Resistivity and Dielectric Constant

Pure single-crystal diamond, with a bandgap of 5.48 eV, is one of the best solid electrical insulators (see Sec. 6.2).l l The high strength of the 

However, as with the optical properties, the presence of impurities can drastically alter its electronic state and the inclusion of sp (graphite) bonds will considerably decrease the resistivity and render the material useless for electronic applications. 

The dielectric constant of diamond (5.7) is low compared to that of other semiconductors such as silicon or germanium but not as low as most organic polymers (in the 2 to 4 range) or glasses (approximately 4). 

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Semiconductors (qv) are materials with resistivities between those of conductors and those of insulators (between 10 and 10 H-cm). The electrical properties of a semiconductor determine the hmctional performance of the device. Important electrical properties of semiconductors are resistivity and dielectric constant. The resistivity of a semiconductor can be varied by introducing small amounts of material impurities or dopants. Through proper material doping, electron movement can be precisely controlled, producing hmctions such as rectification, switching, detection, and modulation. 

In contrast to metals and semiconductors, the valence electrons in polymers are localized in covalent bonds.The small current that flows through polymers upon the application of an electric field arises mainly from structural defects and impurities. Additives, such as fillers, antioxidants, plasticizers, and processing aids of flame retardants, cause an increase of charge carriers, which results in a decrease of their volume resistivity. In radiation cross-linking electrons may produce radiation defects in the material the higher the absorbed dose, the greater the number of defects. As a result, the resistivity of a radiation cross-linked polymer may decrease. Volume resistivities and dielectric constants of some polymers used as insulations are in Table 8.3. It can be seen that the values of dielectric constants of cross-linked polymers are slightly lower than those of polymers not cross-linked. 

Volume Resistivity and Dielectric Constant Values of Polymeric insulating Materials... 

FIG. 11.10 Correlation between electric resistivity and dielectric constant of polymers. 

Figure 4. Charge-transfer time constants characterizing spray liquids as functions of liquid electrical resistivity and dielectric constant. (Reproduced with permission from Ref. 10. Copyright 1978, American Society of Agricultural Engineers.)...

Table 5.22 gives resistivity and dielectric constants of selected polymers. Table 5.22. Resistivity and dielectric constants of some polymers...

Measurement of Bulk Powder Resistivity and Dielectric Constant... 

Graphs of resistivity and dielectric constant vs. temperature are difficult to translate to values of electronic components. The electronic design engineer is more concerned with how much a resistor changes with temperature and if the change drives the circuit parameters out of specification. The following defines the commonly used terms for components related to temperature variation. 

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