Solid-state thin film batteries (TFBs) consisting of amorphous V2O5/Pt/Ti/Si have been fabricated by specially designed dual target magnetron radio frequency (rf) and direct current (dc) sputtering systems at room temperature. It is shown that the discharge capacity of the TFBs is degraded with increasing cycle number; after 450 cycles, the capacity is dropped by similar to54% of the initial value. To investigate the degradation mechanism, the structural properties of as-deposited and cycled LiPON and a-V2O5 films are characterized by transmission electron microscopy (TEM) and x-ray diffraction (XRD) measurements. TEM and, XRD results show that the as-deposited LiPON and V2O5 are amorphous. It is, however, shown that cycling causes the occurrence of crystallites (2-6 nm across) not only in the V2O5 film, but also in the LiPON film. Based on the structural and electrochemical results, the cycle-induced degradation of capacity is correlated to the structural change of the LiPON and V2O5. (C) 2003 American Vacuum Society.