MOS capacitors with hafnium oxynitride(HfON)gate dielectrics were fabricated on Ge and Si substrates using the RF reactive magnetron sputtering method.A large amount of fixed charges and interface traps exist at the Ge/HfON interface.HRTEM and XPS analyses show that Ge oxides were grown and diffused into HfON after post metal annealing.A Si nitride interfacial layer was inserted between Ge and HfON as diffusion barrier.Using this method,well behaved capacitance–voltage and current–voltage characteristics were obtained.Finally hystereses are compared under different process conditions and possible causes are discussed. MOS capacitors with hafnium oxynitride (HfON) gate dielectrics were fabricated on Ge and Si substrates using the RF reactive magnetron sputtering method. A large amount of fixed charges and interface traps exist at the Ge / HfON interface. HRTEM and XPS analyzes show that Ge oxides were grown and diffused into HfON after post metal annealing. A Si nitride interfacial layer was inserted between Ge and HfON as diffusion barrier. Using this method, well behaved capacitance-voltage and current-voltage characteristics were obtained. conditions and possible causes are discussed.