Charge sharing effects in bipolar transistors with sub-halfmicron emitter widths

It is shown by numerical simulation and experiment that, in transistors with a base link-up deeper than the intrinsic base, the electric field in the collector-base junction is reduced for very narrow emitters. This is due to charge sharing of the base link-up and intrinsic collector-base depletion regions in the epi-layer underneath the emitter. These 2-D effect cause a decrease in f/sub T/ and h/sub FE/, but an increase in V/sub eaf/. By keeping the base link-up shallow it is possible to minimize f/sub T/ decrease for narrow emitters. This is demonstrated in a transistor with f/sub T/=24 GHz (V/sub cb/=3 V) and an emitter width W/sub e/=0.1 mu m.<
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