UHVCVD growth of Si/SiGe heterostructures and their applications

The era of integrated circuits based on SiGe heterojunction bipolar transistors arrived with the announcement of a 12-bit digital to analogue converter (DAC) fabricated using an analogue optimization of IBM's SiGe HBT technology. Medium-scale integration was employed, the circuit consisting of approximately 3000 transistors and 2000 passive elements (resistor and capacitors). Operable at 1 GHz, this converter consumes approximately 0.75 W, thus yielding power-delay performance a decade superior to prior devices. It is significant that this DAC was fabricated employing the same technology and toolset as found on a standard silicon-based CMOS product line. In addition to the CMOS toolset, only one unique tool is required to support this technology, a commercial (Leybold-AG) ultrahigh vacuum chemical vapour deposition system for SiGe deposition. It is of interest to note, however, that the processing of these integrated circuits was no different from that employed in fabricating high-performance SiGe high electron mobility transistors (HEMTs), as well as the first N-type SiGe-based resonant tunnelling devices (RTDs), all functional at room temperature. This enables one to combine a wafer-scale manufacturable SiGe-based heterojunction technology with devices that utilize quantum phenomena, made accessible by the use of band offsets and strain-induced band splitting in the Si/SiGe materials system. This new ability to incorporate leading edge developments in SiGe device physics into a standard technology line opens up a host of new areas for exploration.