Radiation effects in Al2O3-based MOS capacitors

We studied the γ-ray (⁶⁰Co) radiation response of MOS capacitors with an atomic layer deposited Al₂O₃ as insulating layer up to a total dose of 6.2 kGy. Preirradiation electrical characterization showed a voltage instability for samples with an n-type substrate due to tunneling transitions between the substrate and preexisting defects inside the dielectric layer. No instability was observed in the case of p-type samples, aming them suitable for the study of the radiation effects in these devices. With respect to the radiation response, real-time capacitance-voltage (C-V) measurements showed a monotonic shift of the C-V characteristic towards negative voltages, indicating and increase of the positive trapped charge with dose, which accords with previous results in the literature. From this results the fraction of generated holes that is captured in a trap could be calculated, resulting in a value of 30%, what suggests a high trapping efficiency. Moreover, from the stretch-out of the C-V curve, an increase in the Si/Al₂O₃ interface trap density was observed up to 4 kGy when saturation occurred.