POLYPYRROLE AS A SOLID-ELECTROLYTE FOR TANTALUM CAPACITORS

Tantalum/tantalum pentoxide (Ta/Ta2O5)-based capacitors, in which poly pyrrole (PP) is used as a solid electrolyte coating, have been studied . Aromatic sulfonate salts were used as the charge-compensating dopant ions due to their ability to impart good thermal and long-term stabil ity. The capacitors prepared showed excellent high frequency performan ce up to 100 kHz and stability. The capacitors were prepared by two me thods. In the first method the Ta2O5 dielectric layer was coated with chemically synthesized PP, followed by electrodeposition of a second l ayer of PP to increase the thickness and integrity of the PP layer. In the second method, chemical polymerization was used alone and the pro cess repeated several times in order to obtain complete coverage of th e Ta/Ta2O5 anodes. The redox properties of the PP synthesized chemical ly and electrochemically were studied by cyclic voltammetry and indica te that the polymers have similar electrochemical properties. Composit ional analyses were carried out using X-ray photoelectron spectroscopy (XPS) before and after the re-anodization process used in the capacit or preparation to enhance the integrity of the Ta2O5 dielectric. UV-Vi s spectroscopy was used to check the stability of the PP to spontaneou s ion exchange during the re-anodization process. The results indicate that aromatic sulfonates remain as the dopant ions when the reformati on is carried out in the same aromatic sulfonate solution, but are par tially substituted by H2PO4- when the reformation is carried out in H3 PO4. For the chemical polymerization, different synthetic conditions w ere used in order to improve the conductivity of PP; specifically, the use of low temperature and the addition of p-nitrophenol reduce the e quivalent series resistance (ESR) of the capacitors.