The Mechanisms and Effects of ESD

Key Takeaways

• Electrostatic discharge (ESD) is a release of static electricity between two electrically charged objects in contact.

• The mechanisms responsible for ESD are triboelectrification, conduction, and inductive charging.

• Sensitivity to ESD appears as insulation breakdown, thermal overstress, metallization failure, or the migration of materials in MOS and bipolar semiconductor devices. 

Electrostatic discharge is one reason electronic circuits malfunction 

Electrostatic discharge (ESD) is one reason electronic circuits or devices might malfunction. Generally, the environment where circuits or devices are placed is prone to static electricity, and the effects of ESD on electronic systems can be catastrophic. The effects of ESD include memory corruption, temporary failures, unexpected latch-ups, or, at times, complete damage to the electronic system. To some extent, the unreliability quotient of electronic circuits can be linked to ESD. That is why it is important to take precautions against ESD.

In this article, we will explore ESD and its effects on electronic circuits in further detail.

Electrostatic Discharge (ESD) Mechanisms

Electrostatic discharge is the release of static electricity between two electrically charged objects in contact. In ESD, there is a building up of charges between two surfaces. When surfaces rub against each other, the charges move and cause excess charges on one surface and deficiency on another.

All objects are capable of generating electrostatic charge. Usually, the contact and separation of the objects contribute to ESD. A common example of ESD is the static discharge generated by the human body. When a person touches an electronic component, the voltage pulse generated in their body gets transferred to the component.

The mechanisms responsible for ESD are triboelectrification, conduction, and inductive charging.

Triboelectrification

Triboelectrification results from two different materials coming in contact and then separating. It is a contact charging process where there is a transfer of charges from one object surface to another. The amount of charge generated in this kind of static discharge depends on the area of contact, friction, and pressure, and the material property influences the polarity of charges on the contact surfaces.

Conduction

In ESD generated by conduction, two charged bodies of different electric potentials come in contact. The charge flows from the body at the higher potential to the one at the lower potential. This process continues until the two bodies become equipotential. 

Inductive Charging

Inductive charging occurs in the presence of induced electric fields. Even though the net charge on a conductor placed in an electric field is zero, there are charges of opposite polarity on either side of the conductor. The relocation of the opposite polarity charges forms a capacitance divider and a voltage is established across the conductor. The voltage level developed in the conductor is dependent on the capacitance value.

Capacitors formed through inductive charging in the conductors discharge when there is a conducting path and the accumulated charges decrease. Usually, electrostatic discharge is characterized by high current pulses lasting up to microseconds. This high level of current is capable of damaging sensitive electronic circuits. 

The Effects of ESD

ESD is a mini version of lightning. As static charges get a conductive path, ESD currents travel to the ground via all available paths in electronic circuits. The paths may involve semiconductor junctions, integrated circuits, or sensitive electronic components. Let’s take a look at how ESD affects each.  

Semiconductors

One-third of field failures in semiconductors are due to ESD. ESD induces failures in semiconductor components such as leakages, contact damages, burnouts, resistor-metal interface damages, or gate-oxide ruptures. As the size of semiconductor electronics gets smaller, it makes components more susceptible to ESD failures, especially the damage of thin gate oxide layers.

The two principal device technologies in semiconductor electronics, bipolar and metal oxide semiconductors (MOS), are vulnerable to ESD. This sensitivity to ESD appears as insulation breakdown, thermal overstress, metallization failure, or the migration of materials in MOS and bipolar semiconductor devices. ESD is capable of developing failure modes in PN junctions both at forward and reverse biased conditions. 

Integrated Circuits

ESD current flow in ICs forms holes in chips. ESD can increase the heat generation in ICs above the temperature limit and cause thermal damage to all components and systems in the vicinity.

Internal Components

All electronic passive components are capable of withstanding one or two events of ESD. However, repeated ESD events degrade the internal components of electronic circuits over time and result in equipment operational disruptions. There can be contact loss and internal components can burn off under ESD conditions.

The effects of ESD are detrimental to the reliability and shelf life of electronic circuits. ESD currents take all possible paths to reach the ground, and, in that process, damage the components and systems in their path. Some ESD damages are catastrophic and others are latent failures. It is always advisable to incorporate ESD protection in electronic circuits to ensure longevity and reliability during manufacturing, testing, freight, and handling. Cadence software can help you design ESD protection circuits for sensitive electronic systems. 

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