Radiation Induced Change in Defect Density in ${\hbox {HfO}}_{2}$-Based MIM Capacitors

The effect of radiation-introduced defects on the behaviour of ${\hbox {HfO}}_{2}$-based metal-insulator-metal (MIM) capacitors as a function of gamma-ray radiation dose from 10 to 1000 krad are reported. Half the capacitors studied showed no degradation after exposure to 1000 krad from a $^{60}{\hbox {Co}}$ 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 $\sim$ 0.46 eV before radiation and 0.37 $\sim$ 0.44 eV after 1000 krad. The failed devices show an substantial increase in the trap density from the as fabricated level of $10^{19}\ {\hbox {cm}}^{-3}$ to in excess of $10^{20}\ {\hbox {cm}}^{-3}$ , 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.