A Comparison of Total-Ionizing-Dose Effects in Silicon and Silicon-Nitride Waveguides

The total-ionizing-dose (TID) responses of silicon and low-loss silicon-nitride (SiN) integrated waveguides are evaluated. Mach-Zehnder interferometers (MZIs), which allow for both TID-induced changes in effective refractive index ( $n_{\mathrm { eff}}$ ) and transmission losses to be observed, were exposed to 10-keV highly localized X-ray pulses facilitating very high dose irradiation for small exposure areas. TID-induced shifts in $n_{\mathrm { eff}}$ and transmission losses were observed for both waveguide types above 3 Mrad(Si), with the silicon waveguides exhibiting better radiation resilience for both metrics. Data collected were used to create Ansys Lumerical simulations to propose potential mechanisms of TID-induced degradation in waveguides. Furthermore, to better understand the effects of $n_{\mathrm { eff}}$ degradation on other passive components, both silicon and SiN TID-damaged ring resonators were simulated in MATLAB. Differences in $n_{\mathrm { eff}}$ changes and transmission losses imply that for high dose environments (>10 Mrad(Si)), when comparing waveguide types, silicon waveguides will provide similar loss performance and comparably smaller shifts in $n_{\mathrm { eff}}$ compared to typically lower-loss SiN waveguides.