• The main option is PG trimming, and since the cell count is low it will not violate the IR-drop limit.

KEY High density: ECO-reroute slack nets, downsize cells, single-cut vias, layer promotion; low density: mainly PG trimming.

Antenna Violation and Its Fix

The antenna ratio is the metal area connected to a gate divided by the gate area; a violation occurs when this ratio exceeds the limit specified for a metal layer. Fixes:

• Layer jumping - route the net up to a higher metal layer so the connected metal area on the offending layer is reduced.
• Add an antenna diode near the gate, which effectively increases the discharge area.

Background: When a metal wire connected to a transistor gate is plasma-etched, it can charge up to a voltage high enough to damage the thin gate oxide. This plasma-induced gate-oxide damage is the antenna effect - it increases gate leakage, shifts the threshold voltage, and shortens transistor lifetime. Longer wires collect more charge and are more likely to damage gates. During the high-temperature plasma etch, diodes formed by the source and drain diffusions can conduct significant current and bleed charge off the wires before the gate oxide is harmed.

KEY Antenna violations are plasma-induced gate-oxide damage; fix them with layer jumping or antenna diodes near the gate.

Fixing an Antenna Violation with a Buffer

Yes. Instead of an antenna diode, a buffer can be used with its output left floating and its input pin connected to the gate. This increases the effective gate area, which lowers the antenna ratio and clears the violation.

KEY Yes - a buffer with floating output, input tied to the gate, raises gate area and reduces the antenna ratio.