Jihang Liu’s research while affiliated with Agency for Science, Technology and Research (A*STAR) and other places

Highly sensitive, selective, and compact hydrogen (H2) sensors for safety and process monitoring are needed due to the growing adoption of H2 as a clean energy carrier. Current resonant frequency-based H2 sensors face a critical challenge in simultaneously achieving high sensitivity, low operating frequency, and miniaturization while maintaining a high figure of merit (FOM). This study addresses these challenges by introducing a novel piezoelectric micro diagram (PMD) H2 sensor that achieves an unprecedented FOM exceeding 10⁴. The sensor uniquely integrates a PMD resonator with a palladium (Pd) sensing layer, operating on a stress-based mechanism distinct from traditional mass-loading principles. Despite a low operating frequency of 150 kHz, the sensor demonstrates a remarkable sensitivity of 18.5 kHz/% H2. Comprehensive characterization also reveals a minimal cross-sensitivity to humidity and common gases and a compact form factor (600 μm lateral length) suitable for IC integration. The sensor’s performance was systematically evaluated across various Pd thicknesses (40–125 nm) and piezoelectric stack covering ratios (50% and 70%), revealing a trade-off between sensitivity and response time. This PMD H2 sensor represents a significant advancement in resonant frequency-based H2 sensing, offering superior sensitivity, compact size, and robust performance for diverse applications in H2 detection and monitoring.