Design and fabrication of a nanoporous micro-hotplate for gas detection with low power and high sensitivity

We present the self-ordered nanoporous array in Si-substrate by means of an anodic aluminum oxide (AAO) template and a micro-hotplate (MHP) fabricated by surface micromachining technology. Finite element analysis (FEA) was performed to ensure uniform temperature gradient and then compared the porous with flat surface on the power consumption before fabrication. Using mixed electrolytes (oxalic acid and phosphoric acid), anodized voltage (40~65 V) and anodized time (3~10 min), we successfully transferred the porous surface to the top of a MHP device. Through r.f. sputtering, we deposited 200 nm of tin oxide as porous gas-sensitive material. Finally, a carbon monoxide (CO) gas test with different concentrations was carried out and lower power dissipation due to the nanoporous surface demonstrated. The AAO process could be easily integrated with microelectromechanical systems (MEMS) technology and applied to nanoporous chemical sensors.