Variation Of Breakdown Voltage Research Articles

Non-linearity in rare earth doped zinc oxide varistor prepared by flash combustion method

A novel processing technique involving flash combustion of nitrate-urea mixtures has been reported for praseodymium doped zinc oxide containing K 2O in the range 0·0–0·5 mol%. The starting average powder particle size was 2 μm with a tap density of 1250 kg/m 3. The non-linear behaviour of the prepared zinc oxide varistor was examined in the field range 200–650 V/mm. The breakdown voltage was seen to attain a maximum value of about 600 V/mm in compositions containing 0·3 mol% K 2O. The variation of breakdown voltage is explained on the basis of the microstructure and K 2O content.

Effect of temperature on the breakdown voltage of paper-covered conductor impregnated with various liquids

Lengths of flat copper conductor insulated with aromatic polyamid (aramid) tape or cellulose tape were bent into rings and secured around the edge of discs. Two discs were placed edge-to-edge in one plane and breakdown voltages were measured between the conductors. The conductor assemblies were dried under vacuum, impregnated and immersed in several low-flammability liquids at temperatures up to 180 degrees C under air. Comparisons were made with mineral oil which was tested up to 130 degrees C under nitrogen. With the discs set to provide a 1-mm liquid gap between the insulated conductors, the variation of breakdown voltage with temperature is limited to a few percent and values tend to their highest at 80 degrees C for both AC and lightning impulse. With the conductors in contact, alternating breakdown voltages vary little, whereas impulse voltages fall appreciably with temperature rise, especially for cellulose.< <ETX xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">&gt;</ETX>

A stress tunable gallium doped germanium infrared detector system

A simple partable cryostat system for studying photoconductivity in semiconductors under variable uniaxial stress at liquid helium temperatures is described. It has been used with a Fourier transform spectrometer to determine the spectral response of the photoconductivity of gallium doped germanium between 10 and 140 cm−1 as a function of stress and electric field. Details are also presented of the variation of breakdown voltage and dynamic resistance as a function of stress under low background conditions.

Effects of drift region parameters on the static properties of power LDMOST

The effects of the drift region geometry and the physical parameters on the thin layer (resurfed) lateral DMOS transistor operation have been studied for both the static on-state and the off-state. The variations of breakdown voltage with drift region parameters were investigated using numerical modeling and compared to the experimental results. The operation of the LDMOST in the on-channel condition was modeled semi-empirically. The analytical and experimental results show that the operation of the device depends strongly on the geometry and the physical parameters of the drift region, particularly at high gate voltages and low drain voltages. Design guidelines for the lateral DMOS transistor for switching applications are discussed.

Coplanar gas-discharge display

The electric field strength between coplanar electrodes is calculated employing conformal transformations. The electron multiplication factor is then computed in the nonuniform field region. These calculations have been made for different gap lengths, voltages, and also for different gases and gas pressures. The configuration results in a curved discharge path. It is found that the electron multiplication is maximum along a particular flux line and the prebreakdown discharge is expected to follow this flux line. Experimental tubes incorporating several coplanar gaps have been fabricated. Breakdown voltages have been measured for various discharge gaps and also for various gases such as xenon, helium, neon, argon, and neon-argon mixture (99.5:0.5) at different filling pressures. The variation of breakdown voltage with pressure and gap length is discussed. The observed discharge paths are curved and this is in agreement with theoretical results. A few experimental single-digit coplanar gas-discharge displays (CGDD's) with digit height of 5 cm have been fabricated and dependence of their characteristics on various parameters, including spacing between top glass plate and bottom substrate, have been studied.

Influence of particles on AC and DC electrical performance of gas insulated systems at extra-high-voltage

High-voltage breakdown measurements were made in two similar particle contaminated coaxial test systems, one with AC and the other with DC voltages. Information is presented on the effects of particle size, shape, and material for both SF <inf xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">6</inf> and N <inf xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">2</inf> gases at pressures up to 15 atm in a plain coaxial gap and a coaxial gap including a post-type support spacer. Particle motion and location were found to strongly influence insulation performance. Measured values of electric fields which lifted and drove the particles, so that they bounced vertically and laterally, compare favorably with calculated levels. Movement into the the higher stress region at the center conductor was correlated with the initiation of sparkover. These breakdowns could be at levels more than a factor of five lower than those obtained when contamination was not introduced. Large variations in breakdown voltage of as much as 3 to 1 encountered under DC correspond to conditions where particle motion could be restricted, presumably by corona discharge, to motion near the outer electrode. AC sparkover levels were typically at the lower limits of the DC range. Both free and attached particles on the dielectric spacer surface would trigger flashover at the same low levels as were measured in the gas gap.

Spectroscopy of impurity levels by measuring the microplasma turn on probabilities in GaP/Zn,O/diodes

The modifying effects of the avalanche breakdown on the space charge density of the depletion layer of GaP/Zn,O/p-n junctions have been studied by the double square pulsed method. The thermal-emission time constant of the impurity levels may be determined from measurements of the microplasma turn-on probability vs the time interval between the two pulses. By making these measurements at various temperatures, one can find the activation energy and also the thermal-capture cross-section of the impurity levels. The analysis of the breakdown-voltage variation with time and temperature permits one to draw conclusions about the type of the individual levels (minority or majority-carrier trap) and also about the impurity impact ionization. Five impurity centers were identified in the temperature interval 77–140°K; among them two centers which might be responsible for the anomalous short minority carrier lifetime, i.e., the low quantum efficiency of the red GaP lamps.

The degradation of MOS transistors resulting from junction avalanche breakdown

During the avalanche breakdown of the junctions of an MOS transistor it is possible for highly energetic carriers from the avalanche region to be injected into the regions of gate dielectric near the source and drain where some become trapped causing significant changes in the device characteristics. The variations of junction breakdown voltage, device gain factor and the channel threshold voltage as a function of avalanche charge for a variety of commercially available devices are shown. The profile of threshold voltage as a function of position in the channel is estimated from gate capacitance-voltage plots showing how the length of channel having the original threshold voltage becomes shorter and the regions near the source and drain electrodes in a p-channel device assume an increasingly positive threshold voltage with increasing avalanche charge. The removal of trapped charge from the dielectric under the influence of elevated temperature is examined and the return of the device parameters to the original “as-processed” values is shown to occur after sufficient heat treatment. The progressive degradation due to junction avalanche of gate-controlled diodes, used for input gate protection in many MOS transistors and integrated circuits, is discussed. It is recommended that the total avalanche charge incurred by a device must be strictly limited, especially in measurements between periods of high-temperature overstress during reliability assessment schedules or for characterization, where the results are intended to be representative of devices and integrated circuits not normally subject to junction avalanche.

Thermal resistance measurement of avalanche diodes

A new method of thermal resistance measurement is presented. The variation of diode breakdown voltage with input power as a function of time is the basis of the method. Diode space-charge resistance and series resistance together with separate components of heat-flow resistance are measured using this method. The technique of the measurement is straightforward and provides results with little ambiguity and high accuracy.

Temperature and current distribution in an avalanching p- n junction

The temperature and current distribution in an avalanching Si p- n junction have been calculated numerically by assuming a linear variation of breakdown voltage with temperature and a constant space charge resistance. As the diode radius is increased the temperature variation across the diode decreases while the current variation increases. For a 60 μ radius junction, the current density at the edge is about a factor of 2 larger than the current density at the center; for a ring diode with the same area the maximum current variation between center and edge is ≈ 20 per cent.

Variation of Breakdown Voltage of a Positive-point/Plane Gap with Applied Voltage Waveshape

IN recent years it has become a well-known experimentally observed fact1–5 that the breakdown voltages of certain non-uniform field gaps are strongly dependent on the shape of the applied voltage impulses. For positive-point negative-plane gaps it has generally been found that, for standard double exponential applied voltage impulses and with gap spacings of 1–5 m, the breakdown voltage decreases with increasing rise-time, for rise-times of 100–200 µsec, beyond which it increases again. The magnitude of the effect increases with increase of gap-length and for a 5-m gap, for example, the breakdown voltage at the minimum can be as little as 50 per cent of that for a 1-µsec rise-time impulse.

Graphical analysis of the parameters affecting the voltage tolerance in silicon p- n or n- p junctions

The variations in breakdown voltage in silicon p- n or n- p junctions are analytically and graphically studied as a function of the variation in base resistivity, the surface concentration of impurity, and the diffusion temperature. Graphs are provided to estimate these factors for 15, 30, 50, 100 and 200 V units quantitatively during the diffusion process, and to predetermine the variation on the nominal rated breakdown voltage.

Dielectric Breakdown in Solid Electrolyte Tantalum Capacitors

The construction of solid electrolyte tantalum capacitors is described briefly. The evidence for flaws in the oxide dielectric is presented and the leakage current flowing during the early stages of breakdown is discussed. A consideration of the variation of breakdown voltage with temperature and time of apolication of voltage leads to the conclusion that thermal breakdown is responsible for failure in the dielectric. A description is given of selfhealing and its significance is considered.

The impulse breakdown voltage and time-lag characteristics of long gaps in air II. The negative discharge

Oscillographic measurement and time-resolved photographic recording have been used to examine the breakdown of rod/rod, rod/sphere and rod/plane gaps with long-duration negative impulse potentials of up to 1 MV crest. As in the positive discharge, the breakdown process is found often to cease for considerable periods on the impulse wave tail. Breakdown then occurs after a long time lag for gaps composed of rod cathodes and rod or small sphere anodes. Where the anode is large, no long time lags are observed. Measurement of the variation of breakdown strength with time during the impulse duration has been made by the superimposition of a second impulse upon the first, following a controllable delay. The results show a minimum probability of breakdown initiation after 15 μs of the applied impulse, and a subsequent slow recovery. It is suggested that this confirms the effect of the initial corona phase in causing space charge fouling of the gap. The breakdown voltage of rod/rod gaps is shown to decrease by up to 30 % when the impulse wave front is reduced from 0.50 to 0.06 μs. The breakdown strength with negative impulses is thus less than with positive impulses for wave fronts faster than 0.20 μs. For the wave form 0.50/2000 μs, the breakdown voltage is found to depend more critically upon the dimensions of the earthed electrode than is the case with positive impulses. The breakdown voltage for a rod/25 cm sphere gap is 73 % greater than for a rod/rod gap, yet also 15 % greater than for a rod/plane gap. For gap lengths between 25 and 65 cm, the breakdown voltage of the rod/plane gap is found to increase with decreasing wave front duration. The variation of the negative impulse corona with rate of potential rise and with crest voltage is examined photographically. Many of the observed variations of breakdown voltage and time-lag characteristics can be accounted for in terms of the impulse corona phase. The time-resolved photography of the negative discharge over a wide range of conditions suggests that in the range of gap lengths investigated the formation of the positive leader rather than the negative leader is the necessary forerunner of sparkover.

LIII.Thermal instability of dielectrics for alternating voltages when the loss angle is dependent upon the field strength

Summary The theory of the thermal instability of dielectrics is extended for alternating voltages with a conductivity dependent upon the field strength. Calculations are made with the simplifying assumption that the field is determined by the distribution of the dielectric constant alone and that the variation with temperature of the latter can be neglected. The equations of thermal stability and of their limiting cases are developed for three main types of the conductivity-temperature function, and formulae for the breakdown voltage are thence derived for several types of conductivity-field strength function. These formulae are illustrated by application to some experimental results, showing the variation of breakdown voltage which may be anticipated from certain materials tested. Certain limitations and extensions required in practice are discussed.

The effect of curved boundaries on the distribution of electrical stress round conductors

The paper investigates by the method of conformal transformation the distribution of electrical stress round certain systems of conductors which are important in high-tension practice. In particular the effect of rounding the edges of the conductors in reducing the high stresses at the edges is found quantitatively.The methods used are applied to calculate the variation of breakdown voltage with spacing distance between the electrodes. The two-thirds power law is derived as a limiting case for some of the electrodes, and the effect of variation of electrode shape and of physical assumptions is shown. The theoretical results are compared with such experimental data as are available.Approximate formulae are derived for the capacity of coaxial rectangular cylinders, which are an extension of the well-known correction for the corner of a Leyden jar, and their application to heat conduction problems is pointed out. The results are reduced to graphical form.