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UBC Theses and Dissertations

Impact of custom interconnect masks on cost and performance of structured ASICs Ahmed, Usman


As process technology scales, the design effort and Non-Recurring Engineering (NRE) costs associated with the development of Integrated Circuits (ICs) is becoming extremely high. One of the main reasons is the high cost of preparing and processing IC fabrication masks. The design effort and cost can be reduced by employing Structured Application Specific ICs (Structured ASICs). Structured ASICs are partially fabricated ICs that require only a subset of design-specific custom masks for their completion. In this dissertation, we investigate the impact of design-specific masks on the area, delay, power, and die-cost of Structured ASICs. We divide Structured ASICs into two categories depending on the types of masks (metal and/or via masks) needed for customization: Metal-Programmable Structured ASICs (MPSAs) that require custom metal and via masks; and Via-Programmable Structured ASICs (VPSAs) that only require via masks for customization. We define the metal layers used for routing that can be configured by one or more via, or metal-and-via masks as configurable layers. We then investigate the area, delay, power, and cost trends for MPSAs and VPSAs as a function of configurable layers. The results show that the number of custom masks has a significant impact on die-cost. In small MPSAs (area < 100 sq.mm), two configurable layers result in the lowest cost, whereas the lowest cost in large MPSAs (area >100 sq.mm) is achieved with three or four configurable layers. The lowest cost in VPSAs is also obtained with four configurable layers. The best delay and power in MPSAs is achieved with three or four configurable layers. In VPSAs, four configurable layers lead to lowest power and delay, except when logic blocks have a large layout area. MPSAs have up to 5x, 10x, and 3.5x better area, delay, and power than VPSAs respectively. However, VPSAs can be up to 50% less expensive than MPSAs. The results also demonstrate that VPSAs are very sensitive to the architecture of fixed-metal segments; VPSAs with different fixed-metal architectures can have a gap of up to 60% in area, 89% in delay, 85% in power, and 36% in die-cost.

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