Design and fabrication of an integrated MEMS O2 sensor based on nanostructured TiO2

Developing the miniaturised gas sensors is an increasingly active area of research. These devices, particularly relying on the low power and small size, have been widely used in a lot of micro equipment. Nanostructured materials can provide critical enhancements in the performances of micro/nano gas sensors on account of their high surface area. This paper proposes an integrated micro-electro-mechanical system (MEMS) O-2 gas sensor based on the hierarchical nanostructured TiO2 aiming at gaining the benefits of both the nanomaterials and the platforms in high-performance micro/nano gas sensors. The sensor chip was designed as a pair of interdigitated electrodes which are connected by the nanostructured TiO2 film, and surrounded by the double loop microheaters on the same layer. The low dimension nanostructured TiO2 was grown onto the micro hotplate via the acid vapour oxidation (AVO) process. In the precondition of solving the problem of how to protect front side micropatterns of the wafer, the integration of the MEMS process and the nanostructured TiO2 film preparation process was studied. The results indicated that the hierarchical nanostructured TiO2 could bridge the two micro interdigitated electrodes, and micro hotplate with the suspension membrane structures was well defined. The integrated sensor provides a general methodology of developing a micro/nano sensor based on the nanostructured materials.