Latch-up

Definition: Latch-up is an unwanted condition in CMOS circuits where parasitic bipolar transistors form a low-impedance path between power and ground, causing excessive current flow.

Key Points:

  • Can lead to circuit malfunction or permanent damage
  • Triggered by voltage spikes or radiation
  • More prevalent in bulk CMOS processes

Causes:

  • Parasitic PNPN structure in CMOS layout
  • Overvoltage on I/O pins
  • Ionizing radiation

Prevention Techniques:

  • Guard rings
  • Substrate/well contacts
  • ESD protection circuits
  • Proper power sequencing

Importance:

  • Critical for IC reliability and robustness
  • Affects layout design and process selection
  • Key consideration in high-reliability applications

Challenges:

  • Increasing susceptibility in advanced nodes
  • Balancing latch-up prevention with area efficiency

Understanding and preventing latch-up is essential for ensuring the reliability of CMOS integrated circuits.