Optimization of SiGe HBT technology for high speed analog and mixed-signal applications

SiGe HBTs have achieved record peak f/sub T/ values values and impressive digital circuit ECL RO delays 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 /spl beta/V/sub A/ product and high f/sub T/ under the constraint of breakdown voltage and effective strain of the SiGe layer. Analytical calculations of /spl beta/, V/sub A/, and f/sub T/ 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 /spl beta/V/sub A/ products of 6160 V, BV/sub CEO/ of 3.5 V and f/sub 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 1 GHz SiGe-HBT 12 bit Digital to Analog Convertor.<
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