TABLE OF CONTENTS Before 1990, heterojunction bipolar transistors were available only in III-V compound semiconductor technologies. The addition of Ge in Si to form strained-SiGe and the incorporation of SiGe in conventional Si BiCMOS technology has created a revolution in the semiconductor industry [1, 2]. The Ge added to form high-performance heterojunction bipolar transistors can operate at speed much higher than standard silicon bipolar transistors. State-of-the-art SiGe HBTs have values of f T beyond 350 GHz and f max 270 GHz [3] and operate at speed previously attainable only with GaAs technology. The performance improvement of SiGe HBTs is due to energy bandgap lowering resulting from adding Ge to the base of the device, and the principle of operation has been described earlier. SiGe HBTs differ from III-V technologies in that the breakdown voltage may be set by collector implants and not predetermined by layer growth. Therefore, the SiGe HBTs with multiple breakdown voltages can be fabricated in the same process by varying the collector implants.
In the high-speed arena, SiGe HBTs today are surpassing even the fastest III-V production devices. The key to this achievement is the superior parasitic control technology available to SiGe device designers, compared to what is available to III-V device designers. SiGe HBTs have the advantage of being built in the existing silicon fabrication using standard silicon production equipment. Research is under way on SiGe heterojunction MOSFETs, which in turn is expected to revolutionise the future of CMOS technology as well.
SiGe HBTs have also...
