Optoelectronic Substrate With High-Aspect-Ratio Optical Through-Hole for Chip-to-Chip Interconnects

Abstract

We report high-aspect-ratio optical through-holes fabricated in optoelectronic substrates for chip-to-chip optical interconnections. They are used for transmitting optical signals vertically through the optoelectronic substrate. They consist of cladding layer and cores that are 50 μm in diameter. Their lengths are 1.2 mm equal to the thickness of the substrate. This small diameter enables the optical through-holes to achieve low-loss optical coupling with a polymer optical waveguide. This thickness of the optoelectronic substrate accommodates embedded capacitor integration under CPUs. The capacitor will improve power supply to the CPU and co-planarity for both package level and board level assembly. We have evaluated the optical characteristics of the high-aspect-ratio optical through holes. We have measured optical loss and crosstalk. Optical coupling dependencies of alignment offset for the optical through-holes are also evaluated to clear the effects of misalignment. The optical loss of core-cladding optical through-hole was 1.3 dB that was 2.9 dB better than that of only one kind of transparent resin and 3.8 dB better than that of a vacant drilled hole. The narrowest 1-dB coupling tolerance was +/− 12 μm from the transmitter optical through-hole to the optical waveguide. Total optical loss was estimated to be 6.8 dB from a vertical-cavity surface-emitting laser through 100-mm polymer waveguide with two 45°-ended mirrors to a photodiode.