Optimization of SiGe HBT Technology for High Speed Analog and Mixed-Signal Applications

SiGe HBTs have achieved record peak fT values values[l-2] and impressive digital circuit ECL RO delays[3] but no analog circuit results have been reported. In this work we investigate the leverage of SiGe HBTs for analog circuits by optimizing the Ge-profile for a high βV_A product and high fT under the constraint of breakdown voltage and effective strain of the SiGe layer. Analytical calculations of β, V_A, and fT of SiGe-HBTs as a function of Ge profile predict the largest performance advantage over Si BJTs for the most steeply graded Ge profile. SiGe-HBT transistors are fabricated with β V_A products of 6160 V, BV_CEO of 3.5 V and f _max of 46 GHz, and compared to Si-BJTs fabricated with the same process. Digital performance is benchmarked by an ECL ring oscillator delay of 17.2 psec. The leverage for analog technology is demonstrated by fabrication of a 1GHz SiGe-HBT 12 bit Digital to Analog Convertor.