Silicon oxynitride thin films were deposited by reactive r.f. sputtering from a silicon target. Different Ar:O-2:N-2 gas atmospheres were used at fixed power density (3.18 W cm(-2)) and pressure (0.4 Pa) to obtain various film composition. Pt-SiOxNy-Pt sandwich type structure was realised for electrical property investigations. The C-V measurements showed the absence of a Schottky barrier and thus confirmed that Pt electrode provides an ohmic contact. The evolution of the current density showed a decrease of the film conductivity when the oxygen concentration in the films increases. The various layer composition leads to two different conduction mechanisms which were identified as space charge limited current (SCLC) and Poole-Frenkel effect. Finally, the structural defects of the films were studied by EPR analysis and the spin densities were correlated to both the composition and the electrical behaviour of the films. (c) 2006 Elsevier B.V. All rights reserved.