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The passage around this formula

Density itself is worth being precise about, because pitch and area density do not scale the same way. If interconnects sit on a roughly square grid of pitch p , the number that fit per unit area scales as $n_{\text{area}}(p) \;\propto\; \frac{1}{p^{2}}$. not as 1/p . imec’s demonstrated step from 400-nanometre to 200-nanometre hybrid-bond pitch [ 4 , 3 ] is therefore not a doubling of achievable interconnect density but close to a quadrupling of it — the reason pitch numbers that look like modest, incremental reductions on a roadmap chart translate into much larger jumps in how many independent signals a bonded pair of dies can actually exchange per square millimetre.

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