Selective deposition of CuO/SnO2 sol–gel on porous SiO2 suitable for the fabrication of MEMS-based H2S sensors

We report the realization of a miniaturized H2S gas sensor using micromachining of silicon substrate assisted by a porous oxide formation for selective patterning of CuO-doped SnO2 layers. The formation of sensing material (SnO2/CuO) is through a sol–gel spin coating process. The sol–gel adhesion to porous silicon dioxide is significantly better than regular plain SiO2 surfaces. The formation of a nano-porous and highly textured oxide layer is feasible through a sequential reactive ion etching process which utilizes one short step of reactive etching followed by another step of passivation. By repeating these subsequences for many times, desired textures are created which in turn would lead to a highly selective deposition of the sol–gel layer on the porous silicon dioxide. The sensor response to various H2S concentrations has been investigated showing a high sensitivity. Since the device is realized on a silicon-based membrane, the effect of electric current passing through the heating element has also been studied. SEM and XRD analyses have been used to investigate the surface morphology and crystallinity of SnO2 and porous SiO2 films.