Laser-Engineered Silicon: Manufacturing Low Cost Photonic Systems

Silicon photonics promises to revolutionize modern optoelectronics by allowing for dense integration of components that feature the best optical and electronic functions of the material. In recent years great progress has been made in this area, with many silicon photonic devices now meeting (or exceeding) the performance requirements of state-of-the-art systems. This includes ultra-low loss interconnects as well as high speed optical regenerators, amplifiers, modulators, and detectors, which form the building blocks for photonic circuits. However, to date, much of this progress has been achieved on silicon-on-insulator (SOI) platforms with a thick buried oxide layer, which are largely incompatible with electronic device development, and relatively expensive, thus precluding truly integrated systems from reaching the high-volume market. Consequently, there are still crucial challenges to overcome before the performance benefits of SOI photonics outweigh the costs and design constraints, leaving the door open for alternative platforms to be considered.

In this programme we propose to develop a low cost and low temperature laser materials processing procedure to fabricate high quality polycrystalline semiconductor photonic platforms that will rival the performance of their SOI counterparts. Laser processed polycrystalline materials are already well-established for use in electronic technologies where some performance can be sacrificed in favour of reduced processing costs, for example, in the backplanes of smart phones and televisions. However, if the polycrystalline grains can be grown as large as the individual components, then the optical (and electronic) properties will approach those of the single crystal materials. By building on the platform established by the electronics community, this work seeks to grow large grain polycrystalline materials to realize low loss photonic components. Importantly, the high localization of this laser crystallization procedure directly alleviates issues associated with multi-material and multi-layer photonic device integration, and can also be used to modify or repair the individual components at a late stage in the fabrication, helping to increase the production yield and reduce the costs of integrated systems. Furthermore, this method offers the unique advantage of removing the substrate dependence from semiconductor photonics, thus offering the possibility to extend the application space through the use of substrate materials with enhanced optical functionality, increased transparencies, or even flexible plastics. By reducing costs and barriers associated with device fabrication, our innovative project will set the scene for wide spread use of laser-engineered semiconductor photonic components in mainstream optoelectronic systems.

This proposal promises to transform the next generation of optoelectronic systems by reducing the barriers and costs associated with silicon photonic device fabrication and integration. This research is perfectly aligned with the EPSRC theme "Photonics for Future Systems", and we believe could ultimately have significant economic and societal impact in the areas of ICT, sensing, and manufacturing. In terms of market size, photonics21 (European Public-Private-Partnership) estimates the global market for optical components will be worth 30B euros in 2015, with the EU share approaching 50%.

ICT: The integrated polysilicon photonics platforms developed through our proposed work have the potential to increase the speed and capacity of data transport systems, whilst at the same time lowering the manufacturing costs, reducing energy requirements, and increasing production yields. Importantly, low cost polysilicon photonic components such as interconnects, modulators, and photodetectors, have already been identified by the leading semiconductor company Intel as a key step towards truly realizing the high density integration of optical and electronic devices. We expect that as the technology matures other major computer (IBM) and communication companies (Finisar) will find similar merit.

Sensing: As the laser-engineering process removes many substrate restrictions, there are several material platforms that could be established for use in biological or chemical sensing. For example, cheap, flexible, and disposable sensors developed on plastic substrates could find use as wearable monitoring systems, supporting growth in several markets such as point of care diagnostics and wearable electronics. Alternatively, more robust systems built on germanium-on-sapphire platforms, that offer the potential to operate over the important molecular 'finger-print' spectral region, could be used for rapid (in-field) identification of different types of hazardous chemicals/materials. Thus, the impact of this work could also feed into the EPSRC themes "Healthcare Technologies" and "Global Uncertainties".

Manufacturing: The UK has a strong laser manufacturing industry (e.g., SPI Lasers, Elforlight, Oxford Lasers), and the importance of laser-based manufacturing has been recognised through the establishment of an EPSRC Centre for Innovative Manufacturing in Laser-Based Production Processes (http://www.cim-laser.ac.uk/). Currently one of the major industrial growth markets for Excimer lasers is in materials processing of low cost electronic semiconductor electronic chips, and we can expect that new markets will open up through the expansion of these processing procedures to photonic components and systems. Our partnership with Elforlight and SPI Lasers demonstrates the relevance of our proposal to this sector and their confidence in this technology, even at this early stage. Furthermore, the low energies and temperatures of our process procedures also align with EPSRCs requirements for green, sustainable manufacturing procedures.

The successful outcomes of our proposed work will ultimately help to shift the focus away from single crystal, single layer optoelectronic platforms to more flexible, 3D integrable polysilicon alternatives. As our programme is largely centred on materials optimization, much of the immediate impact is likely to be within the academic community. However, as there is already interest within the industrial community, we expect that the commercial value of this approach will soon be widely recognized. Thus, by training new staff in this emerging area we will ensure that the UK has a solid skill and knowledge base to quickly capitalize on future industrial developments.