Analysis of Thermal Instability in Power MOSFET

In this paper, the behavior of thermal instability in power MOSFET is investigated. It is shown that the device is at risk of thermal instability when the current has a positive temperature coefficient. The MOSFET current has a positive temperature coefficient when gate voltage is less than temperature compensation point. The model and experimental data show that the sufficient condition for the thermal instability in the device is S>1. The drain voltage has a large effect on the thermal instability of the device, and the device with a large transconductance has poor thermal stability. Finally, the thermal images demonstrate that even at a steady-state temperature field, there is no uniform temperature and current on the surface of the chip, and the difference is greater in the unstable region. The results confirm that the burnout of chip is caused by local hot spot.