through alloy design paves the way for the development of cache-type PCRAM technology to boost the working efficiency of computing systems.

Low-Energy Amorphization of Ti1Sb2Te5 Phase Change Alloy Induced by TiTe2 Nano-Lamellae.

Increasing SET operation speed and reducing RESET operation energy have always been the innovation direction of phase change memory (PCM) technology. Here, we demonstrate that ∼87% and ∼42% reductions of RESET operation energy can be achieved on PCM cell based on stoichiometric Ti1Sb2Te5 alloy, compared with Ge2Sb2Te5 and non-stoichiometric Ti0.4Sb2Te3 based PCM cells at the same size, respectively. The Ti1Sb2Te5 based PCM cell also shows one order of magnitude faster SET operation speed compared to that of the Ge2Sb2Te5 based one. The enhancements may be caused by substantially increased concentration of TiTe2 nano-lamellae in crystalline Ti1Sb2Te5 phase. The highly electrical conduction and lowly thermal dissipation of the TiTe2 nano-lamellae play a major role in enhancing the thermal efficiency of the amorphization, prompting the low-energy RESET operation. Our work may inspire the interests to more thorough understanding and tailoring of the nature of the (TiTe2)n(Sb2Te3)m pseudobinary system which will be advantageous to realize high-speed and low-energy PCM applications.

One order of magnitude faster phase change at reduced power in Ti-Sb-Te.

To date, slow Set operation speed and high Reset operation power remain to be important limitations for substituting dynamic random access memory by phase change memory. Here, we demonstrate phase change memory cell based on Ti0.4Sb2Te3 alloy, showing one order of magnitude faster Set operation speed and as low as one-fifth Reset operation power, compared with Ge2Sb2Te5-based phase change memory cell at the same size. The enhancements may be rooted in the common presence of titanium-centred octahedral motifs in both amorphous and crystalline Ti0.4Sb2Te3 phases. The essentially unchanged local structures around the titanium atoms may be responsible for the significantly improved performance, as these structures could act as nucleation centres to facilitate a swift, low-energy order-disorder transition for the rest of the Sb-centred octahedrons. Our study may provide an alternative to the development of high-speed, low-power dynamic random access memory-like phase change memory technology.

Dry etching of nanosized Ge1Sb2Te4 patterns using TiN hard mask for high density phase-change memory.

Being able to pattern and etch chalcogenide materials in nanometer scale is essential for the integration of high density chalcogenide random access memory. We investigated dry etching methods for the patterning of Ge1Sb2Te4 films in CHF3/O2 gas mixture using reactive-ion etching system. The gas species CHF3/O2 can reach good etched features with smooth sidewall and a taper angle of 86 degrees. The nanosized Ge1Sb2Te4 patterns were defined by electron-beam lithography using hydrogen silsesquioxane as negative type e-beam resist. A hard mask of TiN, to which the selectivity of Ge1Sb2Te4 is as high as 12, was chosen for employing a CHF3/O2 gas mixture for Ge1Sb2Te4 etching. The Ge1Sb2Te4 line with width of 170 nm could be successfully obtained with good profiles and uniformity using these optimized patterning conditions, which could be very helpful for fabricating high density chalcogenide random access memory based on Ge1Sb2Te4.