Capacitance Stability of Polymer Tantalum Capacitors Under Different Environmental Conditions

Polymer Hermetic Sealed (PHS) Tantalum capacitors with pre-polymerized PEDOT cathodes and different dielectric thicknesses were used to study the stability of Polymer Tantalum capacitors under different environmental conditions. In particular, capacitance dependence on temperature, frequency, and dc bias voltage were studied in humid and dry capacitors with varying dielectric thicknesses. Capacitance and ESR measurements were performed to characterize the capacitors.Humid capacitors were observed to have higher capacitance than dry capacitors for all dielectric thicknesses. The capacitance for all dielectric thicknesses was observed to increase with temperature in both humid and dry capacitors. Humid capacitors showed a stronger temperature dependence at lower temperatures while dry capacitors showed a stronger temperature dependence at higher temperatures. These temperature effects were more pronounced in thinner dielectric capacitors, and the results were explained by the integrity of the dielectric-polymer interface. The capacitance for all dielectric thicknesses was also observed to decrease with an increase in frequency, both in humid and dry capacitors. The frequency effect was more pronounced in humid capacitors with thinner dielectrics. These results were explained by the RC ladder effect, secondary transitions of the polar segments of the polymer cathode, and lower reactance and lower self-resonance frequency of the thinner dielectric capacitors