CONICET | Buscador de Institutos y Recursos Humanos

The semiconductor metallic oxides, like pure or doped SnO 2 , have been intensively used for resistive thickfilm gas sensors to detect toxic, fuel or explosive gases: NO x , SO 2 , CO, H 2 , CH 4 or VOCs (VolatileOrganic Compounds) using thick film techniques. For many years, SnO 2 , gas sensors (as based onmicrocrystalline materials) have been considered by its high sensitivity and relatively low operationtemperature T op =350 o C-450 o C for many years. If conventional microcrystalline SnO 2 is substituted bynanocrystalline SnO 2 to build the sensors, the authors have proved that sensor sensitivity increases from30% to 35% and that the T op decreases from (350-450)oC to a range (180-220)oC. In the last decade,nanocrystalline powders with high [surface/volume] ratio have been synthesized and applied reaching aconsiderable improvement of devices. As sensors work in oxygen atmosphere, the sensing mechanismshave been carefully studied for micro- and nanocrystalline SnO 2 . In this case, a H 2 (g) sensor built withpure SnO 2 was chosen to carry out the multi-layered thin film techniques which will be used in a futureexperience to build a doped with Cu 2 O - SnO 2 sensor to measure SH 2 (g) ppm in air. At first, H 2 (g)sensors were built at DEINSO with thick films. Techniques to build the layered nanocrystalline pure SnO 2thin films were performed and they are going to be optimized. The nanocrystalline pure SnO 2 has beensynthesized by three thin film techniques to compare results. Nanomateriales were characterized by DRX:crystallite size was measured by Scherrer equation and lattice stresses as produced by the differentsynthesis methods were also studied by X-rays diffraction. The thin films due to their thickness, to theirdeposit in multiple layers and to the thermal treatments to which they are subjected, produce stressescausing defects, such as: dislocations, grain boundaries, interfaces, vacancies clusters, etc. These defectsaccelerate the gases diffusional processes in the sensor, improving, in consequence, the deviceperformance. Adsorption BET techniques and HRTEM morphology studies were performed on films.SEM was used to measure the films thickness and the surface relief or rugosity.The double meander electronic circuit (built by MEMS) to control sensors (already patented by theauthors) was also improved by a new controlled, modular and portable circuit, being able to program theworking temperature, the sensing operation modes, the heating and the commutation time between them.