B. Wagner

Giant magnetoelectric coefficients in (Fe90Co10)78Si12B10-AlN thin film composites

Thin film magnetoelectric (ME) two–two composites consisting of AlN and amorphous (Fe90Co10)78Si12B10 layers were fabricated by magnetron sputtering on Si (100) substrates. Upon magnetic field annealing they show an extremely high ME coefficient of 737 V/cm Oe at mechanical resonance at 753 Hz and 3.1 V/cm Oe out of resonance at 100 Hz. These are the highest reported ME coefficients in thin film composites ever. Furthermore, the induced magnetic anisotropy by field annealing serves the possibility to obtain a sensor element with a pronounced sensitivity in only one dimension, which allows the realization of a three-dimensional vector field sensor.

Microfabricated actuator with moving permanent magnet

A microactuator is presented which uses electromagnetic force generation within micromachined silicon devices. A rare-earth permanent magnet is bonded on a movable micromachined silicon plate suspended by thin silicon beams. A monolithically integrated planar coil is used to generate a magnetic field which forces the magnet to move vertically. Using a magnet with a dimension of 1.5*1.5*1.0 mm/sup 3/ and a 17-turn coil driven with 300 mA, a static elevation of 70 mu m has been achieved. The actuator concept offers a variety of application-specific design possibilities. The use of a moving permanent magnet allows a magnetic coupling of the actuator force to the environment. By integrating a magnetic field sensor and signal processing, an active, controlled microsystem can be realized. High, long-range forces can be generated in order to realize devices with large deflections.<<ETX>>

Bistable microvalve with pneumatically coupled membranes

The paper reports on a novel bistable electrostatic actuator with pneumatic coupling. Two buckled Si/SiO/sub 2/ membranes span over connected air filled cavities with enclosed driving electrodes. The membranes operate in counteraction. If one electrode is pulled down electrostatically, the other is pushed up pneumatically, and vice versa. The actuator module is designed to achieve a deflection of /spl plusmn/10 /spl mu/m and will be integrated in a microvalve for liquids. With first completed actuator modules the electrostatic/pneumatic driving principle could be demonstrated. Grey-tone lithography has been developed to fabricate curved driving electrodes on the cavity bottom. It is calculated that compared to flat electrodes the driving voltage then can be reduced up to a factor of five. The curved cavity bottom also improves the pneumatic coupling since the enclosed air volume is minimized.

Linear motion of dielectric particles and living cells in microfabricated structures induced by traveling electric fields

Arrangements of microelectrodes as obtained by a microfabrication technique are found to be well suited for a linear transfer of microscopic particles such as biological cells and other objects of microscopic dimensions. The conditions for an effective manipulation of the particles are electrode geometries which correspond to the dimensions of the particle and adapted electrical excitation of the electrodes (traveling high-frequency waves). The motion of particles was found to be a super-position of dielectrophoresis and charge relaxation processes as they are dominant, e.g. in dielectric induction motors. Microparticle velocities of some hundreds mu /s could be achieved by applying phase-shifted rectangular pulses with amplitudes between 5 and 15 volts.<<ETX>>

Radio-frequency microtools for particle and live cell manipulation

Single particles can be manipulated by applying high frequencies to ultramicro electrode arrays fabricated on planar structures. Heat production can be reduced to the extent that intense electric fields can be applied even to unmodified cell culture media. Animal cells grow normally in the high field (up to 100 kV/m) between such continuously energized multielectrodes. As with laser tweezers [1-3], this technique can capture particles and cells in field traps, generate linear movement, and permit cell cultivation. It can also produce micropatterns of pH gradients, field-cast objects, and control cell adhesion. These microtools may be combined to develop cell separators, microsensors, and controlled-biocompatibility surfaces.

Permanent magnet micromotors on silicon substrates

Different types of sliding, rolling, or rotating micromotors with rare-earth-based permanent magnet rotors are presented. The magnets move synchronously with rotating or traveling magnetic fields generated by 25- mu m-thick gold current lines on silicon substrates. The magnets are guided in channels or openings in the silicon itself or in additional glass layers. For magnets with a typical dimension of 1 mm, forces and torques of 150 mu N and 100 nNm could be achieved. Maximum velocities of 24 cm/s and a rotation frequency of 2000 r.p.m. have been measured. Magnetic clamping to the bottom confines the rotor to the system and allows a motor operation at any tilt angle. Noncontact magnetic transmission of forces to drive a ferromagnetic fluid has been demonstrated. >

Low damping resonant magnetoelectric sensors

The signal of magnetic sensors based on resonant cantilevers comprised of elastically coupled piezoelectric and magnetostrictive materials increases as the damping decreases. Here, we demonstrate that air damping which normally is suppressed by evacuation can also be substantially reduced by lowering the resonance frequency. We show that a Si-cantilever structured to include a seismic mass features a resonant magnetoelectric coupling coefficient of 1.8 kV/cmOe at 330 Hz in air.

Pumping of water solutions in microfabricated electrohydrodynamic systems

A microfabricated electrohydrodynamic pump without moving parts driven by low voltages with high-frequency traveling waves is presented. Micron-size scale systems without moving parts fabricated in planar silicon technology are presented and quantitatively described. The operating principle to pump water and weak electrolyte solutions is outlined. It is shown that conductive liquids such as water solutions can be pumped opposite to the direction of the traveling wave. Typical parameters characterizing the advantages and limitations of the pumping principle are discussed. Opportunities for optimization of the micropump in terms of further miniaturization and an increased number of electrodes are noted.<<ETX>>

A smart accelerometer with on-chip electronics fabricated by a commercial CMOS process

Abstract Piezoresistive accelerometers with a monolithically integrated operational amplifier were produced, the fabrication process based on a commercial 3 μm CMOS process. The mechanical structures were realized using wet anisotropic etching of silicon with KOH and the electrochemical etch-stop at p—n junctions. Measurements show that the integration of these necessary micromachining process steps into the IC process do not influence the parameters of the electronic devices. Also, the parameters of the mechanical structures are comparable to discrete devices. The realization of application-specific smart mechanical sensors and actuators using a standard CMOS process is now possible.

Microfabrication of complex surface topographies using grey-tone lithography

This paper reports on a study of a methodology for fabrication of relief shaped microstructures using technologies common to standard IC manufacturing processes. Particular emphasis is put on the design and use of halftone transmission masks for the lithography step required in the fabrication process of mechanical, optical or electronic components. The design and experimental investigation of grey-tone masks is supported by lithography simulation. Results are presented for both, simulated grey-tone patterns as well as experimental profiles.