ESD is the transfer of electrostatic charge between two objects. It is a rapid event that usually results when two objects of different potentials come into contact with each other. ESD may also occur when a high electrostatic field develops between two objects in close proximity. ESD has been known to cause device failures in the semiconductor industry.
There are several industry-standard ESD models that define how semiconductor devices are tested for ESD sensitivity under different situations of electrostatic build-up and discharge. For example, the human body model (HBM) simulates the ESD phenomenon where a charged body directly transfers its accumulated electrostatic charge to an ESD-sensitive device. The machine module (MM) simulates a more rapid and severe electrostatic discharge from a charged machine, fixture, or tool to the ESD-sensitive device at a lower potential. The charged device model (CDM) simulates a transfer of accumulated electrostatic charge from a charged device to another body of lower potential.
Traditional ESD protection devices for power supplies included transistor snapback based circuits. Transistor snapback based circuits make use of the snap back triggering characteristics of parasitic bipolar structure to switch from some critical level of drain-source breakdown into high-conductivity due to avalanche injection. When snapback based circuits were implemented in input/output (I/O) buffers, it was found that they sustained up to approximately 4 KV HBM when configured with a total width of approximately 350 μm.