Dielectric materials, selection and design

Section 3.2 Dielectric Materials Selection and Design. Ashok Maliakal... 

This chapter will focus on the selection and design of the gate dielectric, which is the insulating material separating the active semiconducting material from the... 

The dielectric materials interact with the electrical fields and alter the characteristics of the electrical field. In some cases this is desirable and in others it is deleterious to the operation of the system and must be minimized. This is done by both the selection of the material and the configuration of the dielectric. To see how these concepts are applied, an example is presented of one of the major applications of plastics materials, i.e., to insulate wires, and show how a dielectric is designed to meet the service requirements. The specific requirements on a standard wire are ... 

If the wire is to be used to carry much higher frequency currents, the design problem in geometry and material selection becomes more complicated. A difficult high frequency insulation problem is shown in Fig. 16-2. The dielectric constant and dielectric loss values for the materials become important in the design. At a frequency of one megahertz the effect of the dielectric on the power transmission characteristics of the wire is substantial and, even at frequencies of 10 to 100 kilohertz, the insulation on the wire must be considered as a major electrical element in the circuit. When dealing with low value currents. 

In hquid-phase extraction, provided that there is sufficient dispersed free water - or that an adequate amount of high dielectric constant material has been added to the matrix - it is possible to design a MAP extraction procedure with almost any of the organic solvents routinely used in chemical analysis, bearing in mind that the solvent must be selected for its ability to solubilise the desired product. Bear in mind that the selection of the solvent is not limited to substances that are hquid at ambient temperature and pressure. In fact, the use of hquefied gases, such as CO2 or propane, are especially attractive to food science workers as a result of their low toxicity and the relative ease with which they can he virtually removed from the spent material. The latter comments also apply to gas-phase or solvent-less extraction made possible when using MAP. 

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