Pt–Ti–O Gate Si-MISFET Hydrogen Gas Sensors-Devices and Packagings

A novel hydrogen gas sensor based on platinum-titanium-oxygen gate silicon-metal-insulator-semiconductor field-effect transistors (FETs) 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 sensing amplitude, ΔV_g(V), of the FET hydrogen sensor is well fitted by a linear function of the common 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 0.355 V/decade at 115°C is about ten times higher than the expected 38.5 mV/decade from Nernst equation. The threshold Voltage (Vth) of FETs is reproducible, and shows excellent uniformity over the 5-inch wafers, 3σV_th of 178 mV. Packaged sensors working at 115 °C typically show power consumption of 122.5 mW at room temperature environments.