Wolfgang Ehrfeld

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.

Utilization of Micromixers for Extraction Processes

The aim of the investigation was to evaluate the extraction performance of a mixer settler set-up for miniplant technology using static micromixers as an alternative to conventional stirring apparatuses. A comprehensive experimental study was conducted at BASF AG to broaden the technology base for the “extraction” unit operation which is well established for miniplants in order to be utilized for microplant systems. The work proved that micromixers, or micromixer arrays, are highly efficient apparatuses for extraction purposes. The extraction efficiency was found to be a function of volume flow, which could be explained in light of the volume flow dependence of the mean droplet size and, hence, the specific surface area of the dispersions intermediately formed. At optimal flow conditions, one practical mixer settler stage was found to yield one theoretical plate for most systems investigated.

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.

Combination of excimer laser micromachining and replication processes suited for large scale production

Abstract Results are reported obtained by a process sequence comprising excimer laser ablation of microstructures, inverse replication by an electroplating process and second inverse replication by injection moulding (“Laser-LIGA”). Thus, the original microstructures, made from PMMA and novolak layers applying a commercial 193 nm excimer laser micromachining work-station and showing structural variety and aspect ratios up to 10, were replicated with high structural fidelity by a low cost process suited for large scale production.

Micro gear pumps for dosing of viscous fluids

Gear pumps using micro gear wheels with diameters of 596 and and a height of have been realized at IMM by means of a combination of LIGA technology and precision engineering. Using oil as pumping medium the pumps achieve back pressures of more than 1200 hPa and flow rates of up to . The self-filling pumps tolerate air bubbles and particles contained in the working medium. The gear pumps displace 82 and 213 nl respectively per revolution, i.e. they offer the possibility of very precise dosing of viscous fluids, such as oil.

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.

Microelectro discharge machining as a technology in micromachining

In recent years, machine facilities for Electro Discharge Machining (EDM) have been dramatically improved. Enormous progress has been obtained with respect to form accuracy and structure precision even in the submicron domain, which qualifies EDM as a technology for microfabrication ((mu) EDM). (Mu) EDM therefore extends the family of existing microtechniques e.g. the LIGA process or silicon surface micromachining. The EDM-technology offers 3D microfabrication of conductive materials independent of their mechanical properties like hardness, brittleness, etc. This capability offers new fields of application for the microfabrication of components made e.g. from stainless steel or titanium. In order to demonstrate the successful application of various (mu) EDM processes components and devices like micro gearwheels, microreactors, micro punching tools and mould inserts for micro injection molding of an optical fiber connector are presented, which have been fabricated by EDM in close cooperation between the Institute of Microtechnology Mainz GmbH and the Swiss EDM-manufacturer AGIE Losone. Based on their know-how the partners aim to optimize (mu) EDM for microfabrication purposes.

Microactuators as driving units for microbotic systems

The trend towards the integration of a multitude of functions in e.g. data end-, medical- and communication systems pushes the miniaturization of actuators for linear or rotational motions. Technical advantages of these devices are their low energy consumption, their potential for high precision positioning and their low inertial masses, which allow e.g. huge rotational frequencies. Appreciable forces and torques as well as appropriate mechanical interfaces to integrate these drive units into complete systems are necessary prerequisites for robotic applications, but rarely found up to now. Most of these difficulties arise due to the application of monolithic fabrication techniques, leading to structures of essentially planar nature and severe material restrictions. It turned out that only hybrid concepts and the assembly of components made from the most appropriate material open the chance to build up microactuators which are well suited for microrobotic systems. The contribution starts with a short description of the LIGA technique, which constitutes the major 3-D microfabrication method for the production of individual actuator components with structural heights of up to several millimeters made from a variety of function adapted materials. The assembling of these components results in microactuators with typical dimensions in the millimeter range. Examples are powerful electromagnetic micromotors, delivering torques much larger than one (mu) Nm and high rotational speeds which may be converted by use of LIGA fabricated gear-wheels to furthermore increase the torque. Huge forces are obtained in addition by use of microfabricated fluidic systems. Although small in size, the actuators still offer good handling opportunities and interfacing facilities to build up more complicated robotic systems.

ArF-excimer laser ablation experiments on Cycloolefin Copolymer (COC)

To determine the capability of Cycloolefin Copolymer (COC) for excimer laser microstructuring, ablation experiments have been performed at 193 nm using an ArF excimer laser workstation. A matrix of square holes was structured in COC, the ablated structures were examined qualitatively and quantitatively by optical methods and scanning electron microscopy. It turned out that COC can be structured with high accuracy and is therefore suited for laser rapid prototyping of micro optical and microfluidic devices. The maximum ablation depth of COC (0.17 μm/pulse) is smaller than of PMMA (0.58 μm/pulse), but is sufficient for prototyping and allows fine depth tuning. Flat structures less than 200-μm deep nearly show no amount of redeposited material and yield smooth surfaces.

Injection-moulded fibre ribbon connectors for parallel optical links fabricated by the LIGA technique

Using the LIGA technique prototypes of twelve-fibre-wide ribbon connector ferrules have been developed that provide low-loss physical-contact multimode connections for parallel interfaces. The ferrules are injection moulded and the modular mould insert has been fabricated by means of microtechnology (LIGA) and electro-discharge machining. After assembling, mated couples of these ferrules show average insertion loss values of 0.35 dB and have been used to successfully transmit data with a transfer rate of 250 Mbit per fibre over a 100 m distance.