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

Area of Science:

• Materials Science
• Chemical Engineering
• Electrical Engineering

Background:

• Hydrogen (H₂) is a vital clean-energy carrier, but its flammability necessitates robust leakage monitoring.
• Existing H₂ detection technologies face challenges in sensitivity, speed, and reliability for trace detection.

Purpose of the Study:

• To develop a highly sensitive and fast Micro-Electro-Mechanical Systems (MEMS) based sensor for detecting trace hydrogen (H₂) in air.
• To demonstrate the efficacy of an AlGaN/GaN high-electron-mobility transistor (HEMT) architecture for reliable H₂ sensing.

Main Methods:

• Fabrication of a MEMS sensor using a monolithic AlGaN/GaN platform with a suspended membrane, integrated microheater, and a four-HEMT Wheatstone bridge.
• Utilized Palladium (Pd) gate catalysis for H₂ dissociation and spillover to modulate the Schottky barrier and achieve differential readout.
• Characterized sensor performance including limit of detection (LOD), sensitivity, response/recovery times, selectivity, and long-term stability at 315°C.

Main Results:

• Achieved a limit of detection (LOD) of 0.1 ppm for H₂ at 315°C with a sensitivity of 1.48 mV/V/ppm.
• Demonstrated a wide working range (0.1-1000 ppm) with fast response (5.7 s) and recovery (26.2 s) times at 1000 ppm.
• Exhibited high selectivity to H₂ with negligible cross-sensitivity to common interferents and excellent long-term stability and repeatability.

Conclusions:

• The developed MEMS AlGaN/GaN HEMT sensor offers a promising solution for high-sensitivity, fast, and reliable trace hydrogen leak detection.
• The integrated, differential architecture is well-suited for safety applications in semiconductor manufacturing and fuel-cell systems.
• Projected ppb-level detection limits suggest potential for even more sensitive future iterations.