Steven Van Put

Laser ablation- and plasma etching-based patterning of graphene on silicon-on-insulator waveguides.

We present a new approach to remove monolayer graphene transferred on top of a silicon-on-insulator (SOI) photonic integrated chip. Femtosecond laser ablation is used for the first time to remove graphene from SOI waveguides, whereas oxygen plasma etching through a metal mask is employed to peel off graphene from the grating couplers attached to the waveguides. We show by means of Raman spectroscopy and atomic force microscopy that the removal of graphene is successful with minimal damage to the underlying SOI waveguides. Finally, we employ both removal techniques to measure the contribution of graphene to the loss of grating-coupled graphene-covered SOI waveguides using the cut-back method.

A Multiplexed Microfluidic Platform for Bone Marker Measurement: A Proof-of-Concept

In this work, we report a microfluidic platform that can be easily translated into a biomarker diagnostic. This platform integrates microfluidic technology with electrochemical sensing and embodies a reaction/detection chamber to measure serum levels of different biomarkers. Microfabricated Au electrodes encased in a microfluidic chamber are functionalized to immobilize the antibodies, which can selectively capture the corresponding antigen. An oxidative peak is obtained using the chronoamperometry technique at room temperature. The magnitude of the response current varies linearly with the logarithmic concentration of the relative biomarker and, thus, is used to quantify the concentration of the relative biomarker in serum samples. We demonstrated the implementation, feasibility and specificity of this platform (Osteokit) in assaying serum levels of bone turnover markers (BTMs) using osteocalcin (limits of detection (LOD) = 1.94 ng/mL) and collagen type 1 cross-linked C-telopeptide (CTX) (LOD = 1.39 pg/mL). To our knowledge, this is the first such device fabricated to measure BTMs. Our results also showed that the sensitivity of Osteokit is comparable with the current states of art, electrochemiluminescence (ECLIA).

Laser ablation of micro-photonic structures for efficient light collection and distribution

In this work we report the fabrication of polymer micro-photonic gratings for use in liquid-crystal based actively tunable electro-optic components. The gratings are produced by moving the sample surface sideways across a perpendicularly impinging KrF excimer laser beam (λ = 248 nm), which is shaped by specially designed triangular and trapezoidal masks. To obtain correctly dimensioned and smooth grating surfaces, different materials (SU-8, polycarbonate, Epoclad and Epocore) are subjected to the laser ablation with optimized laser processing parameters. The resulting grating structures on Epocore exhibit the best surface roughness and dimensional fidelity. Optionally, spacers for maintaining the cell gap of the superimposed liquid crystal layer can also be fabricated in the same process. Two different methods were demonstrated: overlapping ablation and double mask ablation. Micro-grating structures were produced that deflect a monochromatic (543 nm) laser beam to the theoretically predicted 11th order with an angle of 7°.

Performance of a new type of module based on back-contact solar cells

Imec has developed a new technology to integrate and interconnect back-contact solar cells into modules, based on embedding cells in silicone on top of a glass substrate. This technology aims at an improved optical performance and reliability (through the use of silicones and low-temperature metallization). One of the additional advantages is that the technology is suitable for integrating very thin cells into modules: whereas standalone interconnection of such fragile thin cells, e.g. tabbing and stringing, would significantly lower the throughput yield due to breakage, the cells are better protected if they are embedded inside silicone. The paper will first elaborate on the process flow, the background and motivation, advantages, drawbacks and limitations, and technical aspects of the developed technology. Then it will present the results of the measurements on the performance of functional solar cells processed into modules using this technology, discussing losses and loss mechanisms. Then, the approach towards determining the reliability of the module will be presented, indicating how imec aims at building up an ageing model, and elaborating the results on the failure mode and effect analysis, modeling, characterization and reliability testing.

Development of a fabrication technology for integrating low cost optical interconnects on a printed circuit board

We present a fabrication technology for integrating polymer waveguides and 45° micromirror couplers into standard electrical printed circuit boards (PCBs). The most critical point that is being addressed is the low-cost manufacturing and the compatibility with current PCB production. The latter refers to the processes as well as material compatibility. Multimode waveguides are patterned by KrF excimer laser ablation in acrylate polymers with 0.13 dB/cm propagation loss at 850 nm. Single mode waveguides using inorganic-organic hybrid polymers show an attenuation loss of 0.62 ± 0.08 dB/cm at 1.3 μm. A process for embedding metal coated 45° micromirrors in optical waveguiding layers is developed. Mirrors are selectively metallized using a lift-off process. Filling up the angled via without the presence of air bubbles and providing a flat surface above the mirror is only possible by enhancing the cladding deposition process with ultrasound agitation. Initial single mode coupling loss measurements at 1.3 μm show an excess mirror loss of 1.55 dB. Multimode coupling loss measurements will improve this excess loss, because of the lower surface roughness of the mirrors using the acrylate polymers for multimode waveguides.

Optical interconnections on PCBs: a killer application for VCSELs

As a result of the constant improvement of performances and reliability of VCSEL-fabrication, parallel short distance optical interconnections are becoming more and more important. Integrating optical interconnections on a board level, covering distances from a few centimeters to a few meters, is however very challenging as the optical interconnection and mounting technology has to be integrated in existing printed circuit board manufacturing technology. Fiber based interconnections, using technologies as Fiber-In-Board and Fiber-based optical backpanels are already available, but new solutions for integrating a guided-wave based optical interconnection layer in a standard FR4-based electrical printed circuit board are emerging. These technologies are based on either organic materials or glass sheets integrated in the FR4-stack. Examples of both technologies will be presented and optical interconnections showing the feasibility of both technologies will be described. The interconnections will be realized using VCSEL-arrays and photodetector arrays which are flip-chip, mounted on the printed circuit boards. The coupling of light in and out of the optical layer in the FR4-stack is done using deflecting micro-optics realized in the optical layer, e.g. using laser-ablation.

Reaction tubes as a platform for silicon nanophotonic ring resonator biosensors

We propose the combination of a simple reaction tube platform with label free SOI photonic biosensors. The device allows for the excellent performance of ring resonator sensors in a user-friendly platform to be used in labs and hospitals.