Field breakdown

Varistors. Varistors are devices that exhibit nonlinear current—voltage behavior. At low voltages, current flow is minimal and the device behaves as an ohmic insulator. As the voltage approaches a critical value, the breakdown field (Fgj ), current flow increases and the device becomes highly... 

Fig. 12. Log—log plot of current density,/, versus appHed electric field, E, for a ZnO varistor at room temperature, ia which the breakdown field. Eg, is iadicated. The exponent d equals the iaverse slope of the curve, log Ej J) = 1/a, and is a measure of device nonlinearity. Units of current density and the...

The removal of pores and internal cracks is also of value where functional ceramics are concerned. Dielectrics such as are used in capacitors in enormous quantities, alumina in particular, have long been made with special attention to removing any pores because these considerably lower the breakdown field and therefore the potential difference that the capacitors can withstand. 

One approach to the production of high-performance dielectrics relies on the use of mixed-metal, multiple-component oxides. These oxides provide convenient means for controlling the dielectric-constant breakdown-field product through incorporation of components that specifically contribute to performance via dielectric constant or breakdown. At the same time, the mixed materials can inhibit crystallization, resulting in deposition of amorphous films with extremely flat surfaces. Common candidates, base oxides for tuning these properties, are listed in Table 4.1. 

This thermal stability comes with a price, however, as low polarizability of the covalent matrix imparts a modest dielectric constant of 5 for A12P055 compositions (although substitution of 33 at% La can boost this value to 8.5). This suboptimal value can be somewhat mitigated by high breakdown fields... 

Em is limited by the breakdown field strength Ebd of silicon, which is about 3x 105 V cm4. The figure on the inner front cover shows the width of the SCR as a function of doping density and applied bias, as well as the limitation by avalanche breakdown. 

An n-type electrode is under reverse bias in this anodic regime, and so only a small dark current density in the order of a few pA cm-2 is observed, as shown in Fig. 4.11. The dark current increases by orders of magnitude if the breakdown field strength is reached at the electrode surface or at a pore tip present in the electrode, as discussed in Section 8.4. 

An anodic oxide grown in pure water at 10 pA cm-2 to thicknesses between 4 and 10 nm and subsequently annealed at 700 °C in N2 for 1 hour, showed an interface charge density (1011 eV 1 cnT2) and a dielectric breakdown field strength (11-14 MV cm-1) that are comparable with known values for thermal oxides [Ga2]. While the breakdown field strength of anodic oxides is comparable to thermal... 

The dielectric constant and breakdown field of a material are not the only considerations. Because a capacitor is used for charge storage, the leakage properties of the film are also critical. These are largely controlled by the defects in the films which can include oxygen (anion) vacancies or mixed valence effects in the cations. It is important that films that are as fully oxidized as possible be studied. 

Bi-Pb-Cu-Ca-Sr-0 composition space 155 BN nanotube 265 Bom-Oppenheimer approximation 211,220 Bosch, C. 55 breakdown field 163 broken symmetry 178 buckyballs 263 bulk modulus 259 burning of air 210 by N-methyltriazolinedione 38... 

There are two geometries for a ballast resistor, a thin film under the CNT (vertical resistor), or a thin film at the side of the CNT (horizontal resistor). Now, the local field for field emission from carbon is extremely high, 109 V/m, which may be 10 times larger than the breakdown field of many insulators. Given the dimensions of an emission system, it is likely that the thickness of any ballast resistor thin film will be smaller than that of the net cathode-anode distance. Thus, the applied field is likely to cause breakdown in any vertical ballast resistor design. Thus, horizontal ballast resistors are a safer option. However, they are more difficult to implement because they must be placed between each emitter and the current feed. 

The present work is a report of the properties of polyimide which define functionality as an interlevel dielectric/passivant. Thus, the planarizing and patterning characteristics and electrical characteristics of current vs voltage, dissipation, breakdown field strength, dielectric constant, charge and crossover isolation are discussed in addition to the reliability-related passivation properties. 

Insulation Integrity. Insulation integrity is a function of an interlayer dielectric/passivant defined by specific electrical, mechanical and passivation properties. The D.C. electrical property of interest is the I-V characteristic which is used to deduce conductivity and breakdown field strength. The corresponding A.C. electrical property is dissipation factor. The pertinent mechanical and passivation properties are, respectively, pinhole density and performance rating as a diffusion barrier to Na" " and H2O. 

The breakdown field strength is a thickness dependent property, a probable reflection of pinhole density variation with thickness. For a typical value of Interlevel dielectric film thickness (1 - 2 p), the breakdown field strength is 1 - 2.5 x 10 V/cm which is adequate for most applications. 

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