Electric Field Shielding Effect Research Articles

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.

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.

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.

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).

Transformation Characteristics of High-Current Vacuum Arcs With Still-Spaced Contacts Under TMF–AMF Combined Magnetic Fields

A novel double-type contact system with still-spaced contacts was proposed to offer a better arc control and a electric field shielding effect to the eroded inner contacts, especially during the capacitive interrupting process. The experimental double-type contact system consisted of the inner moving transverse magnetic field (TMF) contacts and the outer still-spaced axial magnetic field (AMF) contacts, which was called as TMF–AMF contacts. The objective of this paper is to determine the transformation characteristics of high-current vacuum arcs with still-spaced contacts under TMF–AMF combined magnetic fields. The experimental investigation includes the vacuum arcing behaviors, the arc voltage, and the arc current transformation characteristics. The arc current in the tests varied over a range from 0 to 30 kA at 50 Hz. The contacts material was CuCr25 (25% Cr). A high-speed charge-coupled device video camera was used to record the vacuum arc appearance. The experiments indicate that the vacuum arc current can transform successfully from the inner TMF contacts to the outer still-spaced AMF contacts for the novel TMF–AMF double-type contacts. The partial arc current flowed through the outer still-spaced contacts was mainly at the latter half of the vacuum arc duration and less than 50% of the total arc current. The value and polarity of the arc current also play a significant role in the arc current transformation characteristics of the TMF–AMF contacts with still-spaced contacts. Moreover, with the vacuum arc expanding to the still-spaced contacts, the variation of the Lorentz force of the arc column would weaken the rotation of the arc column and strengthen the transformation characteristics of the vacuum arc column to the still-space AMF contacts significantly.

Particle Simulation Model for Self-Field Magnetoplasmadynamic Thruster

In order to clarify the discharge principle of the self-field magnetoplasmadynamic thruster (MPDT), a two-dimensional axisymmetric particle-in-cell/Monte Carlo collision (PIC/MCC) model is proposed. The spatial distribution and the collision characteristics of discharge plasma were calculated using this model. In addition, the influence of the operation parameters on the plasma was analyzed including the voltage and mass flow rate. The effectiveness of the model was verified by comparison to the experimentally induced magnetic field. It was found that the electrons were mainly accelerated by the electric field in the cathode sheath and the electric field shielding effect of plasma was obvious in the bulk plasma region. Due to the pinch effect, the charged particles were constrained near the cathode. The results of the present work implied that the PIC/MCC model provides an approach to investigate the plasma distribution and a kinetic description of particles for the discharge of the self-field MPDT.

Porous equipotential body with heterogeneous nucleation sites: A novel 3D composite current collector for lithium metal anode

Lithium metal is an ideal anode material for lithium battery thanks to its ultra-high specific capacity and lowest redox potential. However, uncontrollable growth of lithium dendrites hinders its application due to local aggregation of lithium ions and anisotropic growth of lithium metal driven by uneven electric field distribution. Here a strategy is proposed to address this issue via utilizing porous equipotential body decorated with heterogeneous nucleation sites as advanced three-dimensional current collector. The conductive network of carbon nanofibers is recognized as a porous equipotential body, where the interior electric filed is zero due to the well-defined electric field shielding effect. In addition, copper nanoparticles as heterogeneous nucleation sites are uniformly anchored on carbon nanofibers, which guide lithium deposition evenly. As a result, lower impedance and higher Coulombic efficiency (∼97%) are achieved in modified lithium-copper cell. In particular, the cycling lifetime of modified symmetric lithium-lithium cell is expanded up to 500 cycles at extremely large current density of 50 mA cm−2.

Impact Moderation of Power Transmission Lines on the Environment by the Shielding of Trees

Dense high voltage power transmission lines limit human living space and affect the natural landscape and environment. Concerns about the environment in the corridor of high voltage power transmission lines and the occupied land area need to be addressed. Trees are a dissipative medium that can affect polarization in electric fields, leading to excitation of the induced electric field and shielding the impact of electric fields. A mathematical model for the electric field calculation of trees was established by selecting, mapping, and calculating the larch tree species in an experimental forest field at Northeast Forestry University, Heilongjiang Province, China. This study used the finite element method of equivalent excitation sources and the equivalent tree model to estimate the electric field shielding effectiveness of trees. The shielding effect of trees on the electric field of high voltage transmission lines was obvious. Planting trees reduced the transmission lines corridor width by 50.7%, and the maximum electric field in the ground decreased by 95.9%. Thus, planting trees to reduce the electric field of power transmission lines was more effective than the currently widely used method of erecting wires.

A novel multiple super junction power device structure with low specific on-resistance

A novel multiple super junction (MSJ) LDMOS power device is proposed to decrease Ron due to lateral and vertical interactions between the N-pillar and P-pillar. In the studied device: multiple layers of SJ are introduced oppositely under surface SJ; when compared with 2D-depleting of the conventional super junction (CSJ), a 3D-depleted effect is formed in the MSJ thanks to vertical electric field modulation; and, current distribution is improved by deep drain, which increases the drift doping concentration and results in a lower on-resistance. The high electric field around the drain region by substrate-assisted depleted effect is reduced due to the charge balance result from the electric field shielding effect of the bottom SJ, which causes the uniform electric field in the drift region and the high breakdown voltage. The numerical simulation results indicate that the specific on-resistance of the MSJ device is reduced by 42% compared with that of CSJ device, while maintaining a high breakdown voltage; the cell pitch of the device is 12 μm.

Conductive pulp fiber sheet-prepared waste newspaper pulp fibers treated by electroless nickel plating and its electric field shielding effect

In order to explore new applications of recovered waste paper, we prepared electrically conductive fibers by plating waste newspaper pulp (WNP) fibers. Further, we mixed them with unplated WNP fibers and filtered the mixture to obtain a conductive pulp fiber sheet, which was to be used for electromagnetic compatibility (EMC) purposes. For the plating of WNP fibers, we used an electroless nickel plating method. We also plated pulp fibers recovered from fine paper, pulp fibers recovered from milk carton, and bleached softwood kraft pulp fibers, which were used for comparison with the plated WNP fibers. All of the four types of plated, recovered waste paper pulp fibers had high conductivity, i.e., an electrical conductivity of 0.1 S/m or more and a conductance of 0.02 S or more. The conductive pulp fiber sheet made of WNP fibers had an electric field shielding effect of 30 dB or more at 10–1000 MHz, provided that the ratio of the plated WNP fibers in the sheet was 40 % or more. Therefore, our conductive WNP fiber sheet is effective in EMC.

Impedance sensor based on shielding effect for cell monolayer functional state detection

It has been established that the electric field shielding effect is observed during cell growth on impedance sensor surface. This effect is caused by cell junction communication formation and arising of impedance real part. An extent of shielding effect depends on sensor sensitive coat and increases when a width between sensor electrodes decreases

The Effect of Apertures Position on Shielding Effectiveness of Metallic Enclosures based on Modal Method of Moments

In this study, an effective numerical method suitable for determination of electric field Shielding Effectiveness (SE) of rectangular enclosure with multiple rectangular apertures is presented. Assuming appropriate electric field distribution on the aperture, Electromagnetic fields inside the enclosure are determined using rectangular cavity Green’s function. Electromagnetic fields outside the enclosure and scattered due to the aperture are obtained using the free space Green’s function. Matching the tangential magnetic field across the apertures, the integral equation with aperture fields as unknown variables is obtained. The integral equation is solved for unknown aperture fields using the Method of Moments. From the aperture fields the electromagnetic SE of the rectangular enclosure is determined. The numerical results of the proposed technique are in very good agreement with data available in the literature and experimental results. It is shown that apertures’ position and shape, aperture’ number, polarization have noticeable effect on the electric field SE.

Research of Shielding Effectiveness of Metallic Experiment Box Based on ModalMethod of Moments

In this paper, electric field shielding effectiveness (SE) of metallic experiment boxwith aperturesilluminated by vertical polarization plane wave has been studied by using modal method of moment technique. Electric field SE has been calculated at three different points on the same plane inside enclosure. The numerical results of the proposed technique are in very good agreement with data available in the literature and experimental results. It is shown that apertures position, aperture number and calculation points have noticeable effect on the electric field SE,four apertures is a better select to improve the shielding ability of an enclosure than one aperture while they have the same area.

Study on the Shielding Effectiveness of a Metallic Rectangular Enclosure with Four Square Apertures having Different Position Arrays

In this paper, electric field shielding effectiveness (SE) of rectangular enclosure with four apertures illuminated by vertical polarization plane wave has been studied by using modal method of moment technique. Electric field SE of enclosure with four square apertures has been calculated at three different points on the same plane inside enclosure. The numerical results of the proposed technique are in very good agreement with data available in the literature and experimental results. It is shown that apertures’ position and aperture’ number have noticeable effect on the electric field SE.

Study of Shielding Properties of a Rectangular Enclosure with Apertures Having Different Shapes but Same Area Using Modal Method of Moments

In this study, electric field Shielding Effectiveness (SE) of rectangular enclosure with apertures illuminated by vertical polarization plane wave has been studied by using modal method of moment technique. Electric field SE of enclosure with different shape apertures but same area has been calculated at three different points inside enclosure. To achieve this, assuming appropriate electric field distribution on the aperture, fields inside the cavity are determined using rectangular cavity Green’s function. Electromagnetic fields outside the cavity and scattered due to the aperture are obtained using the free space Green’s function. Matching the tangential magnetic field across the apertures, the integral equation with aperture fields as unknown variables is obtained. A very good agreement among the results of the proposed technique, results available in the literature and experimental results is observed. The simulation results show that the electric field SE is seriously affected by calculation points, aperture shape and the number of aperture. It has been shown that usual assumption made in EMC literature that lower electric field SE near the aperture than at location inside the enclosure farther away from the aperture is not always true to square aperture at some frequency and square aperture has higher electric field SE than rectangular apertureeven though they have same area.

Investigation of Models of Grid-Like Shields Subjected to Lightning Electromagnetic Field: Experiments in the Frequency Domain

In this paper, frequency-domain measurements of magnetic and electric field shielding effectiveness of grid-like spatial shield models exposed to lightning action are presented. Scaled experimental models of nearby and direct lightning strikes are proposed. Models of single-layer and double-layer wire shields of two different mesh widths are examined. Differences between the shielding effectiveness of magnetic and electric fields are discussed. The measurement results are compared to the results of numerical simulations.

Growth of patterned and aligned carbon nanotube bundles on micro-structured substrate

Microstructures are used as inducement for growth of patterned and aligned carbon nanotube (CNT) bundles by pyrolysis of iron phthalocyanine (FePc) under H 2/Ar. The flow of mixture gas can be influenced by geometry profile of microstructure, and the distribution density of catalyst will be different related to the different microstructure. Many types of substrates with different microstructures are used in this study, and several different profiles of CNT bundles are achieved under different process conditions, especially an apical dominance like plant growth is observed under specific H 2/Ar flow rate. Through using appropriate microstructures and controlling the flow rate, the density of CNT bundles can be adjusted, which is very important for weakening electric field shielding effect.

Electronic structures of organic molecule encapsulated BN nanotubes under transverse electric field

The electronic structures of boron nitride nanotubes (BNNTs) doped by different organic molecules under a transverse electric field were investigated via first-principles calculations. The external field reduces the energy gap of BNNT, thus makes the molecular bands closer to the BNNT band edges and enhances the charge transfers between BNNT and molecules. The effects of the electric field direction on the band structure are negligible. The electric field shielding effect of BNNT to the inside organic molecules is discussed. Organic molecule doping strongly modifies the optical property of BNNT, and the absorption edge is redshifted under static transverse electric field.

The field emission properties of high aspect ratio diamond nanocone arrays fabricated by focused ion beam milling

High aspect ratio diamond nanocone arrays are formed on freestanding diamond film by means of focused ion beam (FIB) milling technology and hot-filament chemical vapor deposition (HFCVD) method. The structure and phase purity of an individual diamond nanocone are characterized by scanning electron microscopy (SEM) and micro-Raman spectroscopy. The result indicatesthat the diamond cones with high aspect ratio and small tip apex radius can be obtained by optimizing the parameters ofFIB milling and diamond growth. The diamond nanocone arrays were also used to study the electron field emission propertiesand electric field shielding effect, finding high emission current density, low threshold and weak shielding effect, all attributable to the high field enhancement factor and suitable cone density of the diamond nanocone emitter.

Self-organized carbon nanotubes grown at the grain boundary of iron-nitride

Chemical vapor deposition of carbon nanotubes (CNTs) is the most promising method for fabricating CNTs based nanodevices [1] and sensors [2] because CNTs can be selectively grown by structuring the catalyst in a predefined arrangement. However, only dense aligned CNTs can be produced using transition metal catalysts (Fe, Co, and Ni) by plasma-enhanced chemical vapor deposition (PECVD) [3]. It is well known that electric field shielding effects from closely packed arrays of nanotubes adversely affect their field emission characteristics [3] and [4]. Therefore, it is desirable to control the density of CNTs so as to reduce the electric field shielding effect from adjacent CNTs. Although the density of CNTs can be controlled by various patterning technologies [3], [4] and [5], it is still crucial to develop self-organizing techniques that do not require any pre-patterning for the growth of CNT arrays. In addition, it has been found that the nucleation and growth of CNTs may be significantly enhanced by introducing N2 or NH3 in the CVD process [6]. Although the mechanism of the enhanced CNT growth in N2/NH3 environment is not yet clear, nitriding the catalyst surface seems to play an important role in CNT growth [7] and [8]. In this work, we show that aligned CNTs are preferably grown at the grain boundaries of iron nitride (Fe–N) films. This simple growth technique may lead to the development of controllable self-assembled CNT arrays for electron emitter and sensor applications.