A static frequency divider with a maximum operating frequency of up to 50 GHz and a multiplexer (MUX) and a demultiplexer (DEMUX) that both operate at 40 Gb/s were developed for future optical-fiber-link systems. These digital circuits were fabricated using ultra-high-speed self-aligned selective-epitaxial-growth SiGe-base heterojunction bipolar transistors (HBTs) with self-aligned stacked metal/in-situ doped poly-Si electrodes. These HBTs provide a 95-GHz cutoff frequency, a 108-GHz maximum oscillation frequency, and a minimum emitter-coupled-logic (ECL) gate delay of 8 ps. The excellent results from this digital chipset show that SiGe HBT technology, with its high reliability and cost-effectiveness, will play an important role in future multi-gigabit per second optical-fiber-link systems.
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