AlN recently gained much attention for its potential applications in semiconductor power devices. Sputtered AlN can be an alternative to the conventional SiO2 hard mask. For GaN etching and regrowth, the use of AlN hard mask can eliminate the possibility of Si and O elements acting as shallow donors to the regrown GaNe. In this work, deposition, patterning and etching of AlN are explored to examine its potential as a good hard mask that has near-vertical and smooth sidewall profiles. In addition, AlN with wide energy bandgap of 6.2 eV confers its electrical isolation properties for high breakdown field; combined with its high dielectric constant up to 8.5, AlN can be used as a high-k dielectric material for MOS device applications. In this work, metal-insulator-semiconductor (MIS) capacitors are fabricated, the dielectric constant and breakdown field of sputtered AlN are determined as ~6.7 and ~4.3 MV/cm by C-V and I-V measurements. Time-dependent dielectric breakdown (TDDB) behaviors of sputtered AlN in MIS capacitors are also evaluated for understanding the dielectric breakdown mechanism and reliability under long-term electrical stress.