A new sub-micron 24 V SiGe:C resurf HBT

For the first time a SiGe:C heterojunction bipolar transistor (HBT) is presented that uses the resurf effect to improve the cutoff frequency (f/sub T/) for a specified collector-base junction breakdown voltage (BV/sub CB0/). By using trenches filled with intrinsic silicon adjacent to the collector drift region, the electric field profile can be reshaped so that a high breakdown voltage (>20 V) can be combined with a high drift doping concentration. This allows for high current densities and consequently a high f/sub T/. Experimental results show an increase of the f/sub T//spl times/BV/sub CB0/ product of up to a factor of two by using resurf, the maximum value obtained is 670 GHzV.