A Microelectromechanical-Cantilever Hydrogen Sensor with Palladium-Driven Bending and Piezoresistive Readout

Abstract

Hydrogen gas (H₂) is considered a promising source of environmentally friendly and sustainable energy of benefit for global decarbonization. However, given the flammable and explosive nature of H₂, highly sensitive and selective detection systems with fast response are needed to enable leakage monitoring to ensure safe deployment and use. To address this need, we propose a microelectromechanical (MEMS) platform for H₂ sensing with the aim of achieving sub-1-ppm sensitivity. Our platform employs a MEMS structure that has H₂-responsive palladium (Pd) features. Once exposed to H₂, the Pd lattice expands as H₂ diffuses into it. This results in the structural deflection of a mechanically-mobile feature, in particular a cantilever. This deflection is measured using piezoresistors, which are embedded in the cantilever using a spin-on glass doping process. Piezoresistors enable rapid high-accuracy detection and quantification of H₂, as will be shown in this thesis through a combination of modeling, sensor development, sensor fabrication, and basic experimental characterization. In this thesis, we have successfully developed a fabrication plan, demonstrated the two key aspects of our fabrication, namely beam release and piezoresistor fabrication, shown beam bending driven by absorption of hydrogen by palladium, and shown that our piezoresistors respond to beam bending. Our physical results match our theoretical predictions for a beam of size 100 µm by 20 µm and a resistor with resistance 115 kΩ fabricated on SOI chips. This beam could be used to detect H₂ below 1 ppm.