Lithium phosphorus oxynitride (LiPON) solid state amorphous film electrolytes were synthesized by ion beam assisted deposition (IBAD) using Li3PO4 target under nitrogen reactive plasma. IBAD presents an advantage of controllable nitrogen content of the films by adjusting N-2 and Ar flow ratio. X-ray diffraction (XRD), scanning electron microscopy (SEM), X-ray photoelectron spectroscopy (XPS), nanoindenter, and profiler were employed to characterize LiPON films. Our results indicate that the film at N-2 and Ar flow ratio of 1:8 showed the best surface morphology and mechanical properties. The highest N atomic percentage of 2.32% was also obtained at this synthesis circumstance, and the resultant LiPON film electrolyte showed higher ionic conductivity of 4.5 x 10(-6) S/cm at room temperature, as well as the highest hardness of 6.8 GPa and the lowest compressive stress of 147.2 MPa. It is believed that as-prepared UPON solid state electrolyte film optimized can effectively prevent delamination from electrodes, showing some promising application in thin film lithium ion batteries. Copyright (C) 2014, Hydrogen Energy Publications, LLC. Published by Elsevier Ltd. All rights reserved.