Negative Charge Injection Research Articles

Estimation of charge injection at Al/LDPE interface based on space charge and external current measurement

Space charge accumulation in polymer is a key problem for the electrical aging of insulation under DC condition. Space charge accumulation is strongly determined by the charge injection rate. The estimation of charge injection with steady state current contains the extraction current and is not accurate. This paper proposes a quantitative estimation method of the charge injection at the metal/polymer interface with space charge and current simultaneous measurement. A double-layer sample with a blocking layer is employed to make a quasi-unipolar condition to remove the extraction current. In addition, the displacement current is removed by considering the change in electric field on the electrode. The relationship between the electrode electric field and the pure injection current is analyzed. It is found that the square root of electric field intensity and the logarithm of injection current at the Al/LDPE (low density polyethylene) interface are linear with each other. The coefficients β for negative and positive charge injection at Al/LDPE interface are about 8.44 × 10−24 and 8.32 × 10−24, respectively. It indicates that both negative and positive charge injection at Al/LDPE interface fit the mathematical relationship of the Poole–Frenkel effect, rather than the Schottky effect which is mostly used in the study on the charge transport at polymer/metal. The negative and positive charge injection barriers are 1.23 and 1.24 eV, respectively.

Toward rational design of ceramic coatings generated on valve metals by plasma electrolytic oxidation: The role of cathodic polarisation

Plasma electrolytic oxidation (PEO) has attracted significant attention as a promising eco-friendly technology for the deposition of ceramic-like oxide coatings with superior wear- and corrosion resistance as well as biomedical, catalytic, magnetic, dielectric and optical properties. However, the industrial implementation of PEO has been hindered by a poor understanding of the mechanisms underlying plasma-assisted electrochemical coating formation. This study compares the characteristics of PEO processes on different valve metals in a dilute aqueous solution of NaOH and Na2SiO3 under pulsed unipolar and bipolar polarisation conditions. The focus is given to the influence of the nature of the valve metal on the transition to the soft sparking regime characterised by reduced energy consumption whilst yielding sintered coating materials enriched with crystalline phases. In-situ dynamic voltammetry analysis was employed to study the effects of the net current ratio and local negative charge injection using diagnostic pulses embedded in the polarisation signal. It has been demonstrated that soft sparking is a characteristic feature of valve metals such as Mg, Al, Zr and Ta that form insulating surface oxides with negligible electronic conductivity, whereas Ti and Nb form semiconducting oxides, which do not exhibit a characteristic voltage drop, although some features of spark softening were detected. This generalisation paves a way for implementation of a model known as ‘digital twin’ to the rational design of the PEO processes for deposition of the functional ceramics.

Analysis of the negative charges injected into a SiO2/SiNx stack using plasma charging technology for field‐effect passivation on a boron‐doped silicon surface

AbstractWe investigated field‐effect passivation by injecting negative charges into SiO2/SiNx stack using a plasma charge injection technique. The Si/SiO2/SiNx samples exhibited a very high flat‐band shift with a high injected negative charge density (>3.0 × 1013 cm2) after plasma negative charge injection; this density was higher than that for the well‐known Al2O3 layer. Most injected negative charges were present within approximately 90 nm of the surface of the SiNx layer deposited by plasma‐enhanced chemical vapor deposition (PECVD) when comparing the capacitance–voltage analysis results obtained while etching the SiNx film considering four assumptions of the injected negative charge distribution. The saturation current density in a 90‐ohm/sq boron emitter decreased from ~90 to 50 fA/cm2 after negative charge injection, which is equivalent to the J0e of the structure passivated with an Al2O3/SiNx stack. Six‐inch n‐type bifacial cells with an approximately 100‐ohm/sq boron emitter passivated with SiO2/SiNx displayed an approximately 0.2% increase in absolute cell efficiency after negative charge injection. In addition, n‐PERT bifacial cells with a high boron sheet resistance of ~150 ohm/sq exhibited a 1.0% or higher absolute efficiency enhancement from a relatively low precharging efficiency of approximately 19.0%. We also demonstrated that the final efficiency after charging was comparable with n‐PERT bifacial cells with Al2O3 passivation, suggesting that the proposed process is a potential low‐cost alternative method that could replace expensive Al2O3 processes.

Effect of Graphene Coating on Space Charge Characteristic of XLPE and Semiconductive Layer at Different Temperatures

DC cross-linked polyethylene (XLPE) power cables are being used recently for HV/EHV applications, the reliability of which is claimed to be significantly affected by space charge accumulation in the insulating material. Many methods have been provided for limiting the injection and accumulation of space charge. In the paper, three kinds of specimens with graphene coating applied on a sandwich composed of XLPE and semiconductive layer were made. Space charge distribution of specimens was measured at 10 kV/mm and 40 kV/mm under room temperature and 60 °C. The measurement results show that positive charges are injected and accumulate in reference XLPE specimen. Negative charge accumulates in XLPE, and the quantity of positive charge injected from anode is significantly reduced, when graphene is coated on the semiconductive side. Little space charge is injected into XLPE coated with graphene, and positive charge accumulates near the interface between XLPE and electrode, which lowers electric field near the anode. Graphene layer introduced deeper trap distribution, thus making difficult negative charge injection from the cathode into XLPE.

Asymmetric injection and distribution of space charges in propylene carbonate under impulse voltage

Space charge can distort the electric field in high voltage stressed liquid dielectrics and lead to breakdown. Observing the evolution of space charge in real time and determining the influencing factors are of considerable significance. The spatio-temporal evolution of space charge in propylene carbonate, which is very complex under impulse voltage, was measured in this study through the time-continuous Kerr electro-optic field mapping measurement. We found that the injection charge from a brass electrode displayed an asymmetric effect; that is, the negative charge injection near the cathode lags behind the positive charge injection near the anode. Physical mechanisms, including charge generation and drift, are analyzed, and a voltage-dependent saturated drift rectification model was established to explain the interesting phenomena. Mutual validation of models and our measurement data indicated that a barrier layer, which is similar to metal-semiconductor contact, was formed in the contact interface between the electrode and propylene carbonate and played an important role in the space charge injection.

Emulsion Electrospinning of Polytetrafluoroethylene (PTFE) Nanofibrous Membranes for High-Performance Triboelectric Nanogenerators.

Electrospinning is a simple, versatile technique for fabricating fibrous nanomaterials with the desirable features of extremely high porosities and large surface areas. Using emulsion electrospinning, polytetrafluoroethylene/polyethene oxide (PTFE/PEO) membranes were fabricated, followed by a sintering process to obtain pure PTFE fibrous membranes, which were further utilized against a polyamide 6 (PA6) membrane for vertical contact-mode triboelectric nanogenerators (TENGs). Electrostatic force microscopy (EFM) measurements of the sintered electrospun PTFE membranes revealed the presence of both positive and negative surface charges owing to the transfer of positive charge from PEO which was further corroborated by FTIR measurements. To enhance the ensuing triboelectric surface charge, a facile negative charge-injection process was carried out onto the electrospun (ES) PTFE subsequently. The fabricated TENG gave a stabilized peak-to-peak open-circuit voltage (Voc) of up to ∼900 V, a short-circuit current density (Jsc) of ∼20 mA m-2, and a corresponding charge density of ∼149 μC m-2, which are ∼12, 14, and 11 times higher than the corresponding values prior to the ion-injection treatment. This increase in the surface charge density is caused by the inversion of positive surface charges with the simultaneous increase in the negative surface charge on the PTFE surface, which was confirmed by using EFM measurements. The negative charge injection led to an enhanced power output density of ∼9 W m-2 with high stability as confirmed from the continuous operation of the ion-injected PTFE/PA6 TENG for 30 000 operation cycles, without any significant reduction in the output. The work thus introduces a relatively simple, cost-effective, and environmentally friendly technique for fabricating fibrous fluoropolymer polymer membranes with high thermal/chemical resistance in TENG field and a direct ion-injection method which is able to dramatically improve the surface negative charge density of the PTFE fibrous membranes.

Charging behavior of Al2O3 and AlN under positive and negative charge injection using a kV electron beam

Under electron irradiation, insulating materials may charge either negatively or positively depending on their electron emission properties and characteristics of the incident electrons. The electrical behavior of these materials is linked to the sign of the injected charge. The aim here is to describe an electron beam based method that can be used to study the electrical behaviors of insulators under either positive or negative charge injection. The method was tested on ceramics samples, Al2O3 and AlN. It was shown that the electrical behaviors of both materials under e-irradiation are very different according the sign of the injected charge. Negative charging results to stable space charge for Al2O3 and on the contrary it leads to a fast charge-decay for AlN. Remarkably, reversed trends are observed for positive charge injection. The practical consequences of these results are then discussed.

Space charge behavior and its modified electric field in the cross-linked polyethylene under applied voltage DC and different temperatures

Abstract In this paper, space charge behavior in dielectric material and the capacitive charge at an electrode-dielectric interface, at room temperature under an applied electric field, has been investigated. This was done for a single sample and for a combination of the sample and a non-stressed sample using the pulsed electro-acoustic (PEA) method. A negative charge injected at the dielectric interface under an electric field (polarization) and high temperatures was focused on. It was found that negative charge injection takes place under all the test conditions, and this charge can be affected by the electric field and the temperature.

Influence of moisture on space charge dynamics in multilayer oil-paper insulation

The main insulation system in HVDC transformer consists of oil-paper insulation. The formation of space charge in oil/paper insulation system can not only affect the dielectric strength, but also relate to the stability and security of HVDC transformer. Moisture has detrimental effect on the electrical breakdown strength and insulation life of oil-paper insulation. Thus a better understanding the influence of moisture on the charge distribution in multi-layer oil-paper insulation system becomes increasingly practical importance. In the present study, the space charge dynamics in three layers oil-paper insulation system with three different moisture concentrations (0.28, 1.32 and 4.96%) were investigated using the PEA technique under 6 kV. The influence of moisture on the charge distribution in multi-layer oil-paper insulation system was provided. Results show that the higher the moisture content of the oil-paper sample, the higher the mobility of the trapped charges, and the more obvious the positive charge injection and negative charge injection were observed. The negative charges can inject across the paper-paper interface near to the cathode when the moisture content increases to 4.96%. The higher moisture content of the oil-paper sample, the faster the dissipation rate of the charges trapped in the sample. Moreover, the higher mobility of the trapped charges leads to less slow moving charges trapped in the sample with higher moisture content.

Investigation of charge behavior in low viscosity silicone liquid by kerr electro-optic field measurement

From the viewpoints of less flammability and environment protection, a new type of electrical insulating liquid for power transformers is strongly required. Low viscosity silicone liquid (20 cSt) is suitable for the requirements owing to the following excellent features; high flash point, low environmental impact concerning pollution and high chemical stability. In this paper, we investigated the charge behavior under dc voltage application by direct measurement of the electric field using Kerr electro-optic method. At first, Kerr constant of 20 cSt silicone liquid was investigated. Then, the time dependence of electric field strength in silicone liquid / pressboard (PB) composite systems was measured. The time constant of the decay was much larger in silicone liquid than in mineral oil. We discussed the charge behavior based on the physical properties of silicone liquid and we suggested that the influence of negative charge injection from a negative electrode¿s surface in silicone liquid played a significant role because of the high volume resistivity.

Ab Initio Investigation about the Possibility of Ferromagnetism Induced by Boron Vacancy in BN Nanotubes

We study structural deformation, electronic states, and intrinsic magnetism induced by the cation vacancy (VB) in boron nitride nanotubes (BNNTs), in comparison with the BN sheet, using spin-polarized density functional theory. Two types of vacancy configurations are observed in tubes, depending on the nature of the vacancy and the local stress. The underlying formation mechanisms are discussed from the viewpoint of the electronic and geometrical (or stress-induced) effects. Under additional stress, the VB prefers the open configuration to the closed 5-1DB configuration, showing different properties and potential applications. Due to the strong localization, the magnetic interaction between the VB-induced moments is short-range along either the axis or the circumference, meaning the ferromagnetism is difficult to be present. The simulation of negative charge injection implies VB-defective BNNTs might be promising candidates for spin-transport devices. In addition, the effects of surrounding H and F atoms on the spin-polarized states and magnetism of defective BNNTs are also explored.

2D Device Simulation of AlGaN/GaN HFET Current Collapse Caused by Surface Negative Charge Injection

Drain collapse in AlGaN/GaN HFET is analyzed using a two-dimensional device simulator. Two-step saturation is obtained, assuming hole-trap type surface states on the AlGaN surface and a short negative-charge-injected region at the drain side of the gate. Due to the surface electric potential pinning by the surface traps, the negative charge injected region forms a constant potential like in a metal gate region and it acts as an FET with a virtual gate. The electron concentration profile reveals that the first saturation occurs by pinch-off in the virtual gate region and the second saturation occurs by the pinch-off in the metal gate region. Due to the short-channel effect of the virtual gate FET, the saturation current increases until it finally reaches the saturation current of the intrinsic metal gate FET. Current collapses with current degradation at the knee voltage in the I-V characteristics can be explained by the formation of the virtual gate.

Controlled positive and negative surface charge injection and erasure in a GaAs/AlGaAsbased microdevice by scanning probe microscopy

In this paper, we show that positive and negative charges can be injected into the surface ofSiO2/Si3N4/SiO2/GaAs/AlGaAs heterostructure material by using a biased tip of a scanning probe microscope.Furthermore, the injected charges can be erased with the same tip once grounded, workingin slow scan and contact mode. Surface potential measurements by quantitative analysis ofKelvin probe force microscopy after drawing and erasing charges at room temperature arepresented and discussed.

ANALYSES OF ELECTRIC AND FLOW FIELDS IN CHARGE INJECTION TYPE OF ELECTROSTATIC OIL FILTER

This paper presents experimental and numerical simulation results of the electric and flow fields in a charge injection type of electrostatic oil filter. A previous work has shown that flow is generated from the tips of the projections of the emitter electrode towards the smooth electrodes because of ion drag phenomenon and that the flow may detach part of the contaminant particles captured on the smooth electrodes and may be the principal cause of the saturation of the filtration speed at higher applied voltages and oil temperatures. In order to minimize the bad influence of the ion drag flow on the filter performance, it is important to be able to predict the flow in filters of various configurations by numerical simulation. Experimental results of the flow field are compared to numerical simulation results. In addition, electric potential distribution is measured and is compared between experiment and simulation. It is shown that the magnitude of the ion drag flow is increased with increasing applied voltage, is decreased with decreasing electrode spacing and is larger for negative charge injection than for positive charge injection. Similar results can be obtained by numerical simulations but the improvement of simulation accuracy is necessary.

In situ measurement of plasma charging on SiO 2 hole bottoms and reduction by negative charge injection during etching

Charging damage in the fabrication of a micro- and nanoelectronic device is one of the electrical damages during plasma etching and caused basically by a huge difference of the flux velocity distribution between positive ions and electrons toward the wafer to be processed. Beam-like positive ions are accumulated on the bottom of a miniaturized structure during etching. With the evolution of the technology node, charging damage will increase due to several factors, increase of plasma exposure time, decrease of annealing temperature, and narrow process window, etc., caused by the increase of the number of metal layers and the introduction of new materials such as low-k and high-k instead of SiO 2. The progress of a top-down nanotechnology depends on the development of in situ diagnostics regarding plasma damage to lower-level elements and on the development of charging-free plasma process. In this paper, in situ charging measurements by using a test chip and negative charge injection to the wafer by optical computerized tomography are first demonstrated. Second, we discuss the characteristics of the charging potential on the bottom of SiO 2holes during etching in a two-frequency capacitively coupled plasma (2f-CCP), and refer to the procedure to reduce the positive potential by utilizing the negative charge acceleration to the hole bottom under the artificial formation of a double-layer close to the wafer. In addition, the charging’s effect on the aspect ratio of the hole and the antenna ratio are discussed.

Design for Reliability: The RF Power LDMOSFET

The design of lateral diffused MOSFETs operating under continuous peak power in RF communication applications is one of the most demanding among semiconductor applications. This paper discusses design parameters related to the optimum performance of the transistor and constraints introduced by the fabrication process in achieving them. Nonstandard processing steps include thick pad oxides, a sinker to connect source to the bottom substrate, metal silicided gates, a source shield over the drift region, and often gold metallization for improved electromigration. Additionally, the device requires careful optimization for control of hot-carrier-related bias drift. The impact of negative charge injection in the gate oxide is to degrade the power gain and at higher output power levels, the linearity. The difficulties in assessment of the true impact of hot carriers on these parameters via measurement are highlighted. The contribution of matching impedances and class of bias on hot-carrier degradation is extracted via modeling. A ldquodesign for reliabilityrdquo approach for this product is investigated with four designs of the drift region, evaluated in terms of transconductance, on-resistance, breakdown voltage, capacitance, and hot-carrier immunity. A second-generation source shield demonstrates a tradeoff via significant reduction of feedback capacitance at a cost to transconductance. A deep drift design shows optimization in terms of gain without compromise to the hot-carrier immunity. Recent advances made in terms of packaging and electromigration are reviewed.

High-Field Degradation of Poly-Si Gate p-MOS and n-MOS Devices With Nitrided Oxides

In this paper, the authors investigate polysilicon gate MOS capacitors and MOSFET devices with nitrided oxides. These devices are known to also show a strong negative bias temperature instability (NBTI) effect. The authors analyze the dependence of oxide-trap generation in p-channel and n-channel devices on negative and positive Fowler-Nordheim (FN) charge injection stress by application of various C-V and charge pumping (CP) measurement methods yielding information on traps at different oxide locations. In the case of p-channel devices, a strong evidence for a preexistent very high oxide-trap concentration near the gate already before stress application is obtained. This feature is accompanied by a fast degradation of the p-channel devices under a negative bias stress similar to NBTI degradation. The CP measurements, which, in contrast to classical methods, are able to distinguish between actually fast interface traps and the slower near-interface oxide traps (NIOTs), showed that in all devices, a stress polarity dependence of trap generation occurs only for NIOTs and not for interface traps

Charge Storage in Corona-Charged Polypropylene Films Analyzed by LIPP and TSC Methods

Negatively corona-charged 50-/spl mu/m-thick polypropylene (PP) film is measured using laser-induced pressure pulse (LIPP) and thermally stimulated current (TSC) in order to study the charge storage mechanism in the PP film. The LIPP can reveal the space-charge distribution in the depth direction of the PP films and the TSC can be used to measure the energetic depth of the charge trap. The LIPP shows that negative charge is deposited on the charged surface of the sample. Almost all surface charges are removed by soaking the sample in ethanol. However, about 5% of the surface charge is injected into the sample up to a depth of about 7 /spl mu/m from the surface. The injected charge is not removed by the dip-in-ethanol method because the ethanol does not penetrate into the sample. The injection of the surface charge increases with corona-charging temperature. Besides the negative charge injection, the injection of positive charge from the opposite surface is also observed when the sample is charged at higher than 60/spl deg/C. In addition, negative bulk charge is formed when the sample is charged at higher than 80/spl deg/C. The LIPP profile is compared with the TSC spectrum. It is shown that the space charge observed using LIPP disappears when the temperature of the sample exceeds 80/spl deg/C. However, TSC is observed at even higher than 80/spl deg/C. This indicates that the TSC is observed even after the disappearance of the space charge measured using LIPP.

Negative charge injection to a wafer in a pulsed two-frequency capacitively coupled plasma for oxide etching; diagnostics by emission-selected computerized tomography

In order to develop charging-free plasma processing, we investigated the function of negative charge injection to a SiO2 wafer, during etching in a pulsed two-frequency capacitively coupled plasma under various external conditions in CF4/Ar at low pressures, by using emission-selected computerized tomography. The formation of a negatively-charged layer by an excess negative charge in the interface close to the wafer and the degree of acceleration of negative charges were experimentally estimated through the spatiotemporal characteristics of the net excitation rate of the short-lived Ar(2p1) used as a probe. A bias pulse operation with a single positive component at the wafer during the off-phase of very high frequency (100 MHz) plasma production resulted in the most efficient formation of the negatively-charged layer close to the wafer. The influence of the external plasma conditions on the negatively-charged layer is observed in detail.

Prediction of a Radial Variation of Plasma Structure and Ion Distributions in the Wafer Interface in Two-Frequency Capacitively Coupled Plasma

Two-frequency capacitively coupled plasmas (2f-CCP) are widely used as one of the powerful tools for SiO/sub 2/ etching. We numerically performed the design of SiO/sub 2/ etching by using VicAddress. Radial variation of plasma structure and ion distributions having a direct influence on etching were investigated in a 2f-CCP in CF/sub 4/(5%)/Ar, which consists both of a power source [very high frequency (VHF) 100 MHz] for high-density plasma production and a bias source (1 MHz) for the acceleration of ions toward the wafer. Degradation of the radial uniformity was observed near the wafer edge due to the distortion of surface potential mainly caused by the nonuniformity of electron flux at a wafer. Furthermore, we proposed a way of reducing the charge build-up inside the micro trench with the aid of negative charge injection by using a pulsed operation of VHF power source, especially at the low pressure condition.