IBM Technology Could Make Optical Chip Connections a Reality

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YORKTOWN HEIGHTS, NY - 21 Jun 2004: IBM today announced it has developed a high-speed photodetector that could greatly increase the speed at which information travels to and from microchips, boosting performance in computers and other types of electronic systems.

While the performance of microprocessors and other chips has increased dramatically, bottlenecks still exist in getting information to and from the chip. The new photodetectors could relieve those bottlenecks by allowing chips to talk with the other parts of an electronic system using high-speed light pulses and optical connections instead of the relatively slow electrical pulses and wires used today.

While optical connections have long been recognized as a potential avenue for increasing chip communications, prior attempts to incorporate this capability were incompatible with chip manufacturing processes. IBM's photodetectors are based on a newly-developed germanium-on-insulator (GOI) technology that could now, for the first time, allow them to be readily incorporated into many standard chips.

"This is a major step toward overcoming the biggest bottleneck in system performance, the interconnection between chips," said T.C. Chen, VP Science and Technology, IBM Research. "Opto-electronic components such as these GOI photodetectors will be essential for future high-performance computing systems."

Computer chips using these new photodetectors could save space, cut costs and dramatically increase the speed of information exchange inside PCs, servers and among computers networks. The new detectors are necessary because existing silicon (Si) photodetectors are inadequate for the speeds needed for optical interconnects. Using current Si detectors is like trying to use 1960s transistor technology for today's microprocessors -- it simply doesn't make sense.

The new detector is compatible with standard microchip technology because the germanium can be placed selectively in the regions where the photodetectors reside. This compatibility opens the door for making opto-electronic circuits on the same chips as microprocessors and other electronic components.

The photodetectors are unique in that they simultaneously exhibit nearly all of the desirable properties needed for optical interconnects, including high bandwidth (speed), high efficiency, low voltage operation, wide spectral window and compatibility with standard microchip fabrication facilities. It is this combination of properties that makes these detectors so ideal for use in optical interconnects.

Existing photodetectors can achieve some of these properties, but not all at the same time.

The new devices utilize GOI technology to create a photodetector that has an optical frequency response of nearly 30 GHz, making it, in principle, suitable for detecting signals at speeds over 50 Gbps. The devices also operate at low voltages (1V), are very efficient (over 40%), can detect light over a wide range of wavelengths, and are compatible with standard CMOS chip manufacturing technology.

This technology takes advantage of outstanding absorption properties of germanium (Ge) at the wavelength typically used for optical transmission over short distances. At this wavelength (850nm), Ge absorbs light about 70 times more efficiently than Si, the semiconductor used to make microprocessors. Since germanium absorbs light so well, the detectors are much smaller and faster than Si photodetectors, and Ge is compatible with the Si fabrication processes.

IBM will detail this photodetector breakthrough at the Device Research Conference in Notre Dame, Indiana, on June 22, 2004. The paper is entitled "High-efficiency, Ge-on-SOI lateral PIN photodiodes with 29 GHz bandwidth," by Steven J. Koester, Jeremy D. Schaub, Gabriel Dehlinger, Jack O. Chu, Q. Christine Ouyang, and Alfred Grill.

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