Total-Ionizing-Dose Effects in Integrated Silicon Phase Shifters Using Localized X-Ray Pulses

This study investigates the effects of total ionizing dose (TID) damage on silicon photonic (SiPh) phase shifters using Mach-Zehnder modulators (MZMs). By employing a microbeam X-ray source to irradiate one phase shifter in the MZM structure, we were able to isolate radiation-induced effects on phase shifter performance. The results demonstrate three key TID effects on the Si phase shifter: radiation-induced attenuation (RIA), radiation-induced refractive index change (RIRIC), and phase shifter pinch-off. Using the measured MZM transfer function, we developed formulations of radiation-induced effect, providing a quantitative tool for assessing how TID impacts SiPh modulator performance. Our findings suggest that multiple factors influence the variations in TID effects observed across different dose levels, including TID-induced changes to material structure, free carrier modulation, and band-to-band absorption due to radiation-induced defects. This study highlights the complexity of radiation effects in SiPh devices and provides insights that can guide future efforts to improve radiation tolerance in SiPh systems operating in extreme environments.