GROWTH OF HIGH QUALITY ALUMINA DIELECTRIC FILMS

Abstract

Insulating layers are now being widely used in 1415 structures in addition to thin film devices and integrated circuits, in achieviftg numerous new impor-tant device functions. A process of growing high quality alumina dielectric films by wet anode. ,at .on has been. fully developed and investigated. The process is extre. mely simple, highly reliable and requires' very little investment in establish .ng facilities. Two electrolytic baths have been developed '(a) bath consisting of 78 grams of boric acid, 200 grams of ethylene glycol and 25% aqueous NH4OHi solution added to make pH 7 (b) bath consisting of 100 ml of 3% tartaric acid. 25% aqueous NH4OH solution added to make pH 6, and 200 ml of propy-lene glycol added as dilutant. Control of the pH value of the electrolyte was found essential to prevent the dissolution of alumina film or etching of the aluminum film during anodisation. since the detailed information about the first one is not available, it has therefore been studied and reported here to a great detail. The electrical characteristics of the grown altm Una layers have been studied by fabricating thin film Al-alumina-Al capacitors. The alumina dielectric layers were formed (iv) electrochemically by anodising a part of the base electrode deposited on 'a glass substrate. The success-ful anodisation of an aluminum film on glass substrate depends highly on the quality of the aluminum film deposited on the substrate particularly as regards to the pin hole density and adhesion of the film. The preheating and post.•balcing of the films have enormous effect on the quality of the film. The heating conditions were optimised by several. -experiments for aluminum deposition for base and counter electrodes. Capacitors with dielectric areas O. olo7 erns` to 1 cros2 and dielectric thickness 700 A° to 2300 A have been fabricated. itie results of both the bathe have been caapared. Alumina dielectric films produced by anodisat .on in a bath of boric acid and ethylene glycol at 50V showed lower capa-citence density, lower dissipation factor,, higher break-down voltages and lesser leakage current as compared. to alumina dielectric films produced by anodisation in a bath of Tartaric acid and Propylene