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In view to develop gas sensors, a first generation of lead-free thin films was deposited by different techniques on commercial Si and Al2O3 substrates. During our research project, the correlation between the micro structure of films, the structure of the embedded sensors and the applied temperature range, is being studied. In the first year, doped and undoped BaTiO3, KNbO3 and ZnO thin films have been deposited by sol-gel and PLD techniques. BT and BST films have shown a polycrystalline structure with very fine and regular grains, while disoriented grains with an average size ranging from 50 to 200 nm were observed on the KNbO3 film surface, and ZnO films exhibited a columnar growth. All films were characterized and finally embedded to make semiconductor gas sensors which have been tested under different gases. In this first generation of sensors, ZnO sensors have shown encouraging preliminary results under CO and H2S gases. Keywords : thin films, lead-free oxide, sensor, gas.

This paper reports a study of Ba0.9Sr0.1TiO3 films deposited on Pt/Ti/SiO2/Si substrates. The annealing temperatures were 750°C, 850°C and 950°C. An increase of the average size of grains was observed, from 60 nm at 750°C to 110 nm at 950°C, as well as an increase of the dielectric constant, remnant polarization and tunability. When the annealing time was decreased from 1 hour to 15 min, the dielectric constant and remnant polarization values have been increased. The optimized annealing conditions (950°C for 15 min) give the following results: εr = 780 and tgδ = 0.01 at 100 kHz, Pr = 13 µC/cm², Ec = 63 kV/cm and a tunability of 55%.