of breaking down the gate oxide. In particular, reactive-ion etching of the first metal layer can result in exactly the situation shown - the metal on each net is disconnected from the initial global metal layer, and the plasma etching is still adding charges to each piece of metal. Leaky gate oxides, although bad for power dissipation, are good for avoiding damage from the antenna effect. A leaky oxide can prevent a charge from building up to the point of causing oxide breakdown. This leads to the somewhat surprising observation that a very thin gate oxide is less likely to be damaged than a thick gate oxide, because as the oxide grows thinner, the leakage goes up exponentially, but the breakdown voltage shrinks only linearly. Antenna rules Antenna rules are normally expressed as an allowable ratio of metal area to gate area. There is one such ratio for each interconnect layer. The area that is counted may be more than one polygon —it is the total area of all metal connected to gates without being connected to a source/drain implant. If the process supports different gate oxides, such as a thick oxide for higher voltages and a thin oxide for high performance, then each oxide will have different rules. There are cumulative rules, where the sum (or partial sum) of the ratios over all interconnect layers sets the limit. There are rules that consider the periphery of each polygon, as well. 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