Electric Field Shielding Research Articles

Ultrafast creation of a light-induced semimetallic state in strongly excited 1T-TiSe2.

Screening, a ubiquitous phenomenon associated with the shielding of electric fields by surrounding charges, has been widely adopted as a means to modify a material's properties. While most studies have relied on static changes of screening through doping or gating thus far, here we demonstrate that screening can also drive the onset of distinct quantum states on the ultrafast timescale. By using time- and angle-resolved photoemission spectroscopy, we show that intense optical excitation can drive 1T-TiSe2, a prototypical charge density wave material, almost instantly from a gapped into a semimetallic state. By systematically comparing changes in band structure over time and excitation strength with theoretical calculations, we find that the appearance of this state is likely caused by a dramatic reduction of the screening length. In summary, this work showcases how optical excitation enables the screening-driven design of a nonequilibrium semimetallic phase in TiSe2, possibly providing a general pathway into highly screened phases in other strongly correlated materials.

The role of а buffer layer at the contact with silicon in structures with an insulating gap made of a material replacing SiO2

The shape of high-frequency capacitance-voltage characteristics of structures with an insulating layer replacing silicon oxide is considered. It is shown that the buffer layer interaction on the interface with silicon substrates is related to the shielding of external electric fields by charges of the electron traps. It is found that the presence of two plateaus in the high-frequency capacitance-voltage characteristics does not necessarily indicate deep depletion and strong enrichment of a semiconductor. The presence of both capacitive plateaus in the case of strong screening can be explained by the pinning of the Fermi level of Si on electron traps of the buffer layer with a high concentration and a U-shaped spectrum. An algorithm is formulated for calculating the band bending in a semiconductor from the minimal values of the high-frequency capacitance of a sample in the region of depletion effects on the substrate. The theoretical construction was used for determining the characteristics of a structure with an insulating HfO2 layer and it was shown that in this case the buffer layer almost completely shields external electric fields, which prevents significant band bending in the silicon substrate.

(Invited) Benchmarking of Beyond the State-of-the-Art Vertical GaN Devices

In this paper theoretical benchmarking of semi-vertical and vertical gallium nitride (GaN) MOSFETs with rated voltage of 1.2 kV to 3.3 kV is performed against silicon carbide (SiC) devices. Limitations of the semi-vertical and vertical state-of-the-art GaN structures have been investigated by simulations. Specific design features and technology requirements for realization of high voltage vertical GaN MOSFETs are discussed and implemented in simulated structures. The main modifications to the structures are reduced cell pitch and introduction of electric field shielding implantation and thick oxide at the gate trench bottom and p-type implanted junction termination. The main findings are: (a) specific on-resistance of vertical GaN devices is 75% and 40% of that for 1.2 kV and 3.3 kV SiC MOSFETs, respectively, (b) semi-vertical GaN show no advantage over SiC MOSFETs for medium and high voltage devices over 1 kV, (c) vertical GaN has potential advantage for high and ultra-high voltage devices.

A novel 4H‐SiC accumulation mode MOSFET with ultra‐low specific on‐resistance and improved reverse recovery capability

AbstractA novel 1440‐V 4H‐SiC accumulation mode MOSFET (ACCUFET) with ultra‐low specific on‐resistance and improved reverse recovery performance is proposed in this article. As for the proposed SiC ACCUFET, the channel region can be completely depleted by the P‐type heavily doped polysilicon gate to build an electron barrier and realize a normally‐off device. And a Schottky barrier diode (SBD) is integrated below the trench gates on both sides, which brings the feasibility of realizing reverse conduction function of the proposed ACCUFET. Also, the p‐shield regions under the Schottky contact metal provide a good electric field shielding effect for the gate oxide. Compared with the conventional SiC trench MOSFET, the numerical simulation results show that the specific on‐resistance (Ron,sp) of the proposed ACCUFET is reduced by more than 64%. The high‐frequency figures‐of‐merit HFOM [Ron,sp × Cgd] and HFOM [Ron,sp × Qgd] of the proposed device are improved by 53.19% and 58.74%, respectively. The reverse recovery time (trr), and reverse recovery charge (Qrr) are reduced by 23.28% and 82.73%, respectively. In addition, the results also indicate that the proposed device has a better latch‐up immunity compared with the conventional SiC trench MOSFET. The excellent device performance and the simple manufacturing process provide a good prospect for the application of the proposed device.

Effects of Position of an Electric Field Shield on the Neutralization Characteristics of a Corona Discharge Air Ionizer

The effect of the position of the electric field shield on the static neutralization characteristics of an AC corona discharge air ionizer was investigated. The shield was placed at a position DES between 50 mm and 450 mm below the ionizer, and the neutralizing current density JW and the electric field EW at the work area were measured. The ratio of JW to EW was calculated since a high neutralizing current density and a low electric field are required for ionizers. The ratio was lower when the shield was located near the emitter or near the worktable. The ratio for the ionizer with the shield located at a distance DES of 250 mm shows maximum value and was 31 times higher than that for the unshielded ionizer. © 2023 Institute of Electrical Engineers of Japan. Published by Wiley Periodicals LLC.

Performance and Short-Circuit Reliability of SiC MOSFETs With Enhanced JFET Doping Design

In this article, the influence of the JFET width and JFET doping concentration on the 1.2-kV planar-gate silicon carbide (SiC) MOSFETs’ static characteristics, <italic xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">C</i> – <italic xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">V</i> characteristics, and short-circuit (SC) reliability is discussed. With the increase of the JFET width, the specific ON-resistance decreases first and then increases (but the quasi-saturated current continues to increase), the blocking voltage decreases, and the reverse capacitance increases. The SC tests under 400-V dc bus voltage are carried out to compare the SC capability of the devices. With the increase of the JFET width, the SC peak current first increases and then decreases, and the SC withstanding time keeps decreasing. The increase of peak current is due to the weaker electric field shielding effect by the P-well. With the further increase of the JFET width, the peak current decreases because the depletion layer appears in the middle position of the JFET region below the gate oxide and the channel density decreases with the wider JFET width. Compared with the winner of the traditional design, the winner with enhanced JFET doping is preferred because it achieves an increased Baliga’s figure of merit (BFOM) by 15.9% and 1/high-frequency figure of merit (HF-FOM) by 84.2% without sacrificing too much SC reliability, which is more competitive.

High Voltage Winding Internal Electric Field Shielding Structure for Medium Voltage High Frequency Transformers

In this letter, an internal electric field shielding layer for high voltage winding of medium voltage high frequency transformer used in a modular cascaded medium voltage solid state transformer is proposed. Without breaking the litz wire insulation layer, the high electric field is effectively shielded by a semiconducting layer and an unclosed copper foil spiral, which are electrically connected together. Not only the electric field in the main wall insulation is uniformed but also the peak value of the internal field is greatly reduced, which will help to achieve lower partial discharge and higher insulation reliability. With this structure, the difficulties of pouring process and electric field estimation for the litz wire winding are both avoid. Finally, a no partial discharge 100 kW medium voltage high frequency transformer prototype with 75 kV base insulation level is built and verified with the insulation tests.

Near-Field Shielding Analysis of Conformal Coating Materials for Integrated Circuits

This article analyzes a near-field shielding performance of conformal shielding materials for integrated-circuits (ICs) by experiments. Two test boards with loop-type and patch-type patterns are designed to generate magnetic-field and electric-field, respectively. These sources mimic typical electromagnetic radiations from actual ICs. For shielding analysis, single-layered conductive materials, multilayered conductive and magnetic materials, hybrid materials with a mixture of conductive and magnetic pastes are considered as conformal shielding materials, which are coated on the test boards for measurements. Magnetic-field and electric-field shielding effectiveness (SE) of the materials evaluate by measurements using loop-probe, strip-line, and gigahertz transverse electromagnetic cell at the frequency range from 300 kHz to 3 GHz. Near-field SEs measured by three methods correspond generally well with each other at the frequency range up to a few hundred MHz. At the higher frequency, the ambient EM environment can affect the accuracy of the near-field measurements by the loop-probe and strip-line. For validation, numerical simulation is fulfilled and compared with measured results. Theoretical interpretation based on the Schelkunoff's SE decomposition is also addressed.

Planar Common-Mode EMI Filter Design and Optimization for High-Altitude 100-kW SiC Inverter/Rectifier System

Silicon-carbide (SiC) devices are receiving popularity for high-power converter systems in aircraft due to many advantages over silicon counterparts. However, the electromagnetic interference (EMI) problems are more serious with the SiC devices operating at higher switching speeds and higher switching frequencies. The common-mode (CM) EMI filter design of the high-power SiC converter is especially challenging for high-altitude applications due to the harsher requirements of insulation and heat dissipation. The optimization of the parameters and physical design of a CM EMI filter in a 100-kW SiC inverter/rectifier system operating at 50 000 ft is conducted in this article to obtain the highest power density. The effect of the switching frequency on the EMI filter volume and the total power density of the converter system is analyzed. The lower breakdown voltage of air and the higher thermal resistance of natural convection make the conventional design of the CM choke infeasible at high altitudes. A printed circuit board (PCB)-based planar CM choke is designed with the consideration of partial discharge (PD) and heat dissipation at the altitude of 50 000 ft. The structure of the CM choke is optimized with embedded electric-field shielding plates, which controls the electric-field intensity in the air below 300 V/mm. The PCB windings improve the efficiency of heat dissipation at high altitudes and reduce the profile of the CM choke. A Pareto optimization is conducted to minimize the size of the choke and the volume of the final design is only 155 cm3. The experimental results show that the CM noise is reduced effectively with the CM EMI filter. PD is not observed even at the altitude of 50 000 ft and the thermal performance is excellent with a current of 190 A. With the optimization and the dedicated design of the CM EMI filter, the power density of the converter system is up to 33.3 kW/L.

The basic concepts determining electromagnetic shielding

Shielding involves much more than just putting a conductive screen in between an emitting source and a susceptible device. Starting from Maxwell's equations, the concept of electromagnetic shielding is formally explained. The physical working mechanisms behind the two basic forms of shielding, electric field and magnetic field shielding, are given, and the link between them at higher frequencies is clarified. Several aspects, like the effect of gridding or weaving a shield, the effect of the finite size of a shield, and the penetration through the metal of a shield, are discussed based on very simple canonical shielding topologies that can be solved analytically. Although the classical paradigm to explain shielding based on the notions of skin depth and eddy current is not followed, conceptual links with this classical paradigm are explained.

Influence of an external electric field on the energy dissipation at the initial stage of laser ablation

A density-dependent two-temperature model is applied to describe laser excitation and the following relaxation processes of silicon in an external electric field. Two approaches on how to describe the effects of the external electric field are presented. The first approach avoids the buildup of internal electric fields due to charge separation by assuming ambipolar diffusion and adds an additional carrier-pair current. In the second approach, electrons and holes are treated separately to account for charge separation and the resulting shielding of the external electric field inside the material. The two approaches are compared to experimental results. Both the first approach and the experimental results show similar tendencies for optimization of laser ablation in the external electric field.

Influence of Installation Mode of Sensing Board on Accuracy of Smart Voltage Measurement in Switch Cabinets

Based on the working principle of capacitor voltage transformer, this paper analyzes the influence of the installation mode of induced voltage board in the switchgear on the spatial stray capacitance by taking the switchgear, which is widely used as the carrier. Ansys finite element analysis software is used to establish the models of the voltage sensing board under different installation modes, and the influence of environmental factors such as the position, structure and temperature of the voltage sensing board on the stray capacitance between the bus bar and the sensing board is analyzed; The three-dimensional model of electric field shield plate structure is established for simulation. The installation mode of the voltage sensing board and the influence of the shielding board on the stray capacitance are revealed.

A Novel MOS-Channel Diode Embedded in a SiC Superjunction MOSFET for Enhanced Switching Performance and Superior Short Circuit Ruggedness

In this study, a novel MOS-channel diode embedded in a SiC superjunction MOSFET (MCD SJ-MOSFET) is proposed and analyzed by means of numerical TCAD simulations. Owing to the electric field shielding effect of the P+ body and the P-pillar, the channel diode oxide thickness (tco) of MCD can be set to very thin while achieving a low maximum oxide electric field (EMOX) under 3 MV/cm. Therefore, the turn-on voltage (VF) of the proposed structure was 1.43 V, deactivating the parasitic PIN body diode. Compared with the SJ-MOSFET, the reverse recovery time (trr) and the reverse recovery charge (Qrr) were improved by 43% and 59%, respectively. Although there is a slight increase in specific on-resistance (RON), the MCD SJ-MOSFET shows very low input capacitance (CISS) and gate to drain capacitance (CGD) due to the reduced active gate. Therefore, significantly improved figures of merit RON × CGD by a factor of 4.3 are achieved compared to SJ-MOSFET. As a result, the proposed structure reduced the switching time as well as the switching energy loss (ESW). Moreover, electro-thermal simulation results show that the MCD SJ-MOSFET has a short circuit withstand time (tSC) more than twice that of the SJ-MOSFET at various DC bus voltages (400 and 600 V).

Design of liquid composite materials for shielding electromagnetic fields

This paper reports the principles of design and the examined protective properties of liquid materials for shielding the electric, magnetic, and electromagnetic fields over a wide frequency range. The materials were made on the basis of iron ore concentrate and a pigment additive, with water-dispersed and geopolymer paints used as a matrix. The tests of protective properties for the electrical and magnetic components of the electromagnetic field of industrial frequency showed that the electric field shielding coefficients at a concentration of the screening substance of 15−60 % (by weight) equaled 1.1−8.6; magnetic field – 1.2−5.3. The shielding coefficients of the material based on a water-dispersed paint are lower than those of a geopolymer one, which can be explained by the oxidation of an iron-containing component and a decrease in electrical conductivity. The shielding coefficients of the electromagnetic field with a frequency of 2.45 GHz are 1.2−7.9. The highest coefficients are inherent in the material with filler made of iron ore concentrate and titanium-containing pigment powder in a ratio of 1:1. To design materials with the required (predictable) protective properties, the relative magnetic, dielectric permeability of materials was calculated. It is shown that the obtained data are acceptably the same as the results from direct measurements of magnetic and dielectric permeability and could be used to calculate the wave resistance of the material and the predicted reflection coefficient of electromagnetic waves. Thus, there is reason to assert the need to build a database on the frequency dependence of effective magnetic and dielectric permeability in order to automate the design processes of composite materials with predefined protective properties.

Debye shield formed by track potential and transport of secondary electrons in heavy ion irradiation

Plasma created by heavy ion irradiation was studied through Debye shield formation, track potential (TP), and the transport of secondary electrons. The Debye shield addressed here is expected to be useful for damage evaluation of the target. Here, the Debye shield is the electric-field shield produced by electrons surrounding locally positioned ions, and the TP is the potential created from the electric field near the incident ion's path (IP). To study the Debye shield formation, the probability (Pset) of secondary electrons escaping the TP was simulated. It was found that (i) the electron densities, which form the Debye shield, resulting from simulation near the IP are controlled by the Poisson's equation, (ii) these densities are given only by a function of cross-sections of incident ion impact ionization when the incident ion energy and the number density of molecules in the target are fixed, and (iii) a simple formula derived from a solution of the Poisson's equation almost reproduces the simulated probability Pset.

Enhanced photocatalytic overall water splitting via MOF-derived tetragonal BiVO4-based solid solution

In this work, BiVO4-based solid solutions, Bi0.5Y0.5VO4, were prepared via the MOF-derived method initially. The physical and chemical properties of the Bi0.5Y0.5VO4 samples were characterized by XRD, Raman spectra, XPS, HRTEM, element mapping, UV–vis DRS spectrum, TRPL and electrochemical analysis. The results showed that Y sources will be beneficial for the generation of tetragonal phase BiVO4, which made Bi0.5Y0.5VO4 samples constructed by tetragonal Bi0.5Y0.5VO4 and amorphous Bi0.5Y0.5VO4. The ratio of the tetragonal Bi0.5Y0.5VO4 was changed if the variation of the calcined time increased, which could be ascribed to the conversion of the amorphous Bi0.5Y0.5VO4. Consequently, photocatalytic overall water splitting property was enhanced and the results exhibited that Bi0.5Y0.5VO4-10 h samples exhibited the best performance with a rate of 124.2 μmol H2 and 61.7 μmol O2 per hour. The reason could be attributed to the variation of twisting degree, which thus influencing the internal electric field of the materials. More importantly, after metallic Pt particles as co-catalysts deposited, the ratio of H2:O2 was decreased. It could be proposed that the electric field shield effect will emerge to regulate the interfacial internal electric field further, which could play an essential role in the procedure of photocatalytic water splitting, especially for the reduction procedure.

Electric field shielding of ultracold molecules

Ultracold Chemistry Because reactive collisions limit the lifetime of ultracold molecular ensembles, controlling chemical reactivity at ultralow temperatures has been a long-standing goal. Using large electric fields that trigger resonant dipolar interactions between potassium-rubidium molecules trapped in a quasi–two-dimensional geometry, Matsuda et al. report suppression of the reactive loss rate in the vicinity of the dipolar-mediated resonances by up to an order of magnitude below the background value. The proposed shielding mechanism is general and is expected to be effective in three-dimensional geometry. It could also be used for creating long-lived quantum molecular gases of other polar molecules under strong electric fields. Science , this issue p. [1324][1] [1]: /lookup/doi/10.1126/science.abe7370

Residual Image Reduction Using Electric Field Shield Metal in Plastic Organic Light-Emitting Diode Display.

A plastic organic light-emitting diode display is a device that emits light in an organic layer in proportion to the amount of current applied from a thin film transistor, which constitutes a pixel. However, it was confirmed that the residual image was shown by the operation of the thin film transistor. To suppress residual image, the effect of electric field was studied in operation of a-IGZO thin film transistor. The a-IGZO thin film transistor, in which a polyimide film was used as a substrate, was applied as a driving thin film transistor for pixel circuits in a plastic organic light-emitting diode display, and the effect of the electric field behavior inside the film on residual images was studied. Residual images were strongly connection with the electric field distribution characteristics inside the polyimide substrate, and they were reduced by introducing an electric field shield metal layer in the a-IGZO thin film transistor. The correlation between residual image generation and the operation of the a-IGZO thin film transistor was further explained through technology computer-aided design simulation (Silvaco Group Inc.).

Residual Image Suppression Through Annealing Process of Amorphous Indium Gallium Zinc Oxide Thin Film Transistor for Plastic Organic Light-Emitting Diode Display.

For the evaluation of the residual image suppression, the amorphous indium-gallium-zinc-oxide thin film transistor was manufactured with electric field shield metal on silicon oxide multi-buffer layer, without the need for a silicon crystallization process through the excimer laser process, and is advantageous for the manufacture of large-scale plastic organic light-emitting display. We conducted a study on the propensity to suppress a residual image according to the temperature of the annealing process in amorphous indium gallium zinc oxide. The evaluation divided by the ambient process temperature conditions to measure the change and restoration tendency of the gray current by the black/white current of thin film transistors, and for precise measurement of the current change intervals, the current was analyzed in 0.004 seconds per point. Through the study, residual image of amorphous Indium Gallium Zinc Oxide transistor was found to be suppressed as the temperature of the annealing crystallization increased from 250°C to 325°C, and there was no improvement effect on the 325°C or higher. The trend of threshold voltage shift of thin film transistors according to the two process temperature conditions, 250°C and 325°C, was analyzed by Two sample T analysis method, and the analysis confirmed that the trend of current deterioration is different through p-value 0.007.

Optimization approach for axisymmetric electric field cloaking and shielding

In this paper we study inverse problems of electric conductivity that arise in the design of spherical shielding or cloaking shells and other functional devices used to control static electric fields. The shells are considered consisting of a finite number of layers filled with homogeneous isotropic or anisotropic medium. The inverse problems under study are reduced to control problems with the layers electric conductivities taken as controls. A different choice of minimized functionals allows us to solve a wide range of design problems using one approach. A numerical algorithm to solve these problems is based on particle swarm optimization. Various results of numerical experiments are discussed in order to find the most effective designs. The findings obtained in this study describe a broad set of specific easy-to-manufacture structures that have the highest cloaking or shielding performance in the class of layered shells.