Atomic Layer Deposition (ALD) via substrate motion, rather than pulse-purge cycling on a fixed substrate, is emerging as a promising path to high speed low cost roll to roll deposition of high quality ALD gas diffusion barriers. To date the majority of research in ALD barrier films has been conducted using Al2O3 in the thickness range of 20-100nm, with multiple groups reporting Water Vapor Transmission Rates (WVTR) below the detection limits of commonly used testing methods. A smaller body of research has examined TiO2 films, which in some cases show comparable barrier performance over a similar thickness range. Here we report a Plasma Enabled ALD process incorporating mixtures of Al2O3 and TiO2 from TMA, TiCl4, and oxygen-containing plasma, formed by alternating single ALD cycles of each material in a spatial ALD reactor. RBS data indicates the resulting film has a volumetric ratio of Al2O3 to TiO2 of approximately 1.5:1, reflecting the growth rates of each individual material. Use of the mixed material substantially reduces the required film thickness for a given WVTR performance compared to either pure Al2O3 or TiO2. The relationship between barrier performance and ALD film thickness is examined over the range of 2nm to 25nm, with WVTR rates in the range of 10-4 g/m2/day for coatings of 5nm to 10nm thickness, and the mid 10-6 range, near the limit of the calcium test employed, for the thickest films. The process has been ramped from the spatial ALD reactor to a Pilot scale roll to roll reactor configured to deposit the mixed film on rolls of polymer 300mm wide by up to 500m long.