GB907666A - - Google Patents

Abstract

907,666. Anodizing and etching a film-forming metal; capacitors. WESTERN ELECTRIC CO. Aug. 18, 1960 [Sept. 21, 1959], No. 28635/60. Drawings to Specification. Classes 37 and 41. A method of making a capacitor having an improved dielectric oxide layer, e.g. a printed capacitor, comprises (a) anodizing a first electrode of a film-forming metal such as Ta, Al, Nb, Hf or Zr to form a dielectric oxide film thereover; (b) etching the metal at positions where there are irregularities or defects in the oxide film by immersing the electrode in a non- aqueous electrolyte comprising ions of at least one halide and biasing the electrode anodically; (c) reanodizing the electrode to oxidize the etched parts; and (d) disposing a second electrode such that the dielectric film is interposed between the first and second electrodes whereby the first and second electrodes and the dielectric therebetween form the capacitor. The etching electrolyte may employ, for example, CH 3 OH, C 2 H 5 OH, acetone, nitrobenzene phenol or aniline as solvent and salts such as AlCl 3 , LiCl NH 4 Br, KF, NaI and NaF as sources of halide ions. The etching current should be in the range 1-10 mA per sq. cm. and the etching may be carried out in one step at a voltage above the operating voltage of the capacitor being produced or in a series of steps at increasing voltages to a voltage above the operating voltage with reanodizing after each step. In one example of making a capacitor, Ta was sputtered on to a glass substrate and the Ta anodized in an electrolyte containing oxalic acid, water and ethylene glycol. Etching was in a solution of LiCl in CH 3 OH. After reanodizing, a counter electrode of Au was deposited in contact with the anodized surface. In other examples, solid electrolytic condensers have anodized Nb anodes e.g. coated with MnO 2 and wet electrolytics have anodized porous A1 anodes. Specifications 747,051 and 863,596 are referred to.