3D-IC Signal TSV Assignment For Thermal And Wirelength Optimization

In the field of integrated circuit,the technology of three-dimensional integrated circuits(3DICs)has emerged as a new method of system-level architecture.It packs a stack of planar device by using Through-Silicon-Vias(TSVs)as the vertical electrical connection.Compared with the traditional 2D-ICs,this techonology enables smaller footprint area,improves the electrical interconnection performance,and reduces the fabrication cost.However,the impacted stacking style not only results in high power density but also restricts the thermal dissipation.So the thermal problem becomes a key design challenge.Signal TSVs connect the multi-layer signal nets and play the role of signal interconnection.Many related works which dealing with the signal TSV assignment problem only focus on wire length result without taking thermal issue into consideration.Therefore,it is improtant for 3D-ICs design if the algorithm could provide better solution with wire length reduction,as well as improve the thermal behaviour.This work mainly solves the problem of 3D-IC signal TSV assignment for both thermal and wire length optimization.The thermal analysis model is the first problem to be solved.Traditionl thermal simulation tool is computationally expensive,and is not suitable for the iterative assignment algorithm.In this work,a TSV thermal estimation model is built to evaluate temperature,where compression storage method with LU decomposition is proposed to improve algorithm efficiency.Given the system input,the signal TSV assignment is further formulated as a multi-objective optimization problem.On one hand,the grid coarsening and uncoarsening method improves the algorithm efficiency.And a multi-level node-weight-oriented flow assignment algorithm is proposed to reduce wire length and temperature simultaneously.On the other hand,a simulated annealing based remove-and-reassign optimization method is applied which helps further optimize the assignment.With the proposed grid expansion and variable separation method,the signal TSV assignment result finally achieves temperature and wire length reduction with ideal algorithm efficiency.