Thin films of lithium phosphorus oxynitride were grown using a plasma-assisted, directed vapour deposition technique. In this approach, a high voltage electron beam was used to vaporize a Li3PO4 source and a supersonic, nitrogen-doped, helium gas jet then transport the vapour towards a substrate. A hollow cathode technique was then used to create an argon plasma just above the substrate. This sufficiently ionized the nitrogen in the gas jet to allow its incorporation into the Li3PO4 film reactively forming lithium phosphorus oxynitride. Increasing the nitrogen flux in the gas jet also increased the deposition rate from 113 to 178nm/min for the deposition conditions used here, significantly reduced the pore volume fraction in the films and increased the N/P ratio from 0 to 0.75 as the gas jet nitrogen flux was increased from zero to 4.3 x 1018 molecules/cm2 /s. Using substrate rotation, pore and columnar-free dense Lipon films could be grown by this method. The Li-ion conductivity increased from 3.7 x 10−9 to 5.2 x 10−7S/cm as the nitrogen concentration was increased from zero to 2.1 x 1018 molecules/cm2s and was correlated with an increase in the film's Li/P ratio. An optimum nitrogen flux was identified. As the nitrogen flux was increased above this value, the Lipon films suffered lithium loss and partial crystallization, resulting in a decrease in their Li-ion conductivity.

The Influence of the Nitrogen-Ion Flux on Structure and Ionic Conductivity of Vapor Deposited Lithium Phosphorus Oxynitride Films. Y.G.Kim, H.N.G.Wadley: Journal of Power Sources, 2011, 196[3], 1371-7