A thin sub-layer ( 12) host material. The sub-layer may be formed by atomic layer deposition (ALD). The layer and sub-layer are annealed to form a composite dielectric layer. The host material crystallizes, but the crystalline lattice and grain boundaries are disrupted near the impurity sub-layer, impeding the migration of electrons. The impurity may be a material with a lower dielectric constant than the high-k material, added in such a small relative amount that the composite dielectric is still high-k. Metal-insulator-metal capacitors may be fabricated by forming the composite dielectric layer between two electrodes.