Fabrication of thermoelectric gas sensors on micro-hotplates

We present a series of fabrication processes of high-performance thermoelectric gas sensor micro-devices including a membrane–releasing process in KOH for the mass production of hot-plate type membrane devices. The fabricated devices are hydrogen gas sensors based on the thermoelectric detection of the catalytic hydrogen combustion. The KOH wet etching membrane–releasing process, using protective wax or polymer coating shows fabrication yields of over 70% and 80%. Most sensors detect wide range hydrogen concentration from several part-per-million, ppm, to percent in air demonstrating robust sensor process. As the device working principle of the Seebeck effect is linear phenomena, a good linear relationship between voltage signal and hydrogen concentration can be achieved, 1 mV = 1000 ppm, down to 50 ppm hydrogen in air. The test method for a large number of sensor devices has been developed, and the validation study for mass production of gas sensors is carried out.