Introduction

When designing integrated circuits, one of the important considerations is the protection against electrostatic discharge (ESD). Unprotected ICs can be damaged or destroyed by ESD events that occur during normal use. ESD protection diodes are used to shunt away the excess energy from these events, protecting the IC. Two types of ESD protection diodes are commonly used in IC designs: unidirectional and bidirectional. In this article, we'll compare the two types to help you make an informed decision for your design.

Unidirectional ESD Protection Diodes

Unidirectional ESD protection diodes are designed to shunt current in only one direction. They're also called TVS (transient voltage suppression) diodes. They're ideal for applications where the ESD events occur in one direction. They offer a lower capacitance and a faster response time compared to bidirectional diodes. They're also simpler to integrate into the IC design.

Bidirectional ESD Protection Diodes

Bidirectional ESD protection diodes are designed to shunt current in both directions. They're ideal for applications where the ESD events can occur in both directions. They offer a higher capacitance and a slower response time compared to unidirectional diodes. They're also more complex to integrate into the IC design.

Comparison: Unidirectional vs Bidirectional ESD Protection Diodes

Here's a table comparing the key parameters of unidirectional and bidirectional ESD protection diodes:

From the table, we can see that unidirectional diodes offer a higher current capacity, a lower clamping voltage, a faster response time, and a lower capacitance compared to bidirectional diodes. They're also simpler to integrate into the IC design. However, they're only effective in protecting against ESD events that occur in one direction.

On the other hand, bidirectional diodes offer a lower current capacity, a higher clamping voltage, a slower response time, and a higher capacitance compared to unidirectional diodes. They're also more complex to integrate into the IC design. However, they offer protection against ESD events that occur in both directions.

Conclusion

When choosing between unidirectional and bidirectional ESD protection diodes for your IC design, you need to consider the direction of the ESD events and the other parameters such as current capacity, clamping voltage, response time, capacitance, and integration complexity. If your application requires protection against ESD events in one direction, unidirectional diodes are the best choice. If your application requires protection against ESD events in both directions, bidirectional diodes are the best choice.

References

1. S. E. Laux, "ESD Protection Diodes for Advanced CMOS Technologies", IEEE Journal of Solid-State Circuits, vol. 36, no. 3, 2001.
2. "ESD Suppressor Selection Guide", Toshiba Corporation, Application Note, 2014.
3. "Bidirectional TVS Diode Series Datasheet", Littelfuse, 2021.