Zero-change manufacturing of photonic interconnects for silicon electronics

The silicon electronics industry has two major challenges in the development of new products: demand for increasing levels of processing power on a single chip and the amount of energy required to run these chips. The two challenges are linked, since the more components and communications links that are integrated into the chip, the higher the associated energy usage. While the energy consumption of a single chip is relatively low, this rapidly scales to environmental levels when considering the huge volume of units produced each year is in the order of 10's of billions. Already, large scale data-centres consume around 1% of global electricity demand, so any efficiency gains in the energy consumption of integrated chips will have significant effects.

As device dimensions reach fundamental physical limits, chip designers are developing new architectures in order to continue to deliver growth in chip performance. These designs require high bandwidth communications across millimetre length scales, currently realised as simple electronic tracks. By replacing these tracks with optical interconnects, system power consumption can be reduced and communications bandwidth improved. The fundamental challenge for any alternative technology is that it must be compatible with current electronics manufacturing, where vast investments have been made over the last decades.

This project will develop an optical interconnect layer that has a link power consumption lower than equivalent electronic lines. The optical layer will be realised as a thin film chip that can be interposed between the silicon device and its packaging, meaning that this process is zero-change with respect to the manufacture of the electronic chips. Recent advances pioneered at the Universities of Strathclyde and Sheffield in ultra-high precision micro-assembly of opto-electronic membrane systems will enable a two stage process that is designed to be compatible with production at scale. Firstly, membrane optical sources, waveguides and detectors will be assembled on a glass chip that incorporates electrical vias. This interposer with integrated optical interconnects will be integrated between the electronic chip and its packaging using micro-assembly processes.

The project is supported by industrial partners Alter Technologies and Fraunhofer UK who will provide resources and expertise in opto-electronic packaging and optical systems engineering. This will ensure new process developments with industrial standards and design rules.

The proposal aligns with EPSRC's ICT and Manufacturing the Future themes and the Photonics for Future Systems priority, addressing specific portfolio areas such as Manufacturing Technologies, Optical Communications, Optical Devices & Subsystems, Optoelectronic Devices & Circuits, Components & Systems.

By the end of the project we will have demonstrated an optical transmission link with energy consumption lower than an equivalent electronic line. This link will be integrated with a commercially available silicon transceiver chip to demonstrate feasibility of developing this technology as a back-end process in the silicon electronics industry.

Potentially, the impact of this project could be substantial in the field of manufacturing for silicon electronics, and opto-electronics packaging in general. Furthermore, development of an optical interconnect layer that is integrated as a back-end process to electronic chips has the potential to significantly reduce energy consumption. Although this effect is likely to be modest at the chip-scale, in the order of a few %, this would represent large energy savings at the scale of data-centre deployment. Specific activities that will be undertaken to progress the exploitation of research results towards these large scale industrial targets are detailed in the Pathways to Impact document.

In the shorter term the research will produce impact in a number of different areas:

Academic impact
The research is expected to generate results in key portfolio research areas such as Manufacturing Technologies, Optical Communications, Optical Devices & Subsystems, Optoelectronic Devices & Circuits, Components & Systems. The outcomes of the proposal will provide a new standard for integration that is directly relevant to the applications being targeted by most of these research areas. To maximise the academic impact, the outcomes of our research will appear in open-access journal papers and be accessible through the web pages of the investigators and the university libraries. Also, with the support from Alter Technologies and Fraunhofer CAP, we aim to establish a UK transfer printing capability available to academic researchers.

Industrial Impact
The vast levels of historical investment into the silicon electronics manufacturing industry and large infrastructure and running costs are prohibitive barriers to new entrants to the market. Nevertheless, next generation electronic systems will rely strongly on advanced packaging solutions and back-end processing of silicon chips. This is an area where the UK has significant expertise and infrastructure, putting it in an excellent position to lead early efforts in this area. This programme will enable the development of back-end silicon electronics manufacturing compatible with the existing industry, currently dominated by large corporations in the US and Asia. Our industrial partners Alter Technologies and Fraunhofer UK, will enable commercial access to prototyping demonstrations of technologies developed by this project, by the end of its duration. The methods and processes developed, when translated through to commercial exploitation, will enable a wide range of SMEs in the UK and around the world that require compact, low size weight and power opto-electronic systems integration. These include optical backplane technologies for small satellites and server racks, high-power electronics for switching, and optical switch network nodes.

Researcher/student Impact
The training of PhD students and PDRAs in the methods and technologies developed under this project will be a key outcome of this work. At least 3 PhD students will be trained under this programme and equipped with the required skills to become valuable resources for UK industry. The PhD students will be exposed to a rich academic and industrial research environment and will undertake advanced level training that includes skills in distributed working, collaboration, entrepreneurship and business planning skills. The project PDRAs will be encouraged to take advantage of the various opportunities, resources and support for early career researchers, such as the transferable skills training programmes that include several courses for personal, professional and career development (e.g. relating to teaching, enterprise, knowledge exchange, employability, public engagement, fellowship and proposal writing, project management). Given the close links with industrial partners, there will be significant opportunities for junior researchers to benefit from follow-on projects under the knowledge exchange agenda.