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Ionic migration degrades not only the characteristics of halide perovskite solar cells, but also those of perovskite X-ray detectors. Here Yang et al. employ heteroepitaxial BiOBr to passivate Cs2AgBiBr6 double perovskite, which suppresses ionic migration and obtain high performance X-ray detectors.

Recently, due to the development of big data and computer technology, artificial intelligence (AI) has received extensive attention and made great progress. Edge intelligence pushes the computing center of AI from the cloud to individual users, making AI closer to life, but at the same time puts forward higher requirements for the realization of hardware, especially for edge acceleration. Taking convolutional neural networks (CNNs) as an example, which show excellent problem‐solving capabilities in different fields of academia and industry, it still faces issues of enormous computing volume and complex mapping architecture. Based on the computing‐in‐memory property and parallel multiply accumulate (MAC) operations of the emerging nonvolatile memristor arrays, herein the recent research progress of the edge intelligence memristive convolution accelerator is summarized. Furthermore, aiming at improving memristive convolutional accelerators, two potential optimization schemes are also discussed: The compression methods represented by quantization show great potential for static image processing, and the combination of a CNN with a long short‐term memory (LSTM) neural network makes up for the CNN's shortcomings of dynamic target processing. Finally, the future challenges and opportunities of edge intelligence accelerators based on memristor arrays are also discussed.

The exact composition and structure of conductive filaments in hafnia-based memristors are still not fully understood, but recent theoretical investigations reveal that hexagonal HfOx phases close to the h.c.p. Hf structure are probable filament candidates. In this work we list h.c.p. Hf, Hf6O, Hf3O and Hf2O as possible phases for the filament in hafnia memristors. Their differences in lattice parameters, electronic structures and O charge states are studied in details. Migration of O ions for both in-plane and out-of-plane directions in these phases is investigated using first-principles calculations. Both single-phase supercells and filament-in-dielectric models are used for migration barrier calculations, while the latter is proven to be more accurate for the c-direction. The migration of O ions is fastest in metal Hf, while slowest in Hf2O. The existence of O interstitials in Hf tends to hinder the transport of O.

We have coated phase change materials (PCMs) on rough and flexible substrates to achieve multicolor changeable devices. The principle of the device is based on an earlier discovery that lights have strong interference effect in PCM films, leading to various colors by reflection. In this work, paper substrates are laminated by parylene layers to protect the device from water before coated with functional PCM films. The PCM-based color printing (PCP) on paper is not affected by rough surfaces and shows a similar color appearance as that on smooth surfaces. In particular, the color-printed device can be patterned by UV lithography to display a clear and tunable optical image, and it exhibits a low sensitivity to the angle of view. Such PCP has potential applications for low-cost, disposable, and flexible displays.

A study was conducted to examine the effect of In and Ge doping in the form of [In.sub.2][Ge.sub.8][Sb.sub.85][Te.sub.5] on optical and thermal properties of eutectic [Sb.sub.70][Te.sub.30] alloys. The use of ultrafast and thermally stable [In.sub.2][Ge.sub.8][Sb.sub.85][Te.sub.5] phase change material as mask layer in aperture-type super-resolution near-field phase change disk was realized to increase the carrier-to-noise ratio and thermal stability.

Recent experiments demonstrated giant osmotic effects induced in a single-atomic-layer MoS2 nanopore by imposing a KCl concentration bias, thereby highlighting the prospect of ultrathin nanopores as power generators. In this work, we report on an electrokinetic analysis of the ionic transport in the MoS2 nanopore system. By taking membrane surface chemistry into account, we found profound roles of surface charges in and out of the nanopore on the cross-pore ion transport, which shed light on the intriguing experimental observations of a high pore conductance with a large open-circuit voltage in the MoS2 system. The present work establishes a theoretical model capable of dealing with ultrathin membrane surface charges for evaluating the energy conversion performance of nanopore power generators constructed with two-dimensional materials. [ABSTRACT FROM AUTHOR]

Memristors are attracting considerable interest for their prospective applications in nonvolatile memory, neuromorphic computing, and in-memory computing. However, the nature of resistance switching is still under debate, and current fluctuation in memristors is one of the critical concerns for stable performance. In this work, random telegraph noise (RTN) as the indication of current instabilities in distinct resistance states of the Pt/Ti/HfO2/W memristor is thoroughly investigated. Standard two-level digital-like RTN, multilevel current instabilities with non-correlation/correlation defects, and irreversible current transitions are observed and analyzed. The dependence of RTN on the resistance and read bias reveals that the current fluctuation depends strongly on the morphology and evolution of the conductive filament composed of oxygen vacancies. Our results link the current fluctuation behaviors to the evolution of the conductive filament and will guide continuous optimization of memristive devices. [ABSTRACT FROM AUTHOR]

Maskless phase-change lithographic technology is developed as a photoresist of phase-change materials. The controllable growth behavior of the crystallization region on an amorphous thin film of Ge2Sb2Te5 (GST) irradiated by a laser beam is investigated; the GST thin film is deposited on a silicon substrate by the sputtering method. The results of a series of the experiments and the simulations all show that the width of a crystalline pattern is not only closely related to laser power and pulse duration, but also is apparently affected by the interactive area between the focused laser spot and thin film. The width maintains a nonlinear growth with the enhancement of the laser power until the thin film approaches melting, whereas it gradually reaches a constant value due to the local thermal equilibrium. This equilibrium makes the width irrelevant to the moving velocity with certain constraints when the laser works in continuous-wave mode. Within a defocus range of 15 µm, the widths of the crystalline patterns are obtained in a broad range from 690 nm to 8.13 µm under a 0.4-NA objective lens. By adjusting the defocus amount, some crystalline square patterns with expected widths in a wide range are fabricated, and the mean percentage error between the expected and fabricated widths is only 1.495%. [ABSTRACT FROM AUTHOR]

The general model of a phase-change memory (PCM) cell is very complex due to electrical property, thermal transfer and crystal growth. In this paper the general model is equivalent to an RC circuit, via which the dependence of the cell resistance on the number of pulses (Set or Reset) was investigated. Moreover, as for dual-port asynchronous operations of a pore-type PCM cell, a double-capacitor-based cell model was proposed. By simulation on the model we verified feasibility of the cell’s logic and arithmetic operations. In addition, the simulation results of addition and subtraction show that the resistance changes linearly with a short pulse sequence. [ABSTRACT FROM AUTHOR]

Owing to the capability of integrating the information storage and computing in the same physical location, in-memory computing with memristors has become a research hotspot as a promising route for non von Neumann architecture. However, it is still a challenge to develop high performance devices as well as optimized logic methodologies to realize energy-efficient computing. Herein, filamentary Cu/GeTe/TiN memristor is reported to show satisfactory properties with nanosecond switching speed (<60 ns), low voltage operation (<2 V), high endurance (>104 cycles) and good retention (>104 s @85 °C). It is revealed that the charge carrier conduction mechanisms in high resistance and low resistance states are Schottky emission and hopping transport between the adjacent Cu clusters, respectively, based on the analysis of current–voltage behaviors and resistance–temperature characteristics. An intuitive picture is given to describe the dynamic processes of resistive switching. Moreover, based on the basic material implication (IMP) logic circuit, we proposed a reconfigurable logic method and experimentally implemented IMP, NOT, OR, and COPY logic functions. Design of a one-bit full adder with reduction in computational sequences and its validation in simulation further demonstrate the potential practical application. The results provide important progress towards understanding of resistive switching mechanism and realization of energy-efficient in-memory computing architecture. [ABSTRACT FROM AUTHOR]

Memristive stateful logic has emerged as a promising next-generation in-memory computing paradigm to address escalating computing-performance pressures in traditional von Neumann architecture. Here, we present a nonvolatile reprogrammable logic method that can process data between different rows and columns in a memristive crossbar array based on material implication (IMP) logic. Arbitrary Boolean logic can be executed with a reprogrammable cell containing four memristors in a crossbar array. In the fabricated Ti/HfO2/W memristive array, some fundamental functions, such as universal NAND logic and data transfer, were experimentally implemented. Moreover, using eight memristors in a 2  ×  4 array, a one-bit full adder was theoretically designed and verified by simulation to exhibit the feasibility of our method to accomplish complex computing tasks. In addition, some critical logic-related performances were further discussed, such as the flexibility of data processing, cascading problem and bit error rate. Such a method could be a step forward in developing IMP-based memristive nonvolatile logic for large-scale in-memory computing architecture. [ABSTRACT FROM AUTHOR]

Bi2Te3 thin films and GeTe/B2Te3 superlattices of different thicknesses are prepared on the silicon dioxide substrates by magnetron sputtering technique and thermally annealed at 573 K for 30 min. Thermoelectric (TE) measurements indicate that optimal thickness and thickness ratio improve the TE performance of Bi2Te3 thin films and GeTe/B2Te3 superlattices, respectively. High TE performances with figure-of-merit (ZT) values as high as 1.32 and 1.56 are achieved at 443 K for 30 nm and 50 nm Bi2Te3 thin films, respectively. These ZT values are higher than those of p-type Bi2Te3 alloys as reported. Relatively high ZT of the GeTe/B2Te3 superlattices at 300–380 K were 0.62–0.76. The achieved high ZT value may be attributed to the unique nano- and micro-structures of the films, which increase phonon scattering and reduce thermal conductivity. The results indicate that Bi2Te3-based thin films can serve as high-performance materials for applications in TE devices. [ABSTRACT FROM AUTHOR]

The temperature dependence of crystallization kinetics of phase-change materials raises a series of reliability issues, while phase-change memory cells work at high temperature or thermal-disturbance condition. These issues hinder the development of ultrahigh-density storage devices. We investigate the evolution of SET switching characteristics of phase-change memory cells at high operating temperature. We show that the high temperature strongly impacts the SET state resistance. As a result, SET failure has been observed with elevated ambient temperature. Our SPICE simulations indicate that transient amorphization behavior during a complete SET pulse period is considered as the potential mechanism of SET failure. By modifying the SET pulse intensity and width linearly, we successfully reduce the SET failure in the experiments. The results illustrate that the demonstrated linear properties may optimize SET pulse performance. [ABSTRACT FROM AUTHOR]

Spin Hall magnetoresistance (SMR) has been investigated in Ta/CoFe2O4 nanostructures grown on different substrates. Spin currents in CoFe2O4 films are electrically detected in adjacent Ta layers owing to inverse spin Hall effects. The sign of the magnetic-field-dependent resistivity signal shows different polarities along different axes, showing different spin-dependent electron transports. A cosinelike curve of the angular dependence signal with opposite polarity is observed in two orthogonal magnetization planes, whereas a basic line is observed in another plane, revealing the spin accumulation phenomenon. The roughness of the CoFe2O4 surface tuned by substrate strains is responsible for the extent of spin accumulations and the strength of the SMR signal in the nanostructures. [ABSTRACT FROM AUTHOR]

A model of an optical disk containing data pits with a range of depths and orientation angles is simulated to investigate how the Stokes parameters of the light reflected from these pits vary. Pits carrying multiple bits of information can be recovered according to the Stokes parameters, particularly S0 and S1, which show different variation trends versus the depth and orientation angles. In addition, the signal width of S0 ceases to be constant, and instead varies as a function of the orientation angle during laser scanning. This can double the available modulation range of the orientation angle and further enhance disk storage densities. [ABSTRACT FROM AUTHOR]