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Kleine A.,University of Paderborn | Hilleringmann U.,Fraunhofer Institute for Electronic Nanosystems
Smart Systems Integration 2016 - International Conference and Exhibition on Integration Issues of Miniaturized Systems, SSI 2016 | Year: 2016

The efficiency of dye sensitized solar cells (DSSCs) is strongly influenced by the quality of the front electrode. To remove dispersal additives and to enable sintering effects the TiO2 layer has to be heated up to 450°C for one hour. Nevertheless, for flexible DSSCs the process temperature is limited by the foil to about 150°C. Hence, a sintering of the particles is not possible and the cleaning effect is also declined, but both can be compensated with the development presented in this paper. This paper demonstrates that after 90 min of permanent intensive UV-irradiation nearly all additives are evaporated. Furthermore, to decrease the stress on the foil a pulsed UV-irradiation is performed and the pulse-pause-ratio optimized.


Petrov D.,University of Paderborn | Hilleringmann U.,Fraunhofer Institute for Electronic Nanosystems
Smart Systems Integration 2016 - International Conference and Exhibition on Integration Issues of Miniaturized Systems, SSI 2016 | Year: 2016

Developed at the Paderborn University since 2010, the solar-powered model aircraft has elicited interest in the media and among students of electrical engineering. The plane is equipped with solar cells on its wings, which charge the aircraft batteries during the flight and power the aircraft engine and the electronics. Different sensors are used for navigation and for collecting information about the ambient.


Wang W.-S.,Fraunhofer Institute for Electronic Nanosystems | Lullin J.,CNRS Femto ST Institute | Froemel J.,Fraunhofer Institute for Electronic Nanosystems | Wiemer M.,Fraunhofer Institute for Electronic Nanosystems | And 5 more authors.
Proceedings of SPIE - The International Society for Optical Engineering | Year: 2015

The paper presents the multi-wafer bonding technology as well as the integration of electrical connection to the zscanner wafer of the micromachined array-type Mirau interferometer. A Mirau interferometer, which is a key-component of optical coherence tomography (OCT) microsystem, consists of a microlens doublet, a MOEMS Z-scanner, a focusadjustment spacer and a beam splitter plate. For the integration of this MOEMS device heterogeneous bonding of Si, glass and SOI wafers is necessary. Previously, most of the existing methods for multilayer wafer bonding require annealing at high temperature, i.e., 1100°C. To be compatible with MEMS devices, bonding of different material stacks at temperatures lower than 400°C has also been investigated. However, if more components are involved, it becomes less effective due to the alignment accuracy or degradation of surface quality of the not-bonded side after each bonding operation. The proposed technology focuses on 3D integration of heterogeneous building blocks, where the assembly process is compatible with the materials of each wafer stack and with position accuracy which fits optical requirement. A demonstrator with up to 5 wafers bonded lower than 400°C is presented and bond interfaces are evaluated. To avoid the complexity of through wafer vias, a design which creates electrical connections along vertical direction by mounting a wafer stack on a flip chip PCB is proposed. The approach, which adopts vertically-stacked wafers along with electrical connection functionality, provides not only a space-effective integration of MOEMS device but also a design where the Mirau stack can be further integrated with other components of the OCT microsystem easily. © 2015 SPIE.


Sowade E.,TU Chemnitz | Blaudeck T.,TU Chemnitz | Baumann R.R.,TU Chemnitz | Baumann R.R.,Fraunhofer Institute for Electronic Nanosystems
Crystal Growth and Design | Year: 2016

The manufacturing of three-dimensional colloidal structures on solid substrates is an important topic of applied research, aiming for photonic components especially in photovoltaic and sensor applications. Whereas conventional techniques such as wet self-assembly are based on engineering of the substrate surface energy, alternative strategies envisage the independence of the interfacial conditions. We report on inkjet printing of colloidal suspensions of monodisperse silica or polystyrene nanoparticles or both and their self-assembly to spherical colloidal photonic crystals. The formation process of the colloidal nanoparticles into stable spherical colloidal assemblies (SCAs) is achieved by a self-assembly process inside tiny droplets of a stochastic mist generated intentionally instead of a jet of individual single droplets using inkjet printing. The mist-jetted, shrinking droplets serve as confined geometries for the solidification of the nanoparticles during the evaporation; thus the particles are packed into stable ball-shaped assemblies. We show how fine-tuning of the jetting parameters allows the reliable generation and deposition of three-dimensional (3D) spherical colloidal assemblies of nanoparticles variable in size and with a high packing order. Microreflectance spectroscopy proves that the degree of order in the SCA is such that photonic stop bands occur inherent for photonic crystals. © 2016 American Chemical Society.


Sowade E.,TU Chemnitz | Blaudeck T.,TU Chemnitz | Baumann R.R.,TU Chemnitz | Baumann R.R.,Fraunhofer Institute for Electronic Nanosystems
Nanoscale Research Letters | Year: 2015

We report on inkjet printing of aqueous colloidal suspensions containing monodisperse silica and/or polystyrene nanosphere particles and a systematic study of the morphology of the deposits as a function of different parameters during inkjet printing and solvent evaporation. The colloidal suspensions act as a model ink for an understanding of layer formation processes and resulting morphologies in inkjet printing in general. We investigated the influence of the surface energy and the temperature of the substrate, the formulation of the suspensions, and the multi-pass printing aiming for layer stacks on the morphology of the deposits. We explain our findings with models of evaporation-driven self-assembly of the nanosphere particles in a liquid droplet and derive methods to direct the self-assembly processes into distinct one- and two-dimensional deposit morphologies. © 2015, Sowade et al.

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