Electronic-Photonic Integration Facility

MIT Lincoln Laboratory has established a state-of-the-art facility for developing optoelectronic components and photonic integrated circuits (PICs), CMOS electronic integrated circuits (EICs), and hybrid electronic-photonic integration techniques. The facility includes internal resources for design, epitaxial-material growth, fabrication, packaging, and characterization of components and integrated subsystems.

The photonics capabilities include both silicon and compound-semiconductor (III-V) PICs. Fabrication of both the silicon PICs and the CMOS EICs are enabled by Lincoln Laboratory's 70,000 ft2 Microelectronics Laboratory, which houses a production-class 200-mm-diameter-wafer equipment set with sub-90-nm lithographic resolution. This sub-90-nm resolution allows direct optical lithography of gratings required for distributed Bragg reflector (DBR) and distributed feedback (DFB) lasers, and surface-normal optical couplers. Scanning electron-beam lithography (SEBL) having 5-nm resolution is also available. Components currently available in the silicon PIC toolbox include low-loss waveguides, optical modulators, narrowband optical filters, wavelength division multiplexers (WDMs), germanium (Ge) photodetectors, and waveguide-to-fiber couplers. These silicon PIC components have been used to implement optical communication receivers, wideband ladar transmitters, photonic analog-to-digital converters, microwave photonic filters, and low-loss delay lines.

In addition to silicon PICs, Lincoln Laboratory also has resources to grow and fabricate III-V PICs in a variety of material systems (InP, GaAs, GaSb, GaN) covering optical wavelengths from <0.4 μm to >10 μm. Fabrication processes have been developed for III-V wafers having 2-, 3-, 4-, 6-, and 8-inch diameters. Components currently available in the III-V toolbox include DBR lasers, quantum-cascade lasers (QCLs), optical modulators (electroabsorption and Mach-Zehnder), watt-class semiconductor optical amplifiers (single element and arrays), mode-locked lasers, and high-current photodiodes. Lincoln Laboratory's 90-nm CMOS EIC process has been used to realize circuits containing >500M transistors. Hybrid electronic-photonic integration capabilities include precision flip-chip alignment and soldering of electronic and photonic components, wafer-scale 3D integration using oxide-to-oxide bonding and micron-scale through-oxide interconnects, and wafer-bonded silicon/III-V hybrid integration.

Examples of some of the areas being developed include:

  1. Monolithic Compound-Semiconductor PICs
    This activity involves the integration of multiple active and passive components onto a compound semiconductor substrate such as InP or GaAs. Monolithic integration techniques that have been developed at the Laboratory include quantum-well intermixing (QWI), patterning of waveguide gratings using electron-beam lithography, and epitaxial material regrowth. These techniques have been used to fabricate and integrate SOAs, distributed Bragg reflector (DBR) lasers, electroabsorption modulators (EAMs), phase modulators, photodetectors, and saturable absorbers.  Work is ongoing to integrate these conventional components with Lincoln's novel slab-coupled optical waveguide (SCOW) platform.

  2. Monolithic Silicon PICs
    The Laboratory has developed a silicon PIC toolbox utilizing the 90-nm fabrication capability available in its Microelectronics Laboratory. Components available in this toolbox include low-loss waveguides, optical modulators, narrowband optical filters, wavelength division multiplexers (WDMs), and waveguide-to-fiber couplers, and germanium (Ge) photodetectors. Components from the toolbox have been used to implement photonic ADCs, RF filters, and low-loss delay lines.

  3. Hybrid PICs
    Hybrid integration involves the heterogeneous integration of compound semiconductor materials and devices with silicon photonics and low-loss dielectric waveguides. Both wafer-bonded and pick-and-place hybrid integration approaches are being developed. The Laboratory is also actively pursuing electronic-photonic integration to reduce size, weight, and power (SWaP) and to improve the performance of optical transmitters, receivers, and signal processing subsystems. Electronic-photonic integration techniques that have been developed include wire bonding of side-by-side chips, flip-chip bonding, and wafer-scale oxide-bonded 3D integration.

  4. Microwave Photonic Subsystems
    Microwave photonics (MWP) involves interactions between the RF/microwave/millimeter-wave and optical portions of the electromagnetic spectrum. Photonics is utilized for the generation, transmission, detection, processing, and control of microwave signals with direct applicability to antenna systems (e.g., wireless and array), sensing, and instrumentation. The Laboratory is working to develop MWP techniques and subsystems for radar, electronic warfare, and communications applications. It is anticipated that electronic-photonic integration will be needed to achieve the performance and SWaP required for these applications.

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