SnO2 thin films from metalorganic precursors: Synthesis, characterization, microelectronic processing and gas-sensing properties

SnO2 thin films were prepared by spin-coating of Sn(II) 2-ethylhexanoate solutions onto silicon substrates, followed by heat-treatment at 500 °C. From the study of the starting solutions and of the final films by Fourier transform infrared spectroscopy (FTIR), X-ray diffraction (XRD) and X-ray photoelectron spectroscopy (XPS) it was concluded that the film formation started with weak physical interactions between the individual precursor molecules and then proceeded through an extensive cross-linking as the heat-treatment took place. In this way mechanically resistant and well-adhering sensing layers were prepared. High-resolution transmission electron microscopy (HRTEM), in agreement with XRD, further revealed that the sensing films heat-treated at 500 °C consisted of SnO2 grains with diameters of about 10 nm. The films heat-treated at 500 °C were able to withstand a full microelectronic processing sequence, including wet etching, Ti/Pt contact formation, and heater processing on the backside of the sensor substrates. Gas-sensing tests have evidenced responses to CO and NO2 that are comparable to commercial thick film sensors, demonstrating a clear potential toward the achievement of high-performance low power consumption gas-sensing devices.