Improved sensing characteristics of MISiC Schottky-diode hydrogen sensor by using HfO2 as 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 HfO2 sensor is more sensitive than its SiO2 counterpart. This should be mainly attributed to the larger barrier-height at the Pt/HfO2 interface which can reduce the current of the sensor before hydrogen exposure. Moreover, the sensitivity initially increases with the thickness of the HfO2 film because a thicker oxide layer can provide a larger barrier-height reduction upon hydrogen exposure. However, further increasing the thickness of the HfO2 dielectric 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.