Influence of sputtering pressure on the structure and ionic conductivity of thin film amorphous electrolyte

摘要

Ionic conducting thin film amorphous electrolytes are promising candidates for microelectronics applications. This study presents an investigation into the structure and composition of lithium phosphorus oxynitride (LiPON) thin film electrolyte prepared using radio frequency (RF) sputtering on Li _3PO_4 target. The ionic conductivity of LiPON thin films has been dramatically improved by decreasing N_2 pressure. X-ray photoelectron spectra (XPS) were used to determine the structure and composition of LiPON thin films. It was found that increasing the N_2 pressure during the deposition process resulted in a greatly decreased formation of triply coordinated -N<(N_t) as compared to doubly coordinated -N=(N_d) in LiPON thin films. These results indicate that the Nt structural unit plays an important role in the improvement of ionic conductivity as compared to the N_d structural unit. It also shows that PO_2N _2 tetrahedra with two N_t structural units exist in LiPON thin films at low N_2 pressures. Consequently, the improved ionic conductivity of the LiPON thin film deposited at low pressure results from the existence of PO_2N_2 tetrahedra with two Nt structural units in LiPON thin film. PO_2N_2 tetrahedra with two Nt structural units provides higher cross-linking density of the glass network and lower electrostatic energy than with two Nd structural units.