Global | July 31, 2024

Electromigration in High-Voltage FACTS Semiconductors

How to mitigate electromigration, a critical challenge in high-voltage semiconductors, particularly those used in Flexible AC Transmission Systems.

 

Image for illustration purposes.

Introduction

Electromigration is a significant issue in high-voltage Flexible AC Transmission Systems (FACTS) semiconductors. It involves the physical displacement of metal atoms caused by the momentum transfer from conducting electrons, leading to the degradation of semiconductor materials. This phenomenon can severely impact the reliability and longevity of FACTS devices.

Understanding Electromigration

Electromigration occurs when high-density electric currents cause metal atoms to drift, leading to the formation of voids and hillocks in the metal lines. Over time, these defects can cause open circuits or short circuits, compromising the functionality of the semiconductor device. In high-voltage FACTS applications, where semiconductors are subjected to substantial electrical stresses, electromigration becomes a critical reliability concern.

Causes and Effects

Causes and environmental factors include:

  • Current Density: High current densities accelerate the electromigration process. In high-voltage semiconductors, the current density is often elevated, increasing the risk of electromigration-induced failures.
  • Temperature: Elevated temperatures enhance atomic mobility, exacerbating electromigration. High-voltage semiconductors in FACTS devices often operate under high thermal conditions, making them more susceptible to this phenomenon.
  • Material Properties: The choice of materials for interconnects and contacts plays a crucial role. Materials with higher atomic mobility are more prone to electromigration.

The effects of electromigration include:

  • Open Circuits: Voids created by the movement of metal atoms can lead to open circuits, interrupting the flow of current.
  • Short Circuits: Hillocks formed by accumulated metal atoms can cause short circuits between adjacent metal lines.
  • Increased Resistance: The formation of voids and hillocks increases the resistance of metal lines, degrading the performance of the semiconductor device.

Mitigation Strategies

  • Material Selection: Using materials with lower atomic mobility, such as copper instead of aluminium, can reduce the susceptibility to electromigration. Copper has a higher resistance to electromigration and is increasingly used in high-voltage semiconductors.
  • Design Improvements: Optimising the design of interconnects to distribute current more evenly can mitigate the effects of electromigration. Techniques such as widening metal lines and using redundant interconnects can enhance reliability.
  • Thermal Management: Effective thermal management strategies, such as improved cooling systems and heat sinks, can lower the operating temperature of semiconductors, reducing the rate of electromigration.
  • Current Density Reduction: Reducing the current density by designing circuits that operate at lower currents can significantly decrease the risk of electromigration.
  • Advanced Manufacturing Techniques: Employing advanced manufacturing techniques, such as electroplating and chemical vapour deposition, can improve the quality and reliability of metal interconnects, making them more resistant to electromigration.

Conclusion

Electromigration is a critical challenge in high-voltage FACTS semiconductors, affecting reliability and longevity. Material selection, design improvements, thermal management, current density reduction, and advanced manufacturing techniques are all essential in addressing electromigration in high-voltage semiconductors. These measures ensure the reliable operation of FACTS devices, contributing to the stability and efficiency of modern power systems.

Source: EE Power