Technical Field
Embodiments described herein are related to the field of semiconductor integrated circuits, and more particularly to electrostatic discharge protection circuits employed to reduce damage to circuits caused by electrical overstress.
Description of the Related Art
In general terms, electrical overstress (EOS) refers to an electronic component or semiconductor integrated circuit (IC) being exposed to a voltage and/or current with a value greater than the component is designed to handle. EOS may cause an IC to operate incorrectly (e.g., “glitch”) or, in more extreme cases, can cause physical damage to circuits in the IC. EOS can have various causes, such as, for example, improper power source, incorrect power-on sequencing, electro-magnetic interference (EMI), or electrostatic discharge (ESD).
ESD is a sudden electrical current flow between two differently charged surfaces. As implied in the name, ESD is caused by an accumulation of static charge on a given surface. The accumulated charge may result in a significant difference in voltage potential between the charged surface and another surface. When the two surfaces are electrically shorted together, come into contact, or a dielectric breakdown occurs, the charged surface may discharge onto the surface with a lower voltage potential until the difference in voltage between the surfaces is low enough to prevent further discharging. Since the voltage difference prior to discharge may be large, the corresponding currents during discharge may also be large.
Semiconductor ICs may be particularly vulnerable to the adverse effects of ESD. The large currents that can be produced by ESD can damage or destroy circuitry. Accordingly, during manufacturing and installation of electronic systems utilizing ICs, special handling procedures may be followed to prevent damage resulting from an ESD event. Furthermore, many ICs may have ESD protection circuitry built in. Such circuitry may include a sensor and a clamp circuit. The sensor may sense the occurrence of an ESD event, and in response to sensing the ESD event, the sensor may cause activation of the clamp circuit to provide an electrical path through which the current may be safely discharged.