MOX gas sensors using multilayer aerogel

In this work for the first time we have demonstrated the feasibility of multilayer silica aerogel interleaved with thin layers of SiO₂, to replace the micromachined air pit used in fabrication of metal oxide (MOX) gas sensors. Microhotplate is the most important structure of MOX gas sensors since it provides the desired uniform temperatures ranging from 200 ^oC to 500 ^oC for the sensing material. Based on our previous work, in order to achieve this operating temperature we must have a thick layer of 5 to 20 μm aerogel. However, in the literature we cannot find reports that indicate multilayer spin-coated aerogel is possible. In our laboratory we have successfully spin coated two layers of aerogel with high porosity of 85% and low refractive index of 1.05. We have investigated the formation of thicker multilayer aerogel by having sputtered SiO₂ as interlayer. The heat insulation capability of multilayer is reported in both steady state and transient mode.