When latch-up occurs in an IGBT

When latch-up occurs in an Insulated Gate Bipolar Transistor (IGBT), it refers to a failure mode where the device starts to conduct uncontrollably, essentially short-circuiting. This situation happens when the parasitic thyristor structure inherent in the IGBT’s design (formed by the P-layer, N-layer, and the substrate) is inadvertently turned on. Latch-up can be triggered by several factors, including:

1. Overcurrent Conditions: When the current flowing through the IGBT exceeds its rated value, the excessive electron-hole pairs generated can turn on the parasitic thyristor.

2. High dv/dt or di/dt Rates: Rapid changes in voltage (dv/dt) or current (di/dt) can induce latch-up by rapidly injecting charge carriers into the layers of the IGBT, creating conditions that enable the parasitic thyristor to conduct.

3. Overvoltage: Overvoltage conditions, especially on the collector-emitter voltage, can also lead to an excessive electric field in the device, potentially triggering latch-up.

4. Thermal Runaway: Excessive heating can lead to an uneven temperature distribution across the IGBT, which may result in localized hot spots. These hot spots can lower the turn-on voltage of the parasitic thyristor, making latch-up more likely.

5. ESD Events: Electrostatic discharge (ESD) events can create sudden, high-voltage spikes that trigger the