REDUCTION OF BASE-COLLECTOR CAPACITANCE IN INP INGAAS HBTS USING A NOVEL DOUBLE POLYIMIDE PLANARIZATION PROCESS/

The parasitic base-collector capacitance (C-BC) in InP/InGaAs heteroju nction bipolar transistors (HBT's) has been reduced using a novel doub le polyimide planarization process which avoids damage of the extrinsi c base layer, The extrinsic base metal outside the base-collector mesa is placed on the polyimide by polyimide coating and etch-back to the base layer.We obtained f(T) of 81 GHz and f(MAX) of 103 GHz with a 2 x 10 mu m emitter. Performance comparison between two devices nith the same area of 2 x 2 mu m but with different base-collector mesa area sh owed 56% reduction of C-BC and 35% increase of f(T) and f(MAX).