Intro: need for scaling

Scaling limitations of today’s manufacturing technology for optical transceivers: Even with the recent rapid growth of the amount of devices that can be monolithically integrated on a photonic integrated circuit (PIC), manufacturing such an optical transceiver still requires a large amount of sequential assembly steps. Indeed an optical transceiver consist of one or more Photonic Integrated Circuits, one or more high-speed Electronic Integrated Circuits, which need to be assembled together. In addition, fiber attachment needs to be done. In Caladan, the integration of Photonics and Electronics will be done fully at the wafer level through the use of micro transfer printing. This significantly simplifies the assembly flow, reducing overall manufacturing costs.

Micro transfer printing

Micro transfer printing is a technology in which devices or materials are selectively removed from a source wafer (or substrate) and deposited in parallel to a host wafer (or any other suitable platform) as a printing process. Micro transfer printing has a number of appealing properties

• Excellent positional accuracy: with the transfer tool positional accuracies as low as +/-1.5µm have been demonstrated over 200mm wafers with yields in excess of 99%. The process cycle time is less than 30seconds. In terms of wafer or substrate preparation, the only requirement is a flat area on the host wafer and in some cases application of adhesive materials such as BCB (which also can be done on a wafer level).
• Electrical connections between the transfer printed structure and the components on the host wafer can be fabricated using lithographic or laser tools. The use of lithographically defined metal interconnect implies that very fine pitches and clearances can be achieved (in the order of a few micrometer) which effectively allows elimination of the bondpads conventionally needed to electrically connect circuits.
• Much more efficient use can be made of the materials
• Direct integration between materials that are otherwise not compatible is now possible: for example III-V material can be combined with CMOS (Silicon Photonic) wafers which combined with specific patterns in the CMOS (grating couplers) allow to produce laser cavities.

SiPhotonics

IMEC SiPhotonics: iSiPP50G - the imec-ePIXfab SiPhotonics full platform technology consists of:

• Substrate: SOI with 220mm Si, 2um buried oxide
• WG module (waveguide): 220nm full Si etch for strip waveguides, photonic crystals, etc.
• FC module (FiberCoupler): 70nm partial Si etch for fiber couplers, rib waveguides, etc.
• SK module (Socket): 150nm partial Si etch
• Poly-Si module: extra etch-level for efficient fiber couplers
• 4 P and N-type doping levels for electro-optic modulator design and heaters for thermo-optic modulation
• Ge photodiodes as detectors
• High speed Ge electro-absorption modulators
• 2 levels of metal interconnect
• Edge coupler

GaAs quantum dot lasers

 A significant challenge for any optical transceiver that needs to cope with the intra data center environment is the high temperatures at which the transceivers need to function. In CALADAN GaAs quantum dot lasers will be used as the light source, which are known to lase up to temperatures well in excess of 100C. Externally modulated lasers will be considered which will be micro transfer printed onto Silicon Photonic Integrated Circuits. Spray coating (at the wafer level) of thin adhesive materials will be used to ensure solid integration of the laser with the Silicon Photonic Integrated Circuits.

SiGe BiCMOS SG13G2 technology

SG13G2 is a 0.13um BiCMOS technology with superior bipolar performance of fT/fMAX = 300/500GHz. The backend offers 3 thin and 2 thick metal layers.

The performance is summarized hereafter:

Bipolar 

CMOS section

Passives section