Effects of a polyimide coating on the hydrogen selectivity of MIS sensors

To enhance the selectivity of metal–insulator–semiconductor (MIS) sensors for hydrogen detection in mixed-hydrocarbon streams, a palladium MIS sensor has been modified by depositing a polyimide (PI) layer above the palladium surface. Response measurements indicate that PI-coated sensors inhibit the effect of gases, such as carbon monoxide, acetylene, ethylene, and methane on H2 response, dramatically improving selectivity to hydrogen. The effect of coated layer thickness on sensor response is also evaluated, and it is found that the sensor response rate strongly depends on PI film thickness. The modified performance of the PI coated sensor to hydrogen in gas mixtures is explained by both the permselective properties of the membrane and metal surface modification resulting from the PI coating.