1.5.3 Environmental Hardness of Pt-Ti-O gate Si-MISFET Hydrogen Gas Sensors from Siloxane, Humidity, and Radiation

Platinum-titanium-oxygen (Pt-Ti-O) gate Si-MISFET hydrogen gas sensors have been found to show large sensing amplitude (∆Vg) of 624.4 mV with σ ∆Vg of 7.27 mV for nine repeated measurements even under nitrogen-diluted 1.0% hydrogen gas, which are nearly the same values of 654.5 mV with σ∆Vg of 3.77 mV under air-diluted 1.0% hydrogen gas. The Pt-Ti-O sensor devices can work stably as hydrogen sensors up to about 300 °C and also show environmental hardness as follows: When nitrogen-diluted 10ppm HMDS (hexamethyldisiloxane) was exposed to the sensor FETs for 40 minutes at working temperature of 115 °C, the sensing amplitude (∆Vg) little changed within repeating errors before and after HMDS exposures. The variations of ∆Vg between relative humidity of 20% and 80% are very small within ± 6 % around 50 % under the 40 °C atmosphere. The radiation hardness of developed hydrogen sensor chips from γ ray (Co) and/or X-ray (Synchrotron Radiation) is sufficiently strong enough even at extremely high integral dose such as 1.8 MGy. It comes from the robustness of PN-junction between drain and p-well due to large device dimensions.