A novel approach for nanoporous gas sensor fabrication using anodic aluminum oxidation and MEMS process

An innovative fabrication method to produce a nanoporous Si or SiO₂ surface by employing anodic aluminum oxidation (AAO) method and reactive ion beam (RIE) etch of MEMS process is presented. To enhance sensitivity and reduce the sensing dimensions of a gas sensor, a nanoporous surface of gas-sensitive material is preferred. This class of sensor devices can be implemented on silicon or silicon-on-insulator (SOI) substrates that feature a thin membrane of micro-hotplate structure with micro-heaters and electrodes, and operate as chemoresistive devices fabricated by CMOS standard process. Being different from conventional CVD process, PVD-based TiO₂ thin films are employed as active layers and deposited onto the AAO-fabricated silicon dioxide porous surface. In this paper an integrated process to fabricate the sensor structure and TiO₂ thin film deposition are developed, and comprehensive gas tests also demonstrate successful results in better sensitivity and faster response time less than 2 min within 4000~6000 ppm of oxygen. Using novel AAO process to fabricate nanoporous gas sensors not only reduces the complexity of conventional surface poration process, but also enhances response performance of gas-sensitive thin films, disclosing a very promising method to produce nanoporous gas sensors in a cost-effective way.