Antenna Check
During plasma etching in fabrication, metal connected to gate terminals accumulates charge. The antenna ratio is the cumulative metal area divided by the gate a
During plasma etching in fabrication, metal connected to gate terminals accumulates charge. The antenna ratio is the cumulative metal area divided by the gate area. Exceeding the foundry limit damages the thin gate oxide - permanently degrading or destroying the transistor.
AR = Σ(Connected Metal Area on Layer L) / Gate Oxide AreaWhen Violation Occurs — Foundries specify max AR per metal layer. Typically AR < 400 for M1, AR < 800 for M2+. Violation occurs when a long wire on lower layers is connected to a gate before any higher layer connection breaks the accumulation path.
Two Fix Strategies — 1. Jump to higher layer (preferred): Re-route wire through a higher metal layer early. Higher layers are deposited later in the fab process - less plasma exposure time → lower charge accumulation. 2. Insert antenna diode: Place a reverse-biased diode (anode to net, cathode to VSS) at the gate. During fab the diode conducts the plasma current safely to ground before oxide damage occurs.