Hydrogen sensors with double dipole layers using a Pd-mixture-Pd triple-layer sensing structure

This paper reports on new GaN sensors using a Pd-mixture-Pd triple-layer sensing structure to enhance their sensitivity to hydrogen at the tens of ppm level. The proposed hydrogen sensor biased with a constant voltage produced relatively high sensing responses of similar to 4.84 x 10(5)% at 10,100 ppm and similar to 8.7 x 10(4)% at 49.1 ppm H-2 in N-2. The corresponding barrier height variations are calculated to be 220 and 168 mV. When the sensor is biased by a constant current with maximum power consumption of 0.4 mW, a sensing voltage as an output signal showed a voltage shift of more than 17V (the highest value ever reported) at 49.1 ppm H-2 in N-2. By comparison to Pd-deposited GaN sensors, the improvement in static-state performance is likely attributed to double dipole layers formed individually at the Pd-GaN interface and inside the mixture. Moreover, voltage transient response and current transient response to various hydrogen-containing gases were experimentally studied. The new finding is that the former response time is shorter than the latter one. Crown Copyright (C) 2009 Published by Elsevier B.V. All rights reserved.