BACKGROUND OF THE INVENTION

Solid electrolytic capacitors (e.g., tantalum capacitors) are typically made by pressing a metal powder (e.g., tantalum) around a metal lead wire, sintering the pressed part, anodizing the sintered anode, and thereafter applying a solid electrolyte. Intrinsically conductive polymers are often employed as the solid electrolyte due to their advantageous low equivalent series resistance (“ESR”) and “non-burning/non-ignition” failure mode. For example, such electrolytes can be formed through in situ chemical polymerization of a 3,4-dioxythiophene monomer (“EDOT”) in the presence of a catalyst and dopant. However, conventional capacitors that employ in situ polymerized polymers tend to have a relatively high leakage current (“DCL”) and fail at high voltages, such as experienced during a fast switch on or operational current spike. In an attempt to overcome these issues, dispersions have also been employed that are formed from a complex of poly(3,4-ethylenedioxythiophene) and poly(styrene sulfonate (“PEDOT:PSS”). While the PEDOT:PSS dispersions can result in some improved properties, the capacitance of such materials tends to significantly degrade at high temperatures, particularly when subjected to relatively high voltages.

As such, a need currently exists for a solid electrolytic capacitor having an improved performance.

SUMMARY OF THE INVENTION

In accordance with one embodiment of the present invention, a capacitor assembly is disclosed that comprises a capacitor element. The capacitor element comprises a porous anode body that contains a valve metal compound, a dielectric that overlies the anode body and includes an oxide of the valve metal compound, and a solid electrolyte that overlies the dielectric. The solid electrolyte includes at least one conductive polymer layer that contains a sulfonyl ion. Further, the capacitor element comprises an organofunctional silane that is bonded to the oxide of the dielectric and is capable of bonding to the sulfonyl ion.

In accordance with another embodiment of the present invention, a method for forming a capacitor element is disclosed. The method comprises anodically oxidizing a sintered porous anode body to form a dielectric that includes an oxide of a valve metal compound; applying a solution to the anode that includes an organofunctional silane compound; applying a dispersion that contains conductive polymer particles and a sulfonyl counterion to form a conductive polymer layer; and bonding the organofunctional silane compound to the oxide of the dielectric.

Other features and aspects of the present invention are set forth in greater detail below.

