High precision microactuators have become key elements for many applications of MEMS, for example for positioning
and handling systems as well as for microfluidic devices. Electromagnetic microactuators exhibit considerable benefits
such as high forces, large deflections, low input impedances and thus, the involvement of only low voltages. Most of the
magnetic microactuators developed so far are based on the variable reluctance principle and use soft magnetic materials.
Since the driving force of such actuators is proportional to their volume, they require structures with rather great heights
and aspect ratios. Therefore, the development of new photo resists, which allow UV exposure of thick layers of resist,
has been essential for the advancement of variable reluctance microactuators. On the other hand, hard magnetic
materials have the potential for larger forces and larger deflections. Accordingly, polymer magnets, in which micro
particles of hard magnetic material are suspended in a polymer matrix, have been used to fabricate permanent magnet
microactuators. In this paper we give an overview of sophisticated electromagnetic microactuators which have been
developed in our laboratory in the framework of the Collaborative Research Center “Design and Manufacturing of
Active Microsystems”. In particular, concept, fabrication and test of variable reluctance micro stepper motors, of
permanent magnet synchronous micromotors and of microactuators based on the Lorentz force principle will be
described. Special emphasis will be given to applications in lab-on-chip systems.
The mergence of partial aspects and functional components of micro actuators and micro fluidic technology allows the
development of complex micro systems, which are more and more interesting for MEMS application, especially for
BioMEMS. This enormous potential is shown in this article showing the realization of an electro magnetic micro pump.
The basic build-up consists of a polymer magnet integrated into a pump chamber of a fluidic PDMS device, which is
located above a double layer micro coil. By applying a current, the polymer magnet performs a bidirectional movement,
which results in a pumping effect by the two arranged passive check valves being perpendicularly arranged to the flow
channels. The valve membrane is flexible and opens the channel towards the flow direction. The advantage of this
configuration is that leakage can be avoided by the special geometrical configuration of the fluid chamber and the valves.
The fabrication process includes UV depth lithography using AZ9260, electroforming of copper for the double layer
spiral coil and Epon SU-8 for insulation, embedding and manufacturing of the valve seat. Furthermore, the fluidic
devices are realized by replica molding of PDMS using a multilayer SU-8 master. Furthermore, a new technology for
realizing micro polymer magnets was optimized and deployed. Using these fabrication processes, a magnetic micro
actuator has already been developed based on the movable plunger principle, which forms the basic set-up of the micro
pump. This actuator is monolithically fabricated and successfully tested. In addition, the fluidic system of the micro
pump was successfully fabricated and tested. In order to connect the valve seats based on SU-8 to the PDMS fluidic
chamber and the valve lips, a special bonding process was developed. The combination of the fluidic system with the
electromagnetic part is currently under investigation. The dimension of the micro pump is about 10 × 6 × 3 mm.
Due to the development of new technologies, more and more complex MEMS applications can be realized. Especially
electromagnetic micro actuators have reached a growing interest in micro technology in addition to commercial
applications during the last years. Their basic construction exists of electric conductors and coil systems as well as of
soft-magnetic and/or hard-magnetic materials that were fabricated in additive technology via UV-depth lithography and
electroplating. For UV-depth lithography, photo resists like Epon SU-8, AZ9260, Intervia-3D-N and CAR44 were
applied and optimized. Layer thickness up to 1 mm and aspect ratios over 60 were achieved. Special micro composites
were developed. This allowed the fabrication of micro magnets with arbitrary shape and properties, revealing a complete
compatibility to existing process chains. With these potential technologies, several complex 3-D micro actuators like
micro motors and micro robots were developed and successfully tested. These developments include in detail: linear and
rotatory reluctance micro stepper motors with compensated attraction force as well as a special "Lorentz force actuator",
which was used for micro robots and micro motors. The micro robots were deployed for assembling and for micro-/nano
positioning. Furthermore "plunger coil actuators" were realized based on a voice coil principle, which were used e.g. for
a micro switch or a micro mirror. Moreover, rotatory synchronous motors were developed and successfully tested. All
these devices have been realized by outstanding fabrication technologies and can be used for a wide range of
applications.
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