Low Switching Speed Research Articles

Ultrafast Self‐Powered Ti–Zn–N Photodetector‐Based Optocoupler for Power Electronics Applications

This study presents an early exploration into the application of a self‐powered photodetector based on titanium zinc nitride (TiZnN) films in power electronics, aiming to overcome inherent limitations of conventional optocouplers such as low switching speed and specific operating voltage requirements. The fabricated device demonstrates excellent performance metrics, including photosensitivity of 136, the responsivity of 3.22 mA W−1at −8 V bias, and a peak detectivity of 1.76 × 108Jones at 0 V bias. Remarkably, ultrafast rise (τs) and decay times (τd) of 0.11 and 0.10 ms, respectively, are achieved, alongside broad‐band spectral absorption characteristics. Experimental validation showcases the efficacy of the TiZnN‐based optocoupler in practical applications, notably in power electronics triggerable relay systems and AC–AC converters. Leveraging the self‐powering capability inherent to the TiZnN photodetector, this optocoupler eliminates external power source dependencies, thereby enhancing its versatility and applicability in diverse electronic systems. The rapid response time of the device and broad spectral absorption further underscore its suitability for high‐speed signal transmission across varied operating conditions. This research paves a path for developing stable, cost‐effective, and self‐powered ultrafast optocouplers, eliminating concerns about compromising electrical signal transit. These advancements hold significant implications for enhancing electronic system performance, reliability, and functionality in critical applications.

Three-Dimensional Lattice Structure to Reduce Parasitic Inductance for WBG Power Semiconductor-Based Converters

Wide bandgap (WBG) power semiconductors can achieve high efficiency and power density due to their low on-resistance and fast switching speeds. However, the fast-switching speed induces voltage to the parasitic inductance in the circuit, causing a significant overshoot in the drain-source voltage of the devices and the ringing of the drain current due to resonance with the parasitic capacitance. Thus, minimizing parasitic inductance is necessary for driving WBG power semiconductors in a stable manner. This paper proposes a three-dimensional lattice structure that reduces parasitic inductance through horizontal and vertical magnetic flux cancellations within a printed circuit board (PCB). The relationship between the magnetic flux cancellation and the parasitic inductance is analyzed, and the magnetic flux cancellation in the proposed structure is described. In addition, a practical PCB layout design procedure based on the proposed structure is provided. Simulation results demonstrate a 55.8% reduction in parasitic inductance, and experimental results show reduced overshoot and ringing at the switching transient, resulting in a 26% reduction in switching loss. As a result, the proposed method can improve the efficiency and stability of WBG device-based power converters.

Atomistic Modeling of Spin and Electron Dynamics in Two-Dimensional Magnets Switched by Two-Dimensional Topological Insulators

To design fast memory devices, we need material combinations that can facilitate fast read and write operations. We present a heterostructure comprising a two-dimensional (2D) magnet and a 2D topological insulator (TI) as a viable option for designing fast memory devices. We theoretically model the spin-charge dynamics between 2D magnets and 2D TIs. Using the adiabatic approximation, we combine the nonequilibrium Green's function method for spin-dependent electron transport and a time-quantified Monte Carlo method for simulating magnetization dynamics. We show that it is possible to switch a magnetic domain of a ferromagnet using the spin torque from spin-polarized edge states of a 2D TI. We show further that the switching of 2D magnets by TIs is strongly dependent on the interface exchange (${J}_{\mathrm{int}}$), and an optimal interface exchange, is required for efficient switching. Finally, we compare experimentally grown Cr compounds and show that Cr compounds with higher anisotropy (such as $\mathrm{Cr}{\mathrm{I}}_{3}$) result in a lower switching speed but a more stable magnetic order.

Polarization independent high-speed spatial modulators based on an electro-optic polymer and silicon hybrid metasurface

Dynamical control of the constitutive properties of a light beam is important for many applications in photonics and is achieved with spatial light modulators (SLMs). Performances of the current demonstrations, such as liquid-crystal or micro-electrical mechanical SLMs, are typically limited by low (∼kHz) switching speeds. Here, we report a high-speed SLM based on the electro-optic (EO) polymer and silicon hybrid metasurface. The specially configured metasurface can not only support a high-Q resonance and large “optical–electrical” overlap factor, but also overcome the challenge of polarization dependence in traditional EO modulators. Combined with the high EO coefficient of the polymer, a 400 MHz modulation with an RF driving source of 15 dBm has been observed in the proof-of-concept device near the wavelength of 1310 nm. The device with the desired merits of high speed, high efficiency, and micrometer size may provide new opportunities for high-speed smart-pixel imaging, free-space communication, and more.

Large Thermal Conductivity Switching in Ferroelectrics by Electric Field-Triggered Crystal Symmetry Engineering

A convenient, reversible, fast, and wide-range switching of thermal conductivity is desired for efficient heat energy management. However, traditional methods, such as temperature-induced phase transition and chemical doping, have many limitations, e.g., the lack of continuous tunability over a wide temperature range and low switching speed. In this work, a strategy of electric field-driven crystal symmetry engineering to efficiently modulate thermal conductivity is reported with first-principles calculations. By simply changing the direction of an external electric field loaded in ferroelectric PbZr0.5Ti0.5O3, near the morphotropic phase boundary composition, we obtain the largest switching of thermal conductivity for ferroelectric materials at room temperature based on the dual-phonon theory, i.e., normal and diffuson-like phonons, with three different criteria. The calculation results indicate that with decreasing crystal symmetry, the degeneracy of phonon modes reduces and the avoid-crossing behavior of phonon branches enhances, leading to the increase of diffuson-like phonons and weighted phonon-phonon scattering phase space. A thermal switch prototype based on PbZr0.5Ti0.5O3 is further shown that can protect the Li-ion battery by modulating its temperature up to 17.5 °C. Our studies would pave the way for designing next-generation thermal switch with high speed, a wide temperature range, and a large switching ratio.

Fast and Reconfigurable Logic Synthesis in Memristor Crossbar Array

Memristor is a potential basic unit for the in‐memory computing system, which is an approach to break the memory wall of the traditional computer. However, low switching speed, nonuniform device characteristics, and inefficient logic synthesis hinder the development of memristor‐based in‐memory computing. Herein, a novel Cu/α‐Si/α‐C/Pt memristor and direct resistance‐coupling logic synthesis scheme to construct high‐efficiency in‐memory computing is presented. The memristor shows excellent uniformity of low/high resistance (relative dispersion σ/μ = 4.68% and 3.28%) and SET/RESET voltage (relative dispersion σ/μ = 3.24% and 5.85%), fast switching speed (≈30 ns), good endurance (>108), and long retention (>105 s at 100 °C). Complete set of Boolean logic and some derived logic operators are efficiently implemented in the Cu/α‐Si/α‐C/Pt crossbar array. Furthermore, the reconfigurable and parallel logic synthesis is experimentally demonstrated by one‐bit full adder and parallel copy operation. This work can greatly improve the logic computing efficiency and flexibility in the memristor crossbar array.

Study on sneak path effect in self-rectifying crossbar arrays based on emerging memristive devices

The high demand for performance and energy efficiency poses significant challenges for computing systems in recent years. The memristor-based crossbar array architecture is enthusiastically regarded as a potential competitor to traditional solutions due to its low power consumption and fast switching speed. Especially by leveraging self-rectifying memristive devices, passive crossbar arrays potentially enable high memory densities. Nonetheless, due to the lack of a switching control per cell, these passive, self-rectifying memristive crossbar arrays (srMCA) suffer from sneak path current issues that limit the range of accurate operation of the crossbar array. In this work, the sneak path current issues in the passive srMCAs based on self-rectifying bipolar and complementary switching memristive devices are comparatively analyzed. Under consideration of the worst-case scenario, three reading schemes are investigated: one wordline pull-up (OneWLPU), all wordline pull-up (AllWLPU), and floating (FL) reading schemes. As a conclusion, despite different switching dynamics, both types of self-rectifying memristive devices can efficiently suppress sneak path current in the srMCAs. In the FL reading scheme, the sneak path current flowing through the unselected reversely biased memristive cells in the srMCA can be considered as an accurate estimation for the practical sneak path current in the srMCA. By analyzing the sneak path current in the srMCAs with a size up to 64 × 64, it is demonstrated that the leakage current plays a crucial role for suppressing the sneak path current, and the sneak path current via an individual cell exhibits a continuous decrease while the accumulated total sneak path current in the unselected reverse biased region is increasing with expanding the crossbar size. The comparative study on the bipolar and complementary memristive devices based srMCAs under diverse reading schemes reveals the influence of the switching dynamics on the sneak path current effect in the srMCAs, and provides a beneficial reference and feasible solutions for the future optimization of the crossbar topology with the intention of mitigating sneak path effects.

Poly(ionic liquid) Gating Materials for High-Performance Organic Thin-Film Transistors: The Role of Block Copolymer Self-Assembly at the Semiconductor Interface.

The widespread realization of wearable electronics requires printable active materials capable of operating at low voltages. Polymerized ionic liquid (PIL) block copolymers exhibit a thickness-independent double-layer capacitance that makes them a promising gating medium for the development of organic thin-film transistors (OTFTs) with low operating voltages and high switching speed. PIL block copolymer structure and self-assembly can influence ion conductivity and the resulting OTFT performance. In an OTFT, self-assembly of the PIL gate on the semiconducting polymer may differ from bulk self-assembly, which would directly influence electrical double-layer formation. To this end, we used poly{[N,N'-bis(2-octyldodecyl)-naphthalene-1,4,5,8-bis(dicarboximide)-2,6-diyl]-alt-5,5'-(2,2'-bithiophene)} (P(NDI2OD-T2)) as a model semiconductor for our OTFTs, on which our PILs exhibited self-assembly. In this study, we explore this critical interface by grazing-incidence small-angle X-ray scattering (GISAXS) and atomic force microscopy (AFM) of P(NDI2OD-T2) and a series of poly(styrene)-b-poly(1-(4-vinylbenzyl)-3-butylimidazolium-random-poly(ethylene glycol) methyl ether methacrylate) (poly(S)-b-poly(VBBI+[X]-r-PEGMA)) block copolymers with varying PEGMA/VBBI+ ratios and three different mobile anions (where X = TFSI-, PF6-, or BF4-). We investigate the thin-film self-assembly of block copolymers as a function of device performance. Overall, a mixed orientation at the interface leads to improved device performance, while predominantly hexagonal packing leads to nonfunctional devices, regardless of the anion present. These PIL gated OTFTs were characterized with a threshold voltage below 1 V, making understanding of their structure-property relationships crucial to enabling the further development of high-performance gating materials.

Novel Design of a Ternary-CMOS With Vertical-Channel Double-Gate Field-Effect Transistors

A tunneling-based ternary CMOS (T-CMOS) offering a low standby current and fast switching speed is developed using a novel device structure for field-effect transistors (FETs). In the new transistor devices, referred to as vertical-channel double-gate (VCDG)-FETs, a vertical current path from drain to source is formed on the drain, and a body placed below the drain is electrically isolated, except for the tunneling junction appearing at the drain and body interface. At the junction, most of the OFF-state current flows, which is independent of the gate voltage. Furthermore, the OFF-state current can be further reduced to the order of 10 <sup xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">−17</sup> A by employing a drain with a retrograded doping profile. In this profile, the channel–drain junction tunneling current, which varies with the gate voltage, is substantially suppressed to less than the body–drain junction tunneling current in the OFF state. In addition, an electrostatic channel controlled using double gates facilitates a small subthreshold swing (SSW) of 65 mV/dec. With p- and n-channel VCDG-FETs, a T-CMOS exhibiting three logic states is developed with a standby current on the order of 1 pA and transfer characteristics with a very narrow transition width.

Cr-doped Sb2Te materials promising for high performance phase-change random access memory

Transition metal doping is an effective strategy to improve the properties of phase-change random access memory (PCRAM), while the underlying mechanism remains to be sufficiently investigated. Herein, a Cr-doped Sb2Te film is fabricated by co-sputtering and the enhancement mechanism of Cr-doping is deeply investigated by experiments and first-principles calculations. The CrxSb2Te film exhibits excellent performances involving high crystallization temperature (238.9 °C) and good data retention (10 years @161.7 °C) for Cr0.56Sb2Te, low density change rate (3.8%) and high reversible switching speed (5 ns) for Cr0.29Sb2Te, providing a variety of options for different applications. The calculated results show that Cr atoms preferentially substitute the Sb1 site and the CrTe bonds display a stronger ionic bond character in contrast to the covalent bonded SbTe, thus improving the crystalline phase stability and crystallization temperature. Moreover, ab initio molecular dynamics simulations demonstrate that in the amorphous phase Cr atoms locate in defective octahedral coordination. Meanwhile, the homopolar SbSb wrong bond increased with Cr doping and the Cr atoms tend to form tight cluster in the amorphous phase which could benefit for the fast phase-change speed. Our present findings of Cr0.29Sb2Te PCRAM device clearly reveal the enhancement mechanism by Cr doping which provides guidance for developing high-performance PCRAM devices.

Latch and flip-flop design in QCA technology with minimum number of cells

Today, the implementation of computer systems and digital circuits is done using CMOS (Complementary Metal-Oxide Semiconductor) technology, but problems such as high-power consumption and physical limitations of CMOS have led researchers to use the emerging technology of point cellular quantum automation (QCA). The most important features of this technology are very high density, low power consumption and high switching speed. In this paper, new structures for type D latch and flip-flops in quantum-dot cellular automat technology are presented.Initially, a majority gate-based D-latch was proposed with 19 cells, a cross-sectional area of 0.01 μm2, and a delay of 0.75 clock cycles. Then, using the proposed D-latch, the reset-based D-latch is also proposed, which has better properties than the previous structures and has only 19 cells, a cross-sectional area of 0.01 μm2 and a delay of 0.75 clock cycles. Also, using the proposed latch, a D-latch with a set and reset terminals is introduced, which has 21 cells, a delay of 0.75 clock cycles and an area of 0.01 μm2. In order to show that the ability of circuits in more complex designs, k properly, the proposed latches have been used to make, 3-bit shift register. The proposed methods are simulated using QCADesigner and QCAPro tools and compared with other designs in terms of cell number, area, latency, and power consumption.

Improving Performance of Silicon Thermo-Optic Switch by Combing Spiral Phase Shifter and Optimized Pulse Driving

For the silicon photonics integrated circuits, the optical switch plays a vital role in many applications. Large scale integration requires low switching power and fast switching speed. However the switching time and switching power of silicon thermo-optic switch are typically limited to tens of micro-seconds and tens of milli-watts, respectively. In this paper, we designed and fabricated a silicon thermo-optic switch with spiral optical phase shifters, which can reduce the switching power from 21.5 mW to 8.73 mW compared to the optical switch with straight phase shifters. Furthermore, we optimized the pulse driving, we proposed the calculation formula of the pulse voltage, and the overall quantitative scheme of the pulse voltage and pulse width. By adopting the optimized pulse driving, the switching time is reduced from 27 μs to 4 μs. The proposed silicon thermo-optic switch unit with optimized pulse driving is very promising for the applications where large scale integration of optical switches is needed.

3D Pine‐Needle‐Like W18O49/TiO2 Heterostructures as Dual‐Band Electrochromic Materials with Ultrafast Response and Excellent Stability

AbstractDual‐band electrochromic (EC) smart windows, which can selectively modulate visible (VIS) and near‐infrared (NIR) light are widely regarded as one of the most attractive options to drastically reduce energy consumption in modern buildings. However, dual‐band EC smart windows still face many challenges such as weak modulation selectivity between VIS and NIR bands, low switching speed, poor durability, and high cost. Here, inspired by pine needles, a unique pine‐needle‐like (PNL) W18O49/TiO2 heterostructure is rationally constructed with W18O49 nanothorns (as branches) and TiO2 nanofibers (as backbones). The PNL‐W18O49/TiO2 heterostructures exhibit superior dual‐band EC performance in both VIS and NIR bands, which can block up to 81.4% of the VIS light at 633 nm and 91.3% of NIR at 1800 nm, and they also show extremely short bleaching/coloring time (0.9/1.2 s) and excellent stability (85% of capacity retention after 20 000 cycles) in a narrow potential window of −0.8 to 0.6 V. Besides, abundant patterned EC layers on a fluorine‐doped‐tin‐oxide‐coated conductive glass and flexible polyester conductive films can also be realized. This work provides an effective way for dual‐band EC materials’ design and their further development in smart windows and intelligent displays.

The origin of hexagonal phase and its evolution process in Ge2Sb2Te5 alloy

Ge2Sb2Te5 (GST) is the most important material for phase change random access memory (PCRAM) applications, while the formation of hexagonal (h-) phase results in low switching speed, large energy consumption, and worse endurance performance. Uncovering the formation mechanism of h-phase is beneficial for the further improvement of GST-based PCRAM devices. In this work, through advanced spherical aberration corrected transmission electron microscopy and transmission electron back-scattered diffraction technique, the mechanism of h-phase microstructure evolution is clearly clarified. We find that the vacancy ordering is more likely to appear around the grain boundary in a face-centered-cubic (f-) phase grain, which is the starting point for the generation of h-phase. More specifically, all the atoms in f-phase undergo a gradual shift into h-lattice positions to complete the f-to-h structural transition. By introducing an elemental dopant, for instance, carbon (C), the aggregation of C clusters prefers to distribute in the grain boundary area, which is the essential reason for postponing the generation and expansion of h-phase and greatly improving the thermal stability of C-GST material. In short, clarification of the origin of h-structure incubated from f-phase guides the optimization strategy of GST-based PCRAM devices.

Numerical design and optimization of a high compact, broadband optical three-mode selective converter by manipulating ITO-based controllable phase shifters integrated on silicon-on-insulator waveguides

Recently, indium tin oxide has been very attractive for thermo-optic (TO)-controlled silicon photonic devices, due to its high transparency, strong TO phase dependency, high conductivity, and CMOS compatibility. These properties enable the reduction of the gap between the silicon core and the heater, leading to a considerably low electric power consumption and high switching speed. We present an investigation of a numerical simulation to design and optimize a compact ITO microheater for tuning the TO phase shift in a proof-of-concept of a three-mode converter (TMC) with broadband and ultralow loss properties. We show that the TMC can operate the 3-dB bandwidth up to 100 nm. In addition, the designed device can attain relatively large fabrication tolerances for width and height of ±50 and ±5 nm, respectively. In addition, the proposed mode converter consumes a total power of less than 90 mW and obtains a fast switching time of less than 8 μs. Moreover, the device can be integrated into an estimated compact footprint of 8 μm × 2160 μm. Such excellent performances make ITO a strong candidate for low-loss TO phase shifters and open up an alternative method for realizing ultrafast and high-speed mode division multiplexing systems and large-scale applications.

All-optical polarization and amplitude modulation of second-harmonic generation in atomically thin semiconductors

Second-harmonic generation is of paramount importance in several fields of science and technology, including frequency conversion, self-referencing of frequency combs, nonlinear spectroscopy and pulse characterization. Advanced functionalities are enabled by modulation of the harmonic generation efficiency, which can be achieved with electrical or all-optical triggers. Electrical control of the harmonic generation efficiency offers large modulation depth at the cost of low switching speed, by contrast to all-optical nonlinear devices, which provide high speed and low modulation depth. Here we demonstrate all-optical modulation of second-harmonic generation in MoS2 with a modulation depth of close to 100% and speed limited only by the fundamental pulse duration. This result arises from a combination of D3h crystal symmetry and the deep subwavelength thickness of the sample, it can therefore be extended to the whole family of transition metal dichalcogenides to provide great flexibility in the design of advanced nonlinear optical devices such as high-speed integrated frequency converters, broadband autocorrelators for ultrashort pulse characterization, and tunable nanoscale holograms.

Carbon & boron substituted-Dibenzo[1,4]azaborinine as a quantum dot-based organic molecular single-electron device for high switching speed applications

The present work investigates the carbon & boron substituted-Dibenzo[1,4]azaborinine molecule as an island or quantum dot(QD) of an organic molecular single electron device(SED). The ‘carbon & boron substituted-Dibenzo[1,4]azaborinine(C13H9BN) as a QD’ is a modified variant of the acene group organic molecule ‘anthracene(C14H10)’, where boron atom are substitution of dangling hydrogens of middle honeycomb and nitrogen substitution of its parent molecule anthracene. Similar to anthracene, the carbon & boron substituted-Dibenzo[1,4]azaborinine is also made up of three linearly fused benzene rings, and has a planar structure with aromatic character. The carbon & boron substituted-Dibenzo[1,4]azaborinine molecule is considered as a QD owing to its impressive stability and conductance that originate from the aromaticity, making it ideal for low power electronic and high switching speed device applications. The calculations have been carried out using the tools AtomisticToolkit-Virtual Nanolab(ATK-VNL) and Gaussian09 packages, which is based on density functional theory (DFT), non-equilibrium green’s function (NEGF) formalisms and ab-initio approach. The charging energies in both isolated and SED conditions, total energy, and the charge stability diagram (CSD) as a function of bias potentials have been used to evaluate the device's efficiency. In comparison to anthracene based SED and its other acene organic molecular derivative SEDs, the proposed ‘carbon & boron substituted-Dibenzo[1,4]azaborinine as a quantum dot based organic molecular SED’ has high switching speed and power efficiency.

ZnO/graphene ambipolar transistor with low sub-threshold swing

We reported on enhanced device performance of ambipolar thin-film transistors (TFTs) with hybrid channel of Zinc oxide (ZnO) and multi-layer graphene (MLG), especially in reduced sub-threshold swing characteristics and increased carrier mobilities for the ambipolar conduction. The Raman spectroscopy and x-ray photoelectron spectroscopy (XPS) showed that the single-layer graphene could be damaged by oxidation during the ZnO growth process. In MLG, we observed that the graphene layers distant from the interface of ZnO/graphene could be protected, leading to enhanced electrical properties in ZnO/graphene hybrid TFTs. These results showed that the ZnO/MLG hybrid structure is a suitable building block to realize advanced TFTs with low power consumption and high switching speed.

Improvement of RF MEMS devices by spring constant scaling laws

The technology for radio frequency micro-electro-mechanical system (RF MEMS) is well established. In the next phase of miniaturization, RF MEMS transforming into RF nano-electro-mechanical system (NEMS) requires scaling laws. For MEMS devices, vertical scaling laws are available in the literature. However, existing scaling laws are isotropic and not valid for the majority of the MEMS devices. Like VLSI technology, the scaling in the MEMS is asymmetric and needs optimization in each direction. In the MEMS, depending upon the working principle, the scaling laws vary from device to device. In the present work, spring constant scaling laws for the electrostatic RF MEMS devices are derived given the device performance. The scaling laws are derived in such a way that existing limitations of the MEMS technology like low switching speed, high pull-in voltage, stiction, etc., are minimized and the response of the switch is improved.

Analysis and Suppression of High Speed Dv/Dt Induced False Turn-on in GaN HEMT Phase-Leg Topology

Gallium nitride high electron mobility transistor (GaN HEMT) is liable to gate false turn-on problem when the gate crosstalk voltage exceeds its threshold voltage in the widely adopted phase-leg topology due to its low threshold voltage and high switching speed. Without considering the gate loop stray inductance, gate internal resistance, nonlinearity of parasitic capacitances and power loop stray parameters, traditional false turn-on analytical method is insufficient to support accurate analysis. And it has been found that GaN HEMT gate-source parasitic capacitance C <sub xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">gs</sub> previously assumed constant is otherwise highly nonlinear and has strong impacts on the gate crosstalk voltage. This paper has measured C <sub xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">gs</sub> by vector network analyzer and constructed an accurate nonlinear model of C <sub xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">gs</sub> , based on which an accurate GaN HEMT behavior model is further fulfilled. The accuracy of the proposed behavior model has been verified by large amounts of experiment results. The proposed GaN HEMT model is used to accurately calculate gate crosstalk voltage and switching losses. Besides, false turn-on induced extra loss has been calculated and is adopted as a criterion to evaluate the severity of false turn-on and optimal design method for false turn-on suppression has been detailed further.