H. Lehr

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.

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.

Incomplete momentum transfer in heavy-ion fusion at 14.5 MeV/nucleon

Abstract The velocity spectra of individually resolved evaporation residue masses produced in reactions induced by 291 MeV 20 Ne ions on targets of 12 C, 27 Al, and 40 CA have been measured. Analyses of these spectra show clear evidence for fusion-like residues with incomplete momentum transfer.

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.

Microfluidic components for biological and chemical microreactors

Miniaturized reaction systems offer many advantages for a large number of applications in chemical engineering and biotechnology. The very large surface-to-volume ratio of miniaturized fluidic components allows for a significantly enhanced process control and heat management, enabling the performance of chemical reactions in quite unusual reaction regimes. Miniaturized chemical systems offer unique possibilities for the distributed point-of-use production of toxic or explosive chemicals. The extremely large number of syntheses necessary for the development of new, for example pharmaceutical, products, demands the use of automated processing systems capable of handling very small amounts of liquids. Current microfabrication techniques offer possibilities to fabricate high precision microfluidic components, like static mixers, heat exchangers and micropumps from a large variety of function adapted materials. Improvements of the microstructuring capabilities of traditional precision mechanics techniques, like spark erosion based processes, lead to a significant enhancement of the range of materials to be used for the construction of micro reaction systems.

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.

Development of micro- and millimotors

Summary. Modern designs for micromotors are based on hybrid concepts involving the fabrication of the miniaturized components and a subsequent assembly process. Successful examples of such micromotors are the reluctance micromotors introduced by IMM as well as the permanent magnet micromotors developed by Dumed/Kinetron or IMM/Faulhaber, respectively. The present contribution covers the description of these motor principles as well as the development of an integrated micro gear wheel box that can be fabricated by injection moulding or by micro electroplating technologies.

Materials for LIGA products

The LIGA process which is based on a combination of deep lithography and replication processes, allows one to generate three dimensional microstructures from metals, polymers, glasses and ceramic materials. Accordingly, application specific materials can be chosen for a wide variety of LIGA microdevices to be utilized for example in information and communication technology, chemical engineering, automation and robotics, environmental engineering and medical technology. Standard materials are various thermoplastic polymers, casting resins, ceramic powders for slurry casting and metals or metal alloys which can be electrodeposited from aqueous electrolytes. Recent development deals with new highly sensitive resists with chemical amplification for deep X-ray lithography, ceramic microstructures generated on the basis of preceramic polymers, and metals like aluminium which can be electrodeposited from nonaqueous electrolytes. Polymers with adjustable index of refraction or non-linear optical properties, biocompatible materials, soft and hard magnetic materials, amorphous metal alloys, high temperature and piezoelectric ceramics and many other materials are typical examples for application specific materials available for the LIGA process.

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.