AVS 52nd International Symposium
    Applied Surface Science Thursday Sessions
       Session AS+TF-ThM

Paper AS+TF-ThM1
Characterization of Nanoscale Ceramic Gradient Coatings for Gas Analytical Microdevices

Thursday, November 3, 2005, 8:20 am, Room 206

Session: Thin Film Characterization
Presenter: M. Bruns, Forschungszentrum Karlsruhe GmbH, Germany
Authors: M. Bruns, Forschungszentrum Karlsruhe GmbH, Germany
V. Trouillet, Forschungszentrum Karlsruhe GmbH, Germany
H. Mueller, Forschungszentrum Karlsruhe GmbH, Germany
E. Nold, Forschungszentrum Karlsruhe GmbH, Germany
R.G. White, Thermo Electron Corporation, England
Correspondent: Click to Email
The key element of the Karlsruhe Micro Nose is a thumbnail sized gas-sensitive microarray which at present consists of 38 sensor elements on an area of 4x8mm@super 2@. It is based on a noble metal-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 initially identical sensors 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 assisted deposition. In this work we focus on mixed membranes combining the gas permeability of silica and the chromatographic discriminating capability of alumina. Different geometries were achieved by shaping the ion beam profile to gradually alter the ion current density across the microarray leading to laterally different deposition rates. Various Al/Si ratios within the membranes were obtained using different substrate temperatures during deposition. In the present paper a comprehensive characterization of differently shaped nanoscale membranes is reported. Auger electron spectroscopy is used for 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 presented as 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.