The typical ESD waveform specified by the IEC61000-4-2 standard is characterized by a less than 1nS rise time and duration of approximately 100nS. In general the event is very short duration, but very high energy. The rising peak can easily cause oxide ruptures inside an IC and the resulting energy can often damage transistors or metal traces leading from the internal pads. The highest level according to the IEC standard is 8kV, or level 4, but many manufacturers test beyond level 4 to ensure greater reliability of their equipment. These requirements and the fact that IC process geometries continue to shrink further necessitate a need for robust, external ESD protection.