Liquid Phase Deposition Based ${\rm SnO}_{2}$ Gas Sensor Integrated With TaN Heater on a Micro-Hotplate

A micromachined liquid-phase deposition (LPD)-based SnO₂ gas sensor that is integrated with a tantalum nitride (TaN) microheater on micro-hotplate is designed and fabricated using microelectromechanical systems technology. TaN is available in many traditional complementary metal oxide semiconductor designs, unlike many other microheater materials. For the initial time, TaN is used in semiconductor metal oxide gas sensor as a heater. The thermal response, thermal distribution, and power consumption of the TaN microheater are measured using a thermal imaging camera. The operating temperature of TaN micro-hotplate can exceed 500°C and they have a favorable thermal distribution within the sensing area. The temperature variation over the sensing area for a TaN microheater with a size of 300×300 μm is ~ 4% at 500°C. Its power consumption is successfully decreased by adopting a structure with ratio of edge length of the membrane to that of the microheater of 2.5. The sensing responses of the LPD-based SnO₂ gas sensor with the TaN microheater to H₂S gas are measured at various operating temperatures. The optimal operating temperature of the designed gas sensors is in the range 250°C -300°C. The designed sensing film with an area of 100×100 μm has greater sensitivity to a staircase concentration of H₂S gas than those with the other two areas (200×200 μm and 300×300 μm).