Reliable clock and power delivery network design for three-dimensional integrated circuits

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Zhao, Xin
Lim, Sung Kyu
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The main objective of this thesis is to design reliable clock-distribution networks and power-delivery networks for three-dimensional integrated circuits (3D ICs) using through-silicon vias (TSVs). This dissertation supports this goal by addressing six research topics. The first four works focus on 3D clock tree synthesis for low power, pre-bond testability, TSV-induced obstacle avoidance, and TSV utilization. The last two works develop modeling approaches for reliability analysis on 3D power-delivery networks. In the first work, a clock synthesis algorithm is developed for low-power and low-slew 3D clock network design. The impact of various design parameters on clock performance, including the wirelength, clock power, clock slew, and skew, is investigated. These parameters cover the TSV count, TSV parasitics, the maximum loading capacitance of the clock buffers, and the supply voltage. In the second work, a clock synthesis algorithm is developed to construct 3D clock networks for both pre-bond testability and post-bond operability. Pre-bond testing of 3D stacked ICs involves testing each individual die before bonding, which can improve the overall yield of 3D ICs by avoiding stacking defective dies with good ones. Two key techniques including TSV-buffer insertion and redundant tree generation are implemented to minimize clock skew and ensure pre-bond testing. The impact of TSV utilization and TSV parasitics on clock power is also investigated. In the third work, an obstacle-aware clock tree synthesis method is presented for through-silicon-via (TSV)-based 3D ICs. A unique aspect of this problem lies in the fact that various types of TSVs become obstacles during 3D clock routing including signal, power/ground, and clock TSVs. These TSVs may occupy silicon area or routing layers. The generated clock tree does not sacrifice wirelength or clock power too much and avoids TSV-induced obstacles. In the fourth work, a decision-tree-based clock synthesis (DTCS) method is developed for low-power 3D clock network design, where TSVs form a regular 2D array. This TSV array style is shown to be more manufacturable and practical than layouts with TSVs located at irregular spots. The DTCS method explores the entire solution space for the best TSV array utilization in terms of low power. Close-to-optimal solutions can be found for power efficiency with skew minimization in short runtime. In the fifth work, current crowding and its impact on 3D power grid integrity is investigated. Due to the geometry of TSVs and connections to the global power grid, significant current crowding can occur. The current density distribution within a TSV and its connections to the global power grid is explored. A simple TSV model is implemented to obtain current density distributions within a TSV and its local environment. This model is checked for accuracy by comparing with identical models simulated using finite element modeling methods. The simple TSV models are integrated with the global power wires for detailed chip-scale power analysis. In the sixth work, a comprehensive multi-physics modeling approach is developed to analyze electromigration (EM) in TSV-based 3D connections. Since a TSV has regions of high current density, grain boundaries play a significant role in EM dominating atomic transport. The transient analysis is performed on atomic transport including grain and grain boundary structures. The evolution of atomic depletion and accumulation is simulated due to current crowding. And the TSV resistance change is modeled.
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