VMOS Electrostatic Protection

Present state of the art MOS devices with 1000 Ã… thick gate oxides have breakdown voltages in the 60-80 volts range. VMOS devices with the same oxide thickness have lower breakdown voltages (25-30 volts) due to higher fields in the oxide at the bottom of the V-groove. A VMOS protection device with higher protection capability than conventional MOS protection devices has been designed and tested. It consists of a poly resistor connected to an nipn diode, followed by an implanted n+ diffusion which acts as a distributed R C network attenuating tihe input voltage spikes. The final section consists of a planar NMOS transistor connected between the n+ diffusion and the VMOS gate. Tests show that this type of protection device is superior to conventional protection devices.