Helmut Strack

A new generation of high voltage MOSFETs breaks the limit line of silicon

For the first time a new device concept for high voltage power devices has been realized in silicon. Our 600 V-COOLMOS/sup TM/ reaches an area specific on-resistance of typically 3.5 /spl Omega//spl middot/mm/sup 2/. Our technology thus offers a shrink factor of 5 versus the actual state of the art in power MOSFETs. The device concept is based on charge compensation in the drift region of the transistor. We increase the doping of the vertical drift region roughly by one order of magnitude and counterbalance this additional charge by the implementation of fine structured columns of the opposite doping type. The blocking voltage of the transistor remains thus unaltered. The charge compensating columns do not contribute to the current conduction during the turn-on state. Nevertheless the drastically increased doping of the drift region allows the above mentioned reduction of the on-resistance.

Power MOS transistors for 1000 V blocking voltage

High-voltage MOS transistors with blocking voltages of up to 1000 V and turn-on resistances of less than 2 Ω were developed and tested. The transistor structure itself is that of a vertical SIPMOS+(1) power transistor. Retaining this technology, a special design of the cell field and a new type of chip edge construction became necessary in order to achieve the quoted values. The required constructional dimensions were obtained with the aid of a two-dimensional modelling program. (+SIPMOS = Siemens Power MOS)

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.

An advanced high voltage bipolar power transistor with extended RBSOA using 5 µm small emitter structures

A novel high voltage bipolar power switching transistor-has been developed. The transistor has 5 µm wide ring emitters with polysilicon resistors in a cell construction and a closemeshed base, using a two layer metalization technique. The blocking capability of VCBO- 1000 volts is not merely a number, but the device can be switched under full current (10A) up to this voltage. There is no second breakdown at switching the device above VCEO(550V) by negative base currents as high as the collector current. The storage time is less than 1 µs and the switching speed is a few 10 ns, i.e. comparable to MOSFETs.