Recently, a vertical power MOSFET (Metal Oxide Semiconductor Field Effect Transistor) opens up a new market in fields such as a high-voltage switching supply and a mobile communication equipment. Since the vertical power MOSFET is used in a power management circuit and the safety circuit of a lithium-ion battery, it is required characteristics of low ON resistance, high breakdown voltage, low voltage operation and reducing switching loss.
The vertical power MOSFET has functions to switch with applied high voltage and to clamp an electrical voltage generated by an avalanche breakdown in the case of applied overvoltage. These functions prevent components in the circuit from being insulation breakdown.
The avalanche breakdown means an amount of current or energy in the avalanche state. It is available to have a low breakdown voltage of a semiconductor device for improving the avalanche breakdown. However, if the vertical power MOSFET has a low breakdown voltage, its ON resistance increases.