Short Switching Time Research Articles

High-speed Ta2O5-based threshold switching memristor for LIF neurons

Due to their high similarity to biological ion channels, low power consumption, small footprint, and the fact that they do not require reset circuits, threshold switching memristors have been intensively studied for simulating neurons in neuromorphic chips. Switching speed is one of the key challenges which limit the application of threshold switching memristors in chips. In this study, Ta2O5 threshold switching memristors with high switching speeds were prepared by doping with silver. The results show that 14 wt. % Ag doped Ta2O5 threshold switching memristors exhibit excellent bi-directional threshold switching performance, featuring fast switching speeds (<20 ns, <18 ns), low leakage currents (<10 pA), and high switching ratio (>107). According to the field nucleation theory, the rapid switching speed can be attributed to the low nucleation energy (0.26 eV) of silver within the Ta2O5 matrix, which is achieved by incorporating 14 wt. % Ag during the doping process. Based on Pspice, a LIF (leaky integrate-and-fire) neuron based on the silver nanoparticles doped Ta2O5 threshold switching memristors is built, and its firing function has been simulated. The results show that the LIF neuron with a short switching time is able to excite pulse spiking with high frequencies. These results demonstrated that the silver nanoparticles doped Ta2O5-based threshold switching memristors hold significant potential for constructing high-speed artificial neural networks.

Ku-band 300 kW high power ferrite phase shifter.

Phase shifter (PS) is a key component of a phased array antenna (PAA) system, which controls the microwave phase and realizes the antenna beam forming and scanning. A ferrite PS (FPS) is a current-controlled PS that uses the ferrite's gyromagnetic properties to realize phase shifting. It has the advantages of short phase switching time, low microwave loss, and high reliability and, therefore, has been widely used in low-power PAA systems. However, the power handling capability of the traditional Ku-band FPS is only a few kW, prohibiting FPS from being used in high-power microwave (HPM) PAA systems. Spurred by this concern, this paper proposes a new dual-toroid FPS structure with an external magnetic excitation. By optimizing the PS configuration, improving the integration process, and enhancing the performance of ferrite materials, a single FPS in the Ku band has reached the power handling capability of more than 300 kW with an insertion loss of less than -1.2 dB, the phase shift range of 0°-360°, the width less than 11.5mm, and the ability of a one-dimensional array. The FPS has the potential to be used in the PAA of an HPM system, laying a foundation for the research of the HPM PAA system.

Biomimetic Exploration and Reflection on Switchable Coordination and Narrow-Band Electrofluorochromic Devices.

Electrofluorochromic (EFC) materials and devices with controllable fluorescence properties show great application potential in advanced anticounterfeiting, information storage and display. However, the low color purity caused by the broad emission spectra and underperforming switching time of the existing EFC materials limit their application. Through biomimetic exploration and the study of reversible electrochemical responsive coordination reactions, boron-nitrogen embedded polyaromatics (B,N-PAHs) with narrow-band emission and high color purity have been successfully integrated into EFC systems, which also help to better understand the role of boron in biological activity. The EFC device achieve good performance containing quenching efficiency greater than 90% within short switching time (ton: 0.6s, toff: 2.4s), and nearly no performance change after 200 cycles test. Three primary color (red, green, and blue) EFC devices are successfully prepared. In addition, new phenomena are obtained and discussed in this biomimetic exploration of related boron reactions. The success and harvest of this exploration are expected to provide new ideas for optimizing properties and broadening applications of EFC materials. Moreover, it may provide ideas and reference significance for further exploring and understanding the function of boron compounds in biological systems.

On the enhanced electrochromic performance of nano-structured V2O5 thin films developed by substrate temperature induced orientated Growth

Electrochromic society is keen to develop devices with multicolor displays with high stability, using eco-friendly inorganic materials. In the present research, Influence of substrate temperature on the electrochromic V2O5 active electrodes deposited using automated nebulizer spray pyrolysis was examined to demonstrate V2O5 nanostructured films with good cyclic stability, high color contrast, and a robust memory effect. The structural characterization of the V2O5 thin films was conducted through R-ray diffraction and thermogravimetric analysis to assess material stability. Nanostructure morphology under different conditions was analysed using SEM and TEM. The electrochromic studies revealed that the higher optical modulation (ΔT) was achieved (with 70.8 % at 550 nm) in a very short switching time. Feature studies on V2O5 under different potentials were conducted to understand the capacitive and diffusion effects. The electrochromic response V2O5 thin films to various potentials was analysed using ex-situ XRD, elucidates phase changes from V2O5 to LiVO5 and V4O9, and a 2000-cycle CV measurement comprehended the material stability. The significantly improved electrochromic performance is primarily attributed to the nanosheet structure of the V2O5 thin films, since the structures enhance the material stability during lithium-ion intercalation/deintercalation processes.

Preparation and electrochromism of amorphous Bi-doped TiO2 film for aqueous-based electrochromic device

Amorphous Bi–TiO2 films with improved electrochromic properties have been successfully fabricated by a facile sol-gel spin-coating technology. The influence of dopant bismuth (Bi) content and sol amount on the electrochromic performance of Bi–TiO2 films was studied. The optimized Bi–TiO2 films show outstanding electrochromic properties, including wide transmittance modulation (ΔT = 74.26 % at 640 nm), short switching times (2.6 s/3 s for bleaching and coloring), and large coloration efficiency (52.77 cm2 C−1). A proton-based electrochromic device was prepared by the amorphous Bi–TiO2 film as the electrochromic film and Cu sheet as the counter electrode. The prepared device has a small operating potential range (1.0 V) in aqueous electrolyte due to the excellent electrochromic performance and high proton activity for the amorphous Bi–TiO2 film. In addition, the device shows excellent performance (ΔT = 67.41 %, 2.5 s/3.9 s for bleaching and coloring), providing an important reference value for the development of high-efficiency electrochromic device.

High‐Speed and Low‐Power 2 × 2 Thermo‐Optic Switch Based on Dual Silicon Topological Nanobeam Cavities

AbstractA 2 × 2 thermo‐optic (TO) switch using dual topological photonic crystal nanobeam (PCN) cavities on the silicon‐on‐insulator (SOI) platform is proposed and experimentally demonstrated. A Fano resonance is observed due to the interference between the topological interface state of the 1D topological PCN cavity and the Fabry‐Perot (F‐P) cavity mode formed between the two facets of the finitely long nanobeam waveguide. Thanks to the sharp rising edge of the spectral response of the Fano resonance and the high confinement of light in the topological PCN cavities, a 2 × 2 TO switch is realized with short switching time and low power consumption. The measured switching power is only 1.55 mW, and the rising time and the falling time are 3 and 5.6 µs, respectively in the on‐off switching experiments. To the best of the knowledge, this is the first time that a dual topological PCN structure is utilized to realize a high‐speed and low‐power TO switch, revealing the possibility of designing high‐performance reconfigurable optical devices and networks using topological photonics.

Effect of exceptional point on the performance of a bistable all-optical switch.

Microring cavities based on whispering-gallery modes (WGMs) have a very high-quality factor (Q) and a small mode volume, greatly improving the interaction between light and matter, which has attracted great attention in microlaser, nonlinear, and sensing fields. Plasmonics in the microcavity further enhance compression of the optical field. Recently, research on enhanced optical sensing sensitivity and low threshold laser based on exceptional points (EPs) is quite impressive. In this work, we propose a new, to our knowledge, all-optical switch by using the bistable effect under the EP of an ultra-compact plasmonic racetrack resonator and perform numerical simulations using the finite-difference time-domain (FDTD) method. The introduction of EPs further enhances the localization of the light field and thus improves the Kerr nonlinear effect of the microcavity; low threshold optical bistability is achieved. The results show that the device under an EP has a relatively lower threshold (input optical power threshold of 2.2 MW/cm2), shorter switching time (1.725 ps), and significantly improved switching contrast (17.16 dB) compared with those without EP. Our research lays the groundwork for optical switches that are chip-integrated, have low power consumption, and exhibit short switching times.

Design and synthesis of multi-coloured electrochromic and electrofluorochromic asymmetric materials by adjusting the central potential of the compounds

Carbazole and triphenylamine derivatives have become popular research topics in the field of electrochromism and electrofluorochromic due to their excellent reversible oxidative activity, reversible colour change and reversible fluorescence change during electrochemical processes. Four asymmetric carbazole-triphenylamine derivatives 6a-d were designed and synthesized. Both ultraviolet absorption (UV) spectra and fluorescence emission (PL) spectra changed with the change in voltage applied to all compounds. These compounds were fabricated into electrochromic and electrofluorochromic devices, and these devices exhibited excellent cycling stability (cycling stability remains above 95% after 11000 s), short switching time (1.1 s ∼ 1.6 s), high PL contrast (146 ∼ 172), and high colour contrast (47.2% ∼ 50.6%). All the samples fluoresced off in the oxidised state and exhibited alternating yellow-green characteristics, and fluoresced on in the reduced state while exhibiting a highly transparent and colourless state. The experimental results indicated that these materials are expected to be used for the preparation of wearable devices and transparent displays. The research demonstrated that rich color changes can be achieved by adjusting the electrochemical properties of dual redox centered materials.

Metal oxide-mixed polymer-based hybrid electrochromic supercapacitor: improved efficiency and dual band switching

The inclusion of charge storage properties in electrochromic devices (ECDs) has gained much interest and has evolved into a promising emerging energy-related field due to multifunctional smart device applications. Here, an organic–inorganic solid-state asymmetric electrochromic supercapacitor device (ESCD) containing nano-CoTiO3-mixed poly-3-hexylthiophene and WO3 as two electrodes has been designed to study electrochromic and supercapacitor properties. The electrochemical properties of CoTiO3 show a pseudocapacitive-type charge storage capability, which has been utilized to enhance the electrochromic performance of the ESCD with additional charge storage ability. The device shows charge storage properties with fast charging and slow discharging, giving very high coulombic efficiency with a specific capacitance of 6.4 mF cm−2 at 0.2 mA cm−2 current density. The device shows excellent electrochromic supercapacitive properties with a color contrast of ∼50% and a short switching time of ∼1 s at a 515 nm wavelength with excellent cyclic stability. The device exhibits the capability to cut near infrared wavelength (700 nm and 850 nm) and has a potential application as a heat filtering device. Thus, the addition of pseudocapacitive-type materials in ECDs enhances the capacitive performance along with electrochromic properties, which makes ECDs more suitable for real life applications.

All-optical ultrafast polarization switching with nonlinear plasmonic metasurfaces.

Optical switching has important applications in optical information processing, optical computing, and optical communications. The long-term pursuit of optical switch is to achieve short switching time and large modulation depth. Among various mechanisms, all-optical switching based on Kerr effect represents a promising solution. However, it is usually difficult to compromise both switching time and modulation depth of a Kerr-type optical switch. To circumvent this constraint, symmetry selective polarization switching via second-harmonic generation (SHG) in nonlinear crystals has been attracting scientists' attention. Here, we demonstrate SHG-based all-optical ultrafast polarization switching by using geometric phase controlled nonlinear plasmonic metasurfaces. A switching time of hundreds of femtoseconds and a modulation depth of 97% were experimentally demonstrated. The function of dual-channel all-optical switching was also demonstrated on a metasurface, which consists of spatially variant meta-atoms. The nonlinear metasurface proposed here represents an important platform for developing all-optical ultrafast switches and would benefit the area of optical information processing.

Fe-Co-Ni trimetallic Prussian blue analogs with tunable electrochromic energy storage properties

Prussian blue (PB) and its analogs (PBAs) have become a research hotspot in the fields of electrochemical energy storage and electrochromism due to their good reversible redox activity, and reversible color change response in different redox states. Herein, a series of trimetallic PBAs (Co/NiHCF with Co to Ni molar ratios of 1:0, 3:1, 1:1, 1:3, and 0:1) are synthesized by a facile co-precipitation method. In particular, the impact of Co to Ni molar ratio on the lithium storage and electrochromic properties of Co/NiHCF materials are systemically investigated. All five samples possess good crystallinity but the particle size decreases with the reduction of Co/Ni molar ratio. The color change, redox reaction potential, and lithium storage activity of the samples can be readily controlled by adjusting the molar ratio of Co to Ni. The lithium storage activity of the samples strengthens with the increase of Ni content in Co/NiHCF, accompanied by a decrease in redox potentials. With the increase of Ni content, the color of the Co/NiHCF film in the oxidation state changes from purple-red to orange, and finally to yellow; in the reduction state, the color of the film changes from green to light green and then to colorless. All the samples exhibit superior rate capability, excellent cycling stability, and short switching time (in the range of 1.6 to 4.3 s). The present work demonstrates a facile strategy for readily tunning the lithium storage activity, redox reaction potentials, and realizing rich color changes of PBA-based bifunctional materials.

Fully printed memristors made with MoS2 and graphene water-based inks.

2-Dimensional materials (2DMs) offer an attractive solution for the realization of high density and reliable memristors, compatible with printed and flexible electronics. In this work we fabricate a fully inkjet printed MoS2-based resistive switching memory, where graphene is used as top electrode and silver is used as bottom electrode. Memristic effects are observed only after annealing of each printed component. The printed memory on silicon shows low SET/RESET voltage, short switching times (less than 0.1 s) and resistance switching ratios of 103-105, comparable or superior to the performance obtained in devices with both printed silver electrodes on rigid substrates. The same device on Kapton shows resistance switching ratios of 102-103 and remains stable at least up to 2% of strain. The memristor resistance switching is attributed to the formation of Ag conductive filaments, which can be suppressed by integrating graphene grown by chemical vapour deposition (CVD) onto the silver electrode. Temperature-dependent electrical measurements starting from 200 K show that memristic behavior appears at a temperature of ∼300 K, confirming that an energy threshold is needed to form the conductive filament. This work shows that inkjet printing is a very powerful technique for the fabrication of 2DMs-based resistive switches onto rigid and flexible substrates.

(Invited) Switching Characteristics of GaN Power Transistors

A shorter switching time is one of the key advantages of GaN power devices over Si IGBTs. [1] In this paper, we report on the simulation of GaN power transistor switching and investigate the effect on the switching time novel design approaches ranging from the gate edge engineering (beyond just using field plates [2] for optimizing the voltage distribution in the drain-to-gate spacing to using the quantum well channel designs [3] that lead to the electron wave function penetration into wide band gap cladding layers with the commensurate increase in the breakdown voltage while keeping the advantage of high mobility in the device channel. We also report on the effect of a low conducting passivation for smoothing or even eliminating the sharp maximum of the electric field in the vicinity of the gate and field plate edges on switching time.[4] Additional contacts in the drain-to-gate spacing for the field control and variable doping implants could also decrease the switching time. Further optimization could be achieved with the perforated channel designs [5] decreasing the parasitic series resistance and improving the heat dissipation.[1] A. Tüysüz, R. Bosshard, and J. W. Kolar, erformance Comparison of a GaN GIT and a Si IGBT for High-Speed Drive Applications, Proceedings of the International Power Electronics Conference - ECCE Asia (IPEC 2014), Hiroshima, Japan, May 18-21, 2014[2] S. Karmalkar, M. S. Shur, G. Simin and M. A. Khan, Field-Plate Engineering for Heterostructure Field Effect Transistors, IEEE Trans. ED, 52, 12, pp. 2516- 2532, December (2005)[3] M. Dyakonov and M. S. Shur, Consequences of Space Dependence of Effective Mass in Heterostructures, J. Appl. Phys. Vol. 84, No. 7, pp. 3726-3730, October 1 (1998)[4] G. Simin, M. Shur and R. Gaska, SETI-0070: Semiconductor device with low-conducting field-controlling element App. No 13/396,059, November 19, 2013 as US Patent No. 8,586,997[5] G. Simin, M. Gaevski, M. Shur, R. Gaska, Perforated Channel Field Effect Transistor, US patent 9,467,105, October 11, 2016

Mechanistic Insights into Anion-Induced Electrochromism of Ru(II)-Based Metallo-Supramolecular Polymer.

The metallo-supramolecular polymer (MSP) is considered one of the most promising electrodes for electrochromic devices due to its intrinsically stable redox properties. Nevertheless, despite extensive work focusing on improving the electrochromic and electrochemical properties of MSPs, little experimental evidence exists from in-depth investigations on the anion-induced electrochromism of MSPs. Herein, Ru-based metallo-supramolecular polymer (polyRu) films with excellent electrochromic performance were fabricated through a novel electrochemical deposition method, and the electrochromic mechanism was further understood. The polyRu films possess fast reaction kinetics with a short switching time of 4.0 s (colored) and 2.8 s (bleached) and highly reversible redox properties due to the resulting impacts on the capacitive behaviors (containing surface, near-surface and intercalation pseudo-capacitance) of the perchlorate ions in the electrochromic process. Moreover, the electrochromic degradation of the polyRu films is considered to stem from the numerous nanopores in the film induced by ClO4- transport and the exchange of counter anions from Cl- to ClO4-. In addition, a physical model, revealing the transport of conduction ions and the evolution of the structure and properties of the polyRu film during the electrochromic process, is presented. It is observed that the charge balance of Ru3+ and Ru2+, achieved through the adsorption/desorption of ClO4- on the film, provides electrochromic and electrochemical reversibility to the polyRu film under positive/negative bias. Correspondingly, a transformation from polyRu·(Cl-)2n to polyRu·(ClO4-)x(Cl-)2n-x in the polyRu film is induced by a counter anion exchange from Cl- to ClO4-. Revealing the detailed perchlorate ion transfer kinetics and electrochromic mechanism in this film can offer new insights into the application of metallo-supramolecular polymers in electrochromic devices.

Granular micromagnetic HAMR model: investigation of damping dependence and parametric optimization for high performance

Heat assisted magnetic recording (HAMR) is a novel high-density magnetic recording technology that relies on thermal assist from a laser during the writing process. To achieve high writing performance, it is important to study and optimize the crucial factors affecting the magnetization reversal mechanism at elevated temperature. In this work, we use a multiscale approach that combines atomistic and micromagnetic models to study the magnetization reversal behavior in the recording medium. The atomistic model allows to parameterize accurately the macroscopic approach, which is utilized to model the system and its dynamics. We perform a parametric investigation of the switching properties as a function of the HAMR setup characteristics as well as the material properties, such as magnetic damping. The results show that high damping and moderate external fields can achieve high-performance HAMR media characterized by high switching probability, short switching time and low peak temperature. We demonstrate that switching occurs via the linear reversal mechanism. By systematic variation of the longitudinal susceptibility we force a transition to coherent reversal and demonstrate that this reduces the switching probability, showing linear reversal to be an important component within the HAMR process.

Capacitor for the voltage-surge suppression in a SiC-MOSFET half-bridge inverter

This paper explores some efforts to suppress the voltage surge appearing during the operation of a SiC-MOSFET-based half-bridge circuit in an inverter topology. The study is important to carry out, as the voltage surge problem does not come up when a Si-IGBT is used as the switching component in the half-bridge; however, some applications demand certain properties like what is found in a SiC MOSFET. Compared to Si-IGBT with rise-time/fall-time larger than 100 ns in general, the use of SiC MOSFET is preferable due to its much shorter switching time, less than 50 ns, which brings about a much lower switching loss and lower operating temperature. However, the choice of the usual electrolytic capacitor in the dc-link would produce an undesired voltage surge during the half-bridge operation. The origin of the surge is sometimes assigned to the inductance parasitic effect of the SiC-MOSFET high frequency. This research proves the benefit of a film capacitor to suppress the surge due to its lower equivalent series resistance (ESR) than that of the electrolytic capacitor. The results contribute to the consideration to take during the circuit realization in various applications, as there are not many papers yet found discussing the use of film capacitor in the dc-link of a SiC-MOSFET half-bridge inverter. This study also reveals the importance of the film capacitor placement during the design stage of SiC-MOSFET applications; moreover, motor controllers being equipped with an inverter such as described in this study have not been found yet in the market. The efforts investigated in this work would help to control the undesirable voltage spikes that frequently occur when applying a SiC-MOSFET to a half-bridge inverter design

Blue/green-to-transmissive electrochromic-supercapacitor bifunctional polymer films via electropolymerization containing 3,4-propylenedioxythiophene derivatives as novel donor units

Developing novel donor-acceptor conjugated polymers is essential to obtain desirable electrochromic properties. Herein, naphthobisthiadiazole, 2,1,3-benzothiadiazole and 2,3-dimethylquinoxaline as electron-deficient units, along with ProDOT-Me2 as an electron-rich block, to create novel donor-acceptor (D-A) type electrochromic polymers (pQWL, pBt and pDBt) for the investigation. The electrochemical/spectroelectrochemistry/colorimetry properties-structure of the ProDOT-Me2-based D-A polymers were systematically investigated. Benefiting from ProDOT-Me2 as an available donor block and matching electron-accepting units for the construction of D-A structures, pQWL and pDBt exhibited blue/green-to-transmissive with excellent electrochromic properties. The pQWL and pDBt exhibited remarkable bifunctional characteristics with reversible colors-to-high transmissive states, shorter switching times, long-term stability, good color memory, excellent coloration efficiency, low color chromaticity in the oxidation state, and large area-specific capacitance. These findings highlight the significant potential of ProDOT-Me2-based D-A polymers as versatile building units for polymer electrochromic-supercapacitor bifunctional materials.

Molecular engineering of novel D-A conjugated polymers for electrochromic energy storage devices toward enhanced performance

Donor-acceptor (D-A) type conjugated polymers with unique redox activity have been received great attention due to their widespread applications in electrochemical devices. In this work, two D-A-D type monomers (TCQH and TCQF) with similar conjugated backbone consisting of bithiophene and camphor substituted quinoxaline units were prepared and further polymerized and directly deposited on ITO glass via electrochemical polymerization. The target conjugated polymers PTCQH and PTCQF showed both electrochromism and charge/discharge behaviors during the redox process. Among them, the polymer PTCQF with additional fluoride atoms on the conjugated backbone exhibited superior performance involving a high optical contrast of 72 % at 740 nm, short switching time (colored time of 1.0 s and bleached time of 0.9 s), good coloration efficiency over 223 cm2/C, an area specific capacitance of 7.2 mF/cm2 at the current density of 0.02 mA/cm2 and a mass specific capacitance of 190F/g at the current density of 0.5 A/g, which was probably benefit from its porous structure morphology. Moreover, electrochromic energy storage devices based on these polymers were fabricated and achieved obvious color change from burgundy to grayish blue during charge/discharge process, which guaranteed their potential application in smart energy storage devices with visualized energy level.

Designing V2O5/MXene van der Waals heterostructure for complementary electrochromic dual-ion capacitor

Developing highly efficient electrochromic energy storage device (EESD) is desirable for yielding ample color variation and large electrochemical capacity from the viewpoint of practical energy-saving. However, only a single type of cation or anion traveled back and forth between the cathode and anode in conventional electrochromic devices (ECDs) results in low coloration efficiency and long switching time. Herein, for the first time, we designed a multicolor complementary electrochromic dual-ion capacitor (EDIC) based on ion insertion/extraction and doping/de-doping of the anodic and cathodic electrochromic materials, respectively, to realize the fast faradic reaction and rich color variation. Significantly, the prepared V2O5/MXene van der Waals heterostructure with improved conductivity and more “active” sites favors the charge transfer, effectively improving the switching speed and coloration efficiency. Since the excellent ion matching and synergy effect of Li+ insertion/extraction in V2O5/MXene anode and ClO4- doping/de-doping at PANI/TiO2 cathode, the complementary EDIC exhibits significant color changes, large optical modulation (51%), short switching time (2.4/7.2 s) and high coloration efficiency (111 cm2 C−1), which is much superior to traditional V2O5-based ECDs. We believe that this work provides a general strategy for building a complementary EDIC with excellent electrochromic and energy storage performances.

(Invited) Switching Characteristics of GaN Power Transistors

A shorter switching time and smaller conduction and switching losses are the key advantages of GaN power devices over Si technology. Further improvements of GaN HEMT technology will require new design approaches including SiC and even, possibly, diamond substrates, gate and drain edge engineering (beyond just using field plates) for optimizing the voltage distribution in the drain-to-gate spacing to using perforated channel design and a low conducting passivation for smoothing or even eliminating the sharp maximum of the electric field in the vicinity of the gate and field plate edges on switching time.