Luxtera makes germanium-enabled photodetector breakthrough

By Ann Steffora Mutschler -- Electronic News, 3/14/2007

Carlsbad, CA-based silicon photonics-focused Luxtera Inc. today reported it has developed an integrated long-wavelength photodetection capability on a standard SOI-CMOS fabrication process by adding pure germanium around optical waveguides.

The company believes this breakthrough is ahead of other efforts in the market and is meant to allow monolithic, fully-integrated opto-electronic semiconductor devices to consume far less power, increase reliability due to fewer components, and help customers realize orders of magnitude in cost reductions that can make photodetectors virtually free.

Luxtera explained that conventional optics manufacturing costs are primarily driven by assembly, test and bill of materials but 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, and 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 for improved receiver performance by a factor of four. As a result, less expensive low-power lasers can be used on the transmit side, reducing the transceiver cost, the company noted.

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

Until now, commercial photodetectors have been implemented in systems using discrete components, where customers were faced with the cost of purchasing individual photodetectors for each photonic receiver.

Luxtera says 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.

At one cost, thousands of photodetectors can now be grown at the same time, allowing engineers to develop new applications and designers can 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 used.

In applications where larger numbers of photodetectors are required, such as chip-to-chip and intra-chip optical connectivity, this invention brings individual photodetector costs from over one-dollar to less than a penny.

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

“This technology … brings us much closer to delivering high performance optical transceivers at cost points associated with legacy copper,” said Alex Dickinson, CEO of Luxtera.

Luxtera is currently demonstrating this technology on complete 10Gbps 130-nm SOI-CMOS receivers using the Freescale Semiconductor foundry fabrication process.

The demonstration receiver consists of a fully integrated die with germanium photodetectors and all required supporting electronic and photonic logic, including optical interface to fiber (fiber-to-the-chip), trans-impedance 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 include areas where large numbers of photodetectors are needed and include optical sensors in infrared cameras, interactive gaming and medical imaging. It is also a major milestone to make future optical chip-to-chip and intrachip connectivity feasible, the company concluded.