Subnanosecond avalanche switching in high-voltage silicon diodes with abrupt and graded p-n junctions

The phenomenon of delayed avalanche breakdown in high-voltage silicon diodes has been studied for the first time using an experimental setup with specially designed resistive coupler as a part of a high-quality matched measuring tract. Three types of diode structures with identical geometric parameters and close stationary breakdown voltages within 1.1–1.3 kV have been studied, including p ⁺-n-n ⁺ structures with abrupt p-n junctions and two different p ⁺-p-n-n ⁺ structures with graded p-n junctions. Upon switching of all structures, a voltage step with an amplitude above 1 kV and a rise time of ～100 ps at a breakdown voltage of about 2 kV is formed in the load. However, switching to a state with low (～150 V) residual voltage has been observed only in the structures with an abrupt p-n junction, while the voltage in structures with graded junctions only decreased to a level of ～1 kV, which is close to the stationary breakdown voltage.     

Fractal analysis of side channels for breakdown structures in XLPE cable insulation

The role of frequency in the range 20 through 300 Hz on the breakdown voltage and the breakdown path is studied in cross-linked polyethylene (XLPE) cable insulation using embedded needle. A maximum breakdown voltage of 25 kV is found at 240 Hz, and side channels are observed on the flank of the main channel of the electrical breakdown path. Fractal analysis of the side channel is carried out and it is induced that the frequency dependence of the fractal dimension D of the side channel are similar to that of the electrical trees before breakdown. It is suggested that the space charge can be injected from the needle tip. This leads to partial discharge causing progress of the electrical tree and the breakdown path. Space charge will also result in field-moderating cloud around the needle tip and turn to sidewall charges in the side channels. The frequency dependence of the breakdown voltage of the XLPE with the embedded needle can be clarified based on the fractal analysis of the side channel and the electrical tree of the XLPE insulation.     

Influence of bubble size and flow velocity on AC electrical breakdown characteristics of LN2

To evaluate insulation design of high voltage for high T_c superconducting (HTS) power apparatus, the effect of bubble and electrode arrangements on the AC breakdown characteristics of LN₂ were investigated. Supposing that an outbreak of quench, the three electrode models were employed for breakdown voltage measurement in LN₂ with bubbles. Experimental results for various quench conditions revealed that the breakdown voltage of LN₂ with increasing the bubble size, flow velocity and electrode distance. Then, the relationship between the bubble conditions and the AC breakdown characteristics of LN₂ were clarified. Also, bubble movement phenomena were observed with an electrode model which consist of plane to cylindrical needle electrode immersed LN₂ for the simulation of the insulation environment in HTS pancake type coils and others of the quenching state.     

Positive and negative effects of dielectric breakdown in transformer oil based magnetic fluids

The transformer oil based magnetic fluids can be considered as the next-generation insulation fluids because they offer exciting new possibilities to enhance dielectric breakdown voltage as well as heat transfer performance compared to pure transformer oils. In this study, we have investigated the dielectric breakdown strength of the fluids with the various volume concentrations of nanoparticles in accordance with IEC 156 standard and have tried to find the reason for changing the dielectric breakdown voltage of the fluids from the magnetic field analysis. It was found that the dielectric breakdown voltage of pure transformer oil is around 12 kV with the gap distance of 1.5 mm. In the case of our transformer oil-based magnetic fluids with 0.08% < Φ < 0.6% (Φ means the volume concentration of magnetic nanoparticles), the dielectric breakdown voltage shows above 40 kV, which is 3.3 times higher positively than that of pure transformer oil. Negatively in the case when the volume concentration of magnetic nanoparticles is above 0.65%, the dielectric breakdown voltage decreases reversely. From the magnetic field analysis, the reason might be considered as two situations: the positive is for the conductive nanoparticles dispersed well near the electrodes, which play an important role in converting fast electrons to slow negatively charged particles, and the negative is for the agglomeration of the particles near the electrodes, which leads to the breakdown initiation.     

Breakdown voltage of glow discharge of pin electrodes

One of the shortcomings of glow discharge tube is its high breakdown voltage. In this paper, 2-pin electrode, 3-pin electrodes and 4-pin electrode are fabricated. The breakdown voltages of glow discharge of these electrodes have been measured within the pressure range of 0.4-2.5 kPa. The breakdown voltages vary obviously for the different kinds of electrodes, and the maximum difference of the breakdown voltages is about 208 V. Electric fields of the electrodes are calculated and the results consist with the experimental results. It is concluded that the breakdown voltage can be significantly reduced by adjusting electrode structure without changing the distance between electrode pins. The proposed electrode structure has potential applications in devices of glow discharge.     

Breakdown voltage of glow discharge of pin electrodes

One of the shortcomings of glow discharge tube is its high breakdown voltage. In this paper, 2-pin electrode, 3-pin electrodes and 4-pin electrode are fabricated. The breakdown voltages of glow discharge of these electrodes have been measured within the pressure range of 0.4–2.5 kPa. The breakdown voltages vary obviously for the different kinds of electrodes, and the maximum difference of the breakdown voltages is about 208 V. Electric fields of the electrodes are calculated and the results consist with the experimental results. It is concluded that the breakdown voltage can be significantly reduced by adjusting electrode structure without changing the distance between electrode pins. The proposed electrode structure has potential applications in devices of glow discharge.     

Electromechanical stability of semi-crystalline polymer

Semi-crystalline polymers are widely used in manufacturing drivers and capacitors. The two opposite surfaces of semi-crystalline polymer are coated with flexible electrodes and are applied with voltage. Because of static electricity field, semi-crystalline polymer film thins down along the thickness direction while extends along the horizontal direction. Reduction of thickness will lead to a higher electric field, and the positive feedback system has been sustained. When the electric field reaches the critical breakdown of electric field of semi-crystalline polymers, electromechanical coupling system of semi-crystalline polymers becomes unstable. Based on the method on electromechanical instability of semi-crystalline polymers under non-linear field, we use exponential model with two material constants to analyze the electromechanical stability of semi-crystalline polymers. Then, we obtain the relationship among the true critical stress, the true critical electric field of different semi-crystalline polymers and stretching rate. The numerical results show that, when the material ratio C (K₂ = CK₁,K₁ and K₂ are the parameters determined by the experimental stress-strain relationship) of the two material constants increases, the true critical electric field and electromechanical stability of semi-crystalline polymers will decrease. In addition, when C = 0, our result coincides with previous results. It is proved that pre-stretching load can increase the critical breakdown voltage of the polymer. Our conclusions may provide the guidance in designing material and manufacturing semi-crystalline polymer.     

Synthesis and structure characterization of low dielectric constant MSQ films by using octamethyl cyclotetrasiloxane (D4) as a porosity promotion agent

Low dielectric methylsilsesquioxane (MSQ) film can be synthesized by spin-coating on P–Si (100) wafer. Octamethyl cyclotetrasiloxane (D4) was used as a porosity promotion agent to MSQ film. Seven samples with different treatment were prepared. The dielectric constants of these MSQ films significantly lowered from 3.0 to 2.1. Fourier transform infrared spectroscopy was used to identify the Si–O–Si network structure, Si–O–Si cage structure and other bonds. The change of structure resulted in significant lowering of the dielectric constant (k). The capacitance–voltage (C–V) characteristic by HP4294A was used to determine the dielectric constant. Current–voltage (I–V) measurement by Keithley6517A was used to determine the breakdown electric field.     

Investigation of reliability measurements with ramped and constant voltage stress on mos gate oxides

MOS gate oxide capacitors over a wide range of oxide thicknesses (10·9–28nm) were stressed using constant voltage, ramped voltage stress and combined ramped/constant voltage stress measurements. The reliability measurements were performed with different bias conditions in order to assess the effect of the measurement conditions on the gate oxide lifetimes. A unipolar pulsed ramp was applied during the ramped voltage stress. It will be verified that this ramp yields identical breakdown distributions to the commonly used staircase ramp. Times to breakdown from ramped and constant voltage stress were directly compared. It was found that for thick oxides the times to breakdown of the ramped stress were greater than those of the constant stress. The measurement results of the combined ramped/constant voltage stress indicate that it is a valuable tool for monitoring extrinsic and intrinsic breakdown properties. The observations made in this work imply that the time to breakdown at a constant voltage is strongly dependent on the peak current injected into the oxide and, therefore, on a pre-stress before the constant stress voltage.     

Room temperature electroluminescence from arsenic doped p-type ZnO nanowires/n-ZnO thin film homojunction light-emitting diode

The highly arrayed arsenic doped p-ZnO nanowires/n-ZnO thin film homojunction light-emitting diode was fabricated on semi-insulated Si substrate. The homojunction was consisted of high-quality n-ZnO thin film grown by metal–organic chemical vapor deposition technology following arsenic doped ZnO nanowires grown by chemical vapor deposition. The device shows good rectification characteristic with a turn-on voltage of ~4.8 V and reverse breakdown voltage of ~18 V. Moreover, two distinct electroluminescence bands centered at 2.35 and 3.18 eV are detected from this device under forward bias at room temperature.     

Electrical characteristics of high-Tc superconducting mini-model cable under mechanical stresses in liquid nitrogen

To develop 22.9 kV class high-T_c superconducting (HTS) cable in Korea, we have been studying electrical insulation properties of dielectric paper, such as breakdown voltage, partial discharge, which is one of the HTS cable structure elements. However, the research on the mechanical stress of dielectric paper compared to breakdown properties of dielectric paper is insufficient. A cracking and variation of the electrical insulation due to mechanical stresses during cooling and bending of HTS cables in cryogenic temperature is a serious problem. Thus, we investigated tensile stress and breakdown stress of dielectric paper under mechanical stress. Moreover, we manufactured mini-model cables investigated breakdown stress under bending stress to design a cable drum for conveyance. In the AC, impulse and partial discharge properties, all test results showed a similar tendency, and the suitable bending radius ratio R/r was decided to be more than 25.     

Validity of the Space-Time Enlargement Law for vacuum breakdown

This paper investigates, theoretically and experimentally, the applicability of the Space-Time Enlargement Law to vacuum-insulated systems. A discussion on how characteristics of possible vacuum breakdown mechanisms determine the distribution function of the breakdown voltage random variable is presented. By superimposing effects of electrode surface enlargement and inter-electrode gap enlargement, expressions for the mean value and standard deviation of the breakdown voltage random variable are obtained. In the case of time extensions, the assumption of complete independence of consecutive discharge processes is discussed. Experimental testing of the Enlargement Law was performed on Rogowski type two-electrode systems, with different electrode surface areas, inter-electrode gaps and vacuum pressures. Measurements were conducted using industrial ac voltage, dc voltage with 50 V/s rate of rise, standard atmospheric pulse voltage (1,2/50 μs), and commutational pulse voltage (250/2500 μs). The final conclusion, based on the comparison of theoretical considerations and the experimental results, is that the Space-Time Enlargement Law can be applied in the design phase during the development of vacuum devices, with certain limitations, regardless of the type of the applied voltage.     

The influence of operating parameters on pulsed D.C. magnetron sputtering plasma

This paper describes the breakdown voltage characteristics in a pulsed D.C. magnetron sputtering system under varying conditions of frequency, current and pulse-off time. The behaviour of the breakdown voltage with pulsing frequency at different pressures and constant pulse-off time was recorded and revealed that the breakdown voltage decreased consistently as the frequency increased up to 70 kHz. Above this frequency, perturbation in the breakdown voltage was noted, possibly due to the rise in pre-breakdown current during the few microseconds of pulse-on time. This perturbation effect was no longer observed when the operating current was increased. The breakdown voltage was seen to decrease when the pulse-off time was increased while keeping the total period of the pulse constant.     

Scintillation in anodic Ta2O5 films

The scintillation of anodic tantalum oxide was investigated by counting the number of breakdown events during anodization at a constant current density. A theory is developed which qualitatively explains the variation in the number of breakdown pulses with time and voltage for different current densities and different electrolyte resistivities. The theory also allows definition of a limiting anodization voltage which increases with the logarithm of the current density. Several experiments are presented which are in agreement with the theory.     

Aging characteristics of cryogenic insulator for development of HTS transformer

In the response to the demand for electrical energy, much effort aimed to develop and commercialize high temperature superconducting (HTS) power equipments has been made around the world. Especially, HTS transformer is one of the most promising devices. For the development of HTS transformer, the cryogenic insulation technology should be established. In this paper V−t characteristics of polyimide (Kapton) tape and GFRP used as turn-to-turn and structural insulations, respectively were studied. Moreover, breakdown hole site of GFRP after breakdown was also discussed. The experimental results show that the time to breakdown is conditioned on applied electric stress and the lifetime indices n of Kapton tape decrease slightly as the number of tape increases while the lifetime indices n of GFRP decrease strongly with increasing thickness. Furthermore, the breakdown holes of GFRP were not at the contact point, at which the electric field is maximum value, between sphere electrode and GFRP sample and its location depends on applied voltage as well as sphere diameter.     

An investigation into the parameters affecting the breakdown voltage and inter-particle bonding in the electrical discharge compaction of metal powders

The aim of present investigation is to gain deeper understanding of breakdown behavior and inter-particle bonding by conducting experimental tests. This may lead to improve the state of compaction by relative arrangement of initial parameters to maintain uniform distribution of current density and producing compacts with sufficient mechanical strength. Experimental work was carried out using two different set-ups. The first arrangement was employed to provide steady-state alternating voltage. The effect of column geometry and particle size on breakdown voltage was investigated under this condition. The second set-up, capacitor discharge circuit, was used to provide impulse voltage. Under this condition, the influence of column geometry, particle size, application of axial pressure, evacuation of air, energy input, electrode material and configuration on breakdown voltage was studied. Also, scanning electron microscopy was employed to study the effect of different parameters on inter-particle bonding. The results of experiments conducted on the influence of each of the voltage and capacitance on the compaction properties are also discussed.     

微弧氧化时电流、声信号和光信号与涂层形成电压的关系

介绍了电流、电信号、光信号等参数对微弧氧化形成涂层性质、厚度等的影响.用测量法和计算法证明了各形成电压范围下微弧击穿的后果及涂层厚度与其形成电压的密切关系.     

Self-healing breakdown in NaCl epitaxial capacitors

The single-hole non-shortening breakdown characteristics of single-crystal films of NaCl were investigated. Thin film epitaxial Ag/NaCl/Ag capacitors were fabricated on heated NaCl substrates in a vacuum. The breakdown events were found to be uniformly distributed over the whole capacitor area. The three main features of the breakdown are as follows: (1) when breakdown occured at room temperature the voltage waveforms showed an abrupt voltage drop to zero indicating that a voltage threshold does not exist; (2) as the temperatures increases the voltage drop becomes erratic and the repetition frequency of the breakdowns increases; (3) when the base electrode is negatively based self-healing is promoted but when it is positively based the self-healing response deteriorates.     

Parameters of silicon carbide diode avalanche shapers for the picosecond range

Parameters of ultrafast avalanche switching of high-voltage diode structures based on 4H-SiC have been estimated theoretically. The calculation was carried out using the analytical theory of the impact ionization wave of the TRAPATT type, which makes it possible to determine the main characteristics of a wave for arbitrary dependences of the impact ionization coefficients and carrier drift velocity on electric field. It is shown that, for a high-voltage (1–10 kV) 4H-SiC structure, the time of switching from the blocking to the conducting state is ~10 ps, which is an order of magnitude shorter than that for a Si structure with the same stationary breakdown voltage, and the concentration of the electron-hole plasma created by the wave is two orders of magnitude higher. Picosecond switching times can be reached for 4H-SiC structures with a stationary breakdown voltage exceeding 10 kV.