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München, Germany

Gossner U.,University of Federal Defense Munich | Hoeftmann T.,Plan Optik AG | Wieland R.,Fraunhofer EMFT | Hansch W.,University of Federal Defense Munich
Applied Physics A: Materials Science and Processing | Year: 2014

In high-tech products, there is an increasing demand to integrate glass lenses into complex micro systems. Especially in the lighting industry LEDs and laser diodes used for automotive applications require encapsulated micro lenses. To enable low-cost production, manufacturing of micro lenses on wafer level base using a replication technology is a key technology. This requires accurate forming of thousands of lenses with a diameter of 1-2 mm on a 200 mm wafer compliant with mass production. The article will discuss the technical aspects of a lens manufacturing replication process and the challenges, which need to be solved: choice of an appropriate master for replication, thermally robust interlayer coating, choice of replica glass, bonding and separation procedure. A promising approach for the master substrate material is based on a lens structured high-quality glass wafer with high melting point covered by a coating layer of amorphous silicon or germanium. This layer serves as an interlayer for the glass bonding process. Low pressure chemical vapor deposition and plasma enhanced chemical vapor deposition processes allow a deposition of layer coatings with different hydrogen and doping content influencing their chemical and physical behavior. A time reduced molding process using a float glass enables the formation of high quality lenses while preserving the recyclability of the mother substrate. The challenge is the separation of the replica from the master mold. An overview of chemical methods based on optimized etching of coating layer through small channels will be given and the impact of glass etching on surface roughness is discussed. © 2014 Springer-Verlag Berlin Heidelberg.

Zanella F.,Swiss Center for Electronics and Microtechnology | Zanella F.,Ecole Polytechnique Federale de Lausanne | Marjanovic N.,Swiss Center for Electronics and Microtechnology | Ferrini R.,Swiss Center for Electronics and Microtechnology | And 14 more authors.
Organic Electronics: physics, materials, applications | Year: 2013

Sub-micrometer channel length (0.5 μm) organic thin-film transistors (OTFTs) are demonstrated using a process flow combining nano-imprint lithography (NIL) and self-alignment (SA). A dedicated test structure was designed and samples were fabricated on 4-in. plastic foils using a p-type sublimated small molecule (pentacene) as semiconductor. Field-effect mobilities, in saturation, between 0.1 and 1 cm2/Vs were obtained not only for the supermicron OTFTs but also for the submicron OTFTs. Those devices were used to select a model based on the "TFT Generic Charge Drift model" which works well for a broad range of channel lengths including the submicron OTFTs. We show that these OTFTs can be accurately modeled, thus giving access to complex circuit simulations and design. © 2013 Elsevier B.V.

Bose I.,Fraunhofer EMFT | Tetzner K.,TU Dresden | Borner K.,Fraunhofer EMFT | Bock K.,TU Dresden
Electronics | Year: 2015

We report on a micro-dispensing system for 6,13-Bis(triisopropylsilylethynyl) pentacene (TIPS-pentacene) to enable homogenous crystallization and uniform film morphology of the dispensed droplets using a two-solvent mixture along with the use of an insulating binder. This solution composition results in a controlled evaporation of the droplet in ambient air such that the Marangoni flow counteracts the outward convective flow to enable uniform radial crystal growth from the edge towards the center of the drops. The consequence of this process is the high degree of uniformity in the crystallization of the drops, which results in a reduction in the performance spread of the organic field effect transistors (OFET) created using this process. The addition of the insulating binder further improves the reduction in the spread of the results as a trade-off to the reduction in mobility of the transistors. The transfer curves of the OFETs show a tight grouping due to the controlled self-alignment of the TIPS-pentacene crystals; this repeatability was further highlighted by fabricating p-type inverters with driver to load ratios of 8:1, wherein the output inverter curves were also grouped tightly while exhibiting a gain of greater than 4 in the switching region. Therefore, the reliability and repeatability of this process justifies its use to enable large area solution-processed printed circuits at the cost of reduced mobility. © 2015 by the authors; licensee MDPI, Basel, Switzerland.

Wolf H.,Fraunhofer EMFT | Gieser H.,Fraunhofer EMFT
Electrical Overstress/Electrostatic Discharge Symposium Proceedings | Year: 2015

By means of a floating handheld electronic product this work describes the influence of secondary discharge events during system level ESD testing on the failure threshold of the involved electronic circuit. In order to increase the robustness it was necessary to determine the discharge current target levels by a dedicated test set-up which was also used to verify the success of system modifications. This was a prerequisite for identifying the sensitive pins and for increasing the ESD robustness of the system.

Strohhofer C.,Fraunhofer EMFT | Forster T.,Fraunhofer EMFT | Chorvat D.,International Laser Center | Chorvat D.,Polymer Institute Dubravska | And 6 more authors.
Physical Chemistry Chemical Physics | Year: 2011

This article reports the full characterisation of the optical properties of a biosynthesised protein consisting of fused cyan fluorescent protein, glucose binding protein and yellow fluorescent protein. The cyan and yellow fluorescent proteins act as donors and acceptors for intramolecular fluorescence resonance energy transfer. Absorption, fluorescence, excitation and fluorescence decays of the compound protein were measured and compared with those of free fluorescent proteins. Signatures of energy transfer were identified in the spectral intensities and fluorescence decays. A model describing the fluorescence properties including energy transfer in terms of rate equations is presented and all relevant parameters are extracted from the measurements. The compound protein changes conformation on binding with calcium ions. This is reflected in a change of energy transfer efficiency between the fluorescent proteins. We track the conformational change and the kinetics of the calcium binding reaction from fluorescence intensity and decay measurements and interpret the results in light of the rate equation model. This visualisation of change in protein conformation has the potential to serve as an analytical tool in the study of protein structure changes in real time, in the development of biosensor proteins and in characterizing protein-drug interactions. This journal is © the Owner Societies.

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