Luxtera develops long-wavelength photodetector on SOI-CMOS wafer

March 15, 2007 – Luxtera Inc., a fabless semiconductor company that specializes in silicon photonics, has announced that it is the first company to use a standard SOI-CMOS fabrication process to develop an integrated long-wavelength photodetection capability by strategically adding pure germanium (Ge) around optical waveguides. According to Luxtera, the technology enables monolithic, fully integrated optoelectronic semiconductor devices to consume less power, gain reliability due to fewer components, and significantly reduce the cost of photodetectors.

Conventional optics manufacturing costs are primarily driven by assembly, test, and bill of materials. This new integrated photodetector significantly reduces the costs for all three areas. By embedding the photodetectors directly on the wafer, costs associated with assembly and test of multiple components are eliminated. Furthermore, by placing the photodetector immediately adjacent to the receiver electronics on a common CMOS die, electronic noise is reduced, enabling the photodetector to detect much lower power signals. This improves receiver performance 4x; therefore, less expensive low-power lasers can be used on the transmit side, reducing the transceiver cost.

“By integrating photodetectors, Luxtera has made a significant breakthrough that’s years ahead of its competition,” says Jag Bolaria, senior analyst with The Linley Group. “By quickly productizing this technology, Luxtera should be in a position to lower the cost of optics for future high-volume deployment.”

Commercial photodetectors traditionally are implemented in systems using discrete components; customers were consequently faced with the cost of purchasing individual photodetectors for each photonic receiver. Luxtera claims its new technology allows a nearly unlimited number of photodetectors to be grown directly on a die during wafer manufacturing, and to be economically tested at the wafer scale. The company says designers will be able to use large numbers of photodetectors freely instead of sparingly because the cost of the final product will no longer be affected by the number of photodetectors. In applications where more photodetectors are required, such as chip-to-chip and intrachip optical connectivity, this innovation reportedly brings individual photodetector costs from more than $1.00 to less than a penny.

To achieve photonic-to-electronic signal conversion, Luxtera applies small amounts of pure Ge along optical waveguides on a CMOS die and connects it to the chip-level metallic interconnect by using a step that is common with CMOS transistors and Ge photodetectors. This integration capability has the potential to make discrete photodetectors obsolete in the future, just as very-large-scale integration (VLSI) took over for discrete transistors in electronic design.

“This technology is revolutionary for the industry — it brings us much closer to delivering high performance optical transceivers at cost points associated with legacy copper,” says Alex Dickinson, CEO of Luxtera. “We are the only company in the industry that has done this, well ahead of the competition.”

Luxtera is currently demonstrating this technology on complete 10-Gbit/sec 130nm SOI-CMOS receivers using the Freescale Semiconductor foundry fabrication process. The demonstration receiver consists of a fully integrated die with Ge photodetectors and all required supporting electronic and photonic logic, including optical interface to fiber (fiber-to-the-chip), transimpedance amplifier, and limiting amplifier. The first commercial application is expected to target Luxtera’s next-generation transceivers for optical connectivity in communications and consumer markets. Other potential applications may include optical sensors in infrared cameras, interactive gaming, and medical imaging.


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