Pd/PVDF thin film hydrogen sensor system based on photopyroelectric purely-thermal-wave interference

A novel sensitive solid-state sensor system for trace hydrogen gas detectio n has been developed as a next generation device to earlier photopyroelectr ic (PPE) hydrogen sensors. The basic principle of the sensor is based on th e technique of PPE purely-thermal-wave interferometry recently developed in this Laboratory. The active element of the sensor is a thin polyvinylidene fluoride (PVDF) pyroelectric film, sputter-coated with Pd on one surface a nd with a Ni-Al alloy electrode on the other surface. Unlike the convention al PPE hydrogen sensors, this new sensor produces a coherent differential P PE signal in a single detector, rather than using two detectors (one active , the other reference) and complicated electronics. The measurement results show that the signal noise level, the detectivity and the signal dynamic r ange are improved by more than one order of magnitude compared with the con ventional single-beam method. The operating characteristics have been exami ned for three different thicknesses of Pd coating on the same thickness PVD F-film detector. The signal generating mechanism, attributed to the change of the optical absorptance of the Pd coating when exposed to hydrogen, and/ or the shift in the Pd work function, is also discussed. (C) 1999 Elsevier Science S.A. All rights reserved.