High-speed self-aligned SiGe HBT and application to optical-fiber-link ICs

SiGe base heterojunction bipolar transistor (HBT) has high-frequency and high-speed performance comparable to compound semiconductor devices, and also has high cost because the existing Si process is used. Hence, this HBT is expected to be a key device for high-speed optical transmission systems and microwave/millimeter-wave wireless systems. The self-aligned SiGe HBT developed here has a PASS structure with selective epitaxial growth by UHV/CVD and buffered polycrystalline Si in the lower layer of the external base polycrystalline Si. In this way, high-speed operation of the intrinsic transistor and reduction of the parasitic capacitance and resistance are realized at the same time. The cutoff frequency and maximum oscillation frequency of this SiGe HBT are 122 and 163 GHz, and the gate delay time of the ECL circuit is an extremely fast 5.5 ps. Further, an IC to form a 40 Gbit/s optical receiver is fabricated. A preamplifier with a 45-GHz bandwidth, a limit amplifier with a gain of 32 dB, a frequency divider of 60-GHz operations, and a 1:4 DEMUX with a decision circuit operating at 40 Gbit/s are realized. It is shown that the 40 Gbit/s optical receiver IC chip set with the present SiGe HBTs reached a practical level.