Switching performance of vertical siemens power MOSFET´s

A novel vertical power MOSFET technology with ultrashort channel transistors has been developed. The channels are implemented by ion implantation of the source and channel regions using the tapered edge of the polysilicon gate oxide as a mask. The resulting devices have lower threshold voltage, higher transconductance and current carrying capability than any other power MOSFETs available today. They can be driven directly from 5 V TTL or VLSI output level, or from microcomputer output ports. Devices designed for 0.1 - 2 ohm on resistance and 50 - 600 V drain voltage have been realized. An investigation of the switching behaviour showed the switching waveform of such devices to be determined mainly by the Miller capacitance and the output impedance of the driving circuit. The rapid rise of the Miller capacitance at output voltages lower than the gate voltage results in a unique waveform characterized by a gradual decrease in "on" resistance at the start and a gradual increase at the end of the switching cycle. Whereas the data sheets of commercial power MOSFETs disregard this behaviour and list only Crssat UGS<UDSand the ID(t) pulse, it would be more advantageous to know the switching performance at and the capacitances UGS>UDSas well. Since all the capacitances show only a limited response to temperature and current, the switching speed is practically independent of the temperature and the switched power. Although the input signal levels greatly affect the switching speed, the simple mode of operation of power MOSFETs makes the circuit configuration built around them easy to design.