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First 500GHz silicon-germanium transistors demonstrated

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A RESEARCH team from IBM and the Georgia Institute of Technology has demonstrated the first silicon-germanium (SiGe) transistor able to operate at frequencies above 500GHz. Though the record performance was attained at extremely cold temperatures, the results suggest that the upper bound for performance in SiGe devices may be higher than originally expected.

John D Cressler, Byers Professor in Georgia Tech’s School of Electrical and Computer Engineering and a researcher in the Georgia Electronic Design Center (GEDC) at Georgia Tech, said ultra-high-frequency SiGe circuits have potential applications in many communications, defence, space electronics platforms and remote sensing systems.

“Achieving such extreme speeds in silicon-based technology – which can be manufactured using conventional low-cost techniques – could provide a pathway to high-volume applications. Until now, only integrated circuits fabricated from more costly III-V compound semiconductor materials have achieved such extreme levels of transistor performance,” he explained.

“But for the first time, Georgia Tech and IBM have demonstrated that speeds of half a trillion cycles per second can be achieved in a commercial silicon-based technology, using large wafers and silicon-compatible low-cost manufacturing techniques. This work redefines the upper bounds of what is possible using SiGe nanotechnology techniques.”

The SiGe heterojunction bipolar transistors built by the IBM-Georgia Tech team operated at frequencies above 500GHz at 4.5K – a temperature attained using liquid helium cooling. At room temperature, these devices operated at approximately 350GHz. Performance measurements were made using a specialised high-frequency test system in the GEDC.

The devices used in the research are from a prototype fourth-generation SiGe technology fabricated at IBM on a 200mm wafer using an older unoptimised mask set. Simulations suggest that the technology could ultimately support much higher (near-terahertz) operational frequencies at room temperature, Cressler said.

The next step in this research will be to understand the physics behind the SiGe devices, which display some unusual properties at these extremely low temperatures.

Beyond Cressler, the research team included Georgia Tech PhD students Ramkumar Krithivasan and Yuan Lu; Jae-Sun Rieh of Korea University in Seoul (formerly with IBM); and Marwan Khater, David Ahlgren and Greg Freeman of IBM Microelectronics in East Fishkill, New York.

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