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Silicon Nitride Photonic Integrated Circuit Pilot line for Life Science Applications in the Visible Range

Periodic Reporting for period 3 - PIX4LIFE (Silicon Nitride Photonic Integrated Circuit Pilot line for Life Science Applications in the Visible Range)

Reporting period: 2018-07-01 to 2020-09-30

Silicon based integrated photonics has become a well-developed platform. It has proven value in demonstrating that many optical functions can be realized in a much more compact and cost-effective way by integrating the required functionality on a single chip. Photonics ICs, or PICs, have tremendously changed the data- and telecommunication landscape by compact on-chip implementations of required optical functionalities. It was proved that MPW services are critical to force fabs to standardize the technology offering and develop design kits. This standardization has enabled an ecosystem of actors specializing in various parts of the product development chain, such as design houses, packaging vendors, design aggregators, technical consultants etc. The success of this scheme is reflected in transfer of the silicon photonics MPW service entirely to Europractice-IC.
The PIX4life ambition was to mature a high performance, high yielding SiN Photonic IC pilot line together with the accompanying supply chain for applications in the visible range (400-1000 nm) in order to become the world’s premier pilot line for multitype integrated biophotonic applications.
Now, PIX4life is the European pilot line that offers an open-access manufacturing platform for photonic integrated circuits. The PIX4life silicon nitride photonic platform is ideally suited to develop products that require visible light or slightly higher wavelengths (400-1100 nm), making this platform interesting to a broad range of industrial customers active in the life science domain or beyond. Besides the manufacturing, PIX4life has an attractive website and accompanying gateway in place to enable customers to easily find their way to the offering, supported with photonic knowhow and design and testing expertise. Not only having this supply chain is key, also education of the target field is of utmost important to make sure SiN technology will be widely adopted. In that respect ePIXfab, a not-for-profit open alliance of academic and industrial organizations with a mission to promote silicon photonics science, technology and applications is offering training activities for the PIX4Life pilot line.
1. The aim to mature SiN photonic integrated circuit technology via Multiple Project Wafers (MPW) and via generic photonic building blocks and interfaces.
Both foundries, imec and LioniX optimized their BioPIX and TriPleX platforms, respectively. Both platforms are ideally suited to develop visible light applications as demonstrated by e.g; the use case partners in the PIX4life project and customers of the pilot line that developed life science applications.
2. Improved accessibility to the technology, by developing an end-to-end supply chain reaching from design to packaged and characterized chip components.
PIX4life has set up an end-to-end supply chain, including design –manufacturing- photonic testing and packaging (this latter one in close collaboration with the PIXAPP pilot line)
3. Demonstration of the potential of the SiN photonics technology by realizing complex photonic ICs meeting the application driven specifications for miniaturized biosensors, optical coherence tomography imagers, multispectral sources for microscopy, and point of care cytometry.
In the PIX4life project, 4 inspiring demonstrator cases were chosen. An OCT on-chip demonstrator has been successfully implemented. The OCT system was able to detect (artificial polymer based-) tissue with a SNR of around 20dB.
• The Multi-DOF-sensor shows the high sensitivity of silicon photonic sensors, but the development of functional ion-sensitive layers showed not to be straightforward. However, based on a similar PIC implementation a proof-of-concept demonstration of an integrated refractive index gas sensor for environmental safety monitoring with detection limit in the sub-ppm level was achieved.
• Two different types of multispectral light sources have been implemented.
• A module, including a light source with the pattern generation PIC, a beam shaping lens system, and the sample flow sub-assembly have been integrated with light collection optics for the full cytometric application demonstration.
4. build and validate an open access model for customers internal and external to the consortium with the aim to lower barriers to entry for European companies, SME’s and universities to test and validate photonic concepts in the visible range.
5 MPW runs were organized with early access users. The services are accessible for the customers via the PIX4life website (gateway operated by VLC photonics), via Europractice and the two foundries (imec and LioniX).
Manufacturing: Back in 2015 the most mature CMOS compatible integrated photonics platform was based on crystalline silicon waveguide (SOI) technology. Obviously, the silicon photonic platform is not usable in the visible. Silicon Nitride technology, on the other hand, could become that material. Both imec and Lionix were already exploring SiN back then. The LPCVD based TriPleX technology of LioniX is a promising platform, where photonic structures are realized with CMOS compatible fabrication equipment and measurements on low-contrast TriPleX waveguide showed waveguide losses as low as 0.1 dB/m. In 2012 imec started its new activity in SiN waveguides on silicon in the 200mm CMOS pilot line. This was the start of the BioPIX platform based on low temperature PECVD SIN deposition. The main interest of this platform is not the low waveguide losses (<1dB/cm) but its full compatibility with CMOS processes and the possibility to post-process on CMOS wafers containing e.g. COMS imagers of electrical circuits. In PIX4life both technology platforms were matured, and additional features have been added and made available for customers via MPW service.
Building blocks: There was already a vast knowlegde on passive components and building blocks in telecom wavelength regime, mainly for silicon but also for silicon nitride. The visible frequencies ware much less developed. Besides passive components many applications require modulators to switch and modulate the light on the chip. Here less building blocks were available. As such during PIX4life 162 building blocks were designed in BIOPIX (80) and TriPlex (82) technology with wavelengths covering the full visible and very near IR.
Design tools: The Design tools of partner Synopsis and Luceda were in place at the start of the project to design on both the TripleX and BioPIX platforms. Early process design rules for both technologies are available but lack standardization of both the technologies and the building blocks. In the PIX4life project further work has been invested to standardize these photonic components as photonic building blocks libraries.
Integration options: Integration and packaging of photonic devices remains a hurdle to the commercialization of photonic based chip technologies. Several partners in the project made major progress in source integration with SiN. The flip chip edge coupling of external cavity lasers to waveguides was demonstrated by RWTH Aachen, Toptica and imec. Chalmers and Tyndall developed the hybrid integration of angled flip-chipped VCSELs onto PICs with appropriately designed grating couplers and demonstrated a potentially viable process. Chalmers has worked with imec on the development of VCSELs for micro-transfer printing on the PIX4life SiN waveguide platform
Photograph of the assembled single output multi-spectral light source for microscopy applications.