Electrical devices containing conductive polymers

Details Electrical devices containing conductive polymers Electrical devices containing conductive polymers

1997-03-13

1999-02-23

Gellner, Michael L.

Electrical resistors

Resistance value responsive to a condition

Current and/or voltage

338225D, 338327, 338328, 427103, H01G 710

Patent

active

058748857

DESCRIPTION:

BRIEF SUMMARY
BACKGROUND OF THE INVENTION

1. Field of the Invention
This invention relates to electrical devices comprising conductive polymer compositions and to circuits comprising such devices.
2. Introduction to the Invention
Electrical devices comprising conductive polymer compositions are well-known. Such devices comprise an element composed of a conductive polymer. The element is physically and electrically connected to at least one electrode suitable for attachment to a source of electrical power. Those factors determining the type of electrode used include the specific application, the configuration of the device, the surface to which the device is to be attached, and the nature of the conductive polymer. Among those types of electrodes which have been used are solid and stranded wires, metal foils, perforated and expanded metal sheets, and conductive inks and paints. When the conductive polymer element is in the form of a sheet or laminar element, metal foil electrodes which are directly attached to the surface of the conductive polymer, sandwiching the element, are particularly preferred. Examples of such devices are found in U.S. Pat. Nos. 4,426,633 (Taylor), 4,689,475 (Matthiesen), 4,800,253 (Kleiner et al), 4,857,880 (Au et al), 4,907,340 (Fang et al), and 4,924,074 (Fang et al), the disclosures of which are incorporated herein by reference.
As disclosed in U.S. Pat. Nos. 4,689,475 (Matthiesen) and 4,800,253 (Kleiner et al), microrough metal foils having certain characteristics give excellent results when used as electrodes in contact with conductive polymers. Thus U.S. Pat. No. 4,689,475 discloses the use of metal foilswhich have surface irregularities, e.g. nodules, which protrude from the surface by 0.1 to 100 microns and have at least one dimension parallel to the surface which is at most 100 microns, and U.S. Pat. No. 4,800,253 discloses the use of metal foils with a microrough surface which comprises macronodules which themselves comprise micronodules. Other documents which disclose the use of metal foils having rough surfaces, but which do not disclose the characteristics of the foils disclosed in U.S. Pat. Nos. 4,689,475 and 4,800,253, are Japanese Patent Kokai No. 62-113402 (Murata, 1987), Japanese Patent Kokoku H4-18681 (Idemitsu Kosan, 1992), and German Patent Application No. 3707494A (Nippon Mektron Ltd). The disclosure of each of these U.S., Japanese, and German documents is incorporated herein by reference.


SUMMARY OF THE INVENTION

We have found that still better results for electrodes which are in contact with a conductive polymer can be obtained by using rough-surfaces metal foils having one or both of two characteristics which are not found in the metal foils which have been used, or proposed for use, in the past. These characteristics are minimum average height (and preferably a certain maximum average height), as expressed by a value known as the "center line average roughness", whose measurement is described below. In addition, the protrusions from the surface of the foil have a certain minimum irregularity (or "structure"), as expressed by a value known as the "reflection density", whose measurement is also described below. the surface of the foil comprise a second metal. The first metal is selected to have high thermal and electrical conductivity, and is preferably easily manufactured at a relatively low cost. In addition, the first metal is often more likely to cause degradation of the conductive polymer than the second metal. Fracture of the protrusions, caused by thermal cycling of the device, and/or thermal diffusion of the metals at elevated temperature, exposes the second metal rather than the first metal. conductive polymer penetrates into the surface of the foil sufficiently to provide a good mechanical bond. However, if the height of the protrusions is too great, the polymer will not completely fill the crevices between the protrusions, leaving an air gap which will result in accelerated aging of the conductive polymer and/or more rapid corrosion of the polymer/metal inte

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