We present a comparative study of the growth of the technologically highly relevant gate dielectric and encapsulation mated at aluminum oxide in inorganic and also organic heterostructures. Atomic force microscopy studies indicate strong similarities in the surface morphology of aluminum oxide films grown on these chemically different substrates. In addition, from X-ray reflectivity measurements we extract the roughness exponent beta of aluminum oxide growth on both substrates. By renormalising the aluminum oxide roughness by the roughness of the underlying organic film we find good agreement with P as obtained from the aluminum oxide on silicon oxide (0=0.38 +/- 0.02), suggesting a remarkable similarity of the aluminum oxide growth on the two substrates under the conditions employed. (c) 2008 Elsevier B.V. All rights reserved.