The design of Si-based Fresnel-zone lens for 3D IC optical interconnect applications

In this work, we design a Si-based Fresnel-zone lens for a hybrid 3D integrated circuit (3D IC) solution. The 3D IC solution consists of two layers of transceiver modules which are mounted at several points on an optical printed circuit board (OPCB) for seamleß transmißion of signal through each layer to the OPCB and vice versa. Each transceiver module is made up of a Si-subcarrier (Si layer), transceiver IC, laser diode (VCSEL) and photodiode (PD). The transceiver IC, LD and PD are flip-chip bonded to the Si-subcarrier. Fresnel-zone lens are designed on the transmißion surface of each of the Si-subcarriers to improve coupling efficiency, transmittance through the silicon substrate, reduce surface scattering, and improve focusing. Each of the Si-subcarrier with the transceiver modules are flip-chip bonded together and also flip-chip bonded to the optical PCB. A 2-level and 4-level Fresnel-zone lens are designed at 1.3μm and 1.55μm. Based on design parameters such as coupling efficiency, transmittance, leß design complexity, and ease of fabrication, the 4-level Fresnel zone lens was selected as the optimal design for 3D IC and optical PCB applications. The optimal 4-level Fresnel-zone lens are designed for λ=1.3μm, where the focal length, f is 350μm, and diameter, D, is 167μm; and for λ=1.55μm, where the focal length, f is 350μm, and diameter, D, is 169.2μm. Also the plots of coupling efficiency and transmittance are provided for applications in 3D IC optical interconnects.