ST makes good progress with silicon photonics

The company announced the licensing of silicon photonics technology from Luxtera in March 2012 and, since then, has been developing a 300mm line at its Crolles fab for production of silicon photonics. "We think we are the only ones doing the processing in a 12in line," said Flavio Benetti, pictured, general manager of ST's mixed processes division. The company has a manufacturing agreement with Luxtera and the two continue to collaborate. "We have all the seeds to have a long term collaboration," Benetti said, adding: "We also have the freedom to develop our own products." ST is a long term supplier of cmos and bicmos ics to optical module makers and will make the ics and photonic circuits separately. The photonic circuits will be made using 65nm lithography, chosen as it offers a good trade off between manufacturing cost and device feature precision. Test wafers have been run through the manufacturing line. "We are very satisfied with the progress," claimed Benetti. One challenge with silicon photonics is the ability to get the light in and out of the circuit. Benetti said: "If you use a 90nm cmos process, it may cost less, but 65nm is a good compromise between cost and technical performance." The resulting photonic device and the electronics ic are bonded in a 3d structure and are interfaced using copper pillars. This approach has performance benefits and is more economical. Customers will also hasve more freedom in the choice of the companion chip. Benetti is already seeing interest from equipment makers to use such silicon photonics designs directly, bypassing the optical module makers.