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When a chip is manufactured, long metal wires acts like an antenna and picks up charge. If this long wire is connected to a MOS gate, it can blow the gate. So, manufactures typically have max length of metal that can be connected to a gate. You can add diodes or jump layers to help fix antenna violations. Diodes will discharge the charges picked up. Jumping layers help by disconnected the long wire from the gate during processing of the long wire.
(Example: long m1 - short m2 - short m1 - gate. During processing of the m1, the gate is connected to only short piece of m1. When processing m2, only short m2 is processed, so less charge picked up.)
during process of plasma etching, charges get accumulated along the metal stripe. the longer the strip the more charges are accumulated. if a small transistor gate is present here, the gate oxide can be destroyed due to the large electric field forming over thin electric. This is called as antenna affect and if this phenomenon occurs in ur design it leads to antenna violations.
ways to prevent this is by jogging the metal strip, which is atleast one metal above the layer to be protected. i,e if antenna violation occurs in metal2 then u need to jog it with metal3 to remove the violation
The reason why we jog to upper metal layers only, is because the nets remain floating and thus preventing the transistor gates from desturction,The alternate technique is reverse biased diodes.
Added after 2 minutes:
* reamin floating during the process of metallisation, so the positively charged plasma
wouldn't charge the transistor gate.
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