Design And Fabrication Of Grating-coupled Silicon-based Hybrid Integrated Germanium Photodiodes

The bottleneck of copper interconnects in speed, power consumption and crosstalk haslimited the information transmission capacity. Recently, silicon photonics have achievednumerous break-throughs which provide the solution for inter-chip and on-chip opticalinterconnects. However, the absorption efficiency of silicon is rather low in the near infraredband to obtain effective photodetectors. By integrating germanium materials or germaniumphotodiodes heterogeneously with silicon waveguide, which have good optoelectronicresponse in the near infrared, the absorption efficiency for the hybrid Si/Ge photodiode canbe increased significantly for applications.Based on grating coupler, a highspeed hybrid intergrated PIN Germanium photodiode isdone, confirming the feasibility of benzocyclobutene (BCB) bonding technology applicablein active silicon optoelectronics devices. This work is achieved as following:(1) To achieve a highly efficient coupling of light from fiber to waveguide, then todetector, optimized simulation results show that a grating coupler behaves a coupling to fiberefficiency of64.5%and3dB bandwidth of57nm. Fine tunablity of the fiber tilt angle canguarantee the peak wavelength of1550nm with fabrication tolerance. A chirped grating isemployed to achieve a perfect vertical coupling with a45%upward input efficiency.(2) Based on the principle of thermocuring, experiments have been made to achieve thebasic BCB bonding process. By using of Chemical Mechanical Polishing, Scanning ElectronMicroscope and tensile strength tests, a BCB bonding process is developed with acontrollable bonding layer thickness and large bonding strength. The interlayer thickness iscontrolled to300nm in the bonded detector, while a super thin BCB bonding (<100nminterlayer thickness) is achieved for future application.(3) SOI grating coupler is fabricatied by Electron Beam Lithography and InductivelyCoupled Plasma Etching, of which coupling efficiency is measured by vertical fiber couplingsetup. The bonding alignment precision is1μm through near infrared transmission aligner.Finally, DC measurement of the bonded hybrid silicon-based Ge photodiodes is done.