Breakdown Voltage Measurements Research Articles

637. Breakdown voltage measurements in alkali-metal-seeded rare gases at elevated temperatures and atmospheric pressure: H I Ellington, Brit J Appl Phys, (J Phys D), 1 (1), 1968, 49–53

637. Breakdown voltage measurements in alkali-metal-seeded rare gases at elevated temperatures and atmospheric pressure: H I Ellington, Brit J Appl Phys, (J Phys D), 1 (1), 1968, 49–53

Breakdown voltage measurements in alkali-metal-seeded rare gases at elevated temperatures and atmospheric pressure

The results of breakdown voltage measurements in various rare-gas - alkali-metal mixtures at atmospheric pressure and elevated temperature are given, the diluent gases being helium, neon and argon, and the seed metals, caesium, potassium and sodium. The breakdown voltage is shown to increase linearly as the electrode spacing rises from 1 to 15 mm, and to show little systematic variation with changing temperature over the range 650-950°C. The breakdown voltage falls slowly as the seed pressure rises from very low values, passes through a broad minimum in the region of 1 torr, then rises sharply at high pressures.For a given seed, the breakdown voltages with helium as diluent are considerably higher than those with argon as diluent, with neon occupying an intermediate position. This is attributed to the different electron collision cross sections of the three gases, the breakdown voltage apparently rising as the electronic mean free path falls. Sodium-seeded plasmas require much higher breakdown voltage values than those seeded with caesium or potassium, but little difference is shown to exist between the latter two seeds, caesium being only slightly superior. It is concluded that the most promising mixtures from the magnetohydrodynamic point of view are caesium and potassium in argon, as they have the lowest breakdown voltage values under all conditions.

Zur durchbruchspannung diffundierter pn-übergänge in silizium

The investigated p-n junctions are produced by diffusion of Ga at 1250°C into n-type Si which has specific resistivities between 0·1 and 350 Ω-cm. After the diffusion process the dependence of the breakdown voltage on the resistivity is found to be and after a following gettering process with O 2-P 2O 5 the dependence becomes The increased breakdown voltage is explained by a reduction of dielectric precipitations during the gettering process. With dopings lower than 10 14 cm −3 the measured breakdown voltages of the diffused p-n junctions are smaller than the values calculated for abrupt junctions by means of the ionization coefficients. Measurements of the barrier capacitance are used to calculate the concentration gradient at the p-n junction and the width of the space-charge region at breakdown. The dependencies on the breakdown voltage given by experiment are in good agreement with calculated results.

The Breakdown Voltage of Cylindrical Positive Corona Discharges in Hydrogen†

ABSTRACT The experimental measurements of breakdown voltage for corona discbarges between cylindrical electrodes are compared with those predicted by Werner's theory. It is shown that Werner's theory is approximately obeyed only for a limited range of conditions where pra lies between 1 and 10 torr-crh, p being the hydrogen pressure and ra the anode radius. This result is accounted for by applying the Townsend breakdown equation to cylindrical systems using available basic plasma data. By integrating the Townsend equation an analytic expression has been developed which gives very close agreement with the experimental results over a range of pra from 1 to 300 torr-cm.

Avalanche Breakdown Voltages of Selectively Diffused p-n Junction

Voltage breakdown in a selectively diffused p-n junctions, differs from that for a planar junction due to the concentration of the field by its geometry. In this discussion, the breakdown voltage of the junction is related to diffusion condition parameters at first, the three-dimensional Fick's equation is solved to get the equation of junction geometry involving diffusion parameters; secondly, from this equation the predominant maximum curvature which effectively determines break-down voltage is calculated; and thirdly, the Poisson's equation for curved junction is solved to get the breakdown voltage-junction curvature relations. These analysis are made for 2 typical diffusion conditions, i. e. (i) instantaneous source and (ii) continuous source. Experimental verifications are made by using silicon for the former and germanium for the latter, and correspondence between calculated and measured breakdown voltage is satisfactory.

Breakdown voltage of planar silicon junctions

It is shown that the breakdown voltage of silicon diodes fabricated by the “planar” process is lower than that of corresponding geometrically plane diodes because of the increased electric field intensity in the curved portion of “planar” junctions. Measured breakdown voltages of “planar” silicon diodes are shown to follow Armstrong's theory for cylindrical step p-n junctions over a wide range of variables indicating the absence of significant surface effects on breakdown voltages.

Vacuum Electrical Breakdown between Plane-Parallel Copper Electrodes

Measurements have been made of prebreakdown currents between thoroughly outgassed plane-parallel copper electrodes in ultrahigh vacuum, for electrode separations in the range 0.03 cm to 0.2 cm. These currents are found to be in good agreement with the Fowler-Nordheim theory of field emission from the pure metal surface. From combined measurements of prebreakdown current and breakdown voltage at different electrode separations it is deduced that the cathode microscopic field at breakdown is constant and of magnitude (6±1)×107 V/cm. Spectroscopic measurements of both resonance line absorption and line fluorescence have revealed that the density of neutral copper vapor present in the interelectrode space during the application of electric fields only fractionally (<1%) less than the breakdown field is considerably less than that necessary for volume ionization to occur. For the same experimental conditions, infrared radiation observations have revealed no hot spots on the anode surface. From the measurements it is concluded that mechanisms involving the amplification of field-emission current in electrode vapor produced by steady evaporation from either the anode or the cathode do not explain the electrical breakdown of vacuum between extended copper surfaces. Further, the production of electrode vapor by the detachment of heated anode material under the influence of the force of the applied electric field is unlikely.

The Gaseous Anodization of Aluminum

Gaseous anodization of aluminum has been investigated as an alternative procedure to forming thin oxide films by such standard techniques as electrolytic anodization and air oxidation. Oxide films are formed on an aluminum surface when positioned in the plateau region of a glow discharge of oxygen. Process variables such as the oxygen pressure and the applied voltage are found to affect the time for film formation. The films are further evaluated on the basis of capacitance and breakdown voltage measurements as well as breakdown pattern observations. Some information as to the rate and nature of film formation is deduced from probe current versus time measurements.

Open-base Breakdown in Diffused N-P-N Junction Transistors†

ABSTRACT A one-dimensional analysis is presented on the open-base breakdown characteristics of diffused n-p-n transistors. From breakdown voltage measurements upon selected devices—in conjunction with breakdown voltage calculations—‘ effective ’ values are established for the ionization rate of electrons in germanium and silicon p-n junctions, when biased substantially below avalanche breakdown. These ‘ effective ’ electron ionization rates are used to calculate the open-base breakdown voltage for transistors exhibiting a large collector punch-through voltage ; such calculations are graphically illustrated throughout iv range of parameters applicable to many practical situations. A discussion is also presented on the influence of an abrupt conductivity increase within the collector junction space-charge layer, of the typo encountered in an idealized epitaxial structure.

Measurements on Gas Breakdown

After a brief survey of the two main theories of spark breakdown in gases, an account is given of certain empirical laws relating to breakdown voltages, gap lengths and pressure of the gas. Other factors which affect measured breakdown voltages are discussed namely; humidity, Proximity of neighbouring objects, irradiation, electrode geometry and polarity of unidirectional voltages. The discussion has been confined to phenomena in air but qualitatively the conclusions reached would apply to other gases.

New Derivation of the Vacuum Breakdown Equation Relating Breakdown Voltage and Electrode Separation

An analysis of the published measurements of breakdown voltage for various gap lengths for uniform and approximately uniform fields shows that the results may be represented by the breakdown equation V = Cxα and that the values of α lie in the range 0.1 to 1.1 with a mode of 0.7. A theory is developed which leads both to a breakdown equation of the same form and to a general expression to account for the range of values of α. This expression is confirmed for gaps up to 0.075 cm by direct experiment. The development is based on the postulate that an electron beam is emitted from the cathode, diverges, and bombards the anode to cause breakdown when a critical power flux is reached. The factor C is shown to include the critical power flux and to be related to both field and electrode separation. In support of the theory, the radii of craters produced on the anode are measured and shown to be related to the radius of an electron beam at the anode. Calculation shows the current carried by the beam to be of the order of 10−4 amp. Values of the critical power flux obtained from the equation V = Cxα and from anode crater data, respectively, agree within a factor of 1.5 and are of the order of 108 w cm−2. To explain the observed phenomena, a multiple electron beam system is proposed.

MINIMUM SPARK BREAKDOWN AND GLOW VOLTAGES

Measurements of the spark breakdown voltage between carbon electrodes in hydrogen, argon, nitrogen, and air are given for ranges of the product p (mm. Hg) × d (cm.) between 0.1 and 1000 mm. Hg cm. The results show that in each gas Paschen's Law is obeyed for pd > 10 mm. Hg cm. For pd < 10 mm. Hg cm. deviations from Paschen's Law were observed at the longer gap lengths. The minimum spark breakdown voltage, Vsm, occurred near pd = 1 mm. Hg cm. The normal cathode-fall voltage, Vcn, was also measured, and was found to be less than Vsm in hydrogen, argon, and air, and greater than Vsm in nitrogen. A theoretical analysis is made which predicts the relationship Vcn = 1.110 Vsm and the reasons why this condition is seldom found in practice are discussed.

Grain Boundary Barriers in Germanium

High resistance at crystal grain boundaries in $n$-type germanium is investigated. The resistance is symmetrical with respect to the direct on of the current and resembles the characteristics of a rectifier in the blocking direction. Such barriers are also photosensitive. The barrier is eliminated when the material is converted to $p$-type by nucleon bombardment or heat treatment. A theory is developed assuming the existence of surface states at the boundary. The ability of the barriers to withstand high voltages, around 100 volts, is explained by showing that the surface charge increases with increasing voltage. The dc conductance of the barrier, measured at different temperatures, agrees with theory in the dependence on temperature as well as in the order of magnitude. At sufficiently low temperatures the barriers show a capacitance independent of the frequency, whereas at higher temperatures the barrier admittance is strongly frequency dependent. These results are in agreement with the theory, showing that at low temperatures the current across the boundary is mainly carried by electrons, the hole current becoming increasingly important as the temperature is raised. The height of the potential barrier above the Fermi level is determined and found to be independent of temperature. A small difference in the measured breakdown voltage for the two directions of current is attributed to a difference in impurity concentration on the two sides of the boundary, which is confirmed by the ac measurements. The number of electrons on the boundary states is found to be of the order ${10}^{12}$ ${\mathrm{cm}}^{\ensuremath{-}2}$ at the breakdown, which may be the saturation of the boundary states. However, the field at breakdown is only a few times lower than the critical value for the onset of the Zener current, and this mechanism cannot be definitely ruled out.

Polonium Alloy for Spark Plug Electrodes

A method of improving the starting characteristics of spark plugs involving the use of polonium is described. Results of experiments concerned with the measurement of the apparent breakdown voltage under laboratory conditions and the starting characteristics of spark plugs in internal combustion motors at low temperatures are given. These results indicate that the use of polonium in commercially practical concentrations in standard electrode alloys definitely improves the starting performance of spark plugs. Large scale methods of extraction of polonium from residues of a radium refinery and the method of introducing polonium into the electrode alloy are to be discussed in a subsequent article.

Apparatus for the Measurement of Breakdown Voltage Between Metal Electrodes in Vacuum

This paper describes apparatus used for the measurement of breakdown voltages between electrodes in vacuum with potentials up to the order of 500 kv. The use of a direct voltage of this magnitude required special shielding to limit electrical stresses in the lead-in bushing of the vacuum tank. The source of power was an electrostatic belt generator with a corona-leak voltage control. Voltage was measured with a xylene alcohol high resistance voltmeter. Incidental work with stand-off insulators in vacuum is described. The results of a series of breakdown measurements are shown with a curve.