We report on the versatile application potential of SU8 photoepoxy for movable micromechanical components. Its outstanding resolution, aspect ratio, and attainable ®lm thicknesses enable the design of structures that allow lateral mechanical interaction of voluminous micro parts. We additionally developed a sacri®cial layer process enabling the release of in situ fabricated micro parts as well as large area parts used for capping and packaging. The applicability of this technology is demonstrated on gearwheels in a turbine con®guration, a micro¯uidic channel with integrated check valve, and an advanced multilayer capping technology with precise feather key ®t. 1 Introduction So far, Epon SU8 has mainly been used and investigated for various high aspect ratio patterning purposes such as masking for deep RIE etching [1], electroplating moulds [2, 3], and injection moulding masters [4]. Besides the use for micro¯uidic components [5] and structural parts for micro motors [6], there is little usage of this material for mechanical and especially movable micro parts. SU8 offers material properties that are useful for mechanical applications [7].The SU8 monomere provides a very high group functionality of eight. Cured SU8 forms a highly cross linked matrix of covalent bonds, resulting in glass like mechanical properties. Other advantages are the relatively low price, the feasibility of batch processing, and the high chemical resistance, which becomes important for (bio-) chemical and medical applications. Moreover, the optical transparency allows for monitoring processes or movements inside the SU8 housing.The material properties and the outstanding structural anisotropy in the fabrication of micro structures open up a promising ®eld of applications. In [7] the fabrication and application of in-plane compliant SU8-structures are demonstrated. In contrast, this paper deals with free movable SU8 parts. In order to reduce process steps and unnecessary mounting of micro parts, the movable structures are fabricated in situ. Fabrication processWe optimized a high aspect ratio SU8 process for single layer thicknesses of 300±400 lm. Multilayer processing allows for device fabrication with vertical dimensions of up to 1 mm. Almost vertical side walls and aspect ratios of up to 36 were achieved [3,7]. The process consists of spin coating in a spinning tool with rotating lid, bakes on ramped hot plates, and successive development in two solutions (GBL and PGMEA). These measures were optimized in order to guarantee uniform ®lm thickness with low residual stress, resulting in crack free structures, even for laterally large structures.Using the optimized parameters, it is also possible to fabricate structures with more than one SU8 layer, resulting in three dimensional micro parts. This was used for caps with feather keys which were lifted off completely and precisely ®t onto micro¯uidic systems. The only restriction for multi layer processing is the fact that the structures in superior layers have to be smaller or same sized as the l...
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 x 6 x 3 mm.
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