26 electrostatic discharge - ESD PROTECTION CIRCUITS ESD...

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ESD PROTECTION CIRCUITS
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ESD event - Charge generation mechanism creating an imbalance of electron between two bodies - Transient discharge of this static charge - IC’s response to the inrush of the charge - The capability of the IC to absorb this energy leads to survival or failure
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Origins of ESD ESD event occurs because of charge imbalance between IC and another object. - Moving parts from place to place during manufacturing and distribution main cause for charge imbalance - Charges stored in machine or human body are discharged to the chip on contact or by static induction. Charging process occur when dissimilar materials rub together and separate.
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Charge Generation Triboelectrification: - requires physical contact between two materials. Most common in manufacturing or laboratory environment. - When contact exchange of free electrons takes place based on materials respective work functions .
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- When separated the free electrons redistribute and balance if both materials are conductors, but if one or both are insulators a residual charge is left in the insulator. - This excess charge generates the voltage differential. - Measured voltage based on the capacitance of the system - Triboelectrification enhanced by smooth surface, large contact area, high applied pressure and high rubbing speed.
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Induction - A conductive object B comes into close proximity with a charged object A . Part of the field terminates on B resulting in an internal separation of charge. When A is removed from the area a net charge exists on B with opposite polarity. Grounding B balances the charge. This type of event generates current pulses, limited by the impedance of the grounding path. The magnitude of this energy in this transient depends on the strength of the field and the device coupling to that field.
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Conduction - A charged body is brought into contact with an isolated object of lower potential. - During the time of contact charge is transferred to the lowest biased object until the potentials balance - When objects are separated body A has accumulated a charge of same polarity as body B. - The charges on each related by the capacitance of each body.
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ESD Event ESD event can be modeled as a two body system. A charge imbalance develops between these two bodies by one of the generation mechanisms. The charge imbalance translates into a voltage imbalance based on capacitance of each body. Charge transfers from higher potential body to the lower potential body The characteristics that define current during the event are the capacitances of the two bodies and the impedances between them.
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Electrostatic discharge (ESD) is one of the most important reliability problems in the integrated circuit (IC) industry. Electrical overstress is defined as damage to a product caused by exceeding data-sheet maximum ratings EOS usually leads to gross damage in an integrated circuit resulting from high-energy events such as electrostatic discharge, ESD is a relatively rapid,high-current event resulting from the high voltage created when electrostatic charges are rapidly transferred between bodies at different potentials.
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There are two main dangers of ESD stress. One is the danger of
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This note was uploaded on 09/24/2010 for the course EEE MEL G621 taught by Professor Gurunarayanan during the Fall '08 term at Birla Institute of Technology & Science, Pilani - Hyderabad.

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26 electrostatic discharge - ESD PROTECTION CIRCUITS ESD...

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