Abstract A process for growing high quality aluminium oxide dielectric layers by wet anodization of aluminium film over a large area was developed and is reported in this paper. The electrolytic bath used is boric acid buffered with ammonium hydroxide and diluted with ethylene glycol. The properties of dielectric films grown with this bath were found to be superior to those of films grown in a tartaric acid bath under similar environmental conditions and using chemicals of the same grade. Several MIM structures were fabricated to demonstrate the high quality and reproducibility of the results. The high quality and low loss of the as-grown aluminium oxide films were determined by studying the characteristics of a distributed parameter notch filter fabricated with aluminium oxide as the dielectric.