If two nets of the same layer and length, but one has double width, which has more delay and why?

The net with double width will generally have less delay.

o   Reasoning (RC Delay): Wire delay is primarily determined by the product of its resistance (R) and capacitance (C).

o    Resistance (R): Resistance is inversely proportional to the cross-sectional area of the wire. For a fixed thickness (T), resistance is inversely proportional to width (W). R ∝ 1 / (W * T). Doubling the width (W -> 2W) approximately halves the resistance (R -> R/2).

o    Capacitance (C): Capacitance has components to ground/substrate (Area Capacitance, Fringe Capacitance) and coupling capacitance to neighbors.

§  Ground Capacitance: Roughly proportional to width (W). Doubling width (W -> 2W) might almost double this component.

§  Coupling Capacitance: it can be lateral and vertical coupling. Vertical coupling increases with width and lateral coupling depends on thickness.

Scaling Impact: https://www.vlsisystemdesign.com/kunal58625/php/scaling.php