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Preparation of thin insulating films by plasma anodization Olive, Graham

Abstract

The plasma anodization of polycrystalline niobium samples has been undertaken using a d.c. glow discharge in oxygen. The apparatus used, which has facilities for in situ ellipsometry measurements and sample temperature control, is described. Anodizations were carried out at various constant current densities up to 1.5 mA cm⁻² , and Langmuir probes were used to estimate the volt drop across the oxide during growth. The ellipsometry measurements yield oxide thickness and refractive index, and indicate that the films have a two-layer structure. Ionic currents are calculated from growth rates using Faraday's Law. Ionic current and oxide field strength data are analyzed and compared with published solution anodization results on the basis of the classical model of ionic conduction at high field strengths. The permittivity and loss factor of the oxide films are deduced from bridge measurements on capacitor structures produced by depositing counterelectrodes on the oxide surface. The introduction of water into the discharge was investigated, and found to affect the oxide growth rate.

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