The anodic oxidation of Aluminum (Al), which is a low temperature process, was used to form an aluminum oxide (Al2O3) film for use as an insulating layer. The anodization was done in a diluted, approximately 10% by volume, sulferic acid solution (H2SO4). Constant anodization voltages of 10, 15, and 20 volts, were maintained to obtain layers of Al2O3 ranging in thickness and refractive index from 3375-4077A and 1.46-1.95 receptively.
"Growth of Anodic Al2O3 Films,"
Journal of the Microelectronic Engineering Conference: Vol. 1
, Article 26.
Available at: http://scholarworks.rit.edu/ritamec/vol1/iss1/26