HOW A LIMITED MASS-TRANSFER IN THE GAS-PHASE MAY AFFECT THE STEADY-STATE RESPONSE OF A PD-MOS HYDROGEN SENSOR

The hydrogen sensitivity of palladium MOS sensors in an oxygen-containing atmosphere is shown to depend on the area of the Pd film, the rate of the gas flow, the total pressure and the type of carrier gas. All observations can be explained by the influence of a limited mass transfer in the gas phase. This model is confirmed by mass spectrometric studies using a local gas-sampling technique. Requirements upon the sensor size and the H-2 supply to minimize mass-transfer influence are discussed.