AlGaN/GaN HEMT H₂ sensor with integrated Wheatstone bridge and on-chip microheater for 0.1-ppm detection.

Hydrogen (H₂) is a key clean-energy carrier in the transition to sustainable energy systems, but its extreme flammability and low ignition energy demand highly reliable leakage-monitoring technologies for safe deployment. This study presents a MEMS AlGaN/GaN high-electron-mobility transistor (HEMT) H₂ sensor that achieves high sensitivity and fast detection of trace hydrogen in air. The device implements a four-HEMT Wheatstone bridge-two Pd-gated sensing HEMTs and two passivated reference HEMTs-with an integrated microheater, all monolithically fabricated on a suspended GaN membrane. Pd-catalyzed H₂ dissociation and spillover lower the effective gate work function and modulate the Schottky barrier, and the differential readout suppresses common-mode drift. At 315 °C, the sensor achieves a limit of detection (LOD) of 0.1 ppm with a corresponding sensitivity of 1.48 mV/V/ppm. A combined device model and noise analysis further projects a detection limit approaching the ppb level. The baseline-corrected output is monotonic and well described by a four-parameter logistic model, thereby defining a practical, quantifiable working range of 0.1-1000 ppm (spanning four orders of magnitude). At 1000 ppm, the response and recovery times are 5.7 s and 26.2 s, respectively. The sensor exhibits high selectivity to H₂ with negligible cross-sensitivity to typical interferents (e.g., alcohols, SO₂, CH