A lithium phosphorous oxynitride (LiPON) film sputtered from unsintered Li3PO4 powder target

A lithium phosphorous oxynitride (LiPON) film has been made by sputtering an unsintered Li3PO4 powder target in nitrogen gas. The Li content in the film is only ~ 60% of that in a conventional LiPON film obtained from a Li3PO4 target sintered at 700 °C. The ionic conductivity is 1.7 × 10− 6 S/cm at 25 °C, which is also slightly smaller than that of the conventional film (2.1 × 10− 6 S/cm at 25 °C). The lower content of Li in the new film is compensated by adding Li2O in the target in an amount as much as 50 mol% of Li3PO4. Although the composition of the Li compensated film is almost the same as that of the conventional LiPON film, the ionic conductivity was improved to as large as 3.1 × 10− 6 S/cm at 25 °C. X-ray photoelectron spectra (XPS) revealed that three-coordinated N atoms (P–N< P P ), responsible for the good ionic conductivity of LiPON films, are dominant in these newly fabricated films. This is quite different from the conventional LiPON films wherein two-coordinated N atoms (P–N=P) are predominant. The P 2p peaks in the new films shifted toward the high energy side for ~ 0.7 eV and this is attributed to the effect of the three-coordination of N atoms.