FET hydrogen-gas sensor with direct heating of catalytic metal

A method for heating field-effect-transistor (FET) gas sensors with minimum power is proposed. The time of the FET sensor response to target gases depends on temperatures of catalytic metals laminated on gate insulators. Therefore, maximum heating efficiency can be obtained by applying current to each catalytic metal directly and using those catalytic metals as heaters. FET hydrogen gas sensors have been fabricated on 7.5 mm × 3 mm × 0.73 mm silicon chips, and narrow palladium catalytic metal has been deposited and terminated by two electrodes. The FET sensor can be heated to 100 °C by applying current corresponding to 0.2 W, and the response speed to 1000 ppm by volume hydrogen gas increases by about a factor of six. No morphological change caused by the heating current has been observed in the catalytic metal. Moreover, numerical and experimental simulations demonstrate that the required power and time to heat the FET sensor to 100 °C can be further reduced to 20-30 mW and 1 s, respectively, by miniaturizing the senor chip to 2 mm × 2 mm × 0.15 mm. We are planning to apply the FET sensors with this heating method to our hydrogen-leak detection system that is being developed to make hydrogen energy structures safe and secure. Such detection systems consist of many sensor nodes powered by batteries, so reducing power consumption is important to extend battery lifetimes.