A team of Ph.D. students in the Cornell Broadband Communications Research Lab (CBCRL) took 3rd place in a microchip design contest, winning $10,000 for their lab. A second Cornell team was a finalist. The SiGe Design Challenge, sponsored by an industry consortium, sought new applications for chips fabricated from a combination of Silicon and Germanium (SiGe).
The material has recently seen widespread use in cellular phones, but has yet to find other large-scale uses. One Cornell team developed a fiber-optic transceiver for use in high-speed networks operating at 10 Gigabits per second (more than 1,000 times faster than a typical home Internet connection). The other team designed a cellular phone chip that increased battery life by as much as 60 percent.
Most chips, such as those used for computer processors, are fabricated from “plain vanilla Silicon,” according to Prof. Kevin Kornegay, director of CBCRL. Adding Germanium changes the electrical properties of the chip material, lending it several benefits: SiGe devices can run quickly more easily than Silicon devices, cost less than devices from other high-speed materials, and often use less electricity than devices made from those materials.
Components in cell phones, fiber-optic transceivers and some radar systems are all perfect candidates for SiGe chips because of the high speed demanded by such tools. Prior to SiGe technology, these devices often used exotic, highly expensive materials such as Gallium Arsenide, according to Kornegay. He also pointed out that along with the price and power differences, SiGe technology lets engineers pack more components onto a single chip, further lowering costs. “With Silicon Germanium, a processor and a radio transceiver can coexist on the same substrate [chip],” he said.
But SiGe chips have yet to move beyond the cell phone market. “It hasn’t stretched its application wings yet,” Kornegay said. “The slowdowns in industry have hindered SiGe from catching other markets, such as [fiber] optical. But it’s only a matter of time.”
Two members of the team that placed third, Daniel Kucharski grad and Drew Guckenberger grad, are currently interns at IBM, a pioneer in SiGe chip fabrication. The third member, Jing-Hong Conan Zhan grad, said he plans to continue work on the team’s fiber-optic transceiver, which integrated a number of components that usually require separate chips. Fiber-optics are used in large networks such as the internet, and in high-performance computers.
Without SiGe technology, Zhan said they could not have created the transceiver “at that frequency and that cheap.” He added, “There are other processes available, but they are much more expensive. And there are also cheaper processes, but they can’t operate at the frequencies we need. So it seems like Silicon Germanium is the best choice.”
The other team from CBCRL was one of 15 finalists selected from an initial pool of 59 entrants. IBM fabricated actual chips matching the designs submitted by these finalists, and the teams then tested the chips against their earlier simulations. The second Cornell team was not among the three winners, but Kornegay praised their creativity and effort. “Both teams did extremely well,” he said. “Our students had that combination of intelligence, competitiveness, creativity and also pride.”
The second team, comprising Guckenberger, David Fried grad and Ian A. Rippke grad, combined several cell phone components onto a single SiGe chip and built in new power-saving features as well. “The device that consumes most of your power [in cell phones] is your power amplifier,” Kornegay said, “and it wastes a lot of energy.”
The amplifier in the students’ design adjusts its strength as needed, so when the phone is closer to a tower it performs less amplification, saving electricity. “The power-handling and current drive capability of Silicon Germanium … made it possible,” Fried said. “What we tried to do is called monolithic integration. The benefit is if we can take 15 or 20 parts that are currently individual parts in your cell phone and integrate them into a single part — it’s cheaper, it’s smaller, and it uses less power.”
Fried also praised the facilities at CBCRL as essential to his team’s work. “We have a really solid design infrastructure that gives us all the tools needed to do this kind of advanced design,” he said. “When you get up into the gigahertz regime it gets much harder to test … and the CBCRL provides us with a great testing infrastructure.”
Kornegay emphasized that both the lab and his students were crucial to the projects’ success. “This work was born out of the efforts of [CBCRL],” he said, adding, “You need the best graduate students to create the best possible research environment. You present them with this infrastructure and you just turn them loose.”
“The contest is kind of a benchmark of how our research team did relative to other universities,” he said. “So based on this, we have an outstanding program. The other winners, the faculty advisors were working in these areas for years and years. We just started three years ago and look where we are today.”
Archived article by Peter Flynn