Volatile Ultrafast Switching at Multilevel Nonvolatile States of Phase Change Material for Active Flexible Terahertz Metadevices

Phase change materials provide unique reconfigurable properties for photonic applications that mainly arise from their exotic characteristic to reversibly switch between the amorphous and crystalline nonvolatile phases. Optical pulse based reversible switching of nonvolatile phases is exploited in various nanophotonic devices. However, large area reversible switching is extremely challenging and has hindered its translation into a technologically significant terahertz spectral domain. Here, this limitation is circumvented by exploiting the semiconducting nature of germanium antimony telluride (GST) to achieve dynamic terahertz control at picosecond timescales. It is also shown that the ultrafast response can be actively altered by changing the crystallographic phase of GST.  The ease of fabrication of phase change materials allows for the realization of a variable ultrafast terahertz modulator on a flexible platform. The rich properties of phase change materials combined with the diverse functionalities of metamaterials and all-optical ultrafast control enables an ideal platform for design of efficient terahertz communication devices, terahertz neuromorphic photonics, and smart sensor systems.     

Nonvolatile Floating‐Gate Memories Based on Stacked Black Phosphorus–Boron Nitride–MoS2 Heterostructures

Research on van der Waals heterostructures based on stacked 2D atomic crystals is intense due to their prominent properties and potential applications for flexible transparent electronics and optoelectronics. Here, nonvolatile memory devices based on floating‐gate field‐effect transistors that are stacked with 2D materials are reported, where few‐layer black phosphorus acts as channel layer, hexagonal boron nitride as tunnel barrier layer, and MoS₂ as charge trapping layer. Because of the ambipolar behavior of black phosphorus, electrons and holes can be stored in the MoS₂ charge trapping layer. The heterostructures exhibit remarkable erase/program ratio and endurance performance, and can be developed for high‐performance type‐switching memories and reconfigurable inverter logic circuits, indicating that it is promising for application in memory devices completely based on 2D atomic crystals.     

Dispersion-Enabled Symmetry Switching of Photonic Angular-Momentum Coupling

Photonic spin-orbit interactions describe the interactions between spin angular momentum and orbital angular momentum of photons, which play essential roles in subwavelength optics. However, the influence of frequency dispersion on photonic angular-momentum coupling is rarely studied. Here, by elaborately designing the contribution of the geometric phase and waveguide propagation phase, the dispersion-enabled symmetry switching of photonic angular-momentum coupling is experimentally demonstrated. This notion may induce many exotic phenomena and be found in enormous applications, such as the spin-Hall effect, optical calculation, and wavelength division multiplexing systems. As a proof-of-concept demonstration, two metadevices, a multi-channel vectorial vortex beam generator and a phase-only hologram, are applied to experimentally display optical double convolution, which may offer additional degrees of freedom to accelerate computing and a miniaturization configuration for optical convolution without collimation operation. These results may provide a new opportunity for complex vector optical field manipulation and calculation, optical information coding, light-matter interaction manipulation, and optical communication.     

硫系玻璃集成光子器件综述(特邀)

硫系玻璃具有超宽的红外透过光谱范围、较高的线性折射率、极高的光学非线性和超快的非线性响应,近年来在集成光子器件研究领域备受关注。首先回顾了硫系玻璃集成光波导的制备,综述了硫系集成光子器件在红外传感和高性能非线性应用方面取得的进展,然后介绍了硫系相变光子器件在光开关、光存储和光计算等方面的前沿进展,最后对目前硫系玻璃光子器件研究存在的问题进行了归纳,并对未来的研究方向进行了展望。     

Tunable Volatility of Ge2Sb2Te5 in Integrated Photonics

The operation of a single class of optical materials in both a volatile and nonvolatile manner is becoming increasingly important in many applications. This is particularly true in the newly emerging field of photonic neuromorphic computing, where it is desirable to have both volatile (short‐term transient) and nonvolatile (long‐term static) memory operation, for instance, to mimic the behavior of biological neurons and synapses. The search for such materials thus far have focused on phase change materials where typically two different types are required for the two different operational regimes. In this paper, a tunable volatile/nonvolatile response is demonstrated in a photonic phase‐change memory cell based on the commonly employed nonvolatile material Ge₂Sb₂Te₅ (GST). A time‐dependent, multiphysics simulation framework is developed to corroborate the experimental results, allowing us to spatially resolve the recrystallization dynamics within the memory cell. It is then demonstrated that this unique approach to photonic memory enables both data storage with tunable volatility and detection of coincident events between two pulse trains on an integrated chip. Finally, improved efficiency and all‐optical routing with controlled volatility are demonstrated in a ring resonator. These crucial results show that volatility is intrinsically tunable in normally nonvolatile GST which can be used in both regimes interchangeably.     

A New Family of Ultralow Loss Reversible Phase‐Change Materials for Photonic Integrated Circuits: Sb2S3 and Sb2Se3

Phase‐change materials (PCMs) are seeing tremendous interest for their use in reconfigurable photonic devices; however, the most common PCMs exhibit a large absorption loss in one or both states. Here, Sb₂S₃ and Sb₂Se₃ are demonstrated as a class of low loss, reversible alternatives to the standard commercially available chalcogenide PCMs. A contrast of refractive index of Δn = 0.60 for Sb₂S₃ and Δn = 0.77 for Sb₂Se₃ is reported, while maintaining very low losses (k < 10^?5) in the telecommunications C‐band at 1550 nm. With a stronger absorption in the visible spectrum, Sb₂Se₃ allows for reversible optical switching using conventional visible wavelength lasers. Here, a stable switching endurance of better than 4000 cycles is demonstrated. To deal with the essentially zero intrinsic absorption losses, a new figure of merit (FOM) is introduced taking into account the measured waveguide losses when integrating these materials onto a standard silicon photonics platform. The FOM of 29 rad phase shift per dB of loss for Sb₂Se₃ outperforms Ge₂Sb₂Te₅ by two orders of magnitude and paves the way for on‐chip programmable phase control. These truly low‐loss switchable materials open up new directions in programmable integrated photonic circuits, switchable metasurfaces, and nanophotonic devices.     

Biocompatible and Flexible Chitosan‐Based Resistive Switching Memory with Magnesium Electrodes

A flexible and transparent resistive switching memory based on a natural organic polymer for future flexible electronics is reported. The device has a coplanar structure of Mg/Ag‐doped chitosan/Mg on plastic substrate, which shows promising nonvolatile memory characteristics for flexible memory applications. It can be easily fabricated using solution processes on flexible substrates at room temperature and indicates reliable memory operations. The elucidated origin of the bipolar resistive switching behavior is attributed to trap‐related space‐charge‐limited conduction in high resistance state and filamentary conduction in low resistance state. The fabricated devices exhibit memory characteristics such as low power operation and long data retention. The proposed biocompatible memory device with transient electrodes is based on naturally abundant materials and is a promising candidate for low‐cost memory applications. Devices with natural substrates such as chitosan and rice paper are also fabricated for fully biodegradable resistive switching memory. This work provides an important step toward developing a flexible resistive switching memory with natural polymer films for application in flexible and biodegradable nanoelectronic devices.     

Physics of switching and memory effects in chalcogenide glassy semiconductors

Switching and memory effects in chalcogenide glassy semiconductors have been known for nearly fifty years. However, the physics of these effects remains unclear. Recent interest in this problem is caused by active developments of a new generation nonvolatile memory based on the chalcogenide glass-crystal phase transition. In this paper, we review the main experimental features of switching and memory effects, review and analyze the models of the switching effect. Consider the main characteristics of phase-change memory cells made of various materials. On these grounds, the main advantages of modern phase-change memory cells are presented in comparison with first-generation memory elements.     

Reconfigurable Logic‐in‐Memory and Multilingual Artificial Synapses Based on 2D Heterostructures

Nonvolatile logic devices have attracted intensive research attentions recently for energy efficiency computing, where data computing and storage can be realized in the same device structure. Various approaches have been adopted to build such devices; however, the functionality and versatility are still very limited. Here, 2D van der Waals heterostructures based on direct bandgap materials black phosphorus and rhenium disulfide for the nonvolatile ternary logic operations is demonstrated for the first time with the ultrathin oxide layer from the black phosphorus serving as the charge trapping as well as band‐to‐band tunneling layer. Furthermore, an artificial electronic synapse based on this heterostructure is demonstrated to mimic trilingual synaptic response by changing the input base voltage. Besides, artificial neural network simulation based on the electronic synaptic arrays using the handwritten digits data sets demonstrates a high recognition accuracy of 91.3%. This work provides a path toward realizing multifunctional nonvolatile logic‐in‐memory applications based on novel 2D heterostructures.     

Functional Coatings on High‐Performance Polymer Fibers for Smart Sensing

Above a critical temperature, high‐performance fibers may lose their mechanical properties resulting in catastrophic events of damage when, e.g., used as load‐carrying ropes. Here, a method to functionalize polymer fibers with thermochromic optical coatings that enable signaling of damaging thermal history is introduced. These smart coatings are comprised of an index‐tunable anti‐reflection coating based on chalcogenide phase change materials (PCM). It is demonstrated that the insulator?metal phase transition of these materials can be aligned with the critical deterioration temperature of both polyethylene terephthalate (PET) monofilaments and liquid‐crystal polyester (LCP) yarns by composition tuning. The carefully designed optical system amplifies the change in optical properties of its constituents upon phase change. The thermal and mechanical degradation of these fibers can thus be monitored and displayed by eye.     

无机相变信息存储材料研究新进展

硫族化合物合金GeSbTe(GST)和AgInSbTe等相变材料(PCM)已经在光存储技术中得到广泛的应用,用相变电存储器件作为闪存的替代产品已成为国内外研究的热点.与此同时,相变材料在一些领域也取得了新的应用.总结了近年来国内外在相变材料的存储机制、光/电存储性能的改进以及新应用等方面的最新研究成果,并展望了相变材料的研究前景.     

Novel Digital Nonvolatile Memory Devices Based on Semiconducting Polymer Thin Films

Recent increases in the demand for mobile devices have stimulated the development of nonvolatile memory devices with high performance. In this Communication, we describe the fabrication of low‐cost, high‐performance, digital nonvolatile memory devices based on semiconducting polymers, poly(o‐anthranilic acid) and poly(o‐anthranilic acid‐co‐aniline). These memory devices have ground‐breaking and novel current–voltage switching characteristics. The devices are switchable in a very low voltage range (which is much less than those of all other devices reported so far) with a very high ON/OFF current ratio (which is on the order of 10⁵). The low critical voltages have the advantage for nonvolatile memory device applications of low operation voltages and hence low power consumption. With this very low power consumption, the devices demonstrate in air ambient to have very stable ON‐ and OFF‐states without any degradation for a very long time (which has been confirmed up to one year so far) and to be repeatedly written, read and erased. Our study proposes that the ON/OFF switching of the devices is mainly governed by a filament mechanism. The high ON/OFF switching ratio and stability of these devices, as well as their repeatable writing, reading and erasing capability with low power consumption, opens up the possibility of the mass production of high performance digital nonvolatile polymer memory devices with low cost. Further, these devices promise to revolutionize microelectronics by providing extremely inexpensive, lightweight, and versatile components that can be printed onto plastics, glasses or metal foils.     

Characteristics of chalcogenide nonvolatile memory nano-cell-element based on Sb2Te3 material

Phase-change nonvolatile memory cell elements composed of Sb₂Te₃ chalcogenide have been fabricated by using the focused ion beam method. The contact size between the Sb₂Te₃ phase change film and electrode film in the cell element is 2826 nm² (diameter: 60 nm). The thickness of the Sb₂Te₃ chalcogenide film is 40 nm. The threshold switching current of about 0.1 mA was obtained. A RESET pulse width as short as 5 ns and the SET pulse width as short as 22 ns for Sb₂Te₃ chalcogenide can be obtained. At least 1000 cycle times with a RESET/SET resistance ratio >30 times is achieved for Sb₂Te₃ chalcogenide C-RAM cell element.     

Interface‐Engineered Amorphous TiO2‐Based Resistive Memory Devices

Crossbar‐type bipolar resistive memory devices based on low‐temperature amorphous TiO₂ (a‐TiO₂) thin films are very promising devices for flexible nonvolatile memory applications. However, stable bipolar resistive switching from amorphous TiO₂ thin films has only been achieved for Al metal electrodes that can have severe problems like electromigration and breakdown in real applications and can be a limiting factor for novel applications like transparent electronics. Here, amorphous TiO₂‐based resistive random access memory devices are presented that universally work for any configuration of metal electrodes via engineering the top and bottom interface domains. Both by inserting an ultrathin metal layer in the top interface region and by incorporating a thin blocking layer in the bottom interface, more enhanced resistance switching and superior endurance performance can be realized. Using high‐resolution transmission electron microscopy, point energy dispersive spectroscopy, and energy‐filtering transmission electron microscopy, it is demonstrated that the stable bipolar resistive switching in metal/a‐TiO₂/metal RRAM devices is attributed to both interface domains: the top interface domain with mobile oxygen ions and the bottom interface domain for its protection against an electrical breakdown.     

光控相控阵雷达发展动态和实现中的关键技术

本文讨论了光控相控阵雷达的原理和发展现状,介绍了光控技术在宽带宽角扫描相控阵雷达中的应用和优点,详细阐述了不同光实时延迟线(OTTD)的主要构成原理和技术特点,讨论了雷达微波信号的光调制技术和探测技术现状,指出了光控相控阵雷达技术可能的应用方向.文中重点讨论了光控相控阵雷达实现中需解决的关键技术,包括总体设计方案中的系统指标分配,雷达阵面结构设计时光器件温度特性的考虑,微波信号光纤传输中的幅相一致性、动态范围、非线性相位等,OTTD设计加工中的波束切换时间、插入损耗、隔离度、延时精度等.针对OTTD加工中难免存在的加工误差,文中提出了子阵OTTD与阵元移相器联合波控的方法.     

In Situ Reversible Ionic Control for Nonvolatile Magnetic Phases in a Donor/Acceptor Metal‐Organic Framework

Reversible magnetic control by electrical means, which is highly desired from the viewpoint of fundamentals and technological applications such as data storage devices, has been a challenging topic. In this study, the authors demonstrate in situ magnetic phase switching between the ferrimagnetic and paramagnetic states of an electron‐donor/‐acceptor metal‐organic framework (D/A‐MOF) using band‐filling control mediated by the Li⁺‐ion migration that accompanies redox reactions, i.e., “magneto‐ionic control”. By taking advantage of the rechargeability of lithium‐ion battery systems, in which Li⁺‐ions and electrons are simultaneously inserted into/extracted from a cathode material, the reversible control of nonvolatile magnetic phases in a D/A‐MOF has been achieved. This result demonstrates that the combination of a redox‐active MOF with porous flexibility and ion‐migration capability enables the creation of new pathways toward magneto‐electric coupling devices in the field of ionics.     

自动交换光网络中光电子器件的进展

光网络正在向高速大容量、良好的扩展性和智能化的方向发展。自动交换光网络的出现是光传送网技术的重要突破,光电子器件功能的增强与性能的提高将对其实现与发展起决定性作用。本文介绍了自动交换光网络中一些光电子器件的重要特性和发展趋势。     

Spintronics

Investigations of the dynamics of spin-polarized electronic current through and near materials with spin-dependent electronic structures have created a rich new field dubbed "spintronics". The implications of spintronics research extend deep into the realm of fundamental material properties, yet spintronics applications have also revolutionized the magnetic-storage industry by providing efficient room-temperature magnetic sensors. Control of nonequilibrium spin-polarized populations of electrons through and near magnets has led to the dominance of linear (resistive) spintronic devices for magnetic readout in commercial magnetic storage. Rapid progress in understanding the fundamental physics of nonlinear spin-polarized electronic transport in metals and semiconductors suggests new applications for spintronic devices in fast nonvolatile memory as well as logic devices, with or without magnetic materials or magnetic fields. Ongoing study of the interaction between such spintronic elements and optical fields, particularly in semiconductors, promises the future development of optical spintronic devices     

Phase-change memory devices with stacked Ge-chalcogenide/Sn-chalcogenide layers

Non-volatile memory devices with two stacked layers of chalcogenide materials comprising the active memory device have been investigated for their potential as phase-change memories. The devices tested consisted of GeTe/SnTe, Ge₂Se₃/SnTe, and Ge₂Se₃/SnSe stacks. All devices exhibited resistance switching behavior. The polarity of the applied voltage with respect to the SnTe or SnSe layer was critical to the memory switching properties, most likely due to the voltage induced movement of either Sn or Te into the Ge-chalcogenide layer.     

Optically Modulated Threshold Switching in Core–Shell Quantum Dot Based Memristive Device

The threshold switching (TS) phenomenon in memristors has drawn great attention for its versatile applications in selectors, artificial neurons, true random number generators, and electronic integrations. The transition between nonvolatile resistive switching and volatile TS modes can be realized by doping, varying annealing and voltage sweeping conditions, or imposing different compliance current. Here, a strategy is reported to achieve such transition by the noninvasive UV light stimulus based on InP/ZnS quantum dot (QD) memristor. The core–shell InP/ZnS QDs with quasi‐type II band alignment ensures photoexcited electrons localized in InP core, photoexcited hole state distributed in the outer shell, and subsequent lifetime controlling of conductive filament under light irradiation. Systematic mechanism investigations indicate that UV photogenerated holes are accumulated on the surface of the QD film, which is consistent with rapid transfer of photogenerated holes in the core–shell InP/ZnS structure. Based on the light‐modulated effect, a reconfigurable 9 × 9 visual data storage array with a key pattern and a simple leaky integrate‐and‐fire circuit are constructed. These results suggest the potential of direct optical modulation of memory mode through energy band engineering, leading to future optoelectronic and electronic device for the implementation of neuromorphic visual system and artificial neural networks.