Polymer nanocomposite dielectrics with high electrocaloric effect for flexible solid-state cooling devices

Nanocomposite dielectrics show great promising application in developing next generation wearable all-solidstate cooling devices owing to the possessed advantages of high cooling efficiency, light-weight and small volume without the induced greenhouse effect or serious harm to ozone layer in the exploited refrigerants. However, low electrocaloric strength in nanocomposite dielectric is severely restricting its wide-spread application because of high applied operating voltage to improve electrocaloric effect. After addressing the chosen optimized ferroelectric ceramic and ferroelectric polymer matrix in conjunction with the analysis of crucial parameters, recent progress of electrocaloric effect(ECE) in polymer nanocomposites has been considerably reviewed. Subsequently, prior to proposing the conceptual design and devices/systems in electrocaloric nanocomposites, the existing developed devices/systems are reviewed. Finally, conclusions and prospects are conducted, including the aspects of materials chosen, structural design and key issues to be considered in improving electrocaloric effect of polymer nanocomposite dielectrics for flexible solidstate cooling devices.

Resistive Switching Behavior of Ag/Mg0.2Zn0.8O/ZnMn2O4/p^+-Si Heterostructure Devices for Nonvolatile Memory Applications

The Ag/Mg0.2Zn0.8O/ZnMn2O4/p^＋-Si heterostructure devices were fabricated by sol-gel spin coating technique and the resistive switching behavior,conduction mechanism,endurance characteristic,and retention properties were investigated.A distinct bipolar resistive switching behavior of the devices was observed at room temperature.The resistance ratio R_（HRS）/RLRS of high resistance state and low resistance state is as large as four orders of magnitude with a readout voltage of 2.0 V.The dominant conduction mechanism of the device is trap-controlled space charge limited current（SCLC）.The devices exhibit good durability under 1×10^3cycles and the degradation is invisible for more than 10^6 s.

A review of thermal rectification in solid-state devices

Thermal rectification,or the asymmetric transport of heat along a structure,has recently been investigated as a poten-tial solution to the thermal management issues that accompany the miniaturization of electronic devices.Applications of this concept in thermal logic circuits analogous to existing electronics-based processor logic have also been proposed.This review highlights some of the techniques that have been recently investigated for their potential to induce asymmetric thermal con-ductivity in solid-state structures that are composed of materials of interest to the electronics industry.These rectification ap-proaches are compared in terms of their quantitative performance,as well as the range of practical applications that they would be best suited to.Techniques applicable to a range of length scales,from the continuum regime to quantum dots,are dis-cussed,and where available,experimental findings that build upon numerical simulations or analytical predictions are also high-lighted.

Review of resistive switching mechanisms for memristive neuromorphic devices

Memristive devices have attracted intensive attention in developing hardware neuromorphic computing systems with high energy efficiency due to their simple structure,low power consumption,and rich switching dynamics resembling biological synapses and neurons in the last decades.Fruitful demonstrations have been achieved in memristive synapses neurons and neural networks in the last few years.Versatile dynamics are involved in the data processing and storage in biological neurons and synapses,which ask for carefully tuning the switching dynamics of the memristive emulators.Note that switching dynamics of the memristive devices are closely related to switching mechanisms.Herein,from the perspective of switching dynamics modulations,the mainstream switching mechanisms including redox reaction with ion migration and electronic effect have been systemically reviewed.The approaches to tune the switching dynamics in the devices with different mechanisms have been described.Finally,some other mechanisms involved in neuromorphic computing are briefly introduced.

Effect of Switching on Metal-Organic Interface Adhesion Relevant to Organic Electronic Devices

Considerable efforts are currently being devoted to investigation of metal-organic, organic-organic and organic-inorganic interfaces relevant to organic electronic devices such as organic light emitting diode (OLEDs), organic photovoltaic solar cells, organic field effect transistors (OFETs), organic spintronic devices and organic-based Write Once Read Many times (WORM) memory devices on both rigid and flexible substrates in laboratories around the world. The multilayer structure of these devices makes interfaces between dissimilar materials in contact and plays a prominent role in charge transport and injection efficiency which inevitably affect device performance. This paper presents results of an initial study on how switching between voltage thresholds and chemical surface treatment affects adhesion properties of a metal-organic (Au-PEDOT:PSS) contact interface in a WORM device. Contact and Tapping-mode Atomic Force Microscopy (AFM) gave surface topography, phase imaging and interface adhesion properties in addition to SEM/EDX imaging which showed that surface treatment, switching and surface roughness all appeared to be key factors in increasing interface adhesion with implications for increased device performance.

CMOS-compatible neuromorphic devices for neuromorphic perception and computing: a review

Neuromorphic computing is a brain-inspired computing paradigm that aims to construct efficient,low-power,and adaptive computing systems by emulating the information processing mechanisms of biological neural systems.At the core of neuromorphic computing are neuromorphic devices that mimic the functions and dynamics of neurons and synapses,enabling the hardware implementation of artificial neural networks.Various types of neuromorphic devices have been proposed based on different physical mechanisms such as resistive switching devices and electric-double-layer transistors.These devices have demonstrated a range of neuromorphic functions such as multistate storage,spike-timing-dependent plasticity,dynamic filtering,etc.To achieve high performance neuromorphic computing systems,it is essential to fabricate neuromorphic devices compatible with the complementary metal oxide semiconductor(CMOS)manufacturing process.This improves the device’s reliability and stability and is favorable for achieving neuromorphic chips with higher integration density and low power consumption.This review summarizes CMOS-compatible neuromorphic devices and discusses their emulation of synaptic and neuronal functions as well as their applications in neuromorphic perception and computing.We highlight challenges and opportunities for further development of CMOS-compatible neuromorphic devices and systems.

Recent Advances on Polyoxometalate-Based Ion-Conducting Electrolytes for Energy-Related Devices

Solid-state electrolytes have attracted considerable attention in new energyrelated devices due to their high safety and broad application platform.Polyoxometalates(POMs)are a kind of molecular-level cluster compounds with unique structures.In recent years,owing to their abundant physicochemical properties(including high ionic conductivity and reversible redox activity),POMs have shown great potential in becoming a new generation of solid-state electrolytes.In this review,an overview is investigated about how POMs have evolved as ion-conducting materials from basic research to novel solid-state electrolytes in energy devices.First,some expressive POM-based ion-conducting materials in recent years are introduced and classified,mainly inspecting their structural and functional relationship.After that,it is further focused on the application of these ionconducting electrolytes in the fields of proton exchange membranes,supercapacitors,and ion batteries.In addition,some properties of POMs(such as inherent dimension,capable of forming stable hydrogen bonds,and reversible bonding to water molecules)enable these functional POM-based electrolytes to be employed in innovative applications such as ion selection,humidity sensing,and smart materials.Finally,some fundamental recommendations are given on the current opportunities and challenges of POM-based ion-conducting electrolytes.

Colorless to black switching with high contrast ratio via the electrochemical process of a hybrid organic-inorganic perovskite

Colorless‐to‐black switching has attracted widespread attention for smart windows and multifunctional displays because they are more useful to control solar energy.However,it still remains a challenge owing to the tremendous difficulties in the design of completely reverse absorptions in transmissive and colored states.Herein,we report on an electrochemical device that can switch between colorless and black by using the electrochemical process of hybrid organic–inorganic perovskite MAPbBr_(3),which shows a high integrated contrast ratio of up to 73%from 400 to 800 nm.The perovskite solution can be used as the active layer to assemble the device,showing superior transmittance over the entire visible region in neutral states.By applying an appropriate voltage,the device undergoes reversible switching between colorless and black,which is attributed to the formation of lead and Br_(2)in the redox reaction induced by the electron transfer process in MAPbBr_(3).In addition,the contrast ratio can be modulated over the entire visible region by changing the concentration and the applied voltage.These results contribute toward gaining an insightful understanding of the electrochemical process of perovskites and greatly promoting the development of switchable devices.

Observation of Resistive Switching Memory by Reducing Device Size in a New Cr/CrO_x/TiO_x/TiN Structure

The resistive switching memory characteristics of 100 randomly measured devices were observed by reducing device size in a Cr/Cr Ox/Ti Ox/Ti N structure for the first time.Transmission electron microscope image confirmed a viahole size of 0.4 lm.A 3-nm-thick amorphous Ti Oxwith 4-nm-thick polycrystalline Cr Oxlayer was observed.A small 0.4-lm device shows reversible resistive switching at a current compliance of 300 l A as compared to other larger size devices(1–8 lm)owing to reduction of leakage current through the Ti Oxlayer.Good device-to-device uniformity with a yield of[85%has been clarified by weibull distribution owing to higher slope/shape factor.The switching mechanism is based on oxygen vacancy migration from the Cr Oxlayer and filament formation/rupture in the Ti Oxlayer.Long read pulse endurance of[105cycles,good data retention of 6 h,and a program/erase speed of 1 ls pulse width have been obtained.

Resistive switching properties of SnO_(2)nanowires fabricated by chemical vapor deposition

Resistive switching(RS)devices have great application prospects in the emerging memory field and neuromorphic field,but their stability and unclear RS mechanism limit their relevant applications.In this work,we construct a hydrogenated Au/SnO_(2)nanowire(NW)/Au device with two back-to-back Schottky diodes and investigate the RS characteristics in air and vacuum.We find that the Ion/Io ff ratio increases from 20 to 10^(4)when the read voltage decreases from 3.1 V to^(-1)V under the condition of electric field.Moreover,the rectification ratio can reach as high as 10^4owing to oxygen ion migration modulated by the electric field.The nanodevice also shows non-volatile resistive memory characteristic.The RS mechanism is clarified based on the changes of the Schottky barrier width and height at the interface of Au/SnO_(2)NW/Au device.Our results provide a strategy for designing high-performance memristive devices based on SnO_(2)NWs.

A Cu/ZnO Nanowire/Cu Resistive Switching Device

A new device has been realized using flip-chip joining two printed circuit boards(PCBs) on which zinc oxide(ZnO) nanowires were synthesized. Energy dispersive X-ray measurement has been conducted for the ZnO nanowires, confirming that Cu elements have been diffused into the nanowires during the chemical growth process. From I-V measurements, this Cu/ZnO nanowire/Cu structure exhibits a resistive tuning behaviour, which varies greatly with the frequency of the applied sinusoidal source.

Repulsive firefly algorithm-based optimal switching device placement in power distribution systems

To achieve optimal configuration of switching devices in a power distribution system,this paper proposes a repulsive firefly algorithm-based optimal switching device placement method.In this method,the influence of territorial repulsion during firefly courtship is considered.The algorithm is practically applied to optimize the position and quantity of switching devices,while avoiding its convergence to the local optimal solution.The experimental simulation results have showed that the proposed repulsive firefly algorithm is feasible and effective,with satisfying global search capability and convergence speed,holding potential applications in setting value calculation of relay protection and distribution network automation control.

A Tri-Salt Composite Electrolyte with Temperature Switch Function for Intelligently Temperature-Controlled Lithium Batteries

The intense research of lithium-ion batteries has been motivated by their successful applications in mobile devices and electronic vehicles.The emerging of intelligent control in kinds of devices brings new requirements for battery systems.The high-energy lithium batteries are expected to respond or react under different environmental conditions.In this work,a tri-salt composite electrolyte is designed with a temperature switch function for intelligently temperature-controlled lithium batteries.Specifically,the halide Li_(3)YBr_(6)together with LiTFSI and LiNO_(3)works as active fillers in a low-melting-point polymer matrix(polyethyleneglycol dimethyl ether(PEGDME)and polyethylene oxide(PEO)),which is further filled into the pre-lithiated alumina fiber skeleton.Above 60°C,the composite electrolyte exists in the liquid state and fully contacts with the working electrodes on the liquid–solid interface,effectively minimizing the interfacial resistance and leading to high discharge capacity in the cell.The electrolyte is changed into a solid state below 30°C so that the ionic conductivity is significantly reduced and the interface resistance is increased dramatically on the solid–solid interface.Therefore,by simply adjusting the temperature,the cell can be turned“ON”or“OFF”intentionally.This novel function of the composite electrolyte has enlightening significance in developing intelligently temperature-controlled lithium batteries.

Dynamic resistive switching in a three-terminal device based on phase separated manganites

A three-terminal device based on electronic phase separated manganites is suggested to produce high performance resistive switching. Our Monte Carlo simulations reveal that the conductive filaments can be formed/annihilated by reshaping the ferromagnetic metal phase domains with two cross-oriented switching voltages. Besides, by controlling the high resistance state（HRS） to a stable state that just after the filament is ruptured, the resistive switching remains stable and reversible, while the switching voltage and the switching time can be greatly reduced.

Single-molecule optoelectronic devices:physical mechanism and beyond

Single-molecule devices not only promise to provide an alternative strategy to break through the miniaturization and functionalization bottlenecks faced by traditional semiconductor devices,but also provide a reliable platform for exploration of the intrinsic properties of matters at the single-molecule level.Because the regulation of the electrical properties of single-molecule devices will be a key factor in enabling further advances in the development of molecular electronics,it is necessary to clarify the interactions between the charge transport occurring in the device and the external fields,particularly the optical field.This review mainly introduces the optoelectronic effects that are involved in single-molecule devices,including photoisomerization switching,photoconductance,plasmon-induced excitation,photovoltaic effect,and electroluminescence.We also summarize the optoelectronic mechanisms of single-molecule devices,with particular emphasis on the photoisomerization,photoexcitation,and photo-assisted tunneling processes.Finally,we focus the discussion on the opportunities and challenges arising in the single-molecule optoelectronics field and propose further possible breakthroughs.

Effects of Direct Switching Dual Bronchodilators between Dry Powder and Soft Mist Inhalers in COPD Patients

Objective: Dual bronchodilation with long-acting muscarinic antagonist and long-acting β2-agonist combinations are available worldwide in COPD patients. However, the choice of agents remains under debate. We hypothesized that switching devices between dry powder and soft mist inhalers without a wash-out period to mimic clinical practice would improve clinical symptoms and lung function. The aim of this study was to examine the effects of switching between once-daily glycopyrronium/indacaterol (GLY/IND) or umeclidinium/vilanterol (UMEC/VI), dry powder inhalers, and tiotropium/olodaterol (TIO/OLO), a soft mist inhaler, in COPD patients. Methods: This was a prospective, open-label, 8-week, observational study with follow-up. Subjects included 57 COPD patients, who attended outpatient clinics at Shizuoka General Hospital for routine check-ups between February and December 2015, receiving GLY/IND (50/110 μg) or UMEC/VI (62.5/25 μg). After an 8-week run-in period, medications were switched to TIO/OLO (5/5 μg). Study outcomes included patient’s global rating (PGR), modified MRC (mMRC), COPD assessment test (CAT), and spirometric and forced oscillatory parameters after 8 weeks. PGR used in this study was a 7-point scale ranging from 1 to 7, with 4 in the middle. Patients who consented to switch from TIO/OLO to GLY/IND or UMEC/VI were followed-up thereafter. Results: In total, 53 patients completed the study (mean age, 75 years;48 males and 5 females;GOLD 1/2/3/4 = 19/27/6/1;mMRC 0/1/2/3/4 = 14/22/12/4/1;UMEC/VI 26, GLY/IND 27). PGR, mMRC, and CAT improved in 20 (38%), 9 (17%), and 15 patients (28%), respectively. Respiratory system resistance at 5 Hz (R5), 20 Hz (R20), and the difference between R5 and R20 (R5 - R20) significantly improved. In a follow-up of 16 patients after switching from TIO/OLO to UMEC/VI (9) or GLY/IND (7), PGR, mMRC, and CAT improved in 5 (31%), 3 (12%), and 4 patients (25%), respectively, and R20 significantly improved (p = 0.011). Conclusions: Switching dual bronchodilators between dry powder and soft mist inhalers improves symptoms and airway narrowing in some COPD patients.

In-fiber photoelectric device based on graphene-coated tilted fiber grating

Graphene and related two-dimensional materials have attracted great research interests due to prominently optical and electrical properties and flexibility in integration with versatile photonic structures.Here,we report an in-fiber photoelec-tric device by wrapping a few-layer graphene and bonding a pair of electrodes onto a tilted fiber Bragg grating(TFBG)for photoelectric and electric-induced thermo-optic conversions.The transmitted spectrum from this device consists of a dense comb of narrowband resonances that provides an observable window to sense the photocurrent and the electrical injection in the graphene layer.The device has a wavelength-sensitive photoresponse with responsivity up to 11.4 A/W,allowing the spectrum analysis by real-time monitoring of photocurrent evolution.Based on the thermal-optic effect of electrical injection,the graphene layer is energized to produce a global red-shift of the transmission spectrum of the TF-BG,with a high sensitivity approaching 2.167×10^(4)nm/A^(2).The in-fiber photoelectric device,therefore as a powerful tool,could be widely available as off-the-shelf product for photodetection,spectrometer and current sensor.

A review of neutral pH polymer electrolytes for electrochemical capacitors:Transitioning from liquid to solid devices

The development of neutral pH polymer electrolytes has enabled high-performance solid-state,thin,and flexible electrochemical capacitors(ECs)to provide power for future consumer electronics and Internet-of-Thing devices.Notwithstanding their promising prospect,there is still some lack of understandings or disconnections from fundamental science to practical applications of these electrolytes.In this review,we provide an overview of stateof-the-art studies on ECs with neutral pH electrolytes in both liquid and solid configurations.Starting from the fundamental studies on the voltage window and ion conduction of salt species in liquid solution to polymer electrolytes,key considerations in developing neutral pH polymer electrolytes are discussed.The performance of the polymer electrolytes along with their enabled solid symmetric and asymmetric EC devices,as well as some enhanced functionalities are presented.The future directions for research on neutral pH polymer electrolytes are proposed,expected to provide reference for further enriching the fundamental knowledge and improving the device performances.

The effects of substrate temperature on ZnO-based resistive random access memory devices

Ag/ZnO/Zn/Pt structure resistive switching devices are prepared by radio frequency magnetron sputtering. The ZnO thin films are grown at room temperature and 400 ℃ substrate temperature, respectively. By comparing the data, we find that the latter device displayed better stability in the repetitive switching cycle test, and the resistance ratio between a high resistance state and a low resistance state is correspondingly increased. After 104-s storage time measurement, this device exhibits a good retention property. Moreover, the operation voltages are very low： -0.3 V/-0.7 V （OFF state） and 0.3 V （ON state）. A high-voltage forming process in the initial state is not required, and a multistep reset process is demonstrated.

Power Semiconductor Devices-an Enabling Technology for Future High Efficient and High Power Density Power Conversion Systems

Power semiconductor devices are the key technology driver for all power electronic system engineering.The main development trend for power devices is going towards higher power handling capability at even smaller Sivolume, faster switching performance,advanced ruggedness and reliability at elevated operating temperature and extended SOA diagrams.To cover all applications in the various fields of industry,consumer,computing and automotive the device optimization is different for low voltage power MOSFET,for high voltage MOSFET,for plasma modulated devices and components based on wide bandgap(WB) material.In the paper,the main development trends will be described and discussed.