IBM's GeOI photodetector boosts optical links
Optical interconnects might eventually relieve the bottleneck of getting information to and from chips via electronic connections, boosting the performance of computers and other types of electronic systems.
"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 at IBM Research. "Optoelectronic components such as these GeOI photodetectors will be essential for future high-performance computing systems."
The new devices utilize GeOI 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 Gbit/s. 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 combination of properties makes the detectors ideal for use in optical interconnects.
The technology takes advantage of the outstanding absorption properties of germanium (Ge) at the wavelength - 850 nm - typically used for optical transmission over short distances. At this wavelength, Ge absorbs light about 70 times more efficiently than Si, and the Ge-based photodetectors are much smaller and faster than equivalent Si devices.
Crucially, the 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 optoelectronic circuits on the same chips as microprocessors and other electronic components.
GeOI technology employs a thin layer of Ge above an insulating oxide layer on a silicon substrate. The oxide reduces the parasitic resistance and capacitance of the device and enables a higher maximum oscillation frequency.
IBM described the photodetector at the Device Research Conference in Notre Dame, Indiana, on June 22, 2004 in a paper entitled "High-efficiency, Ge-on-SOI lateral pin photodiodes with 29 GHz bandwidth" by Steven Koester, Jeremy Schaub, Gabriel Dehlinger, Jack Chu, Q. Christine Ouyang, and Alfred Grill.
