A new 4H-SiC hydrogen sensor with oxide ramp termination

A Pd/SiO2/4H-SiC MOS capacitor with oxide ramp termination has been fabricated and its utilization for hydrogen (H2) sensing is reported. The grown oxide and oxide-semiconductor interface properties investigation by electrical measurements on test capacitors gave an electron tunneling barrier (Φb=2.62 eV) very close to the theoretical one (Φb=2.7 eV). This large electron tunneling barrier shows good oxide insulating properties. The density of interface states (Dit) has a relatively low value for a 31 nm thick oxide, with no post-oxidation annealing. The gas sensing capabilities of the SiC-MOS capacitor were tested at elevated temperatures, for different H2 concentrations. The sensor response increased with temperature, the maximum sensitivity (80%) being reached at 450 K. The flat band voltage (VFB) is left shifted up to 1.51 V at 20 ppm H2 concentration, showing sensitivity at low gas concentrations. The response/recovery times of about 5 to 6 s, respectively, were measured at 10,000 ppm hydrogen in nitrogen. These results recommend this capacitor structure for H2 detection.