Microcapteurs et multicapteurs de gaz

Abstract

Our work involves the design and rigorous evaluation of a new design of Metal Oxide Semiconductor (SMO) gas sensor with different shapes and sizes, in order to evaluate the most efficient implantation geometry in terms of power consumption, membrane stability and temperature distribution. The virtual design implements innovative aspects, allowing for an improvement in the selectivity and energy consumption of gas sensors, making the product suitable for a wide variety of applications. To further support the simulation results, we start the study with a validation of our model from a comparative study of several types of geometries of the heating element using COMSOL Multiphysics. The aim of this study is to provide an improved model, with a more uniform temperature at the level of the active zone (response with the least possible noise), as well as a reduction in the cost of the sensor (power consumed and dimensions of the chip. reduced, minimize the etching steps by embedding the heating element and the electrodes in the same layer above the membrane). After completing the temperature study, the second part of our work turns to an experimental study of electrical conductivity. We started by depositing the layer of tungsten oxide WO3 (50 nm) on transducers manufactured at LAAS in Toulouse, After annealing the samples (500 ° C), we carried out tests on the latter under dry air and vacuum in parallel, using a LabVIEW program which allows to control the temperature of the heater, with temperature round trips (from ambient to 350 ° C, and from 350 ° C to ambient). Several programs were tested, a rise and fall of temperature from 0V to 10V and from 10V to 0V with different steps, and then the tests were repeated by adding different thicknesses of gold layers on the transducers (0.2 nm, 0.3 nm, 0.5 nm, 1 nm, 1.5 nm, 2 nm, and 2.5 nm gold layer). The ozone tests allowed us to validate the activation energies results calculated previously. Indeed, the responses observed from the samples tested under ozone are in agreement with the results of the tests carried out in dry air and under vacuum. The monitoring of metallic and semiconductor behavior of the response through temperature, oxygen pressure, as well as metallic nanograins is a very important parameter in the detection of metal oxide gas sensors. The signal modulation of the response in this case is easy and controllable, so this leads us to an improvement in selectivity which is in particular the main shortcoming of gas sensors based on metal oxides.