Implementation of Polysilicon Subwavelength Grating Reflectors in Standard Bulk CMOS Foundry Process

• Main Authors: Min-chun Hsieh, 謝旻均
• Other Authors: Yung-Jr Hung
• Format: Others
• Language: zh-TW
• Published: 2016
• Online Access: http://ndltd.ncl.edu.tw/handle/62447908066650672227

碩士 === 國立中山大學 === 光電工程學系研究所 === 104 === We have successfully demonstrated HCG reflectors in standard bulk CMOS by simply employing polysilicon gate as the high-index grating layer to reflect the 1310-nm and 1550-nm telecommunication wavelengths under normal incidence. Its design and fabrication strictly follow the foundry regulations without requiring any front-end process modification. The reflection bandwidth, polarization, and center wavelength of the HCG reflector can be adjusted by tuning the grating period, duty cycle, and thickness, but the existence of thin field oxide between polysilicon HCG and silicon substrate leads to a poor peak reflectivity (>90%) and a lower polarization ratio (1.64:1) mainly due to the optical leakage to the substrate. Substrate-removed HCGs show remarkable improvements in peak reflectivity (close to 100%) and polarization ratio (10:1). Measured transmission dips verify that the high-reflection bands of HCG reflectors come from the guided-mode resonances supported by the leaky modes. All measured reflection spectra can be predicted by the RCWA simulations. Leveraging from the CMOS technologies, HCG implementations in bulk CMOS can facilitate the development of not only on-chip VCSELs and OPAs but also the optoelectronic devices that benefits from the high reflection characteristics of HCGs. We are currently working on the hybrid integration of CMOS HCGs with III-V multi-quantum well structure to achieve an on-chip optical amplifier.