Turn-off dynamics of a new very fast switching 1000 V, 50 A bipolar power transistor

The SIRET^®(Siemens Ring Emitter Transistor) is an ultrafast switching bipolar power transistor with a 5 µm fine emitter geometry and a 3 µm short base width. In a 3-stage darlington configuration storage times of less than 2 µs and a MOSFET like fall time of 30 ns at switching 50 amps inductive load without any snubber at 700 V has been achieved (inductive voltage spike up to 1000 volts). For higher operating voltages the inductive voltage spike is clamped by the device itself. Thus for a device with a VCEOof 600 volts an RBSOA up to the VCBOof 1000 volts is possible at full rated current. The transistor can be switched off with negative base current as high as is attainable with strong base drive, but there exists an optimal base current for minimal dissipated turn-off energy. An explanation of this optimum is given by the field and carrier distributions computed by one dimensional modelling of the device. The mechanism of clamping voltage spikes by the device will be explained by one dimensional modelling as well.