TABLE OF CONTENTS In addition to material properties and the internal and external geometry, there are several other variables that may have an impact on the electrical parameters of capacitors [9]. Some of these parameters are expected to have a quasi-static effect, such as do bias, temperature, and aging.
Ceramic materials with a high-dielectric constant tend to have significant sensitivity to the imposed electric field, both static and changing. The dc bias voltage, ac bias voltage, and a combination of them may change capacitance. With a given voltage across the part, thinner ceramic layers will result in a higher electrical field, and hence more change.
Figure 8.38 shows the extracted capacitance versus dc bias voltage as a function of frequency for an organic polymer capacitor. The part was a 7343-size 470- ?F capacitor with a 2.5-V rating. The impedance of the sample was measured in a small fixture with a different dc bias and ac source voltages. It was found that the ac source voltage had no measurable effect on the extracted capacitance. When the dc bias was varied with the proper polarity, the capacitance-frequency curve showed just a slight decay. At 100 Hz, the capacitance was 531 ?F with a 0-V bias. It dropped to 524 ?F with a 2.5-V bias. The capacitance stayed relatively stable up to 1V of reverse bias. With larger...
