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Optimal SiO2 Doping for Enhanced SnO2 Sensitivity and Thermal Stability

Antonio Tricoli1, Markus Graf2, and Sotiris E. Pratsinis1. (1) Particle Technology Laboratory, Institute of Process Engineering, Department of Mechanical and Process Engineering, ETH Zurich, Sonneggstrasse 3, Zurich, CH-8092, Switzerland, (2) Sensirion AG, Laubisruetistrasse 51, Staefa, CH-8712, Switzerland

In metal-oxide gas sensors the relationship between nano-size and thermal stability is very challenging. Miniaturization of the sensitive material down to nano-scale and doping with noble metals has led to successful detection of analytes in ppb concentrations, but long term stability, which may be related to crystal growth, is still unresolved. The sensitivity of SnO2, the most widely used metal-oxide for gas sensors, increases drastically with decreasing grain size from 20 to 5 nm. Preserving these sizes during sensor fabrication and operation is difficult since high process and operation temperatures (200 – 900 °C) are applied. Here one-step synthesis of highly sensitive films of SnO2-SiO2 nanostructures is explored by FSP direct deposition and in-situ annealing resulting thermally stable and, well-adhering cauliflower-like deposits (1) and transparent sensors (2). Control and stabilization of the SnO2 particle and neck size is obtained by varying the SiO2 content during synthesis and direct deposition of these SnO2-based films. Detailed film characterization is carried out to understand the role of SiO2 for inhibiting SnO2 grain and crystal growth as well as the role of primary particle and neck size on film sensitivity of EtOH, a common analyte in sensor development (3).

1. A. Tricoli, M. Graf, F. Mayer, S. Kühne, A. Hierlemann, S.E. Pratsinis “Micropatterning Layers by Flame Aerosol Deposition - Annealing”, Adv. Mater., in press, (2008).

2. S. Kühne, M. Graf, A. Tricoli, F. Mayer, S.E. Pratsinis, A. Hierlemann, “Wafer-level flame-spray-pyrolysis deposition of gas-sensitive layers on microsensors”, J. Micromechanics and Microengineering, 18, 035040 (2008).

3. A. Tricoli, M. Graf, S.E. Pratsinis “Optimal doping for enhanced SnO2 Sensitivity and Thermal Stability”, Adv. Funct. Mater., in press, (2008).