Micro structured coupling elements for 3D silicon optical interposer

Current trends in electronic industry, such as Internet of Things (IoT) and Cloud Computing call for high interconnect bandwidth, increased number of active devices and high IO count. Hence the integration of on silicon optical waveguides becomes an alternative approach to cope with the performance demands. The application and fabrication of horizontal (planar) and vertical (Through Silicon Vias - TSVs) optical waveguides are discussed here. Coupling elements are used to connect both waveguide structures. Two micro-structuring technologies for integration of coupling elements are investigated: mu-mirror fabrication by nanoimprint (i) and dicing technique (ii). Nanoimprint technology creates highly precise horizontal waveguides with polymer (refractive index n(C) = 1.56 at 650 nm) as core. The waveguide ends in reflecting facets aligned to the optical TSVs. To achieve Total Internal Reflection (TIR), SiO2 (n(Cl) = 1.46) is used as cladding. TSVs (diameter 20-40 mu m in 200-380 mu m interposer) are realized by BOSCH process(1), oxidation and SU-8 filling techniques. To carry out the imprint, first a silicon structure is etched using a special plasma etching process. A polymer stamp is then created from the silicon template. Using this polymer stamp, SU-8 is imprinted aligned to vertical TSVs over Si surface. Waveguide dicing is presented as a second technology to create coupling elements on polymer waveguides. The reflecting mirror is created by 45 degrees V-shaped dicing blade. The goal of this work is to develop coupling elements to aid 3D optical interconnect network on silicon interposer, to facilitate the realization of the emerging technologies for the upcoming years.