SiGe HBTs and ICs for optical-fiber communication systems

An ultra-high-speed selective-epitaxial-growth (SEG) SiGe-base heterojunction bipolar transistor (HBT) with self-aligned aligned stacked metal/in-situ doped poly-Si (IDP) (referred to as SMI) electrodes has been developed. A 0.54-μm-wide SiGe base self-aligned to the 0.14-μm-wide emitter, which reduces collector capacitance, was selectively grown by using a UHV/CVD system. SMI electrode technology, which enables low parasitic resistance, allows the intrinsic base profile to be kept shallow, so it is well suited to a SiGe-base HBT. A 2-μm-wide BPSG/SiO₂ refilled trench was introduced to reduce substrate capacitance by reducing its sidewall element. This makes it possible to obtain a 95-GHz cut-off frequency and ultra-high-speed emitter-coupled-logic (ECL) circuit with an 8.0-ps gate-delay. As applications for these SiGe HBTs, various ICs for optical-fiber-link systems have been developed. These include a 1/8 static frequency divider with a maximum operating frequency of up to 50 GHz, a time-division multiplexer and a demultiplexer operating at 40 Gb/s, a preamplifier with a bandwith of 35 GHz, an AGC amplifier core with a bandwidth of 32 GHz, and a decision circuit operating at 40 Gb/s.