TABLE OF CONTENTS The electrical properties of ceramic substrates perform an important task in the operation of electronic circuits. Depending on the applications, the electrical parameters may be advantageous or detrimental to circuit function. Of most interest are the resistivity, the breakdown voltage (or dielectric strength), and the dielectric properties, including the dielectric constant and loss tangent.
The electrical resistivity of a material is a measure of its ability to transport charge under the influence of an applied electric field. More often, this ability is presented in the form of the electrical conductivity, the reciprocal of the resistivity, as defined in Eq. (8.16).
| (8.16) |  |
where ? = conductivity in siemens/unit length
? = resistivity in ohm-unit length
The V-I relationship is governed primarily by injected carriers as opposed to thermal carriers (the opposite of the case with metals) and is given by
| (8.17) |  |
The electrical conductivity of ceramic substrates is extremely low. In practice, it is primarily the result impurities and lattice defects and may vary widely from batch to batch. The conductivity is also a strong function of temperature. As the temperature increases, the ratio of thermal to injected carriers increases. As a result, the conductivity increases and the V-I relationship follows Ohm s law more closely. Typical values of the resistivity of selected ceramic materials are presented in Table 8.8.
| Property | ||||
|---|---|---|---|---|
| Material | Electrical resistivity (?-cm) | Breakdown voltage (AC kV/mm) | Dielectric constant | Loss tangent... |
