Space Charge Behavior Research Articles

In-Situ Space Charge Measurement System for Space Environment Monitoring

An in-situ, internal space charge measurement system for dielectric materials under irradiation has been developed by using the pulsed electroacoustic (PEA) method. This system can observe space charge profiles in dielectric materials under irradiation, and was applied to an irradiation chamber at the Office National d'Etudes et de Recherches Mrospatiales, Centre de Toulouse (ONERA-CERT), supported by Centre National d'Etudes Spatiales (CNES). Space charge profiles in a several kinds of polymeric materials were clearly observed under and after electron beam irradiations. Negative charges accumulated at the position corresponding to the energy of the electron beam in all the specimens. The in-situ observation of the internal space charge behaviour can give valuable information for the investigation of charging and discharging phenomena and of ageing mechanisms of dielectric materials used in the space.

Isothermal and Non-Isothermal DC Measurements to Analyze Space Charge Behavior in Polyamide 11

Isothermal and Non-Isothermal DC Measurements to Analyze Space Charge Behavior in Polyamide 11

Behaviour of space charge correlated with electroluminescence in cross-linked polyethylene

A fundamental study to correlate the transient space charge and electroluminescence (EL) emission in cross-linked polyethylene under high dc stress (ca 136 kV mm−1) is proposed. Space charge profiles were analysed by the pulsed electro-acoustic method under transient conditions in order to infer from where carriers are generated, how they are transported and how the space charge decays after being formed. The information is used to interpret transient EL signals obtained under similar stress conditions.It is shown that both positive and negative charges are injected from the electrodes. Injected positive and negative charges propagate with similar speed and meet in the bulk about 600 s after the application of the step voltage. A strong luminescence is observed soon after the step voltage application and decays quickly within several tens of seconds. Subsequently, the EL intensity shows a gradual increase. The first intense emission was interpreted as an interfacial phenomenon, probably a hot electron effect, associated with heterogeneities in the electrode/insulation interface. The gradual increase of the EL was correlated with the recombination of two kinds of carriers injected from both electrodes. Periodical application of the stress leads to decreasing EL intensity as a function of time, which was the result of cumulative relaxation of the field around the surface heterogeneities.

Photoinduced Gate Modulation and Temperature Dependence in the Coulomb Staircase of Organic Single Electron Tunneling Junctions

Threshold voltage shift in the Coulomb staircase induced by photoirradiation, that is, photoinduced gate modulation, was observed at a temperature of 15 K. The samples denoted by Au/PI/CuttbPc/PI/Al consisted of Kapton-type polyimide (PI) spin-coated films with copper tetra-t-butyl phthalocyanine (CuttbPc), sandwiched between Au and Al electrodes. The temperature dependence of the Coulomb staircase was also examined within the range of 15 K to 300 K. The single electron tunneling process was dominant below 150 K, whereas a thermally assisted electron conduction mechanism such as the hopping mechanism was dominant above 150 K. It was found that the photoinduced gate modulation and the temperature dependence observed in the Coulomb staircase of our junctions could be well explained by taking into account the space charge behavior at the metal/organic ultra-thin film interface.

プリント配線板用絶縁材料の空間電荷挙動と内部電界分布の観測

プリント配線板用絶縁材料の空間電荷挙動と内部電界分布の観測

Space Charge Measurements of Polyimide Films

Polyimide films have been commonly used in industries such as for an insulating material of a printed circuit board. We measured space charge profiles of a polyimide film under dc electric filed, and reported that charges were injected into the film under a dc electric field of 10 kV/mm. However, vaiours types of polyimide films have been developed with different types of monomers. In this study, we observed space charge behaviour of two types of polyimide films and found that charge injection appeared only in one type.

Proposal of Open-PEA Space Charge Measurement System

Pulsed electroacoustic (PEA) method has been widely used to observe space charge in dielectrics. The ordinary PEA unit sandwiches a specimen for applying the pulsed electric field. There have been long awaited demands to monitor space charge profiles under electron beam or radioactive rays irradiations, as well as to observe space charge behaviour during plasma processing. This paper proposes a new PEA system without a top electrode unit. The new system can measure internal space charge profiles without covering irradiation surface of specimens.

Establishment of Space Charge Measurement Technique in Samples with Variation of Temperature

The aim of this research work is to establish an accurate measurement technique using pulsed electro-acoustic method for observing a dynamic space charge behavior in insulating materials during elevating temperature under high electric stress. When the high electric stress is applied to the dielectric materials, so-called space charge accumulates in the bulk of dielectrics. It is said that space charge accumulation strongly affects the characteristics of electrical conduction and breakdown strength in dielectrics. Therefore it is necessary to observe the space charge formation in dielectric materials. It is well known that the space charge accumulation in the insulating materials strongly depends on temperature of materials. However, most of the space charge measurement has been carried out at room temperature except for a few reports. It seems that these have been still remained some difficulties for measuring the charge distribution during elevating temperature. Therefore, in this research work, we would like to establish the measurement technique for dynamic behavior of space charge accumulation in insulating materials at high temperature under high electric stress.

Use of the final thermally stimulated discharge current technique to analyze space charge behavior in dielectrics

The final thermally stimulated discharge current technique is proposed for analyzing space charge (SC) trapping/detrapping. The letter investigates the effects associated with SC behavior in polyamide 11 in an attempt to discriminate between dipolar and SC related effects. An apparent peak, located 5–13 °C above the charging temperature, and a second peak around 96 °C were observed. Both peaks scale linearly with the field revealing a similar behavior of dipolar and interfacial polarization. The peaks position and the apparent activation energy W do not change with the charging field, but are very sensitive to the previous charging/discharging times. A distribution of the apparent activation energies in a range from 0.45 to 2.20 eV is revealed for the apparent peaks. The isothermal decay of SC at 35 °C is proportional to log t, a behavior that may be characteristic for the interfacial polarization.

Short-Duration Space Charge Observation in LDPE at the Electrical Breakdown

The electrical breakdown of insulating materials is strongly affected by the formation of space charge in the bulk of materials. Many researchers have attempted to study the relationship between the space charge and the breakdown, but it has not been clarified yet. Although the pulsed electroacoustic (PEA) method has been widely used to observe the space charge profiles, few works show clear evidence of the influence of space charge on the breakdown. We have developed a new PEA system with an interval of sub-millisecond for observing the space charge distribution continuously. We succeeded to observe the space charge dynamics at the breakdown. In this paper we clarify the space charge behavior of LDPE films throughout the breakdown period.

Space charge behavior in polymer film based on increment of capacitance under AC high field

AbstractPolymer materials have excellent dielectric and insulation properties; however, those properties in AC high field region have not been known well. Recently we established an evaluation method of high‐field AC dissipation current waveform of polymer materials 1. AC dissipation current waveforms of polyethylene and polypropylene films show nonlinear distortion in AC high‐field region. This nonlinearity was thought to be related to the behavior of AC space charge formation in the sample near electrodes. The properties of space charge formed under AC high field at power frequency seem to differ from those formed under DC high field. The measurement of AC space charge distribution is not so easy due to the resolution limit of the space charge measurement.We studied the dielectric properties of biaxially oriented polypropylene (BOPP) film under AC high field up to 120 °C. It was found that tan δ, AC dissipation current (Ixr), and unbalanced component of capacitive current (ΔIxc) increased when the temperature became higher. In particular, ΔIxc increased above some threshold field and was considered to be due to the AC space charge formation. This AC space charge layer near electrode is thought to be formed due to carrier injection under AC high‐field application. Usually, the carrier mobility becomes smaller on lowering the temperature. Most of the carriers injected from the electrode are trapped near the electrode in the sample film. But in the high‐temperature region, the carrier mobility becomes larger and the carrier injection starts to increase from lower field. Many more carriers are injected from the electrode. It is thought that some of the injected carriers are trapped inside the sample film; the others go through the sample to the opposite side. © 2002 Wiley Periodicals, Inc. Electr Eng Jpn, 141(2): 8–16, 2002; Published online in Wiley InterScience (www.interscience.wiley.com). DOI 10.1002/eej.10018

Space charge behaviors of low-density polyethylene blended with polypropylene copolymer

In this study, the space charge behaviors of the blend polymers of low-density polyethylene (LDPE) and polypropylene copolymer were investigated by the pulsed electro-acoustic method (PEA) with the electrode system of aluminium/specimen/semiconductive layer. The blend specimen composed by 90wt% LDPE and 10wt% polypropylene copolymer (B10) showed a larger amount of space charge than pure LDPE (PE) under a DC field of 50MVm−1 at both 30 and 60°C. Positive carriers moved more slowly in B10 than in PE under a positive DC voltage applied to the semiconductive electrode at 30°C. DC currents were also measured under the same experimental condition as the space charge measurement. The DC current of B10 was lower than that of PE at 30°C, but higher at 60°C. The experimental results were explained by the introduction of traps by blending.

異なる低密度ポリエチレン界面における空間電荷挙動

異なる低密度ポリエチレン界面における空間電荷挙動

高温領域でのLDPEフィルムの絶縁破壊と空間電荷分布の過渡的変化

高温領域でのLDPEフィルムの絶縁破壊と空間電荷分布の過渡的変化

Space charge behaviour and corona stabilization effect in SF6 gasviewed from sequential generation of a dc partial discharge

We investigated the sequential generation characteristics of partialdischarge (PD) pulses in SF6 gas under the application of a positive dcvoltage, in order to discuss the PD mechanism based on space charge behaviourand corona stabilization effect. Highly time-resolved measurement of PDcurrent pulses enabled us to discuss the relationship between the PD chargeq and the time interval Δt of sequential PD pulses. Experimentalresults revealed that q-Δt characteristics exhibited negative andpositive correlation at small and large Δt regions, respectively.Numerical calculations of ion diffusion and ion drift verified thetime-dependent characteristics of the space charge behaviour and the resultantcorona stabilization effect.

Transient and steady-state behavior of space charges in multilayer organic light-emitting diodes

A numerical study of space charge effects in multilayer organic light-emitting diodes (OLEDs) is presented. The method of solving the coupled Poisson and continuity equations, previously established for single-layer polymer LEDs, has been extended to treat internal organic interfaces. In addition, we consider the transient current and electroluminescence response. We discuss the accumulation of charges at internal interfaces and their signature in the transient response as well as the electric field distribution. Comparison to experimental transient data of a typical bilayer LED based on tris(8-hydroxyquinolinato)aluminum (Alq3) is provided and good agreement is found. Our results are consistent with commonly assumed operating principles of bilayer LEDs. In particular, the assumptions that the electric field is predominantly dropped across the Alq3 layer and that the electroluminescence delay time is determined by electrons passing through Alq3 to the internal interface are self-consistently supported by the results of the simulation. Moreover, the creation of emissive singlet excitons is found to be strongly confined to the Alq3 side of the internal interface and the emission zone width is dictated by the exciton diffusion length. Design principles for trilayer LEDs with improved power efficiency are also discussed.

TSC study and electro-optical properties of epoxy/acrylic polymer-dispersed liquid-crystal film in DICY thermal cure

We report on the structures and electro-optical properties of epoxy/acrylic polymer-dispersed liquid-crystal (PDLC) films. A thermal stimulated current (TSC) analysis was used to investigate the physical structures of PDLC. In the TSC spectrum of PDLC, three relaxation peaks were observed: the glass transition of the liquid crystal, the glass transition of the polymer matrix, and the ρ transition. The ρ transition represents the discharge behavior of space charges, and its intensity increased as the curing time and content of the curing agent dicyandiamide (DICY) increased. The pre-UV-cured films with different DICY contents were thermally cured at 130 °C for various periods. The electro-optical properties of PDLC, such as the contrast ratio and switching voltage, increased as the curing time of DICY, the content of DICY, or both increased. As the ambient temperature increased from 10 to 40 °C, the contrast ratio and switching voltage of PDLC gradually decreased. © 2001 John Wiley & Sons, Inc. J Polym Sci B: Polym Phys 39: 507–514, 2001

Partial discharge and breakdown mechanisms in ultra-dilute SF/sub 6//N/sub 2/ gas mixtures

With the goal of reducing SF/sub 6/ gas usage, we investigated partial discharge (PD) and breakdown (BD) mechanisms in ultra-dilute (0 to 1%) SF/sub 6//N/sub 2/ gas mixtures. The experimental results and discussions are given in this paper. In particular, we focused our research on the transition characteristics of the electrical insulation performance with an extremely small amount of SF/sub 6/ content, the PD behavior on the applied voltage, and the relation among prebreakdown streamer, return stroke and BD. Moreover, we discussed the PD and so mechanisms with reference of space charge behavior. From these results, the transition threshold at which the influence of SF/sub 6/ gas on the discharge characteristics began to appear, was clarified to be SF/sub 6/ content k=10 ppm for a total pressure of 0.1 MPa.

Effect of stretching on space charge behaviour of poly(vinyl chloride) as analysed by the thermal step method and the thermally stimulated depolarization currents technique

Effect of stretching on space charge behaviour of poly(vinyl chloride) as analysed by the thermal step method and the thermally stimulated depolarization currents technique

The effects of space charge on contrast in images obtained using the environmental scanning electron microscope

We present experimental evidence for the existence of a space charge in the environmental scanning electron microscope. Space charge formation is attributed to differences in the mobilities of negative and positive charge carriers in the imaging gas. A model is proposed for the behavior of space charge during image acquisition. The effects of space charge on images acquired using the gaseous secondary electron detector, ion current, and backscattered electron signals are interpreted using the proposed model.