Metal insulator semiconductor structures using high-k materials have been prepared and investigated for the passivation of 4H-SiC surfaces. Alternate layers of AlN and Al2O3 were deposited on 8 nm thermally grown SiO2 on epitaxial SiC, forming multilayer stacked dielectrics. Atomic layer deposition (ALD) has been used for the deposition. Our results show that the AlN, deposited by ALD, has a columnar polycrystalline structure with boundaries related to the step bunching of SiC epitaxial layer. Capacitance-voltage measurements have been performed at room temperature, 100, 200, and 300 degrees C. Annealing of the samples was also performed at these temperatures and they were consecutively measured at room temperature. Current-voltage measurements have also been performed before and after annealing. It has been observed that the stack with a bottom layer of Al2O3, forming an interface with the thin SiO2, is more stable at high temperatures; however, its breakdown voltage is less than that of the other stack with AlN forming the bottom layer. The breakdown behavior of the stacks is also found to be different depending on the order of AlN and Al2O3 layers. (c) 2010 The Electrochemical Society. [DOI: 10.1149/1.3517137] All rights reserved.