Electrostatic Discharge (ESD): impacts and solutions

Electrostatic discharge (ESD) disrupts the normal operation of electronic components and systems. It can cause leakages, shorts, gate oxide ruptures, junction and metallization burnouts, and deterioration of resistor-metal interfaces. To protect semiconductor devices from ESD, engineers integrate on-chip protective structures that shield core circuits’ input, output, and power supply pins.

This article reviews the three primary devices integrating clamps into semiconductor ESD protection structures. It also discusses the ESD Human Body Model (HBM) and Charged Device Model (CDM) testing standards. It explores the growing challenges of achieving consistent results in complex monolithic system-on-chip (SoC) designs and chiplets. Lastly, the article highlights the importance of full-chip ESD tools, which address floor planning, IP-level reliability, and full-chip layout to ensure effective protection.

Bolstering ESD resistance in ICs

ESD events in integrated circuits (ICs) occur when a high electrostatic field triggers the rapid transfer of an electrostatic charge. These events typically generate electrical currents between 0.1 and 10 amps and dissipate energy ranging from 10 to 100 watts. While insulative and dissipative materials help limit electron flow and provide intermediate resistance levels, designing devices and systems with built-in ESD resistance, such as protective circuits or components, is critical to mitigating these effects.

On-chip ESD protective structures shield core circuits’ input, output, and power supply pins. These structures remain inactive during normal operation and activate only during ESD events. When triggered, they clamp pins to a low voltage and safely discharge excess current to the ground bus or rail. The protection circuitry deactivates once the high electrostatic field dissipates, restoring normal functionality. Electronic design engineers rely on three primary devices when integrating protection clamps:

Diodes: provide highly effective protection for low-voltage ESD applications due to their low turn-on voltage, low on-resistance, and high current-handling capacity under forward bias. Diode performance degrades under reverse bias, exhibiting higher turn-on voltage and resistance.
Figure 1. A detailed illustration of unidirectional and bidirectional TVS diodes protecting data lines in ESD-sensitive circuits. (Image: Cadence)

Transient voltage suppression (TVS) diodes (Figure 1), available in bidirectional (back-to-back) or unidirectional configurations, are the most common diode-based protection devices. Zener diodes also serve as ESD protection components, offering performance equivalent to unidirectional TVS diodes.
Grounded-Gate N-Channel MOSFET (GGNMOS): this device optimizes ESD performance in CMOS-based designs by leveraging layout modifications, such as increasing device spacing and optimizing doping profiles. These modifications improve current handling capacity and reduce thermal stress. GGNMOS devices operate in either active or snapback mode, with snapback providing the most effective ESD protection.
Silicon-controlled rectifiers (SCRs): deliver efficient and robust ESD protection through their bipolar conduction mechanism. Optimized silicon designs address susceptibility to latch-up, where current continues to flow uncontrollably after an ESD event.

For ESD protection, semiconductor manufacturers can implement polymer-based suppressors, multilayer varistors (MLVs), metal oxide varistors (MOVs), PCB spark gaps, and gas discharge tubes. Polymer suppressors, with their ultra-low capacitance (0.05 pF), support high-speed data and RF applications, while ceramic-based MLVs provide broader voltage coverage and automotive-grade options. These devices complement, rather than replace, the three primary on-chip protection clamps, each meeting specific protection requirements in the overall system design.

Key standards for ESD testing: HBM and CDM

ESD accounts for 30% to 40% of semiconductor failures. To verify resistance to transient ESD surges, electronic design engineers rely on two primary standards:

HBM: simulates electrostatic discharge from a person’s fingertip to a device. The test uses a 100-pF capacitor charged through a high-voltage supply and a high-resistance path (typically in the megohm range). Discharge occurs via a switching component and a 1.5 kΩ (1,500 ohms) series resistor. A standard HBM waveform includes a rise time of 2–10 nanoseconds, a peak current of 0.67 amps per kilovolt, and a double-exponential decay lasting 200 nanoseconds.
CDM: simulates discharge when a charged device contacts a grounded object, with the device itself acting as the charge source. During testing, the device is placed on a field plate, charged, and discharged, with all pins tested equally under both positive and negative charging.

CDM events are the leading cause of ESD failures in modern circuits. Although discharge durations often last less than one nanosecond, peak currents can exceed several tens of amperes, resulting in significant voltage drops and dielectric breakdown. Performing CDM tests with consistent results has become increasingly challenging due to the complexity of modern semiconductor designs. Accurate outcomes depend on precise chip and package substrate data, which is difficult to obtain for dense SoCs and chiplets that integrate billions of circuits.

Advanced chip designs also increase ESD vulnerabilities by introducing complex thermal and electrical interactions, necessitating precise simulations to mitigate risks. As designs scale, accurately modeling transient effects — such as inductance, capacitance, snapback, and larger package sizes — is increasingly crucial for ESD reliability.

Figure 2. An illustration of the ESD design window highlighting the voltage-current relationship between circuitry operating voltage, safety margins, and circuitry breakdown voltage. (**Image:** Siemens)

Additionally, achieving reliable ESD protection requires a well-defined design window (Figure 2) that balances precision and safety by specifying voltage and current limits for ESD devices. The device must trigger above the normal operating voltage and fail safely before reaching the breakdown voltage of the protected circuitry.

The importance of full-chip ESD tools

Although static ESD checkers provide useful preliminary analysis, they often report false violations, such as those triggered by decoupling capacitors. While foundries optimize CDM-checking methods for static tools, advanced SoCs and chiplet designs at lower process nodes require more comprehensive solutions. Full-chip ESD tools address the complexities of new processors by identifying at-risk designs, pinpointing vulnerable devices, and generating detailed reports on current density violations and high-resistance paths.

These tools perform transient simulations of the entire chip and package, analyzing interconnects, protective elements, and passive components such as inductors and capacitors. Engineers can run these simulations on pre- and post-layout versus schematic (LVS) clean designs, enabling quick identification and resolution of ESD vulnerabilities. Hierarchical debugging provides high-level overviews and granular insights, ensuring thorough coverage of potential risks.

Full-chip tools verify the robustness of core devices, protective elements, interconnects, and packages by simulating HBM and CDM events. They integrate transient effects and package considerations to accurately model device behaviors, improving reliability and minimizing costly redesigns. Advanced tools with distributed analysis capabilities efficiently handle sophisticated designs, processing up to 15 billion transistors in a single day while eliminating false positives and delivering faster turnaround times with greater coverage.

Aligned with key stages of the design flow, full-chip ESD tools support:

Floor planning: verify the robustness of the power clamp and ESD path interconnect; identify unused or lightly used ESD devices.
IP block layout: assess IP-level ESD device and interconnect reliability.
Complete layout: simulate the full chip to detect HBM and CDM issues.

Conclusion

Designing ESD-resistant silicon becomes increasingly challenging at advanced process nodes. Engineers must integrate billions of circuits into dense SoCs, leaving minimal space for ESD protection elements that require precise placement and verification. Chiplet architectures further compound ESD vulnerabilities, introducing intricate thermal and electrical interactions between processors, memory, and interconnects. Full-chip ESD tools address these complexities by efficiently performing transient simulations of the entire chip, package, and interconnects, processing up to 15 billion transistors daily.

References

Designing Electrostatic Discharge (ESD) Protection for Monolithic SoCs and Multi-Die Systems, Synopsys
New Unified Electrostatic Reliability Analysis Solution Has Your Chip Covered, Synopsys
PrimeESD: Full Chip ESD Simulation, Synopsys
ESD Protection Basics: Design and Simulation, Cadence
Voltus Voice: Demystifying ESD – Touch Ground with a Designer-Centric Protection Scheme, Cadence
What’s an ESD Design Window, and Why do I Care?, Siemens
The Many Aspects of Semiconductor Reliability with Impact on ESD Design, ESDA
ESD Fundamentals, ESDA
Electrostatic Discharge (ESD), Semiconductor Engineering
What Are ESD Countermeasures?, Murata