Fixes For Antenna Violations
In general, antenna violations must be fixed by the router. Possible fixes include:
- Change the order of the routing layers. If the gate(s) immediately connects to the highest metal layer, no antenna violation will normally occur. This solution is shown in Figure 3(a).
- Add vias near the gate(s), to connect the gate to the highest layer used. This adds more vias, but involves fewer changes to the rest of the net. This is shown in Figure 3(b).
- Add diode(s) to the net, as shown in Figure 3(c). A diode can be formed away from a MOSFET source/drain, for example, with an n+ implant in a p-substrate or with a p+ implant in an n-well. If the diode is connected to metal near the gate(s), it can protect the gate oxide. This can be done only on nets with violations, or on every gate (in general by putting such diodes in every library cell). The "every cell" solution can fix almost all antenna problems with no need for action by any other tools. However, the extra capacitance of the diode makes the circuit slower and more power hungry.
Read more about this topic: Antenna Effect
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