Radiation Induced Change in Defect Density in HfO2-Based MIM Capacitors

The effect of radiation-introduced defects on the behaviour of HfO2-based metal-insulator-metal (MIM) capacitors as a function of gamma-ray radiation (lose from 1.0 to 1000 krad are reported. Half the capacitors studied showed no degradation after exposure to 1000 krad from a Co-60 source, whilst the remaining half showed no change to parameters, such as barrier height and dielectric constant. For the good devices, the I-V characteristics are. controlled by Poole-Frenkel model, at a corresponding interface trap energy of 0.39 similar to 0.46 eV before radiation and 0.37 similar to 0.44 eV after 1000 krad. The failed devices show an substantial increase in the trap density from the as fabricated level of 10(19) cm(-3) to in excess of 10(20) cm(-3), in contrast to the good devices which show almost no change. We relate this change in defect density to the failure of devices by means of a percolation model, with a trap separation of around 2 nm.