High-Performance Piezoelectric Micro Diaphragm Hydrogen Sensor.

Highly sensitive, selective, and compact hydrogen (H) sensors for safety and process monitoring are needed due to the growing adoption of H as a clean energy carrier. Current resonant frequency-based H 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) H sensor that achieves an unprecedented FOM exceeding 10. 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/% H. 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 H sensor represents a significant advancement in resonant frequency-based H sensing, offering superior sensitivity, compact size, and robust performance for diverse applications in H detection and monitoring.