Ohmic insulator

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. 11 Intermediate replenishing tank system, ohmic insulated for electrostatic waterbased basecoat application. (Courtesy of LACTEC GmbH, Rodgau, Germany.)...

Contacts are the elementary building blocks for all electronic devices. These include interfaces between semiconductors of different doping type (homojunctions) or of different composition (heterojunctions), and junctions between a metal and a semiconductor, which can be either rectifying (Schotlky junction) or ohmic. Because of their primary importance, the physics of semiconductor junctions is largely dealt with in numerous textbooks [11, 12]. We shall concentrate here on basic aspects of the metal-semiconductor (MS) and, above all, metal-insulator-semiconductor (MIS) junctions, which arc involved in the oiganic field-effect transistors. 

Substituting (14.42) into Eq. (14.19), we sec that, once more, the linear term Vs can be neglected with respect to the exponential term. In other words, most of the gate-source ohmic drop occurs in the insulator, so that Eq. (14.23) becomes simply... 

As discussed in Section IV,E, it is necessary, as well as convenient, in studies such as these to divide the electrode into several insulated sections in order to make accurate limiting-current measurements otherwise the limiting current may be obscured. A limiting-current curve is then obtained for each insulated section. This technique, first introduced by Fenech and Tobias (F3), requires that the potential be kept equal on the various sections as limiting current is approached. Sectional currents are therefore measured by means of potential drop through low-ohmic precision resistors. 

Very often, the electrode-solution interface can be represented by an equivalent circuit, as shown in Fig. 5.10, where Rs denotes the ohmic resistance of the electrolyte solution, Cdl, the double layer capacitance, Rct the charge (or electron) transfer resistance that exists if a redox probe is present in the electrolyte solution, and Zw the Warburg impedance arising from the diffusion of redox probe ions from the bulk electrolyte to the electrode interface. Note that both Rs and Zw represent bulk properties and are not expected to be affected by an immunocomplex structure on an electrode surface. On the other hand, Cdl and Rct depend on the dielectric and insulating properties of the electrode-electrolyte solution interface. For example, for an electrode surface immobilized with an immunocomplex, the double layer capacitance would consist of a constant capacitance of the bare electrode (Cbare) and a variable capacitance arising from the immunocomplex structure (Cimmun), expressed as in Eq. (4). 

There is no sharp distinction between a semiconductor and an insulator. Both can have such a wide band gap that the conductivity of the intrinsic materials is negligible. In this chapter, however, we shall discuss only such solids which by doping can be made conductive to such an extent that ohmic voltage drops in the bulk remain small for the size of currents which can be generated by excited molecules. The other extreme, where the conductivity is only caused by the injected charge carriers, will be treated in the next chapter. 

It is common in many practical battery designs to immobilize a liquid electrolyte phase within a porous solid insulator. The electrolyte conductivity and ohmic loss in such a system are determined by the number of pores, their size, shape and tortuosity. The tortuosity coefficient, /3, is defined as the ratio of the mean distance covered by an ion traversing a porous matrix, to the direct distance of one side of the matrix to the other. The relative reduction in the conductivity of an electrolyte solution caused by confining it in a porous solid is called the conductivity attenuation, 0. For a matrix of uniform cylindrical pores it is given by... 

In a Thought Experiment, the junction is disassembled (Fig. 6.32) by division through the insulator and the two halves are first treated as electrically isolated objects. In the ensuing equations, we use the common symbol for the work function of a material. There are three electron work functions to be considered that of palladium 0pd, that of an arbitrary metal which does not interact with hydrogen 0m, and that of silicon 0su The insulator is considered to be ideal which means that it does not contain mobile charges. Therefore, it does not have a defined Fermi level. Because the two halves are not connected, their energy levels are in an arbitrary undefined position with respect to each other. On the other hand, metal M and palladium (as well as the M and silicon) form ohmic junctions, meaning that the... 

Transport of electrons along conducting wires surrounded by insulators have been studied for several decades mechanisms of the transport phenomena involved are nowadays well understood (see [1, 2, 3] for review). In the ballistic regime where the mean free path is much longer than the wire lengths, l 3> d, the conductance is given by the Sharvin expression, G = (e2/-jrh)N, where N (kpa)2 is the number of transverse modes, a, is the wire radius, a Fermi wave vector. For a shorter mean free path diffusion controlled transport is obtained with the ohmic behavior of the conductance, G (e2/ph)N /d, neglecting the weak localization interference between scattered electronic waves. With a further decrease in the ratio /d, the ohmic behavior breaks down due to the localization effects when /d < N-1 the conductance appears to decay exponentially [4]. 

Corrosion of the current collector or of the active mass itself can lead to a reduction in the cyclability, due to the increase in the contact resistance, formation of a passive insulating film oxide, etc. Corrosion may also involve the electrolyte and cause extra ohmic losses. 

Gate formation Schottky gate on GaN channel Metal gate on dielectric insulator (such as Si3N4, AIN) Ohmic contact to p-GaN gate Schottky gate on AlGaN barrier... 

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