IBM claims to have developed a silicon germanium (SiGe) transistor with a speed of 210GHz. This should drive communications chips at speeds up to 100Gbit/s. A typical chip operates at 40Gbit/s.
The performance has been achieved using a heterojunction bipolar transistor (HBT) designed with vertical electrical flow. HBTs are used in RF circuits in high-bandwidth communications. IBM has reduced the vertical layer to 0.5µm, a reduction of a factor of two on current technology.
Seshadri Subbanna, senior engineering manager, said: "IBM has spent about 15 years developing the SiGe layer. Construction at low temperatures has allowed us to make very thin vertical structures."
Subbanna says the IBM breakthrough disproves a widely held belief that 100GHz was a fundamental limit for transistor performance beyond which silicon technology would not be able to go.
"We believe we have crossed a threshold with this," he said.
Aimed at the optical networking market, the ICs developed with this technology should be capable of meeting the needs of the next generation of optical technology. A 10Gbit/s Ethernet standard is currently state-of-the-art.
"The chips are completely electronic," said Subbanna, "but they will drive an optical link or amplify it. We will also be able to integrate a lot of CMOS logic on to the chip and make bigger chips with a larger transistor count than competing technologies. We should be able to put 100000 transistors on a chip."
IBM constructed the prototype HBT using 0.18µm lithography. As 0.13µm technology becomes more widespread, IBM intends to use it for the HBT, which is claimed will improve the CMOS processing in particular.
IBM has developed the technology with internal and external customers, and anticipates full-scale 8in wafer production in two years' time."