Hydrogen gas is a pollutant-free energy source that is closely related to industry and human life. Recently, intensive research has been conducted on hydrogen as an alternative fuel. Hydrogen gas is used in various fields such as refinery process, cooling system in nuclear power plant, semiconductor process and hydrogen fuel cell vehicle. However, hydrogen is the highly explosive gas with wide explosion range and low ignition energy. Thus, hydrogen gas detection in various conditions is very important for hydrogen-related industry. Especially for hydrogen sensors in hydrogen fuel cell vehicle, proper monitoring of the feed stream is critical to ensure highly efficient energy conversion. In this environment, accurate and reliable detection of hydrogen in highly humid ambient is vital. AlGaN/GaN high electron mobility transistor (HEMT) structure has high density and mobility carriers at 2 dimensional electron gas channel (2-DEG) induced by piezoelectric and spontaneous polarization of AlGaN and GaN interface, from which the drain current response can be amplified through a functionalized gate electrode. Most of GaN based hydrogen sensors including nanowires, Schottky diode, metal oxide semiconductor (MOS) diode, and AlGaN/GaN HEMT employ platinum thin films as catalytic active layer. Hydrogen molecules are dissociated on active Pt surface, influence the channel conductance or Schottky barrier height, and induce the current response.

 In this work, AlGaN/GaN HEMT based hydrogen sensors incorporating nano-porous membrane was demonstrated. Platinum thin film serves as both Schottky contact and sensing material simultaneously. The device showed the excellent sensitivity for 500 ppm hydrogen even in 100% relative humidity. The nano-porous membrane coated on the sensor area effectively permits the approach of hydrogen gas molecules to sensing area while blocking water molecules which tend to cover the active sites of the sensor. The device showed reliable hydrogen gas sensing characteristics even after 25℃ ~ 100℃ heating cycle stress. This results support the potential use of AlGaN/GaN HEMT hydrogen sensor with nano-porous membrane in the applications of fuel cell vehicle.