A novel Pt-Ti-O gate Si-metal-insulator-semiconductor field-effect transistor hydrogen gas sensor

A novel hydrogen gas sensor based on platinum titanium-oxygen (Pt-Ti-O) gate silicon-metal-insulator semiconductor field-effect transistors (Si-MISFETs) was developed. The sensor has a unique gate structure composed of titanium and oxygen accumulated around platinum grains on top of a novel mixed layer of nanocrystalline TiOx and super heavily oxygen-doped amorphous titanium formed on SiO₂/Si substrates. The FET hydrogen sensors show long life times more than ten years as intrinsic chip life time by accelerated temperature aging test, and high sensing amplitude (ΔV_g), which is well fitted by a linear function of the logarithm of air-diluted hydrogen concentration C(ppm), i.e., ΔV_g(V)=0.355Log C(ppm)-0.610, between 100 ppm and 1%. The gradient of 0.355V/decade at 115°C is about ten times higher than that of Pt gate Si-MOSFETs hydrogen sensors. The threshold Voltage (Vth) of FETs is reproducible, and shows excellent uniformity over the 5-inch wafers, 3σVth of 178 mV.