Effect of hydrogen annealing on the hydrogen sensing response of palladium thin films

Annealing treatment can enhance the stability of hydrogen response in Pd thin films by reorganizing the grain structure to some extent, thereby improving the hydrogen-sensing performance. However, the hydrogen-sensing performance of Pd films at low hydrogen concentrations remains inadequate even after annealing in vacuum or air. To address this issue, this study investigates how hydrogen-atmosphere annealing affects the hydrogen-response characteristics of Pd film resistivity, with the aim of further improving the sensing performance of Pd thin films toward low-concentration hydrogen. Pd thin films of different thicknesses (50, 100, and 150 nm) were annealed at 250 °C for 2 h under H2 concentrations of 0, 250, 1000, and 4000 μl/l, and the resulting baseline drift and sensitivity were evaluated and compared with those of unannealed samples. The results indicate that introducing hydrogen at an appropriate concentration during annealing improves the baseline stability of the sensor resistance. However, sensitivity decreases as the hydrogen concentration during annealing increases. To balance the trade-off between baseline stability and sensitivity and achieve optimal low-concentration hydrogen detection performance, we propose a novel evaluation metric based on the “drift-to-response ratio.” Comparative results show that the 100 nm Pd film annealed under 1000 μl/l H2 delivers the best sensing performance, enabling stable detection of hydrogen down to 20 μl/l. This study provides a new strategy for optimizing annealing treatments to enhance the hydrogen-sensing performance of Pd thin films and offers practical guidance for designing annealing parameters.