Fresnel phase plate lenses for through-wafer optical interconnections

While the advantages of optical over electrical interconnects for conventional 2-D VLSI and wafer-scaleintegrated (WSI) circuits have not been clearly demonstrated, for 3-D interconnection structures such as those necessary for stacked wafer and similar architectures, the trade-off between using optical or electrical methods for vertical links is not straightforward. Current work on fabricating a through-wafer optical interconnect within a hybrid-WSI environment is motivated by the need to obtain experimental data on the overall performance of an optical interconnect so that this trade-off can be clarified inthe case of hybrid-WSI and in the general case at least more well defined. This paper details the design and fabrication of SiO(2) Fresnel phase plate lens arrays for use in the experimental 1.3-microm wavelength through-wafer optical interconnects to be constructed. These 0.8-N.A. lenses have submicron minimum linewidths and are VLSI process compatible. Preliminary results are presented indicating that, with the use of these lens arrays, vertical optical interconnect densities comparable with that of on chip bonding pads ( approximately 250-microm pitch) are obtainable within these architectures.