Impact of Substrate Bias on the Switching Behavior of GaN Bidirectional Switches

The gallium nitride (GaN) bidirectional switch (BDS) enables true four-quadrant operation and offers significant benefits in reducing component count and switching losses. However, its unique device structure introduces new reliability challenges. This work investigates the role of substrate biasing on BDS lifetime. Experimental results show that devices with a floating substrate exhibit catastrophic failure within ~30 minutes of operation, while those with the substrate tied to the low-side source remain stable for more than 1000 hours. TCAD simulations reveal that under floating conditions the substrate self-biases to a positive potential, leading to intensified electric fields at the gate side of the device. This localized field intensification provides a direct explanation for the reported lifetime reduction. These results demonstrate that proper substrate biasing is essential for reliable operation of optimized BDS and point to dynamic clamping to the lowest source potential as the preferred solution for the studied device architecture.