Study on ion slicing of iron garnet magneto-optic materials for near and mid-infrared on-chip optical isolators

Achieving high-crystalline-quality, large-size iron garnet magneto-optic (MO) films on silicon substrates remains a critical challenge for CMOS-compatible on-chip non-reciprocal devices like isolators and circulators. In this study, we explored ion slicing on commercial yttrium iron garnet (YIG) crystals, bismuth-doped iron garnet (BIG), and newly developed YIG ceramics. After He⁺ ion implantation, wafer bonding and annealing, the BIG film on silicon was successfully fabricated, but its thickness and crystalline phase deviated from expectations. The underlying causes of these discrepancies were systematically investigated. In contrast, the YIG single crystals and ceramics showed blistering during annealing, which demonstrates their ion-slicing viability. Based on the magneto-optical constant dispersion relationships of the two materials, the nonreciprocal phase shift (NRPS) gap between BIG film on silicon and YIG film on silicon narrows significantly as the wavelength increases from 1.55 µm to 2.1 µm, dropping from 399% to 26%. As a proof of concept, we proposed a design for silicon-based TM-mode on-chip isolators at 1.5 µm and 2.1 µm using ion-sliced YIG ceramics, where the simulated insertion loss decreased from 2.78 dB to 0.35 dB due to the substantial reduction in material absorption with increasing wavelength. These results underscore the feasibility and promise of YIG ceramic ion slicing as a practical solution for CMOS-compatible on-chip isolators, particularly in the mid-infrared range.