Electron spin resonance (ESR) spectra are investigated in order to analyze paramagnetic defects in amorphous
SiOx films with 0.8≤x≤1.87 prepared by a co-sputtering of Si-wafer chips and a SiO2 disk target. Effects of the
thermal annealing at 900 °C and 1100 °C on the ESR spectra are also investigated. Four types of silicon
dangling bond centers with forms of •Si≡Si3−nOn (n=0, 1, 2 or 3) are assumed in order to simulate the ESR
spectra. The random bonding model appears to describe the network structure of the films with x~2, that is,
near the stochiometric composition of SiO2. It is suggested that the structural fluctuation around silicon
dangling bonds is larger in the sputtered SiOx films used in the present work in comparison with those
prepared by plasma-enhanced chemical vapor deposition.