When Organometallic Chemistry and Metal Oxide Nanoparticles Meet Optimized Silicon-based Gas Sensor

International audienceAir quality control in confined places (automotive cabin, transportation and offices or working places) is getting more and more pregnant in the actual pollution levels we are facing in our industrial environment. Despite the intense research work in the field of new silicon sensors and sensitive elements, the need for a high accuracy and low cost metal oxide gas sensors remains a challenge. This is due to the generally admitted drawbacks of this kind of silicon device: the resistance drift of the polysilicon heating element, the harsh mechanical stress of the membrane applied to the sensitive layer and the progressive deactivation of the thin oxide sensitive layer which lead to a decrease of sensor performance upon time.We have developed a very new generation of metal oxide gas sensor, based on the combination of optimized micromachined silicon substrates and highly sensitive nanosized metal oxides derived from organometallic synthesis means [1, 2]. For the first time, an integrated approach for a general sensor design has been employed [3, 4]. This new sensor design has been built in accordance with the upstream constraints coming from the deposition method required by the liquid nature of the sensitive material. A key parameter for an improved response of the sensor is the highly porous nature of the sensitive layer and the number of electrical contact between oxide grains. The more the number of possible current pathway during sensor operation and the less the risk of sensitivity decreases due to deactivation of grain boundaries. As a matter of fact, nanopowders offer the best ratio of grains and grain boundaries for a giving volume of sensitive layer. The presented results show the thermomechanical behavior of the silicon substrate, the electrical and thermal stability of the platinum based heater element, and the very low and controlled membrane deformation when operated. Round membrane shape and contact electrodes are build in respect with the drop deposition technique employed for the sensitive layer. This robust silicon design has been successfully employed with various metal oxide nanoparticles synthesized by organometallic means (SnO2, ZnO) and deposited by a generic ink jet method. High quality and micron thick layers can be obtained with a very low defect level (no cracks, no délamination) and gas sensitivity (under CO, C3H8 and NOx) and air stability are presented in comparison with classical thin films sensitive layers