AUSTIN, Texas — IBM Microelectronics has developed a silicon germanium (SiGe) bipolar transistor with a maximum transistor frequency of 350 GHz, and expects to introduce it commercially in its 9HP BiCMOS process in about two years, said David Harame, an IBM distinguished engineer.
The 9HP BiCMOS process should result in chips operating at 150 GHz, or fast enough to support the Sonet 160-Gbit/second optical networking standard and higher-frequency wireless applications. "For the 350-GHz transistor, by the time we get through enhancing it, we're talking about 400-GHz fmax in the final format," Harame said.
Though optical networking customers are generally the first to adopt the fastest SiGe technologies, Harame said wireless customers are never far behind. By running the more efficient transistor at slower speeds, power consumption declines, he said.
"The networking people gobble this stuff up, because they are hungry for bandwidth. Immediately after that come the wireless customers, because they can trade off gain bandwidth for power," he said.
Last May, IBM engineers described a SiGe heterojunction bipolar transistor (HBT) with an fT of 207 GHz and an fmax of 285 GHz. That transistor is still being readied for use in a 130-nm BiCMOS process for commercial production.
IBM's fastest available 0.18-micron (180-nm) SiGe BiCMOS technology incorporates a 120-GHz fT HBT. Harame said one unnamed customer is using that process for a wireless chip that includes 6,000 HBTs, 7 million CMOS transistors, a noise isolation technology and "a whole host of capacitors. That is our most complicated chip out there — an RF analog system-on-chip that operates at 2 GHz," he said.
The 350-GHz bipolar transistor features thinner layers and some innovations in the structure of the device. (Bipolar performance depends largely on thinning in the vertical dimension.) "We scaled the device, primarily vertically, but also did some lateral scaling. We shrunk the parasitics and greatly speeded up the transit times through all the layers in the device," Harame said.
The transistor will be described in more detail at the International Electron Devices Meeting to be held Dec. 8-11 in San Francisco.
Market research firm IC Insights (Phoenix) estimates that the 2001 market for silicon-germanium-based devices was about $320 million, and is projected to grow to $2.7 billion by 2006. IC Insights estimates that IBM accounts for about 80 percent of the market thus far.
Heightened competition
Fred Zieber, president of Pathfinder Research (San Jose, Calif.), said the IBM announcement heightens the competition between SiGe-based solutions and gallium arsenide and indium phosphide ICs for the very fastest applications. The technical literature has reported a neck-and-neck race between SiGe and InP in terms of the highest frequency devices, Zieber said.
"SiGe technology has made huge strides. Gallium arsenide is the area that has taken a huge hit — digital gallium arsenide appears to be going almost totally to CMOS, with some of the mixed-signal devices moving up into indium phosphide and into SiGe BiCMOS," Zieber said.
SiGe has a commercial advantage in that its bipolar transistors are embedded in a CMOS process that can reach high levels of integration. Also, SiGe "rides the huge amount of money being invested in CMOS" to scale to finer linewidths, Zieber noted.
IBM is facing more competition in the SiGe marketplace. Intel Corp. has announced plans to offer its initial SiGe process at the 90-nm node, for example. Conexant Systems Inc. said its SiGe process will support transistor frequencies of 200 GHz and power maximum frequencies of 180 GHz.
Less well known, Zieber said, is the future competitiveness of Germany's SiGe foundry, Communicant Semiconductor, which said last week that it had secured subsidies from the European Community that would allow it to build its fabrication facility.
— With additional reporting by Mark Lapedus.
