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Field-plate (FP)-terminated 4H-SiC Schottky barrier diodes (SBDs) have been fabricated for the first time using sputter-deposited aluminum nitride (AlNx) and hydrogenated AlN (AlNy:H) as high-k dielectrics. The results are compared to that of conventional plasma-enhanced chemical-vapor-deposition (PECVD) silicon dioxide (SiO2)-based FP devices. Extensive electrical and physical characterizations of these dielectrics on 4H-SiC were carried out. 4H-SiC SBDs fabricated using these dielectrics as FPs are investigated in terms of their breakdown voltage (VB) with respect to dielectric thickness, reverse-bias leakage current, and forward-bias characteristics up to an elevated temperature of 300degC. Our results indicate that a VB as high as 1750 V, which is more than 80% of the ideal theoretical value, can be achieved using Al-based dielectrics. This constitutes an improvement by more than 600 V, or almost 30% of the ideal theoretical VB, over conventional oxide-based FP devices fabricated in this paper using PECVD SiO2 . We attribute these improvements to the much-reduced electric field enhancement at the Schottky corners as a result of the higher dielectric constants of Al-based dielectrics, which is almost ~ 2.2 times that of SiO2. A net negative charge within the dielectric film also provides additional field relief, while an improvement of about ~ 1.3 times in the effective dielectric strength further contributes to the higher breakdown voltage observed.