Leti groups report three 'mature' silicon photonics platforms

19 Nov 2015

PLAT4M project focused on “speeding industrialization” of this technology.

French technical research organization CEA-Leti, based in Grenoble, and its partners in the European FP7 project PLAT4M have announced the successful development of three silicon photonics platforms. The four-year project, which launched in 2013, is aiming to build a European-based supply chain in silicon photonics and speeding industrialization of the technology.

PLAT4M, which is funded by a European Commission grant of €10.2 million, involves 15 leading European R&D institutes and CMOS companies, as well as key industrial and research organizations in design and packaging, and end users in different application fields, working to build the complete supply chain. The supply chain is based on technology platforms of Leti, imec and STMicroelectronics.

Imec said its silicon photonics platform, based on 200mm substrates, “has matured thanks to the PLAT4M project”. This platform is based on SOI substrates with 220nm crystalline silicon on a 2,000nm buried oxide. During this project the existing fabrication processes and integration flow have been fine-tuned to have stable and repeatable performance for all photonics building blocks (couplers, waveguides, phase shifters, photodetectors). PLAT4M partners Thales, Polytec and TNO already are using the technology.

Beyond the 200mm platform, imec has pushed the limits of silicon photonics, exploiting advanced optical lithography with its 193nm immersion lithography scanner. It also has demonstrated very low propagation loss (~0.6dB/cm) for fully etched waveguides with excellent within-wafer linewidth control and sub-100nm features. Deep sub-wavelength features can now be made without requiring e-beam lithography.

Using the imec platform, Thales demonstrated a coherent combination of laser beams (CBC). Ultimately, this application aims at producing high-power, high-energy laser sources for sensing, industry or fundamental physics. The CBC rationale is to push the limits of single laser emitters (typically fiber amplifiers) by using a large number of amplifiers and coherently adding the output beams.

The first generation CBC demonstrator of PLAT4M, which was packaged by Tyndall UCC, included a one-to-16 channel splitter tree, plus 16 independent thermal phase modulators. The CBC experiment showed the successful coherent addition of 16 laser beams at 1.55µm.

Wafer performances

Leti itself has developed a new photonic platform based on 200mm SOI wafers. This process offers multilevel silicon patterning that allows the design of various passive and active devices (such as modulator and photodiode) with thermal tuning capability. Two AlCu levels are available for routing. A process design kit is available for circuit design and an MPW service will be proposed in 2016.

The potential of the new platform has also been demonstrated: insertion losses are below 2dB/cm for monomode waveguide and below 0.2dB/cm for multimode devices. Germanium photodiode responsivity is >0.75A/W for a bandwidth >30GHz. Mach-Zehnder modulator V•L• is in the 2V.cm range for 2V operation with an E/O bandwidth > 25GHz.

Moreover, Leti and III-V Lab have together developed integrated hybrid III-V lasers and electro-absorption modulators on silicon using a wafer-bonding technique. The hybrid lasers operate in the single-mode regime and the EAMs exhibit an extinction ratio higher than 20 dB with a drive voltage lower than 2V. Clear eye diagram has been achieved at a bit-rate of 25 Gb/s, confirming strong potential for telecom applications.

During the project, ST developed an additional silicon-photonic platform in 300mm technology to be used as an R&D tool for proof-of-concept purposes. The technology, called DAPHNE (Datacom Advanced PHotonic Nanoscale Environment), is designed for evaluating new devices and subsystems for demonstration. DAPHNE is a flexible platform that perfectly fits R&D needs. While developing it, ST demonstrated wavelength-division-multiplexing solutions using arrayed waveguide gratings, echelle gratings, cascaded Mach-Zehnder interferometers and side-coupled integrated spaced sequence of resonators.

Midway project report

At the halfway stage of the project, the CEA LETI team has reported that the PLAT4M WP2 work “has led to a qualitative leap of the design flow for silicon photonics, allowing the photonics community to design more complex and more robust circuits. The electronics OpenAccess standard for data sharing between design-automation tools includes an extension for silicon photonics in a beta phase today. Simulation capabilities were leveraged thanks to an extensive characterization effort from the three partner fabs and thanks to the statistical data gathered for variability prediction.”

Besides this, Paris-Sud University has studied theoretically the behavior of different phase shifters and photodetectors for a time-efficient and precise modeling. Mentor Graphics and PhoeniX Software partners have improved phase-aware routing and tool interoperability. Verification and manufacturability have reached industry-requirement standards thanks to the development of new techniques based upon the Mentor Graphics Calibre platform that delivers layout-versus-schematic comparison. Mask preparation is also improving with better pattern-density control and mask correction.

About the Author

Matthew Peach is a contributing editor to optics.org.