HP Labs Technical Reports
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Impact of Low-k ILD and Cu on Circuit Performance
Nakagawa, Sam; Rahmat, Khalid; Oh, Soo-Young; Ray, Gary; Kumar, Rajendra
Abstract: Low dielectric constant of organic interlevel dielectrics (ILD's) and low resistivity of copper can provide substantial improvement in the RC time constant of on-chip interconnect. However, the ultimate impact of these materials must be evaluated in terms of real circuit performance, not just in terms of interconnect RC constant. In this paper we first delimit the design space of driver size and load device capacitance where these new materials make the most impact on circuit performance. The performance advantage varies from no impact at all in short, local routing to 30-40% improvement in a long, interconnect dominated circuit. Then using numerical simulation we evaluated performance improvement in two important circuits in the design of high performance microprocessors, cache random access memory (RAM) and the clock distribution circuit. The improvement varied from about 10% in cache RAM to about 40% in the clock distribution circuit.
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