Chemical and microstructural modifications in LiPON thin films exposed to atmospheric humidity

Lithium phosphorus oxynitride (LiPON), the widely used solid electrolyte for thin film microbatteries, is not compatible with the ambient humid temperatures. The reasons for reduction in ionic conductivity of LiPON thin films from 2.8 × 10− 6 Scm− 1 to 9.9 × 10− 10 Scm− 1 when exposed to air are analyzed with the aid of AC impedance measurements, SEM, XPS and stylus profilometry. Initially, particulate-free film surfaces obtained soon after rf sputter deposition in N2 ambient conditions becomes covered with microstructures, forming pores in the film when exposed to air. LiPON films are deposited on Ti coated silicon in addition to bare silicon, ruling out the possibility of stress-related rupturing from the LiPON/Si interface. The reduction of nitrogen, phosphorus, and increased presence of lithium, oxygen and carbon over the film surface lowers the ionic conductivity of LiPON films when exposed to air.