Marco Queisser

Single-mode glass waveguide platform for DWDM chip-to-chip interconnects

Due to high bandwidth potential, optical single-mode signal transmission is superior to electrical as well as optical multimode signal transmission. For years, optical single-mode fiber cables have been used in telecommunication networks. However, there is a lack of photonic system integration based on optical single-mode interconnects in printed circuit boards and modules for signal transmission between electro-optical components and optical fibers. Therefore, a thin glass-based photonic integration concept for single-mode signal transmission was developed. Optical waveguides and optical free space interconnects are integrated in a single or a stack of thin glass sheets for module and printed circuit board packaging. For light routing inside a thin glass sheet, a singlemode waveguide technology on wafer level (150 mm) was developed promising for scaling up on panel size (45 × 60 cm2). The waveguides show single-mode behavior, low propagation (0.05 dB/cm) and fiber coupling (- 0.3 dB) losses at wavelength of 1550 nm. Different waveguide structures such as 180°-bends, S-bends, splitters and crosses have been integrated in thin glass and characterized in detail. Coupling mechanism and misalignment loss has also been studied. Technologies for fiber laser joining on glass as well as laser structuring of an optical mirror are introduced and first results are presented. Generic module and board-based photonic packaging solutions can be put into practice by applying all introduced technologies and will be demonstrated for a chip-to-fiber module package platform.

Development of micro batteries based on micro fluidic MEMS packaging

A cost effective and reliable technology allowing extreme miniaturization of batteries into silicon, glass chips and electronic packages has been developed, employing a dispense-print process for battery electrodes and liquid electrolyte. Lithium-ion micro batteries (active area 6×8 mm2, 0.2–0.4 mAh) with interdigitated electrodes and glass housing were fabricated, tested and finally compared with the traditional battery architecture of stacked electrodes. All processes for micro battery fabrication were established; in particular a micro fluidic electrolyte filling process that allows simultaneous electrolyte supply of all cells on a planar substrate. Electrode mass reproducibility was sufficient for adequate electrode balancing. Current capability similar to the conventional face-to-face electrode configuration was achieved with interdigital electrodes. The cells were successfully cycled; several 100 cycles can be achieved.

CO 2 -laser drilling of TGVs for glass interposer applications

Glass as a substrate material for interposer application has many benefits compared to conventional packaging materials like silicon, ceramic or polymer based laminates because of its excellent dielectric and transparent properties. Furthermore, the integration potential of glass is superior because of the dimensional stability under thermal load and the coefficient of thermal expansion (CTE) matching to that of silicon ICs. A small pitch size of conductor traces, small scale through-vias and high alignment accuracy are the key requirements that will be achieved from glass based packaging. Also the transparency of glass has benefits for photonic packaging. Glass substrates are available in wafer and large scale panel formats. Very fast CO2-laser drilling of holes and thermal post-treatments for reducing mechanical stress are very promising for fast processing and high reliability. Holes with a diameter smaller 100 μm in different glasses with thicknesses between 145 and 500 μm have been achieved by CO2-laser drilling. The holes have been metallized by sputtering a seed layer and galvanic copper platting. The CO2-laser drilling in combination with copper metallization has high potential for through glass via forming in glass substrates for interposer applications.

Electro-optical circuit board with single-mode glass waveguide optical interconnects

A glass optical waveguide process has been developed for fabrication of electro-optical circuit boards (EOCB). Very thin glass panels with planar integrated single-mode waveguides can be embedded as a core layer in printed circuit boards for high-speed board-level chip-to-chip and board-to-board optical interconnects over an optical backplane. Such singlemode EOCBs will be needed in upcoming high performance computers and data storage network environments in case single-mode operating silicon photonic ICs generate high-bandwidth signals [1]. The paper will describe some project results of the ongoing PhoxTroT project, in which a development of glass based single-mode on-board and board-to-board interconnection platform is successfully in progress. The optical design comprises a 500 μm thin glass panel (Schott D263Teco) with purely optical layers for single-mode glass waveguides. The board size is accommodated to the mask size limitations of the fabrication (200 mm wafer level process, being later transferred also to larger panel size). Our concept consists of directly assembling of silicon photonic ICs on cut-out areas in glass-based optical waveguide panels. A part of the electrical wiring is patterned by thin film technology directly on the glass wafer surface. A coupling element will be assembled on bottom side of the glass-based waveguide panel for 3D coupling between board-level glass waveguides and chip-level silicon waveguides. The laminate has a defined window for direct glass access for assembling of the photonic integrated circuit chip and optical coupling element. The paper describes the design, fabrication and characterization of glass-based electro-optical circuit board with format of (228 x 305) mm2.

Electrical micro-heating structures on glass created by laser ablation

Addressing the need for fast design cycles and tooling in the assembly of small structures, a flexible approach to overcome the obstacles of current time-consuming manufacturing methods is needed. Additionally, assembly of small and especially optical structures is often limited concerning the application and curing of adhesives used for joining. Local heating structures can be seen as an ideal way of solving this issue. This paper shows the simulation and flexible laser structuring of miniaturized heating. Mask-based large panel physical vapor deposition (PVD) processes and subsequent laser processing appear to be economical and flexible, and are compared to standard panel level lithography processes.

Laser-assisted patterning of double-sided adhesive tapes for optofluidic chip integration

Portable high-sensitivity biosensors exhibit a growing demand in healthcare, food industry and environmental monitoring sectors. Optical biosensors based on photonic integration platforms are attractive candidates due to their high sensitivity, compactness and multiplexing capabilities. However, they need a low-cost and reliable integration with the microfluidic system. Laser-micropatterned double-sided biocompatible adhesive tapes are promising bonding layers for hybrid integration of an optofluidic biochip. As a part of the EU-PHOCNOSIS project, double-sided adhesive tapes have been proposed to integrate the polymer microfluidic system with the optical integrated waveguide sensor chip. Here the adhesive tape should be patterned in a micrometer scale in order to create an interaction between the sample that flows through the polymer microchannel and the photonic sensing microstructure. Three laser-assisted structuring methods are investigated to transfer microchannel patterns to the adhesive tape. The test structure design consists of a single channel with 400 μm wide, 30 mm length and two circular receivers with 3 mm radius. The best structuring results are found by using the picosecond UV laser where smooth and straight channel cross-sections are obtained. Such patterned tapes are used to bond blank polymer substrates to blank silicon substrates. As a proof of concept, the hybrid integration is tested using colored DI-water. Structuring tests related to the reduction of channel widths are also considered in this work. The use of this technique enables a simple and rapid manufacturing of narrow channels (50-60 μm in width) in adhesive tapes, achieving a cheap and stable integration of the optofluidic biochip.

Micro patterned test cell arrays for high-throughput battery materials research

A cost effective and reliable technology for the fabrication of electrochemical test cell arrays for battery materials investigation, based on batch fabricated glass micro packages was developed and tested. Semi-automatic micro dispensing was investigated as a process for the standardized application of different electrode materials and SiO2-based separator. The process shows sufficient reproducibility over the whole range of investigated materials, especially for the cells with interdigital (side-by-side) electrodes. Such setup gives rise to an improved reliability and reproducibility of electrochemical experiments. The economic fabrication of our test chips by batch processing allows for their single-use in electrochemical experiments, herby preventing contamination issues due to repeated use as in conventional laboratory test cells. In addition, the integration of micro pseudo reference electrodes was demonstrated. Thus, the presented test cell array together with the developed electrode/electrolyte deposition technology represents a highly efficient tool for combinatorial and high throughput testing of battery materials on system level (full cell tests). The method will speed up electrochemical materials research significantly.

Building blocks for actively-aligned micro-optical systems in rapid prototyping and small series production

In recent years there has been considerable progress in utilizing fully automated machines for the assembly of microoptical systems. Such systems integrate laser sources, optical elements and detectors into tight packages, and efficiently couple light to free space beams, waveguides in optical backplanes, or optical fibers for longer reach transmission. The required electrical-optical and optical components are placed and aligned actively in more than one respect. For one, all active components are actually operated in the alignment process, and, more importantly, the placing of all components is controlled actively by camera systems and power detectors with live feedback for an optimal coupling efficiency. The total number of optical components typically is in the range of 5 to 50, whereas the number of actors with gripping tools for the actual handling and aligning is limited, with little flexibility in the gripping width. The assembly process therefore is strictly sequential and, given that an automated tool changing has not been established in this class of machines yet, there are either limitations in the geometries of components that may be used, or time-consuming interaction by human operators is needed. As a solution we propose and present lasered glass building blocks with standardized gripping geometries that enclose optical elements of various shapes and functionalities. These are cut as free form geometries with green short pulse and CO2 lasers. What seems to add cost at first rather increases freedom of design and adds an economical flexibility to create very hybrid assemblies of various micro-optical assemblies also in small numbers.