Improved sensing characteristics of MISiC Schottky-diode hydrogen sensor by using HfO₂as gate insulator

Hafnium dioxide deposited by RF sputtering is used as the gate insulator of metal-insulator-silicon-carbide (MISiC) Schottky-diode hydrogen sensors. Sensors with different gate insulator thicknesses are fabricated for investigation. Their hydrogen-sensing properties are compared with each other by taking measurements at various temperatures and hydrogen concentrations using a computer-controlled measurement system. Experimental results show that for the same insulator thickness, the HfO2sensor is more sensitive than its SiO2counterpart. This should be mainly attributed to the larger barrier-height at the Pt/HfO2interface which can reduce the current of the sensor before hydrogen exposure. Moreover, the sensitivity initially increases with the thickness of the HfO2film because a thicker oxide layer can provide a larger barrier-height reduction upon hydrogen exposure. However, further increasing the thickness of the HfO2dielectric beyond about 3.3 nm reduces the sensitivity, possibly due to more trapped charges in thicker high-k dielectric which can screen the effect of the polarized hydrogen layer.