Accelerating hydrogen sensing with Pd-Mos capacitors using active controls of trapped charge

Abstract

Hydrogen monitoring with reliable, fast and cheap sensors is crucial to fully exploit the potential of this gas as an energy vector. One of the most appealing technologies for hydrogen sensing is based on MOS capacitors with palladium gate (Pd) made of nanoparticles, which acting as a catalyst for H2 promotes its dissociation. The generated atoms are then injected into the dielectric shifting the C(V) curve. In this work, we show that the use of active controls of trapped charge in dielectrics can radically accelerate the response time of palladium MOS capacitors as H2 sensors. The repeatability of the sensing is also improved, reducing significantly temporal drifts. The control strategy is based on second order sigma-delta modulation, implementing a discrete-time sliding mode control. Results show that the horizontal displacement of the C(V) curve of the capacitors can be cancelled out in real time by the application of voltage waveforms generated by the controls. Consequently, when exposed to hydrogen, a quasi-constant state operation of the capacitors is created, allowing a radical improvement of the time response as hydrogen sensors.