High Electric Field Conduction Research Articles

Significantly enhancing the discharge efficiency of sandwich-structured polymer dielectrics at elevated temperature by building carrier blocking interface

Dielectric materials with high power densities have irreplaceable advantages in electrical energy storage. However, conventional polymer dielectrics are unable to meet the ever-increasing power demands in harsh environments. Here we report a high-temperature dielectric based on judiciously designed all-polymer sandwiched films consisting of polyimide (PI) and polyetherimides (PEIs). Due to the swelling effect of PEIs solution on the PI surface, it built a clear and complete interface with a gradient change molecular stacking structure between the PEIs and PI layers in the sandwiched film, resulting in an increase in the density of deep traps and the accumulation of space charges in the interface. It is found via direct experimental evidence that the high-field electrical conduction at high temperatures can be effectively suppressed. The sandwiched film exhibits excellent comprehensive capacitive performance even at 200 °C, e.g. a discharged energy density of 2.0 J cm−3 and a charge-discharge efficiency of 92% at 300 MV m−1. Along with facile technology compatible with roll-to-roll processing, this work also opens a new avenue to high-energy-density all-polymer dielectric for high-temperature applications by building interface carrier barrier.

Abnormal high voltage resistivity of polyvinylidene fluoride and implications for applications in high energy density film capacitors

Polyvinylidene fluoride (PVDF) based fluoropolymers are promising materials for capacitors in pulsed power applications because of their high dielectric constant compared to other polymers. High energy losses, such as conduction losses or ferroelectric losses, impose great challenges for large-scale commercialization. Here, we present a systematic study on the high field electrical conduction of biaxially oriented PVDF films. The conductivity shows a surprising initial decrease, followed by a gradual increase, with increasing electric field. The unexpected decrease in conductivity arises from ferroelectric switching, and the electric field of the transition point in conductivity is consistent with the switching field for polarization reversal. This suggests that PVDF films with pre-aligned ferroelectric domains could simultaneously exhibit reduced high field conduction losses and ferroelectric losses.

High electric field conduction in low-alkali boroaluminosilicate glass

Electrical conduction in silica-based glasses under a low electric field is dominated by high mobility ions such as sodium, and there is a transition from ionic transport to electronic transport as the electric field exceeds 108 V/m at low temperatures. Electrical conduction under a high electric field was investigated in thin low-alkali boroaluminosilicate glass samples, showing nonlinear conduction with the current density scaling approximately with E1/2, where E is the electric field. In addition, thermally stimulated depolarization current (TSDC) characterization was carried out on room-temperature electrically poled glass samples, and an anomalous discharging current flowing in the same direction as the charging current was observed. High electric field conduction and TSDC results led to the conclusion that Poole-Frenkel based electronic transport occurs in the mobile-cation-depleted region adjacent to the anode, and accounts for the observed anomalous current.

High Field Electrical Conduction and Breakdown in Solid Dielectrics: A Signal Denoising Techniques by Wavelet Transform

High Field Electrical Conduction and Breakdown in Solid Dielectrics: A Signal Denoising Techniques by Wavelet Transform

Peculiarities of high electric field conduction in p-type diamond

The electrical properties of chemical vapour deposited p-type epitaxial diamond layers are studied in high electric field conditions. The quasi-static current-voltage characteristics have been measured using transmission-line pulse method with 100 ns pulses. Reproducible impurity impact ionization avalanche breakdown occurs at a critical electrical field in the range of 100–200 kV cm−1 depending on the acceptor concentration and temperature, leading to complete ionisation of neutral impurities. The current-voltage characteristics exhibit an S-shape with the bi-stable conduction characteristic of impurity impact ionisation.

High electric field conduction in low-alkali boroaluminosilicate glass

It is important to understand electronic and ionic transport in low-alkali boroaluminosilicate glass, which is a promising dielectric for high energy density capacitors. Electric field, thickness, and temperature dependence of the leakage currents for low-alkali boroaluminosilicate (Schott AF 45) were all investigated to elucidate potential conduction mechanisms under high electric field. The bulk conductivity ranged from 10−16 S/m at room temperature to 10−12 S/m at 200 °C. It was also found that conduction significantly increased with electric field and that a single conduction mechanism does not adequately describe leakage current data over wide electric field and temperature ranges. From the systematic analysis applied here we conclude that the conduction was governed by a combination of multiple conduction mechanisms. It is suggested that ion hopping conduction by the sodium ion migration dominated the conduction at the initial stage followed by space-charge-limited conduction from sodium ion depleted regions where electric field is enhanced.

Pulsed laser deposited tetrahedral amorphous carbon with high sp3 fractions and low optical bandgaps

Amorphous carbon films with sp3 bonded carbon fractions over 70% are deposited by pulsed laser deposition. However, the optical bandgap obtained from optical transmittance and spectroscopic ellipsometry analysis shows the values to be below 1.0 eV. A wide range of measurements such as electron energy loss spectroscopy, visible Raman, spectroscopic ellipsometry, optical transmittance, and electrical characterization are performed to elucidate the bonding configurations that dictate microstructural, optical and electrical properties, and their linkage to band structure changes. It is found that stress-induced electronic localized states play an important role in the physical properties of the films deposited. The optical bandgap is shown not to be a good measure of the electrical bandgap, especially for high electric field conduction in these tetrahedral amorphous carbon films.

High Field Electrical Conduction in Pre-Formed Al–ZnS–Al ThinFilms in Metal–Insulator–Metal Devices

The high field electrical conduction mechanism for the widely used ZnSthin films in the microelectronic industry is investigated.Experimental data on the dc conduction as a function of the appliedbias for the Al–ZnS–Al devices is carefully compared with thetheoretical equations given by Schottky and Poole–Frenkel. The resultsyield the value of the coefficient of the barrier lowering compatiblewith the Schottky theory rather than the Poole–Frenkel theory, whichare also in agreement with the results reported earlier by Maekawa[Phys. Rev. Lett. 24 (1970) 1175]

Influence of antioxidants on electrical conduction in LDPE and XLPE

In order to study the effect of antioxidants on high-field electrical conduction of cross-linked polyethylene (XLPE), measurements were made of conduction currents flowing in XLPE specimens containing phenolic and sulfur-type antioxidants. Currents flowing in XLPE insulation containing these antioxidants were found to be less than those flowing in XLPE containing no antioxidants. The smallest detected current occurred in XLPE insulation containing the sulfur-type antioxidant dilauryl thiodipropionate, whereas larger currents were detected in XLPE containing phenolic antioxidants. It was also found that the magnitude of conduction current in XLPE samples containing the sulfur-type antioxidant depended on the concentration of the added antioxidant. The degree of measured crystallinity of XLPE was also found to be less than that of low-density polyethylene (LDPE), while the crystallinity was not found to be influenced by added antioxidants.

High Field Electrical Conduction in the Nanocomposite of Low-density Polyethylene and Nano-SiOX

Molecular structure and morphology of a nanocomposite of low-density polyethylene (LDPE) and nano-SiOx were studied by dynamic mechanical analysis (DMA). The storage modulus (E/) and the glass transition temperature (Tg) of the nanocomposite are higher than those of pure LDPE and vary with nano-SiOx contents in U-shapes. High field electrical conduction in the nanocomposite was investigated in the range of 293K˜353K, which is consistent with a theory based on the conventional thermally activated ionic hopping conduction. The average hopping distance for the nanocomposite containing 1wt % nano-SiOx shifts from 4.3 to 4.7 nm as the temperature increases from 293K to 353K. Space charge distribution was taken to confirm ionic hopping conduction being the dominant one in the nanocompostie. It is interesting that the relationship between nano-SiOx content and DC conduction was similar to a percolation conduction existing in a composite of conductive particles (or semi conductive particles) and a polymer. At last, high field electrical conduction mechanism in the composite was discussed on the basis of microscopic structure of the nanocomposite.

A catchment model of high electric field conduction in high concentration narrow-gap semiconductors

We present a simple model for μ(E), the field dependence of the mobility, in polar semiconductors. The resulting four-parameter expression is based on a streaming motion idea and a catchment model previously applied to layer rigidity in intercalated solids. A fitting parameter p, introduced in the catchment model, is shown to be related to the plasmon screening length. The model is applied to new data for InAs and InSb, and the fit is superior to empirical models of similar complexity. We find that energy loss via pure plasmon or coupled mode scattering is important even for intrinsic InSb.

High-field electrical conduction in polyimide films

Electrical conduction current in polyimide films has been measured at high fields (>1.4 MV cm−1) using a Au metal (M)–polyimide film (P)–p-silicon (S)–MIS structure. On the basis of the current–voltage characteristics coupled with the capacitance–voltage characteristics measured under various conditions, it is found that electrical conduction at high fields is mainly due to Fowler–Nordheim type tunneling injection of electrons from the Au gate electrode if it is negatively biased, or from the PI/Si contact if the Au gate electrode is positively biased. The conduction current is strongly dependent on the concentration and the centroid location of the trapped charges. Computer simulation reveals that the trap concentration is of the order of 6×1017 cm−3 with its centroid located near the electron injecting contact, and that the trap ledge occurs only when the concentration of the net negatively trapped electron charge is large or the location of its centroid is close to the injecting contact. The decay of the dark charging current after the application of a step-function direct current field is associated mainly with the time-dependent trap-filling process. The photoconduction under an ultraviolet light illumination is due mainly to the photogeneration of free holes. Polyimide is very sensitive to the environmental humidity. Electrical conduction current increases and the breakdown strength decreases rapidly with increasing humidity.

Nonlinear Frenkel and Poole effects

Abstract The constant of the Frenkel effect is shown to be dependent on the electric field when the coulombic centre potentials are overlapping for a certain density range. This dependence is such that the Frenkel constant asymptotically approaches the constant for a single centre as the electric field increases or the density of the centres decreases. In increasing the density of the centres, the nonlinear Frenkel effect changes into the nonlinear Poole effect, which in turn asymptotically converts into the linear effect. Tn the last case for the larger electric field this conversion occurs for higher density of the centres. An interpretation of the effect features in terms of the percolation theory is discussed. The experimental data confirming these effects are considered for an example of a high-electric field conductivity of silicon nitride layers.

ポリエチレンフィルムの高電界電気伝導におよぼすアセトフェノンの影響

ポリエチレンフィルムの高電界電気伝導におよぼすアセトフェノンの影響

High field conductivity in polypyrrole

We have measured high electric field conduction properties of polypyrrole films prepared by anodic deposition as a function of temperature. The field dependence is in reasonably good agreement with the model of intergranular tunnelling with Coulomb-like repulsion barriers. The high field results however demonstrate that pure quantum tunnelling probably does not exist at low enough temperatures. The previously observed levelling-off of conductivities as ‘temperature T tends to 0’ is most likely an artefact produced by the finite magnitude of current flowing in the system. Current filaments remove space charge barriers which otherwise would localize carriers at zero temperature ( T=0). Despite this new observation, we argue that the grain tunnelling model is still a better description than variable range hopping. We show that it is reasonable and consistent within this model to expect grains and interfaces to charge up at low temperatures and to produce energy mismatch which then requires inelastic tunnelling. At very high fields, the current has a Fowler—Nordheim tunnelling characteristic which suggests that the grain barriers are slowly varying near the maximum as one might expect.

High-field electrical conduction in thin-film sandwich structures of the metal/organic semiconductor/metal type

The investigated organic compounds are derivatives of the asparagic acid. Thin films of respective compounds were deposited from dimethylformamide solutions. The temperature dependences of the electrical conductivity and Seebeck coefficient are investigated. All compounds have semiconducting properties. The values of some characteristic parameters (activation energy, ratio of carrier mobilities, etc.) have been determined. Using sandwich cells of the type Al/organic compound/Al, the static current–voltage ( J– U) characteristics have been studied. For lower values of intensity of electric field E ( E ≅6×10 2–2×10 3 V cm −1), J– U characteristics are ohmic. At higher values of E , the current density J increases faster than linear. For E ≅10 3–10 4 V cm −1, the obtained experimental data are in good agreement with the Richardson–Schottky law. At fields E >10 5 V cm −1, the experimental points deviate more and more from Schottky characteristics in direction of larger values of J. For explanation of these behaviours, the electron transitions through and over the potential barrier at metal-organic film interface are taken into account.

High electric field conduction mechanisms in electrode poling of electro-optic polymers

We investigated electrical conduction phenomena, which occurred during high electric field electrode poling of side chain χ(2) polymers. Electric current and second harmonic intensity were measured simultaneously in poling experiments performed on samples with and without an additional inorganic poly–methyl–siloxane layer. Current densities appeared to be limited by a Schottky-type potential barrier at the electrode/insulator interface. The field dependence of the current density was found to be Schottky charge emission for medium field strengths (EPOL≤100 V/μm) whereas it was dominated by Fowler–Nordheim tunneling at higher poling fields. In the presence of the siloxane layer, a significant suppression of tunneling current was observed. This leads to a reduced probability of singular dielectric breakdown events and shifts the limit of avalanche breakdown to higher internal effective poling field strengths.

Poole–Frenkel conduction in polycrystalline diamond

High-field electrical conduction has been studied in undoped polycrystalline diamond over a wide temperature range. The current increases exponentially with the electric field with an exponential factor which increases linearly with the inverse of temperature. The activation energy of the conductivity is found to be strongly field dependent and to decrease linearly with the electric field. The experimental data support a Poole–Frenkel conduction with overlapping centers. The centers are found to be located at around 1.1 eV from the band edge with a density of about 2×1017 cm−3.

ポリパラキ.シリレン系薄膜の高電界電導と絶縁破壊

ポリパラキ.シリレン系薄膜の高電界電導と絶縁破壊

High field electrical conduction and breakdown in silicon incorporated polyethylene films

The current-voltage (I-V) characteristics of silicon-incorporated polyethylene films fabricated by plasma polymerization have been measured at very high electric fields. The experimental results show that the electric conduction at high fields is due mainly to Fowler–Nordheim type tunneling injection of holes from the anode, and that the incorporation of silicon in polyethylene creates hole traps, thus suppressing the conduction current and enhancing the breakdown strength. The amount of positive space charge resulting from the hole trapping increases with increasing magnitude and duration of the applied field for a fixed silicon content, and increases with increasing silicon content for a fixed magnitude and duration of the applied field. This positive space charge tends to suppress the actual field at the hole injecting contact and to enhance the actual field at the electron injecting contact. For fields higher than a certain critical value, the rate of the current increase with field changes rapidly. This phenomenon is attributed to the onset of double injection. This means that the contribution of the electron current to the total current becomes significant due to the gradual enhancement of the field at the electron injecting contact by the large amount of accumulated positive space charge. It is concluded that silicon incorporated in polyethylene introduces new hole traps which in turn reduces the hole mobility and creates more positive trapped space charge. The overall effect would be to reduce the conduction current and to increase the breakdown strength of the polyethylene if a proper amount of silicon is incorporated in it.