AVS 53rd International Symposium
    Applied Surface Science Friday Sessions
       Session AS-FrM

Paper AS-FrM11
Synthesis and Characterization of Nanoscale Al-Si-O Gradient Membranes for Gas Analytical Microdevices

Friday, November 17, 2006, 11:20 am, Room 2005

Session: Thin Film Characterization
Presenter: M. Bruns, Forschungszentrum Karlsruhe GmbH, Germany
Authors: M. Bruns, Forschungszentrum Karlsruhe GmbH, Germany
V. Trouillet, Forschungszentrum Karlsruhe GmbH, Germany
E. Nold, Forschungszentrum Karlsruhe GmbH, Germany
R.G. White, Thermo Electron Corporation, England
Correspondent: Click to Email
A microarray of 38 identical sensor elements on an area of 4x8mm@super 2@ is the key element of the Karlsruhe micro nose. It is based on a Pt-doped SnO@sub 2@ layer, the electrical conductivity of which is highly sensitive to the composition of the ambient atmosphere and is measured between adjacent parallel platinum strip electrodes. In order to enable pattern recognition techniques these sensor elements have to be gradually differentiated with respect to their gas response. For this purpose gas-permeable membranes with thickness variation of approximately 2 to 10 nm were deposited across microarray using ion beam induced chemical vapour deposition. This paper focuses on mixed Si-Al-O membranes combining the gas permeability of silica with chromatographic properties of alumina. Shaping of the ion beam profile gradually alters the ion current density and leads to laterally different deposition rates forming the membrane gradient as a projection of the ion beam profile. Various Al/Si concentration ratios within the membrane and even concentration gradients across the array can be obtained by tuning the array temperature during deposition. We present a comprehensive characterization of differently shaped nanoscale membranes with different Al/Si concentration ratios and gradients. Auger electron spectroscopy is used for the evaluation of the geometrical integrity of the uncoated electrode pattern and for the determination of thickness profiles, respectively. Parallel angle resolved X-ray photoelectron spectroscopy provides thickness information for the membranes together with information on chemical binding states in a non-destructive manner. Ellipsometry is a powerful quantification method for the determination of the desired ultra thin membrane thickness profiles. Moreover, after calibration with surface analytical data, ellipsometry allows for rapid evaluation of Al/Si concentrations ratios within the membranes.