Manfred Lacher

Fabrication technologies for microsystems utilizing photoetchable glass

Abstract Photoetchable glass is a very promising material for the production of components for a wide variety of microsystems. High aspect ratio microstructures can be realized by using slightly modified semiconductor equipment and relatively low fabrication costs are achievable already in small scale production. The application potential of photoetchable glass is mainly determined by the fact that this material can be applied in corrosive and high temperature environment which is of major importance for applications in chemistry and biology. Further advantages are transparency, high Youngs modulus and good thermal and electrical insulation. Microstructures generated from photoetchable glass have been produced commercially for various applications mentioned in the text. The photostructuring of this glass is used as an example to show how these microsystems can be manufactured on a large production scale. The principle chemical and physical processes together with the fabrication technologies are explained. In order to promote the utilization of photoetchable glass in microsystems technology the Institute of Microtechnology in Mainz (IMM) and the Schott company have built up a production line for micro devices using FOTURAN produced by Schott. The joint venture covers the design and production of micro devices, the optimization of the fabrication process and the development of advanced equipment for processing FOTURAN in high volume quantities.

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.

In-focus electron microscopy of frozen-hydrated biological samples with a Boersch phase plate

We report the implementation of an electrostatic Einzel lens (Boersch) phase plate in a prototype transmission electron microscope dedicated to aberration-corrected cryo-EM. The combination of phase plate, C(s) corrector and Diffraction Magnification Unit (DMU) as a new electron-optical element ensures minimal information loss due to obstruction by the phase plate and enables in-focus phase contrast imaging of large macromolecular assemblies. As no defocussing is necessary and the spherical aberration is corrected, maximal, non-oscillating phase contrast transfer can be achieved up to the information limit of the instrument. A microchip produced by a scalable micro-fabrication process has 10 phase plates, which are positioned in a conjugate, magnified diffraction plane generated by the DMU. Phase plates remained fully functional for weeks or months. The large distance between phase plate and the cryo sample permits the use of an effective anti-contaminator, resulting in ice contamination rates of <0.6 nm/h at the specimen. Maximal in-focus phase contrast was obtained by applying voltages between 80 and 700 mV to the phase plate electrode. The phase plate allows for in-focus imaging of biological objects with a signal-to-noise of 5-10 at a resolution of 2-3 nm, as demonstrated for frozen-hydrated virus particles and purple membrane at liquid-nitrogen temperature.

Photoetchable glass for microsystems: tips for atomic force microscopy

The authors present the use of photoetchable glasses in the field of microsystem technology. Its properties make it an ideal material for a wide variety of microsystems. A method to fabricate tips for atomic force microscopy out of this material is proposed. The main advantage of these tips with respect to conventional silicon-based tips is their large aspect ratio. Silicon nitride is used as a material for the cantilevers, which are on top of a glass carrier. Experimental results are presented.

Ni, In and Sb implanted Pt and V catalysed thin-film SnO2 gas sensors

Abstract Thin-film technologies lead to low cost and reliable microsystems combining electronics and sensors. However, in competition with microelectronic fabrication sensor technologies exhibit a lack of experience creating difficulties in microsystem integration. In this paper a simple implantation process is introduced to improve thin-film sensor performance. In, Ni and Sb-doped thin-film V and Pt catalysed SnO2 gas sensors are presented. The sensor response due to pulses of H2, COx, NH3, NO2 CH4 and C2H5OH is discussed in the temperature range between 100 and 400 °C.

Ultra-long glass tips for atomic force microscopy

A new variety of ultra-long tips for atomic force microscopy has been fabricated using photoetchable glass. Photoetchable glass is structured by UV exposure through a quartz mask followed by a heat treatment and etch process in hydrofluoric acid. The process is based on different etching rates with a ratio of about 1:20 between unexposed and exposed parts of the glass. Tips longer than with a tip radius down to 20 nm are possible. The cantilevers are made from silicon carbide. The mechanical properties of such long tips are compared, in theory and in practice, with conventional cantilevers from silicon and silicon nitride. Their strong sensitivity to friction forces for contrast formation in atomic force microscopy is discussed.

Practical aspects of Boersch phase contrast electron microscopy of biological specimens

Implementation of physical phase plates into transmission electron microscopes to achieve in-focus contrast for ice-embedded biological specimens poses several technological challenges. During the last decade several phase plates designs have been introduced and tested for electron cryo-microscopy (cryoEM), including thin film (Zernike) phase plates and electrostatic devices. Boersch phase plates (BPPs) are electrostatic einzel lenses shifting the phase of the unscattered beam by an arbitrary angle. Adjusting the phase shift to 90° achieves the maximum contrast transfer for phase objects such as biomolecules. Recently, we reported the implementation of a BPP into a dedicated phase contrast aberration-corrected electron microscope (PACEM) and demonstrated its use to generate in-focus contrast of frozen-hydrated specimens. However, a number of obstacles need to be overcome before BPPs can be used routinely, mostly related to the phase plate devices themselves. CryoEM with a physical phase plate is affected by electrostatic charging, obliteration of low spatial frequencies, and mechanical drift. Furthermore, BPPs introduce single sideband contrast (SSB), due to the obstruction of Friedel mates in the diffraction pattern. In this study we address the technical obstacles in detail and show how they may be overcome. We use X-ray photoelectron spectroscopy (XPS) and Auger electron spectroscopy (AES) to identify contaminants responsible for electrostatic charging, which occurs with most phase plates. We demonstrate that obstruction of low-resolution features is significantly reduced by lowering the acceleration voltage of the microscope. Finally, we present computational approaches to correct BPP images for SSB contrast and to compensate for mechanical drift of the BPP.

Microsystem technology between research and industrial application

Microsystemtechnology is defined in comparison to microelectronics. The development of dedicated microfabrication technologies is summarized and recent developments of microsystems for typical application fields are shown. Specific problems of industrial application are discussed.

Thin-film In-doped V-catalysed SnO2 gas sensors

Abstract Thin-film In-doped V-catalysed SnO2 gas sensors are discussed and compared with Pt-catalysed In-doped or undoped SnO2 gas sensors. The In acceptors are implanted, while the catalysts are directly evaporated onto the active sensor layer. The V/In catalyst/dopant combination leads to thin-film sensors highly sensitive to NO2, while nearly no cross sensitivity to CO, CO2, H2 and CH4 is detectable. The maximum conductivity change of the V-catalyst In-doped SnO2 sensor in NO2-enriched synthetic air occurs at about 200 °C.