Diffusion of oxygen in amorphous HfO2

We carefully prepared 100-nm-thick amorphous hafnia (a-HfO2) thin films of a homogeneous structure, and measured the diffusion profile of oxygen using secondary-ion mass spectrometry with a stable isotope (18O) as a tracer. The diffusion coefficient of oxygen, D , in a-HfO2 was 3.5 x 10-24 to 7.8 x 10-20 m 2 s-1 at annealing temperatures from 300 to 500 degrees C, which are smaller than all previously reported values. The Arrhenius plots of D showed a curvature, from which we determined the activation energy for oxygen diffusion to be 1.42 and 2.24 eV for fast and slow diffusivity, respectively. Our results suggest the atomic movement of oxygen in a-HfO2 is very sensitive to the local structure.