High-Contrast Polysilicon Grating Reflectors Implemented in a Standard Bulk CMOS Line

A high-index-contrast grating (HCG) reflector is implemented in the polysilicon gate of a standard bulk CMOS for the first time. A transverse-electric (TE) preferred CMOS HCG reflector allows a >90% peak reflectivity, a 100-nm reflection bandwidth, and a 1.64:1 TE/transverse-magnetic polarization ratio, which is limited by the thin field oxide layer between the HCG and the silicon substrate, resulting in optical leakage to the substrate. Remarkable improvements in peak reflectivity (close to 100%) and polarization ratio (10:1) are achieved by removing the substrate of HCG devices. Guided-mode resonance reflection in HCGs is further verified by the corresponding transmission dips and is predicted by the rigorous coupled-wave analysis simulations.