Novel ultrathin gas-permeable Al-Si-oxide membranes have been developed by means of ion induced chemical vapor deposition in order to improve the gas analytical performance of an electronic nose. Dependent on the used precursor tailored Al/Si concentration ratios and even concentration gradients are attainable. The diversity in chemical composition and thickness across the gas sensor microarray has been proven by the combination of ellipsometry for the freshly prepared membrane and line scans derived from Auger electron spectroscopy and angle resolved x-ray photoelectron spectroscopy, respectively, for the baked membrane. (c) 2007 American Vacuum Society.