Herbert Freimuth

Fabrication of photonic crystals by deep x-ray lithography

We have developed a new microfabrication technique for the construction of three-dimensional photonic crystals. In particular, we used multiple tilted x-ray lithography exposures in order to construct structures with photonic band gaps in the infrared region. First polymethylmethacrylate (PMMA) resist layers with a thickness of 500 μm were irradiated, then the holes in the resist structure were filled with preceramic polymer and subsequent pyrolysis converts the preceramic polymer into a SiCN ceramic. Theoretical results with fitted values of the dielectric constant are in good agreement with the transmission measurements.We have developed a new microfabrication technique for the construction of three-dimensional photonic crystals. In particular, we used multiple tilted x-ray lithography exposures in order to construct structures with photonic band gaps in the infrared region. First polymethylmethacrylate (PMMA) resist layers with a thickness of 500 μm were irradiated, then the holes in the resist structure were filled with preceramic polymer and subsequent pyrolysis converts the preceramic polymer into a SiCN ceramic. Theoretical results with fitted values of the dielectric constant are in good agreement with the transmission measurements.

A label-free affinity sensor with compensation of unspecific protein interaction by a highly sensitive integrated optical Mach–Zehnder interferometer on silicon

Abstract An integrated optical Mach–Zehnder interferometer (IO-MZI) on silicon was specially designed and tested for application as an affinity sensor. In order to obtain the necessary sensitivity, an optimisation of the refractive index and the thickness of the waveguiding layer was carried out. Refractive measurements with ethanol/water mixtures show a sensitivity of about one order of magnitude higher than the IO-MZIs previously described. The compensation of unspecific protein interaction in an affinity sensor set-up was demonstrated by using both branches of the IO-MZI. One branch was coated with a antigenic structure and blocked with a protein mixture whereas the other was only blocked. A sample with a high background of serum proteins was applied and only the sample containing the specific antibody gave a measurable signal.

Micromolding: a powerful tool for large-scale production of precise microstructures

In recent years a number of micro machining processes have been developed suitable for the realization of industrial process applications, whereby the LIGA technique is considered to be one of the most promising and flexible technologies for the large scale fabrication of three- dimensional microstructure products. LIGA is based on the combination of deep lithography, and electroforming to realize mold inserts with high accuracy for the mass fabrication of microcomponents made from plastic material. The present report deals with the development of micromolding technologies which are applied at IMM. Specifically they are focused on the small dimensions of the molded microstructures, the high aspect ratio, and the demand for sub-micron precision. This includes the technical implementation of molding processes, the production of suitable micro mold inserts, the investigation in simulation software, the screening of polymer materials, ceramics, metallic powders or preceramic polymers and the development of quality qualification systems. The potential of micro molding processes will be demonstrated by presenting a variety of applications like micro gear wheels, micro pumps, micro optical components, splices and connectors, waveguides, optical gratings and components for chemical and biological micro reactors.

Defined crystal orientation of nickel by controlled microelectroplating

Controlled microelectroplating allows the fabrication of microstructures of nickel with defined crystal orientation within the LIGA process. The change in the crystal orientation due to different wetting agents and current densities in the electroplating process has been examined by X-ray diffraction. A careful adjustment of these parameters leads to the electrodeposition of nickel with perfect (110) and (100) orientations or the electrodeposition of nickel with a complete isotropic orientation. The defined crystal orientation permits the control of the magnetic properties of the materials for microactuators based on electromagnetic principles. A new method of analysis has been developed, which results in a quick and easy determination of the crystal orientation by the use of X-ray spectra obtained with a conventional powder diffractometer without the necessity for a special apparatus for texture analysis.

Fabrication of Three-Dimensional Photonic Band Gap Material by Deep X-Ray Lithography

Yablonovitch et al. [1] constructed the “three cylinder” dielectric structure which exhibits a photonic band gap in the whole Brillouin zone. They implemented the diamond structure proposed by Ho et al. [2,3]. This structure can be fabricated mechanically by drilling three sets of holes 35° off vertical into the top of a solid dielectric. However, extremely small dimensions, which are required for high frequencies, cannot be achieved. This problem can be solved by using deep X-ray lithography, which allows the fabrication of structures that can be used up to the infrared range. Three irradiations were performed in which the tilted arrangement of mask and resist was rotated each time by 120°. PMMA resist layers with a thickness of 500 microns were irradiated at the DCI storage ring in Orsay, France. The lattice constants of the structures were 227 and 114 microns corresponding to midgap frequencies of 0.75 and 1.5 THz, respectively.