CFD Simulation Analysis of Inter/Intra Chip Liquid Cooling for 3D Stacked ICs

This paper presents a fundamental study on embedded liquid cooling for 3D-ICs with two active chips stacked vertically. Two types of cooling solutions are introduced including intra-chip cooling and inter-chip cooling. Intra-chip cooling approach utilize silicon etching process to fabricates the microchannel within the backside of the chip for the fluid flow path, whereas inter-chip cooling uses the microgap space between the chips stacked vertically as a fluid path. In this paper, intra-chip cooling with straight channel structure and inter-chip cooling with micro-pillar structure are studied numerically using Computational Fluid Dynamics (CFD) solver ANSYS Fluent 2022 R1. Full-scale 3D model has been developed to analyze the thermohydraulic performance of each cooling methods. Conjugate heat transfer problem was solved to evaluate the heat transfer and pressure drop of each structure under various flow rates and the chip power. The result showed that both types of embedded cooling methods provide significantly higher cooling performance than conventional indirect cooling. In comparison between the two embedded coolings, inter-chip cooling showed superior heat transfer performance although accompanied by higher pressure drop than intra-chip cooling. The heat transfer characteristics of each cooling methods are further investigated by comparing the heat dissipation path along the convective flow, as well as the conduction through the vertical stacking. It is revealed that intra and inter-chip cooling possesses different features of heat dissipation characteristic which stems from inherent structural difference. Also, an optimal stacking placement of chips with different power is studied for both types of cooling. The results provide some insights into the expanded capabilities of thermal management for 3D-ICs by introducing the embedded cooling structures.