Thermal-Electrical Co-Optimization of Block-Level Floorplanning in 3D Integrated Circuits

While the stacking of multiple strata to produce 3D integrated circuits improves interconnect length and hence reduces power and latency, it also results in the exacerbation of the thermal management challenge due to the increased power density. There is a need for design tools to understand and optimize the trade-off between electrical and thermal design at the device and block level. This paper presents results from thermal-electrical co-optimization for block-level floorplanning in a multi-die 3D integrated circuit. A method for temperature computation based on linearity of the governing energy equation is presented. This method is shown to be faster and more accurate than previously used resistance-network based approaches and full-scale FEM simulations. This method is combined with previously reported electrical delay models for 3D ICs to simultaneously optimize both the maximum temperature and the interconnect length. Results outline the various trade-offs between thermal and electrical considerations. It is shown that co-optimization of thermal and electrical objectives results in a floorplan that is attractive from both perspectives. Constraints placed by the 3D IC manufacturing process on design are outlined, showing that the cheapest manufacturing options may not result in optimal electrical and thermal design. In particular, the wafer-on-wafer bonding process requires the two die to be identical, which results in a severe design constraint, particularly on the thermal goal due to the overlap of high power density blocks. Results presented in this work highlight the need for thermal and electrical co-design in multistrata microelectronics, and for reconciling manufacturing and design considerations in order to develop practical design tools for 3D integrated circuits.