Metal Layers & Crosstalk

VLSI Concept · Physical Design

Wires stack on top of each other — and they whisper to their neighbors.

Modern chips route signals across many stacked metal layers, connected vertically by vias — lower layers for short local connections, upper layers for long/global routing and power. Because wires run so close together, a signal switching on one wire can capacitively couple ("crosstalk") onto a quiet neighboring wire, injecting noise or delay.

Layer strategyLower layers = thin/dense/local; upper layers = thick/sparse/long-distance + power.

Why it mattersCrosstalk-induced glitches and delay are a real signoff check (signal integrity analysis), not just a synthesis footnote.

Common mistakeRouting two timing-critical, fast-switching signals directly adjacent to each other on a long parallel run.

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