DC Electrical Breakdown Research Articles

Influence of copper thin film as an electrode on the DC electrical breakdown in the presence of Ar and air

Influence of copper thin film as an electrode on the DC electrical breakdown in the presence of Ar and air

The influence of pre-stressing on breakdown characteristics in liquid silicone rubber

Liquid silicone rubber (LSR) has increasingly been used as one kind of inner insulating material. Studies of space charge and its effect during pre-stressing and breakdown (BD) process in LSR were carried out. DC electrical breakdown field (BDF) of LSR specimens before and after DC electrical pre-stressing was measured. The space charge characteristics of LSR specimens under different DC electrical pre-stressing fields and that during the BD processes were measured by a pulsed electro-acoustic (PEA) method. It was found that the amount of homo space charges near electrodes increases obviously as a rising electric field is applied. Whether the polarity of BDF is the same as that of the pre-stressing field or not, the DC BDF of pre-stressed specimens is higher than that of specimens without pre-stressing. However, the pre-stressing does not show monotone and saturation effects, as generally occurs in the literature. In hetero BD experiments for example, with an increasing pre-stressing field, the DC BDF first increases up to 14.5% at the pre-stressing field of 25 kV/mm and then decreases. The influence of pre-stressing on the BD processes in LSR are discussed. The relationship between space charge and the DC BDF was related to the microstructure of nano-silica and LSR molecules.

Electrical stress effect on Josephson tunneling through ultrathin AlOx barrier in Nb/Al/AlOx/Nb junctions

The effect of dc electrical stress and breakdown on Josephson and quasiparticle tunneling in Nb/Al/AlOx/Nb junctions with ultrathin AlOx barriers typical for applications in superconductor digital electronics has been investigated. The junctions’ conductance at room temperature and current-voltage (I-V) characteristics at 4.2 K have been measured after the consecutive stressing of the tunnel barrier at room temperature. Electrical stress was applied using current ramps with increasing amplitude ranging from 0 to ∼1000Ic corresponding to voltages across the barrier up to ∼0.65 V, where Ic is the Josephson critical current. A very soft breakdown has been observed with polarity-dependent breakdown current (voltage). As the stressing progresses, a dramatic increase in subgap conductance of the junctions, the appearance of subharmonic current steps, and a gradual increase in both the critical and the excess currents as well as a decrease in the normal-state resistance have been observed. The observed changes in superconducting tunneling suggest a model in which a progressively increasing number of defects and associated additional conduction channels [superconducting quantum point contacts (SQPCs)] are induced by electric field in the tunnel barrier. By comparing the I-V characteristics of these conduction channels with the nonstationary theory of current transport in SQPCs based on multiple Andreev reflections by Averin and Bardas, the typical transparency D of the induced SQPCs was estimated as D∼0.7. The number of induced SQPCs was found to grow with voltage across the barrier as sinh(V/V0) with V0=0.045 V, in good agreement with the proposed model of defect formation by ion electromigration. The observed polarity dependence of the breakdown current (voltage) is also consistent with the model. Based on the observed magnitude of breakdown currents, electric breakdown of AlOx barrier during plasma processing was considered to be an unlikely cause of fabrication-induced, circuit pattern-dependent nonuniformities of Josephson junctions’ critical currents in superconductor integrated circuits.

DC Electrical Breakdown in a Metal Pin–Water Electrode System

Electrical breakdown between a metal pin and a water-surface electrode is studied in this paper. The physics of discharges in this electrode geometry are still largely unknown, particularly the breakdown mechanism. Images of the sparks are presented, and the different features are discussed. The formation of a Taylor cone prior to breakdown is studied, and no significant polarity dependence is observed. When the water-surface deformation is small, a glow-to-spark transition is observed when the pin is cathode. When the metal pin is anode, a streamer-to-spark-like transition occurs.

Thermal storage effects on AlGaN/GaN HEMT

The effects of thermal storage on GaN–HEMT devices grown on SiC substrate have been investigated by DC and pulsed electrical measurements, breakdown measurements (by means of a Transmission Line Pulser, TLP), and optical and electron microscopy. After 3000 h of thermal storage testing at 300 °C, only a limited reduction of the DC drain saturation current and of the transconductance peak was observed (20% and 25% decrease, respectively). However, pulsed measurements on aged devices clearly highlight a dramatic current collapse effect that has been attributed to a creation of surface traps in the gate-to-drain and gate-to-source access region. On-state breakdown characterization carried out on aged devices did not highlight any noticeable changes with respect to the untreated devices similarly to the DC characterization. Failure analyses have demonstrated that a loss of adhesion of the passivation layer was responsible for the observed trap formation. An improved passivation deposition process was therefore developed, including a surface cleaning procedure aimed at preventing passivation detaching. The devices fabricated using this new procedure do not show any enhancement of trapping effects up to 500 h of thermal stress at 300 °C.

DC conduction and electrical breakdown of MgO/LDPE nanocomposite

To understand basic electric properties of nano-sized magnesium oxide (MgO) / low-density polyethylene (LDPE) nanocomposite under DC voltage application, the volume resistivity, the space charge distribution and the breakdown strength were investigated. By the addition of nano-sized MgO filler, both the DC breakdown strength and the volume resistivity of LDPE increased. At the average DC electric field of about 85 kV/mm and more, a positive packet space charge was observed in LDPE without MgO nano-filler, whereas a little homogeneous space charge was observed in MgO/LDPE nanocomposite material at the front of electrode. From these results, it is confirmed that the addition of MgO nano-filler leads to the improvement of DC electrical insulating properties of LDPE.

Experimental investigation of dc electrical breakdown of long vapour bubbles in capillaries

The dc electrical breakdown of long vapour bubbles in capillaries generated by external heating of the capillary is studied. The fluid columns in the capillary on both sides of the vapour bubble serve as electrodes for the electrical discharges inside the bubble. When a dc voltage is applied across a static vapour bubble, a self-pulsing corona regime is observed, which is followed by a transient spark. The sparking or breakdown voltage of the vapour bubble decreases with increasing conductivity of the NaCl solution. After the transient spark a constricted glow-like discharge is observed in the bubble whilst the bubble expands due to the energy deposition of the discharge. Electrical and optical emission properties of the corona, spark and glow-like regime are discussed.

Longitudinal magnetic field effect on the electrical breakdown in low pressure gases

The electrical breakdown has been investigated for low-pressure argon and nitrogen discharges under the influence of an external longitudinal magnetic field. Plane-parallel aluminum electrodes (5 cm diameter) separated by a variable distance d (4.0 cm < d < 11.0 cm) were sustained with a dc voltage (0 < V < 1 kV). A Helmholtz coil was used to produce an uniform magnetic field(B) parallel to the discharge axis. Paschen curves were obtained and the secondary electron emission coefficient (g), the first Townsend ionization coefficient (a) and the ionization efficiency(h), were plotted with respect to the variation of the reduced field (E/P). To observe the effect of the magnetic field these curves were plotted for fixed values of B=0 and B=350 Gauss. As consequence of the longitudinal magnetic field, the free paths of the electrons in the Townsend discharge are lengthened and their lateral diffusion is reduced, thus reducing electron losses to the walls. The data presented in this paper give a quantitative description of the B-field effect on the Townsend's coefficients and overall it is concluded that the DC electrical breakdown of the gases is facilitated if a longitudinal magnetic field is applied along the discharge axis.

Electrical breakdown experiments with application to alkali metal thermal-to-electric converters

Electrical breakdown in alkali metal thermal-to-electric converters (AMTECs) limits the number of solid electrolytes that could be connected in series and, hence, the output voltage. Experiments are conducted to measure the DC electrical breakdown voltage in cesium vapor between two planar molybdenum electrodes, 1.6 cm in diameter, separated by a 0.5 mm gap, and relate the results to potential electrical breakdown on the cathode side of AMTECs. Two sets of experiments are conducted. In the first set, in which the electrodes are kept at 560 and 650 K and the cesium pressure varied from 0.71 to 29 Pa, when the cooler electrode is positively biased, breakdown occurs at ∼500 V. When the cooler electrode is negatively biased, breakdown occurs at 700 V. In the second set of experiments, in which the electrodes are held at 625 and 1100 K and the cesium pressure varied from 1.7 to 235 Pa, when the cooler electrode is positively biased, the breakdown voltage is <4 V but in excess of 400 V when the cooler electrode is negatively biased. Because the first ionization potential (3.89 V) and the ionization rate constant of cesium are lower and higher, respectively, than for sodium (5.14 V) and potassium (4.34 V) vapors, the DC electrical breakdown voltage in AMTECs with either a potassium or a sodium working fluid is expected to be higher than measured in this work for cesium vapor. In such converters, the wall should be negatively biased relative to the highest voltage cathode in order to avoid electrical breakdown up to 400 V, or even higher.

Theory of conduction and breakdown in perovskite thin films

The mechanism of the dc electrical conduction and breakdown of perovskite-type titanates was investigated by impedance analysis. Based on an acceptor doped SrTiO3 model material, samples of different microstructures-ceramics, single crystals, and thin films-were employed. This approach allows us to distinguish conduction contributions of the bulk lattice, grain boundaries, and electrode interfaces. Based on defect chemistry studies, a predominant ionic contribution due to mobile oxygen vacancies and an additional p-type conduction were revealed for the bulk. At interfaces, space charge depletion layers of 100-500 nm width are formed in which the local conductivity is reduced by approx. four orders of magnitude compared to the bulk. Thin films show a similar depression of the conductivity. The combination of these facts may be indicative for considering thin films as distributed Schottky barriers. The field enhancement of the conductivity of thin films and of the interface depletion layers is compared and ...

Electrical field breakdown of SF6 in crossed magnetic fields

Reports the DC electrical breakdown data of SF6 in crossed magnetic fields. The sparking potentials are measured between coaxial cylindrical electrodes over the P(R2-R1) range of 0.26<or=P(R2-R1)<or=28 torr cm with the perpendicularly applied magnetic field varying from 0 to 13000 G.

Detection of Joule heating before dielectric breakdown in polyethylene films

Local Joule heating in polyethylene films was detected at room temperature before dielectric breakdown under DC field. When a high-temperature point appeared in a film, the conduction current increased with time. The final breakdown occurred at the point of the highest temperature. This concurrence of the breakdown point and the Joule heating point suggests that a thermal process takes part in the DC electrical breakdown of polyethylene films at room temperature and that there are weak points leading to the breakdown in the film where the current density is above the average. Almost the same results were observed for ethylene-vinyl acetate copolymer films, although the local Joule heating and the electrical breakdown occurred at lower electric fields than those for polyethylene films. >

1356. ac (50 Hz) and dc electrical breakdown of vacuum gaps and with variation of air pressure in the range 10 −9–10 −2 torr using OFHC copper, nickel, aluminium, and niobium parallel planar electrodes : R Hackman and L Altcheh, J Appl Phys, 46 (2), 1975, 627–636

1356. ac (50 Hz) and dc electrical breakdown of vacuum gaps and with variation of air pressure in the range 10 −9–10 −2 torr using OFHC copper, nickel, aluminium, and niobium parallel planar electrodes : R Hackman and L Altcheh, J Appl Phys, 46 (2), 1975, 627–636

Ac (50 Hz) and dc electrical breakdown of vacuum gaps and with variation of air pressure in the range 10−9−10−2 Torr using OFHC copper, nickel, aluminum, and niobium parallel planar electrodes

Breakdown potentials of vacuum gaps are measured over a wide range of air pressure using both direct and alternating (50 Hz) applied voltage and employing four different electrode materials. The air pressure is varied in the range 2×10−9−2.5×10−2 Torr for dc and 6×10−7−2.5×10−2 Torr for ac applied voltage. OFHC copper, nickel, aluminum, and niobium are used to fabricate the electrodes. It is found that the peak ac breakdown voltage is usually higher than the dc voltage for a fixed electrode separation and a fixed gas pressure. Under certain conditions considerable improvement in the insulating property of the gap can be obtained in semivacuum. The improvement in the breakdown voltage of the gap is considerable and can reach up to 62% in some cases. The higher breakdwon voltage is attributed to the increased work function of the metal−gas adsorbate system.

Electrical Breakdown and the Similarity Law in SF6 at Extra-High-Voltages

The DC electrical breakdown of SF6 gas at extra-high- voltages was studied experimentally in coaxial systems of moderate size. The results were compared to a similarity relationship of electric stress for breakdown based on ionization of the gas. For laboratory-clean systems, theory and experiment agree when the macroscopic gradient does not exceed 150 to 200 kV/cm. If the active area of the stressed electrode is small the law remains accurate for higher gradients. Departures from the law are qualitatively explained by including the electrode surface microstructure in its application.

Mechanism of dc Electrical Breakdown between Extended Electrodes in Vacuum

A description is given of vacuum breakdown between extended copper electrodes in dc electric fields in terms of the relevant atomic-collision processes. The theory is based on a model involving avalanche amplification of current in electrode vapor generated by the evaporation of an anode macroparticle during its transit to the cathode. Calculations are presented of the dynamics, heating, and evaporation of the macroparticle leading to the production of the vapor medium in the interelectrode gap. The inferred copper vapor density distribution accounts quantitatively for the absorption of resonance radiation measured just prior to current amplification in the gap. Calculations of electron avalanche multiplication in the vapor lead to predictions of breakdown conditions in agreement with our observations. The predicted size of the anode macroparticle which initiates breakdown is, on the average, of the order of 1 μ in diameter.