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As a promising option to address the memory wall problem, 3-D processor-DRAM integration has recently received many attentions. Since DRAM dies should be stacked between the processor die and package substrate, we have to fabricate a large number of through-DRAM through-silicon vias (TSVs) to connect the processor die and package for power and input/output (I/O) signal delivery. Although such through-DRAM TSVs will inevitably interfere with DRAM design and induce non-negligible power consumption overhead, little prior research has been done to study how to allocate these through-DRAM TSVs on the DRAM dies and analyze their impacts. To address this open issue, this paper first presents a through-DRAM TSV allocation strategy that well fits to the regular DRAM architecture. Meanwhile, due to the longer path between power/ground pads and processor die, power delivery integrity issue may become more serious in such 3-D processor-DRAM integrated systems. Decoupling capacitor insertion is the most popular method to deal with power delivery integrity issue in high-performance integrated circuits. This paper further proposes to use 3-D stacked DRAM dies to provide decoupling capacitors for the processor die. This can well leverage the superior capacitor fabrication ability of DRAM to reduce the area penalty of decoupling capacitor insertion on the processor die. For its practical implementation, a simple uniform decoupling capacitor network design strategy is presented. To demonstrate through-DRAM TSV allocation and decoupling capacitor insertion strategy and evaluate involved tradeoffs, circuit SPICE simulations and computer system simulations are carried out to quantitatively demonstrate the effectiveness and investigate various design tradeoffs.
Very Large Scale Integration (VLSI) Systems, IEEE Transactions on (Volume:19 , Issue: 9 )
Date of Publication: Sept. 2011